951
FXUS21 KWNC 201827
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT APRIL 20 2023
SYNOPSIS: A FORECAST AMPLIFIED MID-LEVEL PATTERN INCREASES CHANCES FOR HEAVY
PRECIPITATION ACROSS PARTS OF THE EASTERN CONTIGUOUS UNITED STATES (CONUS)
EARLY IN THE WEEK-2 PERIOD AS A STORM SYSTEM TRACKS THROUGH THE REGION AHEAD OF
AN AREA OF MID-LEVEL LOW PRESSURE. MEANWHILE, SURFACE LOW-PRESSURE IN THE GULF
OF ALASKA INCREASES CHANCES FOR HEAVY PRECIPITATION FOR PARTS OF SOUTHERN
ALASKA. FLOODING CONCERNS DUE TO SNOWMELT CONTINUE FOR PORTIONS OF THE WEST,
NORTHERN PLAINS AND UPPER MISSISSIPPI VALLEY, AND ARKANSAS.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHEAST, MID-ATLANTIC,
APPALACHIAN MOUNTAINS, AND NORTHEAST, FRI-SUN, APR 28-30.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE KENAI PENINSULA AND
COPPER RIVER BASIN IN ALASKA, FRI, APR 28.
POSSIBLE FLOODING FOR MOST OF CALIFORNIA AND NEVADA.
POSSIBLE FLOODING ALONG PORTIONS OF THE RED RIVER OF THE NORTH, JAMES RIVER,
MISSISSIPPI RIVER, AND THE MINNESOTA RIVER.
POSSIBLE FLOODING ALONG THE WHITE RIVER IN ARKANSAS.
DETAILED SUMMARY
FOR SUNDAY APRIL 23 - THURSDAY APRIL 27:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY APRIL 28 - THURSDAY MAY 04: UNSETTLED WEATHER IS FORECAST ACROSS
PARTS OF THE EASTERN CONUS EARLY IN WEEK-2. DAILY UNCALIBRATED ENSEMBLES SHOW
THE POTENTIAL FOR COASTAL LOW DEVELOPMENT AND TRACKING UP THE EAST COAST AHEAD
OF A DEVELOPING 500-HPA TROUGH AT THE END OF WEEK-1 AND INTO WEEK-2. THE FIRST
SYSTEM, WHICH IS ANTICIPATED TO CONTINUE FROM THE END OF WEEK-1 INTO THE OUTSET
OF WEEK-2, INCREASES CHANCES FOR HEAVY PRECIPITATION ACROSS MUCH OF THE
SOUTHEASTERN CONUS. A SECONDARY AREA OF LOW PRESSURE IS THEN FORECAST TO
DEVELOP AND BRING CHANCES FOR HEAVY PRECIPITATION TO THE MID-ATLANTIC AND
NORTHEAST. THE GEFS AND ECMWF REFORECAST TOOLS BOTH INDICATE AT LEAST A 20%
CHANCE OF 3-DAY ACCUMULATED PRECIPITATION EXCEEDING THE 85TH CLIMATOLOGICAL
PERCENTILE WITH LOCALIZED AREAS EXCEEDING AN INCH OF PRECIPITATION. THEREFORE,
THE SLIGHT RISK OF HEAVY PRECIPITATION IS LARGELY MAINTAINED FROM YESTERDAY AND
INCLUDES MUCH OF THE EAST COAST AND APPALACHIAN MOUNTAINS FOR APR 28-30. DURING
THE MIDDLE OF WEEK-2 PRECIPITATION CHANCES LINGER ALONG THE EASTERN SEABOARD.
HOWEVER, THERE IS DISAGREEMENT BETWEEN THE GEFS AND ECMWF REFORECAST TOOLS
REGARDING THE AMOUNT OF PRECIPITATION AND MEETING HAZARDOUS CRITERIA.
THEREFORE, THE PRECIPITATION HAZARD REMAINS LIMITED TO THE FIRST THREE DAYS OF
WEEK-2.
COLDER AND DRIER AIR IS LIKELY TO MOVE INTO MUCH OF THE EASTERN CONUS
ASSOCIATED WITH STRENGTHENING NEGATIVE 500-HPA HEIGHT ANOMALIES. REFORECAST
TOOLS INDICATE AT LEAST A 20% CHANCE OF MINIMUM TEMPERATURES FALLING BELOW THE
15TH CLIMATOLOGICAL PERCENTILE. HOWEVER, DUE TO THE UNCALIBRATED ENSEMBLE
GUIDANCE SHOWING LIMITED SUPPORT FOR TEMPERATURES FALLING BELOW 40 DEG F ACROSS
REGIONS WITH SENSITIVE VEGETATION, NO CORRESPONDING TEMPERATURE HAZARDS ARE
POSTED.
FOR ALASKA, A SURFACE LOW OVER THE GULF OF ALASKA IS ANTICIPATED TO BRING
ENHANCED ONSHORE FLOW TO PARTS OF THE SOUTHERN MAINLAND. THE GEFS AND ECMWF
REFORECAST TOOLS SHOW 3-DAY PRECIPITATION TOTALS EXCEEDING THE 85TH
CLIMATOLOGICAL PERCENTILE AND ONE INCH DURING THE FIRST THREE DAYS OF THE
WEEK-2 PERIOD. UNCALIBRATED ENSEMBLE GUIDANCE SHOWS THIS EVENT IS LIKELY TO BE
ONGOING FROM THE END OF WEEK-1 INTO WEEK-2, POTENTIALLY BRINGING CLOSE TO THREE
INCHES OF PRECIPITATION OVER A THREE DAY PERIOD BEGINNING LATE IN WEEK-1 AND
ENDING ON DAY 8. THEREFORE, A SLIGHT RISK OF HEAVY PRECIPITATION IS POSTED FOR
APR 28 FROM THE KENAI PENINSULA THROUGH THE COPPER RIVER BASIN.
ABOVE NORMAL TEMPERATURES ARE FAVORED FOR THE INTERIOR WESTERN CONUS DURING
WEEK-2. WITH AN EXCEPTIONAL SNOWPACK TO MELT THROUGH, THERE CONTINUES TO BE A
POSSIBLE FLOOD RISK FOR MOST OF CALIFORNIA AND NEVADA. LINGERING SNOW COVER
REMAINS ACROSS PORTIONS OF THE UPPER MIDWEST, AND ALTHOUGH SUBSTANTIAL MELTING
IS ONGOING, MELTING IS FORECAST TO CONTINUE DURING WEEK-2 WITH THE FLOODING
POTENTIAL FOCUSED NEAR THE MAJOR RIVER BASINS, INCLUDING THE RED RIVER OF THE
NORTH, MISSISSIPPI RIVER, JAMES RIVER, AND THE MINNESOTA RIVER. FINALLY,
FLOODING CURRENTLY OCCURRING ALONG THE WHITE RIVER IN ARKANSAS IS FORECAST TO
CONTINUE INTO WEEK-2 DUE TO ONGOING RAINFALL DURING WEEKS 1 AND 2.
FORECASTER: RYAN BOLT
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