442
FXUS21 KWNC 281902
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT APRIL 28 2023
SYNOPSIS: MID-LEVEL LOW PRESSURE IS FORECAST TO BE CENTERED ALONG OR NEAR THE
EAST AND WEST COASTS OF THE CONTIGUOUS U.S. (CONUS) DURING EARLY MAY, WHILE
MID-LEVEL HIGH PRESSURE BECOMES ESTABLISHED OVER THE NORTH-CENTRAL STATES.
MOISTURE STREAMING IN FROM THE EASTERN PACIFIC MAY RESULT IN HEAVY SNOWFALL FOR
THE SIERRA NEVADA MOUNTAINS. COOLER-THAN-NORMAL TEMPERATURES ARE FORECAST TO
PERSIST ACROSS MUCH OF THE EASTERN CONUS THROUGH EARLY MAY. SPRINGTIME
FLOODING, ASSOCIATED WITH SNOWMELT, IS LIKELY TO PERSIST ACROSS PARTS OF THE
WEST, ALONG WITH THE RED RIVER OF THE NORTH, JAMES RIVER, AND UPPER TO MIDDLE
MISSISSIPPI RIVER. SURFACE HIGH PRESSURE TO THE NORTHEAST OF ALASKA FAVORS NEAR
TO BELOW-NORMAL TEMPERATURES FOR ALASKA.
HAZARDS
SLIGHT RISK OF HEAVY SNOW FOR THE SIERRA NEVADA MOUNTAINS, SAT-FRI, MAY 6-12.
SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR THE EASTERN CORN BELT, UPPER
OHIO VALLEY, AND CENTRAL TO SOUTHERN APPALACHIANS, SAT-TUE, MAY 6-9.
POSSIBLE FLOODING FOR PORTIONS OF CALIFORNIA, IDAHO, NEVADA, WYOMING AND UTAH.
POSSIBLE FLOODING ALONG PORTIONS OF THE RED RIVER OF THE NORTH, JAMES RIVER,
MISSISSIPPI RIVER, AND THE MINNESOTA RIVER.
DETAILED SUMMARY
FOR MONDAY MAY 01 - FRIDAY MAY 05:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SATURDAY MAY 06 - FRIDAY MAY 12: THE RECENT WARMUP ACROSS THE WEST HAS LED
TO MORE SNOWMELT, ELEVATED FLOWS ALONG STREAMS AND RIVERS, AND INCREASED THE
FLOODING RISK FOR PARTS OF CALIFORNIA, NEVADA, IDAHO, AND UTAH. THE AREA OF
POSSIBLE FLOODING HAS BEEN EXPANDED ACROSS SOUTHEASTERN IDAHO AND MUCH OF
WESTERN WYOMING, DUE TO AN EXPECTED WARM-UP BEFORE AND DURING WEEK-2. THE LARGE
AREA OF POSSIBLE FLOODING ACROSS PORTIONS OF THE WEST IS ANTICIPATED TO PERSIST
WELL INTO MAY. THE LONG-WAVE TROUGH PREDICTED NEAR THE WEST COAST COULD ALSO
BRING HEAVY SNOW TO THE HIGHER ELEVATIONS OF THE SIERRAS DURING WEEK-2. A
SLIGHT RISK OF HEAVY SNOW IS ISSUED OVER THE HIGHER ELEVATIONS OF CALIFORNIA
WHERE REFORECAST TOOLS INDICATE INCREASED CHANCES FOR 3-DAY AMOUNTS EXCEEDING
THE 85TH PERCENTILE AND 1 INCH. IN ADDITION TO WARMER TEMPERATURES FAVORED,
RAIN FALLING ON MELTING SPRING SNOWPACK FURTHER INCREASES THE RISK OF FLOODING
OVER SATURATED AREAS.
SINCE LEVELS ALONG THE RED RIVER OF THE NORTH AT AND TO THE SOUTH OF GRAND
FORKS, NORTH DAKOTA, ARE FORECAST TO DECREASE FROM MODERATE TO MINOR FLOOD
STAGE, THE SOUTHERN EXTENT OF THE POSSIBLE FLOODING SHAPE WAS REMOVED
YESTERDAY. HOWEVER, POSSIBLE FLOODING REMAINS TO THE NORTH OF GRAND FORKS ALONG
WITH THE JAMES RIVER IN SOUTH DAKOTA. MODERATE TO MAJOR FLOODING IS FORECAST TO
PERSIST WELL INTO MAY ALONG THE BANKS OF THE UPPER TO MIDDLE MISSISSIPPI RIVER.
THE GFS AND ECMWF ENSEMBLE MEANS DEPICT A PERSISTENT LONG-WAVE TROUGH NEAR THE
EAST COAST THROUGH THE SECOND WEEK OF MAY WHICH IS LIKELY TO DELAY ANY
SIGNIFICANT WARMING TREND EAST OF THE MISSISSIPPI RIVER. A SLIGHT RISK OF MUCH
BELOW-NORMAL TEMPERATURES (MAY 6-9) IS MAINTAINED FOR PARTS OF THE EAST-CENTRAL
CONUS WHERE THE GEFS AND ECMWF REFORECAST TOOLS DEPICT MINIMUM TEMPERATURES
HAVING AT LEAST A 20% CHANCE OF FALLING BELOW THE 15TH PERCENTILE AND 40
DEGREES F.
THIRTY-DAY PRECIPITATION DEFICITS EXCEED 2 INCHES ACROSS MUCH OF MISSOURI,
SOUTHEASTERN IOWA, AND PARTS OF CENTRAL ILLINOIS. AS SEASONAL TEMPERATURES AND
EVAPOTRANSPIRATION RATES INCREASE LATER IN MAY, THESE ANTECEDENT DRY AREAS WILL
BE VULNERABLE TO THE RAPID ONSET OF DROUGHT. GIVEN THE LIKELIHOOD FOR
BELOW-NORMAL PRECIPITATION DURING THE NEXT TWO WEEKS, A RAPID ONSET DROUGHT
HAZARD MAY BE NECESSARY FOR THIS REGION IN SUBSEQUENT OUTLOOKS.
FORECASTER: ANTHONY ARTUSA
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