816
FXUS21 KWNC 112002
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST February 11 2025

SYNOPSIS: Another area of mid-level low pressure favored in the models is
expected to reinforce an anomalously cold air mass east of the Rockies, with
elevated chances for hazardous minimum temperatures focused over the Plains and
Mississippi Valley early in the period.  There is better model agreement
depicting surface low development and an accompanying frontal system over the
southern and eastern contiguous U.S. (CONUS), maintaining an increased risk of
heavy precipitation in the warm sector, while there is better model agreement
supporting increased chances of heavy snowfall, and high winds over the eastern
half of the CONUS during the first several days of week-2.  Upstream,
developing mid-level high pressure is expected to bring drier conditions for
many areas in the western CONUS.

HAZARDS

Moderate risk of much below normal temperatures for portions of the Central and
Southern Plains, Lower and Middle Mississippi, Tennessee and Ohio Valleys,
lower Great Lakes, Wed-Fri, Feb 19-21.

Slight risk of much below normal temperatures for much of the central and
eastern CONUS, excluding parts of New England, Wed-Sun, Feb 19-23.

Moderate risk of heavy precipitation for parts of the Lower Mississippi and
Tennessee Valleys, Southeast, Southern Appalachians, and Mid-Atlantic, Wed, Feb
19.

Slight risk of heavy precipitation for portions of the Southern Plains, Lower
and Middle Mississippi, Ohio, and Tennessee Valleys, Appalachians,
Mid-Atlantic, and Southeast, Wed-Thu, Feb 19-20.

Slight risk of heavy snow for portions of the Central and Southern Plains,
Lower and Middle Mississippi, Ohio, and Tennessee Valleys, Appalachians, Great
Lakes, and the Mid-Atlantic, Wed-Thu, Feb 19-20.

Slight risk of heavy snow for portions of the Northeast, Great Lakes and
Mid-Atlantic, Thu-Fri, Feb 20-21.

Slight risk of high winds for much of the eastern CONUS, east of the
Mississippi, Wed-Fri, Feb 19-21.

Possible flooding for the Lower Mississippi and Tennessee Valleys, Southeast,
and the Appalachians.

DETAILED SUMMARY

FOR FRIDAY FEBRUARY 14 - TUESDAY FEBRUARY 18:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR WEDNESDAY FEBRUARY 19 - TUESDAY FEBRUARY 25: By the beginning of next week,
dynamical models remain in good agreement featuring a strong 500-hPa trough
over the northeastern CONUS, leading to the advection of anomalously cold air
for areas east of the Rockies. With many locations favored to experience
negative temperature departures in the double-digits throughout the Northern
Plains, Great Lakes, and Northeast late in week-1, the GEFS and ECWMF ensembles
continue to feature a secondary shortwave disturbance by the outset of week-2
which is not only expected to reinforce much of the cold air already
established, but also promote the southward extension of the anomalously cold
temperatures into the southern tier and bring a renewed threat of heavy
precipitation and heavy snow across portions of the eastern CONUS towards the
middle of next week.  Upstream, the development of positive 500-hPa height
departures is generally favored to promote drier and warmer conditions
throughout the West during week-2, however episodes of strong winds may become
a factor associated with the development of mean surface high pressure favored
over the Intermountain West and Great Basin later in week-2.



Based on raw temperature guidance and calibrated Probabilistic Extreme Tools
(PETs), a slight risk of much below normal temperatures remains posted but now
covers much of the central and eastern CONUS for Feb 19-23 where there are
increased chances for minimum temperature falling below the 15th climatological
percentile and negative temperatures reaching the double digits early in the
period.  Embedded with this broad slight risk area, a moderate risk of much
below normal temperatures is issued extending from the Ohio Valley
southwestward into the Southern Plains and Lower Mississippi Valley for Feb
19-21. While the ECWMF and GEFS disagree on the duration and magnitude of the
hazardous cold potential, both PETs show elevated chances (30-40%) of minimum
temperatures falling below the 10th percentile later next week, with
deterministic solutions also supportive of temperatures approaching hazard
criteria, depicting apparent temperatures dipping within the range of -10 and 5
deg F in the highlighted region. Consistent with backdoor front activity, the
accompanying surface high pressure descending southward may also produce high
winds along the Front Range and into New Mexico early in week-2, though there
is not sufficient support in the calibrated tools to issue a corresponding wind
shape given climatology for the region.



Ahead of the expanding surface high pressure, ensembles continue to favor a
surface low pressure system ejecting across the Gulf states, bringing yet
another round of potentially heavy precipitation across the southeastern CONUS
following a wet week-1. Consistent with previous guidance, the GEFS remains
weaker with the mean surface low and precipitation amounts compared to the
ECMWF, though both raw and calibrated guidance suggests an eastward expansion
of the heavy precipitation risk over the eastern seaboard as the low tracks
offshore into the Atlantic. Therefore, both the slight and moderate risks of
heavy precipitation have been shifted and expanded eastward accordingly, now
valid for Feb 19 and Feb 19-20, respectively. A flooding possible hazard
remains posted and overlaps both heavy precipitation risk areas, based on
predicted precipitation amounts ranging from 3-7 inches (locally greater) in
week-1, with increased chances for additional amounts exceeding an inch on top
of that in early week-2.



With anomalously cold air advecting eastward and enhanced moisture in place,
both deterministic and ensemble solutions have come into better agreement in
regards to the increased potential for accumulating, and possibly heavy
snowfall on the backside of the low since yesterday.  This is supported in both
the Snow Water Equivalent (SWE) PET from the GEFS, as well as raw snowfall
amounts from the ECMWF ensemble mean with signals reaching as far south as
Southern Plains and Lower Mississippi Valley by the outset of week-2.  However,
even with the increased support for heavy snowfall, there remains a good deal
of uncertainty with the details of the storm track, and the delineation of
precipitation type throughout the duration of the event. Therefore, a broad
slight risk of heavy snow is posted from the ArkLaTex region to the
Mid-Atlantic for Feb 19-20, where there is some overlap with the aforementioned
slight risk area of heavy precipitation to denote this mixed precipitation
potential.  As the low is progged to lift out over the Atlantic and take on a
Noreaster-like track based on the 0z and 6z GFS and 0z ECMWF on days 9 and 10
(Feb 20-21), a separate slight risk area for heavy snow is issued covering the
entire Northeast and parts of the eastern Great Lakes and Mid-Atlantic.
Lastly, with strengthening pressure gradients favored in the wake of the
departing surface low, a slight risk of high winds is also posted for much of
the eastern CONUS for Feb 19-21.



Upstream, ensembles have become more supportive of mid-level ridging building
across the western CONUS, reducing the likelihood of continued onshore flow
over the West Coast. There remains some signals in the precipitation tools for
near to above-normal precipitation over the northwestern CONUS, with increased
snowfall amounts over the higher elevations early in week-2, however there is
less confidence these amounts will exceed hazard criteria and the corresponding
heavy snow hazards over the Cascades and Northern Rockies are removed in the
updated outlook.  With conditions favored to become much drier, especially
across California, and flow looking to become more offshore later in week-2,
portions of the West may see renewed risk of high winds. However, there is
insufficient support in the tools at this time to issue any corresponding wind
hazards, and given the enhanced precipitation received over the West Coast
recently, and precipitation favored during week-1, this part of the country
looks to be less susceptible to any wildfire risk at this time.



Contrary to western CONUS, the development of anomalous mid-level troughing
over the eastern Aleutians, with downstream ridging over western Canada is
expected to bring increased onshore flow, and above-normal precipitation for
much of the southern Mainland and the Southeast during week-2. This is
reflected in both the GEFS and ECMWF PETs, depicting increased chances for
3-day amounts exceeding the 85th percentile, though actual amounts are
unsupportive to post any corresponding hazard. However, it should be noted
though warmer temperatures favored during week-2 could result in higher
freezing levels, where any enhanced precipitation could lead to an increased
risk of runoff with possible landslides.

FORECASTER: Nick Novella

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