Weather Prediction Center

National Oceanic and Atmospheric Administration

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
343 AM EDT Tue Oct 03 2023

Valid 12Z Tue Oct 03 2023 - 12Z Thu Oct 05 2023

...There is a Slight Risk of excessive rainfall over parts of the Western
Gulf Coast on Tuesday and over the Southern Plains and Middle/Lower
Mississippi Valley on Wednesday...

...There is an Enhanced Risk of severe thunderstorms over parts of the
Central/Southern Plains on Tuesday and a Slight Risk over parts of the
Southern High Plains on Wednesday...

...Snow over parts of the highest elevations of Wyoming...

A front extending from the Northern Plains southward to the Southern High
Plains will slowly move eastward to the Upper Great Lakes to the Southern
High Plains by Thursday. Moisture will pool along the boundary, producing
showers and severe thunderstorms over parts of the Plains. Therefore, the
SPC has issued an Enhanced Risk of severe thunderstorms over parts of the
Central/Southern Plains through Wednesday morning. The hazards associated
with these thunderstorms are frequent lightning, severe thunderstorm wind
gusts, hail, and a few tornadoes. Further, there is an increased threat of
hail two inches or greater over parts of the Central/Southern Plains.

Moreover, moisture streaming onshore over the Western Gulf Coast will
produce showers and thunderstorms with heavy rain. Therefore, the WPC has
issued a Slight Risk of excessive rainfall over parts of the Western Gulf
Coast through Wednesday morning. The associated heavy rain will create
mainly localized areas of flash flooding, with urban areas, roads, and
small streams the most vulnerable.

The threat of severe thunderstorms decreases slightly on Wednesday. The
front will produce showers and thunderstorms from the Upper Great Lakes
southward to the Southern Plains. However, the showers and thunderstorms
will become severe over parts of Northwestern Texas and southwestern
Oklahoma. Therefore, the SPC has issued a Slight Risk of severe
thunderstorms over parts of the Southern High Plains from Wednesday into
Thursday morning. The hazards associated with these thunderstorms are
frequent lightning, severe thunderstorm wind gusts, hail, and a few
tornadoes.

Additionally, on Wednesday, the threat of excessive rainfall will move
from the Western Gulf Coast to northeastern Texas, southeastern Oklahoma,
southwestern Missouri, Western Arkansas, and extreme northwestern
Louisiana. Therefore, the WPC has issued a Slight Risk of excessive
rainfall over parts of the Southern Plains and Middle/Lower Mississippi
Valley from Wednesday into Thursday morning. The associated heavy rain
will create mainly localized areas of flash flooding, with urban areas,
roads, and small streams the most vulnerable.

Meanwhile, upper-level troughing associated with the front will aid in
creating rain over parts of the Pacific Northwest, Northern California,
Northern Intermountain Region, and Northern Rockies on Tuesday. The energy
will also create snow at the highest elevations over parts of Wyoming. On
Wednesday, the lingering upper-level troughing will keep rain and
highest-elevation snow over parts of the Northern Rockies.

Furthermore, the upper-level troughing over the Rockies will allow
temperatures to be 10 to 15 degrees below average over parts of the Great
Basin, the Northern Intermountain Region, and the Northern Rockies. East
of the upper-level troughing, upper-level ridging extends from the Gulf
Coast to the Upper Great Lakes that will allow temperatures to be 15 to 25
degrees above normal over parts of the Upper Mississippi Valley/Upper
Great Lakes, Middle Mississippi Valley, Ohio Valley, Lower Great Lakes,
and the Northeast.

Lastly, onshore flow off the Atlantic will aid in producing showers and
thunderstorms over parts of Florida from late Tuesday into Thursday.


Ziegenfelder


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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EDT Tue Oct 03 2023

Valid 12Z Fri Oct 06 2023 - 12Z Tue Oct 10 2023

...Heavy rain and flash flooding threats ramp up in the Northeast
late week...


...Overview...

An upper trough and likely an embedded upper low are forecast to
swing slowly through the Great Lakes region southward late this
week into early next week, while a cold front sweeps through the
eastern U.S. at the surface. Rain chances will increase along and
ahead of the front, and heavy rainfall may cause flooding concerns
in the Northeast on Friday and Saturday. Some rain (with lake
effect enhancement) could linger into early next week underneath
the upper low. Meanwhile an upper ridge should overtake the
western U.S. for warmer than average temperatures and generally
dry conditions, until early next week when a trough and frontal
system could push into the Pacific Northwest.


...Guidance Evaluation/Predictability Assessment...

Model guidance is in reasonably good agreement with the trough
over the Great Lakes, with the past couple model cycles more
agreeable in forming a closed low within the trough likely over
the weekend. The closed low serves to slow down the movement of
the feature, with only a slow drift in its placement early next
week. Deterministic models do have some spread with its eventual
positioning. GFS runs including the 18Z and new 00Z run having the
upper low retrograde to the southwest does seem to be inconsistent
with other deterministic and ensemble guidance, so the GFS was not
preferred at this point.

Behind the upper trough/low, models also are agreeable with an
upper ridge shifting from the West Coast at the start of the
period Friday gradually into the Interior West over the
weekend/early next week and the central U.S. by Tuesday. Troughing
coming into the eastern Pacific stemming from an Alaskan upper low
shows some spread in its axis and depth but pretty minor for a
feature in that region for that lead time.

With the reasonably good consensus for the large scale pattern,
the WPC forecast used a blend of the deterministic guidance
particularly favoring the 18Z GFS and 12Z ECMWF early in the
period, transitioning to incorporate the ensemble means to half by
Day 6 and just over half Day 7 as model spread increased,
especially lessening the GFS proportion. Continuity from the
previous forecast was generally well maintained.


...Weather/Hazards Highlights...

As the upper trough and forming embedded low track across the
Great Lakes late week, Atlantic moisture is likely to flow into
the northeastern U.S., leading to increasing rain totals on Friday
and especially by Saturday along and ahead of the cold front.
Instability may be somewhat limited, but the forcing for ascent
will be strong with the right entrance region of the jet overhead,
and precipitable water anomalies are forecast to be at least above
the 75th if not the 90th percentile. Rain amounts look to increase
by Saturday, with upslope flow/terrain enhancement likely playing
a role in the Interior Northeast. Thus a Marginal Risk remains in
place across the Lower Great Lakes region and parts of the
northern Mid-Atlantic and Northeast for Day 4/Friday, with a
Slight Risk across the Interior Northeast on Day 5/Saturday. Most
heavy rain will exit by Sunday but some lingering showers are
possible underneath the upper low through early next week, with
lake effect rain showers likely.

Farther south, the tail end of the cold front could linger into
South Texas into at least Friday, sparking additional showers and
thunderstorms there after a few wet days. A Marginal Risk remains
in place for the Day 4 ERO/Friday. Rain amounts look to gradually
lessen this weekend into early next week. Meanwhile, conditions in
the West look to be dry under the upper ridge, aside from limited
showers possible in the Southwest. This is likely to change early
next week as a front and upper trough approach the Pacific
Northwest, causing increasing precipitation chances.

The amplified trough and the cold front will lead to cooler
temperatures than average, while the upper ridge to the west of it
supports above normal temperatures. One more warmer than average
day is possible in the Northeast on Friday, while high
temperatures across the Plains into Midwest will be below average
by 10-20F. Lows look to be a little less anomalous Friday morning
but could drop further on Saturday, with low 30s and perhaps a few
temperatures in the upper 20s in the northern half of the Plains,
creating the possibility of the first frost or freeze of the
season. As the upper trough and the cold front(s) march east into
the weekend, temperatures should cool to below average across the
east-central U.S. and eventually making their way to the Eastern
Seaboard by early next week. Meanwhile the arrival of an upper
ridge across the West will first raise temperatures along the West
Coast to 10-15F above normal, with some record warm lows possible.
The shift/expansion of the ridge farther east should lead to
warmer than average temperatures across the northern Rockies into
the High Plains early next week.


Tate


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, excessive rainfall outlook,
winter weather outlook probabilities, heat indices and Key
Messages are at:

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
340 AM EDT Tue Oct 03 2023

Valid 00Z Wed Oct 04 2023 - 00Z Wed Oct 11 2023

A land and sea breeze pattern will be in place over Hawaii for the
next few days, as trades diminish as a result of a weak pressure
gradient due to a surface low well north of the state pushing a
front across the Pacific and hovering north near the islands.
Clouds and any showers that form will favor that land/sea breeze
pattern through Tuesday and Wednesday. The front looks to stall
and dissipate just north of Hawaii around Wednesday
night/Thursday, with the band of moisture ahead of it perhaps
making it into the northwestern islands, but any enhanced rain
looks to stay north. By later in the week, a surface high is
forecast to form northwest of the state and extend its ridge
toward Hawaii, with its pressure gradient sufficient to reform
easterly trades. A hybrid trade/sea breeze pattern looks possible
on Thursday before a more typical trade wind pattern forms on
Friday and should persist through the weekend into early next
week, with any showers focused on windward/mauka areas.

Tate

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
820 PM EDT Mon Oct 02 2023

Day 1
Valid 01Z Tue Oct 03 2023 - 12Z Tue Oct 03 2023

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHERN HIGH PLAINS...


...Southern High Plains...
An upper trough propagating through the West has triggered showers
and thunderstorms across the High Plains, some of which have been
showing training and back building character, thus far. PWATs of
1-1.5" with increasing southerly flow are expected overnight,
which will tap MU CAPE that is currently 1000-3000 J/kg. The
expectation is that this activity will become forward propagating
over the next few hours, which would eventually leave the tail of
the convective activity as more prone to heavy rain issues as it
would ultimately have the longest period with higher instability
available while the more northern activity forward propagates out
of the instability region. The 18z HREF indicates this as well,
with its highest probabilities of 3"+ through 12z lying close to
the Pecos River valley. Excessive rain areas were trimmed on the
western side based on radar reflectivity and mesoscale guidance
trends.


...Florida...
The Marginal Risk area from the last issuance was curtailed to
encompass only southernmost Florida and the surrounding Keys. A
slow moving surface front is expected to continue its southward
trajectory today through the Florida Straits. Any flash flood
threat would be early and over any urban areas within the Marginal
Risk.


...Texas Coast...
Occasional heavy rain has occurred along a convergence zone within
Lower Texas Coast today. Ample instability should continue, but
activity has been pulse as low-level inflow has been modest which
has led to occasional rearrangement of the banding as outflow
boundaries shift its location around. The 18z HREF probabilities
suggest the possibility of 3"+ of rainfall, initially near the
Lower TX Coast but shifting more towards the Upper Texas Coast by
12z as veering low-level flow shifts the convergence zone up the
coast. Any issues would be constrained to urban areas as only
small pockets of the region have experienced average to above
average rainfall this past week.


Roth/Kebede


Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
446 PM EDT Mon Oct 02 2023

Day 2
Valid 12Z Tue Oct 03 2023 - 12Z Wed Oct 04 2023

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE GREAT PLAINS AND THE GULF COAST OF TEXAS...

...21z Update...

Minimal changes were needed for this updated, as guidance remains
in fairly good agreement concerning a broad area of rainfall
across the central portion of the country. Signals remain
insufficient for a targeted Slight introduction, and any excessive
rainfall capable of flash flooding is expected to be localized and
difficult to pinpoint.

Along the Texas coast, the Marginal Risk was expanded a bit based
on the 12z HREF guidance. Conversely, the signals across the
Florida Atlantic Coast did indeed continue a declining trend, so
the Marginal Risk was removed for this update.

Churchill


...Previous Discussion...

...Great Plains...

A broad Marginal Risk of excessive rainfall is in place across the
Great Plains and parts of the Upper Midwest on Tuesday as moisture
streams out ahead of the deepening upper trough emerging over the
High Plains. Showers and thunderstorms will focus around a cold
front extending down across the Plains with the greatest chance
for excessive rainfall occurring closest to the greatest
instability from the Southern Plains up into northern portions of
the Central Plains. Guidance has consistently signaled this, but
has lacked a strong signal for especially high rain rates to
overcome relatively dry soils at this time.

...Texas Coast...

Another Marginal Risk area was introduced for this issuance to
account for another round of convection on Tuesday along a coastal
convergence zone. Operational guidance has picked up a signal for
this and the similarities with today's setup of low level
convergence within an unstable environment and a modest low level
jet support the possibility of excessive rainfall leading to
isolated flash flooding.

...Florida...

Recent rainfall has made much of Florida's Atlantic Coast
susceptible to flash flooding, despite the operational guidance
keeping the heaviest QPF well offshore. The confluence of these
two factors should support a low confidence Marginal Risk area
along the coast for now. If operational QPF trends continue on a
downward trend then the Marginal Risk area might be removed
altogether on the next issuance.


Kebede

Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
447 PM EDT Mon Oct 02 2023

Day 3
Valid 12Z Wed Oct 04 2023 - 12Z Thu Oct 05 2023

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHERN PLAINS...

...21z Update...

Confidence remains relatively high with regard to concentrated
heavy rainfall on Wednesday, as WPC QPF advertises a broad area of
1-3" areal average QPF (generally encompassed by the adjusted
Slight Risk area). This includes much of OK, North TX, northwest
AR, southwest MO, and far southeast KS. Localized totals across
this region are anticipated to range from 3-5", with the best odds
of realizing these localized totals across southeast OK and
adjacent portions of North TX (considered to be on the higher-end
of the Slight Risk probability spectrum). Given a fair amount of
spread in the global guidance (and a lack of CAM guidance through
the period of interest), as well as generally dry antecedent
conditions, we decided to hold off on the introduction of a
Moderate Risk. Should guidance trend upward additionally and come
into better agreement spatially, then a targeted Moderate Risk
upgrade may be needed for subsequent updates. For now, the
forecast is in good agreement with the machine learning CSU first
guess guidance (depicting a high-end Slight Risk area).

Churchill


...Previous Discussion...

...Southern Plains...

There is reasonably high confidence in a heavy rainfall event
unfolding over much of the Southern Plains of Oklahoma and
north-central Texas on Wednesday. The operational models have
consistently signaled 2-4" (locally higher) of 24 hour QPF for
much of the current Slight Risk area centered over the Red River.
The main threat of excessive rainfall will occur during the peak
heating hours of the late afternoon and evening when convection is
expected to initiate. The amplified upper trough swinging through
the Great Plains and upper jet crossing will provide ample forcing
of convection over Texas and Oklahoma. Sufficient instability of
over 1000J/Kg will be in place with low level jet support to allow
for higher rain rates. PWATs of 1.5-2" across the Texas Oklahoma
border region will be approximately 3 standard deviations above
normal. Further upgrades will be considered if confidence
continues to grow.


Kebede

Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
355 PM EDT Mon Oct 02 2023


Moist and unstable inflow will meet up with the cold front pushing
through the south-central U.S. on Thursday, which along with the
right entrance region of the jet providing ample lift will lead to
a continued heavy rain threat mainly in Texas. A Slight Risk
remains in place in the Day 4/Thursday Excessive Rainfall Outlook
for this convection that could produce high rain rates. The front
should continue to push south with time and limit the areal
coverage of rainfall, but some may linger into South Texas late
week. A Marginal Risk is delineated there in the ERO for Friday.
No major changes are necessary for the updated EROs on both days.

Farther north, the cold front should track through the
Midwest/Upper Great Lakes and the Ohio Valley Thursday into
Friday. There is a nonzero threat of embedded heavy rain with this
activity, but hopefully the frontal progression will keep showers
and thunderstorms moving quickly enough not to cause flash
flooding issues. However, this could change by Friday and Saturday
as the tilt/placement of the trough and front may allow for
Atlantic moisture to stream in and increase heavy rainfall
potential as the front gets into the northern
Mid-Atlantic/Northeast. A Marginal Risk is planned for the Day
5/Friday ERO across the Lower Great Lakes region and parts of the
northern Mid-Atlantic and Northeast, as despite some lingering
model discrepancies heavy rain seems like a good possibility,
which could cause flooding issues especially in areas with low
Flash Flood Guidance. Heavy rain and flooding concerns will likely
continue into Saturday for New England.

Much of the CONUS should dry out by Sunday with the exception of
some lake effect rain showers in the Great Lakes region and any
moisture lingering into Maine, southern Texas, and Florida. The
Pacific Northwest though will likely see a ramp-up in
precipitation chances by Monday as a front and upper trough
approach.

The amplified trough and the cold front will lead to cooler
temperatures than average, while the upper ridges to the east and
west of it support above normal temperatures. The Lower Great
Lakes region into the Northeast should see warmer than average
temperatures by 10-20F on Thursday, with highs in the upper 70s to
low 80s. But as the upper trough and the primary and secondary
cold fronts march east into the latter half of the week,
temperatures will cool to below average across the central and
then east-central U.S., eventually making their way to the Eastern
Seaboard by early next week. The first frost or freeze of the
season may occur in the northern High Plains behind the cold
fronts late this week. In the eastern half of the U.S., lows will
generally be around 5-10F below average while highs should be more
like 10-15F below average, locally cooler. Meanwhile the arrival
of an upper ridge across the West will first raise temperatures
along the West Coast to 10-15F above normal, with some record warm
lows possible. The shift/expansion of the ridge farther east
should lead to warmer than average temperatures across the
northern Rockies into the High Plains early next week.


Tate

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
355 PM EDT Mon Oct 02 2023


Moist and unstable inflow will meet up with the cold front pushing
through the south-central U.S. on Thursday, which along with the
right entrance region of the jet providing ample lift will lead to
a continued heavy rain threat mainly in Texas. A Slight Risk
remains in place in the Day 4/Thursday Excessive Rainfall Outlook
for this convection that could produce high rain rates. The front
should continue to push south with time and limit the areal
coverage of rainfall, but some may linger into South Texas late
week. A Marginal Risk is delineated there in the ERO for Friday.
No major changes are necessary for the updated EROs on both days.

Farther north, the cold front should track through the
Midwest/Upper Great Lakes and the Ohio Valley Thursday into
Friday. There is a nonzero threat of embedded heavy rain with this
activity, but hopefully the frontal progression will keep showers
and thunderstorms moving quickly enough not to cause flash
flooding issues. However, this could change by Friday and Saturday
as the tilt/placement of the trough and front may allow for
Atlantic moisture to stream in and increase heavy rainfall
potential as the front gets into the northern
Mid-Atlantic/Northeast. A Marginal Risk is planned for the Day
5/Friday ERO across the Lower Great Lakes region and parts of the
northern Mid-Atlantic and Northeast, as despite some lingering
model discrepancies heavy rain seems like a good possibility,
which could cause flooding issues especially in areas with low
Flash Flood Guidance. Heavy rain and flooding concerns will likely
continue into Saturday for New England.

Much of the CONUS should dry out by Sunday with the exception of
some lake effect rain showers in the Great Lakes region and any
moisture lingering into Maine, southern Texas, and Florida. The
Pacific Northwest though will likely see a ramp-up in
precipitation chances by Monday as a front and upper trough
approach.

The amplified trough and the cold front will lead to cooler
temperatures than average, while the upper ridges to the east and
west of it support above normal temperatures. The Lower Great
Lakes region into the Northeast should see warmer than average
temperatures by 10-20F on Thursday, with highs in the upper 70s to
low 80s. But as the upper trough and the primary and secondary
cold fronts march east into the latter half of the week,
temperatures will cool to below average across the central and
then east-central U.S., eventually making their way to the Eastern
Seaboard by early next week. The first frost or freeze of the
season may occur in the northern High Plains behind the cold
fronts late this week. In the eastern half of the U.S., lows will
generally be around 5-10F below average while highs should be more
like 10-15F below average, locally cooler. Meanwhile the arrival
of an upper ridge across the West will first raise temperatures
along the West Coast to 10-15F above normal, with some record warm
lows possible. The shift/expansion of the ridge farther east
should lead to warmer than average temperatures across the
northern Rockies into the High Plains early next week.


Tate

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
410 AM EDT Tue Oct 03 2023

Valid 12Z Tue Oct 03 2023 - 12Z Fri Oct 06 2023

...Wyoming Rockies...
Day 1...

The upper trough remnant that was a Great Basin low on Monday will
continue to lift northeast from central WY today. Light to locally
moderate precip will continue today with flow becoming westerly
over the WY Rockies. Snow levels dip to around 8000ft this morning
then rise to around 8500ft this afternoon before precip tapers off
with height rises from the approaching upper trough. Day 1 snow
probabilities for additional accumulations after 12Z are 20 to 40
percent for 4"+ for the higher Absarokas (including the Red
Lodge/Beartooth area in MT), Tetons, Wind River, and Bighorns,
with a localized risk for 8" max.

A warm ridge builds over the West into Friday and persists through
the weekend, bringing an end to this early season wintry weather
(and likely melting all but the highest fresh snow packs.


The probability of any ice accumulation across the Continental
U.S. is less than 10 percent.

Jackson

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EDT Tue Oct 03 2023

Valid 12Z Fri Oct 06 2023 - 12Z Tue Oct 10 2023

...Heavy rain and flash flooding threats ramp up in the Northeast
late week...


...Overview...

An upper trough and likely an embedded upper low are forecast to
swing slowly through the Great Lakes region southward late this
week into early next week, while a cold front sweeps through the
eastern U.S. at the surface. Rain chances will increase along and
ahead of the front, and heavy rainfall may cause flooding concerns
in the Northeast on Friday and Saturday. Some rain (with lake
effect enhancement) could linger into early next week underneath
the upper low. Meanwhile an upper ridge should overtake the
western U.S. for warmer than average temperatures and generally
dry conditions, until early next week when a trough and frontal
system could push into the Pacific Northwest.


...Guidance Evaluation/Predictability Assessment...

Model guidance is in reasonably good agreement with the trough
over the Great Lakes, with the past couple model cycles more
agreeable in forming a closed low within the trough likely over
the weekend. The closed low serves to slow down the movement of
the feature, with only a slow drift in its placement early next
week. Deterministic models do have some spread with its eventual
positioning. GFS runs including the 18Z and new 00Z run having the
upper low retrograde to the southwest does seem to be inconsistent
with other deterministic and ensemble guidance, so the GFS was not
preferred at this point.

Behind the upper trough/low, models also are agreeable with an
upper ridge shifting from the West Coast at the start of the
period Friday gradually into the Interior West over the
weekend/early next week and the central U.S. by Tuesday. Troughing
coming into the eastern Pacific stemming from an Alaskan upper low
shows some spread in its axis and depth but pretty minor for a
feature in that region for that lead time.

With the reasonably good consensus for the large scale pattern,
the WPC forecast used a blend of the deterministic guidance
particularly favoring the 18Z GFS and 12Z ECMWF early in the
period, transitioning to incorporate the ensemble means to half by
Day 6 and just over half Day 7 as model spread increased,
especially lessening the GFS proportion. Continuity from the
previous forecast was generally well maintained.


...Weather/Hazards Highlights...

As the upper trough and forming embedded low track across the
Great Lakes late week, Atlantic moisture is likely to flow into
the northeastern U.S., leading to increasing rain totals on Friday
and especially by Saturday along and ahead of the cold front.
Instability may be somewhat limited, but the forcing for ascent
will be strong with the right entrance region of the jet overhead,
and precipitable water anomalies are forecast to be at least above
the 75th if not the 90th percentile. Rain amounts look to increase
by Saturday, with upslope flow/terrain enhancement likely playing
a role in the Interior Northeast. Thus a Marginal Risk remains in
place across the Lower Great Lakes region and parts of the
northern Mid-Atlantic and Northeast for Day 4/Friday, with a
Slight Risk across the Interior Northeast on Day 5/Saturday. Most
heavy rain will exit by Sunday but some lingering showers are
possible underneath the upper low through early next week, with
lake effect rain showers likely.

Farther south, the tail end of the cold front could linger into
South Texas into at least Friday, sparking additional showers and
thunderstorms there after a few wet days. A Marginal Risk remains
in place for the Day 4 ERO/Friday. Rain amounts look to gradually
lessen this weekend into early next week. Meanwhile, conditions in
the West look to be dry under the upper ridge, aside from limited
showers possible in the Southwest. This is likely to change early
next week as a front and upper trough approach the Pacific
Northwest, causing increasing precipitation chances.

The amplified trough and the cold front will lead to cooler
temperatures than average, while the upper ridge to the west of it
supports above normal temperatures. One more warmer than average
day is possible in the Northeast on Friday, while high
temperatures across the Plains into Midwest will be below average
by 10-20F. Lows look to be a little less anomalous Friday morning
but could drop further on Saturday, with low 30s and perhaps a few
temperatures in the upper 20s in the northern half of the Plains,
creating the possibility of the first frost or freeze of the
season. As the upper trough and the cold front(s) march east into
the weekend, temperatures should cool to below average across the
east-central U.S. and eventually making their way to the Eastern
Seaboard by early next week. Meanwhile the arrival of an upper
ridge across the West will first raise temperatures along the West
Coast to 10-15F above normal, with some record warm lows possible.
The shift/expansion of the ridge farther east should lead to
warmer than average temperatures across the northern Rockies into
the High Plains early next week.


Tate


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, excessive rainfall outlook,
winter weather outlook probabilities, heat indices and Key
Messages are at:

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