211
FXUS21 KWNC 121809
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MARCH 12 2024
SYNOPSIS: SURFACE HIGH PRESSURE, WITH ANOMALOUSLY COLD TEMPERATURES, IS
FORECAST TO SHIFT SOUTHEASTWARD ACROSS THE CENTRAL AND EASTERN CONTIGUOUS U.S.
(CONUS) BY EARLY NEXT WEEK. ON MARCH 20, THERE IS AN INCREASED RISK OF A
DAMAGING FREEZE TO PARTS OF THE SOUTHEAST AND MID-ATLANTIC DUE TO THE EARLY
GREEN UP OF VEGETATION. DURING LATE MARCH, MID-LEVEL LOW PRESSURE IS EXPECTED
TO BECOME MORE CENTERED OVER THE ROCKIES OR GREAT PLAINS. A WET PATTERN IS
LIKELY TO RETURN TO THE GULF COAST AND SOUTHEAST BUT TIMING OF THE HEAVIEST
PRECIPITATION IS UNCERTAIN.
HAZARDS
MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PARTS OF THE LOWER
MISSISSIPPI VALLEY, SOUTHEAST, AND MID-ATLANTIC, WED, MAR 20.
SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PARTS OF THE SOUTHERN GREAT
PLAINS, LOWER MISSISSIPPI VALLEY, SOUTHEAST, OHIO VALLEY, AND MID-ATLANTIC,
WED-THU, MAR 20-21.
SLIGHT RISK OF HIGH WINDS FOR THE NORTHEAST, WED, MAR 20.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PARTS OF THE LOWER MISSISSIPPI VALLEY
AND GULF COAST, THU-TUE, MAR 21-26.
SLIGHT RISK OF HEAVY PRECIPITATION FOR THE EAST COAST, FRI-TUE, MAR 22-26.
SLIGHT RISK OF HEAVY SNOW FOR THE NORTHERN TO CENTRAL ROCKIES, WED-SUN, MAR
20-24.
DETAILED SUMMARY
FOR FRIDAY MARCH 15 - TUESDAY MARCH 19:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY MARCH 20 - TUESDAY MARCH 26: THE MAJOR HAZARD DURING MID TO LATE
MARCH IS THE POTENTIAL FOR A WIDESPREAD FREEZE ACROSS THE SOUTHERN GREAT
PLAINS, SOUTHEAST, AND MID-ATLANTIC. MANY OF THESE AREAS HAVE EXPERIENCED AN
EARLY GREEN UP OF VEGETATION AND THE WARMTH LATER THIS WEEK WILL ACCELERATE THE
GREEN UP AND EXPAND IT NORTHWARD. CHANGES FROM YESTERDAY INCLUDE A DECREASE IN
THE COVERAGE OF THE COLD HAZARD ACROSS THE SOUTHERN GREAT PLAINS AS THE COLDEST
MORNING IS EXPECTED TO BE ON MARCH 19TH, PRIOR TO THE OUTLOOK PERIOD. BASED ON
THE LATEST MODEL GUIDANCE AND CONCERN FOR MORE RAPID VEGETATIVE GROWTH LATER
THIS WEEK, THE MODERATE COLD RISK WAS EXPANDED SLIGHTLY TO INCLUDE MORE OF THE
VIRGINIA PIEDMONT AND SOUTHERN MARYLAND. ON MARCH 20, A MODERATE RISK OF MUCH
BELOW-NORMAL TEMPERATURES IS POSTED FOR PORTIONS OF THE LOWER MISSISSIPPI
VALLEY, SOUTHEAST, AND MID-ATLANTIC WHERE A CONSENSUS BETWEEN THE GEFS AND
ECMWF PROBABILISTIC EXTREMES TOOLS (PETS) DEPICT MINIMUM TEMPERATURES HAVING AT
LEAST A 30 PERCENT CHANCE OF FALLING BELOW FREEZING AND WOULD LIKELY BE MOST
VULNERABLE TO A FREEZE. A BROADER SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES
(MARCH 20-21) EXTENDS CLOSER TO THE GULF COAST WHERE THE PETS HAVE A 20 TO 30
PERCENT CHANCE OF MINIMUM TEMPERATURES FALLING BELOW 40 DEGREES F.
DURING THE EARLY TO MIDDLE PART OF NEXT WEEK, THE GEFS, ECMWF, AND CANADIAN
ENSEMBLE MEANS ARE IN GOOD AGREEMENT AND CONSISTENT THAT A SURFACE LOW PRESSURE
SYSTEM DEEPENS OVER THE CANADIAN MARITIMES. THE STRONG PRESSURE GRADIENT
BETWEEN THIS SURFACE LOW AND A 1024-HPA TO 1032-HPA HIGH OVER THE SOUTH-CENTRAL
CONUS IS LIKELY TO BRING GUSTY WINDS TO THE NORTHEAST. ALTHOUGH THE STRONGEST
WINDS ARE EXPECTED PRIOR TO WEEK-2, A SLIGHT RISK OF HIGH WINDS IS WARRANTED ON
MARCH 20.
THE GEFS, ECMWF, AND CANADIAN ENSEMBLE MEANS DEPICTS A RETROGRESSION OF THE
LONGWAVE PATTERN OVER NORTH AMERICA AND THE NORTH PACIFIC DURING LATE MARCH
WITH AN AMPLIFIED 500-HPA RIDGE (TROUGH) BECOMING CENTERED OVER MAINLAND ALASKA
(WEST-CENTRAL CONUS). THE BROAD TROUGH ALONG WITH ENHANCED MOISTURE IN THE
SOUTHERN STREAM FAVORS A WET PATTERN FOR NEARLY ALL OF THE ENTIRE CONUS. THE
HEAVIEST 7-DAY PRECIPITATION AMOUNTS ARE PREDICTED TO BE ACROSS THE LOWER
MISSISSIPPI VALLEY AND EASTERN CONUS. AS EARLY AS DAY 10 (MARCH 22), THE
ENSEMBLE MEANS DIVERGE ON WHERE THE 500-HPA LONGWAVE TROUGH AXIS BECOMES
ESTABLISHED AND HOW FAST A SOUTHERN STREAM SHORTWAVE TROUGH EJECTS EASTWARD.
THE SLIGHT RISK OF HEAVY PRECIPITATION BEGINS ON MARCH 21 ACROSS THE LOWER
MISSISSIPPI VALLEY AND GULF COAST, WITH THE ECMWF AND CANADIAN ENSEMBLE MEANS
FAVORING AN OVERRUNNING PRECIPITATION EVENT. BY MARCH 22, THE SLIGHT RISK
EXPANDS NORTH TO INCLUDE THE EAST COAST. SINCE THE SOUTHERN STREAM IS LIKELY TO
REMAIN ACTIVE BEYOND THE WEEK-2 PERIOD, A SLIGHT RISK OF HEAVY PRECIPITATION IS
VALID THROUGH MARCH 26.
THE BROAD 500-HPA TROUGH ALOFT IS EXPECTED TO BRING PERIODS OF ACCUMULATING
SNOW, POTENTIALLY HEAVY, ACROSS THE NORTHERN TO CENTRAL ROCKIES. BASED ON THE
GEFS SWE AND UNCALIBRATED ECMWF MODEL OUTPUT, A SLIGHT RISK OF HEAVY SNOW IS
DESIGNATED FOR THE NORTHERN TO CENTRAL ROCKIES FROM MARCH 20 TO 24. THERE IS
ALSO INCREASED CHANCE OF ACCUMULATING SNOW ACROSS THE UPPER MISSISSIPPI VALLEY
WITH ANY LOW PRESSURE SYSTEM THAT TRACKS THROUGH THIS REGION. HOWEVER, FORECAST
CONFIDENCE IS TOO LOW FOR A HEAVY SNOW HAZARD AT THIS TIME.
THE MID-LEVEL TROUGH WEST OF THE ALEUTIANS COUPLED WITH MID-LEVEL RIDGING OVER
MAINLAND ALASKA IS LIKELY TO RESULT IN ABOVE-NORMAL TEMPERATURES FOR ALL OF
ALASKA. ALTHOUGH ABOVE-NORMAL PRECIPITATION IS FAVORED ACROSS WESTERN ALASKA,
PRECIPITATION AMOUNTS ARE EXPECTED TO BE BELOW HAZARDS THRESHOLDS.
FORECASTER: BRAD PUGH
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