489
FXUS21 KWNC 211844
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT APRIL 21 2023
SYNOPSIS: A FORECAST AMPLIFIED MID-LEVEL PATTERN INCREASES CHANCES FOR HEAVY
PRECIPITATION ACROSS PARTS OF THE NORTHEASTERN 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. THIS AREA OF MID-LEVEL LOW PRESSURE IS
FORECAST TO BRING BELOW-NORMAL TEMPERATURES AND DRIER CONDITIONS TO PARTS OF
THE EASTERN CONUS, ALTHOUGH THESE TEMPERATURES ARE UNLIKELY TO REACH HAZARDOUS
THRESHOLDS. FLOODING CONCERNS CONTINUE FOR PORTIONS OF THE WEST, NORTHERN
PLAINS AND UPPER MISSISSIPPI VALLEY, AND ARKANSAS.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE MID-ATLANTIC AND
NORTHEAST, SAT-SUN, APR 29-30.
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 MONDAY APRIL 24 - FRIDAY APRIL 28:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SATURDAY APRIL 29 - FRIDAY MAY 05: AN AREA OF LOW PRESSURE IS FORECAST TO
DEVELOP IN THE EASTERN CONUS AND BRING CHANCES FOR HEAVY PRECIPITATION TO PARTS
OF THE MID-ATLANTIC AND NORTHEAST EARLY IN THE WEEK-2 PERIOD. THE GEFS AND
ECMWF REFORECAST TOOLS BOTH INDICATE AT LEAST A 20% CHANCE OF 3-DAY ACCUMULATED
PRECIPITATION EXCEEDING THE 85TH CLIMATOLOGICAL PERCENTILE DURING THE FIRST
THREE DAYS OF WEEK-2. IN THE SOUTHEAST, THE HIGHEST CHANCES FOR HEAVY
PRECIPITATION ARE NOW IN THE WEEK-1 PERIOD AS A LOW PRESSURE DISTURBANCE, THAT
MAY BRING HEAVY PRECIPITATION TO THE SOUTHEAST, EXITS OFF THE COAST BY DAY-8.
THEREFORE, THE SLIGHT RISK OF HEAVY PRECIPITATION IS NOW CONFINED TO PARTS OF
THE NORTHEAST AND MID-ATLANTIC FOR APR 29-30. CHANCES FOR HEAVY PRECIPITATION
LINGER ALONG THE EASTERN SEABOARD DURING THE MIDDLE OF THE WEEK-2 PERIOD IN THE
ECMWF REFORECAST TOOL. HOWEVER, THERE IS DISAGREEMENT BETWEEN THE GEFS AND
ECMWF REFORECAST TOOLS REGARDING THE AMOUNT OF PRECIPITATION AND MEETING
HAZARDOUS CRITERIA. THEREFORE, THE PRECIPITATION HAZARD IS LIMITED TO THE FIRST
TWO DAYS OF WEEK-2.
COLDER AND DRIER AIR IS LIKELY IN MUCH OF THE EASTERN CONUS DURING MUCH OF THE
WEEK-2 PERIOD 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, NEGATIVE HEIGHT ANOMALIES OVER THE ALEUTIAN ISLANDS AND AN
ASSOCIATED SURFACE LOW BRING ENHANCED ONSHORE FLOW TO PARTS OF SOUTHERN ALASKA.
THE GEFS AND ECMWF REFORECAST TOOLS SHOW 3-DAY PRECIPITATION TOTALS EXCEEDING
THE 85TH CLIMATOLOGICAL PERCENTILE DURING THE FIRST THREE DAYS OF THE WEEK-2
PERIOD. HOWEVER, UNCALIBRATED ENSEMBLE GUIDANCE SHOWS LOW CHANCES OF TOTAL
PRECIPITATION REACHING HAZARDOUS THRESHOLDS. THEREFORE, NO CORRESPONDING
PRECIPITATION HAZARDS ARE POSTED.
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. ALTHOUGH MUCH OF THE
SNOW COVER HAS MELTED IN THE UPPER MIDWEST, OR WILL BY WEEK-2, MAJOR RIVER
BASINS REMAIN IN FLOOD STAGE DUE TO ANOMALOUSLY HIGH SNOW COVER EARLIER THIS
YEAR, 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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