Weather Prediction Center

National Oceanic and Atmospheric Administration

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
445 AM EDT Tue Jun 18 2024

Valid 12Z Tue Jun 18 2024 - 12Z Thu Jun 20 2024

...Significant heavy rain/flash flooding threat with gusty winds well
ahead of Potential T.C. One expected to impact southern Texas on
Wednesday...

...More rounds of heavy rain and severe thunderstorms expected for the
northern Plains and upper Midwest today before shifting south into the
central Plains on Wednesday...

...A heat wave will persist over the Great Lakes, Ohio Valley and the
Northeast through midweek...

...Late-season wet snow continues across the high-elevations of the
northern Rockies today before tapering off early on Wednesday...

An active weather pattern continues across the U.S. mainland. This
weather pattern that features snow, heat, heavy rain, severe
thunderstorms, strong winds, and fire weather is now bringing Potential
Tropical Cyclone One in the midst. A low pressure system currently
intensifying along a frontal boundary is fostering another round of heavy
rain and severe thunderstorms across the northern Plains into the upper
Midwest early this morning. The potent upper trough and the associated
dome of cold air have continued to result in a round of late-season wet
snow across the higher-elevations of the northern Rockies together with
rather strong wind gusts. With less potent jet stream energy behind this
system, the low pressure system will quickly eject into southern Canada by
this evening, bringing the inclement weather across the northern Plains to
an end by Wednesday morning. However, a sharp front trailing south and
southwest from the low center will likely trigger an axis of heavy rain
and severe thunderstorms from the central Plains to the upper Midwest by
tonight into Wednesday morning. From Wednesday into Thursday morning, the
rain/storms should gradually become more scattered in nature across the
central Plains as a cool high pressure system passes to the north. This
high pressure system will also push the widely scattered showers and
embedded thunderstorms farther east into the lower Great Lakes and
interior New England through Thursday morning.

In stark contrast to the cool, windy, rainy and even snowy weather in the
West, a heat wave will settle and persist across the Great Lakes, Ohio
Valley and the Northeast through the next few days. Forecast highs today
and Wednesday will reach into the mid- to upper 90s, even the century mark
Wednesday and Thursday afternoon at the hottest locations in interior
northern New England. Widespread, numerous record-tying/breaking high
temperatures are possible. Additionally, morning lows will remain in
about the mid-70s, at record-tying/breaking levels, providing little
relief from the heat overnight. The early arrival of this magnitude of
heat, the duration, abundant sunshine, and lack of relief overnight will
increase the danger of this heatwave beyond what the exact temperature
values would suggest. This is especially true for those without adequate
air conditioning, which becomes more of a concern for locations further
north that are not as accustomed to periods of persistent heat.

Another big weather story over the next couple of days will be in the Gulf
of Mexico where the National Hurricane Center has already initiated
advisories on Potential Tropical Cyclone One. An elongated upper trough
digging into the southern Plains and northeastern Mexico has already drawn
a plume of tropical moisture northward into the central Gulf Coast region.
This upper trough will be instrumental in drawing the tropical moisture
well north of the center of PTC One into southern Texas mainly on
Wednesday as PTC One tracks west toward northern Mexico. An axis of very
heavy rain may develop just inland of the Texas coastline behind a coastal
front with dynamic support from the elongated upper trough. This pattern
could result in locally heavy rainfall in excess of 10 inches near or just
inland of the lower to middle Texas coast which would result in
significant flash flooding. The heavy rain is forecast to push farther
inland across the Rio Grande Valley early on Thursday. In addition to the
heavy rainfall, some coastal flooding along with tropical-storm-force
winds can be expected up the Texas coast on Wednesday. See the latest
advisory from the National Hurricane Center for additional detailed
updates. Meanwhile, fire danger across the Four Corners region should
gradually ease over the next few days with the arrival of slightly cooler
air followed by the arrival of moisture from the northern edge of
Potential Tropical Cyclone One.

Kong/Putnam


Graphics available at
https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
303 AM EDT Tue Jun 18 2024

Valid 12Z Fri Jun 21 2024 - 12Z Tue Jun 25 2024

...Record-breaking heat from the Midwest to the East Coast expected
to moderate by early next week...


...Heavy rainfall threat from the northern Plains into Upper
Great Lakes into Friday-Saturday...


...Overview...

Latest models and ensembles continue to show the large scale
pattern transitioning toward a more typical early summer regime
late weekend and early next week, as initially strong ridging over
the eastern half of the country gives way to a leading trough
crossing the northern tier U.S. and southern Canada (reaching the
East Coast by around next Tuesday) while a system reaching the
Northeast Pacific and West Coast this weekend continues eastward
thereafter. Although weakening, the eastern upper ridge will still
support a broad area of hazardous heat with potential for daily
records extending from the Ohio Valley/Lower Great Lakes into the
Mid-Atlantic Friday into the weekend. The northern Plains into
Upper Great Lakes should see a continued threat for heavy rainfall
through Friday-Saturday as developing northern Plains into Great
Lakes/Ontario low pressure and associated fronts interact with
anomalous moisture already in place. Some of this rainfall will
extend into the Northeast. A trailing Northeast Pacific system will
likely bring a well-defined front into the West by Sunday,
continuing east thereafter. To the south of the upper ridge
ultimately settling over the far southern tier, Potential Tropical
Cyclone One (see NHC for updates) should dissipate over Mexico by
Friday while NHC is monitoring potential for another feature over
the western Gulf mid-late period.


...Guidance/Predictability Assessment...

The latest forecast based on 12Z/18Z guidance started with an
operational model composite early in the period and then gradually
increased ensemble input (18Z GEFS and 12Z ECens/CMCens) to a total
of 60 percent by the end of the period next Tuesday. ECMWF input
was split between the 12Z and 00Z/17 run mid-late period due to
some questionable details in the 12Z run.

At least in principle, an average of dynamical and ECMWF machine
learning (ML) guidance agreed fairly well with the upper ridge
settling over the far southern tier while a fairly vigorous system
develops/tracks along the northern tier/southern Canada through the
period, leading to a moderate upper trough/leading cold front near
the East Coast by next Tuesday. The mean of ML models was close to
the dynamical guidance average for the surface system's depth,
while displaying some detail differences after most guidance agreed
to an embedded upper low aloft as of Sunday. With the trailing
Pacific system, sporadic GFS runs (like the 12Z and new 00Z
versions) have been shearing some upper energy while leaving the
main upper low behind near the British Columbia coast. The 18Z GFS
looked more like consensus. Meanwhile the ML models are generally
showing somewhat higher heights and less potential for a weakness
at the surface and aloft over or near the Gulf of Mexico versus
some GFS/ECMWF runs.


...Weather/Hazards Highlights...

The most prominent focus for heavy rainfall during the period will
be from the northern Plains into Upper Great Lakes during Friday-
Saturday as upper dynamics emerging from western North America
encourage northern Plains into Great Lakes/Ontario surface
development. This system and associated fronts will interact with
anomalous moisture that has been persisting over the region for
multiple days. The Day 4 Excessive Rainfall Outlook for Friday
maintains a Slight Risk area from parts of the Dakotas into the
U.P. of Michigan (close to continuity) while the Day 5 ERO for
Saturday proposes a Slight Risk area from northeastern
Minnesota/northern Wisconsin into northern Michigan. Surrounding
Marginal Risk areas account for less extreme but still locally
significant rainfall potential over the northern Plains (Day 4) and
over the Midwest along the trailing cold front (Day 5). Some areas
across the northern tier will be sensitive to additional rainfall
due to already wet ground heading into Friday.

Elsewhere, the new Day 4 ERO maintains continuity with a Marginal
Risk area over parts of the southern Rockies/Four Corners region
due to the abundant moisture arriving from the east and some
forecast instability, along with some model signals for locally
enhanced rainfall. Guidance suggests that the greatest moisture
anomalies should get pushed to the south and west during Saturday,
with rainfall over the region likely to be lighter and more
scattered--thus not meriting a risk area for Day 5. Meanwhile the
Northeast continues to merit monitoring from Friday into the
weekend. The combination of moisture and instability along with an
east-west front settling over the region could support some
locally enhanced rainfall rates and training/repeat activity.
However antecedent conditions should be rather dry by that time,
stream flows are already near to below normal, and model QPF is
not exceptionally heavy thus far. Therefore the outlooks continue
to depict no risk area at this time.

Continued progression of the system that should be near the Great
Lakes as of early Sunday will bring the trailing cold front through
the eastern U.S. and trailing back into the Plains by the start of
next week, bringing areas of showers and thunderstorms of varying
intensity. The front reaching the Northwest this weekend may bring
some light/scattered rainfall over northern areas. Continued
progress of this front may generate some showers/thunderstorms over
the central U.S. by the first half of next week. Some scattered
diurnal convection may persist over the southern Rockies.
Occasional showers/storms are possible along the Gulf Coast,
but with increasing uncertainty over specifics of the Gulf of
Mexico pattern at the surface and aloft by early next week keeping
confidence low regarding any potential increase in moisture at that
time.

With a cold front reaching New England by Friday and providing a
cooling trend there, the greatest temperature anomalies from late
this week into the weekend should extend from the Midwest and Ohio
Valley/Lower Great Lakes into the Mid-Atlantic and Northeast, with
readings tending to be 10-15F above normal. This would translate
to highs well into the 90s, along with lows in the upper 60s to
upper 70s providing little overnight heat relief. Daily records for
max/warm min temperatures will be possible within the above areas,
up through warm mins early Monday (if they hold on through the
calendar day). Meanwhile much of the West will trend warmer/hotter
late this week into the weekend with highs reaching 10F or more
above normal for a couple days or so. The front reaching the
Northwest should bring cooler air to that region by Sunday-Monday,
while some of the leading western heat should reach the northern-
central High Plains at that time--connecting with lingering heat
over parts of the Plains into southern half of the East. Clouds
and rainfall will support below normal highs over the southern
Rockies/High Plains late this week.

Rausch


Additional 3-7 Day Hazard information can be found on the WPC
medium
range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation forecast (QPF), excessive rainfall
outlook (ERO), winter weather outlook (WWO) probabilities, heat
indices, and Key Messages can be accessed from:

https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml
https://www.wpc.ncep.noaa.gov/#page=ovw

Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
333 AM EDT Tue Jun 18 2024

Valid 00Z Wed Jun 19 2024 - 00Z Wed Jun 26 2024

Guidance continues to agree in depicting a persistent trade
pattern through the period, favoring windward and mountain focus
for showers but with moisture straying to other locations at
times. High pressure to the north of the state will support brisk
to strong winds through the period, especially from Wednesday
onward. Latest models and ensembles have been trending drier/more
suppressed with an axis of moisture that has been forecast to
cross the state from east to west during Tuesday-Wednesday on the
east side of a departing upper low. Consensus still shows some
drier air passing through on Thursday, a rebound Friday-Saturday
(higher precipitable water values brushing the northwestern
islands), and then a decrease toward below-climatology values for
the first half of next week. Within this pattern of fluctuating
moisture, guidance indicates most rainfall will be in the lighter
half of the spectrum.

Rausch

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1158 AM EDT Tue Jun 18 2024
Day 1
Valid 12Z Tue Jun 18 2024 - 12Z Wed Jun 19 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR THE UPPER AND
MIDDLE TEXAS COASTS...

...Upper and Middle Texas Coasts...

16Z... The morning update from NHC did not make enough change to
require any QPF adjustments, therefore no adjustments were made to
the Moderate, Slight or Marginal Risk areas across Texas and the
Gulf Coast. Another assessment will be made this afternoon.

Campbell

Potential Tropical Cyclone 1 (PTC1) will continue to organize
across the southern and western Gulf today. Associated moisture
originating in the Caribbean will stream northwestward into the
Texas coast around the northern and eastern periphery of the
storm. IVT values are very impressive...building to the upper end
of the scale at 1,500 kg/m/s. This means PWATs with the storm will
consistently increase through the day, approaching 3 inches by the
time the storm's full brunt moves into the coast tonight. PWATs
approaching 3 inches mean the atmosphere will be carrying about as
much moisture as it can possibly carry...and storms that form in
this environment will be capable of extremely heavy rainfall rates
due to highly efficient rainfall processes. Moisture lost by the
rainfall will be quickly replaced as moisture advection (signified
by the extremely high IVT values) will be optimal.

All of this to say, as the plume of moisture associated with PTC1
and supported by advection straight out of the Caribbean moves into
the upper Texas coast tonight, it will contain convection capable
of 3 inch per hour rainfall rates. These rates will easily
overwhelm local streams and creeks as they track northwestward, no
matter how dry/empty they were prior to the start of the rain. This
will likely catch many off guard, so it's important to avoid
crossing flooded roadways.

With the better-forecast organization of PTC1, it's expected that
the associated plume of moisture and heavy rainfall will be more
consolidated as it approaches the Texas coast as compared with
previous forecasts. This means the timing of the heavy rainfall has
been slightly delayed, and is less likely to extend too far north
from the coast. Thus...the inherited ERO risk areas have been
trimmed from the north from inherited. It's likely that it will
take until after 06Z tonight before consistent and steady heavy
rainfall begins moving into the coast, with only scattered
convection expected prior to that. However, given the
aforementioned heavy rainfall rates expected when the directly
associated rainfall with PTC1 moves ashore, numerous instances of
flash flooding are likely late tonight in the Moderate Risk area.
Further west in the Slight Risk area, there will be slightly less
time for the heavy rainfall to cause flash flooding since it will
be starting later.

For Louisiana, the forecast track of PTC1 and aforementioned
consolidation of the precipitation shield should keep most of the
heavy rainfall offshore, so the Moderate Risk area was trimmed out
of the southwestern coast of the state with this update.

...Central Plains into the Midwest...

16Z update... The latest guidance did show an increase in
potential for heavier showers to move through the panhandles of
Oklahoma and Texas with hourly rain rates approaching 2.5/3 inches
per hour. The Slight Risk and Marginal Risk areas were expanded a
couple row of counties to the southwest to account for this trend
and lowered FFG.

Campbell

Ongoing heavy convection across the Dakotas and northern Minnesota
is associated with a low over western Nebraska. The low will track
northward into eastern SD and eventually into the Red River of the
North by tonight. The convection is likely to be ongoing into
northern Minnesota by the start of the period at 7am this morning.
The heavy rain will persist there and far northwestern Wisconsin
for a few hours this morning, resulting in widely scattered
instances of flash flooding. The inherited Slight Risk for this
area is little changed, and will likely be able to be trimmed out
of northern MN and WI with the midday update today.

Further south, the cold front associated with the low is expected
to stall across Kansas, eastern Nebraska, and western Iowa today.
Late this afternoon, convection is expected to break out along the
front, and increase in coverage and intensity through the evening.
A small area of high pressure over the western Dakotas tonight will
support northerly flow to the north of the front. Meanwhile, the
typical strengthening of the LLJ and southerly flow over the
southern Plains will advect plentiful Gulf moisture into the front
from the south. The clashing of the 2 air masses will keep the
front from moving very much tonight, allowing the clashing to
continue over the same areas for multiple hours tonight. The
resulting convection will also train and backbuild over the same
areas along and immediately south of the front. This will support
widely scattered instances of flash flooding across much of the
rest of the Slight risk area from southwest Kansas northeast to
western Iowa.

The greatest risk of flash flooding will be over Kansas tonight, as
this will be the southern end of the front, where the 2 clashing
air masses will be most opposed to each other. This will keep any
storms that form from moving very much, and the influx of moisture
from the LLJ will support additional convective development. There
has been the typical uncertainty and inconsistency in the guidance
as to where the southern end of the front will be. 24 hours ago it
was expected to be in north-central Kansas and into eastern
Nebraska. Now there's much better agreement across southwestern
Kansas. Thus, this area is at highest risk of flash flooding.
Meanwhile further north and east, amounts should come down a
bit...but unidirectional southwesterly flow parallel to the front
will still support training storms and potential for flash
flooding. Thus, the Slight Risk area from Kansas north and east was
nudged east a bit with guidance trends, but is largely unchanged.

...Central Appalachians...

16Z update... The latest hi-res guidance continues to support
storms capable of producing rain fall rates up to 2 inches/hour
through the afternoon and into the evening hours. There was a trend
for increasing coverage of these storms across portions of central
and southern West Virginia and across eastern New York and
Pennsylvania, especially for the late afternoon and evening hours.
Given these trends the Marginal Risk area was expanded southward
and eastward.

Campbell

"Ridge-running" precipitation is expected to track across eastern
Ohio through central New York today. The storms will be supported
by an air mass with PWATs up to 1.75 inches. The storms will be
capable of local rainfall rates to 1.5 inches per hour, which
depending on where they form may cause isolated instances of flash
flooding. There is somewhat better agreement for a bit better
organization of convection in this area. Thus, a Marginal Risk area
was introduced with this update.

Wegman

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1158 AM EDT Tue Jun 18 2024
Day 2
Valid 12Z Wed Jun 19 2024 - 12Z Thu Jun 20 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHERN TEXAS AND PORTIONS OF THE MIDDLE AND UPPER TEXAS COASTS...

...South Texas...

Potential Tropical Cyclone 1 (PTC1) is expected to turn westward
across the western Gulf on Wednesday and make landfall in the
southern Mexican state of Tamaulipas Wednesday night based on the
4am CDT update from the National Hurricane Center. While the center
will be well south of Texas, a nothing short of impressive plume of
moisture characterized by IVTs pushing the top of the scale at
1,500 kg/m/s will continue advecting northwestward out of the
Caribbean, across the Gulf, and into south Texas on Wednesday. PTC1
will tap into this moisture plume as it tracks westward towards
Mexico. This will greatly expand the associated precipitation
shield north of the center of the storm. Thus, a prolonged period
of heavy rain is likely across all of south Texas Wednesday and
Wednesday night.

Heavy rain will be ongoing across nearly all of the Texas coast at
the start of the Day 2/Wednesday period at 7am Wednesday. With
PWATs approaching 3 inches from Houston/Galveston southwestward
down the entire Texas coast, the convection that will be embedded
within the broader precipitation shield associated with PTC1 will
be capable of extremely heavy rainfall rates as high as 3 inches
per hour with the strongest storms. Rates this high will easily
overwhelm smaller streams and creek watersheds with water falling
close to all at once. Thus, rapid-onset flash flooding is likely
across much of southern Texas with this storm.

For most of the Moderate Risk area, the bulk of the rainfall with
PTC1 will occur during this Day 2/Wednesday period. The rain will
overspread south Texas from east to west. Thus, areas along the
coast will see their heaviest rain during the day Wednesday, while
towards the Rio Grande the heavier rain will be towards evening and
into Wednesday night. Think the greatest rainfall rates will be
with the parent easterly wave associated with PTC1, though heavy
rain will be likely due to moisture availability well before and
after the passage of the wave. As the bands of rain track westward
and inland, they will very gradually weaken with time as they
become separated from their moisture source...the Gulf. However,
the extreme IVT will support them well inland from the coast.
Nonetheless, the highest rainfall totals associated with PTC1 are
likely closer to the coast, with only gradually diminishing
rainfall totals as you move inland, as upsloping into the terrain
plays an increasingly important role in the development and support
of heavy rain. 5 to 10 inches of rain with isolated totals as high
as 15 inches are expected across the Moderate Risk area.

Many portions of the Moderate Risk area have been very dry of late,
so empty rivers and streams will initially preclude much
flooding...though as mentioned the extreme rainfall rates will
locally exceed FFGs, regardless of how dry the area was before the
storm. By the tail end of the event numerous instances of flash
flooding are likely, so the Moderate Risk remains in effect with
few changes from inherited. Note the antecedent dry conditions may
lead many to a false sense of security as regards flooding...and
rapid onset flash flooding will be common.

The surrounding Slight Risk area was dramatically trimmed on the
northern end out of north Texas with this update. As mentioned, the
consolidated nature of the convection should hold much of the
associated rainfall closer to the storm center over south Texas.
Thus, much less rainfall is expected into north Texas, and the
Slight Risk area was cancelled into the DFW Metroplex.

...Central Plains...

A small Slight risk area was introduced with this update across
portions of southwest and south-central Kansas. Ongoing convection
from the overnight period Tuesday night is expected across this
region, with ongoing widely scattered instances of flash flooding
ongoing. The southern/eastern end of the line of convection will
track across the Slight Risk area through the morning Wednesday
before dissipating.

The inherited Slight risk area across portions of north-central
Kansas and eastern Nebraska was downgraded with this update. This
is in regards to the uncertainty with where the southern end of the
front would be from Day 1/Tuesday. Since the general consensus in
the guidance is for the southern end of the front to now be in
southern Kansas, north Kansas into eastern Nebraska will miss out
on the heaviest rain, so the signal for heavy rain in this area has
diminished significantly.

...Midwest...

Elsewhere the large Marginal from the Plains into the Great Lakes
is largely in deference to the various waves of moisture streaming
across the area on the northern end of the large high pressure area
in the upper levels over the Southeast. Convection will likely be
fast moving and largely disorganized, but since various sections of
the Marginal risk area have seen heavy rains in recent days, the
threat for isolated instances of flash flooding from these storms
is there right through central New York.

Wegman

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1158 AM EDT Tue Jun 18 2024
Day 3
Valid 12Z Thu Jun 20 2024 - 12Z Fri Jun 21 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE RIO GRANDE
VALLEY OF TEXAS TO THE LOWER TEXAS COAST AS WELL AS FROM EASTERN
SOUTH DAKOTA TO WESTERN WISCONSIN...

...Texas...

Residual rainfall from what will likely be dissipated PTC1 will
continue across the Rio Grande Valley Thursday morning. The Slight
was expanded to include the entire Lower Rio Grande Valley and
Lower Texas Coast largely due to expected ongoing flash flooding at
the start of the period Thursday morning. Additional rainfall
during the day Thursday should be mostly light, but abundance of
moisture will still support some widely scattered convection
capable of producing flash flooding. The heaviest rain this period
will be across the Big Bend region, where a higher-risk Slight is
in effect. 2-4 inches of rain with locally higher amounts are
likely in the Big Bend region. This is highly unusual in such a
widespread manner from a tropical cyclone. Thus, this area has a
low, but non-zero potential for further upgrades with future
updates due to the infrequency of this amount of rain in this
usually very dry area. There is a bit more uncertainty with how far
north up the dry line into West Texas/southeast New Mexico the
persistent heavy rain gets as the whole plume quickly weakens, so
future adjustments to the Marginal Risk in this area are likely.

...Northern Plains and Portions of the Upper Midwest...

A Slight Risk area was left largely unchanged with this update. A
shortwave and right entrance region of a small 100 kt jet streak
will track over a front over the area with attendant southerly flow
of moisture up the central Plains and into this area. Recent heavy
rain, including in some areas where its ongoing as of this writing
will lead to wet soils that are more susceptible to flooding from
heavy convection. The convection is most likely to impact this
region Thursday night.

...4 Corners Region...

The meeting of the remnant upper level energy from PTC 1 will
interact with a slow moving trough over California. Residual
moisture will interact with the terrain in this area. The result
will be scattered showers and thunderstorms capable of heavy rain
that may cause isolated flash flooding since this area is typically
a dry area and not able to handle much heavy rain before flooding
occurs.

Wegman

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
303 AM EDT Tue Jun 18 2024


The most prominent focus for heavy rainfall during the period will
be from the northern Plains into Upper Great Lakes during Friday-
Saturday as upper dynamics emerging from western North America
encourage northern Plains into Great Lakes/Ontario surface
development. This system and associated fronts will interact with
anomalous moisture that has been persisting over the region for
multiple days. The Day 4 Excessive Rainfall Outlook for Friday
maintains a Slight Risk area from parts of the Dakotas into the
U.P. of Michigan (close to continuity) while the Day 5 ERO for
Saturday proposes a Slight Risk area from northeastern
Minnesota/northern Wisconsin into northern Michigan. Surrounding
Marginal Risk areas account for less extreme but still locally
significant rainfall potential over the northern Plains (Day 4) and
over the Midwest along the trailing cold front (Day 5). Some areas
across the northern tier will be sensitive to additional rainfall
due to already wet ground heading into Friday.

Elsewhere, the new Day 4 ERO maintains continuity with a Marginal
Risk area over parts of the southern Rockies/Four Corners region
due to the abundant moisture arriving from the east and some
forecast instability, along with some model signals for locally
enhanced rainfall. Guidance suggests that the greatest moisture
anomalies should get pushed to the south and west during Saturday,
with rainfall over the region likely to be lighter and more
scattered--thus not meriting a risk area for Day 5. Meanwhile the
Northeast continues to merit monitoring from Friday into the
weekend. The combination of moisture and instability along with an
east-west front settling over the region could support some
locally enhanced rainfall rates and training/repeat activity.
However antecedent conditions should be rather dry by that time,
stream flows are already near to below normal, and model QPF is
not exceptionally heavy thus far. Therefore the outlooks continue
to depict no risk area at this time.

Continued progression of the system that should be near the Great
Lakes as of early Sunday will bring the trailing cold front through
the eastern U.S. and trailing back into the Plains by the start of
next week, bringing areas of showers and thunderstorms of varying
intensity. The front reaching the Northwest this weekend may bring
some light/scattered rainfall over northern areas. Continued
progress of this front may generate some showers/thunderstorms over
the central U.S. by the first half of next week. Some scattered
diurnal convection may persist over the southern Rockies.
Occasional showers/storms are possible along the Gulf Coast,
but with increasing uncertainty over specifics of the Gulf of
Mexico pattern at the surface and aloft by early next week keeping
confidence low regarding any potential increase in moisture at that
time.

With a cold front reaching New England by Friday and providing a
cooling trend there, the greatest temperature anomalies from late
this week into the weekend should extend from the Midwest and Ohio
Valley/Lower Great Lakes into the Mid-Atlantic and Northeast, with
readings tending to be 10-15F above normal. This would translate
to highs well into the 90s, along with lows in the upper 60s to
upper 70s providing little overnight heat relief. Daily records for
max/warm min temperatures will be possible within the above areas,
up through warm mins early Monday (if they hold on through the
calendar day). Meanwhile much of the West will trend warmer/hotter
late this week into the weekend with highs reaching 10F or more
above normal for a couple days or so. The front reaching the
Northwest should bring cooler air to that region by Sunday-Monday,
while some of the leading western heat should reach the northern-
central High Plains at that time--connecting with lingering heat
over parts of the Plains into southern half of the East. Clouds
and rainfall will support below normal highs over the southern
Rockies/High Plains late this week.

Rausch

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
303 AM EDT Tue Jun 18 2024


The most prominent focus for heavy rainfall during the period will
be from the northern Plains into Upper Great Lakes during Friday-
Saturday as upper dynamics emerging from western North America
encourage northern Plains into Great Lakes/Ontario surface
development. This system and associated fronts will interact with
anomalous moisture that has been persisting over the region for
multiple days. The Day 4 Excessive Rainfall Outlook for Friday
maintains a Slight Risk area from parts of the Dakotas into the
U.P. of Michigan (close to continuity) while the Day 5 ERO for
Saturday proposes a Slight Risk area from northeastern
Minnesota/northern Wisconsin into northern Michigan. Surrounding
Marginal Risk areas account for less extreme but still locally
significant rainfall potential over the northern Plains (Day 4) and
over the Midwest along the trailing cold front (Day 5). Some areas
across the northern tier will be sensitive to additional rainfall
due to already wet ground heading into Friday.

Elsewhere, the new Day 4 ERO maintains continuity with a Marginal
Risk area over parts of the southern Rockies/Four Corners region
due to the abundant moisture arriving from the east and some
forecast instability, along with some model signals for locally
enhanced rainfall. Guidance suggests that the greatest moisture
anomalies should get pushed to the south and west during Saturday,
with rainfall over the region likely to be lighter and more
scattered--thus not meriting a risk area for Day 5. Meanwhile the
Northeast continues to merit monitoring from Friday into the
weekend. The combination of moisture and instability along with an
east-west front settling over the region could support some
locally enhanced rainfall rates and training/repeat activity.
However antecedent conditions should be rather dry by that time,
stream flows are already near to below normal, and model QPF is
not exceptionally heavy thus far. Therefore the outlooks continue
to depict no risk area at this time.

Continued progression of the system that should be near the Great
Lakes as of early Sunday will bring the trailing cold front through
the eastern U.S. and trailing back into the Plains by the start of
next week, bringing areas of showers and thunderstorms of varying
intensity. The front reaching the Northwest this weekend may bring
some light/scattered rainfall over northern areas. Continued
progress of this front may generate some showers/thunderstorms over
the central U.S. by the first half of next week. Some scattered
diurnal convection may persist over the southern Rockies.
Occasional showers/storms are possible along the Gulf Coast,
but with increasing uncertainty over specifics of the Gulf of
Mexico pattern at the surface and aloft by early next week keeping
confidence low regarding any potential increase in moisture at that
time.

With a cold front reaching New England by Friday and providing a
cooling trend there, the greatest temperature anomalies from late
this week into the weekend should extend from the Midwest and Ohio
Valley/Lower Great Lakes into the Mid-Atlantic and Northeast, with
readings tending to be 10-15F above normal. This would translate
to highs well into the 90s, along with lows in the upper 60s to
upper 70s providing little overnight heat relief. Daily records for
max/warm min temperatures will be possible within the above areas,
up through warm mins early Monday (if they hold on through the
calendar day). Meanwhile much of the West will trend warmer/hotter
late this week into the weekend with highs reaching 10F or more
above normal for a couple days or so. The front reaching the
Northwest should bring cooler air to that region by Sunday-Monday,
while some of the leading western heat should reach the northern-
central High Plains at that time--connecting with lingering heat
over parts of the Plains into southern half of the East. Clouds
and rainfall will support below normal highs over the southern
Rockies/High Plains late this week.

Rausch

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
1031 AM EDT Mon May 13 2024

Valid 00Z Tue May 14 2024 - 00Z Fri May 17 2024

...WPC Winter Weather Desk no longer routinely staffed this
summer...

Pending any significant winter weather, the WPC Winter Weather Desk
will not be staffed this summer. The desk will resume continuous
staffing starting in late September 2024.

Most of the winter products from WPC will continue to be produced,
including the Winter Storm Severity Index (WSSI), Probabilistic
Winter Storm Severity Index (WSSI-P), and the Probabilistic Winter
Precipitation Forecasts (PWPF).

WPC

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
303 AM EDT Tue Jun 18 2024

Valid 12Z Fri Jun 21 2024 - 12Z Tue Jun 25 2024

...Record-breaking heat from the Midwest to the East Coast expected
to moderate by early next week...


...Heavy rainfall threat from the northern Plains into Upper
Great Lakes into Friday-Saturday...


...Overview...

Latest models and ensembles continue to show the large scale
pattern transitioning toward a more typical early summer regime
late weekend and early next week, as initially strong ridging over
the eastern half of the country gives way to a leading trough
crossing the northern tier U.S. and southern Canada (reaching the
East Coast by around next Tuesday) while a system reaching the
Northeast Pacific and West Coast this weekend continues eastward
thereafter. Although weakening, the eastern upper ridge will still
support a broad area of hazardous heat with potential for daily
records extending from the Ohio Valley/Lower Great Lakes into the
Mid-Atlantic Friday into the weekend. The northern Plains into
Upper Great Lakes should see a continued threat for heavy rainfall
through Friday-Saturday as developing northern Plains into Great
Lakes/Ontario low pressure and associated fronts interact with
anomalous moisture already in place. Some of this rainfall will
extend into the Northeast. A trailing Northeast Pacific system will
likely bring a well-defined front into the West by Sunday,
continuing east thereafter. To the south of the upper ridge
ultimately settling over the far southern tier, Potential Tropical
Cyclone One (see NHC for updates) should dissipate over Mexico by
Friday while NHC is monitoring potential for another feature over
the western Gulf mid-late period.


...Guidance/Predictability Assessment...

The latest forecast based on 12Z/18Z guidance started with an
operational model composite early in the period and then gradually
increased ensemble input (18Z GEFS and 12Z ECens/CMCens) to a total
of 60 percent by the end of the period next Tuesday. ECMWF input
was split between the 12Z and 00Z/17 run mid-late period due to
some questionable details in the 12Z run.

At least in principle, an average of dynamical and ECMWF machine
learning (ML) guidance agreed fairly well with the upper ridge
settling over the far southern tier while a fairly vigorous system
develops/tracks along the northern tier/southern Canada through the
period, leading to a moderate upper trough/leading cold front near
the East Coast by next Tuesday. The mean of ML models was close to
the dynamical guidance average for the surface system's depth,
while displaying some detail differences after most guidance agreed
to an embedded upper low aloft as of Sunday. With the trailing
Pacific system, sporadic GFS runs (like the 12Z and new 00Z
versions) have been shearing some upper energy while leaving the
main upper low behind near the British Columbia coast. The 18Z GFS
looked more like consensus. Meanwhile the ML models are generally
showing somewhat higher heights and less potential for a weakness
at the surface and aloft over or near the Gulf of Mexico versus
some GFS/ECMWF runs.


...Weather/Hazards Highlights...

The most prominent focus for heavy rainfall during the period will
be from the northern Plains into Upper Great Lakes during Friday-
Saturday as upper dynamics emerging from western North America
encourage northern Plains into Great Lakes/Ontario surface
development. This system and associated fronts will interact with
anomalous moisture that has been persisting over the region for
multiple days. The Day 4 Excessive Rainfall Outlook for Friday
maintains a Slight Risk area from parts of the Dakotas into the
U.P. of Michigan (close to continuity) while the Day 5 ERO for
Saturday proposes a Slight Risk area from northeastern
Minnesota/northern Wisconsin into northern Michigan. Surrounding
Marginal Risk areas account for less extreme but still locally
significant rainfall potential over the northern Plains (Day 4) and
over the Midwest along the trailing cold front (Day 5). Some areas
across the northern tier will be sensitive to additional rainfall
due to already wet ground heading into Friday.

Elsewhere, the new Day 4 ERO maintains continuity with a Marginal
Risk area over parts of the southern Rockies/Four Corners region
due to the abundant moisture arriving from the east and some
forecast instability, along with some model signals for locally
enhanced rainfall. Guidance suggests that the greatest moisture
anomalies should get pushed to the south and west during Saturday,
with rainfall over the region likely to be lighter and more
scattered--thus not meriting a risk area for Day 5. Meanwhile the
Northeast continues to merit monitoring from Friday into the
weekend. The combination of moisture and instability along with an
east-west front settling over the region could support some
locally enhanced rainfall rates and training/repeat activity.
However antecedent conditions should be rather dry by that time,
stream flows are already near to below normal, and model QPF is
not exceptionally heavy thus far. Therefore the outlooks continue
to depict no risk area at this time.

Continued progression of the system that should be near the Great
Lakes as of early Sunday will bring the trailing cold front through
the eastern U.S. and trailing back into the Plains by the start of
next week, bringing areas of showers and thunderstorms of varying
intensity. The front reaching the Northwest this weekend may bring
some light/scattered rainfall over northern areas. Continued
progress of this front may generate some showers/thunderstorms over
the central U.S. by the first half of next week. Some scattered
diurnal convection may persist over the southern Rockies.
Occasional showers/storms are possible along the Gulf Coast,
but with increasing uncertainty over specifics of the Gulf of
Mexico pattern at the surface and aloft by early next week keeping
confidence low regarding any potential increase in moisture at that
time.

With a cold front reaching New England by Friday and providing a
cooling trend there, the greatest temperature anomalies from late
this week into the weekend should extend from the Midwest and Ohio
Valley/Lower Great Lakes into the Mid-Atlantic and Northeast, with
readings tending to be 10-15F above normal. This would translate
to highs well into the 90s, along with lows in the upper 60s to
upper 70s providing little overnight heat relief. Daily records for
max/warm min temperatures will be possible within the above areas,
up through warm mins early Monday (if they hold on through the
calendar day). Meanwhile much of the West will trend warmer/hotter
late this week into the weekend with highs reaching 10F or more
above normal for a couple days or so. The front reaching the
Northwest should bring cooler air to that region by Sunday-Monday,
while some of the leading western heat should reach the northern-
central High Plains at that time--connecting with lingering heat
over parts of the Plains into southern half of the East. Clouds
and rainfall will support below normal highs over the southern
Rockies/High Plains late this week.

Rausch


Additional 3-7 Day Hazard information can be found on the WPC
medium
range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation forecast (QPF), excessive rainfall
outlook (ERO), winter weather outlook (WWO) probabilities, heat
indices, and Key Messages can be accessed from:

https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml
https://www.wpc.ncep.noaa.gov/#page=ovw