682
FXUS21 KWNC 092014
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST January 09 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
early in week-2 progressing east over time 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.

HAZARDS

Slight risk of much below normal temperatures for portions of the Ohio,
Tennessee, Middle and Lower Mississippi Valleys, Southeast, and Mid-Atlantic,
Fri-Sat, Jan 17-18.

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.

Slight risk of much below normal temperatures for parts of the Southern Plains,
Lower Mississippi Valley, Tennessee and Ohio Valleys, Southeast and Great
Lakes, Mon-Thu, Jan 20-23.

Slight risk of heavy precipitation for portions of the Lower Mississippi
Valley, Southern Plains, and Tennessee Valley and Southeast, Fri-Tue, Jan 17-21.

Slight risk of heavy snow for portions of the Central and Southern Rockies and
Plains, Middle and Upper Mississippi, Ohio, and Tennessee Valleys, Great Lakes,
Central and Southern Appalachians, Mid-Atlantic and Northeast, Fri-Tue, Jan
17-21.

Slight risk of high winds for portions of the Central and Southern Plains,
Middle Mississippi Valley, and Great Lakes, Sat-Mon, Jan 18-21.

Slight risk for periods of high winds for much of the Four Corners and
surrounding areas, Fri-Mon, Jan 17-20.

DETAILED SUMMARY

FOR SUNDAY JANUARY 12 - THURSDAY JANUARY 16:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR FRIDAY JANUARY 17 - THURSDAY JANUARY 23: There is moderately 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 second trough developing
across the West that will progress east during week-2. Meanwhile, amplified
mid-level ridging is forecast upstream across the northeast Pacific and into
Alaska.



There continues to be good agreement among the model height and temperature
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 20-40% chances of temperatures falling below the 15th climatological
percentile during the coldest time of the year, climatologically, in these
areas early in the week-2 period. Therefore, a slight risk of much below normal
temperatures is posted for Jan 17-18 in this region. While absolute
temperatures may not reach hazardous thresholds, considering apparent
temperatures, these areas may fall below the necessary thresholds.



Following the initial cold across the East, a second trough is favored to
develop across the West and chances increase for much below normal temperatures
across the Northern Rockies and Northern Plains by around day 9 or 10. The
enhanced chances for much below normal temperatures then quickly expand south
and east enveloping a large portion of the country along and east of the Rocky
Mountains for most of the remainder of the week-2 period. There is good
agreement among the GEFS and ECENS PETs for a 20-40% chance temperatures fall
below the 15th climatological percentile in much of the highlighted areas. Raw
ensemble means show daily mean temperatures more than 10 degF below normal. At
this time, it remains difficult to highlight any areas with stronger chances
due to continued disagreement among the tools on the timing and placement of
strongest probabilities. Therefore, two additional slight risks of much below
temperature hazards are posted today. The first is for the Rockies, Northern
and Central Plains, Upper and Middle Mississippi Valleys for Jan 19-22. The
second is south and east of this area across the Southern Plains,
Lower-Mississippi, Tennessee, and Ohio Valleys, and part of the Great Lakes for
Jan 20-23. A brief warm-up is possible following the initial cold chances
across the East before the second wave of colder air arrives.



Ahead of the developing trough across the West one or more areas of surface low
pressure are forecast to develop. These systems 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 17-21.



From the Central and Southern Rockies stretching through the Plains and
Mississippi Valley into the Great Lakes, Central Appalachians and Northeast,
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 multiple chances for heavy snow in these broad regions. Early in
the hazard period, the most likely areas for heavy snow are across the Four
Corners and separately the Great Lakes. As the system in the Rockies develops
and progresses east and snow chances shift into the Plains and Mississippi
Valley. Following the progression of the system into the Plains, dynamical
models then become more diffluent with chances for a second system to develop
and bring additional snow to similar regions but perhaps slightly further south
and east. At this time, it remains difficult to define the individual system
tracks and timing. Therefore, a broad slight risk of heavy snow is posted for a
large portion of the CONUS for Jan 17-21.



Finally, cold air advection following the frontal passage and strong pressure
gradient near the surface low pressure areas increases the risk for high winds
across parts of the Central and Southern Plains, Middle and Upper Mississippi
Valley and western Great Lakes for Jan 18-21.



As mid-level troughing develops across the West, periods of episodic high winds
are forecast to develop across the Four Corners and surrounding areas supported
by the wind PETs from the GEFS and ECENS. A broad slight risk of high winds is
forecast for this area for Jan 17-20. By the end of the period, mid-level
ridging may begin developing across the region, reducing chances for high winds.



In Southern California, tools have lower confidence in the development of an
inverted trough offshore. Surface high pressure across the Great Basin also
does not appear to be as robust as in prior days. Therefore, no hazard is
posted today, but this area will continue to be monitored as there are some
increasing signals for surface high pressure in the Great Basin by the second
half of week-2.



In Alaska, by the middle through the end of the week-2 period, there are
signals for strong high pressure across northern Alaska and in the Yukon.
However, the high may be progressing too rapidly to initiate strong gap winds
in southern Alaska. No hazards are posted today due to this uncertainty but the
area will continue to be monitored.

FORECASTER: Ryan Bolt

$$