633
FXUS02 KWBC 050800
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
400 AM EDT Fri Sep 5 2025

Valid 12Z Mon Sep 08 2025 - 12Z Fri Sep 12 2025


...Overview...

The flow pattern for next week should overall be amplified and
slow to dislodge as highlighted aloft by a warming Rockies to
Plains ridge sandwiched between unsettling multi-stream mean
trough positions over the West Coast and the East. In this
scenario for the lower 48, wavy frontal systems will focus most
rain chances over the Northwest/West and slowly out to the
Rockies/Plains and also downstream over the Upper Midwest/Great
Lakes with northern stream energy, from South Texas and the Gulf
and especially across Florida and in a deep axis along/just off
the coastal Southeast/Carolinas with moist southern stream flow.

...Guidance/Predictability Assessment...

GFS/ECMWF/UKMET and Canadian model solutions seem generally well
clustered for early/mid next week and a favored composite blend is
well supported by ensembles and machine learning guidance in a
pattern with overall seemingly above normal predictability. The WPC
product suite for mid-later next week amid slowly growing forecast
spread was mainly derived from a composite blend of compatible
guidance from the GFS model/GEFS mean, the Canadian model and the
ECMWF ensemble mean. The 12 UTC ECMWF model was discounted given
more progressive downstream progression over the West given the
amplified/slowed nature of the flow. The newer 00 UTC ECMWF has
trended slower, albeit with some continued run-run variances. The
aforementioned blend was used as the WPC forecast basis for these
longer time frames as also supported by machine learning guidance.

...Weather/Hazards Highlights...

Monsoonal rainfall amounts should generally decrease by early next
week Monday, but some lingering moisuture/instability fueling showers
are still possible. Showers and storms could reach into much of
the Plains to Upper Midwest with a tongue of instability near
another front. Consider this activity less than a 5 percent chance
of flash flooding for no WPC Excessive Rainfall Outlook risk areas
are depicted for Day 4/5 Monday/Tuesday at this time given
uncertain local focus, but central U.S. convection could continue
as next week progresses to monitor.

Farther east, the frontal system over Florida and northeast in the
western Atlantic will provide a focus for moisture to pool,
leading to at least scattered diurnal convection each day. Moisture
levels look to decrease slightly over Florida compared to the
short range period, but the saturated grounds from rainfall before
Sunday warrant the addition of Marginal Risk areas for Monday from
roughly Cape Canaveral to the south Florida. Rainfall across the
Carolinas into Georgia is rather uncertain with how much convection
may occur onshore or offshore on any given day. Small shifts in
the frontal boundary could produce significant differences in the
rainfall amounts, but the amplified/slower pattern translation may
allow for some onshore nudge.

It remains the case that an upper low pushing through the eastern
Pacific toward the Northwest will produce multiple days of rainfall
next week, expanding eastward with time from the Pacific
Northwest/northern California into the northern Great Basin and
Intermountain West. This cool season type of rainfall should be
marked by moderate rates that are generally not enough to cause
flooding concerns. The lowering heights aloft yielding cooler
temperatures could produce snow for the highest peaks.

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 (QPF), excessive rainfall
outlook (ERO), winter weather outlook (WWO) probabilities, heat
indices, and Key Messages can be accessed from:

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








$$