341
FXUS21 KWNC 171929
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT APRIL 17 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 DURING THE MIDDLE OF THE WEEK-2 PERIOD. POSSIBLE
FLOODING REMAINS A CONCERN FOR PORTIONS OF CALIFORNIA AND NEVADA AS WELL AS THE
UPPER MISSISSIPPI VALLEY AS SNOWMELT SEASON CONTINUES. CONTINUED FLOODING IS
ALSO POSSIBLE FOR THE WHITE RIVER IN ARKANSAS, WHERE FLOODING IS CURRENTLY
OCCURRING AND CONTINUED PRECIPITATION IN THE FORECAST FOR BOTH WEEKS 1 AND 2.
HAZARDS
MODERATE RISK FOR MUCH BELOW-NORMAL TEMPERATURES FOR PORTIONS OF THE OHIO AND
TENNESSEE VALLEYS, APPALACHIANS, AND NON-COASTAL MID-ATLANTIC AND SOUTHEAST
U.S., TUE, APR 25.
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., TUE-THU, APR 25-27.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE LOWER AND MIDDLE
MISSISSIPPI VALLEY, TENNESSEE VALLEY, AND SOUTHEAST U.S., THU-SAT, APR 27-29.
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 WATERWAYS IN THE UPPER PENINSULA OF MICHIGAN AND
NORTHERN WISCONSIN.
POSSIBLE FLOODING ALONG THE WHITE RIVER IN ARKANSAS.
DETAILED SUMMARY
FOR THURSDAY APRIL 20 - MONDAY APRIL 24:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY APRIL 25 - MONDAY MAY 01: 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 OVER THE EASTERN GREAT LAKES, WITH BROAD SURFACE HIGH PRESSURE SETTLING IN
OVER THE EASTERN CONUS, RESULTING IN A LATE-SEASON COLD SNAP WITH THE POTENTIAL
TO IMPACT EMERGING OR COLD-INTOLERANT VEGETATION. BOTH THE GEFS AND ECMWF
REFORECAST TOOLS INDICATE AT LEAST A 40% PROBABILITY OF LOW TEMPERATURES
FALLING BELOW THE 15TH PERCENTILE AND BELOW FREEZING FOR PORTIONS OF THE
MID-ATLANTIC, APPALACHIANS, OHIO AND TENNESSEE VALLEYS, AND THE SOUTHEAST U.S.
FOR APR 25, AND AT LEAST A 20% PROBABILITY AND LOW TEMPERATURES BELOW 40
DEGREES FOR AFOREMENTIONED AREAS PLUS THE LOWER AND MIDDLE MISSISSIPPI VALLEY
FOR APR 25-27, THEREFORE A MODERATE AND SLIGHT RISK, RESPECTIVELY, 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
PERCENTILE AND 1 INCH TOTAL FOR 3-DAY PRECIPITATION FOR MUCH OF ARKANSAS,
ALABAMA, AND MISSISSIPPI, AND ADJACENT STATES 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 BECOMING FOCUSED NEAR THE
MAJOR RIVER BASINS, INCLUDING THE RED RIVER OF THE NORTH, MISSISSIPPI RIVER,
JAMES RIVER, THE MINNESOTA RIVER, AND WATERWAYS IN THE UPPER PENINSULA OF
MICHIGAN AND NORTHERN WISCONSIN. 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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