Weather Prediction Center

National Oceanic and Atmospheric Administration

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
134 PM EDT Sat May 03 2025

Valid 00Z Sun May 04 2025 - 00Z Tue May 06 2025

...A convoluted pattern with embedded slow-moving systems is expected
across the Lower 48, leading to prolonged periods of unsettled weather
into early next week...

...Heavy precipitation is expected across the Northern Mid-Atlantic States
and from the Southern Rockies into the Great Basin...

Deep layer lows develop over the Ohio Valley and West Coast which will be
slow to move over the next few days. In the East, the first of the systems
is developing over the Ohio Valley. Its cold front makes slow progress
through the Central Gulf Coast and Southeast before stalling on Monday.
Showers and thunderstorms with heavy rainfall, with a few thunderstorms
being severe, are expected over portions of the Southeast and Mid-Atlantic
States with this system from Saturday evening through Monday. Rainfall
totals of 2 to 4 inches in and near portions of southeast New York of
Pennsylvania will foster a Marginal Risk of excessive rainfall/flash
flooding Saturday evening through Monday. Because of the persistent
humidity, record warm low temperatures are anticipated for portions of the
Mid-Atlantic States on Sunday.

A separate deep layer cyclone moves through the Southwest, bringing
showers and thunderstorms Saturday evening into Monday and higher
elevation snows in the Rockies/Intermountain West. A moist, upslope flow
along the southern Rockies should persist as a frontal boundary lingers
south of the region while unstable showers and thunderstorms form closer
to the cyclone during daytime heating. Isolated to scattered instances of
flash flooding will be possible across portions of eastern New Mexico,
particularly for terrain sensitive regions and area burn scars from
Saturday evening through Sunday. On Monday as the system moves towards
the Southern Plains, a scattered instances of flash flooding are expected
across portions of northwestern Texas. Accumulating snow is expected for
some of the higher elevations of regional mountain ranges, most notably
the Sierra Nevada Saturday evening and then portions of the northern
Rockies in Montana and the San Juans in Colorado on Sunday and Monday. Dry
antecedent conditions, gusty winds, and comparatively low relative
humidity over southwestern New Mexico, south of the unsettled weather
covering most of the West, has prompted a Critical Risk of fire weather
conditions from the Storm Prediction Center for Sunday.

Forecast highs under the eastern deep layer cyclone will be well below
average, particularly across portions of the Midwest/Ohio Valley, as
temperatures only reach into the 50s and 60s. Forecast highs under the
western deep layer cyclone will also be well below average,across the
Great Basin Sunday, with highs in the 50s and 60s, and into the Southwest,
with highs only into the 70s. In contrast, temperatures under a building
upper-level ridge between the lows will be well above average as highs
soar into the 70s and 80s across much of the northern/central Rockies and
into the northern Plains/Upper Great Lakes. Some locations along the
northern High Plains may reach the upper 80s on Sunday, upwards of 25-30
degrees above average.

Roth


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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
315 PM EDT Sat May 3 2025

Valid 12Z Tue May 06 2025 - 12Z Sat May 10 2025


...Blocky pattern with closed lows over the West and the East with
areas of heavy rainfall potential early to mid next week...


...Overview...

An omega block will remain in place over the lower 48 into
Tuesday, with an upper low atop the Four Corners region, one over
the Ohio Valley, and upper ridging in between. Both lows should
slowly drift east by Wednesday/Thursday. Moist inflow over the
south-central and southeastern U.S. ahead of the Four Corners upper
low will produce areas of significant rainfall and potential
flooding over portions of the Central and Southern Plains into the
Lower Mississippi Valley on Tuesday and near the central Gulf Coast
Wednesday-Thursday as a front stalls there. Meanwhile some locally
heavy rain is possible in the Northeast ahead of the eastern low.
This eastern low is forecast to be swept up toward the Canadian
Maritimes later next week as a northern stream trough reestablishes
over the Northeast. The western low will likely remain isolated as
it slowly tracks over the Plains toward the Lower Mississippi
Valley next weekend.


...Guidance/Predictability Assessment...

Model guidance seems to be in reasonable agreement early in the
forecast period considering the blocky pattern. The eastern upper
low is forecast to track from the Ohio Valley/Great Lakes Tuesday
and atop the Northeast Wednesday, before pivoting northeast as
northern stream energy drops into the Northeast. This northern
stream energy potentially closing off an upper low shows some
timing differences in the 00/06Z and newer 12Z guidance, with the
12Z GFS the fastest/farthest east into late week. The eastern
trough will also impact surface low pressure systems in the
Northeast and western Atlantic that vary. Tended to favor the
ensemble means with the trough's timing despite the means not being
as deep as the deterministic runs.

The western upper low is forecast to remain cut off at least
through midweek, and recent operational and AI/ML models show it
staying cut off from the main flow even into late week as it drifts
into the Lower Mississippi Valley or Southeast, possibly
interacting with the eastern trough but with some energy held back.
Thus the forecast trended in the direction of an upper low
stalling over the Lower Mississippi Valley even into early next
Saturday, with less phasing with the northeastern trough. The newer
12Z guidance kept this trend but will continue to monitor as the
position of that upper low would considerably affect sensible
weather. Smaller scale features like shortwaves also show spread in
the West, even by Tuesday-Wednesday with the potential for a
compact low in the northern Rockies or High Plains as shown by many
00/06Z models.

The WPC forecast used a blend of the 06Z GFS and 00Z ECMWF and CMC
early in the period, and introduced and gradually increased the
proportion of ensemble means to just over half by the end of the
period to reduce too many individual model differences.


...Weather/Hazards Highlights...

Anomalous moisture is forecast to persist over the southwestern to
south-central U.S. near and ahead of the Four Corners upper low.
Precipitation is likely to remain over the central Great
Basin/Southwest into Tuesday and the southern/central Rockies on
Wednesday, including moderate snowfall in the highest elevations.
But farther east, ample instability pooling ahead of a low
pressure/frontal system in the south-central U.S. will allow for
widespread rain and thunderstorms across the south-central Plains
into the Lower Mississippi Valley on Tuesday. Portions of the
Plains into the Lower Mississippi Valley states will be especially
vulnerable to heavy rain/flooding due to recent heavy rains and
saturated soils. Widespread rainfall amounts of 2-5+" remain likely
across portions of the ArkLaTex and Lower Mississippi Valley, and
a Moderate Risk remains in place for the Day 4/Tuesday ERO for this
activity. Back westward, this ERO issuance expanded the Slight
Risk across the south-central High Plains where rain totals of 1-3"
will be well above average and likely exceed lower-end average
recurrence intervals. Then by Wednesday, the heaviest rain is
likely to shift toward the central Gulf Coast pooling along a
frontal boundary starting to lay even more west to east. Maintained
a Slight Risk similar to the previous issuance, 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 with some rain and storms
likely across the Southeast in general into late week.

Under the eastern upper low, a low pressure system will still be
in the vicinity of the Great Lakes with its frontal system
stretching into the Northeast on Tuesday. After a few days of
moderate to heavy rain in the northeastern U.S. during the short
range period, showers and storms on Tuesday may cause isolated
flooding risks especially in urban and poor drainage areas. By
Wednesday the surface low should be tracking northeastward a little
more progressively, but some wrapback moisture and instability
near the low track could lead to locally heavy rain in the
sensitive terrain of the Interior Northeast. Marginal Risks remain
in place across portions of the Northeast Tuesday and Wednesday,
though shrinking in coverage in this forecast cycle as models come
into slightly better agreement with where rainfall may focus, and
as rain amounts generally decrease.

The upper low over the Southwest early in the week 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.


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
311 AM EDT Sat May 3 2025

Valid 00Z Sun 04 May 2025 - 00Z Sun 11 May 2025

Guidance continues to show a persistent trade pattern over the
next week or so featuring upper ridging over and north of the main
islands into midweek, possibly weakening by next Thursday as weak
troughing approaches from the east. This generally supports light
windward/mountain- focused showers but the modest decrease in
heights aloft may lead to a subtle increase in rainfall later next
week. Winds should remain moderate to brisk, with some increase
in speeds next week due to developing surface high pressure to the
northwest/north of Hawaii next week.

Santorelli

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
437 PM EDT Sat May 3 2025
Day 1
Valid 16Z Sat May 03 2025 - 12Z Sun May 04 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
EASTERN U.S. AND THE SACRAMENTO MOUNTAINS OF NEW MEXICO...

16Z Update...
An upper-level low is forming over the mid-Mississippi region and
becomes cutoff over Kentucky tonight as the jet focuses over
eastern Canada. Low level flow is drawing Gulf moisture through and
ahead of the system from the Gulf Coast up through the Eastern
Seaboard. Several focus areas for thunderstorms are expected
through tonight in the broad area which covered by a contiguous
Marginal Risk.

Ohio Valley to Gulf Coast...
Locally heavy activity has developed ahead of a surface low over
western TN with scattered storms south ahead of the advancing cold
front through MS and north along a stalled boundary that extends to
the upper Ohio Valley. This activity may pivot over eastern
KY/southern OH through the middle afternoon while activity over AL
to the Gulf Coast should be more progressive.

Carolinas, Central Appalachians and Mid-Atlantic...
Lee trough development over the Piedmont in the Carolinas later
this afternoon will allow potentially training activity in deep
SSWly flow there well into the evening, so the Marginal Risk was
expanded east a bit over SC/NC. This activity lifts north through
the central Appalachians into this evening with localized flash
flood threats. Later tonight the activity shifts east with some
training potential, so the Marginal was maintained east through the
Baltimore/Washington urban centers.


Northeast...
The northern end of the moisture plume converges on a frontal zone
over Upstate NY and central New England through this afternoon
bringing potential for excessive rain despite strong deep layer
flow. The Marginal Risk was expanded north into central New
England. A second round of development is expected farther south
this evening in the Hudson Valley and southern New England which
was already covered by a Marginal.


New Mexico...
Afternoon convection over the Sacramento Mtns brings a threat for
runoff issues from burn scars into this evening, so the Marginal
Risk is maintained.


Jackson

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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
437 PM EDT Sat May 3 2025
Day 2
Valid 12Z Sun May 04 2025 - 12Z Mon May 05 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE
EASTERN UNITED STATES AND SOUTHERN ROCKIES AND ADJACENT HIGH
PLAINS...

21Z Update...


New Mexico...
A Slight Risk has been raised for portions of eastern NM based on a
notable increase in QPF from the 12Z guidance consensus. SWly flow
over TX brings robust Gulf moisture up through the southern Rockies
and adjacent High Plains as a closed low develops and stalls
over the Sonoran Desert. Heavy rain develops in the diurnal
activity that then persists over the southern High Plains well into
Sunday night as the low stalls. The PW anomaly reaches 2 sigma over
this area by 00Z Monday. The 12Z HREF mean suggests some repeating
threats for 1"/hr rates through this Slight area with potential for
2-3" over much of the area. The Marginal risk was expanded to the
lower flanks of the San Juans based on updated QPF and FFG.

Great Basin...
Sunday is the second day for the Great Basin under the upper
trough. With PW anomalies of 2-3 sigma over normal with instability
and fairly light deep layer flow should allow some repeating
activity over Nevada and the Mojave Desert where a Marginal Risk is
raised.

Midwest to Northeast...
The slow moving closed low embedded within a broader upper trough
continues to make its way eastward Sunday. Deepest moisture of
1.25 to 1.5 inches will be eventually be shunted off the Mid-
Atlantic coast Sunday afternoon, but still stream in over NY back
through northern Ohio. The Marginal Risk is maintained with an
expansion over the Detroit metro given 12Z QPF consensus along with
lower FFG.


Jackson

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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
437 PM EDT Sat May 3 2025
Day 3
Valid 12Z Mon May 05 2025 - 12Z Tue May 06 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF WEST
TEXAS...

Texas into New Mexico...
The upper low drifts east over southern AZ Monday, causing a minor
shift east in downstream rainfall compared to Sunday. Confidence
remains in a focused area for repeating heavy rain south from the
TX Panhandle to the NM border where a Slight Risk remains (it was
expanded a bit west through the NM border). A bit of a lull in QPF
is expected Monday morning, but diurnal increases expected in the
afternoon that then persist into or through the night. The PW
anomaly is forecast to exceed 2 sigma by 00Z Tuesday with the 1.25"
PW line reaching the Caprock. The 12Z QPF consensus is for 2-4"
over a sizable area just south of the TX Panhandle.


Mojave Desert through Southern Utah...
The broadening upper low over AZ aids instability over the Mojave
Desert through northern AZ and southern/central UT where a Marginal
Risk is raised for Monday. Continued light deep layer flow and PW
anomalies of 2-3 sigma should allow slow moving, heavy
thunderstorms over this area which includes the Slot Canyons of
southern UT.


Northern Mid-Atlantic into southern New England...
Closed low meanders to the Upper OH Valley 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.


Jackson

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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
315 PM EDT Sat May 3 2025


Anomalous moisture is forecast to persist over the southwestern to
south-central U.S. near and ahead of the Four Corners upper low.
Precipitation is likely to remain over the central Great
Basin/Southwest into Tuesday and the southern/central Rockies on
Wednesday, including moderate snowfall in the highest elevations.
But farther east, ample instability pooling ahead of a low
pressure/frontal system in the south-central U.S. will allow for
widespread rain and thunderstorms across the south-central Plains
into the Lower Mississippi Valley on Tuesday. Portions of the
Plains into the Lower Mississippi Valley states will be especially
vulnerable to heavy rain/flooding due to recent heavy rains and
saturated soils. Widespread rainfall amounts of 2-5+" remain likely
across portions of the ArkLaTex and Lower Mississippi Valley, and
a Moderate Risk remains in place for the Day 4/Tuesday ERO for this
activity. Back westward, this ERO issuance expanded the Slight
Risk across the south-central High Plains where rain totals of 1-3"
will be well above average and likely exceed lower-end average
recurrence intervals. Then by Wednesday, the heaviest rain is
likely to shift toward the central Gulf Coast pooling along a
frontal boundary starting to lay even more west to east. Maintained
a Slight Risk similar to the previous issuance, 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 with some rain and storms
likely across the Southeast in general into late week.

Under the eastern upper low, a low pressure system will still be
in the vicinity of the Great Lakes with its frontal system
stretching into the Northeast on Tuesday. After a few days of
moderate to heavy rain in the northeastern U.S. during the short
range period, showers and storms on Tuesday may cause isolated
flooding risks especially in urban and poor drainage areas. By
Wednesday the surface low should be tracking northeastward a little
more progressively, but some wrapback moisture and instability
near the low track could lead to locally heavy rain in the
sensitive terrain of the Interior Northeast. Marginal Risks remain
in place across portions of the Northeast Tuesday and Wednesday,
though shrinking in coverage in this forecast cycle as models come
into slightly better agreement with where rainfall may focus, and
as rain amounts generally decrease.

The upper low over the Southwest early in the week 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.


Tate/Santorelli

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
315 PM EDT Sat May 3 2025


Anomalous moisture is forecast to persist over the southwestern to
south-central U.S. near and ahead of the Four Corners upper low.
Precipitation is likely to remain over the central Great
Basin/Southwest into Tuesday and the southern/central Rockies on
Wednesday, including moderate snowfall in the highest elevations.
But farther east, ample instability pooling ahead of a low
pressure/frontal system in the south-central U.S. will allow for
widespread rain and thunderstorms across the south-central Plains
into the Lower Mississippi Valley on Tuesday. Portions of the
Plains into the Lower Mississippi Valley states will be especially
vulnerable to heavy rain/flooding due to recent heavy rains and
saturated soils. Widespread rainfall amounts of 2-5+" remain likely
across portions of the ArkLaTex and Lower Mississippi Valley, and
a Moderate Risk remains in place for the Day 4/Tuesday ERO for this
activity. Back westward, this ERO issuance expanded the Slight
Risk across the south-central High Plains where rain totals of 1-3"
will be well above average and likely exceed lower-end average
recurrence intervals. Then by Wednesday, the heaviest rain is
likely to shift toward the central Gulf Coast pooling along a
frontal boundary starting to lay even more west to east. Maintained
a Slight Risk similar to the previous issuance, 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 with some rain and storms
likely across the Southeast in general into late week.

Under the eastern upper low, a low pressure system will still be
in the vicinity of the Great Lakes with its frontal system
stretching into the Northeast on Tuesday. After a few days of
moderate to heavy rain in the northeastern U.S. during the short
range period, showers and storms on Tuesday may cause isolated
flooding risks especially in urban and poor drainage areas. By
Wednesday the surface low should be tracking northeastward a little
more progressively, but some wrapback moisture and instability
near the low track could lead to locally heavy rain in the
sensitive terrain of the Interior Northeast. Marginal Risks remain
in place across portions of the Northeast Tuesday and Wednesday,
though shrinking in coverage in this forecast cycle as models come
into slightly better agreement with where rainfall may focus, and
as rain amounts generally decrease.

The upper low over the Southwest early in the week 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.


Tate/Santorelli

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
228 PM EDT Sat May 3 2025

Valid 00Z Sun May 04 2025 - 00Z Wed May 07 2025


...Sierra Nevada...
Days 1-2...

Digging upper trough just off the CA coast this evening will
deepen and close off as it moves into/through SoCal overnight and
early Sunday. The best dynamics will quickly move into the Interior
West, but light upslope-driven snow will continue over the
central/southern High Sierra with snow levels generally near/over
8000ft. Main upper low will move through AZ into the Four Corners
though trailing streams of vorticity from the north will keep light
snow going over the Sierra until late Monday. WPC probabilities
for at least 8 inches of snow are generally 20-60% for the High
Sierra (above 10,000ft).


...Northern and Central Rockies...
Days 1-3...

Combination of the incoming upper low through the Southwest and a
slowly-moving trough axis in the northern stream pushing its way
across Montana will promote a period of unsettled weather for much
of the Interior West/Rockies through the period, including higher
elevation snow. The upper low is forecast to only move from
central AZ Monday morning to around the Four Corners region by
Tuesday morning then onto the western High Plains by the end of the
period as the upper jet carves out breaks down over the region.
This will favor an influx of moisture from the southeast
(TX/western Gulf) in combination with rotating vort maxes around
the main upper low atop a slowly-moving cold front at the surface
to the north (in addition to the one to the south ahead of the main
upper low). Snow levels will be high in the central/southern
Rockies, generally above the Front Range around 8000-10,000ft
(lowest beneath the cold core upper low) but lower farther north
behind the cold front to around 5000-7000ft across MT into WY. Snow
will be light to moderate and should maximize into the San Juans
via southerly flow but then into the CO Rockies and Sangre de
Cristos as the upper low moves eastward and the flow turns to more
southeasterly to easterly and northeasterly later in the evolution
of the system. Snow to the north will be driven by the surface
front and low-level convergence, but with more limited moisture and
lighter snowfall amounts.

For the three-day period, WPC probabilities for at least 8 inches
of snow are above 50% across the terrain of southern UT into CO
above 10,000ft or so and are at least 40% for at least 18 inches of
snow above 12,000 ft. To the north, probabilities are a bit lower
for at least 8 inches of snow through the period (20-50%), mostly
over the Wind River Range, Uintas, and across SW MT.


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


Fracasso

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
315 PM EDT Sat May 3 2025

Valid 12Z Tue May 06 2025 - 12Z Sat May 10 2025


...Blocky pattern with closed lows over the West and the East with
areas of heavy rainfall potential early to mid next week...


...Overview...

An omega block will remain in place over the lower 48 into
Tuesday, with an upper low atop the Four Corners region, one over
the Ohio Valley, and upper ridging in between. Both lows should
slowly drift east by Wednesday/Thursday. Moist inflow over the
south-central and southeastern U.S. ahead of the Four Corners upper
low will produce areas of significant rainfall and potential
flooding over portions of the Central and Southern Plains into the
Lower Mississippi Valley on Tuesday and near the central Gulf Coast
Wednesday-Thursday as a front stalls there. Meanwhile some locally
heavy rain is possible in the Northeast ahead of the eastern low.
This eastern low is forecast to be swept up toward the Canadian
Maritimes later next week as a northern stream trough reestablishes
over the Northeast. The western low will likely remain isolated as
it slowly tracks over the Plains toward the Lower Mississippi
Valley next weekend.


...Guidance/Predictability Assessment...

Model guidance seems to be in reasonable agreement early in the
forecast period considering the blocky pattern. The eastern upper
low is forecast to track from the Ohio Valley/Great Lakes Tuesday
and atop the Northeast Wednesday, before pivoting northeast as
northern stream energy drops into the Northeast. This northern
stream energy potentially closing off an upper low shows some
timing differences in the 00/06Z and newer 12Z guidance, with the
12Z GFS the fastest/farthest east into late week. The eastern
trough will also impact surface low pressure systems in the
Northeast and western Atlantic that vary. Tended to favor the
ensemble means with the trough's timing despite the means not being
as deep as the deterministic runs.

The western upper low is forecast to remain cut off at least
through midweek, and recent operational and AI/ML models show it
staying cut off from the main flow even into late week as it drifts
into the Lower Mississippi Valley or Southeast, possibly
interacting with the eastern trough but with some energy held back.
Thus the forecast trended in the direction of an upper low
stalling over the Lower Mississippi Valley even into early next
Saturday, with less phasing with the northeastern trough. The newer
12Z guidance kept this trend but will continue to monitor as the
position of that upper low would considerably affect sensible
weather. Smaller scale features like shortwaves also show spread in
the West, even by Tuesday-Wednesday with the potential for a
compact low in the northern Rockies or High Plains as shown by many
00/06Z models.

The WPC forecast used a blend of the 06Z GFS and 00Z ECMWF and CMC
early in the period, and introduced and gradually increased the
proportion of ensemble means to just over half by the end of the
period to reduce too many individual model differences.


...Weather/Hazards Highlights...

Anomalous moisture is forecast to persist over the southwestern to
south-central U.S. near and ahead of the Four Corners upper low.
Precipitation is likely to remain over the central Great
Basin/Southwest into Tuesday and the southern/central Rockies on
Wednesday, including moderate snowfall in the highest elevations.
But farther east, ample instability pooling ahead of a low
pressure/frontal system in the south-central U.S. will allow for
widespread rain and thunderstorms across the south-central Plains
into the Lower Mississippi Valley on Tuesday. Portions of the
Plains into the Lower Mississippi Valley states will be especially
vulnerable to heavy rain/flooding due to recent heavy rains and
saturated soils. Widespread rainfall amounts of 2-5+" remain likely
across portions of the ArkLaTex and Lower Mississippi Valley, and
a Moderate Risk remains in place for the Day 4/Tuesday ERO for this
activity. Back westward, this ERO issuance expanded the Slight
Risk across the south-central High Plains where rain totals of 1-3"
will be well above average and likely exceed lower-end average
recurrence intervals. Then by Wednesday, the heaviest rain is
likely to shift toward the central Gulf Coast pooling along a
frontal boundary starting to lay even more west to east. Maintained
a Slight Risk similar to the previous issuance, 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 with some rain and storms
likely across the Southeast in general into late week.

Under the eastern upper low, a low pressure system will still be
in the vicinity of the Great Lakes with its frontal system
stretching into the Northeast on Tuesday. After a few days of
moderate to heavy rain in the northeastern U.S. during the short
range period, showers and storms on Tuesday may cause isolated
flooding risks especially in urban and poor drainage areas. By
Wednesday the surface low should be tracking northeastward a little
more progressively, but some wrapback moisture and instability
near the low track could lead to locally heavy rain in the
sensitive terrain of the Interior Northeast. Marginal Risks remain
in place across portions of the Northeast Tuesday and Wednesday,
though shrinking in coverage in this forecast cycle as models come
into slightly better agreement with where rainfall may focus, and
as rain amounts generally decrease.

The upper low over the Southwest early in the week 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.


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