435
FXUS21 KWNC 011856
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST November 01 2026

SYNOPSIS: Dynamical models are in good agreement regarding very potent
mid-level low pressure moving closer to the west coast of the contiguous U.S.
(CONUS) during the week-2 period. Therefore confidence is increasing for
prolonged impacts from heavy precipitation, coastal high winds, and high
elevation heavy snow, especially across the Pacific Northwest into northern
California. An extension of hazardous weather into central and southern
portions of California and the Southwest is possible later in week-2.
Elsewhere, more tranquil and unseasonably warm weather is forecast across much
of the interior CONUS underneath mid-level high pressure. Surface low pressure
favors potentially unsettled weather along the East Coast early in the period.

HAZARDS

Moderate risk of heavy precipitation across much of the Pacific Northwest into
northern California, Tue-Fri, Nov 10-13.

Moderate risk of heavy snow across portions of the Cascades, Klamath, and
northern Sierra Nevada Mountains, Tue-Fri, Nov 10-13.

Moderate risk of high winds across coastal portions of Washington, Oregon, and
northwestern California, Tue-Fri, Nov 10-13.

Slight risk of heavy precipitation across the Pacific Northwest and northern
California through the San Francisco Bay area, Mon-Sun, Nov 9-15.

Slight risk of heavy precipitation across portions of central and southern
California into Arizona, Wed-Sun, Nov 11-15.

Slight risk of heavy precipitation across portions of the Northeast,
Mid-Atlantic, and Appalachians, Mon-Wed, Nov 9-11.

Slight risk of heavy snow across the Cascades, Klamath, and northern Sierra
Nevada Mountains, Mon-Sun, Nov 9-15.

Slight risk of heavy snow across the southern Sierra Nevada Mountains, Wed-Sun,
Nov 11-15.

Slight risk of high winds across coastal portions of Washington, Oregon, and
northern California through San Francisco Bay, Mon-Sun, Nov 9-15.

DETAILED SUMMARY

FOR WEDNESDAY NOVEMBER 04 - SUNDAY NOVEMBER 08:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR MONDAY NOVEMBER 09 - SUNDAY NOVEMBER 15: The major story for week-2 will be
deep 500-hPa troughing approaching the West Coast of the CONUS, with surface
low pressure over the Gulf of Alaska, leading to increasing Pacific flow and
subsequently increasing confidence for heavy precipitation along with high
elevation heavy snow and coastal high winds. Daily ensemble means from the 0z
GEFS, ECMWF, and Canadian ensembles depict the strongest moisture advection
beginning around day-9 (Nov 10), with daily ensemble mean precipitation totals
upwards of 0.75 to 1-inch across the Pacific Northwest and northern California.
While the ECMWF and GEFS Probabilistic Extremes Tools (PETs) only depict
probabilities in the 20-40 percent range for 3-day amounts exceeding the 85th
climatological percentile, the uncalibrated guidance is much more robust,
indicating some areas with at least a 50 percent chance for 3-day precipitation
to exceed 2-inches, particularly during the middle portion of week-2. Given
these stronger signals and continued eastward progression of the anomalous
mid-level troughing, a moderate risk of heavy precipitation is posted across
the Pacific Northwest into northern California, Nov 10-13. A corresponding
moderate risk of heavy snow is highlighted across the Cascades, Klamath, and
northern Sierra Nevada Mountains, Nov 10-13, where the uncalibrated GEFS and
ECMWF ensembles depict 3-day snow totals exceeding 6 to 12 inches. A moderate
risk of high winds is posted across coastal portions of Washington, Oregon, and
northwestern California for the same time frame, tied to an increasing pressure
gradient and an enhanced chance of wind speeds greater than 40-mph as depicted
in the PETs.



Slight risks of heavy precipitation, heavy snow, and high winds surround the
respective moderate risks and are valid for all of week-2 given the persistence
of the offshore trough. Some of this enhanced moisture may advect into portions
of the Northern and Central Rockies by the second half of the period, resulting
in periods of heavy snow farther inland over higher elevations. The ECMWF
indicates a potential southward expansion of heavy precipitation into southern
California and the Southwest later in week-2, with strong probabilities (above
60 percent) for 3-day precipitation totals exceeding the 85th climatological
percentile being indicated. While these high probabilities are partially
attributed to the lower climatology compared to farther north, the ECMWF PET
indicates some areas of southern California into Arizona with at least a 20
percent chance of 3-day precipitation amounts exceeding 1-inch. Probabilities
in the GEFS PET are notably lower resulting in greater uncertainty across this
area, with only a slight risk of heavy precipitation, Nov 11-15. In addition, a
slight risk of heavy snow is posted across the southern Sierra Nevada
Mountains, also valid Nov 11-15.



Elsewhere across the CONUS, above-normal temperatures are favored for most
areas underneath broad mid-level ridging with the exception of parts of the
Southeast where closer to normal temperatures are forecast. There are no
indications of any hazardous weather across the interior CONUS during the
week-2 period. However, a transient shortwave trough is forecast to move across
the eastern U.S. late in week-1 into the early part of week-2. Surface low
development is possible along the East Coast early in week-2 with the 0z ECMWF
ensemble most robust with a nor-easter-like system along the coast. While the
signal for this system is weaker in the 0z GEFS, both the AI-based 0z ECMWF and
GEFS ensembles lean closer to the dynamical ECMWF with a surface low track
closer to the East Coast. Considering some agreement from the AI tools, a
slight risk of heavy precipitation is posted across the Northeast,
Mid-Atlantic, and Appalachians, Nov 9-11. If this system materializes, gusty
winds are possible on its backside, but the increased uncertainty precludes a
related wind hazard at this time.



While the storm system near the West Coast of the CONUS is likely to result in
periods of strong winds and heavy precipitation along the southern and
southeastern coast of Alaska as well, hazardous thresholds are not expected to
be exceeded so no hazards are posted for Alaska at this time. Above-normal
temperatures are forecast across much of eastern Mainland and Southeast Alaska,
with near- to slightly below-normal temperatures more likely across the western
Mainland and the Aleutians.

FORECASTER: Thomas Collow

$$