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FXUS21 KWNC 271821
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JULY 27 2023
SYNOPSIS: A HEAT WAVE IS EXPECTED TO PERSIST ACROSS THE LOWER MISSISSIPPI
VALLEY AND SOUTHEAST THROUGH EARLY WEEK-2 BEFORE TEMPERATURES BEGIN TO
MODERATE. A MID-LEVEL RIDGE IS FORECAST TO STRENGTHEN OVER THE WEST DURING THE
FIRST WEEK OF AUGUST, LEADING TO AN INCREASING CHANCE OF EXCESSIVE HEAT FOR
PARTS OF THIS REGION. ANTECEDENT DRYNESS, LITTLE TO NO RAINFALL DURING THE NEXT
WEEK, AND THE LIKELIHOOD OF ABOVE-NORMAL TEMPERATURES THROUGH AT LEAST EARLY
AUGUST SUPPORTS A RAPID ONSET DROUGHT RISK ACROSS PARTS OF THE LOWER
MISSISSIPPI VALLEY, GREAT PLAINS, AND NEW MEXICO.
HAZARDS
HIGH RISK OF EXCESSIVE HEAT FOR PARTS OF THE SOUTHEAST, LOWER MISSISSIPPI
VALLEY, AND EASTERN TEXAS, FRI-SAT, AUG 4-5.
MODERATE RISK OF EXCESSIVE HEAT FOR MUCH OF THE SOUTHEAST, LOWER MISSISSIPPI
VALLEY, AND SOUTHERN GREAT PLAINS, FRI-SUN, AUG 4-6.
MODERATE RISK OF EXCESSIVE HEAT FOR PARTS OF ARIZONA, FRI-TUE, AUG 4-8.
SLIGHT RISK OF EXCESSIVE HEAT FOR MUCH OF THE SOUTHERN AND WESTERN U.S.,
FRI-THU, AUG 4-10.
SLIGHT RISK OF HEAVY PRECIPITATION FOR THE NORTHEAST AND MID-ATLANTIC, FRI-SAT,
AUG 4-5.
SLIGHT RISK OF HEAVY PRECIPITATION FOR THE SOUTHEAST AND SOUTHERN MID-ATLANTIC,
FRI-TUE, AUG 4-8.
RAPID ONSET DROUGHT RISK ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY, GREAT
PLAINS, AND SOUTHWEST.
DETAILED SUMMARY
FOR SUNDAY JULY 30 - THURSDAY AUGUST 03:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY AUGUST 04 - THURSDAY AUGUST 10: GFS, ECMWF, AND CANADIAN ENSEMBLE
MEAN SOLUTIONS DEPICT A BROAD ANOMALOUS 500-HPA RIDGE WITH HEIGHTS EXCEEDING
594-DM FROM THE SOUTHERN GREAT PLAINS EASTWARD ACROSS THE LOWER MISSISSIPPI
VALLEY AND GULF COAST STATES THROUGH AUGUST 6. THE MODEL TREND SINCE YESTERDAY
IS FOR A DELAY IN THE WEAKENING OF THIS RIDGE ACROSS THE SOUTHEAST WITH SIGNS
THAT THE HEAT WAVE MAY BE LONGER IN DURATION DURING THE FIRST WEEK OF AUGUST.
BASED ON THIS MODEL TREND ALONG WITH GUIDANCE FROM THE GEFS AND ECMWF
PROBABILISTIC EXTREMES TOOLS (PETS) AND AN UNCALIBRATED GEFS/ECMWF SKILL
WEIGHTED HEAT INDEX FORECAST, A HIGH RISK (60 PERCENT CHANCE) OF EXCESSIVE HEAT
IS POSTED FOR EASTERN TEXAS, THE LOWER MISSISSIPPI VALLEY, AND PARTS OF THE
SOUTHEAST ON AUGUST 4 AND 5. A MODERATE RISK (40 PERCENT CHANCE) AREA IS
SUPPORTED BY THE TOOLS AND COVERS A MORE EXPANSIVE AREA OF THE SOUTH-CENTRAL
AND SOUTHEASTERN CONUS THROUGH AUGUST 6. 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 VALID DURING THE
ENTIRETY OF WEEK-2 FOR THE NEARLY THE ENTIRE SOUTHERN CONUS, TOOLS DEPICT A
MODERATION IN TEMPERATURES ACROSS THE SOUTHEAST LATER IN WEEK-2.
DURING EARLY AUGUST, THE ENSEMBLE MEANS ARE IN GOOD AGREEMENT AND CONSISTENT
THAT 500-HPA HEIGHTS INCREASE THROUGHOUT THE WEST WITH THE PETS SUPPORTING A
BROAD SLIGHT RISK OF EXCESSIVE HEAT ACROSS THE SOUTHWEST, GREAT BASIN, AND
PARTS OF THE PACIFIC NORTHWEST. A MODERATE RISK (AUG 4-8) IS POSTED FOR AREAS
OF ARIZONA WHERE THE PETS DEPICT MAXIMUM TEMPERATURES HAVING NEAR A 40 PERCENT
CHANCE OF EXCEEDING THE 85TH PERCENTILE. THIS INCLUSION OF A MODERATE RISK IS
ALSO CONSISTENT WITH A SUPPRESSED MONSOON.
AN AMPLIFYING TROUGH RESULTS IN A SLIGHT RISK OF HEAVY PRECIPITATION FOR MUCH
OF THE EAST COAST (AUGUST 4-8), WHERE THE ECMWF REFORECAST TOOL HAS AT LEAST A
20 PERCENT CHANCE OF 3-DAY PRECIPITATION AMOUNTS EXCEEDING THE 85TH PERCENTILE
AND ONE INCH. ANY SLOW-MOVING THUNDERSTORMS WITH LOCALLY HEAVY RAINFALL MAY
CAUSE FLASH FLOODING. THIS HEAVY PRECIPITATION HAZARD IS FORECAST TO SHIFT
SOUTHWARD WITH TIME FROM THE NORTHEAST AND MID-ATLANTIC TO THE SOUTHEAST,
TIMING OFF IN THE NORTHEAST BY AUGUST 5 AND IN THE SOUTHEAST AND MID-ATLANTIC
BY AUGUST 8.
THE RAPID ONSET DROUGHT (ROD) RISK WAS EXPANDED ACROSS NORTH DAKOTA WHERE
30-DAY PRECIPITATION DEFICITS ARE NEAR 2 INCHES. THE ROD RISK WAS ALSO EXPANDED
ACROSS THE SOUTHERN TIER OF THE CONUS, TO INCLUDE SOUTHERN NEW MEXICO DUE TO A
LACK OF MONSOON RAINFALL DURING JULY. THE LIKELIHOOD OF INADEQUATE
PRECIPITATION AND ABOVE-NORMAL TEMPERATURES DURING THE NEXT TWO WEEKS SUPPORT
AN ELEVATED RISK OF RAPIDLY DEVELOPING DROUGHT FROM SOUTHERN NEW MEXICO
EASTWARD TO TEXAS AND THE LOWER MISSISSIPPI VALLEY. SINCE THE 6-10/8-14 DAY
OUTLOOKS FAVOR ABOVE-NORMAL PRECIPITATION ACROSS WASHINGTON, THE ROD RISK WAS
DISCONTINUED FOR THIS REGION.
AS OF 2PM EDT ON JULY 27, THE NATIONAL HURRICANE CENTER IS MONITORING A
TROPICAL WAVE SOUTHWEST OF THE CABO VERDE ISLANDS AND FORECAST AT LEAST A 40
PERCENT CHANCE OF IT BECOMING A TROPICAL CYCLONE (TC) DURING THE NEXT WEEK.
BASED ON THE AMPLIFIED TROUGH OVER THE WESTERN ATLANTIC, THIS POTENTIAL TC IS
LIKELY TO RECURVE AWAY FROM THE EAST COAST LATE NEXT WEEK, WHICH RECENT MODEL
RUNS CONTINUE TO DEPICT.
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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