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FXUS02 KWBC 181942
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
342 PM EDT Fri Sep 18 2026

Valid 12Z Mon Sep 21 2026 - 12Z Fri Sep 25 2026


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


...Overview...

An upper low hovering over the Great Lakes next week will interact
with southern stream energy moving northward from the Gulf across
the Eastern Seaboard. At the surface, a frontal system is forecast
to push through the East with a cold air damming wedge of high
pressure behind it. This setup will allow 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...

Latest models and ensembles continue to show good agreement on the
overall pattern evolution described above, but plenty of
uncertainty in the details which have important implications on
sensible weather. Upper troughing in the north-central U.S. could
close off into an upper low as it moves into the Great Lakes by
midweek as weak energy in the Gulf early next week should shear
north and track across the East. This eventually allows for a
deeper trough into the East late week. Guidance is more uncertain
late period on how long this trough/embedded upper low sticks
around.

Southern stream troughing is forecast to hover over the eastern
Pacific and slowly track into California Monday-Tuesday. After that
its evolution becomes questionable as some energy may linger while
some tracks northeastward across the Intermountain West. This
creates some out of phase differences as some models show stronger
ridging than others. Farther north, northeast Pacific troughing
could reach the Northwest by late week with some more notable
timing differences.

Overall, the WPC forecast favored a multi-model blend of the
dynamical and AI guidance early in the period, but transitioned to
favor increasing proportions of ensemble means to a bit more than
majority by Day 7 given the increasing model spread, especially
with the smaller scale features. This helps maintain good
continuity with the previous WPC forecast as well.


...Weather/Hazards Highlights...

Upper-level support and a surface frontal system will lead to
multiple rounds of moderate to heavy rain in the East next week.
The placement of the heaviest amounts will vary from day to day,
but generally the Mid-Atlantic looks like a focus. 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-Wednesday.
This pattern will also allow for onshore winds and potentially some
concern for coastal flooding for portions of the Northeast and
Mid-Atlantic.

Pacific and Gulf moisture are forecast to combine as they stream
into the Interior West, increasing by Tuesday and persisting
through at least Thursday. 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-Thursday.

Meanwhile, a wet pattern will be in place across Florida through
the period, particularly for the Keys and southern portions of the
peninsula. Warmer than average temperatures should stay farther
north across Texas to the Southeast under an upper ridge, but
gradually reducing in scope and magnitude as next week progresses.


Santorelli/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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