916
FXUS21 KWNC 271800
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JUNE 27 2023
SYNOPSIS: THE RECORD-SETTING AND LONG DURATION HEAT WAVE OVER THE SOUTH-CENTRAL
U.S. IS EXPECTED TO EASE NEXT WEEK. HOWEVER, THERE REMAINS AN ELEVATED CHANCE
FOR EXCESSIVE HEAT TO PERSIST INTO EARLY JULY, ESPECIALLY CLOSER TO THE GULF
COAST. LATER IN WEEK-2, THE EXCESSIVE HEAT RISK IS FORECAST TO EXPAND NORTHWARD
AGAIN. SNOWMELT SEASON CONTINUES FOR AREAS 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
SLIGHT RISK OF EXCESSIVE HEAT FOR PARTS OF THE PACIFIC NORTHWEST, WED, JUL 5.
SLIGHT RISK OF EXCESSIVE HEAT FOR THE GULF COAST REGION, RIO GRANDE VALLEY, AND
PARTS OF THE SOUTHWEST, WED-TUE, JUL 5-11.
SLIGHT RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE CENTRAL TO SOUTHERN GREAT
PLAINS AND MIDDLE TO LOWER MISSISSIPPI VALLEY, SAT-TUE, JUL 8-11.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE CENTRAL TO SOUTHERN
GREAT PLAINS, MIDDLE TO LOWER MISSISSIPPI VALLEY, AND OHIO AND TENNESSEE
VALLEYS, WED-SUN, JUL 5-9.
POSSIBLE FLOODING FOR PORTIONS OF CALIFORNIA AND NEVADA.
RAPID ONSET DROUGHT RISK ACROSS PORTIONS OF LOUISIANA AND SOUTHEASTERN TEXAS.
DETAILED SUMMARY
FOR FRIDAY JUNE 30 - TUESDAY JULY 04:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY JULY 05 - TUESDAY JULY 11: THE MAJOR HEAT WAVE OVER THE
SOUTH-CENTRAL U.S. IS FORECAST TO EASE NEXT WEEK WITH THE ENSEMBLE MEANS
DEPICTING 500-HPA HEIGHTS CLOSER TO AVERAGE FROM JULY 5 TO 11. COMPARED TO LATE
JUNE, THIS IS A NOTABLE DECREASE IN 500-HPA HEIGHTS AND WOULD PROVIDE A
MODERATION IN MAXIMUM TEMPERATURES AND HEAT INDEX VALUES. DESPITE THE WEAKER
500-HPA RIDGE, ENSEMBLE MEANS CONTINUE TO FEATURE DAILY MAXIMUM TEMPERATURES
REMAINING SLIGHTLY ABOVE NORMAL ACROSS THIS REGION ALONG WITH AREAS FARTHER
EAST ALONG THE GULF COAST AND FLORIDA. BASED ON REFORECAST TOOLS AND A
CALIBRATED HEAT INDEX TOOL, HEAT ADVISORY CRITERIA IS MOST LIKELY TO BE MET FOR
AREAS CLOSER TO THE GULF COAST REGION WITH A SLIGHT RISK OF EXCESSIVE HEAT
POSTED FOR THE ENTIRETY OF WEEK-2. THE GEFS, ECMWF, AND CMC ENSEMBLE MEANS
REMAIN CONSISTENT THAT THE SUBTROPICAL RIDGE MAY STRENGTHEN DURING THE SECOND
WEEK OF JULY WHICH RESULTS IN A NORTHWARD EXPANSION OF THE SLIGHT RISK AREA TO
KANSAS CITY AND ST LOUIS, BEGINNING ON JULY 8. ANOMALOUS WARMTH IS ALSO LIKELY
TO AFFECT THE MIDWEST AND NORTHEAST THROUGHOUT WEEK-2. HOWEVER, HEAT INDEX
VALUES ARE ANTICIPATED TO REMAIN BELOW EXCESSIVE HEAT THRESHOLDS.
MODEL SOLUTIONS DEPICT ANOMALOUS 500-HPA RIDGING, INITIALLY NEAR THE WEST
COAST, RETROGRADING WESTWARD AT THE BEGINNING OF WEEK-2. AFTER ANOMALOUS HEAT
TO START JULY ACROSS THE WEST, A MODERATION IN TEMPERATURES IS FORECAST LATER
IN WEEK-2. ON JULY 5, A SLIGHT RISK OF EXCESSIVE HEAT IS ONLY POSTED FOR PARTS
OF THE PACIFIC NORTHWEST WHERE THE ECMWF AND GEFS PROBABILISTIC EXTREMES TOOL
(PET) HAVE PROBABILITIES OF MORE THAN 20 PERCENT THAT MAXIMUM TEMPERATURES
EXCEED THE 85TH PERCENTILE AND 90 DEGREES F.
EARLY IN WEEK-2, THE MODEL GUIDANCE DEPICTS AN AMPLIFYING SHORTWAVE TROUGH OVER
THE CENTRAL U.S. WHICH WOULD HELP TO INITIATE SCATTERED CONVECTION WITH LOCALLY
HEAVY RAINFALL FROM THE GREAT PLAINS EASTWARD TO THE OHIO AND TENNESSEE
VALLEYS. BASED ON THE UNCALIBRATED ECMWF MODEL OUTPUT AND PET FROM THE GEFS,
ECMWF, AND CMC, A SLIGHT RISK OF HEAVY PRECIPITATION IS POSTED FOR PARTS OF THE
CENTRAL TO SOUTHERN GREAT PLAINS, MIDDLE TO LOWER MISSISSIPPI VALLEY, AND OHIO
AND TENNESSEE VALLEYS FROM JULY 5 TO 9. A BROAD SLIGHT RISK AREA IS WARRANTED
GIVEN THE UNCERTAINTY ON THE LOCATION OF CONVECTIVE RAINFALL.
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 FAVORS ABOVE-NORMAL PRECIPITATION, LITTLE TO
NO RAINFALL DURING THE NEXT WEEK AND CONTINUED ABOVE-NORMAL TEMPERATURES AND
HIGH EVAPOTRANSPIRATION RATES AT THIS TIME OF YEAR SUPPORT A ROD RISK FOR THIS
REGION..
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 HAZARDOUS
THRESHOLDS.
FORECASTER: BRAD PUGH
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