179
FXUS02 KWBC 190711
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
311 AM 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...

An upper trough/low will slowly track through the Great Lakes
around midweek into the East late week. At the surface, a frontal
system is forecast to push through the East with a cold air damming
wedge of high pressure behind it, while coastal low development
becomes likely. 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...

Model guidance generally continues to show agreement on the larger
scale features of note next week, but quite a bit of uncertainty
in the details. In the East, models show an upper low moving across
the Upper Midwest into the Great Lakes Tuesday-Wednesday, 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 seems set to develop in the western
Atlantic for the latter half of the week, but there are some
notable differences with its placement as well. 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. This of course has implications for sensible
weather like wind speed/direction and QPF. Ensemble members across
the model suites show ample spread too, so confidence in any
particular solution is low. But since GEFS members were generally
farther east of the deterministic GFS, leaned away from the
farthest west solutions.

Models have struggled with the details of southern stream
troughing in the Southwest by Wednesday-Thursday as some energy
tracks north and some stays behind. Finally the 00Z runs are in
better agreement for a shortwave to track north/northeast and reach
the Dakotas early Thursday and temporarily disrupt the ridge, then
feeding into the eastern trough by Friday. Then on the larger
scale, model differences arise by Friday-Saturday in the West.
Troughing will dive through the Pacific, but some guidance shows
separating streams as it does so. Namely, 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. The new 00Z ECMWF may show the
most middle ground depiction of this, with some separation of the
streams but not as aggressive as the AIs.

The WPC forecast was based on a multi-model blend early, with
lessening GFS component by mid-period and overall favoring of the
ensemble means to more than half for Days 6-7, 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.


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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