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FXUS21 KWNC 011943
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT AUGUST 01 2023
SYNOPSIS: A SLOWLY-WEAKENING MID-LEVEL LOW PRESSURE SYSTEM IS FAVORED TO KEEP
COOLER THAN NORMAL TEMPERATURES OVER THE NORTHERN HALF OF THE CONTIGUOUS U.S.
(CONUS). MID-LEVEL HIGH PRESSURE TO THE SOUTH SUSTAINS AN INCREASED RISK OF
EXCESSIVE HEAT ACROSS PARTS OF THE SOUTHERN TIER DURING THE PERIOD. ANTECEDENT
DRYNESS COUPLED WITH LITTLE TO NO RAINFALL AND ABOVE-NORMAL TEMPERATURES
SUPPORTS A RAPID ONSET DROUGHT RISK ACROSS PARTS OF THE LOWER MISSISSIPPI
VALLEY, SOUTHERN GREAT PLAINS, RIO GRANDE VALLEY, AND NEW MEXICO.
HAZARDS
MODERATE RISK OF EXCESSIVE HEAT FROM THE SOUTHERN HIGH PLAINS TO THE LOWER
MISSISSIPPI VALLEY, WED-FRI, AUG 9-11.
SLIGHT RISK OF EXCESSIVE HEAT FOR MUCH OF THE SOUTHERN U.S., WED-TUE, AUG 9-15.
SLIGHT RISK OF HIGH WINDS FOR MUCH OF THE FOUR CORNERS, WED-SAT, AUG 9-12.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PARTS OF THE GREAT PLAINS AND THE
MISSISSIPPI AND TENNESSEE VALLEYS, WED-SAT, AUG 9-12.
SLIGHT RISK OF MUCH ABOVE-NORMAL TEMPERATURES FOR NORTHERN ALASKA, WED-THU, AUG
9-10.
RAPID ONSET DROUGHT RISK ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY,
SOUTHERN PLAINS, AND SOUTHWEST.
DETAILED SUMMARY
FOR FRIDAY AUGUST 04 - TUESDAY AUGUST 08:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY AUGUST 09 - TUESDAY AUGUST 15: HEADING INTO EARLY NEXT WEEK,
DYNAMICAL MODELS HAVE BEEN CONSISTENT IN FAVORING A COOLER PATTERN EMERGING
WITH ANOMALOUS 500-HPA TROUGHING ENVELOPING MOST OF THE NORTHERN HALF OF THE
CONUS. INITIALLY, DECREASING MID-LEVEL HEIGHTS ARE CONCURRENTLY FAVORED ACROSS
THE SOUTHERN TIER OF THE U.S., BUT ABOVE-NORMAL TEMPERATURES REMAIN FAVORED TO
PERSIST, AS WELL AS THE POTENTIAL FOR EXCESSIVE HEAT DURING THE PERIOD. LATER
IN THE PERIOD, ENSEMBLES SHOW THE POTENTIAL FOR ABOVE-NORMAL MID-LEVEL HEIGHTS
TO DEVELOP THROUGHOUT THE CONUS, WITH A RIDGE AXIS BEGINNING TO BUILD OVER THE
WESTERN CONUS, THOUGH ANY RENEWED RISK OF EXCESSIVE HEAT REMAINS UNCLEAR GIVEN
MODEL DISPARITIES IN THE EVOLUTION AND STRENGTH OF THE HEIGHT PATTERN AT THIS
LEAD.
A MODERATE RISK OF EXCESSIVE HEAT IS ISSUED FROM THE SOUTHERN HIGH PLAINS TO
SOUTHERN SECTIONS OF THE LOWER MISSISSIPPI VALLEY, WHERE THE CANADIAN ENSEMBLE,
GEFS, AND ECMWF PROBABILISTIC EXTREMES TOOLS (PETS) INDICATE AT LEAST A 40%
CHANCE OF MAXIMUM TEMPERATURES EXCEEDING THE 85TH PERCENTILE. THE ECMWF PET
CONTINUES TO KEEP HIGHER ODDS FOR EXCESSIVE HEAT ACROSS THE SOUTH-CENTRAL CONUS
THROUGH THE MIDDLE OF WEEK-2, BUT THE GEFS AND CANADIAN TOOLS ARE CONSIDERABLY
LESS SUPPORTIVE, SO NO HIGH RISK DESIGNATION IS ASSESSED. IN THE HIGHLIGHTED
MODERATE RISK AREA, THE ODDS FOR DAYTIME TEMPERATURES TO TOP 110 DEGREES F IN
THE SONORAN DESERT HAVE DECREASED SLIGHTLY, BUT CHANCES FOR 100 DEG F
TEMPERATURES FARTHER EAST IN THE SOUTHERN PLAINS REMAIN ELEVATED, AS THEY WERE
YESTERDAY. A BROAD SLIGHT RISK AREA OF EXCESSIVE HEAT IS POSTED FOR ALL OF
WEEK-2 (AUG 9-15) ALONG MUCH OF THE SOUTH-CENTRAL AND SOUTHWESTERN CONUS GIVEN
THE PREPONDERANCE OF TOOLS INDICATING SLIGHTLY ABOVE-NORMAL 500-HPA HEIGHTS
SHOULD PERSIST THROUGH THE PERIOD, AND PETS INDICATING AT LEAST A 20% CHANCE OF
MAXIMUM TEMPERATURES EXCEEDING THE 85TH PERCENTILE. FARTHER EAST, PET TOOLS ARE
LESS ROBUST THAN YESTERDAY REGARDING ABOVE-NORMAL TEMPERATURES OVER THE FLORIDA
PENINSULA, SINCE IT APPEARS THAT THE RIDGE AXIS FORMING LATE IN WEEK-2 WILL BE
ESTABLISHED FARTHER WEST THAN YESTERDAY. THEREFORE, THE SLIGHT RISK OF
EXCESSIVE HEAT THERE IS ELIMINATED TOWARD THE END OF WEEK-2. WITH THE UNUSUALLY
HIGH TEMPERATURES ESTABLISHED, A SLIGHT RISK OF EPISODES OF HIGH WINDS IS
ISSUED (AUG 9-12) FOR THE FOUR CORNERS WHERE PETS FROM ALL 3 ENSEMBLES INDICATE
AT LEAST A 20% CHANCE OF WIND SPEEDS EXCEEDING THE 85TH PERCENTILE. WITHIN THE
SLIGHT RISK AREA, CONTINUED DRY AND WARM CONDITIONS ARE LIKELY TO FUEL MANY
AREAS CURRENTLY EXPERIENCING ACTIVE WILDFIRES.
RETURN SURFACE FLOW FROM THE GULF OF MEXICO IS FAVORED TO BECOME ESTABLISHED
EARLY IN WEEK-2, SUPPORTING THE POTENTIAL FOR HEAVY PRECIPITATION OVER THE
CENTRAL CONUS. WHILE THE GEFS REMAINS COMPARABLY DRY, BOTH THE ECMWF AND THE
CANADIAN ENSEMBLE TOOLS SHOW AT LEAST A 20% CHANCE FOR 3-DAY RAINFALL
ACCUMULATIONS TO EXCEED THE 85TH PERCENTILE FOCUSED OVER THE CENTRAL PLAINS AND
MIDDLE MISSISSIPPI VALLEY, ALONG WITH ENHANCED PROBABILITIES FOR 3-DAY AMOUNTS
TO EXCEED AN INCH INTO THE MIDDLE OF WEEK-2. THEREFORE, A SLIGHT RISK OF HEAVY
PRECIPITATION IS POSTED FOR AUG 9-12. WITHIN THE SLIGHT RISK AREA, ANY
SLOW-MOVING THUNDERSTORMS WITH LOCALLY HEAVY RAINFALL MAY CAUSE FLASH FLOODING.
A RAPID ONSET DROUGHT (ROD) RISK REMAINS POSTED ACROSS PARTS OF THE LOWER
MISSISSIPPI VALLEY, TEXAS, AND SOUTHERN NEW MEXICO DUE TO THE COMBINATION OF
INCREASING 30-DAY PRECIPITATION DEFICITS, LITTLE TO NO RAINFALL DURING THE NEXT
TWO WEEKS, AND LIKELIHOOD FOR A PROLONGED PERIOD OF HIGH EVAPOTRANSPIRATION
RATES ASSOCIATED WITH MUCH ABOVE-NORMAL TEMPERATURES. FURTHER NORTH, THE ROD
RISK IS DISCONTINUED IN TODAY'S OUTLOOK FOR PARTS OF NORTH DAKOTA WHERE
PRECIPITATION GUIDANCE HAS TRENDED WETTER AND COOLER, AND INCREASED RAINFALL
WAS RECENTLY RECEIVED.
OVER ALASKA, MID-LEVEL TROUGHING FORECAST OVER THE ALEUTIANS IS EXPECTED TO
PROMOTE ENHANCED ONSHORE FLOW AND ABOVE-NORMAL PRECIPITATION FOR PARTS OF THE
SOUTHERN MAINLAND AND SOUTHEAST. HOWEVER, AMOUNTS ARE EXPECTED TO REMAIN BELOW
HAZARD THRESHOLDS AND NO CORRESPONDING HAZARDS ARE ISSUED. FOR TEMPERATURES,
STRONG RIDGING FAVORED EARLY IN WEEK-2 FROM THE NORTH SLOPE NORTHWARD IS
EXPECTED TO BRING MUCH ABOVE-NORMAL TEMPERATURES TO THIS REGION. MANY LOCATIONS
NORTH OF THE BROOKS RANGE COULD SEE DAYTIME TEMPERATURES EXCEED 70 DEGREES F
(10 TO 15 DEGREES ABOVE NORMAL), WHICH MAY BE POTENTIALLY HAZARDOUS TO OUTDOOR
WORKERS WEARING HEAVY EQUIPMENT. A SLIGHT RISK OF MUCH ABOVE-NORMAL
TEMPERATURES IS POSTED THERE FOR EARLY WEEK-2 (AUG 9-10) TO REFLECT THESE
CONDITIONS. FARTHER SOUTH, TEMPERATURES COULD BRIEFLY EXCEED 85 DEGREES F IN
CENTRAL AND EAST-CENTRAL ALASKA EARLY IN WEEK-2 ACCORDING TO THE PET TOOLS, BUT
NO ASSOCIATED HAZARDS ARE POSTED OVER THIS REGION DUE TO THE LACK OF
SIGNIFICANT IMPACTS EXPECTED.
FORECASTER: RICH TINKER
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