Weather Prediction Center

National Oceanic and Atmospheric Administration

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
301 PM EDT Wed Apr 30 2025

Valid 00Z Thu May 01 2025 - 00Z Sat May 03 2025

...Episodes of heavy rain and severe thunderstorms will keep heightened
flash flooding concerns across the south-central U.S. through early
Thursday...

...Showers and embedded severe thunderstorms expected to shift east into
the Mid-Mississippi, Ohio, and Tennessee Valleys on Thursday...

...Potential for strong to severe thunderstorms returns to the
south-central Plains on Friday...

A stalled frontal boundary interacting with upper-level disturbances
ejecting from the southern Rockies will remain the focus for additional
episodes of heavy rainfall and severe thunderstorms across the
south-central U.S. into early Thursday. The heaviest rain threat will be
confined to portions of southeastern Oklahoma into northeastern Texas and
western Arkansas where a moderate risk of flash flooding remains in place.
An enhanced risk of severe thunderstorms is also embedded within this
general area. A slight risk of severe thunderstorms and flash flooding is
expected for a larger portion of the south-central U.S. into tonight. By
Thursday, a low pressure system forming along the front will begin to
track northeastward across the Mid-Mississippi Valley into the Midwest,
which will effectively end the heavy rainfall and severe weather threats
across the south-central U.S. However, on the other side of the system,
showers and embedded severe thunderstorms are forecast to increase and
expand across Mid-Mississippi, Ohio, and Tennessee Valleys. Damaging
winds, hail, and an isolated tornado are the primary concerns from any
severe storms.

Meanwhile, a Pacific frontal system moving across the Intermountain West,
Rockies and northern High Plains is bringing a round of lower elevation
rains and accumulating wet snow in the mountains. In the wake of the
system and cold front, drier weather moves in later tonight into Thursday
as high pressure takes control. By early Friday morning, the cold front
will dip south into the southern High Plains and intersect moisture
returning from the western Gulf to provide increasing chances of strong to
severe thunderstorms extending east into the southern Plains Friday
afternoon.

Across the Northeast, cooler and drier air will gradually filter into the
region this afternoon and evening in the wake of a cold front. High
pressure will be in control on Thursday before showers and thunderstorms
arrive ahead of the low pressure system approaching from the Great Lakes
on Friday.

A strong ridge of high pressure extending across much of the eastern U.S.
will bring well above average warmth to much of the region through mid to
late week. Forecast highs in the 70s and 80s will be common. Overall near
average temperatures are in store for the western and central U.S. through
Thursday before warming up some across the Pacific Northwest heading into
the latter half of the week.

Miller/Kong


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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Wed Apr 30 2025

Valid 12Z Sat May 03 2025 - 12Z Wed May 07 2025


...Blocky Closed Lows for the West and the East...


...Overview...

Recent guidance continues to show the general theme of an
increasingly blocky pattern across the Lower 48, and with better
relative agreement for the upper low closing off over California
during the weekend and drifting gradually inland versus the pattern
over the East. The western upper low will support a broad area of
rain and high elevation snow across the region, as well as an
increasing threat for areas of heavy rain across parts of the
central/southern Plains next week. Meanwhile, solutions diverge
over time in the East, albeit with recent guidance runs adding to
recent trends toward closing of an upper low well inland, leaving
the more progressive GFS/GEFS that alternately builds a ridge into
the east-central U.S. as an outlier in the vast minority of
solutions. The majority scenario increases the probability of a
much wetter pattern for parts of the East this weekend/next week.

...Guidance/Predictability Assessment...

Guidance remains clustered better than normal through med-range
time scales with the development and slow progression of a
significant upper trough/closed low and mid-larger scale features
working into/across the West, eventually affecting the central
U.S.. A model composite seems to provide a reasonable forecast
basis with good continuity and ensemble support.

Over the East, recent individual models and ensemble members, but
especially the GFS/GEFS, have offered less than stellar agreement
from the weekend into early next week with depiction and diggy
nature of a potential closed upper trough/low. However, given well
clustered guidance showing ample flow amplitude upstream, the
pattern continues to strongly favor a solution on the more
amplified/closed side of the full envelope of model and ensemble
solutions. Accordingly, the WPC product suite was primarily derived
from best clustered guidance in this vein with usage of the 00 UTC
ECMWF/Canadian/UKMET and ECMWF/Canadian ensemble means along with
most machine learning models. This solution maintains reasonably
good WPC product continuity. Recent GFS and GEFS runs seemed way
too progressive, but the latest 12 UTC GEFS and GFS based Graphcast
machine learning model trended toward the aforementioned favored
cluster of most other guidance, bolstering forecast guidance.

...Weather/Hazards Highlights...

Latest Machine Learning (ML) models and non-GFS dynamical models
are steadily showing more pronounced clustering toward closure of
an upper low that may persist for a couple days or so to the west
of the Appalachians. This supports some areas of moderate to
locally heavy rainfall depending on the orientation and
persistence of any particular bands and favored terrain lift.
There is still spread for rainfall specifics across areas with
varying soil moisture, but given the growing signal and favorable
pattern recognition, opted to introduce WPC Day 4/Day 5 Excessive
Rainfall Outlook Marginal Risk areas for the southern and central
Appalachians region through the northern Mid- Atlantic for at least
this Saturday and Sunday. A drier scenario of the GFS is trending
lower in probability.

Easterly flow and adequate moisture/instability over the far
southern Plains still offers some threat for spotty locally heavy
rainfall over the southwestern half of Texas into the weekend,
though with a diminished signal compared prior days, so no WPC ERO
Marginal Risk areas remain in place. Meanwhile guidance has been
consistent in showing a band of potentially heavy rainfall aligned
over west-central Nevada on Saturday as the upper low closes off
over California, so that Marginal Risk remains nearly unchanged as
well. By Day 5/Sunday the rainfall signal over the West looks a
little more diffuse but with some guidance clustering toward
enhanced rainfall over the sensitive terrain in the eastern half of
New Mexico as gradual progress of the Southwest upper low pushes a
cold front toward the region. Thus the Day 5 WPC ERO still has a
Marginal Risk area for this threat. Additional gradual drift of the
Southwest upper low should raise the potential for areas of heavy
rainfall over parts of the central/southern Plains from Monday
onward, with details depending on exact path and timing of the
upper low. Otherwise, the system moving into the West will bring a
broad area of rain and high elevation snow to the region, from the
Sierra Nevada and inland Northwest to the northern-central Rockies.

Well above normal temperatures should extend from the northern
Rockies and eastern Great Basin into the northern Plains on
Saturday, with anomalies gradually moderating as the warmth moves
eastward toward the Upper Midwest. Plus 15-25F anomalies should be
most common over far northern areas during Saturday-Sunday. In
contrast, the upper low tracking into the Southwest will bring much
cooler temperatures to the region. Highs should be 10-20F below
normal on Sunday-Monday, with some record cold highs possible near
the upper low's path especially on Sunday. Persistent clouds and
precipitation should keep the southern High Plains highs below
normal as well. The potentially unsettled pattern over the East may
favor temperatures within a few degrees of normal after some
modest warmth along the East Coast on Saturday.

Rausch/Schichtel


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
337 AM EDT Wed Apr 30 2025

Valid 00Z Thu 01 May 2025 - 00Z Thu 08 May 2025

On Wednesday the eastward departure and opening of a nearby upper
low will lead to dissipation of the surface trough that has been
over the state early this week. Expect trades to be light to
moderate initially, but trending more brisk Friday onward with
influence from one surface high passing by to the north around
Friday and another next Tuesday-Wednesday. Guidance is consistent
in showing precipitable water values settling at below normal
values from Friday into at least early next week while upper
ridging prevails over/north of the state. Thus anticipate mostly
light to moderate showers focused primarily over windward/mountain
areas.

Rausch

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
417 PM EDT Wed Apr 30 2025
Day 1
Valid 16Z Wed Apr 30 2025 - 12Z Thu May 01 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHEAST OKLAHOMA, NORTH TEXAS, AND WESTERN ARKANSAS...

The threat of significant flash flooding continues today, with the
focus increasingly shifting to portions of north Texas based on
observational trends and the latest 12Z hi-res model guidance.

A bowing convective line continues to advance eastward through
S OK, with a trailing line of convection extending into N TX on
the southern periphery of strong cold pool and mesohigh situated
over SC OK. Over the past couple hours, the convective line in N
TX has become increasingly oriented NE-SW, or even ENE-WSW; in
other words, more parallel to the mean flow vector. This has
increased the potential for training and backbuilding, especially
into the afternoon hours as the LLJ begins to weaken and low-level
winds start to veer to the southwest. For a more detailed mesoscale
analysis, please refer to MPD #202 issued at 14Z for this region.

The Moderate Risk area was maintained in SE OK and W AR, even
though confidence in flash flooding has decreased somewhat due to
the fairly steady forward progress of the bowing line, and how thin
the convective line has become. However, it was maintained out of
deference to continuity and the potential to reinvigorate the
convection in the next few hours with some clearing occurring ahead
of the line, which could increase rain rates again.

Greater concern now exists in N TX. The forward progression of the
line and associated cold pool in S OK and overall convective
evolution has led to far more west-east orientation to the
convective line in N TX than models had originally been
advertising. This certainly increases flash flood potential and
over the next few hours this places the Dallas-Ft. Worth metro area
squarely in the greatest risk. Hourly rainfall could exceed 2
inches per hour, with unobstructed inflow from a very moist and
unstable air mass (MLCAPE 1500-2000 j/kg with minimal CINH; PWs
1.6 to 1.8 inches per RAP analysis.) In an urban environment, this
could lead to significant and life-threatening flash flooding,
particularly if the rain rates are sustained for a couple hours,
which is a distinct possibility in this case.

As the afternoon and evening progress, the hi-res models do
indicate the potential for the southwestern periphery of the
convective line to continue to slow or stall. While they don't
necessarily agree on the specifics, many HREF members, as well as
the RRFS, indicate backbuilding and training convection could
become more likely in the corridor from Waco to Longview. This
seems to be well supported by observational trends, and in fact
many hi-res members are: (1) already not extending the convective
line far enough southwest based on current radar trends, and (2)
have the convective line oriented far too much in a N-S fashion.
Therefore, they may be underestimating rainfall potential a bit,
and also underselling the potential for a significant rainfall and
flash flood event further to the southwest. Probabilities and
associated risk categories were increased a bit down the I-35
corridor between DFW and AUS, and this will be monitored for
further updates based on observational trends. Rain rates in much
of C/N TX could reach or exceed 2 inches per hour given the
available instability and moisture.

The other biggest change for this outlook was to extend the Slight
Risk a bit further northeast through MO and into W IL based on more
elevated HREF probabilities of exceeding 1hr and 3hr flash flood
guidance and a fairly consistent signal in the guidance for a
corridor of enhanced rainfall associated with an MCV and
corresponding surface low.

Lamers


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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
417 PM EDT Wed Apr 30 2025
Day 2
Valid 12Z Thu May 01 2025 - 12Z Fri May 02 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN SOUTHERN
OKLAHOMA, FAR NORTH TEXAS, AND FAR WESTERN ARKANSAS...

The most significant change for this outlook period was to
introduce a Slight Risk primarily over southern Oklahoma, where
previously the probabilities were below the Marginal Risk (5
percent) threshold. This was due to an emerging consensus in model
guidance that thunderstorms will blossom on Thursday Night ahead of
a digging shortwave in an area of relatively strong upper level
divergence. Although the mid levels will be drier than in recent
days, leading to lower PWs overall, strong instability will be in
place which should support organized convection with more intense
rain rates at times. A key uncertainty at the moment is the overall
structure of convective clusters and lines, and whether they will
be more progressive or include some training. However, the
potential for heavy rain rates in an area that has received a lot
of rainfall already in recent days does raise the risk of flash
flooding. Hourly rainfall on the order of 1-2 inches will be
possible in this environment, and in areas with already wet ground
conditions this would be more than sufficient to cause flash
flooding.

Elsewhere, the broad Marginal Risk that was already in place was
maintained with few changes. A broad plume of moderate to strong
instability will favor scattered lines and clusters of
thunderstorms in advance of a surface low and trailing cold front
with fairly high instantaneous rain rates. The key uncertainty
would be the persistence of those rain rates and the degree to
which any training could occur, but the overall environment with
PWs around 1.3 to 1.4 inches raises the probability high enough to
warrant the broad Marginal Risk. The only exception to the
continuation of the risk area was over much of IL, IN, and MI,
which should largely be behind the cold front by 18Z and so most of
the QPF on model guidance would be associated with post-frontal
showers that would tend to have lower rain rates overall.

Lamers


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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
417 PM EDT Wed Apr 30 2025
Day 3
Valid 12Z Fri May 02 2025 - 12Z Sat May 03 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS FROM THE
SOUTHERN PLAINS INTO THE LOWER MISSISSIPPI VALLEY...

A flash flood event may be ongoing at the beginning of the period,
with convection developing on Thursday Night in southern Oklahoma
and continuing into Friday morning. This may continue beyond 12Z
Friday (into this Day 3 period) in SE OK and AR in the region of
strong upper-level divergence. The existing Slight Risk over TX was
expanded northward to account for this scenario. Whether that round
of convection wanes due to more extensive cloud cover and limited
daytime heating, or progresses southeast and becomes reinvigorated
during the afternoon, the threat of heavy rainfall and flash
flooding should expand southeast on Friday into the Lower
Mississippi Valley (S AR, N LA, W MS) and much of C and E TX. This
would be via progression of the early round of storms, or
redevelopment in the afternoon and evening hours.

Strong instability will remain over much of the warm sector with
CAPE values potentially in excess of 3000 j/kg in some areas, and
PW values are expected to increase above 1.5 inches as SSE flow
increases off the Gulf. The combination of strong instability and
high PWs will favor very heavy rain rates in organized convection,
and this is supportive of the broad Slight Risk on the new
outlook. At the moment, model guidance is showing the most
consistent signal for heavy rain from Texas Hill Country in C TX
east- northeast into the Piney Woods region of E TX. Given the
overall environment, it is possible an upgrade to a Moderate Risk
may be needed at some point.

Lamers

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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Wed Apr 30 2025


Latest Machine Learning (ML) models and non-GFS dynamical models
are steadily showing more pronounced clustering toward closure of
an upper low that may persist for a couple days or so to the west
of the Appalachians. This supports some areas of moderate to
locally heavy rainfall depending on the orientation and
persistence of any particular bands and favored terrain lift.
There is still spread for rainfall specifics across areas with
varying soil moisture, but given the growing signal and favorable
pattern recognition, opted to introduce WPC Day 4/Day 5 Excessive
Rainfall Outlook Marginal Risk areas for the southern and central
Appalachians region through the northern Mid- Atlantic for at least
this Saturday and Sunday. A drier scenario of the GFS is trending
lower in probability.

Easterly flow and adequate moisture/instability over the far
southern Plains still offers some threat for spotty locally heavy
rainfall over the southwestern half of Texas into the weekend,
though with a diminished signal compared prior days, so no WPC ERO
Marginal Risk areas remain in place. Meanwhile guidance has been
consistent in showing a band of potentially heavy rainfall aligned
over west-central Nevada on Saturday as the upper low closes off
over California, so that Marginal Risk remains nearly unchanged as
well. By Day 5/Sunday the rainfall signal over the West looks a
little more diffuse but with some guidance clustering toward
enhanced rainfall over the sensitive terrain in the eastern half of
New Mexico as gradual progress of the Southwest upper low pushes a
cold front toward the region. Thus the Day 5 WPC ERO still has a
Marginal Risk area for this threat. Additional gradual drift of the
Southwest upper low should raise the potential for areas of heavy
rainfall over parts of the central/southern Plains from Monday
onward, with details depending on exact path and timing of the
upper low. Otherwise, the system moving into the West will bring a
broad area of rain and high elevation snow to the region, from the
Sierra Nevada and inland Northwest to the northern-central Rockies.

Well above normal temperatures should extend from the northern
Rockies and eastern Great Basin into the northern Plains on
Saturday, with anomalies gradually moderating as the warmth moves
eastward toward the Upper Midwest. Plus 15-25F anomalies should be
most common over far northern areas during Saturday-Sunday. In
contrast, the upper low tracking into the Southwest will bring much
cooler temperatures to the region. Highs should be 10-20F below
normal on Sunday-Monday, with some record cold highs possible near
the upper low's path especially on Sunday. Persistent clouds and
precipitation should keep the southern High Plains highs below
normal as well. The potentially unsettled pattern over the East may
favor temperatures within a few degrees of normal after some
modest warmth along the East Coast on Saturday.

Rausch/Schichtel

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Wed Apr 30 2025


Latest Machine Learning (ML) models and non-GFS dynamical models
are steadily showing more pronounced clustering toward closure of
an upper low that may persist for a couple days or so to the west
of the Appalachians. This supports some areas of moderate to
locally heavy rainfall depending on the orientation and
persistence of any particular bands and favored terrain lift.
There is still spread for rainfall specifics across areas with
varying soil moisture, but given the growing signal and favorable
pattern recognition, opted to introduce WPC Day 4/Day 5 Excessive
Rainfall Outlook Marginal Risk areas for the southern and central
Appalachians region through the northern Mid- Atlantic for at least
this Saturday and Sunday. A drier scenario of the GFS is trending
lower in probability.

Easterly flow and adequate moisture/instability over the far
southern Plains still offers some threat for spotty locally heavy
rainfall over the southwestern half of Texas into the weekend,
though with a diminished signal compared prior days, so no WPC ERO
Marginal Risk areas remain in place. Meanwhile guidance has been
consistent in showing a band of potentially heavy rainfall aligned
over west-central Nevada on Saturday as the upper low closes off
over California, so that Marginal Risk remains nearly unchanged as
well. By Day 5/Sunday the rainfall signal over the West looks a
little more diffuse but with some guidance clustering toward
enhanced rainfall over the sensitive terrain in the eastern half of
New Mexico as gradual progress of the Southwest upper low pushes a
cold front toward the region. Thus the Day 5 WPC ERO still has a
Marginal Risk area for this threat. Additional gradual drift of the
Southwest upper low should raise the potential for areas of heavy
rainfall over parts of the central/southern Plains from Monday
onward, with details depending on exact path and timing of the
upper low. Otherwise, the system moving into the West will bring a
broad area of rain and high elevation snow to the region, from the
Sierra Nevada and inland Northwest to the northern-central Rockies.

Well above normal temperatures should extend from the northern
Rockies and eastern Great Basin into the northern Plains on
Saturday, with anomalies gradually moderating as the warmth moves
eastward toward the Upper Midwest. Plus 15-25F anomalies should be
most common over far northern areas during Saturday-Sunday. In
contrast, the upper low tracking into the Southwest will bring much
cooler temperatures to the region. Highs should be 10-20F below
normal on Sunday-Monday, with some record cold highs possible near
the upper low's path especially on Sunday. Persistent clouds and
precipitation should keep the southern High Plains highs below
normal as well. The potentially unsettled pattern over the East may
favor temperatures within a few degrees of normal after some
modest warmth along the East Coast on Saturday.

Rausch/Schichtel

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
214 PM EDT Wed Apr 30 2025

Valid 00Z Thu May 01 2025 - 00Z Sun May 04 2025


...Central/Southern Rockies...
Days 1-2...

Cold front associated with a shortwave over the Northern Plains to
the central Rockies will continue southeastward through Colorado
and into New Mexico Thursday. QPF has decreased in the past 24
hours but some light snow over the high mountains will fall,
generally above 8000-9000ft, where WPC probabilities for at least 4
inches of snow are >50% above 10,000ft or so. Snow will end from
north to south over the San Juans and Sangre de Cristos Thursday
evening.

...Sierra Nevada...
Days 1&3...

Combination of a small upper low off the central/southern CA coast
tonight into Thursday with a trough axis across the Great Basin
will bring some light snow to the high Sierra tonight/Thursday.
Amounts may only be an inch or two with low probabilities of at
least 4 inches (<40%) as snow levels remain above 9000ft.

After a break on Day 2, a deeper trough with origins in the
northeastern Pacific will bring in a more robust moisture plume to
the West Coast on Day 3 (Saturday) that will continue into the
medium range. Through 00Z Sun, snow levels will be high (>9000ft)
with the initial surge in (modest) moisture, yielding low
probabilities for at least 4 inches of snow (<30%) in the central
Sierra as well as across the highest peaks of the Oregon Cascades.


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

Fracasso

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Wed Apr 30 2025

Valid 12Z Sat May 03 2025 - 12Z Wed May 07 2025


...Blocky Closed Lows for the West and the East...


...Overview...

Recent guidance continues to show the general theme of an
increasingly blocky pattern across the Lower 48, and with better
relative agreement for the upper low closing off over California
during the weekend and drifting gradually inland versus the pattern
over the East. The western upper low will support a broad area of
rain and high elevation snow across the region, as well as an
increasing threat for areas of heavy rain across parts of the
central/southern Plains next week. Meanwhile, solutions diverge
over time in the East, albeit with recent guidance runs adding to
recent trends toward closing of an upper low well inland, leaving
the more progressive GFS/GEFS that alternately builds a ridge into
the east-central U.S. as an outlier in the vast minority of
solutions. The majority scenario increases the probability of a
much wetter pattern for parts of the East this weekend/next week.

...Guidance/Predictability Assessment...

Guidance remains clustered better than normal through med-range
time scales with the development and slow progression of a
significant upper trough/closed low and mid-larger scale features
working into/across the West, eventually affecting the central
U.S.. A model composite seems to provide a reasonable forecast
basis with good continuity and ensemble support.

Over the East, recent individual models and ensemble members, but
especially the GFS/GEFS, have offered less than stellar agreement
from the weekend into early next week with depiction and diggy
nature of a potential closed upper trough/low. However, given well
clustered guidance showing ample flow amplitude upstream, the
pattern continues to strongly favor a solution on the more
amplified/closed side of the full envelope of model and ensemble
solutions. Accordingly, the WPC product suite was primarily derived
from best clustered guidance in this vein with usage of the 00 UTC
ECMWF/Canadian/UKMET and ECMWF/Canadian ensemble means along with
most machine learning models. This solution maintains reasonably
good WPC product continuity. Recent GFS and GEFS runs seemed way
too progressive, but the latest 12 UTC GEFS and GFS based Graphcast
machine learning model trended toward the aforementioned favored
cluster of most other guidance, bolstering forecast guidance.

...Weather/Hazards Highlights...

Latest Machine Learning (ML) models and non-GFS dynamical models
are steadily showing more pronounced clustering toward closure of
an upper low that may persist for a couple days or so to the west
of the Appalachians. This supports some areas of moderate to
locally heavy rainfall depending on the orientation and
persistence of any particular bands and favored terrain lift.
There is still spread for rainfall specifics across areas with
varying soil moisture, but given the growing signal and favorable
pattern recognition, opted to introduce WPC Day 4/Day 5 Excessive
Rainfall Outlook Marginal Risk areas for the southern and central
Appalachians region through the northern Mid- Atlantic for at least
this Saturday and Sunday. A drier scenario of the GFS is trending
lower in probability.

Easterly flow and adequate moisture/instability over the far
southern Plains still offers some threat for spotty locally heavy
rainfall over the southwestern half of Texas into the weekend,
though with a diminished signal compared prior days, so no WPC ERO
Marginal Risk areas remain in place. Meanwhile guidance has been
consistent in showing a band of potentially heavy rainfall aligned
over west-central Nevada on Saturday as the upper low closes off
over California, so that Marginal Risk remains nearly unchanged as
well. By Day 5/Sunday the rainfall signal over the West looks a
little more diffuse but with some guidance clustering toward
enhanced rainfall over the sensitive terrain in the eastern half of
New Mexico as gradual progress of the Southwest upper low pushes a
cold front toward the region. Thus the Day 5 WPC ERO still has a
Marginal Risk area for this threat. Additional gradual drift of the
Southwest upper low should raise the potential for areas of heavy
rainfall over parts of the central/southern Plains from Monday
onward, with details depending on exact path and timing of the
upper low. Otherwise, the system moving into the West will bring a
broad area of rain and high elevation snow to the region, from the
Sierra Nevada and inland Northwest to the northern-central Rockies.

Well above normal temperatures should extend from the northern
Rockies and eastern Great Basin into the northern Plains on
Saturday, with anomalies gradually moderating as the warmth moves
eastward toward the Upper Midwest. Plus 15-25F anomalies should be
most common over far northern areas during Saturday-Sunday. In
contrast, the upper low tracking into the Southwest will bring much
cooler temperatures to the region. Highs should be 10-20F below
normal on Sunday-Monday, with some record cold highs possible near
the upper low's path especially on Sunday. Persistent clouds and
precipitation should keep the southern High Plains highs below
normal as well. The potentially unsettled pattern over the East may
favor temperatures within a few degrees of normal after some
modest warmth along the East Coast on Saturday.

Rausch/Schichtel


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