159
FXUS21 KWNC 111802
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT APRIL 11 2024
SYNOPSIS: MID-LEVEL LOW PRESSURE IS FORECAST ACROSS THE NORTH-CENTRAL
CONTIGUOUS U.S. (CONUS) EARLY IN WEEK-2. WHILE CHANCES FOR FRONTALLY FOCUSED
PRECIPITATION ARE STILL ELEVATED OVER PORTIONS OF THE EAST-CENTRAL CONUS AT THE
OUTSET OF THE PERIOD, CONFIDENCE DECREASES THEREAFTER AS MODELS DIFFER IN THE
AMPLITUDE OF THE MID-LEVEL LOW AND RESULTANT FLOW PATTERN ACROSS THE EAST. A
MORE SOUTHWESTERLY FLOW PATTERN WOULD ENHANCE PRECIPITATION CHANCES ACROSS MUCH
OF THE EAST, WHILE A MORE AMPLIFIED MID-LEVEL LOW AND RESULTANT INCREASED
NORTHERLY FLOW MAY LIMIT THE GREATEST PRECIPITATION POTENTIAL TO THE GULF
COAST. AS SURFACE HIGH PRESSURE BUILDS SOUTHWARD EARLY IN WEEK-2, ELEVATED WIND
SPEEDS ARE POSSIBLE ALONG ITS PERIPHERY, INCLUDING OVER THE UPPER MISSISSIPPI
VALLEY, GREAT LAKES, SOUTHWEST, AND CENTRAL AND SOUTHERN ROCKIES AND HIGH
PLAINS, WITH UPSLOPE SNOW REMAINING POSSIBLE ACROSS THE CENTRAL ROCKIES.
HAZARDS
MODERATE RISK OF HEAVY PRECIPITATION ACROSS PORTIONS OF THE SOUTHERN PLAINS AND
LOWER AND MIDDLE MISSISSIPPI AND TENNESSEE VALLEYS, FRI, APR 19.
SLIGHT RISK OF HEAVY PRECIPITATION ACROSS PORTIONS OF THE SOUTHERN PLAINS,
LOWER AND MIDDLE MISSISSIPPI, OHIO, AND TENNESSEE VALLEYS, GREAT LAKES,
MID-ATLANTIC, AND NORTHEAST, FRI-SUN, APR 19-21.
SLIGHT RISK OF HEAVY SNOW ACROSS PORTIONS OF THE CENTRAL ROCKIES, FRI, APR 19.
SLIGHT RISK OF HIGH WINDS ACROSS PORTIONS OF THE SOUTHWEST, CENTRAL AND
SOUTHERN ROCKIES, AND CENTRAL AND SOUTHERN HIGH PLAINS, FRI, APR 19.
SLIGHT RISK OF HIGH WINDS ACROSS PORTIONS OF THE NORTHERN PLAINS, UPPER
MISSISSIPPI VALLEY, AND GREAT LAKES, FRI, APR 19.
POSSIBLE FLOODING ACROSS PORTIONS OF NORTHEASTERN TEXAS, EXTREME SOUTHEASTERN
OKLAHOMA, AND MUCH OF THE LOWER MISSISSIPPI VALLEY.
DETAILED SUMMARY
FOR SUNDAY APRIL 14 - THURSDAY APRIL 18:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY APRIL 19 - THURSDAY APRIL 25: AT THE END OF WEEK-1 AND INTO THE
OUTSET OF WEEK-2, THE 0Z GEFS AND ECMWF INDICATE TROUGHING MOVING ACROSS THE
NORTH-CENTRAL CONUS, WITH SURFACE LOW PRESSURE TRACKING INTO EASTERN CANADA.
THE 0Z CANADIAN IS QUICK TO WEAKEN THIS TROUGH AND DEPICTS A STRONGER RIDGE
ACROSS THE EAST EARLY IN WEEK-2, WHILE THE 0Z GEFS DEPICTS A MORE AMPLIFIED
TROUGH ACROSS THE REGION. THE ECMWF IS IN BETWEEN THE TWO EXTREMES, BUT LEANS
MORE ON THE CANADIAN GIVEN ITS DEPICTION OF A WEAKER TROUGH, AND THE 12Z GEFS
HAS TRENDED LESS AMPLIFIED WITH THE TROUGHING COMPARED TO THE 0Z RUN. THE MODEL
DIFFERENCES REDUCE FORECAST CONFIDENCE AS THE AMPLITUDE OF TROUGHING OVER THE
NORTHEAST WILL DICTATE THE SENSIBLE WEATHER. THE ECMWF/CANADIAN SOLUTION WITH A
WEAKER TROUGH WOULD PROMOTE MORE SOUTHERLY FLOW AND AN ENHANCEMENT OF
PRECIPITATION CHANCES ACROSS MUCH OF THE EAST EARLY IN WEEK-2. HOWEVER, THE
MORE AMPLIFIED 0Z GEFS SOLUTION WOULD RESULT IN MORE NORTHERLY FLOW AND A
SOUTHWARD EXTENSION OF SURFACE HIGH PRESSURE, THUS REDUCING PRECIPITATION
CHANCES.
THE ECMWF PROBABILISTIC EXTREMES TOOL (PET) CONTINUES TO DEPICT AT LEAST A 20
PERCENT CHANCE 3-DAY PRECIPITATION EXCEEDS THE 85TH CLIMATOLOGICAL PERCENTILE
AND 1-INCH ACROSS MUCH OF THE EAST-CENTRAL CONUS, WITH THE GEFS PET CONFINING
THESE ELEVATED PROBABILITIES TO THE CENTRAL GULF OF MEXICO COAST. THESE
DIFFERENCES ARE ALSO REFLECTED IN THE UNCALIBRATED GUIDANCE, WITH THE 0Z ECMWF
SHOWING AN EXPANSIVE REGION WITH 24-HOUR PRECIPITATION TOTALS ABOVE A HALF-INCH
ON DAY-8, AND AT LEAST A 20 PERCENT CHANCE FOR EXCEEDING 1-INCH OVER SOME
AREAS. GIVEN THIS, ALONG WITH AN UPTICK IN PRECIPITATION TOTALS IN THE 12Z
GEFS, THE MODERATE RISK FOR HEAVY PRECIPITATION REMAINS IN PLACE FOR DAY-8 (APR
19) ACROSS PORTIONS OF THE SOUTHERN PLAINS AND LOWER AND MIDDLE MISSISSIPPI AND
TENNESSEE VALLEYS, WITH THE POTENTIAL FOR THUNDERSTORMS TO ENHANCE
PRECIPITATION TOTALS LOCALLY. THE SLIGHT RISK EXTENDS FARTHER NORTH INTO THE
OHIO VALLEY AND ALONG THE EASTERN SEABOARD THROUGH APR 21 TO ACCOUNT FOR THE
WETTER ECMWF AND CANADIAN SOLUTIONS. A POSSIBLE FLOOD RISK AREA IS DESIGNATED
FOR PARTS OF NORTHEASTERN TEXAS, EXTREME SOUTHEASTERN OKLAHOMA, AND MUCH OF THE
LOWER MISSISSIPPI VALLEY DUE TO ANTECEDENT WET CONDITIONS ANTICIPATED DURING
WEEK-1 AND POTENTIAL FOR ADDITIONAL HEAVY PRECIPITATION DURING WEEK-2, WHERE
THERE ARE SOME LOCATIONS ALREADY EXPERIENCING FLOOD CONDITIONS.
INCREASED NORTH TO NORTHWESTERLY WINDS ARE POSSIBLE ACROSS THE NORTHERN TIER IN
THE WAKE OF THE DEPARTING SURFACE LOW, WITH A SLIGHT RISK OF HIGH WINDS POSTED
ACROSS PORTIONS OF THE NORTHERN PLAINS, UPPER MISSISSIPPI VALLEY, AND GREAT
LAKES, APR 19. THE GEFS DEPICTION OF A STRONGER TROUGH ACROSS THE NORTHEAST
WOULD ALSO FAVOR INCREASED WIND SPEEDS IN THAT REGION, BUT HOLDING OFF ON
EXPANDING THE HAZARD DUE TO THE DIFFERING FLOW PATTERN IN THE ECMWF AND
CANADIAN ENSEMBLES. SURFACE HIGH PRESSURE BUILDING SOUTHWARD OUT OF CANADA
FAVORS A TIGHT PRESSURE GRADIENT ACROSS THE SOUTHWEST AND THE CENTRAL AND
SOUTHERN ROCKIES AND HIGH PLAINS, WHERE ANOTHER SLIGHT RISK FOR HIGH WINDS IS
HIGHLIGHTED APR 19. THIS MAY ALSO LEAD TO CONTINUED CHANCES FOR UPSLOPE SNOW
ACROSS THE CENTRAL ROCKIES, WITH THE UNCALIBRATED 0Z ECMWF CONTINUING TO
SUPPORT A SLIGHT RISK FOR HEAVY SNOW OVER THE REGION APR 19. ADDITIONALLY, THE
NATIONAL INTERAGENCY FIRE CENTER (NIFC) INDICATES THE GREATEST POTENTIAL FOR
WILDFIRES FOR DAY-7 ACROSS MUCH OF THE FOUR CORNERS AND SOUTHERN PLAINS, AND
THIS SHOULD PERSIST INTO WEEK-2 GIVEN THE CONTINUED POTENTIAL FOR INCREASED
WIND SPEEDS AND LITTLE PRECIPITATION.
A PERIOD OF BELOW-NORMAL TEMPERATURES IS POSSIBLE ACROSS PARTS OF THE GREAT
BASIN, ROCKIES, AND NORTHERN PLAINS EARLY IN THE PERIOD, WITH SOME SPORADIC
AREAS OF MIXED VEGETATION SUSCEPTIBILITY NOTED ACROSS PARTS OF UTAH AND
COLORADO. SUBFREEZING TEMPERATURES ARE POSSIBLE ACROSS THESE AREAS, BUT THE
THREAT OF ANY WIDESPREAD IMPACTS IS MARGINAL, THUS NO RELATED HAZARD IS POSTED.
BY THE MIDDLE OF WEEK-2, THIS ANOMALOUS COLD MAY SHIFT ACROSS PARTS OF THE
EASTERN CONUS, WITH THE GEFS PET INDICATING A MORE EXPANSIVE REGION OF 20
PERCENT OR GREATER CHANCES FOR MINIMUM TEMPERATURES FALLING BELOW THE 15TH
CLIMATOLOGICAL PERCENTILE COMPARED TO THE ECMWF PET. THE GEFS DEPICTION WOULD
POSSIBLY RESULT IN SOME VEGETATION CONCERNS ACROSS THE OHIO VALLEY WITH
TEMPERATURES DROPPING INTO THE 30S DEG F. HOWEVER, NO HAZARD IS ISSUED DUE TO
THE RELATIVELY WARMER ECMWF SOLUTION ACROSS THIS REGION.
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: THOMAS COLLOW
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