174
FXUS02 KWBC 271905
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
305 PM EDT Sun Sep 27 2026

Valid 12Z Wed Sep 30 2026 - 12Z Sun Oct 04 2026


...Major South-Central to East-Central U.S. Heavy Rain/Flooding
threat with tropical moisture connections into mid-later week...


...Guidance/Predictability Assessment...

The models continue to show better agreement on the large scale
pattern across the CONUS for the medium range period but plenty of
differences in the details and timing of individual systems. The
main and most impactful uncertainty exists across the Southern
Plains where a cutoff low weakens but with remnant energy
meandering for several days, leading to a significant multi-day
heavy rainfall event. While confidence is increasing in this
scenario, guidance continues to struggle with how fast the energy
progresses eastward. The GFS/GEFS is a bit faster with the system,
with the ECMWF indicating a bit stronger of a low and more hold
back of energy over the Southern Plains. Do feel like the GFS is
too fast, as there is better consensus for something slightly
slower. The WPC forecast for today reflects this, and is consistent
with the previous WPC forecast as well as the National Blend of
Models.

Otherwise, some timing uncertainties with a shortwave from the
Northwest into the Northern Plains Friday-Sunday and with a longer
wave trough exiting the Northeast. Leaned more heavily on the
deterministic models for the early period for some added detail,
with a transition to 50 percent ensemble means/deterministic by Day
7 to help mitigate the differences.


...Pattern Overview and Weather/Hazards Highlights...

A closed upper trough/low with wavy frontal systems will shift
slowly eastward from the Southwest U.S. to the South-central U.S.
mid-later week in southern stream split flow. Excessive
rainfall/flooding threats over the Southwest/Southern Rockies
states during the short range will then focus over the South-
central U.S. and with Gulf coast frontal genesis mid-later week
into next weekend. This will be fueled by tropical moisture
connections from current East Pacific Hurricane Polo (set to
landfall into Mexico) and also with increasingly deep and sustained
lead Gulf inflow with some tropical influence. This expansive
multi-day threat should prove slow to progress late week/next
weekend blocked between upper ridge developments over both the
Southwest and Southeast U.S.. Accordingly, the WPC Excessive
Rainfall Outlook (ERO) now includes moderate risks from south Texas
into far southern Oklahoma for both Wednesday and Thursday, where
as much as 3-6 inches (locally higher) of rain could fall. There is
also a secondary moderate risk across southeast Colorado and
northeast New Mexico for continued heavy rainfall into the Day 4
period from Day 3, and where soils are already very saturated. For
both days, a large slight risk also surrounds the moderates and
stretches from the central High Plains into the Upper Midwest as
rainfall pools along an approaching cold front. This activity will
continue to progress slowly eastward late week and into next
weekend into the east- central U.S. with additional heavy rainfall
threats likely.

Meanwhile, systems within a more progressive/zonal mean northern
stream flow will support passage of a series of wavy frontal
systems across the U.S. northern tier of the nation from the
Northwest through the Northeast this week. These will act to
provide a northern rainfall shield focus for lifting moisture and
also deliver periods of moderating post-frontal fall temperatures.

Santorelli/Schichtel


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


















$$