478
FXUS21 KWNC 041932
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST February 04 2025

SYNOPSIS: Arctic high pressure increases the chance of much below-normal
temperatures across the interior Pacific Northwest, northern Great Plains, and
Upper Mississippi Valley especially during the early part of week-2. A winter
storm may be ongoing or ending across the Mid-Atlantic and Northeast on
February 12. Periods of rain, potentially heavy, are likely to occur from the
Ohio and Tennessee Valleys south to the Gulf Coast with an increasing flood
risk for parts of Kentucky, Tennessee, and West Virginia.

HAZARDS

High risk of much below-normal temperatures for parts of the northern Great
Plains, Wed, Feb 12.

Moderate risk of much below-normal temperatures for parts of the Pacific
Northwest, northern Rockies, and northern Great Plains, Wed-Thu, Feb 12-13.

Slight risk of much below-normal temperatures for parts of the western and
central U.S., Wed-Tue, Feb 12-18.

Slight risk of heavy snow for the Central Appalachians, Mid-Atlantic, and
Northeast, Wed-Thu, Feb 12-13.

Slight risk of heavy snow for the Cascades, Klamath Mountains, Sierra Nevada
Mountains, and northern Rockies, Wed-Tue, Feb 12-18.

Moderate risk of periodic heavy precipitation for the Ohio Valley and Tennessee
Valleys and parts of the Southeast, Wed-Sat, Feb 12-15.

Slight risk of periodic heavy precipitation for parts of the Ohio Valley,
Southeast, Lower Mississippi Valley, eastern Oklahoma, and eastern Texas,
Wed-Sat, Feb 12-15.

Possible flooding for parts of Kentucky, Tennessee, and West Virginia.

DETAILED SUMMARY

FOR FRIDAY FEBRUARY 07 - TUESDAY FEBRUARY 11:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR WEDNESDAY FEBRUARY 12 - TUESDAY FEBRUARY 18: Prior to the start of week-2,
the GEFS depicts a bridging between anomalous 500-hPa ridges over Alaska and
Scandinavia as high latitude blocking becomes established over the Northern
Hemisphere. Consistent with this pattern change, the GEFS ensemble members
feature a rapid transition to a negative Arctic Oscillation. Arctic high
pressure is forecast to shift south into the lower 48 states later this week
and the high latitude blocking is likely to result in additional Arctic highs
expanding south from Canada. Based on GEFS and ECMWF Probabilistic Extremes
Tools (PETs), a high risk of much below normal temperatures (Feb 12) is posted
for the northern Great Plains where there is near or more than a 60 percent
chance of minimum temperatures falling below the 15th percentile and -10
degrees F. Any enhanced winds could result in wind chill values below -25 or
-30 degrees F, the cold advisory criteria. A broader area of moderate risk,
through February 13, extends west to include the interior Pacific Northwest.
Since the ensemble means favor onshore flow by day 8, the moderate risk was
discontinued to the west of the Cascades. A slight risk of much below-normal
temperatures continues for a larger spatial area of the western and central
U.S., but this shape may need to be modified in subsequent outlooks as the
latest ensemble means depict a weakening of the full-latitude ridge over
Alaska.



Model guidance continues to feature one or two waves of low pressure tracking
from the Tennessee Valley to the Mid-Atlantic and Northeast late in week-1
through the early part of week-2. Although a slight risk of heavy snow is
posted for the Mid-Atlantic and Northeast on February 12 and 13, the latest
model solutions favor the heaviest snowfall ending at the beginning of week-2.
Beyond February 13, the GEFS and ECENS have trended towards higher 500-hPa
heights along the East Coast which would tend to favor a more inland storm
track which reduces forecast confidence for heavy snow.



A series of low pressure systems are forecast to track across the Ohio and
Tennessee Valleys during mid-February. Based on 24-hour precipitation amounts
from the GEFS and ECENS, a moderate risk of periodic heavy precipitation is
posted for these areas on February 12 and 15. A broader region of slight risk
extends south to the Gulf Coast and is valid from February 12 to 15. A possible
flooding hazard was added to parts of Kentucky, Tennessee, and West Virginia
due to frequent rainfall during the next week to ten days. 28-day average
streamflows are running above the 80th percentile across eastern Kentucky and
southern West Virigina.



An anomalous 500-hPa trough along with the GEFS snow water equivalent (SWE) PET
supports a slight risk of heavy snow for the Cascades and northern Rockies
through the entirety of week-2. The snow hazard was extended south today to
include the northern Sierra Nevada Mountains based on a model trend towards
more onshore flow along the West Coast. Although above-normal precipitation is
favored for the coastal Pacific Northwest, 28-day average streamflows are below
normal across northwestern Oregon and western Washington which would limit a
widespread flooding risk. However, if the model trend continues towards more
persistent, onshore flow, then a heavy precipitation hazard may be warranted
for the week-2 hazards outlook released on February 5.



No hazardous weather is expected throughout Alaska during week-2 with near
normal precipitation favored for southwestern Alaska and only a slight lean
towards below-normal temperatures forecast across southeastern parts of the
state.

FORECASTER: Brad Pugh

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