Weather Prediction Center

National Oceanic and Atmospheric Administration

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
348 AM EDT Sun May 04 2025

Valid 12Z Sun May 04 2025 - 12Z Tue May 06 2025

...A continued omega block pattern over the lower 48 will lead to
prolonged periods of unsettled weather and cooler temperatures into early
next week...

...Locally heavy rainfall with flash flooding possible for southern New
England Monday...

...Scattered instances of flash flooding as well as severe weather
forecast for the southern High Plains Sunday and Monday...

An omega block pattern over the Lower 48 is in place this morning as a
strong ridge builds between a pair of upper-level lows over the Ohio
Valley and California/Southwest. This will bring prolonged periods of
unsettled weather and cooler temperatures to portions of the eastern and
western U.S. while north-central areas see dry conditions and well above
average temperatures. First, in the East, the upper-low over the Ohio
Valley as well as an accompanying occluded/cold front arcing southeastward
along the Lower Great Lakes and East Coast will continue to bring
widespread showers and thunderstorms over the next couple of days.
Moderate to locally heavy rainfall can be expected given the slow
progression of the front, with isolated flash flooding possible on Sunday.
On Monday, more focused very moist, onshore flow from the Atlantic ahead
of the cold front over portions of southern New England will lead to the
threat of a few more scattered instances of flash flooding, with a Slight
Risk of Excessive Rainfall (level 2/4) in effect. The southern portion of
the cold front over the Southeast/Carolinas will make the most eastward
progress, bringing an end to rain chances for these areas during the day
Monday as the front clears the coast, while rainfall lingers into Tuesday
for the Lower Great Lakes and Northeast. Forecast temperatures broadly
throughout the Great Lakes and Southeast will remain below average the
next couple of days, particularly for the Ohio/Tennessee Valleys, with
highs mainly in the 50s and 60s. Conditions will be closer to average
along the East Coast ahead of the slow moving front, with highs in the 60s
and 70s for New England and the northern Mid-Atlantic and the 70s and 80s
for the southern Mid-Atlantic/Carolinas.

To the west, widespread precipitation chances also remain in the forecast
across much of the West under the influence of the second upper-level low.
Showers and thunderstorms throughout the northern Rockies, Great Basin,
Four Corners region, and Southwest today will shift a bit eastward on
Monday, bringing greater chances into areas of the central Rockies and the
adjacent High Plains as areas of the western Great Basin dry out. Moderate
to locally heavy rainfall, with some isolated flash flooding possible, is
most likely over the western Great Basin Sunday and the eastern Great
Basin Monday. Higher mountain elevations will see accumulating snowfall,
particularly over portions of the northern/central Rockies on Monday, with
totals of 4-8", locally higher, expected. A more focused corridor of
showers and thunderstorms along with more widespread heavy rainfall is
expected over the southern High Plains as anomalously high moisture from
the Gulf flows northwestward ahead of a surface frontal system emerging
from the mountains over the region. A Slight Risk of Excessive Rainfall is
in place for portions of northeastern New Mexico Sunday with another
Slight Risk over portions of the Texas Panhandle/western Texas on Monday
where the potential for rain rates of 1"/hr and 2-4" totals may lead to
some scattered instances of flash flooding. In addition, sufficient
instability given the moisture in place and cooler air aloft with the
approaching low, along with increasing upper-level winds, will lead to the
threat of some severe weather. The Storm Prediction Center has outlined
portions of southeastern New Mexico with a Slight Risk (level 2/5) Sunday
mainly for the threat of large hail. Another Slight Risk in place Monday
across portions of western Texas for the threat of very large hail,
damaging winds, and a few tornadoes. In contrast to the unsettled weather
to the north, portions of southwestern New Mexico will remain very dry
ahead of the approaching upper-low, with the combination of low humidity
and gusty winds prompting a Critical Risk of fire weather (level 2/3) from
the Storm Prediction Center for Sunday. Conditions across much of the west
and into the southern Plains will be below average given the upper-low
overhead and widespread precipitation. Forecast temperatures Sunday are
mainly in the 50s and 60s across the Interior West with 60s and 70s in the
Desert Southwest and southern Plains. The West Coast will be cooler and
below average as well on Sunday, with highs in the 50s and 60s, before a
warm up into the 60s and 70s on Monday as the upper-low shifts eastward.

Elsewhere, dry conditions and well above average temperatures are expected
across north-central portions of the country as the upper-ridge builds
overhead. Highs will be in the 70s and 80s Sunday across the
northern/central Rockies, northern/central Plains, and Upper Midwest. Some
locations across the northern High Plains may approach 90, upwards of
30-35 degrees above average for this time of year. The approach of the
upper-low and an accompanying eastward moving cold front will bring much
cooler temperatures to the northern/central Rockies and adjacent High
Plains Monday as highs fall into the 50s and 60s.

Putnam


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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
306 PM EDT Sun May 4 2025

Valid 12Z Wed May 07 2025 - 12Z Sun May 11 2025


...Mid to late week heavy rainfall potential for the central Gulf
Coast into the Southeast...


...Overview...

A blocky pattern in the short range should finally begin to break
down by Wednesday as a pair of upper lows over the East and West
weaken and shift east. A stationary or slow moving frontal boundary
draped across the Southeast may continue to support heavy rainfall
across the region, and especially along the Gulf Coast. A
shortwave dropping in from east-central Canada may briefly cut off
another upper low over the Northeast on Friday, while the western
low shifts east and eventually settles over the Southeast next
weekend. This may continue the threat for showers and storms across
the Southeast through much of the period. Upper ridging over the
West Coast will build east into the Rockies/Central U.S. as a
Pacific trough nears the West Coast next Sunday.


...Guidance/Predictability Assessment...

While model guidance agrees in principle on the larger scale
features described above, uncertainty in the details still produce
sensible weather differences. Models show the cutoff upper low
moving slowly from the southwestern to south-central U.S. as the
week progresses. By Thursday-Friday model differences with this
feature include the new 12Z GFS farther south and west with energy
at the low's base near Texas and the Lower Mississippi Valley,
pushing the front offshore into the Gulf for less rain onshore in
the central Gulf Coast area but more QPF filtering into much of
Texas. Did not prefer this 12Z GFS solution as it was against
consensus.

Meanwhile farther north, the initially closed low over the
Northeast should quickly track northeast as additional energy dives
in from Canada. This second round of troughing shows a lot more
spread in placement into later week as it may form a closed low.
Through the 00/06Z model cycle, on Saturday for example the 00Z GFS
and ECMWF were reasonably well aligned with the upper and surface
low position and generally in line with the ensemble means, so
generally favored that cluster, which also jived well with
continuity. The 06Z GFS was farther southwest and the 00Z CMC was
much farther northeast. Many of the AI/ML models were farther
northeast like the CMC so did not want to totally rule that out.
However, now the newer 12Z model guidance is tending to favor
slower/farther southwest positions for that feature. So this
forecast continues to be in flux and further changes may be needed.

In the West, upper ridging should build in the Great Basin and
Rockies behind the upper low. By late week into the weekend greater
model differences start to occur to its west with troughing and a
possible embedded upper low in the eastern Pacific. The 00Z CMC
looks like an outlier bringing a closed low into British Columbia
and the Northwest. 12Z models continue to show some spread in the
trough's timing moving toward the Northwest.

The WPC forecast used a multi-model blend of deterministic
guidance favoring the ECMWF and GFS early in the period. Used the
ensemble means and increased their proportion to over half by Days
6-7 as model spread increased.


...Weather/Hazards Highlights...

By Wednesday, the start of the period, the heaviest rains are
likely to focus near the central Gulf Coast pooling along a frontal
boundary. Heavy rain rates are likely along the cusp of the
instability gradient and training storms are possible generally in
southern Louisiana and vicinity. However, there are some competing
factors for flooding to be too widespread Wednesday, including
model spread with some focusing the front and thus the rainfall
offshore. The farther south axis of heaviest rain compared to the
short range puts the highest QPF atop drier antecedent conditions,
along with higher flash flood guidance in swamplands. Thus
maintained the Slight Risk across much of the Lower Mississippi
Valley rather than any upgrades at this time and will continue to
monitor trends. Urban areas could still be vulnerable to flash
flooding. Heavy rain could persist into Thursday along the central
Gulf Coast and into parts of the Southeast. Again, model spread and
higher flash flood guidance limits flooding potential for now and
will maintain a Marginal Risk for these areas on Day 5/Thursday.
Rain and thunderstorms are likely to persist across the Southeast
late week into the weekend.

Meanwhile farther west and north, precipitation including higher
elevation snow could continue into Wednesday for the south-central
Rockies. Areas of rain are also likely across the central Plains to
Middle Mississippi Valley Wednesday-Thursday and lingering into
Friday in the Lower Mississippi Valley. Areas of rain are also
possible in the northeastern U.S. at times later this week into the
weekend. On Wednesday, some wrapback moisture and instability on
the backside of the associated surface low could allow for modest
rain in Interior Northeast, but with several model and QPF cycles
showing this rain staying well under an inch, removed the Marginal
Risk as any flooding chances should be below 5 percent.

The upper low over the Southwest early in the period will result
in lingering below normal temperatures for the Southwest and south-
central Plains where daytime highs could be 10-20 degrees below
normal. This should moderate with time but may still remain
modestly below normal into late week for the southern Plains. Upper
ridging building over the West as the upper low shifts east will
allow for expanding coverage of above normal temperatures there as
the week progresses, including 100 degree temperatures in the
Desert Southwest. Above average temperatures will stretch into the
northern tier as well, with highs reaching the 70s and 80s in the
northern Plains to Upper Midwest.


Tate/Santorelli


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
319 AM EDT Sun May 4 2025

Valid 00Z Mon 05 May 2025 - 00Z Mon 12 May 2025

Guidance continues to show a persistent easterly trade wind pattern
over the next week or so featuring upper ridging over the main
islands into at least the middle of next week. An upper low out of
the Gulf of Alaska will extend troughing towards Hawaii around
next Thursday, which may support higher moisture and some increase
in windward/mountain-focused showers. Developing surface high
pressure to the north of Hawaii will continue moderate to brisk
wind speeds through next week.

Santorelli

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1152 AM EDT Sun May 4 2025
Day 1
Valid 16Z Sun May 04 2025 - 12Z Mon May 05 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
EASTERN NEW MEXICO...

...16Z Update...

...New Mexico...

The Slight Risk area across New Mexico was expanded slightly south
in keeping with the latest guidance that areas north of Roswell
could see more rainfall than previous forecasts, necessitating the
southward expansion. Otherwise, the forecast is little changed in
this area with a broad 1-2 inches of rain expected, most of which
occurring tonight. Flooding concerns stemming from the slow
movement of the storms, a consistent resupply of Gulf moisture from
the southeast on 20-30 kt southeasterly winds, and nearly
stationary forcing in the form of a cutoff low all support widely
scattered instance of flash flooding consistent with the Slight
Risk. Areas of terrain will be especially vulnerable due to the
terrain focusing the rainfall into narrow valleys that can fill up
and flooding with relatively little rainfall.

...Northeast...

As the cold frontal rainfall moves off the coast over the next few
hours, the Marginal Risk in NC,VA, and MD was trimmed from the
south and west to follow the line of showers with embedded
convection as it moves over the beaches of those states. Isolated
afternoon thunderstorms will be possible given the abundance of
moisture from today's rains across the Piedmont of NC and VA, but
the storms should be few and far between, and therefore not pose a
significant flash flooding threat. From about the Mason-Dixon line
north this afternoon, increasing instability should allow for more
widely scattered convection, as compared to areas further south.
THese storms will be capable of producing isolated instances of
flash flooding.

The Marginal was also trimmed out of MI, IN, and western OH since
the rainfall there is expected to remain the stratiform it is now,
which would preclude any rainfall rates capable of causing flash
flooding. Elsewhere the Marginal remains in place and largely
unchanged.

Wegman

...Previous Discussion...

New Mexico...
There is a slight risk of excessive rainfall over portions of
eastern New Mexico as south to southeasterly flow draws moisture
into the region as height falls begin in response to shortwave
energy approaches. The 04/00Z suite of numerical guidance develops
heavy rainfall developing in the diurnal activity that then
persists over the southern High Plains well into late tonight/early
Monday morning. Precipitable water anomaly values reaches 2 sigma
over this area by 00Z Monday..with the 04/00Z HREF mean suggests
some repeating threats for 1"/hr rates across the Slight area with
potential for 2-3" over much of the area. The eastern portion of
the Marginal risk area was largely left unchanged...but the western
portion of the area was trimmed to minimize overlap with heavy
snow areas (especially over the San Juan mountains).

Great Basin...
While the probability of excessive rainfall is likely non-zero
given the showery nature of precipitation given the upper trough
and cold mid- level temperatures aloft...the amount of rain
shouldn't be a problem unless it all falls in under an hour.
Individual thunderstorms may result in briefly heavy
rates...but thinking is that the thunderstorms will be embedded
within a broader field of showers circulating around the main upper
low. This should help mitigate the overall threat of flooding.

Midwest to Northeast...
The slow moving closed low embedded within a broader upper trough
continues to make its way eastward across the Ohio Valley today and
tonight. Deepest moisture of 1.25 to 1.5 inches will be eventually
be shunted off the Mid- Atlantic coast today but still stream in
over New York back and then drawn back through northern Ohio. The
Marginal Risk is maintained with only nudges to the
western/northern periphery of the Marginal risk area based on the
latest QPF.

Bann

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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1152 AM EDT Sun May 4 2025
Day 2
Valid 12Z Mon May 05 2025 - 12Z Tue May 06 2025

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

Texas into New Mexico...
A closed upper low over the Desert Southwest will continue to
meander eastward on Monday. Confidence remains in a focused area
for repeating heavy rainfall south from the TX Panhandle to the NM
border where a Slight Risk remains without many changes...with main
activity occurring once again around the time of maximum daytime
heating and then persisting into or through the night. The suite
of 04/00Z numerical guidance still shows the magnitude of
precipitable water values to exceed 2 sigma by 00Z Tuesday with the
1.25" precipitable water line reaching the Caprock. The 12Z QPF
consensus is for 2-4" over a sizable area just south of the TX
Panhandle...with locally higher amounts embedded in the broader QPF
area.

Mojave Desert through Southern Utah...
Numerous showers with embedded daytime and evening thunderstorms is
still expected as upper low continues to meander over Arizona as
it begins to fill. Moisture is still anomalous for this time of
year...being some 2 to 3 standardized anomalies above climatology
for early May...but concern would be greater for excessive rainfall
if the actual values of precipitable water values were greater and
intense rainfall rates would be sustained for a longer duration.
As a result...the risk of excessive rainfall appears to be non-zero
but not enough to warrant a Marginal risk area based on
coordination with local offices.

Northern Mid-Atlantic into southern New England...
Closed low will continue to meanders across portions of the Upper
OH Valley through Monday night. Continued onshore flow brings the
threat for repeating locally heavy rain over the northern Mid-
Atlantic into southern New England which will have seen some heavy
rain between now and then. A Marginal Risk is maintained.


Bann

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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1152 AM EDT Sun May 4 2025
Day 3
Valid 12Z Tue May 06 2025 - 12Z Wed May 07 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHERN MISSISSIPPI VALLEY/CENTRAL GULF COAST REGION...

Showers and thunderstorms capable of producing intense rainfall
rates and heavy/excessive rainfall will become more numerous
on Tuesday as height falls make their way out across Texas and as
the parent upper low ejects out over the Southern Plains. With
increasing flow off the Gulf drawing deeper moisture on-
shore....the convection should become increasingly efficient
rainfall makers.especially over portions of Louisiana and
Mississippi. There is still some differences in where models place
the heaviest rainfall...with the GFS and Canadian favoring a faster
solution while the EC/UK favoring the axis from eastern Texas into
northern Louisiana. This forecast cycle nudged the Moderate risk
area a bit eastward but not as far east as the GFS/Canadian.

Bann

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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
255 AM EDT Sun May 4 2025


By Wednesday, the start of the period, the heaviest rains are
likely to focus along the central Gulf Coast pooling along a
frontal boundary. For the Day 4/Wednesday ERO, maintained a Slight
Risk from far southeast Texas into southern Mississippi and
southern Alabama, as heavy rain rates and training could cause
scattered flash floods, but the potential may be limited slightly
by drier antecedent conditions and higher flash flood guidance.
Heavy rain could persist into Thursday along the central Gulf Coast
and into parts of the Southeast, but opted for just a marginal
risk right now given lingering guidance uncertainty and dry soils.
Some rain and storms are likely to persist across the Southeast in
general into late week and the weekend as well.

Under the departing eastern upper low on Wednesday, wrapback
moisture and instability on the backside of the associated surface
low could lead to locally heavy rain in the sensitive terrain of
the Interior Northeast. A Marginal Risk remains in place for the
Wednesday (Day 4) ERO period.

The upper low over the Southwest early in the period will result
in below to well below normal temperatures for the Southwest and
south-central Plains where daytime highs could be 15-20 degrees
below normal. This should moderate with time but may still remain
modestly below normal into late week for the southern Plains. Upper
ridging building over the West as the upper low shifts east will
allow for expanding coverage of above normal temperatures there as
next week progresses, including 100 degree temperatures in the
Desert Southwest. Above average temperatures will stretch into the
northern tier as well, with highs reaching the 70s and 80s in the
northern Plains to Upper Midwest. Slightly above normal
temperatures may move into the Northeast next weekend.


Santorelli

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
255 AM EDT Sun May 4 2025


By Wednesday, the start of the period, the heaviest rains are
likely to focus along the central Gulf Coast pooling along a
frontal boundary. For the Day 4/Wednesday ERO, maintained a Slight
Risk from far southeast Texas into southern Mississippi and
southern Alabama, as heavy rain rates and training could cause
scattered flash floods, but the potential may be limited slightly
by drier antecedent conditions and higher flash flood guidance.
Heavy rain could persist into Thursday along the central Gulf Coast
and into parts of the Southeast, but opted for just a marginal
risk right now given lingering guidance uncertainty and dry soils.
Some rain and storms are likely to persist across the Southeast in
general into late week and the weekend as well.

Under the departing eastern upper low on Wednesday, wrapback
moisture and instability on the backside of the associated surface
low could lead to locally heavy rain in the sensitive terrain of
the Interior Northeast. A Marginal Risk remains in place for the
Wednesday (Day 4) ERO period.

The upper low over the Southwest early in the period will result
in below to well below normal temperatures for the Southwest and
south-central Plains where daytime highs could be 15-20 degrees
below normal. This should moderate with time but may still remain
modestly below normal into late week for the southern Plains. Upper
ridging building over the West as the upper low shifts east will
allow for expanding coverage of above normal temperatures there as
next week progresses, including 100 degree temperatures in the
Desert Southwest. Above average temperatures will stretch into the
northern tier as well, with highs reaching the 70s and 80s in the
northern Plains to Upper Midwest. Slightly above normal
temperatures may move into the Northeast next weekend.


Santorelli

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
251 PM EDT Sun May 4 2025

Valid 00Z Mon May 05 2025 - 00Z Thu May 08 2025


...Intermountain West...
Days 1-3...

The very blocky upper pattern (typical for May during our
atmospheric spindown into summer) is manifesting itself as two
closed lows over the CONUS, the western one of which will be
responsible for a wintry thump of snow over the Rockies. As of
Sunday evening, the upper low will move from the CA deserts/CO
River Valley northeastward through AZ on Monday then into northern
NM Tuesday before finally moving into the Plains Wednesday. The
southern track of the upper system will keep the largest negative
anomalies (height and temperatures) over northern Mexico and
astride the southern US border, meaning snow levels will be on the
higher side over the Rockies (9000ft +/- 500ft). Later, colder air
will eventually advect in from the northeast (modestly) which
should decrease snow levels a bit to around 8000ft (and a bit lower
at times). Significant snow is expected for the mountains in CO
and northern NM with moderate to major impacts near/above the
treeline.

The storm system will progress in phases, with the initial WAA-
driven snow first on southerly flow D1 to be followed by jet/PVA-
driven snow as the upper low approaches northern NM D2 as the flow
turns to more easterly, maximizing upslope potential on the east
side of the Rockies. Finally by D3, as the system unwinds/extends,
and modest snow to start will gradually wind down but not fully end
until just after the end of this D3. Areas in favor of the most
snow include San Juans D1, Sangre de Cristos northward to the
higher elevations of the Front Range D2-3. There, snowfall rates of
1-3"/hr are possible (>50% probs for 2"/hr in the HREF) D2. WPC
probabilities for at least 8 inches of snow over the next three
days are highest (>50%) above 10,000ft with >50% probs for at least
18 inches above 12,000ft. As some colder air filters in early
Wednesday, some snow may fall into the higher elevations of the
I-25 corridor (Palmer Divide and Raton Mesa along the CO/NM
border).

Farther north, an incoming cold front will aid in producing some
mountain snow for the Uintas, Wind River Range, Absarokas and
Bighorns, and southwestern Montana where snow levels will be a bit
lower (6000-8000ft). There, WPC probabilities for at least 8 inches
of snow Days 1-2 are moderate to high (50-80%).

The probability of significant freezing rain across the CONUS is
less than 10%.


Fracasso

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
306 PM EDT Sun May 4 2025

Valid 12Z Wed May 07 2025 - 12Z Sun May 11 2025


...Mid to late week heavy rainfall potential for the central Gulf
Coast into the Southeast...


...Overview...

A blocky pattern in the short range should finally begin to break
down by Wednesday as a pair of upper lows over the East and West
weaken and shift east. A stationary or slow moving frontal boundary
draped across the Southeast may continue to support heavy rainfall
across the region, and especially along the Gulf Coast. A
shortwave dropping in from east-central Canada may briefly cut off
another upper low over the Northeast on Friday, while the western
low shifts east and eventually settles over the Southeast next
weekend. This may continue the threat for showers and storms across
the Southeast through much of the period. Upper ridging over the
West Coast will build east into the Rockies/Central U.S. as a
Pacific trough nears the West Coast next Sunday.


...Guidance/Predictability Assessment...

While model guidance agrees in principle on the larger scale
features described above, uncertainty in the details still produce
sensible weather differences. Models show the cutoff upper low
moving slowly from the southwestern to south-central U.S. as the
week progresses. By Thursday-Friday model differences with this
feature include the new 12Z GFS farther south and west with energy
at the low's base near Texas and the Lower Mississippi Valley,
pushing the front offshore into the Gulf for less rain onshore in
the central Gulf Coast area but more QPF filtering into much of
Texas. Did not prefer this 12Z GFS solution as it was against
consensus.

Meanwhile farther north, the initially closed low over the
Northeast should quickly track northeast as additional energy dives
in from Canada. This second round of troughing shows a lot more
spread in placement into later week as it may form a closed low.
Through the 00/06Z model cycle, on Saturday for example the 00Z GFS
and ECMWF were reasonably well aligned with the upper and surface
low position and generally in line with the ensemble means, so
generally favored that cluster, which also jived well with
continuity. The 06Z GFS was farther southwest and the 00Z CMC was
much farther northeast. Many of the AI/ML models were farther
northeast like the CMC so did not want to totally rule that out.
However, now the newer 12Z model guidance is tending to favor
slower/farther southwest positions for that feature. So this
forecast continues to be in flux and further changes may be needed.

In the West, upper ridging should build in the Great Basin and
Rockies behind the upper low. By late week into the weekend greater
model differences start to occur to its west with troughing and a
possible embedded upper low in the eastern Pacific. The 00Z CMC
looks like an outlier bringing a closed low into British Columbia
and the Northwest. 12Z models continue to show some spread in the
trough's timing moving toward the Northwest.

The WPC forecast used a multi-model blend of deterministic
guidance favoring the ECMWF and GFS early in the period. Used the
ensemble means and increased their proportion to over half by Days
6-7 as model spread increased.


...Weather/Hazards Highlights...

By Wednesday, the start of the period, the heaviest rains are
likely to focus near the central Gulf Coast pooling along a frontal
boundary. Heavy rain rates are likely along the cusp of the
instability gradient and training storms are possible generally in
southern Louisiana and vicinity. However, there are some competing
factors for flooding to be too widespread Wednesday, including
model spread with some focusing the front and thus the rainfall
offshore. The farther south axis of heaviest rain compared to the
short range puts the highest QPF atop drier antecedent conditions,
along with higher flash flood guidance in swamplands. Thus
maintained the Slight Risk across much of the Lower Mississippi
Valley rather than any upgrades at this time and will continue to
monitor trends. Urban areas could still be vulnerable to flash
flooding. Heavy rain could persist into Thursday along the central
Gulf Coast and into parts of the Southeast. Again, model spread and
higher flash flood guidance limits flooding potential for now and
will maintain a Marginal Risk for these areas on Day 5/Thursday.
Rain and thunderstorms are likely to persist across the Southeast
late week into the weekend.

Meanwhile farther west and north, precipitation including higher
elevation snow could continue into Wednesday for the south-central
Rockies. Areas of rain are also likely across the central Plains to
Middle Mississippi Valley Wednesday-Thursday and lingering into
Friday in the Lower Mississippi Valley. Areas of rain are also
possible in the northeastern U.S. at times later this week into the
weekend. On Wednesday, some wrapback moisture and instability on
the backside of the associated surface low could allow for modest
rain in Interior Northeast, but with several model and QPF cycles
showing this rain staying well under an inch, removed the Marginal
Risk as any flooding chances should be below 5 percent.

The upper low over the Southwest early in the period will result
in lingering below normal temperatures for the Southwest and south-
central Plains where daytime highs could be 10-20 degrees below
normal. This should moderate with time but may still remain
modestly below normal into late week for the southern Plains. Upper
ridging building over the West as the upper low shifts east will
allow for expanding coverage of above normal temperatures there as
the week progresses, including 100 degree temperatures in the
Desert Southwest. Above average temperatures will stretch into the
northern tier as well, with highs reaching the 70s and 80s in the
northern Plains to Upper Midwest.


Tate/Santorelli


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