763
FXUS21 KWNC 281835
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JULY 28 2023
SYNOPSIS: A HEAT WAVE IS EXPECTED TO BECOME FOCUSED OVER THE SOUTH-CENTRAL U.S.
FROM AUGUST 5-7, AS A STRONG MID-LEVEL RIDGE BUILDS ACROSS THIS REGION.
ANTECEDENT DRYNESS COUPLED WITH LITTLE TO NO RAINFALL AND ABOVE-NORMAL
TEMPERATURES THROUGH AT LEAST EARLY AUGUST SUPPORTS A RAPID ONSET DROUGHT RISK
ACROSS PARTS OF THE LOWER MISSISSIPPI VALLEY, SOUTHERN GREAT PLAINS, RIO GRANDE
VALLEY, AND NEW MEXICO. THE EAST PACIFIC IS FORECAST TO BECOME MORE ACTIVE WITH
TROPICAL CYCLONES DURING EARLY AUGUST.
HAZARDS
HIGH RISK OF EXCESSIVE HEAT FOR PARTS OF THE LOWER MISSISSIPPI VALLEY AND
SOUTHERN GREAT PLAINS, SAT-SUN, AUG 5-6.
MODERATE RISK OF EXCESSIVE HEAT FOR MUCH OF THE LOWER MISSISSIPPI VALLEY,
SOUTHERN GREAT PLAINS, AND RIO GRANDE VALLEY, SAT-MON, AUG 5-7.
MODERATE RISK OF EXCESSIVE HEAT FOR PARTS OF ARIZONA, SAT-MON, AUG 5-7.
SLIGHT RISK OF EXCESSIVE HEAT FOR MUCH OF THE SOUTHERN U.S., SAT-FRI, AUG 5-11.
SLIGHT RISK OF EXCESSIVE HEAT FOR PARTS OF THE INTERMOUNTAIN WEST, SAT-SUN, AUG
5-6.
SLIGHT RISK OF HEAVY PRECIPITATION FOR THE SOUTHEAST AND SOUTHERN MID-ATLANTIC,
SAT-TUE, AUG 5-8.
SLIGHT RISK OF HEAVY PRECIPITATION FOR THE CENTRAL GREAT PLAINS AND MIDDLE
MISSISSIPPI VALLEY, SAT-FRI, AUG 5-11.
RAPID ONSET DROUGHT RISK ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY, GREAT
PLAINS, AND SOUTHWEST.
DETAILED SUMMARY
FOR MONDAY JULY 31 - FRIDAY AUGUST 04:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SATURDAY AUGUST 05 - FRIDAY AUGUST 11: GFS, ECMWF, AND CANADIAN ENSEMBLE
MEAN SOLUTIONS DEPICT AN AMPLIFYING TROUGH OVER THE EAST FROM AUGUST 5 TO 11,
WITH THE ANOMALOUS 500-HPA RIDGE (HEIGHTS > 594-DM) BECOMING CENTERED OVER THE
SOUTH-CENTRAL AND SOUTHWESTERN CONUS. THIS EVOLVING LONGWAVE PATTERN IS LIKELY
TO RESULT IN MODERATING TEMPERATURES ACROSS THE SOUTHEAST, WHILE AN EXCESSIVE
HEAT RISK REMAINS ELEVATED (> 40% CHANCE) FROM THE LOWER MISSISSIPPI VALLEY
WESTWARD TO THE SOUTHWEST. BASED ON THE GEFS AND ECMWF PROBABILISTIC EXTREMES
TOOLS (PETS) AND GEFS/ECMWF SKILL WEIGHTED HEAT INDEX FORECAST, A HIGH RISK (>
60 PERCENT CHANCE) OF EXCESSIVE HEAT IS POSTED FOR THE LOWER MISSISSIPPI
VALLEY, WESTERN GULF COAST, AND SOUTHERN GREAT PLAINS ON AUGUST 5 AND 6. A
MODERATE RISK (> 40 PERCENT CHANCE) AREA IS SUPPORTED BY THE TOOLS AND COVERS A
MORE EXPANSIVE AREA OF THE SOUTH-CENTRAL CONUS THROUGH AUGUST 7. WITHIN THE
HIGH AND MODERATE RISK AREAS FOR EXCESSIVE HEAT, DAILY MAXIMUM HEAT INDEX (HI)
VALUES ARE LIKELY TO EXCEED 105 DEGREES F WITH AN INCREASED POTENTIAL FOR HI
VALUES TO REACH 110 DEGREES F. ALTHOUGH A SLIGHT RISK OF EXCESSIVE HEAT IS
DESIGNATED DURING THE ENTIRETY OF WEEK-2 FOR NEARLY THE ENTIRE SOUTHERN CONUS,
LATER IN WEEK-2 THE MOST ANOMALOUS HEAT IS EXPECTED TO BE CENTERED ACROSS THE
RIO GRANDE VALLEY AND SOUTHERN GREAT PLAINS GIVEN THE PREDICTED LOCATION OF THE
RIDGE ALOFT.
DURING EARLY AUGUST, THE ENSEMBLE MEANS DEPICT 500-HPA HEIGHTS INCREASING
THROUGHOUT THE SOUTHWEST WITH THE PETS SUPPORTING A MODERATE RISK OF EXCESSIVE
HEAT ACROSS PARTS OF ARIZONA FROM AUGUST 5 TO 7. THE MODERATE RISK COINCIDES
WITH WHERE THE PETS DEPICT MAXIMUM TEMPERATURES HAVING AT LEAST A 40 PERCENT
CHANCE OF EXCEEDING THE 85TH PERCENTILE. THE PERSISTENT RIDGING WITH
ABOVE-NORMAL HEIGHTS SUPPORTS A SLIGHT RISK CONTINUING THROUGH AUGUST 11 ACROSS
THE SOUTHWEST. FARTHER TO THE NORTH ACROSS PARTS OF THE INTERMOUNTAIN WEST, A
SLIGHT RISK OF EXCESSIVE HEAT IS POSTED ON AUGUST 5 AND 6 WHEN THE GEFS AND
ECMWF PETS INDICATE AT LEAST A 20 PERCENT CHANCE OF MAXIMUM TEMPERATURES
EXCEEDING THE 85TH PERCENTILE AND 95 DEGREES F.
AN AMPLIFYING MID-LEVEL TROUGH ACROSS THE EASTERN CONUS SUPPORTS A SLIGHT RISK
OF HEAVY PRECIPITATION FOR THE CAROLINAS AND GEORGIA (AUGUST 5-8), WHERE THE
ECMWF REFORECAST TOOL SHOWS AT LEAST A 20 PERCENT CHANCE OF 3-DAY PRECIPITATION
AMOUNTS EXCEEDING THE 85TH PERCENTILE AND ONE INCH. TO THE NORTH OF THE
ANOMALOUS RIDGE OVER THE SOUTH-CENTRAL U.S., MID-LEVEL SHORTWAVE TROUGHS IN
NORTHWEST FLOW ALOFT ARE EXPECTED TO PROMOTE MESOSCALE CONVECTIVE SYSTEMS FROM
THE CENTRAL HIGH PLAINS SOUTHEASTWARD TO THE MIDDLE MISSISSIPPI VALLEY. A BROAD
AREA IS HIGHLIGHTED WITH A SLIGHT RISK OF HEAVY PRECIPITATION GIVEN THE
UNCERTAINTY ON WHERE THESE MCSS DEVELOP AND TRACK AT THE WEEK-2 TIME SCALE.
WITHIN THESE SLIGHT RISK AREAS, ANY SLOW-MOVING THUNDERSTORMS WITH LOCALLY
HEAVY RAINFALL MAY CAUSE FLASH FLOODING.
RAPID ONSET DROUGHT (ROD) RISK IS HIGH ACROSS PARTS OF THE LOWER MISSISSIPPI
VALLEY, TEXAS, AND SOUTHERN NEW MEXICO DUE TO THE COMBINATION OF INCREASING
30-DAY PRECIPITATION DEFICITS, LITTLE TO NO RAINFALL DURING THE NEXT TWO WEEKS,
AND LIKELIHOOD FOR A PROLONGED PERIOD OF HIGH EVAPOTRANSPIRATION RATES
ASSOCIATED WITH MUCH ABOVE-NORMAL TEMPERATURES. A ROD RISK IS ALSO POSTED FOR
PARTS OF NORTH DAKOTA WHERE 30-DAY PRECIPITATION DEFICITS ARE NEAR TWO INCHES,
BUT FORECAST CONFIDENCE IS LOWER FOR THIS REGION AS THERE COULD BE AN INCREASE
IN MUCH-NEEDED RAINFALL BY EARLY TO MID-AUGUST.
THE GFS AND ECMWF DETERMINISTIC MODELS AND THEIR ENSEMBLE MEANS DEPICT A COUPLE
OF TROPICAL CYCLONES (TCS) DEVELOPING ACROSS THE EAST PACIFIC DURING EARLY
AUGUST. IF ONE OF THESE TCS TRACK NORTHWESTWARD, THEN THERE WOULD BE AN
INCREASED CHANCE OF A NORTHWARD SURGE OF MOISTURE FROM THE GULF OF CALIFORNIA
INTO THE WEST. THIS MAY EVENTUALLY LEAD TO A GREATER RISK OF THUNDERSTORMS
ACROSS THE GREAT BASIN AND INTERMOUNTAIN WEST.
ALTHOUGH ANOMALOUS RIDGING AND ABOVE-NORMAL TEMPERATURES ARE FAVORED FOR
ALASKA, MAXIMUM TEMPERATURES ARE LIKELY TO REMAIN BELOW HAZARDS THRESHOLDS.
FORECASTER: BRAD PUGH
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