236
FXUS02 KWBC 050631
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
231 AM EDT Sun Oct 5 2025

Valid 12Z Wed Oct 08 2025 - 12Z Sun Oct 12 2025


...General Overview...

A trough-ridge-trough upper-air pattern if forecast to set up across
the mainland U.S. by midweek with amplification then through the
weekend. The features are a developing closed/cutoff low
off/along the Pacific Northwest Coast, a subtropical ridge drifting
west from the Gulf Coast and extending up the Rockies by Friday,
and transient troughing over the east bringing cool Canadian air
over the Great Lakes and Northeast later this week. Tropical
moisture well ahead of Priscilla in the eastern Pacific is forecast
to be drawn into the Desert Southwest Thursday night and expand
over the Intermountain West over the weekend.


...Guidance/Predictability Assessment...

The main feature is a strong/positively tilted trough over/off
southwest BC Wednesday morning that digs/amplifies into a closed
low by Thursday. The 18Z GFS (and now 00Z) is in good agreement
with the EC-AIFS as well as ensemble means in keeping this feature
offshore Oregon/Washington through Friday night. The 12Z EC
develops the low onshore (east of the ECENSmean) and continues to
track the low south off the northern California Coast. The 12Z CMC
is similar to the EC while the 12Z UKMET did not close the low and
allowed progression east instead of stalling on/near the coast.
However, the 00Z UKMET/ECMWF/CMC took major leaps toward the
GFS/EC- AIFS solution. Given the two camps, the prowess of the AI
for general synoptic patterns warranted weight toward the GFS
solution (and now the other global guidance is on board with it).
The WPC forecast was heavily based on the 18Z GFS with increasing
reliance on the ECENS/GEFS means by Day 4 to work the solution
toward the 18Z EC-AIFS.

Cold frontal progression through the Southeast and then potential
low development off the Carolina Coast Thursday and Friday is
another focus area. The GFS is more progressive and offshore than
the EC-AIFS which is heavy on developing coastal low pressure. The
WPC frontal forecast and QPF in the Southeast was a
blend/compromise of the GFS and EC-AIFS.

The EC remains the heaviest with tropical moisture from Priscilla
into the Desert Southwest. Some QPF was allowed by Thursday night
from a blend of EC influence and the EC-AIFS. However, the EC is
too potent with QPF by Friday, so the forecast was mainly from the
GFS Friday through the weekend. This should allow some much needed
moisture for the Intermountain West over the weekend as the closed
low eventually opens and ejects east, providing forcing for the
moisture.


...Weather/Hazards Highlights...

Lingering moisture anomaly New Mexico on Wednesday with potential
presence of a stalled frontal boundary warrants raising a Marginal
Risk for the new Day 4 over the Sacramento Mountains and the NM
ranges to the west.

An influx of tropical moisture from the eastern Pacific ahead of
Priscilla may reach into the Desert Southwest Thursday night. This
solution is driven by the ECMWF which has been much more
progressive with this moisture than other guidance the past several
runs. However, the EC-AIFS is on board with some rainfall in
north-central Arizona, so a Day 5 Marginal Risk is raised for the
lower Colorado River area (northern Sonoran Desert). This moisture
surge has better agreement by Friday with expansion over the
Intermountain West through the weekend, so this western rain (and
mountain snow) potential will need to be monitored.

A cold front progresses through the Mid-Atlantic and the Carolinas
Wednesday and Thursday. As of now this appears progressive enough
to consider it beneficial rain and no ERO at this time. The EC-AIFS
is featuring low pressure/trough development along the Carolina
coast Friday through this weekend which would bring significant
rains, so this will need to be monitored.

Cool conditions with max temperatures five or so degrees below
normal shift east with a cold front from the Great Lakes Wednesday
through the Northeast and Eastern Seaboard for Thursday/Friday.
Meanwhile, ridging over the Gulf Coast drifts west through Texas
and amplifies up the Rockies this weekend which will maintain above
normal temperatures over south-central states through next weekend
with much above normal temperatures expected to build through the
Great Plains Thursday through this weekend.


Jackson


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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