518
FXUS21 KWNC 251814
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT APRIL 25 2023
SYNOPSIS: COOLER-THAN-NORMAL TEMPERATURES ARE FORECAST TO PERSIST ACROSS THE
EASTERN AND CENTRAL CONTIGUOUS U.S. (CONUS) THROUGH THE FIRST WEEK OF MAY, BUT
TEMPERATURES ARE EXPECTED TO MODERATE BY MID-MAY. AS MID-LEVEL LOW PRESSURE
SHIFTS EASTWARD TO THE WEST COAST, ANOMALOUSLY WET WEATHER IS LIKELY THROUGHOUT
MUCH OF THE WESTERN CONUS. SPRING FLOODING REMAINS A MAJOR CONCERN ALONG THE
RED RIVER OF THE NORTH AND UPPER TO MIDDLE MISSISSIPPI RIVER ALONG WITH PARTS
OF CALIFORNIA AND NEVADA. SURFACE HIGH PRESSURE IS FORECAST TO STRENGTHEN OVER
NORTHERN MAINLAND ALASKA, RESULTING IN NEAR TO BELOW-NORMAL TEMPERATURES FOR
MUCH OF THE STATE.
HAZARDS
MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES ACROSS THE EASTERN CORN BELT,
OHIO VALLEY, AND CENTRAL TO SOUTHERN APPALACHIANS, WED-THU, MAY 3-4.
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES ACROSS PARTS OF THE EASTERN AND
CENTRAL U.S., WED-FRI, MAY 3-5.
SLIGHT RISK OF HEAVY SNOW FOR THE SIERRA NEVADA MOUNTAINS, WED-TUE, MAY 3-9.
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 FRIDAY APRIL 28 - TUESDAY MAY 02:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY MAY 03 - TUESDAY MAY 09: A LARGE-SCALE BLOCKING PATTERN IS
FORECAST TO PERSIST OVER EASTERN NORTH AMERICA AND THE NORTHERN ATLANTIC INTO
THE BEGINNING OF MAY. A HIGHLY AMPLIFIED TROUGH IS FORECAST TO MAINTAIN
BELOW-NORMAL TEMPERATURES ACROSS THE EAST-CENTRAL CONUS INTO WEEK-2, BUT A
MODERATING TREND IS ANTICIPATED LATER IN THIS PERIOD. THIS TEMPERATURE CHANGE
IS RELATED TO THE NEGATIVE NORTH ATLANTIC OSCILLATION (NAO) INDEX GOING TO ZERO
AND THE LONGWAVE PATTERN OVER NORTH AMERICA BECOMING MORE PROGRESSIVE. ON MAY 3
AND 4, MODEL CONTINUITY AND THE TEMPERATURE TOOLS CONTINUE TO SUPPORT A
MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES ACROSS THE OHIO VALLEY AND
CENTRAL TO SOUTHERN APPALACHIANS. THE MODERATE RISK AREA IS POSTED FOR AREAS
WHERE THE GEFS AND ECMWF REFORECAST TOOLS DEPICT MINIMUM TEMPERATURES HAVING
MORE THAN A 40 PERCENT CHANCE OF FALLING INTO THE LOWEST 15TH PERCENTILE AND
BELOW 40 DEGREES F (PROXY FOR FROST). A FROST OR LIGHT FREEZE MAY DAMAGE TENDER
VEGETATION AND THE PERSISTENTLY COOL TEMPERATURES FROM LATE APRIL INTO THE
BEGINNING OF MAY COULD DELAY SPRING PLANTING ACROSS THE CORN BELT. A BROADER
SLIGHT RISK FOR MUCH BELOW NORMAL TEMPERATURES (MAY 3-5) COVERS MORE OF THE
CORN BELT AND THE PIEDMONT AREAS OF THE MID-ATLANTIC AND SOUTHEAST.
A RELATIVELY WET START TO MAY IS LIKELY THROUGHOUT MUCH OF THE WEST AS AN
AMPLIFIED TROUGH PERSISTS NEAR THE WEST COAST DURING WEEK-2. DECREASING 500-HPA
HEIGHTS, ASSOCIATED WITH THIS TROUGH, ALONG WITH SNOWFALL AMOUNTS FROM RECENT
DETERMINISTIC GFS MODEL RUNS SUPPORT A SLIGHT RISK OF HEAVY SNOW FOR THE SIERRA
NEVADA MOUNTAINS. BASED ON THE GFS, ECMWF, AND CANADIAN ENSEMBLE MEANS
DEPICTING A PERSISTENT TROUGH NEAR THE WEST COAST, THIS SLIGHT RISK OF HEAVY
SNOW EXTENDS THROUGH THE ENTIRETY OF WEEK-2. DESPITE THE STRONG LIKELIHOOD FOR
ABOVE-NORMAL PRECIPITATION ACROSS CALIFORNIA AND THE GREAT BASIN FROM MAY 3 TO
9, RAINFALL AMOUNTS ARE EXPECTED TO REMAIN BELOW HAZARDS THRESHOLDS. WITH
ANOMALOUS WARMTH DURING THE FINAL WEEK OF APRIL AND SUFFICIENTLY WARM
TEMPERATURES ACROSS THE WEST DURING WEEK-2 TO SUPPORT SNOWMELT, A POSSIBLE
FLOOD RISK CONTINUES TO BE DESIGNATED FOR MUCH OF CALIFORNIA AND NEVADA.
POSSIBLE FLOODING REMAINS DESIGNATED FOR THE RED RIVER OF THE NORTH, UPPER TO
MIDDLE MISSISSIPPI RIVER, JAMES RIVER, AND THE MINNESOTA RIVER. FINALLY,
FLOODING CURRENTLY OCCURRING ALONG THE WHITE RIVER IN ARKANSAS IS FORECAST TO
CONTINUE DUE TO HEAVY RAINFALL PRECEDING WEEK-2.
FORECASTER: BRAD PUGH
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