564
FXUS21 KWNC 142013
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST January 14 2025

SYNOPSIS: Multiple model ensemble means indicate amplified mid-level low
pressure over the eastern half of the contiguous U.S. (CONUS) from the end of
week-1 into week-2, likely bringing hazardous cold temperatures to the area
until the middle of week-2. There may be a transition to mid-level high
pressure across the eastern third of the CONUS by the end of the period while
mid-level low pressure develops across the western two-thirds as amplified
mid-level high pressure over the Northeast Pacific retrogrades and weakens.
Surface high pressure is predicted to build over the Great Basin with surface
low pressure developing along central and southern coastal California
increasing chances for enhanced wind speeds across parts of Arizona and
southern California, which could prolong the risk of wildfires in the region.
Santa Ana winds are most likely for the beginning to middle of week-2, with
winds having a more onshore component associated with mid-level low pressure by
the end of the period. A forecast cold front across the southeastern CONUS and
Mid-Atlantic may lead to heavy precipitation across parts of the Gulf Coast
states and the Mid-Atlantic, with the potential of some areas having frozen
precipitation.

HAZARDS

High risk of much below normal temperatures across parts of the Great Lakes,
Appalachians, Mid-Atlantic, Texas, Southeast, and Ohio, Tennessee, and Lower
Mississippi Valleys, Wed, 22.

Moderate risk of much below normal temperatures across many parts of the
eastern third of the CONUS, Middle and Lower Mississippi Valley, and Southern
Plains, Wed-Thu, Jan 22-23.

Slight risk of much below normal temperatures for areas east of the Rockies,
Wed-Sat, Jan 22-25.

Slight risk of heavy precipitation for portions of the Mid-Atlantic and Gulf
Coast states, Wed-Thu, Jan 22-23.

Moderate risk of periods of high winds across coastal portions of southern
California, Wed-Sat, Jan 22-25.

Slight risk of periods of high winds for parts of Arizona and southern
California, Wed-Tue, Jan 22-28.

DETAILED SUMMARY

FOR FRIDAY JANUARY 17 - TUESDAY JANUARY 21:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR WEDNESDAY JANUARY 22 - TUESDAY JANUARY 28: Multiple model ensemble means
continue to depict amplified mid-level low pressure lingering over the eastern
half of the CONUS from the end of week-1 into the middle of week-2. However, by
day 11 (Jan 25), there is increased model uncertainty. Ensemble means generally
indicate amplified mid-level ridging over the northeast Pacific retrograding
and weakening by day 11, with a downstream positively tilted trough extending
from the Southwest to Upper Mississippi Valley by day 11, although with varying
amplitude. The ECENS and CMCE means favor a much more amplified trough compared
to the GEFS. These model differences translate to uncertainty regarding the
duration of anticipated hazardous cold temperatures.



A high risk (60-80% chance) of much below normal temperatures is designated for
parts of the Great Lakes, Appalachians, Mid-Atlantic, Southeast, Texas, and
Ohio, Tennessee, and Lower Mississippi Valleys, Jan 22, where the ECENS, GEFS,
and CMCE Probabilistic Extremes Tools (PETs) shows at least a 60% chance of
minimum temperatures falling to the lowest 15th percentile climatologically.
The GEFS PET actually indicates greater probabilities than the ECENS of
temperatures reaching these thresholds, whereas the ECENS showed greater
chances than the GEFS in yesterdays guidance.  A moderate risk (40-60% chance)
is posted for a larger area extending to parts of the Northeast, Oklahoma, and
the Middle Mississippi Valley, Jan 22-23. A broad area of slight risk (20-40%)
is highlighted across much of the CONUS east of the Rockies, excluding southern
Florida, Jan 22-25. Sub-freezing temperatures are predicted across the South,
while much of the interior Northeast and Upper Midwest is predicted to
experience temperatures falling below zero deg F, with dangerously low wind
chill values possible for many areas. Recent deterministic model guidance
indicates the possibility of temperature anomalies falling at least 16 deg F
below normal in some risk areas.



Model guidance shows the potential for a cold front forming across the
southeastern CONUS which could support heavy precipitation in the region. A
slight risk of heavy precipitation is designated for portions of the
Mid-Atlantic and Gulf Coast states, Jan 22-23, where PETs indicate at least a
20% chance of 3-day liquid precipitation totals exceeding 0.75 inches, with
deterministic model runs indicating some areas receiving greater than 2 inches
in a 24-hour period. Anticipated freezing temperatures could support frozen
precipitation across some of the highlighted risk areas.



Multiple model ensemble means depict surface high pressure building over the
Great Basin with an inverted surface trough developing along the coast of
central and southern California from the beginning to middle of week-2. This
pattern is favorable for Santa Ana winds and enhanced wind speeds across
southwestern portions of the CONUS. A moderate risk of episodic high winds is
maintained for the southern coast of California Jan 22-25. There is increasing
model uncertainty regarding the synoptic pattern across the West with multiple
models showing a less favorable pattern for Santa Ana winds by Jan 26. A
broader area of slight risk is highlighted for parts of Arizona and southern
California for the entire week-2 period, although enhanced winds at the end of
week-2 would likely have a more onshore component and be associated with the
mid-level trough rather than Santa Ana winds. Predicted high winds, warm
temperatures, and dry conditions would exacerbate the risk of wildfires during
week-2, especially in areas already experiencing active wildfires.

FORECASTER: Melissa Ou

$$