124
FXUS21 KWNC 222026
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST November 22 2024

SYNOPSIS: Multiple models continue to show surface high pressure advancing
southeastward from the Canadian Prairies across most of the central and eastern
contiguous U.S. (CONUS), which increases the chances for much below normal
temperatures for parts of the north-central and Midwestern states. The cold air
overrunning the unusually warm Great Lakes is expected to contribute towards
the generation of lake-enhanced snow showers and squalls over the
climatologically favored areas downwind of the Lakes. Much of the anomalous
cold air is favored to advect southward and eastward in week-2, bringing
increased chances for first freezes across the southern tier of the CONUS. For
most of the eastern CONUS, significant uncertainty continues among the model
guidance, especially with respect to the location, timing, and track of
individual low pressure systems within the week-2 period. This makes it very
difficult to specify details of weather-related hazards.

HAZARDS

Moderate risk of much below normal temperatures across much of the Northern
Plains and adjacent parts of Minnesota, Sat-Mon, Nov 30-Dec 2.

Slight risk of much below normal temperatures across the north-central and
Midwestern states, Sat-Tue, Nov 30-Dec 3.

Slight risk of much below normal temperatures and expected first freeze of the
season across most of the Southeast and Lower Mississippi Valley, much of the
Southern Plains, Tennessee Valley, and southern Ohio Valley, Sat-Fri, Nov
30-Dec 6.

Slight risk of periods of heavy lake-enhanced snowfall across the
climatologically favored snowbelt areas downwind of the Great Lakes, Sat-Tue,
Nov 30-Dec 3.

Slight risk of high winds for the north-central CONUS, from the eastern
foothills of the Rockies eastward to the western Great Lakes region, southward
to the Tennessee Valley, Mon-Wed, Dec 2-4.

Slight risk of episodic high winds from the eastern Great Lakes, Upper Ohio and
Tennessee Valleys eastward to the Atlantic Coast from Maine to North Carolina,
Sat-Fri, Nov 30-Dec 6.

DETAILED SUMMARY

FOR MONDAY NOVEMBER 25 - FRIDAY NOVEMBER 29:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR SATURDAY NOVEMBER 30 - FRIDAY DECEMBER 06: The GEFS and ECENS ensemble
means indicate a broad trough stretching across the eastern half of the CONUS
during week-2. There continues to be significant uncertainty among the various
deterministic and ensemble mean models regarding the development and expected
evolution of low pressure systems and related impactful weather across the
central and eastern CONUS during this busy Thanksgiving travel period.



A series of high pressure centers and related cold air masses initially over
west-central Canada are predicted to advance southeastward across most of the
central and eastern CONUS during week-2. There is a slight risk (20-40% chance)
of much below normal temperatures posted for the north-central and Midwestern
states, Nov 30-Dec 3. In the Northern Plains and Upper Midwest, minimum
temperatures may fall below -10 deg F with wind chills reaching or falling
below -20 deg F, well below the historical 15th percentile. Farther south and
east within the highlighted slight risk area, minimum temperatures may dip into
the teens, with wind chill values approaching -10 deg F. A moderate risk
(40-60% chance) of much below normal temperatures is included for much of the
Northern Plains and adjacent parts of Minnesota, Nov 30-Dec 2, where the cold
signals are strongest in the Probabilistic Extreme Tools (PETs). There is
another slight risk area of much below normal temperatures posted for much of
the southeastern and south-central states, valid Nov 30-Dec 6, which have yet
to experience their first freeze of the season. A few very localized areas may
experience their first freeze of the season prior to the start of the week-2
period.



Cold air streaming across the unusually warm waters of the Great Lakes is
likely to promote lake-enhanced snowfall for the climatological downwind
snowbelt areas. A slight risk of heavy snow (locally 6 inches or more) is
predicted for these areas from Nov 30-Dec 3. Blowing and drifting snow may
drastically reduce visibility within snowbands, posing a serious danger to
commuters. With the predicted dominance of cold, dry air masses and
northwesterly flow east of the Rockies, the best chance for any rain is near
the Gulf Coast during the middle and latter portions of the forecast period.
However, given the large uncertainty among todays deterministic and ensemble
mean solutions, no hazardous (non-snow) precipitation areas are posted due to
reduced confidence.



A slight risk of episodic high winds (at least 25 mph) is depicted from the
eastern Great Lakes, Upper Ohio and Tennessee Valleys eastward to the Atlantic
Coast from Maine to North Carolina, Nov 30-Dec 6, associated with the expected
passage of several low pressure systems during the period. These are most
likely to be clipper-type systems that originate over the Canadian Prairies and
travel quickly southeastward, embedded deep within cold, dry air masses. As
such, these clipper systems often produce fairly light snowfall accumulations,
as opposed to other mid-latitude systems that tend to travel along the southern
and eastern boundaries of arctic air masses and have access to warmer and more
moist air. A second slight risk area for high winds is depicted for the
north-central CONUS, from the eastern foothills of the Rockies eastward to the
western Great Lakes region, and about as far south as Tennessee, Dec 2-4. This
is associated with enhanced pressure gradients resulting from the interaction
of strong surface arctic highs and clipper-type disturbances.



A series of surface lows are predicted to form over the Gulf of Alaska, which
may bring unsettled weather to south-central and southeastern portions of the
state. Conditions are not anticipated to support widespread hazards at this
time.

FORECASTER: Anthony Artusa

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