885
FXUS21 KWNC 181844
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT APRIL 18 2023
SYNOPSIS: A LOW PRESSURE SYSTEM AND ASSOCIATED COLD FRONT IS ANTICIPATED TO
MOVE ACROSS THE CONTIGUOUS U.S. (CONUS) DURING THE WEEK-1 TIME PERIOD, USHERING
IN A SHORT-LIVED ROUND OF POTENTIALLY IMPACTFUL BELOW-NORMAL TEMPERATURES.
MOIST RETURN FLOW OFF THE GULF OF MEXICO IS FAVORED TO DEVELOP IN THE WAKE OF
FRONTAL PASSAGE, RESULTING IN A CHANCE FOR HEAVY PRECIPITATION FOR PORTIONS OF
THE LOWER MISSISSIPPI VALLEY AND SOUTHEAST U.S. EARLY IN THE FORECAST PERIOD.
POSSIBLE FLOODING REMAINS A CONCERN FOR PORTIONS OF CALIFORNIA AND NEVADA AS
WELL AS THE UPPER MISSISSIPPI VALLEY WHERE SNOWMELT SEASON CONTINUES. CONTINUED
FLOODING IS ALSO POSSIBLE FOR THE WHITE RIVER IN ARKANSAS, WHERE FLOODING IS
CURRENTLY OCCURRING AND ADDITIONAL PRECIPITATION IS FORECAST FOR BOTH WEEKS 1
AND 2.
HAZARDS
SLIGHT RISK FOR MUCH BELOW-NORMAL TEMPERATURES FOR PORTIONS OF THE LOWER AND
MIDDLE MISSISSIPPI, OHIO, AND TENNESSEE VALLEYS, APPALACHIANS, AND NON-COASTAL
MID-ATLANTIC AND SOUTHEAST U.S., WED, APR 26.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE LOWER AND MIDDLE
MISSISSIPPI VALLEY, TENNESSEE VALLEY, AND SOUTHEAST U.S., WED-SAT, APR 26-29.
POSSIBLE FLOODING FOR MOST OF CALIFORNIA AND NEVADA.
POSSIBLE FLOODING FOR PARTS OF NORTHERN MONTANA.
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 FRIDAY APRIL 21 - TUESDAY APRIL 25:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY APRIL 26 - TUESDAY MAY 02: MODEL ENSEMBLES CONTINUE TO DEPICT A
MID-LEVEL TROUGH MOVING QUICKLY ACROSS THE WESTERN AND CENTRAL CONUS DURING THE
WEEK-1 TIME PERIOD. BY THE OUTSET OF WEEK-2 MODEL CONSENSUS PLACES THE TROUGH
AXIS OUT OVER THE ATLANTIC OCEAN, WITH SURFACE HIGH PRESSURE MOVING OFF THE
EAST COAST AS WELL, BUT THE POTENTIAL FOR IMPACTFULLY BELOW-NORMAL LOW
TEMPERATURES REMAINS. BOTH THE GEFS AND ECMWF REFORECAST TOOLS INDICATE AT
LEAST A 20% PROBABILITY OF TEMPERATURES FALLING BELOW THE 15TH CLIMATOLOGICAL
PERCENTILE AND BELOW FREEZING FOR PORTIONS OF THE MID-ATLANTIC, APPALACHIANS,
OHIO AND TENNESSEE VALLEYS FOR APR 26, THEREFORE A SLIGHT RISK FOR MUCH
BELOW-NORMAL TEMPERATURES IS POSTED FOR THESE REGIONS.
AS THE HIGH PRESSURE BRINGING THIS IMPACTFUL COLD SHIFTS OFFSHORE OF THE
SOUTHEASTERN CONUS, MODEL SOLUTIONS FAVOR THE DEVELOPMENT OF MEAN LOW PRESSURE
IN THE LEE OF THE ROCKIES, WHICH SETS UP MOIST RETURN FLOW OFF THE GULF OF
MEXICO, BRINGING THE POTENTIAL FOR ENHANCED PRECIPITATION OVER THE MISSISSIPPI
VALLEY. A SLIGHT RISK FOR HEAVY PRECIPITATION IS POSTED WHERE THE GEFS AND
ECMWF REFORECAST TOOLS BOTH INDICATE A 20% PROBABILITY OF EXCEEDING THE 85TH
CLIMATOLOGICAL PERCENTILE AND 1 INCH TOTAL FOR 3-DAY PRECIPITATION FOR PORTIONS
OF THE TENNESSEE AND LOWER MISSISSIPPI VALLEYS AS WELL AS PARTS OF THE
SOUTHEAST U.S. FOR APR 27-29.
ABOVE NORMAL TEMPERATURES ARE SLIGHTLY 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: DANNY BARANDIARAN
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