233
FXUS02 KWBC 062020
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
420 PM EDT Mon Oct 6 2025

Valid 12Z Thu Oct 09 2025 - 12Z Mon Oct 13 2025


...General Overview...

A deep upper low is expected to develop off the Pacific Northwest
coast by Thursday and then swing onshore on Saturday while opening
into a trough and drawing tropical moisture up through the
Intermountain West from tropical cyclone Priscilla in the process.
Meanwhile, there continues to be increasing model support for a
coastal storm to develop off the coast of the southeastern U.S.
this weekend before possibly tracking up the Mid-Atlantic coast.
In between these systems is persistent upper-level ridging centered
over Texas with an axis that extends up the Great Plains this
weekend and then gradually shifts east into the Great Lakes.


...Guidance/Predictability Assessment...

The medium-range period begins with continued excellent model
agreement on the formation of a closed upper low off the coast of
the Pacific Northwest on Thursday and then drifts southward on
Friday. Thereafter, model guidance today generally shows a faster
eastward progression of the upper low onshore by Saturday while
opening up into a trough. The GEFS mean has been most notable in
this eastward shift relative to the more consistent EC mean. In
general, models are trending toward bringing more QPF into
northern California and up the coast of the Pacific Northwest this
weekend.

Farther south across the Southwest, model guidance continues to
indicate a higher degree of uncertainty than desired regarding the
plume of tropical moisture that is forecast to be drawn northward
from tropical cyclone Priscilla in the eastern Pacific. Given the
relatively broad circulation and deep convection associated with
the intensifying Priscilla, today`s GFS has shifted toward a
faster and farther northward track in much better agreement with
the more consistent and faster ECMWF forecast track for Priscilla.
This has resulted in a higher QPF footprint near the Four Corners
region with the GFS/GEFS solutions but it remains farther southeast
than the EC/EC mean solutions. The WPC QPF for this tropical plume
for today is based on 65% from the 00Z EC/EC mean solutions and
the remainder from the 06Z GFS/GEFS, and 00Z CMC/CMC mean.

Near the East Coast this weekend, models continue to signal a
synoptic pattern that favors coastal cyclogenesis. The EC-AIFS has
been the most consistent guidance in depicting a nor`easter type
of cyclone to form and track up the East Coast this weekend to
early next week. Other dynamical global models have since followed
suit to depict cyclogenesis to some extent near the East Coast but
with a wide range of possible solutions. The latest 12Z ECMWF now
shows the possibility of a cyclone that never reaches the latitude
of North Carolina as it turns west toward the coast and acquires
some tropical characteristics. The WPC medium-range forecast
charts today were based on a consensus blend of 65% from the 00Z
EC/EC mean, 20% from the 06Z GFS/GEFS, and 15% from the 00Z
CMC/CMC mean, with subjective manual modifications for the East
Coast cyclone Day 6-7. Agreement with the previous WPC forecast
package was reasonably good but with the position of the low
closer to the West Coast early next week.


...Weather/Hazards Highlights...

An influx of tropical moisture from the eastern Pacific ahead of
Priscilla is expected Friday through the weekend with the initial
surge of moisture still possible into the Desert Southwest
Thursday night. The Day 4 ERO maintains a Marginal over north-
central AZ. Greater moisture surge on Friday warrants a larger
Marginal for Day 5 which should eventually have some Slight Risks
given the 2 to 3 standard deviation positive moisture anomaly but
uncertainties remain higher than desired to specify its placement.
The tropical moisture surge then overspreads the Intermountain
West this weekend, though the ejection of the trough from the West
Coast still has some timing uncertainty which will define where and
when the heavy rain threat is. Higher QPF is indicated today across
northern California due to the faster approach of the upper low.
Expect mountain snow under the upper trough when it passes.

Low pressure looks to develop along a stalled boundary off the
Southeast Coast Friday night with a surge of heavy rain along the
Carolina Coast. A Day 5 Marginal ERO is maintained along the
Carolina Coast. This nor`easter should slowly move up the East
Coast and will need to be further monitored this weekend for
significant rain and wind potential.

Cool conditions with max temperatures five or so degrees below
normal overspread the Northeast and Eastern Seaboard for
Thursday/Friday. Meanwhile, ridging over Texas amplifies up the
Rockies and Great Plains this weekend which will maintain above
normal temperatures. Cool conditions are expected over the West
behind the cold front once the low off the Pacific Northwest ejects
east.

Kong/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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