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FXUS21 KWNC 121817
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT APRIL 12 2024
SYNOPSIS: DYNAMICAL MODELS HAVE COME INTO AGREEMENT FOR AN AREA OF STRONG
MID-LEVEL LOW PRESSURE OVER THE NORTHEASTERN CONUS AND SOUTHEASTERN CANADA
EARLY IN THE WEEK-2 PERIOD. SURFACE HIGH PRESSURE IS FORECAST TO PROGRESS INTO
THE EASTERN CONUS FROM CANADA EARLY IN THE PERIOD. THIS PATTERN WOULD SUPPORT
MUCH BELOW NORMAL TEMPERATURES EARLY IN THE PERIOD THAT MAY DAMAGE SENSITIVE
VEGETATION. THE MID-LEVEL LOW WOULD ALSO SUPPORT INCREASED CHANCES FOR HIGH
WINDS OVER THE NORTHEASTERN CONUS. IN THE SOUTH, CHANCES FOR HEAVY
PRECIPITATION REMAIN ELEVATED ACROSS PORTIONS OF THE SOUTHERN PLAINS, LOWER
MISSISSIPPI VALLEY AND SOUTHEAST WHILE FLOODING REMAINS POSSIBLE IN PARTS OF
THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY.
HAZARDS
MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE OHIO,
TENNESSEE, AND MIDDLE MISSISSIPPI VALLEYS, GREAT LAKES, CENTRAL AND SOUTHERN
APPALACHIANS, AND MID-ATLANTIC, SAT-MON, APR 20-22.
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE CENTRAL
PLAINS, MISSISSIPPI, TENNESSEE, AND OHIO VALLEYS, GREAT LAKES, CENTRAL AND
SOUTHERN APPALACHIANS, MID-ATLANTIC, AND NORTHEAST, SAT-TUE, APR 20-23.
SLIGHT RISK OF HIGH WINDS ACROSS PORTIONS OF THE GREAT LAKES, NORTHEAST, AND
MID-ATLANTIC, SAT-SUN, APR 20-21.
SLIGHT RISK OF HEAVY PRECIPITATION ACROSS PORTIONS OF THE SOUTHERN PLAINS AND
LOWER MISSISSIPPI VALLEY, SAT-SUN, APR 20-21.
POSSIBLE FLOODING ACROSS PORTIONS OF NORTHEASTERN TEXAS AND MUCH OF THE LOWER
MISSISSIPPI VALLEY.
DETAILED SUMMARY
FOR MONDAY APRIL 15 - FRIDAY APRIL 19:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SATURDAY APRIL 20 - FRIDAY APRIL 26: OVER THE PAST SEVERAL RUNS OF THE
DYNAMICAL MODEL TOOLS, THERE HAS BEEN A RAPID CHANGE IN THE FORECAST FOR THE
BEGINNING OF THE WEEK-2 PERIOD. THERE IS NOW GOOD AGREEMENT FOR AN AREA OF
DEEPLY NEGATIVE 500-HPA HEIGHT ANOMALIES OVER THE NORTHEASTERN CONUS AND
SOUTHEASTERN CANADA RELATIVE TO POSITIVE 500-HPA ANOMALIES FORECAST FOR THIS
TIME PERIOD A FEW DAYS AGO. AS THIS MID-LEVEL LOW PRESSURE PROGRESSES EAST,
NORTHERLY MID-LEVEL AND SURFACE FLOW IS FORECAST. AN AREA OF SURFACE HIGH
PRESSURE IS ALSO FORECAST TO DESCEND OUT OF CANADA TOWARDS THE OHIO VALLEY
EARLY IN WEEK-2. THIS PATTERN WOULD INCREASE CHANCES FOR FROST OR FREEZING
TEMPERATURES OVER MUCH OF THE EASTERN CONUS.
THE PROBABILISTIC EXTREMES TOOLS (PETS) FROM THE GEFS AND ECENS ARE IN GOOD
AGREEMENT FOR AT LEAST A 30% CHANCE FOR TEMPERATURES TO FALL BELOW THE 15TH
CLIMATOLOGICAL PERCENTILE OVER MUCH OF THE EASTERN CONUS. THE PETS ALSO
INDICATE AT LEAST A 40% CHANCE OF TEMPERATURES FALLING BELOW 40 DEG F. AS FAR
SOUTH AS THE TENNESSEE VALLEY, EAST TO THE SHENANDOAH VALLEY, AND WEST TOWARDS
KANSAS CITY. FURTHER NORTH, THE PETS INDICATE AT LEAST A 20% CHANCE FOR BELOW
FREEZING TEMPERATURES EXTENDING TO THE OHIO RIVER. THESE TEMPERATURES WOULD
SUPPORT A RISK OF FROST AND FREEZE THAT COULD IMPACT SENSITIVE VEGETATION IN
THESE REGIONS PARTICULARLY IN LOW-LYING PLACES. THE MIDWEST REGIONAL CLIMATE
CENTER (MRCC) INDICATES THAT THERE IS SENSITIVE VEGETATION THROUGHOUT THE OHIO
VALLEY AND SOUTH. FURTHER, WEEK-1 IS FORECAST TO BE WARMER AND WETTER ACROSS
THESE REGIONS AND WOULD SUPPORT THE CONTINUED EXPANSION OF SENSITIVE VEGETATION
BY THE BEGINNING OF WEEK-2. THE COLD SURFACE HIGH PRESSURE IS FORECAST TO
REMAIN IN PLACE OVER THE EASTERN CONUS UNTIL THE MIDDLE OF THE WEEK-2 PERIOD.
THEREFORE, A MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES IS POSTED FOR
APRIL 20-22 FOR THE OHIO, TENNESSEE, AND MIDDLE MISSISSIPPI VALLEYS, GREAT
LAKES, CENTRAL AND SOUTHERN APPALACHIANS, AND THE MID-ATLANTIC. A BROADER
SLIGHT RISK RUNS THROUGH APRIL 23 FOR PORTIONS OF THE CENTRAL PLAINS,
MISSISSIPPI, TENNESSEE, AND OHIO VALLEYS, GREAT LAKES, CENTRAL AND SOUTHERN
APPALACHIANS, MID-ATLANTIC, AND NORTHEAST. FOLLOWING THIS SHOT OF COLD AIR,
TEMPERATURES ARE LIKELY TO MODERATE BY THE MIDDLE TO END OF THE WEEK-2 PERIOD
AS SURFACE HIGH PRESSURE SHIFTS EASTWARD OVER THE WESTERN ATLANTIC OCEAN.
ASSOCIATED WITH THE MID-LEVEL LOW PRESSURE ACROSS THE NORTHEASTERN CONUS, AN
AREA OF HIGH WINDS MAY IMPACT PARTS OF THE REGION. THE ECENS PET SUPPORTS THIS
POTENTIAL INDICATING AT LEAST A 20% CHANCE OF WINDS EXCEEDING THE 85TH
PERCENTILE. THEREFORE, A SLIGHT RISK OF HIGH WINDS IS POSTED FOR PARTS OF THE
GREAT LAKES, NORTHEAST, AND MID-ATLANTIC FOR APRIL 20-21.
DUE TO THE RECENT FORECAST CHANGES FROM THE DYNAMICAL TOOLS, THE RISK OF HEAVY
PRECIPITATION IS MUCH REDUCED RELATIVE TO PRIOR FORECASTS. THE HIGHEST CHANCES
FOR HEAVY PRECIPITATION ARE ACROSS PARTS OF THE SOUTHERN PLAINS AND LOWER
MISSISSIPPI VALLEY. IN THESE REGIONS, THE PETS CONTINUE TO PREDICT AT LEAST A
20% CHANCE OF THREE DAY PRECIPITATION TOTALS EXCEEDING THE 85TH PERCENTILE AND
1 INCH. THEREFORE, A SLIGHT RISK OF HEAVY PRECIPITATION IS POSTED FOR APRIL
20-21 FOR THESE AREAS. THIS REGION HAS ALSO SEEN A SIGNIFICANT AMOUNT OF
PRECIPITATION OVER THE PAST FEW WEEKS. SOILS REMAIN QUITE SATURATED AND ANY
ADDITIONAL PRECIPITATION WOULD LIKELY INDUCE AT LEAST MINOR FLOODING.
THEREFORE, A FLOODING POSSIBLE SHAPE REMAINS IN PLACE ACROSS PARTS OF EASTERN
TEXAS, LOUISIANA AND SOUTHERN ARKANSAS.
ACROSS ALASKA, THE WEEK-2 MEAN PATTERN IS PREDICTED TO START WITH POSITIVE
500-HPA HEIGHT ANOMALIES, WITH INCREASING NORTHERLY FLOW AND TROUGHING
EXTENDING SOUTHWARD FROM THE ARCTIC FAVORING INCREASED CHANCES FOR BELOW-NORMAL
TEMPERATURES. SURFACE LOW FORMATION IS POSSIBLE OVER THE GULF OF ALASKA DURING
WEEK-2, ALTHOUGH THIS IS NOT ANTICIPATED TO SUPPORT ANY HAZARDS AT THIS TIME.
FORECASTER: RYAN BOLT
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