338
FXUS21 KWNC 161934
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT October 16 2025

SYNOPSIS: Strong low pressure at the surface and mid-levels is favored to shift
eastward from the northeastern Pacific and bring an elevated risk of hazardous
winds, heavy precipitation, and high elevation heavy snowfall across many parts
of the West Coast and Interior West throughout the forecast period. Additional
mid-level low pressure favored over the Great Lakes late next week looks to
promote enhanced northwesterly flow, and anomalously cold temperatures where
frost and/or first autumn freezes may adversely impact vulnerable vegetation
from the Mississippi Valley to the East Coast.

HAZARDS

High risk of heavy precipitation for parts of northern California and southern
Oregon, Sat-Sun, Oct 25-26.

High risk of high elevation heavy snow over the northern Sierra Nevada and
Klamath mountains, Sat-Sun, Oct 25-26.

Moderate risk of heavy precipitation from the Bay Area of California northward
to the Pacific Northwest, Fri-Mon, Oct 24-27.

Moderate risk of high elevation heavy snow over portions of the Sierra Nevada,
Klamath, and Cascade Mountains, Fri-Mon, Oct 24-27.

Moderate risk of high winds from the Bay Area of California northward to the
Pacific Northwest, Fri-Mon, Oct 24-27.

Moderate risk of high elevation heavy snow for portions of the northern Rockies
and northern Intermountain, Sat-Mon, Oct 25-27.

Moderate risk of high winds over parts of the Great Basin, Central and Northern
Rockies, and the Central and Northern High Plains, Sat-Mon, Oct 25-27.

Slight risk of heavy precipitation for portions of California and the Pacific
Northwest, Fri-Thu, Oct 24-30.

Slight risk of heavy snow for the Sierra Nevada, Klamath, and Cascade
Mountains, Fri-Thu, Oct 24-30.

Slight risk of heavy snow for portions of Northern Intermountain, Northern and
Central Rockies, Fri-Thu, Oct 24-30.

Slight risk of high winds for the northwestern CONUS, Fri-Thu, Oct 24-30.

Slight risk of much below normal temperatures for portions of the Great Lakes,
Ohio and Tennessee Valleys, Appalachians, Southeast, and Mid-Atlantic, Fri-Sun,
Oct 24-26.

Slight risk of high winds for the southern Mainland and southeast Alaska,
Fri-Sun, Oct 24-26.

Flooding possible across parts of northwestern Washington.

DETAILED SUMMARY

FOR SUNDAY OCTOBER 19 - THURSDAY OCTOBER 23:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR FRIDAY OCTOBER 24 - THURSDAY OCTOBER 30: Late next week, there is good
agreement between the 0z GEFS and ECMWF ensemble mean 500-hPa height anomaly
forecasts featuring strong troughing overspreading the northeastern Pacific, an
anomalous ridge center over south-central Canada and the central CONUS, and
downstream troughing over the northeastern CONUS. Consistent with previous
guidance, models remain bullish with the high amplification of this upstream
troughing feature, which is favored to promote an elevated risk of multiple
weather related hazards for many portions of the western CONUS throughout the
period. Meanwhile, ensembles have also trended more strongly with troughing
over the eastern U.S. since yesterday, where more northwesterly flow looks to
bring a round of anomalously cold temperatures for parts from the Mississippi
Valley to the East Coast early in week-2.



Tied to the amplified troughing and associated strong mean surface low pressure
encroaching the West Coast late next week, there is continued support in the
guidance favoring enhanced onshore flow from the Pacific consistent with
Atmospheric River (AR) activity. As such, potentially hazardous precipitation
and high elevation heavy snowfall looks to be on tap for much of the Pacific
Northwest and California, along with high winds associated with tight pressure
gradients over the northwestern CONUS. Relative to yesterday, deeper and
stronger troughing is favored aloft between the GEFS and ECWMF ensembles early
in the period, with a southward expansion of the precipitation signals along
the West Coast. This is reflected in the Probabilistic Extremes Tools (PETs)
depicting at least 40% chances for 3-day amounts exceeding the 85th percentile
mainly over northern California and southern Oregon early in the period.
Substantially higher chances are indicated in the ECMWF PET (in excess of 80%)
are collocated with the GEFS PET maximum in percentile space, however caution
is being exercised with this tool given its tendency to overestimate heavy
precipitation potential over this part of the country. Notwithstanding, the
enhanced moisture signals are significant and consistent with the mid-level
pattern, where raw tools are also supportive of this southward expanded
precipitation risk. Based on daily precipitation totals peaking on days 9 and
10 (Oct 25-26), with at least 50% chances for 3-day totals exceeding two inches
over northern California and southern Oregon in the ECWMF uncalibrated tools, a
high risk for heavy precipitation, along with a corresponding high risk area
for high elevation heavy snow is posted for this part of the West Coast for Oct
25-26.



Due to persistence of wet signals further north (>30% chances for 3-day amounts
exceeding 2 inches), previously designated moderate risk areas for heavy
precipitation and heavy snow remain issued over the Pacific Northwest, with
their coverage expanded southward to the Bay Area of California, and valid
through day 11 before much of the mean troughing begins to deamplify. Although
soils are not currently oversaturated over portions of northwestern Washington,
a flooding possible hazard is posted as the basins highlighted for this part of
the State are more responsive to flooding given the heavy precipitation risk,
with increased precipitation amounts favored here during week-1 to help prime
conditions. At the base and ahead of the amplifying trough axis, a moderate
risk for high winds also remains issued (Oct 24-27), and is also expanded in
coverage to include more of the West where PETs depict higher chances (30-40%)
for wind speeds exceeding the 85th percentile.



As much of the amplified troughing shifts eastward, enhanced Pacific moisture
over high elevation areas of the Interior West supports the potential for heavy
snowfall over portions of the Rockies and the Northern Intermountain. Relative
to yesterday, higher snowfall totals are favored over this part of the country
in the uncalibrated ECMWF, and a moderate risk of heavy snow is issued for Oct
25-27. A separate moderate risk area for high winds is also posted for the same
period over the higher elevations of the Interior West based on PETs and raw
tools favoring elevated chances wind speeds exceeding 20 knots and gusts of
over 34 knots. Broader slight risk areas for heavy precipitation, heavy snow,
and high winds are posted, and valid for the entirety of week-2 as ensembles
hint at some of the anomalous troughing reloading late in October.



Downstream of the ridging depicted over the Great Plains, stronger and deeper
troughing favored over Great Lakes is likely to bring more northwesterly flow
and a round of anomalous cold air into portions of the eastern U.S. This is
reflected in both the raw and calibrated temperature tools early in the period,
and while both GEFS and ECMWF PETs are weak in percentile space (less than 20%
chances for minimum temperatures falling below the 15th percentile), there is
better support for sub 40 degree F minimum temperatures as far south as the
Tennessee Valley. Because many areas across the eastern CONUS have not yet
experienced their first autumn freezes and/or frost, and infringing cold
temperatures potentially impact vulnerable vegetation, a slight risk of much
below normal temperatures is highlighted from the Middle Mississippi Valley to
the East Coast for Oct 24-26.



Over Alaska, a slight risk of high winds is posted (Oct 24-26) with its
coverage now focused over the southern Mainland and the Southeast. While much
of the stronger mid-level troughing has shifted southward to affect the western
CONUS, PETs still maintain increased signals for wind speeds exceeding the 85th
percentile over the region.

FORECASTER: Nick Novella

$$