112
FXUS21 KWNC 081930
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST January 08 2025

SYNOPSIS: Ongoing cold in the East may continue into early week-2 as mid-level
low pressure remains forecast in the eastern contiguous U.S. (CONUS) leading to
increased chances for much below normal temperatures. Another mid-level low is
forecast to develop and intrude into the Northwest and Great Plains by the end
of the week-2 triggering the next round of potential hazardous weather. The
associated frontal system enhances the likelihood for multiple hazards
including heavy precipitation in the South, snow from the Central Rockies into
the Great Lakes, and high winds across the western and central CONUS. Behind
this system, increased risk for much below normal temperatures are anticipated
to return across parts of the Rockies and Great Plains. Santa Ana winds remain
possible into early week-2 across parts of Southern California.

HAZARDS

Moderate risk of much below normal temperatures for portions of the
Mid-Atlantic, Central and Southern Appalachians, the upper Ohio and upper
Tennessee Valleys, and Southeast into portions of Florida, Thu, Jan 16.

Slight risk of much below normal temperatures for portions of the Ohio,
Tennessee, Middle and Lower Mississippi Valleys, Southeast, and Mid-Atlantic,
Thu-Sat, Jan 16-18.

Slight risk for periods of high winds for portions of Southern California,
Thu-Fri, Jan 16-17.

Slight risk for periods of high winds for much of the Four Corners, Rockies,
and Northern Plains, Thu-Mon, Jan 16-20.

Slight risk of heavy precipitation for portions of the Lower Mississippi
Valley, Southern Plains, and Tennessee Valley, Fri-Mon, Jan 17-20.

Slight risk of heavy snow for portions of the Central Rockies, Central and
Southern Plains, Middle and Upper Mississippi Valley, and Great Lakes, Sat-Mon,
Jan 18-20.

Slight risk of high winds for portions of the Central and Southern Plains,
Middle Mississippi Valley, and Great Lakes, Sat-Mon, Jan 18-20.

Slight risk of much below normal temperatures for parts of the Northwest,
Rockies, Central and Northern Plains, and the Upper and Middle Mississippi
Valley, Sun-Wed, Jan 19-22.

DETAILED SUMMARY

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

FOR THURSDAY JANUARY 16 - WEDNESDAY JANUARY 22: There is good agreement among
the dynamical models regarding the mid-level height forecast during the week-2
period. The forecast pattern remains amplified and progressive through much of
the week-2 period. A mid-level trough forecast across the East early in the
period will progress into the Atlantic with a new trough developing across the
West that will progress east during week-2. Meanwhile, amplified mid-level
ridging develops upstream across the northeast Pacific and into Alaska.



There continues to be good agreement among the model height forecasts and the
Probabilistic Extremes Tools (PETs) for portions of the Mid-Atlantic, Central
and Southern Appalachians, eastern Kentucky and Tennessee, and Southeast into
parts of Florida. PETs from the GEFS and ECENS indicate 40-60% chances of
temperatures falling below the 15th climatological percentile during the
coldest time of the year, climatologically, in these areas. Therefore, a
moderate risk of much below normal temperatures is posted for Jan 16 in this
region. A broader area is highlighted with a slight risk of much below-normal
temperatures for the first three days of week-2, Jan 16-18, across the
southeastern CONUS extending north into the Ohio Valley and Mid-Atlantic. The
PETs in the broader area forecast 20-40 percent chances of minimum temperatures
falling below the 15th climatological percentile across these regions. The
western portions of the slight risk are most likely to see hazardous conditions
early in the period with chances falling by days 9 and 10. While absolute
temperatures may not reach hazardous thresholds, considering apparent
temperatures, these areas may fall below the necessary thresholds.



Along or just offshore of Southern California, an inverted trough may develop
and surface high pressure is forecast across the Great Basin. This pattern
would bring increased chances for Santa Ana winds to the region. As such, a
slight risk of high winds is posted Jan 16-17 across coastal areas of Southern
California.



As mid-level troughing develops across the West, periods of episodic high winds
are forecast to develop across a broader area of the Four Corners, Central
Rockies, and into the Central and Northern Plains supported by the wind PETs
from the GEFS and ECENS. A broad slight risk of high winds is forecast for this
area for Jan 16-20. By the end of the period, mid-level ridging may begin
developing across the region, reducing chances for high winds.



Ahead of the developing trough across the West an area of surface low pressure
is forecast to develop in the lee of the Rockies. This system would bring
elevated chances of heavy rain and snow, and high winds to parts of the central
CONUS. In the Lower Mississippi Valley and surrounding areas the precipitation
hazard would likely come in the form of heavy rain. This is consistent with the
GEFS and ECENS PETs showing increased chances for 3 day precipitation amounts
exceeding the 85th percentile and 1 inch. Therefore, a slight risk of heavy
precipitation is posted for these areas for Jan 17-20. Further north, from the
Central Rockies stretching through the Plains and Mississippi Valley into the
Great Lakes, there are increased chances for heavy snow. This is consistent
with the GEFS Snow Water Equivalent (SWE) PET and raw guidance from the ECENS
showing the potential for a swath of snow in this region and a slight risk of
heavy snow is posted for Jan 18-20. Finally, cold air advection following the
frontal passage and strong pressure gradient near the surface low pressure
increases the risk for high winds across parts of the Central and Southern
Plains, Middle and Upper Mississippi Valley and western Great Lakes for the
same time period.



Behind the frontal passage, another round of much below normal temperatures is
possible across parts of the Rockies, Plains, and into the Mississippi Valley.
PETs show enhanced chances for temperatures to fall below the 15th
climatological percentile across a broad region beginning by the middle of
week-2 and progressing east with time. Therefore, a broad slight risk of much
below-normal temperatures is posted for Jan 19-22 across these regions. Raw
ensemble means forecast minimum temperatures to be more than 10 degrees below
normal for much of the highlighted region for the second half of week-2. One
area of uncertainty is that the forecasted mid-level trough is not quite as
deep today as yesterday in the ensemble guidance leading to slightly less cold
temperatures across portions of the Northern Plains relative to yesterdays
forecast.



In Alaska, by the middle through the end of the week-2 period, there are
increased signals for gap winds to develop in southern Mainland Alaska with
surface high pressure developing in the Mainland or over the Yukon. However,
the forecasted ridge across the northeastern Pacific is reduced in strength
relative to yesterday subsequently reducing the strength of surface high
pressure in Alaska. No hazards are posted today due to the increased
uncertainty but the area will continue to be monitored.

FORECASTER: Ryan Bolt

$$