974
FXUS02 KWBC 042009
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
409 PM EDT Sat Oct 4 2025

Valid 12Z Tue Oct 07 2025 - 12Z Sat Oct 11 2025


...General Overview...

A slowly amplifying trough-ridge-trough synoptic pattern across
the mainland U.S. is forecast to be sandwiched between a
subtropical High traveling westward along the Gulf Coast, and
progressive baroclinic troughs in the westerlies across Canada
through next week. An upper trough that digs down western Canada
midweek next week will likely develop into a closed low along/off
the Pacific Northwest coast during the latter half of next week.
In addition, tropical moisture well ahead of what likely to be the
next tropical cyclone in the eastern Pacific is forecast to be
drawn northward through the Southwest and the Intermountain region
late next week.


...Guidance/Predictability Assessment...

The main synoptic system in the forecast period will be a digging
trough across British Columbia on Tuesday that closes into an
upper low off the Pacific Northwest coast on Wednesday and then
persists/drifts off/along the coast into the weekend as a cutoff.
The general consensus of the past couple of days has been for the
upper low to close off farther off the coast of the Pacific
Northwest by next Thursday, resulting in a trend toward a more
amplified upper- level pattern to set up just off the West Coast
late next week. Meanwhile, the next tropical cyclone is forecast to
develop in the eastern Pacific and generally track northwestward
to a position west of the southern Baja Peninsula late next week.
The amplitude and placement of the upper low off the West Coast in
relation to how far north the tropical cyclone ultimately tracks
will influence how much and how fast tropical moisture will be
drawn northward into the Southwest by late next week. The ECMWF
cluster remains on the fastest side of the guidance in bringing the
tropical cyclone closer to Mexico and therefore more abundant flow
of moisture into the Southwest. Meanwhile, the GFS cluster keeps
the tropical cyclone farther offshore and thus less moisture
reaching into the U.S. Despite the uncertainty on exactly how these
two systems will ultimately interact one another, it appears that
the presence of the upper low off the West Coast alone will bring a
good chance of terrain-enhanced precipitation northward across the
Southwest and then through the Intermountain West late next week.

Elsewhere, there is a trend toward bringing more tropical moisture
into the east coast of southern Florida early next week with a
better-defined low pressure center tracking onshore along a
weakening or dissipating frontal boundary. The Icon model has been
the most aggressive and consistent guidance in this regard.

The WPC medium-range forecasts were based on the consensus of 40%
from the 00Z EC/EC mean, 40% from the 06Z GFS/GEFS, and 20% from
the 00Z CMC/CMC mean, with mainly the consensus of the ensemble
means for Days 6 to 7. This blend agrees reasonably well with the
previously WPC forecast package.


...Weather/Hazards Highlights...

A cold front ahead of a powerful trough shifts from the Midwest
through the central Appalachians Tuesday/Tuesday night. Despite the
generally progressive nature of this pre-frontal activity,
sufficient moisture (PW two sigma above normal) warrants a Day 4
Marginal Risk over the middle/upper Ohio Valley to the crest of the
central Appalachians and interior New England. The GFS shows a
wave of low pressure developing on the front over New England which
would enhance rainfall in New England on Wednesday. This scenario
is considered an outlier at this point.

Moisture anomalies increase over New Mexico Tuesday from continued
surges of moisture from the western Gulf onto a frontal wave that
is stalled over northern NM. Maintain the Marginal Risk now for Day
4 with some further expansion over NM. An influx of tropical
moisture from the eastern Pacific into the Desert Southwest looks
to still occur, but possible not until Friday. An upper-low
lingering off the West Coast through this time would allow the
tropical moisture to surge over much of the western U.S. by next
weekend.

Cool conditions shift east with a cold front from the Northern
Plains Tuesday, the Midwest Wednesday, and the Eastern Seaboard for
Thursday/Friday. Meanwhile, ridging drifting over the Gulf Coast
through Texas will maintain above normal temperatures over The
South through next week.

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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