107
FXUS21 KWNC 212105
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST November 21 2024

SYNOPSIS: Multiple models continue to show surface high pressure advancing
southeastward from west-central Canada across most of the central and eastern
contiguous U.S. (CONUS), which increases the chances for much below normal
temperatures for much of the Great Plains. The cold air overrunning the
anomalously 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 eastward later 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 today, 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 most of the Northern
Plains into parts of Minnesota, Fri-Mon, Nov 29-Dec 2.

Slight risk of much below normal temperatures across much of the northern half
of the Plains and the Upper Mississippi Valley, Fri-Thu, Nov 29-Dec 5.

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, Sun-Thu, Dec 1-5.

Slight risk of periods of heavy lake-enhanced snowfall across the
climatologically favored snowbelt areas downwind of the Great Lakes, Fri-Mon,
Nov 29-Dec 2.

Slight risk of episodic high winds for parts of the Lower Mississippi,
Tennessee, and Ohio Valleys, Appalachians, Mid-Atlantic, Great Lakes, and
Northeast , Fri-Sun, Nov 29-Dec 1.

Slight risk of episodic high winds across the Northern Plains and western
Minnesota, Fri-Mon, Nov 29-Dec 2.

DETAILED SUMMARY

FOR SUNDAY NOVEMBER 24 - THURSDAY NOVEMBER 28:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR FRIDAY NOVEMBER 29 - THURSDAY DECEMBER 05: The GEFS and ECENS ensemble
means indicate a broad trough stretching across the eastern two-thirds 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 most of the northern half
of the Great Plains and Upper Mississippi Valley for the duration of week-2.
Minimum temperatures may fall below -10 deg F, and below the historical 15th
percentile. Wind chill values in this region may reach or exceed -20 deg F. A
moderate risk (40-60% chance) of much below normal temperatures is included for
most of the Northern Plains and western parts of Minnesota, Nov 29-Dec 2. There
is another slight risk area of much below normal temperatures posted for much
of the southeastern and south-central states, which have yet to experience
their first freeze of the season. The most likely period for the anticipated
occurrence of this areas first freeze is from Dec 1-5.



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 29-Dec 2. Blowing and drifting snow may
drastically reduce visibility within snowbands, posing a serious danger to
commuters. Given the large uncertainty among todays deterministic and ensemble
mean solutions, no hazardous (non-snow) precipitation areas are posted due to
reduced confidence. The uncertainty also makes it extremely difficult to
determine potential coverage of rain and snow over the Northeast.



A slight risk of high winds (at least 25 mph) is depicted over a large portion
of the eastern CONUS from Nov 29-Dec 1, in the wake of a low pressure system
that is forecasted to move through this region. The broad extent of this wind
area underscores the large differences in model predictions regarding the
storms intensity, timing, and exact track. Over the general vicinity of the
Northern Plains, there is a slight risk for high winds from Nov 29-Dec 2, as a
fairly strong surface high and related pressure gradient, and easterly upslope
flow, are expected to be in place during this period. Accumulating snowfall in
this area is possible due to the favored cold temperatures and above-normal
precipitation that is favored during the period.



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

$$