115
FXUS02 KWBC 301944
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
344 PM EDT Wed Sep 30 2026

Valid 12Z Sat Oct 03 2026 - 12Z Wed Oct 07 2026


...Major South/Southeast U.S. Excessive Rainfall/Flooding threat
with tropical connections this weekend and early-mid next week...


...Guidance/Predictability Assessment...

The latest 00/06/12Z guidance remains fairly well clustered
through most of the period on the main synoptic features. An
initial upper-wave departing the East Coast will leave a trailing
cold front that becomes quasi-stationary through the southeastern
to south-central U.S. A second upper-wave/trailing cold front
upstream will progress eastward, with the amplifying upper-wave
helping to drive both fronts southward towards the Atlantic/Gulf
Coasts. Meanwhile, amplified upper-ridging will remain in place in
the West. Later into the period, the guidance agrees on another
upper- wave/frontal system traversing the northern tier by mid-next
week. Naturally, some of the greatest uncertainty lies with the
smaller- scale details such as the progression of the frontal
boundaries and subsequent precipitation coverage as an active
pattern remains in place across the southeastern to south-central
U.S. THe latest NBM QPF trended a bit closer to a faster
progression of the boundaries that the deterministic guidance has
been consistent about the last couple of days, though a preference
for incorporating a greater contribution ECMWF/GFS and ECMWF
AIFS/AI GFS Sunday-Monday to continue to better focus the highest
QPF axis along the leading front as it pushes towards the coast is
still preferred. Thereafter, the guidance showed better agreement
overall with boundary/QPF placement along the Atlantic and Gulf
Coasts with a likely greater focus offshore. The updated WPC
forecast package overall used a composite blend of the determinist
guidance given the noted consistent agreement allowing for good
forecast continuity. A contribution from the GEFS/ECens means was
added for the latter part of the period as spread increases, though
the main features still remain well captured overall.


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

A main upper trough and wavy/wet frontal system will shift slowly
eastward from the South-central U.S. into the weekend in separated
southern stream flow. Leading excessive rainfall/flooding threats
working into the South/Southeast will be fueled by tropical
moisture from the remnants of Hurricane Polo and an increasingly
deep and protracted lead Gulf inflow pattern with tropical
influence. WPC Excessive Rainfall Outlook Marginal Risk areas with
embedded Slight Risk areas cover from coastal Texas through the
Gulf Coast states and Tennessee Valley/southern Appalachians then
the Southeast for Day4/Saturday and Day5/Sunday. Meanwhile, systems
within a more progressive northern stream flow will support
passage of a series of wavy frontal systems down from the U.S.
northern tier. These fronts will act to provide a northern rainfall
shield focus and over-running boundary for lifting moisture/clouds
before delivering a post-frontal fall temperatures/drier airmass
southward with high pressure settling. This will act to shift
southward and confine the lead focus for heavy rainfall/flooding
threats down towards the Gulf Coast through early-mid next week to
monitor given the ample repeat activity threat.

Elsewhere, upper-ridging will lead to a period of above-average
temperatures over the western U.S. including highs into the 90s and
low 100s for central/southern California and the Desert Southwest.
The heat will reach hazardous levels in southern California into
the weekend and at least through early next week.


Putnam/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






























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