933
FXUS02 KWBC 240732
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
332 AM EDT Thu Sep 24 2026

Valid 12Z Sun Sep 27 2026 - 12Z Thu Oct 01 2026


...Impactful coastal storm meanders near the northern Mid-
Atlantic/Northeast into early next week...

...Widespread precipitation likely in the Four Corners states and
reaching the Plains/Mississippi Valley early to mid-next week...


...Overview...

The western Atlantic surface low will still be lingering near the
Northeast Sunday-Monday before exiting eastward. Though the low
should be weakening, additional strong/gusty winds with potential
for coastal flooding, beach erosion, and rip currents are possible,
along with heavy rain in coastal New England. Meanwhile, an
amplified upper trough will enter the West early next week and move
east as the week progresses. Precipitation will be widespread
ahead of this trough, for potentially multiple days of rain/storms
and mountain snow in the Interior West/Four Corners states, and
spreading into the Plains and Mississippi Valley as the week
progresses.


...Guidance/Predictability Assessment...

At the start of the period Sunday, the primary model diagnostics
concern continues to be the western Atlantic coastal low position,
as relatively minor differences in position could cause
significantly different sensible weather impacts like wind speed
and direction. There is general agreement for the low to meander
south or southeast of Long Island on Sunday and Sunday night. The
00Z ECMWF seems (hopefully) like an outlier with its trend toward a
stronger low in the 980s and farther west closer to the New Jersey
coast. There is some support from the AIFS/some AIFS ensemble
members for a position like that, but weaker. For now, will prefer
a blend of the slightly farther east guidance like the GFS and 12Z
EC mean. The AI-GFS has been persistently farther northeast with
the low. The upper and surface lows should weaken and move
northeast by Tuesday-Wednesday.

After the trough comes into the West Coast Sunday, models have
struggled with how to handle its progression eastward. The 12/18Z
dynamical model guidance kept the trough mostly phased for a steady
progression east into the central U.S., while the EC-AIFS and
AIGFS instead agreed upon a split flow pattern where a southern
stream upper low formed with slower movement through the Southwest
and the northern stream trough progressed quickly eastward. Now
with the recent 00Z guidance, the ECMWF and CMC have transitioned
to show a split flow pattern as well, and the GFS is the only
primary model that keeps the trough phased. Even the 00Z ECens and
CMCe means seem to pull some southern stream energy southwest now.
The pattern will have an impact on Hurricane Polo`s track, and the
slower moving upper low in the Four Corners states could pull
energy and moisture from Polo north into it. See NHC for Polo`s
official forecast track.

The WPC gridded forecast was based on the 01Z NBM with some edits,
which uses the 12/18Z model cycle. But the fronts/pressures
forecast used the 00Z guidance, mostly leaning away from the ECMWF
with the Atlantic low early, and leaning away from the GFS later
since the bulk of guidance now shows split flow. Expect more
changes to continuity than normal with this large model change.


...Weather/Hazards Highlights...

The meandering surface low in the western Atlantic will lead to
broad onshore flow across the Mid-Atlantic and Northeast continuing
into early next week. The persistent pattern could lead to coastal
flooding and beach erosion, as well as marine hazards like rip
currents and high surf. Heavy rain could cause inland flooding
across southeastern New England into Sunday. See WPC`s Key Messages
regarding this coastal low for further information.

Some light to moderate rain is possible in the Dakotas and parts
of the Lower/Middle Mississippi Valley on Sunday. More broadly,
Pacific moisture should make a return ahead of the large-scale
trough in the West, bringing some rain to the Four Corners states
northward Sunday-Monday. After that, uncertainty in the pattern
makes rainfall placement and amounts uncertain. The current
forecast shows moderate to heavy rain spreading across the Plains
and Upper Midwest Monday and tracking east to reach the Mississippi
Valley on Tuesday and Wednesday. But given the model trends, this
may need to transition to a wetter pattern in the Four Corners
states with a lingering upper low and potential Hurricane Polo
influence, while rain chances are more progressive in the north-
central U.S. Stay tuned for forecast updates in this uncertain
pattern. Some snow is possible in the higher peaks of the
Intermountain West/Rockies with the precipitation, as the trough
aloft helps to cool temperatures.

Warmer than average temperatures will persist in the south-central
U.S. into early next week under an upper ridge, and highs in the
90s are forecast through the southern Plains and Lower Mississippi
Valley. On the other hand, cooler than average temperatures
(especially for highs) are forecast for the West under troughing
aloft, gradually spreading eastward early next week and helping to
moderate temperatures in the Plains by midweek. Temperatures could
reach around 10 degrees above normal in the East ahead of the
trough Wednesday-Thursday.


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


$$