790
FXUS21 KWNC 241851
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT APRIL 24 2023
SYNOPSIS: MID-LEVEL LOW PRESSURE IS PREDICTED ACROSS PORTIONS OF THE WEST COAST
STATES AND SOUTHWEST AND MUCH OF THE EAST DURING WEEK-2, BRINGING ANOMALOUSLY
COOL TEMPERATURES TO THESE REGIONS. AMPLIFIED MID-LEVEL LOW PRESSURE OVER THE
EASTERN CONTIGUOUS U.S. (CONUS) MAY BRING MUCH BELOW NORMAL TEMPERATURES TO
PARTS OF THE EAST WHICH COULD IMPACT VEGETATION. TEMPERATURES ARE ANTICIPATED
TO MODERATE BY THE MIDDLE OF THE PERIOD AS THE MID-LEVEL LOW PRESSURE WEAKENS
AND SHIFTS EASTWARD. SURFACE LOW FORMATION IS POSSIBLE OVER THE LOWER AND
MIDDLE MISSISSIPPI VALLEY BY THE MIDDLE OF WEEK-2, BRINGING UNSETTLED WEATHER
TO PARTS OF THE EAST. SURFACE HIGH PRESSURE OVER PARTS OF ALASKA MAY BRING
ANOMALOUS COLD TO CENTRAL AND SOUTHERN PORTIONS OF THE STATE, ALTHOUGH
TEMPERATURES ARE NOT DEEMED HAZARDOUS.
HAZARDS
MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES ACROSS PARTS OF THE MIDDLE AND
LOWER MISSISSIPPI, OHIO, AND TENNESSEE VALLEYS, AND APPALACHIANS, TUE-WED, MAY
2-3.
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES ACROSS PARTS OF THE CENTRAL AND
EAST, TUE-THU, MAY 2-4.
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 THURSDAY APRIL 27 - MONDAY MAY 01:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY MAY 02 - MONDAY MAY 08: DYNAMICAL MODELS ARE GENERALLY FAVORING A
LESS AMPLIFIED MEAN WEEK-2 MID-LEVEL PATTERN COMPARED TO YESTERDAY. AMPLIFIED
MID-LEVEL TROUGHING IS PREDICTED OVER THE EASTERN CONUS AT THE BEGINNING OF THE
PERIOD, BRINGING ELEVATED CHANCES FOR ANOMALOUS COLD TEMPERATURES TO THE
REGION. A SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES IS HIGHLIGHTED ACROSS
PARTS OF THE EAST, MAY 2-4, WHERE THERE IS GOOD AGREEMENT BETWEEN THE GEFS AND
ECMWF REFORECAST TOOLS INDICATING AT LEAST A 20% CHANCE OF MINIMUM TEMPERATURES
FALLING TO THE LOWEST 15TH PERCENTILE AND BELOW 40 DEG F AND THERE IS
SUSCEPTIBLE VEGETATION TO FREEZES. AN EMBEDDED MODERATE RISK AREA IS DESIGNATED
ACROSS PARTS OF THE MIDDLE AND LOWER MISSISSIPPI, OHIO, AND TENNESSEE VALLEYS,
AND APPALACHIANS, MAR 2-3, WHERE BOTH REFORECAST TOOLS SHOW AT LEAST A 40%
CHANCE OF EXCEEDING THESE THRESHOLDS. THE ECMWF REFORECAST TOOL HAS A STRONGER
SIGNAL FOR THESE ANOMALOUS COLD SIGNALS, WITH BOTH REFORECAST TOOLS INDICATING
THE GREATEST PROBABILITIES FOR REACHING HAZARDOUS THRESHOLDS (> 50% CHANCE)
ACROSS THE TENNESSEE VALLEY AND SOUTHEAST.
POSSIBLE SURFACE LOW FORMATION OVER THE LOWER AND MIDDLE MISSISSIPPI VALLEY
COMBINED WITH MOIST SOUTHERLY FLOW FROM THE GULF OF MEXICO MAY BRING LOCALIZED
HEAVY PRECIPITATION TO PARTS OF THE SOUTHEASTERN QUADRANT OF THE CONUS DURING
THE MIDDLE OF WEEK-2. THE REFORECAST TOOLS ARE IN GOOD AGREEMENT SHOWING AT
LEAST A 20% CHANCE OF 3-DAY PRECIPITATION TOTALS EXCEEDING THE 85TH PERCENTILE,
CLIMATOLOGICALLY, AND ONE INCH DURING DAYS 10-12 (MAY 4-6). HOWEVER, DUE TO
HIGH UNCERTAINTY IN THE DETERMINISTIC AND UNCALIBRATED ENSEMBLE MEANS, A HEAVY
PRECIPITATION HAZARD IS NOT POSTED AT THIS TIME AND WILL BE MONITORED IN THE
UPCOMING DAYS.
WITH ANTICIPATED ANOMALOUS WARMTH DURING WEEK-1 AND SUFFICIENTLY WARM
TEMPERATURES ACROSS THE WEST DURING WEEK-2 TO SUPPORT SNOWMELT, POSSIBLE FLOOD
RISK CONTINUES TO BE DESIGNATED FOR MUCH OF CALIFORNIA AND NEVADA WITH
SIGNIFICANT AMOUNTS OF SNOWPACK REMAINING IN MANY AREAS. ALTHOUGH MUCH OF THE
SNOW COVER HAS MELTED IN THE UPPER MIDWEST, OR WILL BY WEEK-2, MAJOR RIVER
BASINS REMAIN IN FLOOD STAGE DUE TO ANOMALOUSLY HIGH SNOW COVER EARLIER THIS
YEAR, INCLUDING THE RED RIVER OF THE NORTH, MISSISSIPPI RIVER, JAMES RIVER, AND
THE MINNESOTA 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.
SURFACE HIGH PRESSURE IS PREDICTED OVER THE ALASKA MAINLAND, SUPPORTING
INCREASED CHANCES FOR COOLER THAN NORMAL TEMPERATURES ACROSS CENTRAL AND
SOUTHERN MAINLAND AND UPPER PARTS OF THE SOUTHEAST. TEMPERATURES ARE NOT
ANTICIPATED TO REACH HAZARDOUS CRITERIA.
FORECASTER: MELISSA OU
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