177
FXUS21 KWNC 011804
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT April 01 2025

SYNOPSIS: Mid-level low pressure is favored over eastern portions of Canada and
the U.S, with surface high pressure overspreading much of the central and
eastern CONUS early in week-2. While this is expected to bring a period of
welcomed dryness for areas affected by heavy precipitation in week-1, the
synoptic setup favors elevated chances for much below normal temperatures which
may adversely impact emerging springtime vegetation following a very warm March
for much of the southeastern CONUS. Upstream, mean mid-level high pressure
forecast is expected to keep much of the western CONUS free of weather related
hazards, with any enhanced onshore flow limited to the higher elevations of
western North America.

HAZARDS

Moderate risk of much below normal temperatures for portions of the Southern
Plains, Lower and Middle Mississippi, Tennessee, and Ohio Valleys,
Appalachians, Mid-Atlantic, and Southeast, Wed, Apr 9.

Slight risk of much below normal temperatures for much of the south-central and
eastern CONUS, Wed-Thu, Apr 9-10.

Slight risk of high winds for the northeastern CONUS, Wed, Apr 9.

DETAILED SUMMARY

FOR FRIDAY APRIL 04 - TUESDAY APRIL 08:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR WEDNESDAY APRIL 09 - TUESDAY APRIL 15: There continues to be good
consistency in the dynamical models advertising a large-scale pattern change,
with amplified mean ridging (troughing) becoming established over western
(eastern) North America by early next week. Tied to this latter mid-level
feature, both the GEFS and ECWMF ensembles show the mean surface high pressure
center shifting over the Tennessee Valley and the Appalachians behind a
departing low pressure system over the Canadian Maritimes.  Although the
troughing is favored to deamplify by the middle of next week, a slight risk of
high winds remains posted for portions of the Great Lakes, Ohio Valley,
Mid-Atlantic and Northeast for Apr 9 based on lingering signals in the
Probabilistic Extreme Tools (PETs). Any residual moisture being wrapped in the
deepening low may lead to accumulating snowfall over parts of the Northeast and
Appalachians, though models are unsupportive of any amounts exceeding heavy
snow thresholds.



Accompanying the mean surface high pressure, the GEFS and ECMWF ensembles
continue to show elevated chances (>50%) for negative temperature anomalies in
the double digits, with the strongest cold signals now focused over the
southeastern CONUS. This is well reflected in the GEFS and ECMWF PETs,
depicting >30% chances for minimum temperatures falling below the 10th
percentile and below 40 degrees F on day 8 (Apr 9).  One key difference between
the raw and calibrated tools is the ECMWF maintains more of a westerly
extension of the cold signal into Texas than the GEFS before temperatures begin
to moderate.  As a result, a moderate risk of much below temperatures remains
issued for Apr 9, with much of its coverage mainly confined to areas east of
the Mississippi, and a broader slight risk area of much below normal
temperatures (Apr 9-10) with more coverage in the Southern Plains and Lower
Mississippi Valley out of deference to the ECMWF.  While the anomalous cold is
well out of reach of wintertime hazard criteria, such cold temperatures could
be quite a shock following a very warm March in the lee of the Rockies, and
potentially bring adverse impacts to emerging springtime vegetation across many
parts of the southcentral and southeastern CONUS



Later in week-2, ensembles continue to feature a reloading mean trough by days
10 and 11, implying a renewed hazardous cold risk for the eastern CONUS. In
addition, there is increased support in guidance favoring surface low formation
along the lower Eastern Seaboard at this lead. However, both raw and calibrated
tools are not yet supportive of including any additional temperature and/or
precipitation related hazards, but this potential will continue to be monitored
in upcoming outlooks. While less supported in the ECMWF and Canadian ensembles,
additional lee cyclogenesis is also possible later in week-2, which could bring
elevated winds to parts of the Southern High Plains where there remains dry
fuels that could enhance the risk of wildfire activity.



With the development of strong mid-level ridging favored over the western
CONUS, unseasonably warmer and drier conditions are forecast compared to
week-1, resulting in no weather related hazards for the western CONUS for
week-2. Any enhanced onshore flow to promote above-normal and possibly heavy
precipitation would most likely be limited to the higher latitudes of North
America extending from the upper Pacific Northwest to the southern Alaska
Mainland. This is reflected in the PETs which depict increased chances for
3-day precipitation amounts exceeding the 85th percentile. However, forecast
actual totals do not presently meet hazard criteria, as heavy precipitation
potential remains tenuous due to the favored weakening of mid-level troughing
over the northeastern Pacific during week-2.

FORECASTER: Nick Novella

$$