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
258 AM EDT Thu May 1 2025

Valid 12Z Sun May 04 2025 - 12Z Thu May 08 2025


...Blocky pattern with closed lows over the West and the East with
areas of heavy rainfall potential...


...Overview...

Models and ensembles continue to show a blocky pattern becoming
established over the Lower 48 by around the start of the period
early Sunday and continuing over most areas into next Thursday. The
dominant features will be two upper lows, one that likely drifts
from California to the central High Plains and the other over or
near the Ohio Valley early in week and then possibly lifting out
thereafter. These systems will produce some significant rain and
high elevation snow over the West plus heavy rain over parts of the
Plains, and farther east another area of rain that should be
heaviest over portions of the Mid-Atlantic/Northeast. The majority
of guidance shows an East Pacific upper ridge tracking across
western/central Canada, ultimately leading to some eastern Canada
into Northeast U.S. troughing that could help to eject the eastern
upper low. Then the leading edge of an upstream trough should reach
the Northwest by midweek or so, along with a leading cold front.

...Guidance/Predictability Assessment...

18Z and 00Z GFS trends have now greatly improved overall guidance
agreement for the upper low over or near the Ohio Valley early next
week. There are still some typical position differences to be
worked out, but current clustering finally offers good overall
forecast confidence after a number of days of wildly divergent and
inconsistent solutions over the East that were more reminiscent of
model behavior from 20 years ago. Meanwhile guidance consensus
looks fairly stable for the Southwest upper low, but some
individual solutions have starting showing a little more
variability with individual vort lobes, especially from the
southern edge of a remaining northern stream trough. A composite of
the 18Z GFS and 12Z ECMWF/CMC/UKMET offered a good starting point
for Sunday-Monday.

A couple issues arise by Tuesday-Thursday. Recent GFS runs and to
some degree the GEFS have been showing much flatter flow across
southern Canada in contrast to a ridge that crosses the far
northern tier U.S. and western- central parts of southern Canada in
most other dynamical and machine learning (ML) guidance. The
majority pattern leads to some eastern Canada into Northeast U.S.
trough amplification by next Thursday. This troughing could
encourage the departure of the initial Ohio Valley upper low (which
displays increasing north-south spread in the guidance along with
spread for its departure speed). Flatter flow in the GFS leads to
slower upper low timing. Within the non-GFS cluster there are
meaningful differences for the character of eastern Canada trough
amplification, favoring increasing ensemble mean input to
complement remaining operational runs. To reflect preferences for
this time frame, the forecast blend removed the GFS while
increasing total 12Z ECens/CMCens weight to 60 percent and
splitting ECMWF input equally between the 12Z and 00Z/30 runs.

...Weather/Hazards Highlights...

Confidence continues to increase with the forecast of an Ohio
Valley upper low and wavy East Coast front early next week,
supporting some areas of moderate to locally heavy rainfall. The
Days 4-5 Excessive Rainfall Outlooks covering early Sunday into
early Tuesday depict a Marginal Risk area over parts of the
northern Mid-Atlantic and Northeast where the persistent pattern
should direct the best moisture. Overall guidance signals suggest
Day 5/Sunday could have the higher rainfall totals over northern
Mid-Atlantic urban areas and thus requiring closer monitoring going
forward. Rainfall leading into and during the period will
initially be beneficial given the drought conditions over some
areas, but could trend less favorable with time if sufficiently
heavy on a localized basis. Additional rain should fall over the
Northeast through or beyond midweek, with decreasing confidence in
specifics given spread of the upper low and how northern stream
flow may interact.

The upper low drifting across the Southwest/Four Corners and a
leading frontal boundary will initially produce a broad area of
rain and high elevation snow across the Interior West and Rockies
plus support increasing heavy rain potential over the southern half
of the Plains Monday onward. Guidance maintains some signal for
enhanced rainfall over the sensitive terrain over and near the
eastern half of New Mexico on Day 4/Sunday, so that ERO maintains
continuity with a Marginal Risk area. Continued eastward drift of
the upper low and leading wavy surface front by Day 5/Monday should
generate heavier rainfall over the southern High Plains at that
time. The best model clustering and first-guess guidance recommend
a Slight Risk area emphasizing northwestern Texas and far eastern
New Mexico with a little added extent to the north. The surrounding
Marginal Risk area extends somewhat northward along the eastern
slopes of the Rockies. Expect southern Plains heavy rain potential
to continue through midweek. During the Days 4-5 period there are
some indications for enhanced rainfall over other areas of the
Interior West/Rockies/High Plains but with not enough consensus to
suggest a risk area at this time.

The northern High Plains in particular will see well above normal
temperatures on Sunday, with some plus 15-25F anomalies for highs.
Temperatures will steadily moderate as this area of warmth migrates
eastward early next week. 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. The Southwest
will slowly trend closer to normal after midweek. Persistent
clouds and rainfall should keep the southern High Plains below
normal for highs as well. The Northwest will see a warmer trend
next week, with some highs reaching 10-15F or so above normal. Over
the East, locations under and southwest of the Ohio Valley upper
low should see moderately below normal highs Sunday-Monday and then
some moderation. The Northeast will tend to see above normal lows.


This is the final forecast of my career. It has been an honor and
a source of great satisfaction to work in NOAA/NWS for the past 30+
years while witnessing the tremendous advances in weather
forecasting over that time. Now it's on to a retirement that
hopefully offers as much excitement as the weather. Best wishes to
all, and to all happy forecasting!

Rausch


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

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

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

Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
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
900 PM EDT Tue Apr 29 2025
Day 1
Valid 01Z Wed Apr 30 2025 - 12Z Wed Apr 30 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHERN PLAINS...


...Southern Plains to the Mid Mississippi Valley...
01Z Update...

Continued the southern adjustment, especially on the northern edge,
of the outlook areas extending from western Texas northeastward
across Oklahoma. Recent runs of the HRRR, as well as the 18Z HREF,
indicate multiple convective rounds training northeastward across
the region, producing several inches of rain, with numerous flash
floods likely across portions of the region. The latest guidance
shows the greatest threat extending from Northwest Texas across the
Wichita Falls area into southwestern and south-central Oklahoma --
brushing the southern extent of the OKC metro. Deterministic runs
of the HRRR show accumulations of 7+ inches, while the HREF shows
high neighborhood probabilities for accumulations of 5 inches or
more through the overnight across this region. The Slight and
Moderate Risk areas were shifted a bit farther south across the
southern Texas Panhandle and western Oklahoma, where limited
instability in the most recent analysis supports guidance
indicating a lesser threat for heavy rainfall rates and flash
flooding.

Further to the east, pulled the Marginal and the Slight Risk areas
back west of the Mississippi. Relatively drier and more stable air
is expected to persist until showers and storms now developing
back to the southwest spread into the region late in the period,
with the general model consensus showing relatively lighter amounts
and a lesser flooding threat.

...Ohio Valley to the Central Appalachians...
01Z Update...

In addition to brief heavy downpours across sensitive areas, some
training along the southwest flank of the storms currently moving
across the region may raise the threat for locally heavy rains and
flash flooding. But overall, storms are expected to move
progressively across the area, limiting the potential for
widespread heavy rainfall and flash flooding concerns.

Pereira

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

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

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
NORTHEAST TEXAS AND NORTHWEST LOUISIANA...

01Z Update...

Updates to the previous ERO were based upon recent runs of the
HRRR, the 18Z HREF, and current observation trends.

The greatest heavy rain and flash flooding concerns through the
evening hours focus along the southwest flank of ongoing
convection and a coincident slow-moving boundary from the ArkLaTex
southeastward back through the Waco area. Current radar shows
storms training along the boundary, with rainfall rates of 1-2
inches/hour within some of the stronger cells. Cell-training and
heavy rainfall will remain a concern for at least the next few
hours as deep layer flow is aligned with the boundary. The Moderate
Risk was adjusted to align with the training convection, which
agrees well with the higher HREF neighborhood probabilities for
additional accumulations of 3 inches or more during the
evening/overnight.

Farther to the north across Arkansas, the threat for heavy
rainfall and flash flooding is diminishing where the convective
line has become more progressive.

Areas back to the north and west, where the rainfall has ended,
were removed from the outlook.

Pereira


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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
856 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
856 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
303 AM EDT Thu May 1 2025

Valid 12Z Thu May 01 2025 - 12Z Sun May 04 2025


...Sierra Nevada...
Day 3...

A potent closed low will dig along the CA coast Saturday into
Sunday, with rapid amplification of this feature expected by Sunday
morning. This is reflected by NAEFS height anomalies falling to
below the 1st percentile with respect to 700-500mb heights over
southern CA by 12Z Sunday. Although the accompanying jet streak
will intensify as well as it pivots around the upstream side of
this trough and through the base, the overall evolution will keep
the most intense ascent displaced south/east of the Sierra, but
sufficient lift and increasing moisture will still result in
periods of snowfall D3. Snow levels during this time will begin
around 8000-9000 ft, so only the higher Sierra Passes will begin as
snow, but as the upper low digs across CA, snow levels are progged
to fall to as low as 7000 ft, bringing at least some accumulations
to Donner Pass as well. Overall, significant snowfall accumulation
will be confined to above pass level, where WPC probabilities for
more than 6 inches of snow are as high as 50%, but light snow down
to most Sierra Pass levels is also likely before precip winds down
by Sunday morning.


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

Weiss

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
258 AM EDT Thu May 1 2025

Valid 12Z Sun May 04 2025 - 12Z Thu May 08 2025


...Blocky pattern with closed lows over the West and the East with
areas of heavy rainfall potential...


...Overview...

Models and ensembles continue to show a blocky pattern becoming
established over the Lower 48 by around the start of the period
early Sunday and continuing over most areas into next Thursday. The
dominant features will be two upper lows, one that likely drifts
from California to the central High Plains and the other over or
near the Ohio Valley early in week and then possibly lifting out
thereafter. These systems will produce some significant rain and
high elevation snow over the West plus heavy rain over parts of the
Plains, and farther east another area of rain that should be
heaviest over portions of the Mid-Atlantic/Northeast. The majority
of guidance shows an East Pacific upper ridge tracking across
western/central Canada, ultimately leading to some eastern Canada
into Northeast U.S. troughing that could help to eject the eastern
upper low. Then the leading edge of an upstream trough should reach
the Northwest by midweek or so, along with a leading cold front.

...Guidance/Predictability Assessment...

18Z and 00Z GFS trends have now greatly improved overall guidance
agreement for the upper low over or near the Ohio Valley early next
week. There are still some typical position differences to be
worked out, but current clustering finally offers good overall
forecast confidence after a number of days of wildly divergent and
inconsistent solutions over the East that were more reminiscent of
model behavior from 20 years ago. Meanwhile guidance consensus
looks fairly stable for the Southwest upper low, but some
individual solutions have starting showing a little more
variability with individual vort lobes, especially from the
southern edge of a remaining northern stream trough. A composite of
the 18Z GFS and 12Z ECMWF/CMC/UKMET offered a good starting point
for Sunday-Monday.

A couple issues arise by Tuesday-Thursday. Recent GFS runs and to
some degree the GEFS have been showing much flatter flow across
southern Canada in contrast to a ridge that crosses the far
northern tier U.S. and western- central parts of southern Canada in
most other dynamical and machine learning (ML) guidance. The
majority pattern leads to some eastern Canada into Northeast U.S.
trough amplification by next Thursday. This troughing could
encourage the departure of the initial Ohio Valley upper low (which
displays increasing north-south spread in the guidance along with
spread for its departure speed). Flatter flow in the GFS leads to
slower upper low timing. Within the non-GFS cluster there are
meaningful differences for the character of eastern Canada trough
amplification, favoring increasing ensemble mean input to
complement remaining operational runs. To reflect preferences for
this time frame, the forecast blend removed the GFS while
increasing total 12Z ECens/CMCens weight to 60 percent and
splitting ECMWF input equally between the 12Z and 00Z/30 runs.

...Weather/Hazards Highlights...

Confidence continues to increase with the forecast of an Ohio
Valley upper low and wavy East Coast front early next week,
supporting some areas of moderate to locally heavy rainfall. The
Days 4-5 Excessive Rainfall Outlooks covering early Sunday into
early Tuesday depict a Marginal Risk area over parts of the
northern Mid-Atlantic and Northeast where the persistent pattern
should direct the best moisture. Overall guidance signals suggest
Day 5/Sunday could have the higher rainfall totals over northern
Mid-Atlantic urban areas and thus requiring closer monitoring going
forward. Rainfall leading into and during the period will
initially be beneficial given the drought conditions over some
areas, but could trend less favorable with time if sufficiently
heavy on a localized basis. Additional rain should fall over the
Northeast through or beyond midweek, with decreasing confidence in
specifics given spread of the upper low and how northern stream
flow may interact.

The upper low drifting across the Southwest/Four Corners and a
leading frontal boundary will initially produce a broad area of
rain and high elevation snow across the Interior West and Rockies
plus support increasing heavy rain potential over the southern half
of the Plains Monday onward. Guidance maintains some signal for
enhanced rainfall over the sensitive terrain over and near the
eastern half of New Mexico on Day 4/Sunday, so that ERO maintains
continuity with a Marginal Risk area. Continued eastward drift of
the upper low and leading wavy surface front by Day 5/Monday should
generate heavier rainfall over the southern High Plains at that
time. The best model clustering and first-guess guidance recommend
a Slight Risk area emphasizing northwestern Texas and far eastern
New Mexico with a little added extent to the north. The surrounding
Marginal Risk area extends somewhat northward along the eastern
slopes of the Rockies. Expect southern Plains heavy rain potential
to continue through midweek. During the Days 4-5 period there are
some indications for enhanced rainfall over other areas of the
Interior West/Rockies/High Plains but with not enough consensus to
suggest a risk area at this time.

The northern High Plains in particular will see well above normal
temperatures on Sunday, with some plus 15-25F anomalies for highs.
Temperatures will steadily moderate as this area of warmth migrates
eastward early next week. 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. The Southwest
will slowly trend closer to normal after midweek. Persistent
clouds and rainfall should keep the southern High Plains below
normal for highs as well. The Northwest will see a warmer trend
next week, with some highs reaching 10-15F or so above normal. Over
the East, locations under and southwest of the Ohio Valley upper
low should see moderately below normal highs Sunday-Monday and then
some moderation. The Northeast will tend to see above normal lows.


This is the final forecast of my career. It has been an honor and
a source of great satisfaction to work in NOAA/NWS for the past 30+
years while witnessing the tremendous advances in weather
forecasting over that time. Now it's on to a retirement that
hopefully offers as much excitement as the weather. Best wishes to
all, and to all happy forecasting!

Rausch


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

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

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