555
FXUS21 KWNC 111912
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT March 11 2025

SYNOPSIS: An area of redeveloping mid-level low pressure favored over the
western contiguous U.S. (CONUS) is expected to renew precipitation across
portions of the West during week-2, but precipitation amounts are not expected
to reach hazardous thresholds. While not as potentially impactful as a frontal
system favored during week-1, additional surface low formation in the lee of
the Rockies increases the risk for heavy precipitation over the Central and
Eastern CONUS, accumulating snow over the northern tier of the U.S, with
episode of high winds over much of the Central and Eastern Lower 48 states. The
combination of elevated winds and very dry conditions is expected to lead to an
increased wildfire risk with Rapid Onset Drought (ROD) over parts of the
Southern Plains. Across Alaska, enhanced onshore flow supports an increased
risk of heavy precipitation for the Southeast.

HAZARDS

Moderate risk of high winds for the Central and Southern Plains, and adjacent
parts of the Mississippi Valley, Wed-Thu, Mar 19-20.

Slight risk of high winds for many portions of the central and eastern CONUS,
Wed-Thu, Mar 19-20.

Slight risk of heavy precipitation for parts of the Ohio, Tennessee, and
Mississippi Valley, Great Lakes region, Appalachians and parts of the
Southeast, Wed, Mar 19.

Slight risk of heavy precipitation for Southeast Alaska, Wed-Fri, Mar 19-21.

Slight risk of heavy snow from the Central Plains northeastward to the Upper
Great Lakes region, Wed, Mar 19.

Slight risk of much above normal temperatures for southern Texas, Wed, Mar 19.

Rapid onset drought risk across portions of the Southern Plains.

DETAILED SUMMARY

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

FOR WEDNESDAY MARCH 19 - TUESDAY MARCH 25: Following a very active weather
pattern tied to a highly amplified 500-hPa trough and an accompanying strong
frontal system during week-1, the GEFS and ECWMF ensembles are consistent in
favoring a mean trough centered over the central CONUS at the beginning of
week-2, with a mean ridge downstream near the East Coast. Another mean trough
is forecast to approach the northern Pacific Coast early in week-2, accompanied
by precipitation amounts up to 1.5 inches across coastal areas of this region.
There is enough uncertainty at this time to preclude the posting of any weather
hazards across the western CONUS at this time.



With mean troughing favored to overspread the Interior West later in week-1,
surface low development is again favored in the lee of the Rockies just prior
to the start of week-2. The resulting storm system is expected to track across
the Middle Mississippi Valley towards the central and eastern Great Lakes
region. The strength of the shortwave energy at mid-levels and lee cyclogenesis
does not appear to be as robust as previously advertised with the surface low
now favored during week-1. However, there is sufficient support during the
first half of the forecast period to depict a favorable synoptic setup
consisting of a heavy precipitation threat over much of the Central and Eastern
CONUS, high winds, and accumulating and potentially heavy snow on the backside
of the low as it tracks across the Middle Mississippi Valley. A slight risk of
heavy precipitation is posted for parts of the Ohio, Tennessee, and Mississippi
Valleys, Great Lakes region, Appalachians and parts of the Southeast, Wed, Mar
19. There is reasonable agreement in the Probabilistic Extremes Tools (PETs)
and several recent deterministic solutions indicating at least a 20% chance for
3-day amounts exceeding the 85th percentile and close to 1 inch. The potential
flood hazard that was issued over the southern Ohio, Tennessee, and Lower
Mississippi Valleys several days ago is dropped today, since sufficient breaks
in precipitation timing are expected. This storm system and the associated
advancing trough aloft also support a slight risk of heavy snow from the
Central Plains northeastward into the Upper Great Lakes area on March 19, based
on the predicted track of the mean surface low. Within the highlighted region,
the raw ECMWF favors a slight risk for accumulations upwards of 4 inches early
in week-2.



Strengthening surface pressure gradients are again featured in the
deterministic and ensemble means associated with the surface low. Both the GEFS
and ECMWF depict a fairly deep trough axis extending into the Southern High
Plains and northern Mexico on day 8. The PETS and the very latest 12z
deterministic ECMWF solution also support wind speeds exceeding the 85th
percentile (20-40%) and 25 mph extending into day 9. Given this, and in
consideration of a continued wildfire risk with drought conditions registered
(ranging from D0 to D4), with suppressed precipitation favored during week-1 in
the southern half of the Plains, a moderate risk of high winds is posted for
Mar 19-20. A broader slight risk area for high winds is posted (Mar 19-20) over
much of the central and eastern CONUS based on consistent, elevated wind
signals in the PETs as the surface low tracks northeastward. Prior to the low
shifting into the Mississippi Valley to bring cooler temperatures into the
Plains, a slight risk of much above normal temperatures is posted over southern
Texas for Mar 19, where there is support in the PETs for temperatures exceeding
the 85th percentile and 90 degrees F by the outset of week-2. The combination
of very little precipitation, above-normal temperatures, and gusty winds, also
supports the continuation of a Rapid Onset Drought (ROD) hazard over portions
of the Southern Plains.



Over Alaska, enhanced onshore flow associated with amplified troughing over the
Bering Sea and western Alaska early in week-2 is expected to bring above-normal
precipitation to most of Southeast Alaska. While the ECMWF is more pronounced
with this pattern than the GEFS, both PETs indicate 20-40% chances for 3-day
amounts exceeding the 85th percentile, with amounts nearing hazard thresholds
to support a slight risk of heavy precipitation for Mar 19-21.



During the second half of week-2, ensemble guidance generally favors a more
deamplified, and zonal pattern over the CONUS, lessening concerns for continued
weather-related hazards later in March. One exception may be the Pacific
Northwest, where there is modest support for enhanced onshore flow to promote
the potential for heavy precipitation and high elevation snow over the
northwestern CONUS, though there is a good amount of disagreement in the
ensembles regarding the location and evolution of a 500-hPa ridge encroaching
upon the West Coast. Another notable aspect of the extended range guidance
concerns the shortening of wavelengths featured in some of the latest
solutions. This is typical of height patterns entering boreal spring, but it
does pose predictability challenges in terms of how well models can adjust,
which adds to forecast uncertainty moving forward.

FORECASTER: Anthony Artusa

$$