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FXUS21 KWNC 021838
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT AUGUST 02 2023
SYNOPSIS: A SLOWLY-WEAKENING MID-LEVEL LOW PRESSURE SYSTEM IS FAVORED TO KEEP
COOLER THAN NORMAL TEMPERATURES OVER THE NORTH-CENTRAL AND NORTHEASTERN
CONTIGUOUS U.S. (CONUS). MEANWHILE, MID-LEVEL HIGH PRESSURE TO THE SOUTH
SUSTAINS AN INCREASED RISK OF EXCESSIVE HEAT ACROSS MOST OF THE SOUTHERN TIER
DURING WEEK-2, AND BUILDING 500-HPA HEIGHTS WILL BRING A SIMILAR RISK FOR
EXCESSIVE HEAT INTO THE INTERIOR PACIFIC NORTHWEST FOR THE LAST HALF OF THE
PERIOD. SURFACE FLOW FROM THE SOUTH WILL BRING WET WEATHER INTO PARTS OF THE
CENTRAL CONUS FOR THE FIRST HALF OF THE PERIOD WHILE FARTHER SOUTH, 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, NEW MEXICO, AND ARIZONA.
HAZARDS
MODERATE RISK OF EXCESSIVE HEAT FROM THE SOUTHERN HIGH PLAINS TO THE LOWER
MISSISSIPPI VALLEY, THU-FRI, AUG 10-11.
SLIGHT RISK OF EXCESSIVE HEAT FOR MUCH OF THE SOUTHERN CONUS AND FOUR CORNERS
REGION, THU-WED, AUG 10-16.
SLIGHT RISK OF EXCESSIVE HEAT FOR MUCH OF THE FLORIDA PENINSULA, THU-WED, AUG
10-16.
SLIGHT RISK OF EXCESSIVE HEAT FOR THE INTERIOR PACIFIC NORTHWEST, SUN-WED, AUG
13-16.
SLIGHT RISK OF HIGH WINDS FOR MUCH OF THE FOUR CORNERS AND SOUTHERN CALIFORNIA,
THU-SAT, AUG 10-12.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PARTS OF THE GREAT PLAINS, THU-SUN, AUG
10-13.
RAPID ONSET DROUGHT RISK ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY,
SOUTHERN PLAINS, AND SOUTHWEST.
DETAILED SUMMARY
FOR SATURDAY AUGUST 05 - WEDNESDAY AUGUST 09:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY AUGUST 10 - WEDNESDAY AUGUST 16: HEADING INTO EARLY NEXT WEEK,
DYNAMICAL MODELS HAVE BEEN CONSISTENT IN FAVORING A COOLER PATTERN OVER THE
CENTRAL AND NORTHERN CONUS 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. LATER IN THE PERIOD, ENSEMBLES HAVE BACKED OFF SLIGHTLY IN SHOWING
POTENTIAL FOR ABOVE-NORMAL MID-LEVEL HEIGHTS TO DEVELOP THROUGHOUT THE CONUS,
BUT A WEAK MID-LEVEL RIDGE AXIS IS STILL FORECAST TO BUILD SLOWLY OVER THE
WESTERN CONUS EVEN THOUGH THE 500-HPA POSITIVE HEIGHT ANOMALIES ARE SLIGHTLY
SMALLER TODAY IN ALL MODEL ENSEMBLE MEANS. IN ADDITION, THE PROBABILISTIC
EXTREME TOOLS (PETS) STILL SHOW AT LEAST SOME ELEVATED RISK FOR EXCESSIVE HEAT
ACROSS MOST OF THE SOUTHERN TIER OF STATES THROUGHOUT WEEK-2. TO THE NORTHWEST,
MOST TOOLS SHOW INCREASING 500-HPA HEIGHTS AND ASSOCIATED SURFACE TEMPERATURES
DURING THE LAST HALF OF THE PERIOD, RAISING THE POSSIBILITY FOR EXCESSIVE HEAT
IN THE PACIFIC NORTHWEST DURING THE LATTER HALF OF WEEK-2.
A MODERATE RISK OF EXCESSIVE HEAT IS ISSUED FROM THE SOUTHERN HIGH PLAINS TO
SOUTHERN SECTIONS OF THE LOWER MISSISSIPPI VALLEY, WHERE THE GEFS AND ECMWF
PROBABILISTIC EXTREMES TOOLS (PETS) INDICATE A 40% TO 70% CHANCE OF MAXIMUM
TEMPERATURES EXCEEDING THE 85TH PERCENTILE ON THE FIRST DAY OF WEEK-2 (AUG 10)
WHICH SLOWLY DECLINES AS THE WEEK PROGRESSES. UNCERTAINTY IS INTRODUCED BY THE
CANADIAN ENSEMBLE PET, WHICH SHOWS ONLY SLIGHTLY ELEVATED CHANCES FOR
TEMPERATURES TO EXCEED THE 85TH PERCENTILE, WHILE THE GEFS AND ESPECIALLY THE
ECMWF PETS KEEP HIGHER ODDS FOR EXCESSIVE HEAT ACROSS THE SOUTH-CENTRAL CONUS
UNTIL THE MIDDLE OF WEEK-2. AS A RESULT, NO HIGH RISK DESIGNATION IS ASSESSED
AT THIS TIME. IN THE HIGHLIGHTED MODERATE RISK AREA, CHANCES FOR 100 DEGREES F
TEMPERATURES IN THE SOUTHERN PLAINS REMAIN ELEVATED, AND THERE ARE SLIGHTLY
INCREASED ODDS RELATIVE TO YESTERDAY FOR TEMPERATURES TO EXCEED 105 DEGREES F
AS FAR NORTH AS THE MIDDLE RED RIVER VALLEY ALONG THE TEXAS/OKLAHOMA BORDER AUG
10-11. A BROAD SLIGHT RISK AREA OF EXCESSIVE HEAT IS POSTED FOR THE ENTIRETY OF
WEEK-2 (AUG 10-16) ALONG MUCH OF THE SOUTH-CENTRAL AND SOUTHWESTERN CONUS, AND
OVER THE FLORIDA PENINSULA. THE PREPONDERANCE OF TOOLS INDICATE SLIGHTLY LOWER
500-HPA HEIGHTS ALONG THE SOUTHERN TIER OF THE CONUS TOWARD THE END OF THE
PERIOD COMPARED TO YESTERDAY, BUT THERE ARE NOT ENOUGH TOOLS SHOWING AN END TO
THE EXCESSIVE HEAT LATER WEEK-2 TO JUSTIFY ENDING THE RISK FOR ANY PART OF THE
PERIOD.
ONE NOTABLE CHANGE FROM YESTERDAY’S MODELS IS AN INCREASE IN MID-LEVEL HEIGHTS
OVER OR WEST OF THE PACIFIC NORTHWEST DURING THE LATTER HALF OF THE WEEK,
RAISING THE POSSIBILITY OF EXCESSIVE HEAT IN THE REGION. MODEL INCONSISTENCIES
AND QUESTIONS ABOUT THE EVOLUTION OF THE ANOMALOUS MID-LEVEL RIDGING REMAIN,
BUT ENOUGH INDICATORS POINT TOWARD A PERIOD OF EXCESSIVE HEAT TO JUSTIFY
POSTING A SLIGHT RISK DURING THE LATTER HALF OF WEEK-2. THE RISK IS LIMITED TO
INTERIOR VALLEYS OF WASHINGTON AND OREGON AT THIS TIME, WHERE THE ECMWF AND
GEFS PET TOOLS SHOW A SIGNIFICANT RISK FOR TEMPERATURES TO TOP 90 DEGREES F.
WITH THE UNUSUALLY HIGH TEMPERATURES ESTABLISHED, A SLIGHT RISK OF EPISODES OF
HIGH WINDS IS ISSUED (AUG 10-12) FOR THE FOUR CORNERS WHERE PETS FROM ALL 3
ENSEMBLES INDICATE AT LEAST A 20% CHANCE OF WIND SPEEDS EXCEEDING THE 85TH
PERCENTILE FOR PART OF THE PERIOD. THE HIGH WIND THREAT IS EXTENDED WESTWARD
ACROSS SOUTHERN CALIFORNIA TODAY. ANY ANOMALOUSLY STRONG WINDS IN THE SLIGHT
RISK REGION WILL EXACERBATE CONTINUED DRY AND WARM CONDITIONS, INCREASING
CHANCES FOR THE RAPID DEVELOPMENT AND SPREAD OF WILDFIRES.
RETURN SURFACE FLOW FROM THE GULF OF MEXICO IS FAVORED TO BECOME ESTABLISHED IN
THE CENTRAL CONUS THROUGH THE MIDDLE OF WEEK-2, SUPPORTING THE POTENTIAL FOR
HEAVY PRECIPITATION THERE. WHILE THE GEFS REMAINS COMPARABLY DRIER, 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 10-13. 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, SOUTHERN NEW MEXICO, AND SOUTHEASTERN ARIZONA 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.
OVER ALASKA, BOTH MID-LEVEL TROUGHING AND ANOMALOUSLY LOW SEA-LEVEL PRESSURES
ARE FORECAST FROM THE SOUTHERN BERING SEA INTO THE WESTERN GULF OF ALASKA. AS A
RESULT, UNUSUALLY ROBUST ONSHORE FLOW, POSSIBLY PRODUCING ABOVE-NORMAL
PRECIPITATION AND HIGH WINDS AT TIMES DURING WEEK-2 IN MUCH OF THE SOUTHERN
MAINLAND AND SOUTHEAST. MODELS ARE A LITTLE MORE ROBUST WITH PRECIPITATION
AMOUNTS THAN YESTERDAY, AND THE CANADIAN AND ECMWF PET TOOLS BOTH SHOW
INCREASED CHANCES FOR PRECIPITATION TOTALS ABOVE THE 85TH PERCENTILE AND
EXCEEDING TWO INCHES IN THIS AREA AT TIMES DURING THE PERIOD. HOWEVER, GIVEN
THE STORMY CLIMATOLOGY FOR THE REGION THIS TIME OF YEAR, NO CORRESPONDING
HAZARD FOR HEAVY PRECIPITATION NOR HIGH WINDS APPEARS JUSTIFIED AT THIS TIME.
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 ON
DAY 8 (AUG 10). MANY LOCATIONS NORTH OF THE BROOKS RANGE COULD SEE DAYTIME
TEMPERATURES EXCEED 70 DEGREES F (10 TO 15 DEGREES ABOVE NORMAL), WHICH COULD
PROVE HAZARDOUS TO OUTDOOR WORKERS WEARING HEAVY EQUIPMENT. BUT ODDS FOR
EXTREME TEMPERATURES ARE A LITTLE LOWER TODAY THAN YESTERDAY IN MOST GUIDANCE,
SO NO ENHANCED RISK OF MUCH ABOVE-NORMAL TEMPERATURES IS POSTED THERE. FARTHER
SOUTH, ODDS FOR TEMPERATURES EXCEEDING 85 DEGREES F IN CENTRAL AND EAST-CENTRAL
ALASKA ARE ALSO LOWER THAN YESTERDAY EARLY IN WEEK-2 ACCORDING TO THE PET
TOOLS, SO NO ASSOCIATED HAZARDS ARE POSTED OVER THIS REGION.
FORECASTER: RICH TINKER
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