310
FXUS21 KWNC 082010
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST November 08 2025

SYNOPSIS: Mid-level low pressure is forecast to approach the West Coast later
next week and then eventually shift eastward over the West by the middle of
Week-2. This brings slight risks of hazardous precipitation, snow, and wind to
several areas from the West Coast through the Rockies. Surface low pressure is
expected to develop in the southern High Plains early week-2 and move eastward.
This system may bring increased chances for heavy precipitation to parts of the
Lower Mississippi and Tennessee Valleys, and may abet high winds from the
Rockies through much of the central Conterminous U.S. (CONUS). Stormy weather
is possible at times throughout southern Alaska November 16-22, but
precipitation and winds are likely to remain below hazardous thresholds.

HAZARDS

Slight risk of heavy precipitation for much of the Southwest, southern
California, and southern Rockies, Sun-Mon, Nov 16-17.

Slight risk of heavy precipitation for the north half of the Sierra Nevada and
from northern California through the Pacific Northwest, Sun, Nov 16.

Slight risk of heavy precipitation for much of the Tennessee, Lower and Middle
Mississippi, and Lower Ohio Valleys, and adjacent areas of the southern Plains
and Southeast, Mon-Wed, Nov 17-19.

Slight risk of heavy snow over the north half of the Sierra Nevada, the
Cascades, and much of the Rockies, Sun-Wed, Nov 16-19.

Slight risk of heavy snow for the Mogollon Rim of Arizona, Sun, Nov 16.

Slight risk of high winds from the Rockies through much of the Great Plains and
parts of the Upper Mississippi Valley, Sun-Wed, Nov 16-19.

DETAILED SUMMARY

FOR TUESDAY NOVEMBER 11 - SATURDAY NOVEMBER 15:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR SUNDAY NOVEMBER 16 - SATURDAY NOVEMBER 22: A mid-level trough is forecast
to move onshore the West Coast at the end of week-1 or early in week-2,
continuing a period of active weather across the West. The GEFS and CMCE
continue to predict a deep trough supporting increased chances of heavy
precipitation across portions of the West. But the ECENS mean has backed off
somewhat with the strength of the trough and is farther north today, though
with a weaker secondary piece of vorticity farther south near the base of the
trough. Also, the other two ensemble means show a more positively-tilted trough
that is not quite as wet dynamically as indicated yesterday, especially in
central California and the southern Sierra Nevada. The PETs, especially from
the ECENS, focus the best odds for precipitation totals over the 15th
percentile farther south, remaining under 30 percent in the central and
northern Far West.



Given the expected positive tilt to the mid-level trough and lesser indications
of heavy precipitation in both the statistical and dynamical models, moderate
risks of heavy precipitation and snow for the foothills and higher elevations
of the Sierra Nevada, respectively, are discontinued today. A slight risk for
heavy precipitation remains in place for the north half of the Sierra Nevada
and from northern California through the Pacific Northwest day 8 (Nov 16). The
GEFS PET snowfall guidance continues to indicate some enhanced probabilities
for heavy snow in the Sierra Nevada, but dynamical model output is lower than
yesterday, and probabilistic output from the GEFS and ECENS shows only 30-40%
chances for more than a few inches of snow in any 24-hour period in the Sierra
Nevada. As a result, slight risks for hazardous precipitation and snowfall are
removed from the southern half of the Sierra Nevada, but continue to cover many
of the higher elevations across the West. With increased uncertainty in the
evolution of the mid-level trough comes increased uncertainty in the amount and
timing of any snowfall in the higher elevations, the slight risk of heavy snow
extends through the middle of week-2 before all guidance shows the mid-level
trough dissipating. Also, a heavy snow threat lingers beyond the heavy
precipitation threat in the Cascades due to declining snowfall elevations with
the arrival of the mid-level trough, meaning a greater proportion of any
precipitation that falls would be in the form of snow. As a result, a slight
risk of heavy snow extends through mid-week in the Cascades as well as other
high elevations across the West.



The southern end of the mid-level trough is expected to slow down somewhat and
maintain at least moderate amplitude early week-2, especially in the ECENS raw
mean output and PET. Today, the Probabilistic Extremes Tools (PET) based on the
ECENS and to a lesser extent the GEFS focus the greatest chances for
precipitation in the top 15% of the historical envelope across the Southwest
and parts of the Intermountain West and Rockies early week-2. The ECENS PET
shows greater chances than the others, in the 50-70% range in Arizona and
southern California. Meanwhile, the GEFS PET keeps the odds below 40%, and CMCE
PET under 30%. This guidance and dynamical model output - especially from the
ECMWF - supports a slight risk of heavy precipitation from the Southwest
through much of the southern Rockies for the first couple days of week-2 before
surface low pressure development in the lower High Plains shifts the chances
for heavy precipitation farther east. Any locally heavy precipitation increases
the risk of urban flash flooding and mudslides in burn scar areas across
southern California. Consistent with the enhanced precipitation signal and
relatively cold air at higher elevations, a slight risk of heavy snow is posted
for the Mogollon Rim of Arizona on the first day of week-2.



A piece of the weakening longwave trough over the interior West pulls eastward,
potentially triggering leeside surface low development in the lower High Plains
which eventually pulls off to the east-northeast. This in turn increases the
risk of high winds from the Rockies east into the Great Plains and Upper
Mississippi Valley from November 16-19. The ECENS PET shows odds for winds in
the top 15th percentile of the historical envelope exceeding 40 percent
November 18-19 in part of New Mexico, and both the GEFS and ECENS PET shows
odds exceeding 30 percent for much of the Southwest November 16-18. As this
system tracks eastward and taps moisture from the Gulf, it brings a threat for
heavy precipitation to much of the Tennessee, Lower and Middle Mississippi, and
Lower Ohio Valleys, and adjacent areas of the southern Plains and Southeast
during the middle of week-2.



In Alaska, ensemble means are stronger with a mid-level trough approaching the
state during the first part of week-2, supporting a deepening low pressure
system in the Bering Sea early in week-2 alongside a substantial surface high
across the eastern Pacific. This could lead to high winds and heavy
precipitation across the Aleutians and southern Alaska. However, there is a lot
of inconsistency in the guidance regarding the strength and evolution of the
features involved, so while this situation will need to be monitored, no hazard
is posted at this time.

FORECASTER: Rich Tinker

$$