904
FXUS21 KWNC 181829
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT October 18 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. The
persistence of above-normal and potentially heavy precipitation may lead to
flooding across parts of the Northwest. Tied to the evolution of the mid-level
troughing, surface low development is favored in the lee of Rockies, increasing
chances for heavy precipitation across the central and eastern contiguous U.S.
(CONUS) during the middle and latter portions of the period. Additional
mid-level low pressure favored over the Great Lakes late next week looks to
promote enhanced northwesterly flow and cooler minimum temperatures where frost
and/or first autumn freezes may adversely impact vulnerable vegetation east of
the Mississippi.

HAZARDS

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

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

Moderate risk of heavy precipitation for a large portion of northern California
northward across southwestern Oregon, Sun-Mon, Oct 26-27.

Moderate risk of high elevation heavy snow over portions of the northern and
central Sierra Nevada, Klamath, and southern Cascade Mountains, Sun-Mon, Oct
26-27.

Moderate risk of heavy precipitation over the Pacific Northwest, Sun-Fri, Oct
26-31.

Moderate risk of high elevation heavy snow over the Cascades, Sun-Thu, Oct
26-30.

Moderate risk of high winds from the Bay Area of California northward to the
Pacific Northwest, Sun-Tue, Oct 26-28.

Moderate risk of high elevation heavy snow for portions of the northern
Rockies, Sun-Tue, Oct 26-28.

Moderate risk of high winds over parts of the Great Basin, Southwest,
south-central Rockies and adjacent High Plains, Sun-Wed, Oct 26-29.

Slight risk of heavy precipitation for much of northern and central California
and the Pacific Northwest, Sun-Sat, Oct 26-Nov 1.

Slight risk of heavy snow for the Sierra Nevada, Klamath, and Cascade
Mountains, Sun-Fri, Oct 26-31.

Slight risk of heavy snow for portions of Northern Intermountain region, and
Northern and Central Rockies, Sun-Thu, Oct 26-30.

Slight risk of high winds for much of the western two-thirds of the CONUS,
Sun-Thu, Oct 26-30.

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

Slight risk of heavy precipitation for much of the eastern half of the CONUS,
Tue-Fri, Oct 28-31.

Slight risk of high winds for the southern Mainland and southeast Alaska,
Sun-Tue, Oct 26-28.

Flooding possible across parts of the Pacific Northwest and northern California.

DETAILED SUMMARY

FOR TUESDAY OCTOBER 21 - SATURDAY OCTOBER 25:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR SUNDAY OCTOBER 26 - SATURDAY NOVEMBER 01: The week-2 hazards perspective
remains on track today with much of the outlook focusing on potential
Atmospheric River (AR) activity producing multiple weather related hazards of
elevated risk throughout the western CONUS. Early in week-2, good agreement
exists among the dynamical model ensemble mean 500-hPa height forecasts
featuring a potent 500-hPa trough encroaching the West Coast, with a 850-hPa
flow pattern favorable for ample incoming Pacific moisture to supply locally
heavy precipitation. Some differences between the 0z GEFS and 0z ECMWF
ensembles are in the details of the upper-level features, with the latter
favoring a slightly deeper trough, along with a stronger jet protruding into
California. As a result, there is the potential for more AR activity farther
south in California in the ECENS compared to the GEFS, however both models
continue to well agree in regards to the timing of this potential event with
the highest AR related risks occurring on day 8 (Oct 26). Thereafter, these
risks are anticipated to retreat northward into the Pacific Northwest and ease
by days 9 and 10 over California as the trough axis shifts farther inland and
mid-level heights begin to rise over the southwestern CONUS. During this time,
however, ensembles continue to point to additional troughing offshore in the
eastern Pacific, which looks to maintain above-normal precipitation for the
northwestern CONUS and potentially bring a renewed threat of heavy
precipitation later in October.



Based on GEFS and ECENS Integrated Vapor Transport (IVT) tools, as well as the
latest raw and calibrated precipitation guidance, high risks for heavy
precipitation and high elevation heavy snow remain issued for parts of northern
California and southern Oregon for Oct 26. Within these highlighted areas, the
ECMWF Probabilistic Extreme Tools (PET) indicates at least a 60% chance of
3-day amounts exceeding the 85th climatological percentile, with the
uncalibrated ECMWF and GEFS favoring 1.0-1.5 inches of precipitation on day 8.
Across the Pacific Northwest, the GEFS PET depicts a 40% chance of amounts
exceeding 1.5 inches over the 3-day period, days 8-10. To better account for
the evolution of the heavy precipitation risk across the West Coast, moderate
risk areas of heavy precipitation and high elevation heavy snow remain issued
for portions of California and Oregon for Oct 26-27, with a separate pair of
moderate risk areas for heavy precipitation and high elevation heavy snow
focused over the Pacific Northwest, both valid through Oct 30. Although soils
are not currently oversaturated over parts of the West Coast, a flooding
possible hazard remains posted as this area may be more responsive to flooding
given the elevated precipitation risks, and with increased precipitation
amounts favored during week-1 to help prime conditions. At the base of the
amplified troughing, a moderate risk for high winds also remains issued (Oct
26-28) where PETs depict higher chances (30-40%) for wind speeds exceeding the
85th percentile into the middle of week-2. Broader slight risk areas for heavy
precipitation and heavy snow are still posted for the West Coast, and remain
valid through Oct 31 due to the potential for anomalous troughing reloading
later in October.



With much of the anomalous mid-level troughing shifting eastward next weekend,
enhanced Pacific moisture being advected over high elevation areas of the
Interior West supports the potential for heavy snowfall over portions of the
Rockies and the Northern Intermountain region. Based on raw snow tools and the
Snow Water Equivalent (SWE) PET, a moderate risk of heavy snow remains issued,
and is valid through Oct 28, with a broader slight risk area extending further
southward into the Four Corners, valid through Oct 30. A separate moderate risk
area for high winds is also posted (Oct 26-29) over the higher elevations of
the Interior West, with its coverage also expanded southward into the Southwest
and Southern Rockies in the updated outlook where PETs and raw tools favor
higher signals for wind speeds exceeding the 85th percentile with gusts of over
25-30 knots. A broad slight risk area of high winds is posted for nearly the
western two-thirds of the CONUS to capture the wind potential associated with
the amplified mid-level pattern favored during week-2.



Early in week-2, anomalous troughing favored over the Great Lakes looks to
bring more northwesterly flow and a round of anomalously cold temperatures into
portions of the eastern U.S. While both GEFS and ECENS PETs are weak in
percentile space (less than 20% chances for minimum temperatures falling below
the 15th percentile) associated with this cooler air, there continues to be
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, infringing cold temperatures could
impact vulnerable vegetation, and a slight risk of much below normal
temperatures is highlighted for Oct 26 before temperatures are expected to
moderate later in the period.



Towards the middle of week-2, models are showing stronger signals for shortwave
energy moving across the Great Plains associated with the building heights over
the southwestern CONUS, leading to surface low development in the lee of the
Rockies. The ECMWF is more pronounced with this potential cyclogenesis, and
given the mean surface high pressure (associated with the aforementioned cold
air early in week-2) that is favored to the east to bring moist return flow
from the Gulf, the precipitation response is becoming increasingly reflected in
the raw and calibrated tools. Therefore, a slight risk of heavy precipitation
is posted over most of the eastern half of the CONUS, Oct 28-31.



Over Alaska, a slight risk of high winds is posted (Oct 26-28) with its
coverage remaining 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 (especially the ECENS) still maintain increased signals for
wind speeds exceeding the 85th percentile over the region.

FORECASTER: Anthony Artusa

$$