Weather Prediction Center

National Oceanic and Atmospheric Administration

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
221 AM EDT Tue Sep 22 2026

Valid 12Z Tue Sep 22 2026 - 12Z Thu Sep 24 2026

...Significant Heavy Rainfall/Flooding Threat across New Mexico and the
Southern High Plains through Wednesday...

...Heavy Rainfall/Flooding Threat across portions of the Ohio Valley,
Mid-Atlantic, and Southeast through Wednesday...

...Severe Thunderstorm Threat across portions of the Southeast through
Tuesday...

A upper-level low/trough will dig into the Southwest and interact with
both the Pacific and Gulf moisture, leading to showers and thunderstorms
across portions of the Four Corners, southern and central Plains/Rockies,
and the Great Basin. The combination of deep tropical moisture, sufficient
instability, and upper-level forcing will lead to high rainfall rates and
excessive rainfall across portions of the Four Corners and western Texas
on Tuesday. Additionally, WPC has issued a Moderate Risk (level 3/4) of
excessive rainfall for southern New Mexico, while a broader area of Slight
Risk (level 2/4) covers much of New Mexico. The flash flooding threat is
expected to increase on Wednesday, as the primary shortwave energy lifts
northward through New Mexico. Therefore, the Marginal and Slight Risk for
excessive rainfall will expand into central Plains, while a broad area of
Moderate Risk will encompass much of eastern New Mexico. The southwest
moisture will gradually transport northeastward along a slow-moving
boundary, bringing showers and thunderstorms across the northern/central
Plains into the Upper Midwest by late Wednesday into early Thursday.

Furthermore, a upper-level troughing over the Great Lakes will gradually
shift eastward toward the Mid-Atlantic and Northeast, while the frontal
boundary will settle southward across the southern Plains into the
Southeast, Ohio Valley, and Mid-Atlantic. A developing coastal low
offshore will help maintain low-level moisture ahead of the slow-moving
frontal boundary, supporting period of showers and thunderstorms from
portions of the Ohio Valley/Mid-Atlantic into the Appalachians and
Southeast. Pockets of elevated instability may develop along the frontal
boundary, leading to severe thunderstorm concerns across the Southeast.
Additionally, slow storm motions and efficient warm moisture will lead to
locally high rainfall rates within the strongest storms, leading to flash
flooding concerns over portions of the Ohio Valley/Mid-Atlantic and
Southeast.

By Wednesday, the boundary over the Mid-Atlantic and Ohio Valley will move
further south, but shortwave troughs will reinforce another round of
showers and thunderstorms across the area. This will lead to another day
of flash flooding concerns over the Mid-Atlantic and Ohio Valley,
especially over areas where soil remains saturated from previous rainfall.
Further south, a moist and unstable airmass will persist across southern
Florida leading to scattered to numerous showers and thunderstorms, with
locally heavy downpours possible through Thursday.

Temperature-wise, a strong surface high will bring colder than average
temperatures across the northern/central Plains into the Mid-Atlantic and
Northeast behind the frontal boundary, while the southern Plains into the
Southeast will remain warm and humid.

Oudit


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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
334 AM EDT Tue Sep 22 2026

Valid 12Z Fri Sep 25 2026 - 12Z Tue Sep 29 2026


...Impactful coastal storm meanders near the Mid-Atlantic and
Northeast
late week/weekend...


...Overview...

An upper low will stall atop the Mid-Atlantic and Northeast late
week into the weekend, supporting a meandering coastal surface low.
This pattern will lead to strong/gusty onshore winds for multiple
days, leading to coastal flooding, rip currents and high surf, and
potential beach erosion. An upper ridge persisting in the south-
central U.S. will promote warm temperatures, while a couple of
upper troughs come into the northwestern and north-central U.S.
through the period and bring rounds of precipitation to those
regions.


...Guidance/Predictability Assessment...

Models continue to agree that a coastal low will be in the western
Atlantic Friday into the weekend underneath a stalling upper low.
The surface low should be rather deep, reaching the 980s or at
least 990s (mb) around Saturday. The low will likely be pretty
stacked and seems to be warm core per phase space diagrams,
indicating there could be a warm seclusion and/or have some
subtropical characteristics. Its position from day to day at it
meanders is much more uncertain. The EC and UKMET develop the low
farther south in the Atlantic Friday-Saturday and reach near Long
Island by Sunday, compared to the farther northeast GFS/AIGFS/CMC,
with the EC-AIFS looking like a reasonable middle ground like the
EC mean. By Monday-Tuesday the low should be weaker but with
remaining questions on when it pulls away. All in all there is
still ample spread with the details, which could have sensible
weather impacts like wind speed/direction and how much rain falls
onshore or offshore.

Elsewhere, guidance shows good consensus on the upper ridge in the
south-central U.S., though varying positions of weak fronts and
precipitation potential cause uncertainties in the temperatures.
The ridge looks to extend north and traverse the Midwest/Great
Lakes Friday and over the weekend, contributing to the blocky
pattern as it stretches into southeast Canada north of the Atlantic
upper low. Meanwhile a couple of trough axes will track across the
northwestern to north-central U.S. with typical spread in their
timing and depth. Guidance generally shows one crossing the Pacific
Northwest at the start of the period Friday, tracking across the
northern tier and lifting into central Canada on Sunday. Then an
upstream trough is forecast to move into the West Coast Sunday and
continue tracking east. By Monday into Tuesday models show varying
degrees of stream separation that affects the trough's timing. Will
also mention that Hurricane Polo in the eastern Pacific still has
some model spread in its track, but number of models/ensemble
members are decreasing for having it curve into Baja California.
Polo's track will affect potential moisture inflow into the
Southwest.

The WPC forecast used a model and ensemble blend even early in the
forecast period, given the spread with the eastern low. Increased
the proportion of ensemble means to well over half by Days 6-7 to
mitigate the individual model differences in the details of the
pattern.


...Weather/Hazards Highlights...

The surface low in the western Atlantic meandering will lead to
broad onshore flow across the Mid-Atlantic and Northeast for
multiple days. This persistent pattern could lead to coastal
flooding and beach erosion concerns, especially when combined with
high astronomical tides. Exact placement of the surface low from
day to day and thus any heavy rain is more uncertain. The current
forecast supports that coastal New England may see heavy rainfall
on Friday into the weekend. However, stay tuned for forecast
updates, as small shifts in the low track would lead to significant
forecast shifts in rainfall amounts. See WPC's Key Messages for
this coastal low for further information.

Pacific moisture is forecast to advect around the western side of
the south-central U.S. upper ridge and lead to some rain across
parts of the central U.S. on Friday. If/where additional rain falls
in New Mexico, there could be flooding concerns after the forecast
heavy rainfall event in the short range causes very wet antecedent
conditions. Meanwhile farther east and northeast into the Plains,
moderate to locally heavy rainfall may be possible, but on less
sensitive ground. Rain chances persist in the Upper/Middle
Mississippi Valley into Saturday. Meanwhile, upper troughing will
bring precipitation to the Pacific Northwest and northern Rockies,
including higher elevation snow chances, on Friday. Scattered
showers and thunderstorms are again possible in parts of the
Plains/Mississippi Valley on Sunday, but a more widespread rainy
pattern with potentially heavier amounts is possible by Monday as
Pacific and Gulf moisture combine and stream into the central U.S.
ahead of troughing in the West.

Temperatures are forecast to remain cooler than average by 5-10
degrees in the Mid-Atlantic and Northeast into the weekend
underneath the upper low, and highs will generally be in the 60s.
On the other hand, broad upper ridging over the south-central U.S.
could maintain highs in the 90s for the southern Plains and Lower
Mississippi Valley. Cooler than normal temperatures are likely in
the Northwest given troughing aloft, which should push into the
northern Rockies/High Plains after a warmer than average period
into Friday.


Tate


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

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation forecast, excessive rainfall outlook,
winter weather outlook probabilities, heat indices and Key Messages
are at:

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

Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
456 AM EDT Tue Sep 22 2026

Valid 00Z Wed 23 Sep 2026 - 00Z Wed 30 Sep 2026

...Heavy rain and flooding potential with T.D. 15-E remnants...

Above average moisture along with broad, weak energy aloft will
support scattered showers which contain locally heavy
rainfall...especially in windward/mauka areas under moderate
trades which strengthen to strong trades during the latter part of
the week.

Convection with what had been Tropical Depression 15E continued to
move west-northwestward across the Pacific and was several
hundred miles south of the Hawaiian islands as of late Monday
evening. This system will be increasing chances of organized
showers and thunderstorms and associated flooding during the next
several days. The areal extent of flooding and any concern for
wind-related hazard will depend upon the amount of
strengthening/reorganization occurs as the convection moves into
more favorable environmental conditions.

Multiple deterministic ECMWF runs and the EC ensemble spread some
degree of heavy rain and strong winds across much of the state,
while the recent GFS re-curves a closed surface low westward to
the south of the Big Island...limiting the impacts mainly to that
island.

As a result...heavy to excessive rainfall is possible and
flooding will be a concern, at least for the Big Island but
possibly across other islands as well while the concern for strong
winds looks more confined to the southern islands. Stay tuned for
forecast updates on the details. The higher moisture values look
to clear out next weekend and early next week.

Bann

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
418 AM EDT Tue Sep 22 2026
Day 1
Valid 12Z Tue Sep 22 2026 - 12Z Wed Sep 23 2026

..THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF SOUTHERN NEW MEXICO...

...New Mexico and West Texas...
A potentially high impact multi-day heavy rainfall event is set to
begin across NM and far southwest TX today into tonight. An upper
level trough approaching from the west will help strengthen an
upper level jet, persistently placing the region in the favorable
right entrance region. Deep southerly flow will transport tropical
moisture northward, driving PW values toward mid to late September
record levels by later today into Wednesday.

Lift will be further augmented by low level easterly upslope flow
and well defined mid level shortwave energy lifting north out of
Mexico by later tonight into Wednesday. Daytime hours today will
see scattered thunderstorm activity and at least some flash flood
potential. Large scale forcing intensifies overnight allowing for
a more concentrated rain shield with embedded heavier convective
cores to impact southern NM.

Neighborhood probabilities from both the 00z HREF and REFS show a
40-70% chance of rainfall exceeding 3" across NM today, though 5"
probabilities drop off significantly. This suggests a reasonable
max rainfall footprint of 2-4" through early Wednesday. Minimal
changes were made to the inherited Slight and Moderate risk areas,
as they still look in good shape. Scattered to numerous instances
of flash flooding are anticipated, some of which could be locally
significant. This threat includes the sensitive burn scar areas
within the Sacramento Mountains.

...Ohio Valley and Mid-Atlantic...
A setup for heavy rainfall will unfold across the Mid-Atlantic
today into tonight as an approaching mid level trough aligns with
the favorable right entrance region of an upper level jet. At the
surface, strong high pressure to the north will drive a backdoor
front southward, with strong easterly flow providing enhanced low
level convergence. The 00z HREF and REFS show generally good
agreement on two primary axes of elevated FFG exceedance
probabilities.

The first axis is from southeast VA into SC. Positioned along a
coastal convergence zone and the backdoor front, this corridor
will feature greater instability and support efficient warm rain
processes. High neighborhood probabilities exist in both ensemble
suites for 3" of rain. While 5" exceedance probabilities in the
REFS are likely inflated due to its known high convective QPF
bias, the HREF still depicts low to medium probabilities,
indicating a few localized 5" totals are possible. FFG neighborhood
exceedance probabilities of 15-40% justify a Slight risk, though
overall coverage may end up on the lower end of Slight risk
criteria.

The second axis is across WV into southwest VA. Focused along an
inverted trough, this area should see lower overall QPF magnitudes
than the farther southeast axis mentioned above. However,
antecedent conditions are wetter, resulting in much lower FFG
thresholds. Strong convergence along the inverted trough combined
with sufficient instability will allow for convective development,
with FFG neighborhood exceedance probabilities over 25% in both
the HREF and REFS. A Slight risk is warranted to cover this
threat, with at least a few instances of flash flooding
anticipated.

Farther north into the Mid-Atlantic, insufficient instability will
keep rainfall predominately stratiform, keeping rain rates below
flash flood thresholds. Although strong low level forcing over top
the backdoor front will still support a broad area of rainfall,
with some areas receiving 1-2" of rain.

...South Florida...
A Marginal Risk has been maintained for portions of South Florida.
PWs remain elevated and well above average, supporting heavy
rainfall rates and a localized urban flash flood risk today.
Neighborhood probabilities of exceeding 5" of rain in the HREF and
REFS are around 20-40%.

Chenard


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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
418 AM EDT Tue Sep 22 2026
Day 2
Valid 12Z Wed Sep 23 2026 - 12Z Thu Sep 24 2026

..THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF CENTRAL AND EASTERN NEW MEXICO...

...New Mexico and West Texas...
The heavy rainfall threat established on day 1 will continue and
potentially peak over NM on day 2 as large scale forcing gets even
stronger. A well defined mid level shortwave is forecast to lift
northward across the state, accompanied by robust upper level
divergence and the likely development of a surface low. PW values
will remain near record levels for this time of year, with an
anomalously deep moisture profile.

With such strong forcing and widespread moisture in place, the
primary limiting factor for heavy convective rates will be the
extent of cloud cover and its impact on destabilization. While
widespread clouds are a concern, daytime heating should allow at
least the eastern edge of the rainfall shield to sufficiently
destabilize, aided by broad easterly upslope flow. Thus while some
areas may see predominately stratiform rain, a concentrated swath
of intense convective rainfall remains likely.

As convection attempts to propagate eastward, strong easterly
inflow will act to slow this progression, increasing the threat of
training convective cells. Model guidance generally favors central
to eastern NM for the maximum QPF axis, as supported by the high
res 00z RRFS, REFS, FV3 and 3km NAM, and the global AIGFS and AIFS.
The 00z ECMWF remains the furthest west solution, and given the
expectation of some eastward convective propagation and instability
advecting in from the east, its maximum QPF placement is
probably too far west.

Only minor changes were made to the inherited Moderate risk area.
High res guidance supports localized swaths of 3 to 5 inches of
rain, which appears plausible given the environmental ingredients
in place. Scattered to numerous instances of flash flooding are
anticipated, and locally significant, life-threatening impacts are
possible...particularly across sensitive terrain, urban areas and
burn scars.

...Mid-Atlantic...
A complex synoptic pattern will be present over the eastern U.S. as
a mid to upper level low slowly drifts from the Ohio Valley
towards the Mid-Atlantic, while a separate coastal low develops
offshore. Meanwhile, surface high pressure positioned to the north
will advect drier and more stable air into the corridor between
these two features.

Much of the deepest moisture and instability will remain offshore
with the coastal low. The primary threat for heavy rainfall over
land should focus closer to the cold core of the upper low from
the OH Valley down through western NC and into north GA. While PW
values will have lowered across this area, model guidance still
indicates CAPE exceeding 1000 J/kg within a trough axis over the
region.

This localized axis of instability, coupled with a stationary
convergence axis, will support the development of slow moving
convective cells. Even with the reduction in deep moisture, locally
heavy rainfall rates are likely. Given that at least some of this
region will have compromised FFG and heightened hydrologic
sensitivity from previous rainfall, some flash flood risk is
expected to continue.

Based on signals from the 00z REFS and HREF members, as well as
the GFS and ECMWF, a small Slight risk has been introduced
stretching from eastern TN into eastern KY and southern WV, where
the focus for slow moving convection is expected to be greatest.

...Florida...
A Marginal risk continues across south FL where above normal PWs
and instability will continue to pose a localized flash flood
risk.

Chenard


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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
418 AM EDT Tue Sep 22 2026
Day 3
Valid 12Z Thu Sep 24 2026 - 12Z Fri Sep 25 2026

..THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
NEW MEXICO AND THE TEXAS PANHANDLE...

...Southwest...
The stronger mid level forcing and highest PW anomalies will shift
northward out of NM and into Colorado and the central PLains on
Thursday. Despite the loss of stronger large scale forcing,
daytime destabilization over NM is actually forecast to increase
in the wake of the exiting system compared to prior days. While PW
values decrease some, they will remain above the climatological
75th percentile.

With less concentrated forcing and somewhat reduced moisture, the
overall areal coverage of heavy rainfall across NM should diminish
relative to days 1 and 2. However, the combination of stronger
instability and sufficient moisture will still support intense
localized convective rainfall rates capable of producing
significant rainfall totals. Given the hydrologic sensitivity
built up from preceding days of heavy rain, a Slight risk will be
maintained for NM into the TX Panhandle. Locally significant flash
flood impacts will remain possible. Isolated flash flooding will
also be possible across portions of AZ, southeast UT, and CO as
shortwave energy lifts northward across the region.

...Central Plains...
The deep moisture plume will maximize over the Central Plains on
Thursday, pushing PW values toward late September record levels.
The mid to upper pattern coupled with a robust low level moisture
transport axis supports a favorable setup for organized convection
across portions of KS and NE, with backbuilding/training a
possibility.

We will maintain a Marginal risk to cover this threat. While
confidence is growing in a heavy rainfall setup, model spread
regarding the exact convective axis and uncertainty around the
degree of instability warrant holding at a Marginal for now.
An upgrade to an embedded Slight risk may be needed in subsequent
updates as confidence increases.

Chenard

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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
418 AM EDT Tue Sep 22 2026
Day 4 and Day 5

Valid 12Z Fri Sep 25 2026 - 12Z Sun Sep 27 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHERN US/WESTERN PLAINS AS WELL AS EASTERN NEW
ENGLAND...

...Southern Rockies to Central and High Plains...

Ty Friday...some of the convection will be moving into parts of
the central Plains which should also have lowered flash flood
guidance due to rainfall in the preceding days. The previously
issued Marginal Risk areas in southern Rockies and in the High
Plains were maintained with some adjustment to the areal outline on
Friday. On Saturday...the concern for the Plains shifts eastward to
Iowa. In neither case are the rainfall amounts or rainfall rates
expected to be blockbusters but the concern for flooding arises
from the antecedent conditions from earlier rainfall.

Eastern New England...
Model solutions are getting in better agreement that a strong
coastal low pressure system will be developing over the Atlantic
that moves in a general eastward direction. However, the spread in
the track forecast remains large. There was enough of a model
signal to keep indicating the potential for heavy rains to impact
portions of southeastern New England to keep the Marginal risk in
place on Friday and continue it into Saturday...especially if the
GFS and ECMWF continue to keep shifting their track closer to the
coast as they started to do on their 22/00Z runs.

Bann

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
418 AM EDT Tue Sep 22 2026
Day 4 and Day 5

Valid 12Z Fri Sep 25 2026 - 12Z Sun Sep 27 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHERN US/WESTERN PLAINS AS WELL AS EASTERN NEW
ENGLAND...

...Southern Rockies to Central and High Plains...

Ty Friday...some of the convection will be moving into parts of
the central Plains which should also have lowered flash flood
guidance due to rainfall in the preceding days. The previously
issued Marginal Risk areas in southern Rockies and in the High
Plains were maintained with some adjustment to the areal outline on
Friday. On Saturday...the concern for the Plains shifts eastward to
Iowa. In neither case are the rainfall amounts or rainfall rates
expected to be blockbusters but the concern for flooding arises
from the antecedent conditions from earlier rainfall.

Eastern New England...
Model solutions are getting in better agreement that a strong
coastal low pressure system will be developing over the Atlantic
that moves in a general eastward direction. However, the spread in
the track forecast remains large. There was enough of a model
signal to keep indicating the potential for heavy rains to impact
portions of southeastern New England to keep the Marginal risk in
place on Friday and continue it into Saturday...especially if the
GFS and ECMWF continue to keep shifting their track closer to the
coast as they started to do on their 22/00Z runs.

Bann

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
154 PM EDT Wed May 6 2026

Valid 00Z Thu May 07 2026 - 00Z Sun May 10 2026

...WPC Winter Weather Desk no longer routinely staffed until
late September, 2026...

Pending any significant winter weather, the WPC Winter Weather Desk
will not be staffed through the summer. The desk will resume
continuous staffing starting in the fall.

The WPC winter products will continue to be produced, however, and
all products except the heavy snow discussion (HSD) will be
available. This includes the Winter Storm Outlook (WSO), Winter
Storm Severity Index (WSSI), and Probabilistic Winter Precipitation
Forecasts (PWPF).


WPC

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
334 AM EDT Tue Sep 22 2026

Valid 12Z Fri Sep 25 2026 - 12Z Tue Sep 29 2026


...Impactful coastal storm meanders near the Mid-Atlantic and
Northeast
late week/weekend...


...Overview...

An upper low will stall atop the Mid-Atlantic and Northeast late
week into the weekend, supporting a meandering coastal surface low.
This pattern will lead to strong/gusty onshore winds for multiple
days, leading to coastal flooding, rip currents and high surf, and
potential beach erosion. An upper ridge persisting in the south-
central U.S. will promote warm temperatures, while a couple of
upper troughs come into the northwestern and north-central U.S.
through the period and bring rounds of precipitation to those
regions.


...Guidance/Predictability Assessment...

Models continue to agree that a coastal low will be in the western
Atlantic Friday into the weekend underneath a stalling upper low.
The surface low should be rather deep, reaching the 980s or at
least 990s (mb) around Saturday. The low will likely be pretty
stacked and seems to be warm core per phase space diagrams,
indicating there could be a warm seclusion and/or have some
subtropical characteristics. Its position from day to day at it
meanders is much more uncertain. The EC and UKMET develop the low
farther south in the Atlantic Friday-Saturday and reach near Long
Island by Sunday, compared to the farther northeast GFS/AIGFS/CMC,
with the EC-AIFS looking like a reasonable middle ground like the
EC mean. By Monday-Tuesday the low should be weaker but with
remaining questions on when it pulls away. All in all there is
still ample spread with the details, which could have sensible
weather impacts like wind speed/direction and how much rain falls
onshore or offshore.

Elsewhere, guidance shows good consensus on the upper ridge in the
south-central U.S., though varying positions of weak fronts and
precipitation potential cause uncertainties in the temperatures.
The ridge looks to extend north and traverse the Midwest/Great
Lakes Friday and over the weekend, contributing to the blocky
pattern as it stretches into southeast Canada north of the Atlantic
upper low. Meanwhile a couple of trough axes will track across the
northwestern to north-central U.S. with typical spread in their
timing and depth. Guidance generally shows one crossing the Pacific
Northwest at the start of the period Friday, tracking across the
northern tier and lifting into central Canada on Sunday. Then an
upstream trough is forecast to move into the West Coast Sunday and
continue tracking east. By Monday into Tuesday models show varying
degrees of stream separation that affects the trough's timing. Will
also mention that Hurricane Polo in the eastern Pacific still has
some model spread in its track, but number of models/ensemble
members are decreasing for having it curve into Baja California.
Polo's track will affect potential moisture inflow into the
Southwest.

The WPC forecast used a model and ensemble blend even early in the
forecast period, given the spread with the eastern low. Increased
the proportion of ensemble means to well over half by Days 6-7 to
mitigate the individual model differences in the details of the
pattern.


...Weather/Hazards Highlights...

The surface low in the western Atlantic meandering will lead to
broad onshore flow across the Mid-Atlantic and Northeast for
multiple days. This persistent pattern could lead to coastal
flooding and beach erosion concerns, especially when combined with
high astronomical tides. Exact placement of the surface low from
day to day and thus any heavy rain is more uncertain. The current
forecast supports that coastal New England may see heavy rainfall
on Friday into the weekend. However, stay tuned for forecast
updates, as small shifts in the low track would lead to significant
forecast shifts in rainfall amounts. See WPC's Key Messages for
this coastal low for further information.

Pacific moisture is forecast to advect around the western side of
the south-central U.S. upper ridge and lead to some rain across
parts of the central U.S. on Friday. If/where additional rain falls
in New Mexico, there could be flooding concerns after the forecast
heavy rainfall event in the short range causes very wet antecedent
conditions. Meanwhile farther east and northeast into the Plains,
moderate to locally heavy rainfall may be possible, but on less
sensitive ground. Rain chances persist in the Upper/Middle
Mississippi Valley into Saturday. Meanwhile, upper troughing will
bring precipitation to the Pacific Northwest and northern Rockies,
including higher elevation snow chances, on Friday. Scattered
showers and thunderstorms are again possible in parts of the
Plains/Mississippi Valley on Sunday, but a more widespread rainy
pattern with potentially heavier amounts is possible by Monday as
Pacific and Gulf moisture combine and stream into the central U.S.
ahead of troughing in the West.

Temperatures are forecast to remain cooler than average by 5-10
degrees in the Mid-Atlantic and Northeast into the weekend
underneath the upper low, and highs will generally be in the 60s.
On the other hand, broad upper ridging over the south-central U.S.
could maintain highs in the 90s for the southern Plains and Lower
Mississippi Valley. Cooler than normal temperatures are likely in
the Northwest given troughing aloft, which should push into the
northern Rockies/High Plains after a warmer than average period
into Friday.


Tate


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

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation forecast, excessive rainfall outlook,
winter weather outlook probabilities, heat indices and Key Messages
are at:

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