655
FXUS02 KWBC 191930
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
330 PM EDT Sat Sep 19 2026

Valid 12Z Tue Sep 22 2026 - 12Z Sat Sep 26 2026


...Wet pattern with possible flooding threat in the Southern High
Plains/Rockies next week...


...Overview...

During this period an upper trough/low will advance through the
Great Lakes region ushering a frontal system through the East
with a cold air damming wedge of high pressure behind it, while
coastal low development becomes likely. This pattern will be
favorable for multiple rounds of rain in the East, as well as
cooler temperatures and notable onshore flow across the Northeast
and Mid-Atlantic. Meanwhile, an eastern Pacific/southwestern U.S.
upper trough and warm upper ridging sticking around the south-
central U.S. will direct moist southerly monsoonal flow into parts
of the western U.S. to the Plains. Multiple days of heavy rain are
possible in the Southern Rockies/High Plains in particular, which
could cause flooding concerns.

...Guidance/Predictability Assessment...

The latest suite of guidance has overall decent agreement on the
larger pattern with continued variances on smaller scale features.
Across the East, models depict an upper low tracking east across
the Upper Midwest into the Great Lakes midweek, while Gulf energy
shears northward tracking across the East. These combining features
allow for the upper low/trough to slowly track atop the East late
week, with differences in how broad and far south it gets. A
surface low will spin up over the western Atlantic and lift
northward toward the later part of the extended period. There
continues to be notable differences with its placement, strength
and track that will impacts QPF and winds/wind gusts particularly
for the Mid-Atlantic and Northeast coastal areas. The 00Z GFS, AI-
GFS, and CMC show the low quite close to the coast and a bit
faster to track north, while the ECMWF, EC- AIFS, and UKMET are
farther offshore and slower. Ensemble members continue to show
ample spread too, so confidence in any particular solution is low.
Followed persistence by leaning away from the farthest west/wetter
solutions.

Multiple cycles have struggled with the details of southern stream
troughing in the Southwest by Wednesday-Thursday as some energy
tracks north and some stays behind. However consensus has started
to improve with the shortwave tracking north/northeast, reaching
the Dakotas by early Thursday. This in turn will briefly disrupt
the ridge, then feeding into the eastern trough by Friday. By the
end of the week guidance has differences with the troughing over
the West on whether streams will separate. The AIFS and AIGFS leave
some southern stream troughing behind and track the northern
stream more quickly eastward across central Canada by next
Saturday, with ridging in the West. The GFS and CMC keep a phased
positively tilted trough moving into the West while the ECMWF seems
to be a middle ground depiction, with some separation of the
streams but not as aggressive as the AIs.

The WPC forecast was based on a multi-model blend early before
transitioning to a heaviest weighting of the ensemble means to
account for the increasing model differences.


...Weather/Hazards Highlights...

Upper-level support and a surface frontal system with a developing
coastal low will lead to multiple rounds of moderate to heavy rain
in the East next week. Generally the Appalachians to Mid-Atlantic
could see heavy rain through midweek, potentially transitioning to
the Northeast by late week if and when the coastal low tracks
north. A relatively strong surface high for September should set up
over Quebec and spill a cold air damming wedge south behind the
front, yielding colder than average temperatures across the
Northeast/Mid-Atlantic, with highs generally in the 60s and upper
50s Tuesday-Thursday. This pattern will also allow for onshore
winds and potentially some concern for coastal flooding for
portions of the Northeast and Mid-Atlantic.

Pacific (including a potential tropical connection) and Gulf
moisture are forecast to combine as they stream into the Interior
West, increasing by Tuesday and persisting through at least Friday.
Rain amounts may become heavy in New Mexico in particular, and
flooding will be possible--see the Excessive Rainfall Outlooks for
more information. Some chance of rain will extend north across the
Rockies to High Plains Tuesday and into the Plains Wednesday-
Friday.

Meanwhile, a wet pattern will be in place across Florida through
the period, particularly for southern portions of the peninsula and
the Keys. Above average temperatures well into the 90s are
forecast to linger across Texas into the Southeast through Tuesday,
but gradually reduce in scope and magnitude as the week
progresses.


Campbell/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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