704
FXUS02 KWBC 080800
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
400 AM EDT Mon Sep 8 2025

Valid 12Z Thu Sep 11 2025 - 12Z Mon Sep 15 2025


...Overview...

The upper flow pattern for this medium range period begins with
amplified mean troughs settled over both the eastern and the
western lower 48 to sandwich a warming central U.S. ridge. These
will be slow to move out initially, but energy ejecting out of the
West should help to finally dislodge the pattern during this period.
In terms of sensible weather, wavy frontal systems will focus rain
chances from the Northwest/West to the Rockies/Plains with gradual
flow translation and also downstream through the Great Lakes region
with frontal passage as northern stream energy digs to the lee of
the ridge. Heavy rain potential will persist from Florida through
the coastal Carolinas as deepened moisture interacts with a wavy
western Atlantic front. This activity will focus on the leading
edge of a cool Canadian airmass over the central to eastern U.S..

...Guidance/Predictability Assessment...

Model and ensemble pattern evolutions through medium range time
scales solutions seem reasonably clustered over the lower 48 and
vicinity and a broad composite of latest guidance along with the
National Blend of models was favored. This plan will tend to
mitigate smaller scale/embedded system variance as consistent with
individual predictabiliy to best maintain WPC product continuity.

...Weather/Hazards Highlights...

It overall remains the case that a persistent and wavy frontal
system over the Gulf and Florida also extends just off/up the
Eastern Seaboard. This will provide a main focus for tropical
moisture to pool, leading to daily enhanced and diurnally driven
rainfall potential associated with scattered thunderstorms.
Saturated grounds from pre-cursor rainfall warrants Marginal Risk
of Excessive Rainfall Outlook (ERO) threat areas for the
central/southern Florida Peninsula into Thursday and Friday.
Farther north, rains for the coastal Southeast/Carolinas still
offer uncertainty for how much convection occurs onshore/offshore
on any given day. Small shifts in the wavy frontal boundary may
produce significant differences in onshore rainfall amounts.

For the West, a series of upper troughs/closed lows set to work
over the Northwest/West will support locally enhanced rainfalls
into later this week and again into early next week. Rainfall
areas with each system may translate slowly from the Pacific
Northwest/northern California to the Great Basin/Intermountain
West. Terrain and frontal lift may focus some runoff threat over
the northern Rockies/High Plains and also southwest Colorado and
vicinity where deeper moisture may channel between ejecting
western U.S. troughing and the central U.S. ridge. Marginal Risk
ERO threat areas have been introduced into Thursday/Friday. Also,
this pattern may yield cooler temperatures supportive of some snow
for the highest elevations. Gradual flow and frontal translation
downstream may also support rainfall through the Great Lakes
region and vicinity with frontal passage as northern stream energy
digs to the lee of the main ridge to reinforce an already cooled
airmass settled over much of the central to eastern U.S..


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




















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