723
FXUS21 KWNC 291920
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JUNE 29 2023
SYNOPSIS: FOLLOWING A PERIOD OF COOLER TEMPERATURES FAVORED OVER THE GREAT
PLAINS AND MISSISSIPPI VALLEY LATE IN WEEK-1 AND HEADING INTO WEEK-2, A RENEWED
RISK OF EXCESSIVE HEAT IS EXPECTED ACROSS PARTS OF THE SOUTHERN U.S. TIED TO A
REBUILDING OF MID-LEVEL HIGH PRESSURE FAVORED DURING THE PERIOD. FORECAST
FRONTAL ACTIVITY IS EXPECTED TO PROMOTE AN INCREASED RISK OF HEAVY
PRECIPITATION FROM THE GREAT PLAINS TO THE EASTERN U.S. 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
MODERATE RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE LOWER FOUR CORNERS,
SUN-MON, JUL 9-10.
SLIGHT RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE SOUTHWEST, GREAT BASIN,
SOUTHERN PLAINS, LOWER MISSISSIPPI VALLEY, AND SOUTHEAST SAT-THU, JUL 8-13.
SLIGHT RISK OF EXCESSIVE HEAT FOR PARTS OF THE PACIFIC NORTHWEST, FRI-MON, JUL
7-10.
SLIGHT RISK OF EPISODES OF HIGH WINDS FOR THE SOUTHWESTERN CONUS, SUN-THU, JUL
9-13.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE CENTRAL AND EASTERN
CONUS, FRI-MON, JUL 7-10.
POSSIBLE FLOODING FOR PORTIONS OF CALIFORNIA AND NEVADA.
RAPID ONSET DROUGHT RISK ACROSS PORTIONS OF LOUISIANA AND EASTERN TEXAS.
DETAILED SUMMARY
FOR SUNDAY JULY 02 - THURSDAY JULY 06:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY JULY 07 - THURSDAY JULY 13: THE WEEK-2 HAZARDS PERSPECTIVE REMAINS
LARGELY ON TRACK SINCE YESTERDAY. LEADING UP TO THE WEEK-2 PERIOD, DYNAMICAL
MODELS CONTINUE TO FAVOR MID-LEVEL SHORTWAVE TROUGHING OVER THE WESTERN AND
CENTRAL U.S. WHICH IS EXPECTED TO BRING A SHOT OF ANOMALOUS COLD AIR INTO MANY
PARTS OF THE GREAT PLAINS AND MISSISSIPPI VALLEY. AT THE SURFACE, THE SOUTHERN
REACH OF THE FRONTAL BOUNDARY FORECAST STILL REMAINS IN QUESTION BASED ON
VARIOUS MODEL SOLUTIONS. THERE IS HOWEVER INCREASED CONFIDENCE THAT COOLER
TEMPERATURES WILL PROVIDE SOME RELIEF TO MANY AREAS IN THE SOUTHERN TIER OF THE
U.S. AFFECTED BY THE ONGOING MAJOR HEAT WAVE AND STIFLING TEMPERATURES SINCE
JUNE. BY THE FOLLOWING WEEKEND, MUCH OF THE NEGATIVE HEIGHT DEPARTURES IN THE
ENSEMBLE MEANS ARE FAVORED TO WEAKEN AND LIFT OUT, AS MID-LEVEL HEIGHTS LOOK TO
REBUILD AND PROMOTE THE POSSIBLE RESURGENCE OF THE EXCESSIVE HEAT CONDITIONS
ACROSS THE SOUTHERN CONUS.
RECENT RUNS OF THE ECMWF ENSEMBLE HAVE GROWN MORE BULLISH WITH THE RELOADING
SUBTROPICAL RIDGE, AND NOW FEATURE A LARGER COVERAGE OF POSITIVE HEIGHT
DEPARTURES WITH A MEAN RIDGE MAXIMA EXCEEDING 594 DAM OVER THE FOUR CORNERS
REGION TOWARDS THE MIDDLE OF THE PERIOD. THE GEFS IS WEAKER BY CONTRAST, BUT
HAS BEEN CONSISTENT IN FAVORING INCREASING MID-LEVEL HEIGHTS AND THE RETURN OF
POSITIVE TEMPERATURE ANOMALIES DURING WEEK-2. A SLIGHT RISK OF EXCESSIVE HEAT
REMAINS ISSUED FOR JUL 9-13 WHERE PROBABILISTIC EXTREME TOOLS (PETS) FROM THE
GEFS AND ECMWF SHOW AT LEAST A 20% CHANCE OF DAYTIME MAXIMUM TEMPERATURES
EXCEEDING THE 85TH PERCENTILE. THE HIGHLIGHTED SLIGHT RISK AREA IS EXPANDED TO
INCLUDE MORE OF THE FOUR CORNERS AND ALONG THE GULF COAST INCLUDING THE FLORIDA
PENINSULA GIVEN INCREASED SUPPORT IN THESE TOOLS RELATIVE TO YESTERDAY. TIED
TO THE AMPLIFYING RIDGE, HIGHER PROBABILITIES (30-40% CHANCES) FOR MAXIMUM
TEMPERATURES EXCEEDING THE 85TH CLIMATOLOGICAL PERCENTILE ARE EVIDENT IN BOTH
THE GEFS AND ECMWF BASED PETS TO SUPPORT THE ADDITION OF A MODERATE RISK OF
EXCESSIVE HEAT VALID OVER PARTS OF THE FOUR CORNERS FOR JUL 10-11. THESE TOOLS
INDICATE AT LEAST 40% CHANCE FOR MAXIMUM TEMPERATURES EXCEEDING 110 DEGREES F
OVER THE SONORAN DESERT AND OVER A 100 DEGREES F FARTHER EAST ALONG THE U.S.
BORDER INTO TEXAS. BY DAY 12 (JUL 11), THE PETS DIVERGE IN REGARDS TO THE
MAGNITUDE OF THE HEAT SIGNALS RESULTING IN REDUCED OUTLOOK CONFIDENCE FOR THE
REMAINDER OF WEEK-2. ADDITIONALLY, THE COMBINATION OF THE INCREASING HEAT
SIGNALS AND PREDICTED DRIER THAN NORMAL PRECIPITATION IS ALSO EXPECTED TO BE
CONDUCIVE FOR AN INCREASED RISK OF FIRE WEATHER ACROSS THE PORTIONS OF THE
GREAT BASIN, FOUR CORNERS AND SOUTHERN PLAINS. WHILE LESS SUPPORTED IN THE
GEFS, THE ECMWF AND CANADIAN PET SHOWS AT LEAST A 20% CHANCE FOR WIND SPEEDS
EXCEEDING THE 85TH PERCENTILE, THUS A BROAD SLIGHT RISK AREA OF HIGH WINDS IS
ALSO ISSUED FOR JUL 9-13.
OVER THE GULF OF ALASKA AND WESTERN NORTH AMERICA, THERE IS GOOD AGREEMENT
AMONG THE DYNAMICAL MODELS DEPICTING AN AMPLIFIED RIDGE WITH POSITIVE HEIGHT
DEPARTURES EXTENDING INTO THE PACIFIC NORTHWEST, KEEPING TEMPERATURES ON THE
WARM SIDE DURING THE PERIOD. BOTH THE GEFS AND ECMWF PETS CONTINUE TO SHOW AT
LEAST 20% CHANCES FOR MAXIMUM TEMPERATURES EXCEEDING THE 85TH PERCENTILE AND 90
DEGREES F (95 DEGREES IN EASTERN WASHINGTON), SUPPORTING THE CONTINUATION OF A
SLIGHT RISK OF EXCESSIVE HEAT ACROSS THE REGION. THE HIGHLIGHTED REGION IS
EXPANDED SLIGHTLY SOUTHWARD INTO WESTERN OREGON COMPARED TO YESTERDAY, AND
REMAINS VALID THROUGH DAY 11 (JUL 10) BEFORE THE ANOMALOUS RIDGING BEGINS TO
RETROGRADE WESTWARD.
TIED TO THE MID-LEVEL SHORTWAVE TROUGHING EARLY IN THE PERIOD, MODELS ARE
CONSISTENT REGARDING THE ENHANCEMENT OF PRECIPITATION FOR MANY AREAS EAST OF
THE ROCKIES. SCATTERED CONVECTION AND LOCALLY HEAVY RAINFALL ALONG THE FRONTAL
BOUNDARY REMAINS POSSIBLE EARLY IN THE PERIOD, WHERE THE UNCALIBRATED ECMWF
SHOWS A LARGER COVERAGE OF INCREASED CHANCES FOR 3-DAY AMOUNTS EXCEEDING 1 INCH
OVER THE NORTHEASTERN CONUS COMPARED TO YESTERDAY. THE EXPANSION OF THE HEAVY
PRECIPITATION POTENTIAL IS WELL REFLECTED IN THE ECMWF PET, INDICATING AT LEAST
20-30% CHANCES OF 3-DAY AMOUNTS EXCEEDING THE 85TH PERCENTILE OVER PARTS OF THE
MID-ATLANTIC AND THE NORTHEAST. WHILE THE GEFS PET IS SOMEWHAT LESS SUPPORTIVE
OF THIS RISK, UNCALIBRATED DAILY PRECIPITATION AMOUNTS FROM THE GEFS ALIGN WELL
WITH THE PRECIPITATION RISK FROM THE FRONTAL PASSAGE, RESULTING IN THE SLIGHT
RISK OF HEAVY PRECIPITATION REMAINING POSTED (JUL 7-10), INCLUDING MUCH OF THE
NORTHEASTERN CONUS.
ANTECEDENT DRYNESS ALONG WITH A CONTINUED DRY PATTERN THROUGH THE NEXT WEEK AND
THE ONGOING HEAT WAVE INCREASES THE RISK FOR RAPID ONSET DROUGHT (ROD) ACROSS
PARTS OF LOUISIANA AND EASTERN TEXAS. THE HIGHLIGHTED ROD AREA HAS BEEN
EXPANDED WESTWARD INTO CENTRAL TEXAS WHERE MANY LOCATIONS HAVE REGISTERED LESS
THAN HALF OF THEIR NORMAL RAINFALL ACCUMULATION IN THE LAST 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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