643
FXUS02 KWBC 121907
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
307 PM EDT Sun Oct 12 2025

Valid 12Z Wed Oct 15 2025 - 12Z Sun Oct 19 2025


...Guidance/Predictability Assessment...

The models into the medium range period continue to show good
agreement on an amplified pattern consisting initially of a Western
U.S. deep trough and building ridge downstream from the central to
eastern states. The evolution of this, as the Western trough/low
opens up and progresses eastward, is generally in good agreement
but with some variability in the details and timing of the trough
next weekend. Around Friday, the GFS is a bit faster with a
northern stream shortwave into southern Canada and also faster and
more aggressive with a following shortwave, resulting in a deep
closed low over the Great Lakes next Sunday. The better consensus
would be for something a bit slower and more open and the WPC
forecast today weighted a bit more towards the ECMWF/CMC early
period and the ensemble means later in the period. The guidance
agrees on another amplified shortwave moving into the Pacific
Northwest late period, but again with some question on the timing.
For the sensible weather grids, the 13z NBM served as a good
starting point and basis, but with some modifications based on the
ECMWF which was the preferred model. Overall, maintained good
continuity with the previous WPC forecast.


...Weather/Hazards Highlights...

A lead short range coastal storm will be working well out to sea
across the western Atlantic by midweek but still support continued
unsettled/windy conditions over New England through late week with
impulses digging behind the system bring some lingering showers.

An incoming upper low/amplified trough slated to bring rain/snow
to California early week will lift increasingly inland across the
West/Rockies mid-late week. A Day 4/Wednesday WPC Excessive
Rainfall Outlook Marginal Risk area remains over New Mexico and
southern Colorado where leading moisture levels may fuel some
lingering local downpours with runoff issues. Upper system and wavy
frontal progression will also drive organized rain/snow over the
north-central Intermountain West/Rockies Wednesday/Wednesday night.
Much of the West will see at least some rain or snow, with snow
levels lowering as colder air moves in. Temperatures will be well
below normal into Wednesday (by 10-20 deg) with some slight
moderation for the rest of the week, but still cooler than normal.
Later period, there is also some upstream guidance signal
supporting approach of another amplified Northeast Pacific storm
system toward the Pacific Northwest/Northwest next weekend that may
offer quite unsettled flow and enhanced rainfall to monitor.

Downstream for the central states, southwesterly upper flow will
increase the chances of rain for mid-late week over the Northern
Plains into the Upper Midwest closer to the jet stream with wavy
surface system translation/genesis. Mild and more moisture-laden
air to the south over the central Plains and Mid-Mississippi Valley
will support a growing pattern with showers and thunderstorms
ahead of the western/Rockies system into Thursday/Friday. Activity
may flourish as focus shifts slowly with more uncertainty into the
east-central states into next weekend in an emerging return flow
pattern to monitor for enhanced rainfall/runoff issue potential.


Santorelli/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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