292
FXUS21 KWNC 191831
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT APRIL 19 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 OHIO AND TENNESSEE
VALLEY, SOUTHEAST, MID-ATLANTIC AND NORTHEAST, THU-SAT, APR 27-29.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE KENAI PENINSULA, COPPER
RIVER BASIN, AND SOUTHEAST ALASKA, THU-FRI, APR 27-28
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 SATURDAY APRIL 22 - WEDNESDAY APRIL 26:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY APRIL 27 - WEDNESDAY MAY 03: UNSETTLED WEATHER IS FORECAST ACROSS
PARTS OF THE EASTERN CONUS EARLY IN WEEK-2. DAILY UNCALIBRATED ENSEMBLES SHOW
THE POTENTIAL OF TWO OR MORE SYSTEMS DEVELOPING AND TRACKING ACROSS THE EAST,
AHEAD OF A DEVELOPING 500-HPA TROUGH. 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 LOW
PRESSURE IS THEN FORECAST TO DEVELOP IN THE OHIO VALLEY AND TRACK INTO SOUTHERN
CANADA ENHANCING 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 AT THE
BEGINNING OF THE PERIOD. THEREFORE, THE SLIGHT RISK OF HEAVY PRECIPITATION IS
SHIFTED EAST, RELATIVE TO YESTERDAY, AND EXPANDED NORTH ALONG THE EASTERN
SEABOARD TO INCLUDE MUCH OF THE EAST COAST AND APPALACHIAN MOUNTAINS FOR APR
27-29.
FOLLOWING THESE STORM SYSTEMS, 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 MUCH BELOW
NORMAL 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 AND SOUTHEAST ALASKA.
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. THEREFORE, A SLIGHT RISK
OF HEAVY PRECIPITATION IS POSTED FOR APR 27-28 FROM THE KENAI PENINSULA THROUGH
ALL OF SOUTHEAST ALASKA.
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. SNOW COVER ALSO REMAINS
HIGH ACROSS PORTIONS OF THE UPPER MIDWEST, AND ALTHOUGH SUBSTANTIAL MELTING IS
ONGOING DUE TO A SIGNIFICANT WARM-UP, 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. SPRING MELT FLOODING IS ALSO POSSIBLE OVER PORTIONS OF
MONTANA, ALONG THE MILK 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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