Valid Tuesday March 26, 2024 to Monday April 01, 2024
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM
EDT March 18 2024
Synopsis: By early next week, a potentially
potent low pressure system tracking across the Midwest leads to an increased
risk for heavy precipitation across the Mississippi, Tennessee and Ohio
Valleys, accumulating heavy snowfall, along with a widespread threat for
episodes of high winds for much of the central and eastern U.S. In the wake of
the low pressure system, anomalously cold air is favored to dive southeastward
renewing the risk of early spring frost and/or freezes for many parts of the
southeastern CONUS. Predicted mid-level low pressure returning across the West
promotes the risk of high elevation heavy snow over parts of California and
Oregon.
Hazards - Slight risk of heavy precipitation
for parts of the Mississippi, Tennessee, and Ohio Valleys, and Southeast,
Tue-Wed, Mar 26-27.
- Slight risk of high winds for parts for much of the Midwest, and regions
east of the Mississippi River, Tue-Thu, Mar 26-28.
- Slight risk of much below normal temperatures for parts of the Great
Plains, Mississippi, Tennessee, and Ohio Valleys, and the Southeast, Wed-Fri,
Mar 27-29.
- Slight risk of heavy snow for the northern and central Rockies, eastward to
the Great Lakes, Tue-Thu, Mar 26-27.
- Slight risk of high elevation heavy snow of the Sierra Nevada of
California, and the Cascades of the Pacific Northwest, Wed-Sat, Mar 27-30.
Detailed SummaryFor Thursday March 21 - Monday March
25:
WPC Days 3-7 U.S. Hazards For Tuesday March 26 - Monday
April 01: Early in week-2, dynamical models are in fair agreement
featuring amplified ridging centered over the northeastern Pacific and Alaska,
with deep troughing downstream consisting of a broad distribution of negative
500-hPa heights overspreading much of the western and central CONUS. In regards
to the ridging upstream, both the GEFS and ECMWF ensembles have trended more
towards a more amplified mean solution over the past few days, resulting in
stronger northwesterly flow and the potential for anomalous cold air advection
over the central CONUS by early next week. Additionally, lee cyclogenesis and
a fairly potent low pressure system shifting into the Great Lakes remains
favored in the ensembles, which is expected to sustain the increased risk of
heavy precipitation across the southeastern CONUS, with the potential for
accumulating heavy snowfall on the backside of the tracking low, along with the
episodes of high winds.
Tied to the amplified troughing aloft by the outset of week-2, the GEFS,
ECMWF and Canadian ensembles have been consistent with the timing and location
of increased daily precipitation amounts in the warm sector of the predicted
low pressure system. A slight risk of heavy precipitation is issued over
portions of the Mississippi, Tennessee and Ohio Valleys and the Southeast,
where Probabilistic Extremes Tools (PETs) show at least a 20% chance of 3-day
accumulations exceeding the 85th percentile and 1 inch. A moderate risk was
considered for issuance based on the ECMWF PET favoring higher chances (>40%)
for meeting hazard criteria over parts of the eastern Gulf states, however this
is much less supported in the uncalibrated daily guidance and GEFS PET.
Localized flooding is also possible across parts of the Gulf states due to
above-normal precipitation received during the past two weeks leaving several
locations at minor flood stage, and enhanced precipitation favored in the
region during week-1. Later in week-2, there is some support in the PETs for
the heavy precipitation risk emerging over parts of the coastal Mid-Atlantic
and Northeast associated with a secondary surface low developing over the
Southeast in the ECMWF, though this is not well represented in the GEFS and
Canadian. At the base of the eastward shifting troughing aloft, a slight risk
of high winds is also posted over a broad area of the eastern CONUS for Mar
26-28 which is also supported by PETs.
In the wake of the predicted frontal system, the uncalibrated GEFS depicts
stronger mean surface high pressure compared to previous runs, with negative
temperature departures in the double digits (Deg F) over the Northern Plains
and upper Midwest during the first few days of the period. These trends are
also reflected in the PETs, which depict elevated chances (40-60%) for minimum
temperatures falling below the 15th percentile over the upper Midwest. Despite
these strong cold signals, no corresponding hazards are issued over this part
of the country, as actual temperatures are not expected to reach hazard
criteria (especially with higher sun angles later in March). However, as the
troughing aloft shifts eastward with time, so does the anomalously cold air
mass, where early spring frost and/or freezes may adversely impact emerging
spring vegetation over parts of the Plains, Mississippi, Tennessee and Ohio
Valleys and the Southeast. Weaker signals are depicted in the PETs as the cold
air mixes southeastward by the middle of next week, but these tools maintain at
least a 20% chance for minimum temperatures falling below the 15th percentile
and 40 degrees F, supporting a slight risk of much below normal temperatures
Mar 27-29. With the anomalous cold in place, accumulating snowfall looks
increasingly likely on the backside of the low over north-central CONUS, as
well as farther west across portions of the Rockies associated with upslope
flow. Based on the uncalibrated ECMWF and the GEFS Snow Water Equivalent (SWE)
PET, a slight risk of heavy snow is issued (Mar 26-27) from the Rockies to the
Great Lakes and excludes parts of the Northern Plains where drier air is
favored.
As much of the anomalous troughing weakens and begins to lift out by the
middle of week-2 over the eastern CONUS, both the GEFS and ECMWF ensembles
continue to feature additional 500-hPa troughing encroaching the West Coast.
While much less amplified in comparison to the troughing downstream, additional
shortwave activity is expected to promote the return of above-normal
precipitation over the western CONUS, with potentially heavy precipitation over
parts of California and the Pacific Northwest. Both the GEFS and ECWMF PETs are
in agreement depicting a broad area with increased chances for 3-day amounts
exceeding the 85th percentile with, with 30-40% chances over the central West
Coast. However, the heaviest totals in the uncalibrated tools and PETs appear
limited to the higher elevations of California and Oregon. As a result, no
corresponding risk of heavy precipitation is issued, but a slight risk of high
elevation snow is posted over these areas for Mar 27-30.
No hazards are issued over Alaska as much of the state is favored to be
under the influence of a strong 500-hPa ridge. While this ridge is favored to
gradually deamplify later in week-2, much of the Mainland and Southeast are
expected to be unseasonably warm through late March. Enhanced wind speeds are
possible associated with developing mean low pressure over the Bering Sea and
Gulf of Alaska, though wind speeds are not expected to exceed hazard
thresholds.
Forecaster: Nick Novella
$$
Please consult local NWS Forecast Offices for short range forecasts and region-specific information.
Resources
Week-2 Probabilistic Extremes Tool
GFS Ensemble Forecasts