669
FXUS02 KWNH 060718
PREEPD

Preliminary Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
316 AM 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 linger there through Friday night before
opening into a trough that digs down the West Coast before
ejecting east later this weekend. This trough will draw tropical
moisture ahead of Priscilla through the Intermountain West.
Meanwhile, there is increasing model support for a coastal storm
to develop along the Carolina Coast this weekend before tracking
up to the Mid-Atlantic coast. In between these systems is
persistent upper level ridging centered over Texas with an axis up
the Great Plains through this weekend.


...Guidance/Predictability Assessment...

There was excellent agreement in the 12Z/18Z global guidance suite
on the closed upper low off the Pacific Northwest Thursday that
then retrogrades farther offshore into Friday. Model divergence
began Friday night with how to bring the low/opening trough
onshore. The 18Z EC-AIFS was slowest with this ejection west which
lined up pretty well with the 18Z GFS through Saturday with the
other guidance quicker to eject east and farther south with the
base of the trough into central CA. However, for the 00Z suite, the
EC-AIFS trended a bit slower while the GFS/UKMET jumped toward a
more progressive solution (and now the 00Z ECMWF/CMC have come in
farther west. So uncertainty reigns with this trough which also
means there is uncertainty with the timing and strength of the
tropical moisture plume from Priscilla out ahead of this trough
which brings much needed precip to the Intermountain West. Given
this was the major feature on the map, the WPC forecast charts and
QPF were based on a general model blend that favored the 18Z GFS
(as a proxy for the EC-AIFS) along with ensemble means which were
slower than the ECMWF and CMC. An updated recommendation for the
00Z suite is for a switch to the EC/CMC which are in decent
alignment.

The other major feature is what looks to be a nor`easter
developing Friday night and lingering on the Carolina Coast through
this weekend which the EC- AIFS has been featuring/ramping up
further over the past several runs. Physical guidance has ramped up
this feature with the 00Z solution, while the EC-AIFS continues an
upward trend with heavy rain pushing farther inland as well.
The ECMWF remains the most progressive north with this system,
though the 00Z GFS nearly reaches as far up the northern Mid-
Atlantic coast as the 12Z ECMWF.


...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 new Day 4 ERO remains Marginal, but shifted
east 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. The tropical moisture surge 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. 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 introduced south from Cape
Lookout through Myrtle Beach. This nor`easter should slowly move up
the East Coast and will need to be 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.

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


$$