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FXUS21 KWNC 132040
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JULY 13 2023
SYNOPSIS: MULTIPLE DYNAMICAL MODEL ENSEMBLE MEANS FAVOR MID-LEVEL HIGH PRESSURE
ACROSS THE WESTERN CONTIGUOUS U.S. (CONUS) AND MUCH OF THE SOUTHERN CONUS
DURING WEEK-2. ACROSS THE EASTERN LOWER 48 STATES, AN APPROACHING AREA OF
MID-LEVEL LOW PRESSURE WILL DISPLACE THE MID-LEVEL HIGH FARTHER TO THE SOUTH
ALONG WITH ANY ACCOMPANYING REGION OF EXCESSIVE HEAT, CONFINING IT PRIMARILY TO
THE GULF COAST AND FLORIDA. DURING THE MIDDLE AND LATTER PORTIONS OF THE WEEK-2
FORECAST PERIOD, THERE ARE INCREASED CHANCES OF EXCESSIVE HEAT OVER THE
NORTHERN HIGH PLAINS. FROM EASTERN TEXAS TO CENTRAL LOUISIANA, ABNORMALLY DRY
CONDITIONS COMBINED WITH EXCESSIVE HEAT INCREASES THE RISK OF RAPID ONSET
DROUGHT (ROD). THE FLOOD RISK INDICATED FOR THE JAMES RIVER IN NORTHEASTERN
SOUTH DAKOTA HAS BEEN REMOVED, AS RIVER STAGE LEVELS ARE EXPECTED TO FALL BELOW
HAZARDOUS THRESHOLDS BEFORE THE BEGINNING OF THE WEEK-2 PERIOD.
HAZARDS
MODERATE RISK OF EXCESSIVE HEAT FOR THE FOUR CORNERS REGION AND SOUTHERN
PLAINS, FRI-SAT, JUL 21-22.
SLIGHT RISK OF EXCESSIVE HEAT FOR THE CENTRAL VALLEY OF CALIFORNIA,
INTERMOUNTAIN WEST, MUCH OF THE ROCKIES, SOUTHERN GREAT PLAINS, LOWER
MISSISSIPPI VALLEY, AND NEAR THE GULF COAST (INCLUDING FLORIDA), FRI-THU, JUL
21-27.
SLIGHT RISK OF EXCESSIVE HEAT FOR THE NORTHERN HIGH PLAINS, SUN-THU, JUL 23-27.
RAPID ONSET DROUGHT RISK FROM PORTIONS OF EASTERN TEXAS TO CENTRAL LOUISIANA.
DETAILED SUMMARY
FOR SUNDAY JULY 16 - THURSDAY JULY 20:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY JULY 21 - THURSDAY JULY 27: THE GFS, ECMWF, AND CANADIAN ENSEMBLE
MEANS PREDICT MID-LEVEL RIDGING OVER THE WESTERN AND MUCH OF THE SOUTHERN CONUS
DURING WEEK-2. AS MID-LEVEL TROUGHING APPROACHES THE APPALACHIANS AND EAST
COAST, 500-HPA HEIGHTS WILL LOWER ACROSS MUCH OF THE EAST, RESULTING IN COOLER
SURFACE TEMPERATURES ACROSS THE REGION. THE AREA OF MID-LEVEL RIDGING AND
ASSOCIATED EXCESSIVE HEAT OVER THE SOUTHEAST AT THE START OF THE PERIOD ARE
EXPECTED TO SHIFT SOUTHWARD, BEING CONFINED LATER IN WEEK-2 PRIMARILY TO THE
GULF COAST AND FLORIDA.
THERE IS A SLIGHT (20%) CHANCE OF EXCESSIVE HEAT FROM THE INTERIOR WEST
EASTWARD ACROSS PORTIONS OF THE ROCKIES, SOUTHERN PLAINS, LOWER MISSISSIPPI
VALLEY, AND SOUTHERN PORTIONS OF THE SOUTHEAST FOR THE WEEK-2 PERIOD, JUL
21-27. THIS IS BASED ON A BROAD CONSENSUS BETWEEN THE ECMWF, GEFS, AND CANADIAN
PROBABILISTIC EXTREMES TOOLS (PET), WHICH PREDICT AT LEAST A 20% CHANCE OF
MAXIMUM TEMPERATURES EXCEEDING THE 85TH CLIMATOLOGICAL PERCENTILE, AND 95 DEG
F. THIS IS ALSO SUPPORTED BY THE CALIBRATED EXCESSIVE HEAT FORECAST TOOL FOR
WEEK-2, WHICH CONSIDERS BOTH AIR (OR DRY-BULB) TEMPERATURE AND HEAT INDEX. AN
IMPORTANT CONSIDERATION IN THE DEEP SOUTH AND FLORIDA IS THE PREDICTED ELEVATED
OVERNIGHT MINIMUM TEMPERATURES IN THE MID TO UPPER 70’S, WHICH DO NOT PERMIT
MUCH RELIEF FROM THE DAYTIME HEAT. FOR CALIFORNIA’S CENTRAL VALLEY, NEAR-RECORD
AND RECORD TEMPERATURES ARE FORECAST IN THE NEXT FEW DAYS, WITH HEAT INDEX
VALUES RANGING FROM 102-110 DEG F. ALTHOUGH A SLIGHT REDUCTION IN TEMPERATURES
(AND THEREFORE MINIMAL RELIEF) IS EXPECTED FOR THIS AREA DURING WEEK-2, THERE
IS NO COMPELLING REASON FOR DROPPING THE SLIGHT RISK POSTED FOR EXCESSIVE HEAT.
FARTHER NORTH, EXCESSIVE HEAT IS EXPECTED OVER THE INTERIOR NORTHWEST, THOUGH
THIS IS LIKELY TO BE INTERRUPTED AT TIMES DUE TO PASSING SHORTWAVE ENERGY AND
FRONTAL SYSTEMS ASSOCIATED WITH A BROAD MID-LEVEL TROUGH FORECAST OVER THE
NORTHEAST PACIFIC/GULF OF ALASKA. WITHIN THE LARGE SLIGHT RISK AREA OF
EXCESSIVE HEAT INDICATED OVER THE WESTERN AND SOUTHERN CONUS, THERE IS A
MODERATE (40%) CHANCE OF EXCESSIVE HEAT ACROSS THE FOUR CORNERS REGION AND
SOUTHERN PLAINS. THIS IS SUPPORTED BY THE PET TOOL, WITH MAXIMUM TEMPERATURES
PREDICTED TO EXCEED THE 85TH CLIMATOLOGICAL PERCENTILE, AND 100 DEG F.
ANTICIPATED HOT, DRY CONDITIONS ACROSS THE SOUTHWESTERN CONUS AND SOUTHERN
PLAINS MAY SUPPORT AN ENHANCED WILDFIRE RISK, ESPECIALLY WHERE THE NATIONAL
INTERAGENCY FIRE CENTER (NIFC) SHOWS A MODERATE RISK OF SIGNIFICANT FIRE
POTENTIAL AND HIGH RISK TRIGGERS BY THE END OF WEEK-1.
OVER THE NORTHERN HIGH PLAINS, A SLIGHT (20%) CHANCE OF EXCESSIVE HEAT IS
INDICATED FOR JUL 23-27, BASED ON THE PET AND CALIBRATED EXCESSIVE HEAT WAVE
TOOL WHICH ALSO TAKES HUMIDITY INTO ACCOUNT. OF THE GFS, ECMWF, AND CANADIAN
ENSEMBLE MEANS, THE GEFS IN PARTICULAR FAVORS AN EXTENSION OF THE EXCESSIVE
HEAT AREA FROM THE SOUTHERN PLAINS INTO THE MIDWEST. RECENTLY, THE GEFS
PREDICTIONS FOR EXCESSIVE HEAT IN THE MIDWEST HAVE NOT VERIFIED, THEREFORE,
THERE IS A GREATER RELIANCE ON THE ECMWF ENSEMBLE, AND NO CORRESPONDING HAZARD
IS POSTED FOR THIS REGION.
THE ELEVATED RISK OF RAPID ONSET DROUGHT DEVELOPMENT IS CONTINUED FOR PARTS OF
EAST TEXAS AND LOUISIANA, DUE TO RECENT (IN SOME CASES RECORD) HEAT IN RECENT
WEEKS AND EXPECTED EXCESSIVE HEAT FORECAST TO PERSIST THROUGH MUCH OF THE
WEEK-2 PERIOD. AS SUCH, A RISK OF RAPID ONSET DROUGHT (ROD) IS MAINTAINED FROM
MUCH OF EASTERN TEXAS TO CENTRAL LOUISIANA.
NO HAZARDS ARE POSTED FOR ALASKA DURING WEEK-2. ABOVE NORMAL TEMPERATURES ARE
FAVORED FOR MOST OF THE MAINLAND, WHILE BELOW NORMAL TEMPERATURES ARE INDICATED
FOR SOUTHEAST ALASKA. FOR MUCH OF CENTRAL AND EASTERN PORTIONS OF ALASKA ABOVE
NORMAL PRECIPITATION IS FAVORED, WITH NEAR NORMAL PRECIPITATION FAVORED
ELSEWHERE.
FORECASTER: ANTHONY ARTUSA
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