877
FXUS02 KWBC 211852
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
252 PM EDT Mon Sep 21 2026

Valid 12Z Thu Sep 24 2026 - 12Z Mon Sep 28 2026


...Coastal storm meanders near the Mid-Atlantic/Northeast late
week/weekend...

19Z Update: The 12Z model guidance shows good overall agreement on
the synoptic scale across the country for the beginning of the
forecast period Thursday, with a general deterministic model
compromise used for fronts and pressures, and gradually increasing
portions of the ensemble means through the remainder of the
forecast period. For the low pressure system off the Northeast
U.S. coast, the GFS and the GEFS take the low farther east and away
from the coast starting Friday night and continuing into the
weekend, whereas the non-NCEP consensus is more aligned with a
solution closer to southeast New England and thus brings more
impacts to the coast in terms of higher winds and heavier rainfall.
Recent runs of the ECENS have seemed to stabilize some with run-
to-run differences over the past 24 hours, so a position close to
the ECENS mean was primarily used as the forecast point for the
main surface low. For the north-central U.S., the CMC has trended
closer to the model consensus compared to its 00Z run, which was a
faster outlier with the low over southern Canada and the front
crossing the Dakotas.

In terms of NBM changes, high temperatures were slightly lowered
across portions of the Ohio Valley and the Northeast where the
upper trough and increased clouds likely keep readings lower. By
next Monday, moisture from the eventual remnants of T.S. Polo
should increase across the Desert Southwest, and QPF was raised
some across this region for that time to account for this. The
previous forecast discussion is appended below for reference.
/Hamrick
-------------------------

...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, which may lead to coastal flooding and beach erosion. An
upper ridge persisting in the south-central U.S. could promote warm
temperatures, while Pacific moisture flows around it to produce
additional rainfall across the Southwest late week, though with
lower amounts than the very wet pattern likely Tuesday-Wednesday.
This moisture should spread into the Plains as well for rain
chances that also reach the Mississippi Valley over the weekend. A
cool pattern is forecast in the Northwest with rounds of upper
troughing and precipitation.


...Guidance/Predictability Assessment...

Models are agreeable that an upper low will move from atop the
Appalachians/Mid-Atlantic Thursday to be centered over the western
Atlantic Friday, stalling there through the weekend and early next
week. A surface low underneath could be on the strong side, in the
990s to possibly reaching the 980s (mb) over the weekend. The low
will likely be pretty stacked and seems to be warm core per phase
space diagrams, indicating there could be a warm seclusion. The
position of the surface low from day to day is somewhat
questionable. In the 00Z model cycle, the ECMWF/GFS/EC-AIFS show a
pretty good consensus with the low placement through around
Saturday, with the CMC and AIGFS a bit east. The ECMWF and GFS stay
pretty well in lockstep in showing the low retrograding toward the
Mid-Atlantic Sunday, and then the GFS approaches the Delmarva a
little closer by next Monday. Though the EC/GFS happen to agree
pretty well, the spread in ensemble members and the other other
guidance shows that this track is certainly not definite and could
continue to change.

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, 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 U.S. with
typical spread in their timing and depth.

The WPC forecast used a multi-model blend of the deterministic and
AI guidance early on, favoring the ECMWF, AIFS, and GFS. Quickly
ramped up the proportion of ensemble means as the period
progressed, reaching well over half the blend by Days 6-7 given the
spread 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
tidal cycles as typical and the full moon later this week. Exact
placement of the surface low from day to day and thus any heavy
rain is more uncertain. The current forecast supports that eastern
North Carolina could see enhanced rain on Thursday, and then
coastal New England Friday-Saturday. However, stay tuned for
forecast updates, as small shifts in the low track would lead to
significant forecast shifts in rainfall amounts.

For Thursday-Friday, a pattern of Pacific moisture inflow (with
some moisture connection to T.S. Polo) will persist across parts of
the Southwest and Plains, but becoming more limited compared to
the short range period and shifting east a bit. 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/reload
across the central U.S. over the weekend. Another round of
moisture may reach the Southwest on Sunday as well.

Elsewhere, scattered showers and thunderstorms could impact South
Florida through the period, though the highest moisture should be
pushed farther south by then. The Pacific Northwest and northern
Rockies could see a round of precipitation late week, including
higher elevation snow chances, and then perhaps additional
precipitation by Sunday.

Temperatures will be cooler than average in the East, particularly
the Mid-Atlantic, underneath the upper low and with a cold air
damming pattern at the surface. 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
late week.


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





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