597
FXUS21 KWNC 281831
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JUNE 28 2023
SYNOPSIS: THE ELEVATED RISK OF EXCESSIVE HEAT THROUGHOUT THE SOUTHERN TIER OF
THE U.S. IS EXPECTED TO WANE WITH MORE MID-LEVEL LOW PRESSURE FAVORED OVER THE
CENTRAL CONTIGUOUS U.S. (CONUS) EARLY IN THE PERIOD. HOWEVER, EXCESSIVE HEAT
POTENTIAL LOOKS TO RETURN ACROSS PARTS OF THE SOUTHERN U.S. TIED TO A
REBUILDING SUBTROPICAL RIDGE FAVORED LATER IN THE PERIOD. FORECAST FRONTAL
ACTIVITY IS EXPECTED TO PROMOTE AN INCREASED RISK OF HEAVY PRECIPITATION FROM
THE GREAT PLAINS TO THE OHIO VALLEY. 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 PORTIONS OF THE SOUTHWEST, SOUTHERN PLAINS,
AND LOWER MISSISSIPPI VALLEY, SAT-WED, JUL 8-12.
SLIGHT RISK OF EXCESSIVE HEAT FOR PARTS OF THE PACIFIC NORTHWEST, THU-SUN, JUL
6-9.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE GREAT PLAINS,
MISSISSIPPI, TENNESSEE AND OHIO VALLEYS, GREAT LAKES, AND SOUTHEAST, THU-SUN,
JUL 6-9.
POSSIBLE FLOODING FOR PORTIONS OF CALIFORNIA AND NEVADA.
RAPID ONSET DROUGHT RISK ACROSS PORTIONS OF LOUISIANA AND SOUTHEASTERN TEXAS.
DETAILED SUMMARY
FOR SATURDAY JULY 01 - WEDNESDAY JULY 05:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY JULY 06 - WEDNESDAY JULY 12: WITH THE MAJOR HEAT WAVE OVER THE
SOUTH-CENTRAL U.S. EXPECTED TO EASE INTO NEXT WEEK, DYNAMICAL MODELS FAVOR THE
DEVELOPMENT OF A BROAD COVERAGE OF NEGATIVE HEIGHT DEPARTURES OVER PORTIONS OF
THE WESTERN AND CENTRAL U.S. TOWARDS THE MIDDLE OF NEXT WEEK. THE 0Z AND 6Z
GEFS HAVE BECOME MORE AMPLIFIED WITH THIS MID-LEVEL FEATURE, AND THERE IS GOOD
AGREEMENT IN THE ENSEMBLES DEPICTING COOLER TEMPERATURES OVERSPREADING THE
CENTRAL AND NORTHERN GREAT PLAINS BY LATE NEXT WEEK. ONE AREA OF UNCERTAINTY
CONCERNS HOW FAR SOUTH THE ACCOMPANYING FRONTAL BOUNDARY AND COOLER
TEMPERATURES EXTEND INTO THE SOUTHERN CONUS. WHILE THE DAILY RAW TEMPERATURE
ANOMALIES ARE MODESTLY POSITIVE, THE ECMWF AND CANADIAN PROBABILISTIC EXTREMES
TOOLS (PETS) KEEP MUCH OF THE EXCESSIVE HEAT POTENTIAL AT BAY ACROSS THE
SOUTH-CENTRAL AND SOUTHEASTERN CONUS EARLY IN THE PERIOD. HOWEVER, THE LOWERED
RISK OF EXCESSIVE HEAT LOOKS TO BE SHORT-LIVED AS ENSEMBLES REMAIN CONSISTENT
IN THE REBUILDING OF 500-HPA HEIGHTS OVER THE SOUTH-CENTRAL CONUS TOWARDS THE
MIDDLE OF THE PERIOD. THIS IS REFLECTED IN THE GEFS AND ECMWF PETS SHOWING AT
LEAST A 20% CHANCE OF MAXIMUM TEMPERATURES EXCEEDING THE 85TH PERCENTILE FROM
THE LOWER MISSISSIPPI VALLEY TO THE DESERT SOUTHWEST, AND A SLIGHT RISK OF
EXCESSIVE HEAT IS POSTED FOR JUL 8-12. ALTHOUGH POSITIVE TEMPERATURE ANOMALIES
ARE ALSO FAVORED TO GRADUALLY ENVELOP MANY PARTS OF THE MIDWEST AND
NORTHEASTERN CONUS, A CORRESPONDING TEMPERATURE HAZARD IS NOT POSTED GIVEN
REDUCED CONFIDENCE FOR MAXIMUM TEMPERATURES REACHING HAZARDS CRITERIA.
ACROSS THE NORTHWESTERN CONUS, THE LATEST ECMWF AND GEFS ENSEMBLES HAVE BACKED
OFF ON A RETROGRADING 500-HPA RIDGE COMPARED TO PREVIOUS RUNS, AND INSTEAD
FAVOR MORE OF THE PERSISTENCE OF ANOMALOUS MID-LEVEL RIDGING TO KEEP
TEMPERATURES ON THE WARM SIDE THROUGHOUT THE PERIOD. AS A RESULT, A SLIGHT RISK
OF EXCESSIVE HEAT REMAINS POSTED WHERE PET GUIDANCE SHOWS AT LEAST A 20% CHANCE
OF MAXIMUM TEMPERATURES EXCEEDING THE 85TH PERCENTILE AND 90 DEGREES F (95
DEGREES IN EASTERN WASHINGTON) FOR JUL 6-9. MUCH OF THE MID-LEVEL RIDGING IS
FAVORED TO WEAKEN, WHICH SHOULD ALLOW FOR SOME MODERATION OF TEMPERATURES LATER
IN THE PERIOD.
TIED TO THE SHORTWAVE TROUGHING EARLY IN THE PERIOD, THERE IS GOOD CONTINUITY
IN THE RAW AND CALIBRATED TOOLS FAVORING ABOVE-NORMAL PRECIPITATION FROM THE
GREAT PLAINS EASTWARD TO THE TENNESSEE AND OHIO VALLEYS. SCATTERED CONVECTION
AND LOCALLY HEAVY RAINFALL ALONG THE FRONTAL BOUNDARY REMAINS POSSIBLE, WHERE
THE CALIBRATED ECMWF SHOWS A LARGER COVERAGE OF INCREASED CHANCES FOR 3-DAY
AMOUNTS EXCEEDING 1 INCH COMPARED TO YESTERDAY. ELEVATED CHANCES (>40%) FOR
3-DAY AMOUNTS EXCEEDING THE 85TH PERCENTILE ARE ALSO DEPICTED IN THE ECMWF PET
MAINLY OVER THE CENTRAL PLAINS, THOUGH THE GEFS AND CANADIAN ARE LESS
SUPPORTIVE OF THIS ELEVATED POTENTIAL. THEREFORE, THE SLIGHT RISK OF HEAVY
PRECIPITATION REMAINS POSTED (JUL 6-9), AND IS EXPANDED FURTHER WESTWARD OVER
THE GREAT PLAINS TO CAPTURE THE INCREASED WET SIGNALS IN THE ECMWF BASED
GUIDANCE.
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 HIGHLIGHTED ROD AREA HAS
ONLY RECEIVED ABOUT 25% OF NORMAL PRECIPITATION DURING THE PAST 30 DAYS.
ALTHOUGH THE WEEK-2 OUTLOOK FAVORS ABOVE-NORMAL PRECIPITATION, LOW RAINFALL
AMOUNTS DURING THE NEXT WEEK AND CONTINUED ABOVE-NORMAL TEMPERATURES TO INDUCE
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.
NO HAZARDS ARE POSTED FOR ALASKA AS THE COOLER AND WETTER CONDITIONS REMAIN
FAVORED UNDER THE INFLUENCE OF PERSISTENT MID-LEVEL TROUGHING OVER THE BERING
SEA. THESE CONDITIONS ARE EXPECTED TO MAINTAIN A REDUCED RISK OF WILDFIRE
POTENTIAL THROUGHOUT MUCH OF THE STATE. LESS THAN 1500 ACRES HAVE BURNED
STATEWIDE SO FAR THIS YEAR WHICH CURRENTLY REGISTERS AS THE LOWEST ACREAGE
TOTAL ON RECORD FOR LATE JUNE.
FORECASTER: NICK NOVELLA
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