723
FXUS21 KWNC 261839
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JUNE 26 2023
SYNOPSIS: THE RECORD-SETTING AND LONG DURATION HEAT WAVE OVER THE SOUTH-CENTRAL
U.S. IS FORECAST TO EASE BY NEXT WEEK. THE STRONGEST AREA OF MID-LEVEL HIGH
PRESSURE IS FORECAST TO BE CENTERED NEAR THE WEST COAST BY THE 4TH OF JULY.
THIS WOULD INCREASE THE RISK OF EXCESSIVE HEAT ACROSS MUCH OF THE WEST AT THE
BEGINNING OF JULY. SNOWMELT SEASON CONTINUES FOR ALONG AND NEAR THE SIERRA
NEVADA MOUNTAINS AFTER EXCEPTIONAL SNOWFALL ACCUMULATIONS, LEADING TO THE
CONTINUED POTENTIAL FOR FLOODING, WHILE ABNORMALLY DRY CONDITIONS OVER
LOUISIANA AND TEXAS RESULT IN THE POTENTIAL FOR RAPID ONSET DROUGHT (ROD).
HAZARDS
MODERATE RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE PACIFIC NORTHWEST, TUE, JUL
4.
SLIGHT RISK OF HEAT FOR MUCH OF THE WEST, TUE-WED, JUL 4-5.
SLIGHT RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE CENTRAL TO SOUTHERN PLAINS
AND MIDDLE TO LOWER MISSISSIPPI VALLEY, SAT-MON, JUL 8-10.
SLIGHT RISK OF EXCESSIVE HEAT FOR THE CENTRAL AND SOUTHERN FLORIDA PENINSULA,
TUE-WED, JUL 4-5.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE CENTRAL TO SOUTHERN
GREAT PLAINS, MIDDLE TO LOWER MISSISSIPPI VALLEY, AND TENNESSEE VALLEY,
TUE-SAT, JUL 4-8.
POSSIBLE FLOODING FOR PORTIONS OF CALIFORNIA AND NEVADA.
RAPID ONSET DROUGHT RISK ACROSS PORTIONS OF LOUISIANA AND SOUTHEASTERN TEXAS.
DETAILED SUMMARY
FOR THURSDAY JUNE 29 - MONDAY JULY 03:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY JULY 04 - MONDAY JULY 10: MODEL SOLUTIONS DEPICT ANOMALOUS 500-HPA
RIDGING NEAR THE WEST COAST THROUGH EARLY WEEK-2, FOLLOWED BY A RETROGRESSION
OF THE RIDGE AXIS WELL OFFSHORE BY DAY 10 (JULY 6). THE ECMWF ENSEMBLE MEAN
REMAINS THE MOST BULLISH WITH THE STRENGTH OF THE 500-HPA RIDGE WITH IT PEAKING
IN STRENGTH ON DAYS 6 AND 7, AND DAILY POSITIVE HEIGHT ANOMALIES OF MORE THAN
60 METERS ON DAY 8. A MODERATE RISK OF EXCESSIVE HEAT ON JULY 4 IS POSTED FOR
PARTS OF THE PACIFIC NORTHWEST WHERE THE ECMWF AND CMC PROBABILISTIC EXTREMES
TOOL (PET) HAVE PROBABILITIES OF MORE THAN 30 PERCENT THAT MAXIMUM TEMPERATURES
EXCEED THE 85TH PERCENTILE AND 90 DEGREES F. A BROADER SLIGHT RISK AREA FOR
EXCESSIVE HEAT COVERS MUCH OF THE PACIFIC NORTHWEST, GREAT BASIN, AND
CALIFORNIA WHERE THE PET FROM THE GEFS, ECMWF, AND CMC ALL HAVE A 20 TO 30
PERCENT CHANCE THAT MAXIMUM TEMPERATURES EXCEED THE 85TH PERCENTILE. RECENT
MODEL RUNS HAVE CONTINUED TO FEATURE UNUSUALLY STRONG SUBTROPICAL RIDGING OVER
THE FLORIDA PENINSULA AT LEAST THROUGH THE EARLY PART OF WEEK-2. GIVEN THAT THE
CALIBRATED GEFS/ECMWF SKILL WEIGHTED TOOL DEPICTS A 20 PERCENT CHANCE THAT HEAT
INDEX VALUES EXCEED THE 95TH PERCENTILE, A SLIGHT RISK OF EXCESSIVE HEAT IS
POSTED FOR THE CENTRAL AND SOUTHERN FLORIDA PENINSULA ON JULY 4 AND 5.
ALTHOUGH THE MAJOR HEAT WAVE OVER THE SOUTH-CENTRAL U.S. IS FORECAST TO EASE
NEXT WEEK, ENSEMBLE MEANS FEATURE DAILY MAXIMUM TEMPERATURES REMAINING AT OR
SLIGHTLY ABOVE NORMAL ACROSS THIS REGION. THE ECMWF AND GFS ENSEMBLE MEANS
DEPICT A RESTRENGTHENING OF THE SUBTROPICAL RIDGE OVER THE SOUTH-CENTRAL U.S.
LATER IN WEEK-2. BASED ON PREDICTED 500-HPA HEIGHTS NEARING 592 DAM AND
CALIBRATED HEAT INDEX TOOLS, A SLIGHT RISK OF EXCESSIVE HEAT IS POSTED FOR THE
CENTRAL TO SOUTHERN GREAT PLAINS AND MIDDLE TO LOWER MISSISSIPPI VALLEY FROM
JULY 8 TO 10. ANOMALOUS WARMTH IS ALSO LIKELY TO AFFECT THE MIDWEST AND
NORTHEAST THROUGHOUT WEEK-2. HOWEVER, HEAT INDEX VALUES ARE ANTICIPATED TO
REMAIN BELOW HEAT ADVISORY CRITERIA.
EARLY IN WEEK-2, THE ECMWF ENSEMBLE MEAN DEPICTS AN AMPLIFYING SHORTWAVE TROUGH
OVER THE CENTRAL U.S. WHICH WOULD HELP TO INITIATE SCATTERED CONVECTION WITH
LOCALLY HEAVY RAINFALL ACROSS THE MIDDLE TO LOWER MISSISSIPPI VALLEY, TENNESSEE
VALLEY, AND PARTS OF THE GULF COAST. BASED ON THE UNCALIBRATED ECMWF MODEL
OUTPUT AND PET FROM THE GEFS, ECMWF, AND CMC, A SLIGHT RISK OF HEAVY
PRECIPITATION IS POSTED FOR THESE AREAS FROM JULY 4 TO 8.
ANTECEDENT DRYNESS ALONG WITH THE CONTINUED DRY PATTERN THROUGH THE NEXT WEEK
AND THE ONGOING HEAT WAVE INCREASE THE RISK FOR RAPID ONSET DROUGHT (ROD)
ACROSS PARTS OF LOUISIANA AND SOUTHEASTERN TEXAS. THE AREA OUTLINED IN THE ROD
RISK HAS ONLY RECEIVED ABOUT 25% OF NORMAL PRECIPITATION DURING THE PAST 30
DAYS. ALTHOUGH THE WEEK-2 OUTLOOK SLIGHTLY FAVORS ABOVE-NORMAL PRECIPITATION,
ABOVE-NORMAL TEMPERATURES AND ASSOCIATED HIGH EVAPOTRANSPIRATION RATES AT THIS
TIME OF YEAR SUPPORT A ROD RISK FOR THIS REGION. THE RISK AREA WAS SLIGHTLY
REDUCED TODAY ACROSS NORTH-CENTRAL LOUISIANA AND SOUTHWESTERN MISSISSIPPI AS A
MCS WITH LOCALLY HEAVY RAINFALL TRACKED THROUGH THE MORNING OF JUNE 26TH.
THE LONG SNOWMELT SEASON CONTINUES ACROSS THE WESTERN CONUS AFTER ACCUMULATING
A VERY LARGE AND IN SOME CASES RECORD-BREAKING SNOWPACK, INDUCING RIVER
FLOODING ESPECIALLY ACROSS HIGHER ELEVATIONS FOR SOME AREAS IN THE WEST. AS
SNOWMELT CONTINUES IN PARTS OF THE SIERRA NEVADA MOUNTAINS, FLOODING MAY
CONTINUE TO OCCUR ALONG SOME RIVERS, AND IN AREAS ADJACENT TO THE HIGHER
ELEVATIONS.
THE PERSISTENT 500-HPA TROUGH OVER THE BERING SEA IS LIKELY TO MAINTAIN
WETTER-THAN-NORMAL CONDITIONS ACROSS THE ALEUTIANS AND WESTERN MAINLAND ALASKA
DURING WEEK-2, BUT PRECIPITATION IS EXPECTED TO REMAIN BELOW HAZARDS
THRESHOLDS.
FORECASTER: BRAD PUGH
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