645
FXUS21 KWNC 081938
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST MARCH 08 2024
SYNOPSIS: A COLD FRONT IS FORECAST TO MOVE THROUGH THE EASTERN CONTIGUOUS U.S.
(CONUS) LATE IN WEEK-1 AND INTO THE START OF WEEK-2. THIS FRONT FAVORS ENHANCED
CHANCES FOR HEAVY PRECIPITATION ACROSS PARTS OF THE SOUTHEAST AND SOUTHERN
MID-ATLANTIC, ALONG WITH AN ELEVATED FLOODING RISK OVER SOME OF THESE AREAS. AS
THIS FRONT MOVES OFF THE ATLANTIC COAST, AND MID-LEVEL LOW PRESSURE AMPLIFIES
OVER EASTERN NORTH AMERICA, A RELATIVELY COLDER AIR MASS IS FORECAST TO BUILD
INTO THE EASTERN CONUS, WITH THE INCREASED POTENTIAL FOR TEMPERATURES COLD
ENOUGH TO LEAD TO ADVERSE IMPACTS ON VEGETATION ACROSS PARTS OF THE SOUTH.
MID-LEVEL HIGH PRESSURE IS FORECAST TO BUILD ACROSS ALASKA RESULTING IN
DECREASING CHANCES FOR HEAVY PRECIPITATION ACROSS THE SOUTHEASTERN PART OF THE
STATE COMPARED TO THE LATE WEEK-1 TIMEFRAME.
HAZARDS
MODERATE RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHEAST, SAT, MAR 16.
SLIGHT RISK OF HEAVY PRECIPITATION ACROSS PORTIONS OF THE LOWER MISSISSIPPI AND
TENNESSEE VALLEYS, SOUTHEAST, SOUTHERN APPALACHIANS, AND SOUTHERN MID-ATLANTIC,
SAT-SUN, MAR 16-17.
SLIGHT RISK OF HIGH WINDS ACROSS MUCH OF THE EASTERN CONUS, SAT-WED, MAR 16-20.
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE MIDDLE AND
LOWER MISSISSIPPI AND TENNESSEE VALLEYS, AND SOUTHEAST, MON-WED, MAR 18-20.
POSSIBLE FLOODING FOR PARTS OF THE LOWER MISSISSIPPI AND TENNESSEE VALLEYS,
SOUTHEAST, AND SOUTHERN APPALACHIANS.
DETAILED SUMMARY
FOR MONDAY MARCH 11 - FRIDAY MARCH 15:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SATURDAY MARCH 16 - FRIDAY MARCH 22: THERE IS GOOD AGREEMENT AMONG THE 0Z
GEFS, ECMWF, AND CANADIAN ENSEMBLES IN REGARDS TO MID-LEVEL TROUGHING ACROSS
THE EASTERN CONUS AT THE OUTSET OF THE PERIOD. THIS TROUGH IS FORECAST TO
AMPLIFY OVER EASTERN NORTH AMERICA AND LEAD TO POTENTIALLY IMPACTFUL WEATHER
ACROSS PORTIONS OF THE EAST, ESPECIALLY EARLY IN WEEK-2 AS A COLD FRONT MOVES
ACROSS THE REGION. WHILE PARTS OF THE GREAT PLAINS AND MISSISSIPPI VALLEY ARE
LIKELY TO DRY OUT WITH HIGHER PRECIPITATION CHANCES SHIFTING INTO THE WEEK-1
PERIOD, FORECAST TOOLS CONTINUE TO DEPICT FRONTALLY FOCUSED PRECIPITATION
ACROSS PARTS OF THE SOUTHEASTERN CONUS, AND POSSIBLY EXTENDING NORTHWARD ALONG
THE EASTERN SEABOARD AT THE START OF WEEK-2. THE GEFS AND ECMWF PETS GENERALLY
DEPICT PROBABILITIES OF 20-40 PERCENT FOR 3-DAY PRECIPITATION TOTALS EXCEEDING
THE 85TH CLIMATOLOGICAL PERCENTILE AND 1-INCH OVER SOME OF THESE AREAS,
INCREASING TO ABOVE 40 PERCENT ACROSS FLORIDA IN THE ECMWF PET. UNCALIBRATED
GUIDANCE ALSO MAINTAINS ELEVATED PRECIPITATION AMOUNTS, WITH THE LARGEST
24-HOUR TOTALS (GREATER THAN A HALF-INCH IN THE 0Z ECMWF AND GEFS ENSEMBLE
MEANS) ACROSS SOUTHERN ALABAMA, GEORGIA, AND NORTHERN FLORIDA ON DAY-8 (MAR
16), AND SHIFTING MORE SOUTH INTO THE FLORIDA PENINSULA BY DAY-9 (MAR 17).
THEREFORE, A MODERATE RISK FOR HEAVY PRECIPITATION REMAINS HIGHLIGHTED ACROSS
PARTS OF THE SOUTHEAST FOR MAR 16, WITH A SLIGHT RISK COVERING A LARGER AREA
INCLUDING PORTIONS OF THE LOWER MISSISSIPPI AND TENNESSEE VALLEYS, SOUTHERN
APPALACHIANS, AND SOUTHERN MID-ATLANTIC THROUGH MAR 17. BY MAR 17, THE GREATEST
PRECIPITATION POTENTIAL IS LIKELY TO SHIFT TO THE SOUTHERN PORTIONS OF THE
SLIGHT RISK AREA, PARTICULARLY ACROSS FLORIDA, WITH MORE NORTHERN AREAS LIKELY
TO HAVE DECREASING PRECIPITATION CHANCES AS THE FRONT MOVES OFF THE ATLANTIC
COAST. ANTECEDENT HEAVY PRECIPITATION PREDICTED DURING WEEK-1 BASED ON
FORECASTS FROM THE WEATHER PREDICTION CENTER, COMBINED WITH EXPECTED HEAVY
WEEK-2 PRECIPITATION, SUPPORTS A POSSIBLE FLOOD RISK FOR PORTIONS OF THE
SOUTHEASTERN CONUS.
AS THE TROUGH AND ASSOCIATED FRONTAL SYSTEM PROGRESS EASTWARD, GUSTY NORTHERLY
TO NORTHWESTERLY FLOW IS LIKELY ACROSS A LARGE PORTION OF THE EASTERN CONUS.
THE PETS ARE NOT OVERLY EXPANSIVE, WITH ONLY THE ECMWF PET DEPICTING AT LEAST A
20 PERCENT CHANCE OF WIND SPEEDS EXCEEDING THE 85TH CLIMATOLOGICAL PERCENTILE
AND 20-MPH OVER THE NORTHEAST. HOWEVER, THE TIGHT PRESSURE GRADIENT BETWEEN THE
SURFACE LOW OVER SOUTHEAST CANADA AND SURFACE HIGH PREDICTED TO BUILD ACROSS
THE MIDWEST AND SOUTH FAVORS A BROADER AREA OF SLIGHT RISK OF HIGH WINDS ACROSS
MUCH OF THE EASTERN CONUS, MAR 16-20. MULTIPLE EPISODES OF HIGH WINDS ARE
POSSIBLE THROUGHOUT THE PERIOD WITH NOT ALL AREAS IMPACTED AT ANY GIVEN TIME.
THE INCREASED NORTHERLY FLOW MAY ALSO BEGIN TO USHER IN RELATIVELY COOLER
TEMPERATURES ACROSS THE EASTERN HALF OF THE CONUS TOWARD THE END OF WEEK-2,
WITH THE POTENTIAL NEGATIVE ARCTIC OSCILLATION AND MJO PROGRESSION FAVORING
THIS COOLER PATTERN INTO LATE MARCH. THE ECMWF PET HAS INCREASED SIGNALS
COMPARED TO YESTERDAY, NOW SHOWING PARTS OF THE SOUTH HAVING AT LEAST A 20
PERCENT CHANCE OF MINIMUM TEMPERATURES FALLING BELOW THE 15TH CLIMATOLOGICAL
PERCENTILE AND 40 DEG F DURING THE DAYS 10-12 (MAR 18-20) PERIOD. THE GEFS ALSO
DEPICTS INCREASED COVERAGE OF THESE ELEVATED PROBABILITIES, BUT IS NOT AS
EXPANSIVE AS THE ECMWF PET. HOWEVER, GIVEN ANTECEDENT WARM CONDITIONS AND
INCREASING VEGETATION GREEN-UP, A SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES
IS HIGHLIGHTED ACROSS PARTS OF THE MIDDLE AND LOWER MISSISSIPPI AND TENNESSEE
VALLEYS, AND SOUTHEAST, MAR 18-20 DUE TO POSSIBLE ADVERSE IMPACTS ON VEGETATION
RESULTING FROM THE FLIP TO A COOLER PATTERN.
DYNAMICAL MODELS CONTINUE TO FAVOR MID-LEVEL RIDGING BUILDING OVER ALASKA
DURING WEEK-2, WHICH FAVORS DIMINISHING HEAVY PRECIPITATION CHANCES OVER
SOUTHEAST ALASKA AS THE GREATEST POTENTIAL IS NOW IN THE LATE WEEK-1 PERIOD.
THEREFORE, THE SLIGHT RISKS FOR HEAVY PRECIPITATION AND HIGH WINDS HAVE BEEN
DISCONTINUED, WITH NO ADDITIONAL HAZARDS POSTED FOR ALASKA.
FORECASTER: THOMAS COLLOW
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