734
FXUS21 KWNC 261902
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT APRIL 26 2023
SYNOPSIS: COOLER-THAN-NORMAL TEMPERATURES ARE FORECAST TO PERSIST ACROSS THE
EASTERN CONTIGUOUS U.S. (CONUS) THROUGH AT LEAST THE FIRST WEEK OF 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, NEVADA, IDAHO, AND UTAH.
SURFACE HIGH PRESSURE IS FORECAST TO STRENGTHEN TO THE NORTHEAST OF ALASKA,
RESULTING IN NEAR TO BELOW-NORMAL TEMPERATURES FOR MUCH OF THE STATE.
HAZARDS
MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES ACROSS THE UPPER OHIO VALLEY
ALONG WITH THE CENTRAL TO SOUTHERN APPALACHIANS, THU, MAY 4.
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES ACROSS PARTS OF THE EASTERN AND
CENTRAL U.S., THU-SAT, MAY 4-6.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PARTS OF THE SOUTHERN GREAT PLAINS AND
LOWER MISSISSIPPI VALLEY, THU-MON, MAY 4-8.
SLIGHT RISK OF HEAVY SNOW FOR THE SIERRA NEVADA MOUNTAINS, THU-WED, MAY 4-10.
POSSIBLE FLOODING FOR PORTIONS OF CALIFORNIA, IDAHO, NEVADA, AND UTAH.
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 29 - WEDNESDAY MAY 03:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY MAY 04 - WEDNESDAY MAY 10: 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 EASTERN CONUS INTO THE BEGINNING OF
WEEK-2. ON MAY 4, MODEL CONTINUITY AND THE TEMPERATURE TOOLS CONTINUE TO
SUPPORT A MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES ACROSS THE UPPER 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 4-6) COVERS MORE OF
THE CORN BELT AND THE PIEDMONT AREAS OF THE MID-ATLANTIC AND SOUTHEAST. UNLIKE
YESTERDAY, THE GEFS AND ECMWF ENSEMBLE MEANS ARE MAINTAINING AN AMPLIFIED
500-HPA TROUGH ALONG THE EAST COAST FOR A LONGER TIME WHICH COULD CONTINUE
BELOW-NORMAL TEMPERATURES FOR PARTS OF THE EASTERN CONUS INTO THE SECOND WEEK
OF MAY.
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. THIS ANOMALOUS
TROUGH COULD RESULT IN PERIODS OF SNOW ACROSS THE HIGHER ELEVATIONS OF THE
SIERRA NEVADA MOUNTAINS. ALTHOUGH THE LATEST DETERMINISTIC GFS MODEL RUNS HAVE
BACKED OFF SNOWFALL AMOUNTS, A SLIGHT RISK OF HEAVY SNOW IS MAINTAINED FOR
CONTINUITY. DESPITE THE STRONG LIKELIHOOD FOR ABOVE-NORMAL PRECIPITATION ACROSS
CALIFORNIA AND THE GREAT BASIN FROM MAY 4 TO 10, RAINFALL AMOUNTS ARE EXPECTED
TO REMAIN BELOW HAZARDS THRESHOLDS. DOWNSTREAM OF THE LONGWAVE TROUGH AXIS
ALONG THE WEST COAST, THERE IS AN INCREASING CHANCE OF SHORTWAVE TROUGHS TO
EJECT EASTWARD ACROSS THE SOUTHERN TIER OF THE CONUS. THESE SHORTWAVE TROUGHS,
RETURN FLOW FROM THE GULF OF MEXICO, AND REFORECAST PRECIPITATION TOOLS SUPPORT
A SLIGHT RISK OF HEAVY PRECIPITATION ACROSS PARTS OF THE SOUTHERN GREAT PLAINS
AND LOWER MISSISSIPPI VALLEY FROM MAY 4 TO 8.
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. THE
POSSIBLE FLOOD RISK AREA IS EXPANDED TO INCLUDE SOUTHEASTERN IDAHO AND THE
WASATCH MOUNTAINS OF UTAH AS SIGNIFICANT RISES ON STREAMS AND RIVERS IN THESE
AREAS ARE ANTICIPATED HEADING INTO EARLY MAY. 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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