830
FXUS21 KWNC 031914
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT AUGUST 03 2023
SYNOPSIS: AS MID-LEVEL LOW PRESSURE IS FAVORED TO WEAKEN OVER THE NORTH-CENTRAL
AND NORTHEASTERN CONTIGUOUS U.S. (CONUS) EARLY IN THE PERIOD, STRENGTHENING
MID-LEVEL HIGH PRESSURE INCREASES THE RISK OF EXCESSIVE HEAT CONDITIONS
EMERGING FOR MUCH OF THE WEST, WHILE THE RISK OF EXCESSIVE HEAT IS EXPECTED TO
CONTINUE OVER THE SOUTHERN TIER OF THE U.S. 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
HIGH RISK OF EXCESSIVE HEAT OVER PARTS OF THE SOUTHERN PLAINS, FRI-SAT, AUG
11-12.
MODERATE RISK OF EXCESSIVE HEAT FROM THE DESERT SOUTHWEST TO THE LOWER
MISSISSIPPI VALLEY, FRI-SUN, AUG 11-13.
MODERATE RISK OF EXCESSIVE HEAT OVER PORTIONS OF THE PACIFIC NORTHWEST AND
NORTHERN INTERMOUNTAIN, SUN-TUE, AUG 13-15.
SLIGHT RISK OF EXCESSIVE HEAT FOR MUCH OF THE SOUTHERN CONUS AND FOUR CORNERS
REGION, FRI-THU, AUG 11-17.
SLIGHT RISK OF EXCESSIVE HEAT FOR MUCH OF THE FLORIDA PENINSULA, FRI-THU, AUG
11-17.
SLIGHT RISK OF EXCESSIVE HEAT FOR MUCH OF THE WEST COAST AND INTERIOR WEST,
SAT-THU, AUG 12-17.
SLIGHT RISK OF HIGH WINDS FOR MUCH OF THE SOUTHWESTERN CONUS, FRI-THU, AUG
11-17.
RAPID ONSET DROUGHT RISK ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY,
SOUTHERN PLAINS, AND SOUTHWEST.
DETAILED SUMMARY
FOR SUNDAY AUGUST 06 - THURSDAY AUGUST 10:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY AUGUST 11 - THURSDAY AUGUST 17: LATE IN WEEK-1, THERE IS GOOD
AGREEMENT IN THE DYNAMICAL MODELS FEATURING ANOMALOUS 500-HPA TROUGHING
ESTABLISHED THROUGHOUT THE NORTHERN HALF OF THE CONUS, AND A BROAD COVERAGE OF
POSITIVE HEIGHT DEPARTURES REMAINING ENTRENCHED OVER THE SOUTHERN TIER OF THE
U.S. AS MUCH OF THE TROUGHING LOOKS TO WEAKEN AND SHIFT SLIGHTLY EASTWARD
TOWARDS THE END OF NEXT WEEK, THERE HAS BEEN CONSISTENCY IN THE GEFS AND ECMWF
OVER THE PAST FEW ENSEMBLE RUNS FEATURING AN AMPLIFYING RIDGE OVER WESTERN
NORTH AMERICA, WHERE LARGE 500-HPA ANOMALIES LOOK TO PERSIST OVER THE PACIFIC
NORTHWEST AND SOUTHWESTERN CANADA. AS A RESULT, THERE IS INCREASED CONFIDENCE
FOR ABOVE-NORMAL TEMPERATURES PREVAILING DURING WEEK-2, ACCOMPANIED BY A RISK
OF EXCESSIVE HEAT CONDITIONS EMERGING OVER THIS PART OF THE COUNTRY. ACROSS
THE SOUTH-CENTRAL AND SOUTHWESTERN CONUS, THE GEFS AND ECMWF DIVERGE SOMEWHAT
ON THE EVOLUTION OF THE MID-LEVEL PATTERN. THE GEFS FOCUSES MUCH OF THE RIDGING
OVER THE WESTERN CONUS WITH DECREASING HEIGHTS TO THE EAST, WHEREAS THE ECMWF
MAINTAINS MORE AMPLIFIED RIDGING OVER THE SOUTHERN PLAINS, WHICH INTRODUCES
SOME UNCERTAINTY IN REGARDS TO THE PERSISTENCE OF EXCESSIVE HEAT CONDITIONS
OVER THE SOUTH-CENTRAL CONUS DURING THE PERIOD.
ON DAY 7 (AUG 10), POSITIVE MAXIMUM TEMPERATURE DEPARTURES IN THE DOUBLE DIGITS
ARE FORECAST OVER PARTS OF WESTERN AND CENTRAL TEXAS ACCORDING TO THE WEATHER
PREDICTION CENTER (WPC), WHICH CONTINUES TO SUGGEST EXCESSIVE HEAT CONDITIONS
ALREADY ESTABLISHED IN THE REGION. RELATIVE TO YESTERDAY, POSITIVE MID-LEVEL
HEIGHT ANOMALIES HAVE TRENDED STRONGER HEADING INTO THE BEGINNING OF WEEK-2,
WHERE THE ECMWF ENSEMBLE NOW SHOWS HEIGHTS IN EXCESS OF 597-DM CENTERED OVER
THE U.S./MEXICO BORDER. WITH SOUTHERLY SURFACE FLOW FORECAST TO ADVECT MOISTURE
AND ELEVATE HEAT INDEX VALUES, AND SUPPORT FROM THE NATIONAL BLEND OF MODELS
(NBM) ANALYSIS INDICATING DAYTIME HIGHS EXCEEDING 105 DEGREES F (APPROACHING
DAILY RECORDS THROUGHOUT NEW MEXICO AND TEXAS), AS WELL AS SUPPORT FROM THE
PROBABILISTIC EXTREME TOOL (PET) GUIDANCE, A HIGH RISK OF EXCESSIVE HEAT (AUG
11-12) IS ISSUED FROM EASTERN NEW MEXICO TO SOUTHEASTERN TEXAS. PET GUIDANCE
ALSO DEPICTS A MORE EXPANSIVE AREA OF ELEVATED (40%) CHANCES FOR MAXIMUM
TEMPERATURES EXCEEDING THE 85TH PERCENTILE. THEREFORE, THE MODERATE RISK OF
EXCESSIVE HEAT REMAINS POSTED, AND IS EXPANDED WESTWARD TO INCLUDE THE DESERT
SOUTHWEST AND EXTENDED TO DAY 10 (AUG 13) WHICH IS ALSO SUPPORTED BY
UNCALIBRATED TEMPERATURE GUIDANCE. A BROADER SLIGHT RISK AREA OF EXCESSIVE HEAT
REMAINS POSTED (AUG 11-17) FOR MUCH OF THE SOUTHERN TIER OF THE CONUS AND
INCLUDING THE FLORIDA PENINSULA, WHERE PETS MAINTAIN AT LEAST A 20% CHANCE OF
MAXIMUM TEMPERATURE EXCEEDING THE 85TH PERCENTILE.
AS ANOMALOUS RIDGING BUILDS WESTWARD, BOTH RAW AND CALIBRATED TEMPERATURE TOOLS
SHOW A SUBSTANTIAL UPTICK IN ANOMALOUSLY WARM TEMPERATURES TOWARDS THE MIDDLE
OF THE PERIOD. A SEPARATE SLIGHT RISK AREA OF EXCESSIVE HEAT IS ISSUED FOR THE
WEST COAST AND INTERIOR WEST WHERE BOTH THE GEFS AND ECWMF PETS SHOW AT LEAST A
20% CHANCE OF MAXIMUM TEMPERATURES EXCEEDING THE 85TH PERCENTILE (AND 95
DEGREES F IN MANY LOCATIONS) BEGINNING ON DAY 9 (AUG 12) AND VALID THROUGH THE
END OF THE PERIOD. ALTHOUGH THE GEFS REMAINS COMPARABLY WEAKER WITH THE 500-HPA
RIDGING THAN THE ECMWF DURING THE MIDDLE OF WEEK-2, BOTH MODELS FAVOR A
STRONGER COVERAGE OF ANOMALOUS MID-LEVEL HEIGHTS COMPARED TO YESTERDAY. GIVEN
INCREASED SUPPORT IN THE PETS DEPICTING AT LEAST A 30% CHANCE OF DAYTIME
TEMPERATURES EXCEEDING THE 85TH PERCENTILE, A MODERATE RISK OF EXCESSIVE HEAT
IS ISSUED FOR PARTS OF OREGON AND WASHINGTON (AUG 13-15).
BY THE OUTSET OF WEEK-2, ENSEMBLES CONTINUE TO SHOW SURFACE LOW PRESSURE OVER
THE PLAINS AND MISSISSIPPI VALLEY LEADING TO INCREASED PRECIPITATION AMOUNTS.
THIS IS REFLECTED IN THE GEFS AND ECMWF PETS, DEPICTING INCREASED CHANCES FOR
3-DAY AMOUNTS EXCEEDING THE 85TH PERCENTILE OVER THE CENTRAL CONUS AS WELL AS
OVER THE MID-ATLANTIC AND NORTHEAST. HOWEVER, ACTUAL PRECIPITATION AMOUNTS
APPEAR TO FALL BELOW HAZARD CRITERIA AND NO CORRESPONDING PRECIPITATION HAZARDS
ARE ISSUED, AS MODELS ALSO SEEM TO BE OUT OF PHASE WITH THE TIMING AND STRENGTH
OF A POTENTIAL STORM TRACK. ACROSS THE TROPICS, THERE ARE GROWING INDICATIONS
IN THE GEFS AND ECMWF ENSEMBLES FAVORING A TROPICAL WAVE PROPAGATING FROM THE
MAIN DEVELOPMENT REGION (MDR) INTO THE CARIBBEAN. PROBABILISTIC TROPICAL
CYCLONE (TC) GENESIS TOOLS ARE FAIRLY WEAK WITH THE SIGNALS ASSOCIATED WITH
THIS WAVE, HOWEVER, A FEW ENSEMBLE MEMBERS FROM THE 0Z GEFS SHOW DEEPENING LOW
CENTERS ENTERING THE GULF OF MEXICO WITH ENHANCED PRECIPITATION AMOUNTS IN THE
ENSEMBLE MEAN OVER PARTS OF THE GULF STATES BY MID TO LATE WEEK-2. NO
CORRESPONDING PRECIPITATION HAZARD IS ISSUED AT THIS TIME DUE TO LARGE
UNCERTAINTY AT THIS LEAD, BUT THE TROPICS WILL CONTINUE TO BE MONITORED IN
SUBSEQUENT OUTLOOKS AS THE ATLANTIC OCEAN TYPICALLY EXPERIENCES AN UPTICK IN TC
ACTIVITY LATER IN AUGUST.
A SLIGHT RISK OF EPISODES OF HIGH WINDS REMAINS ISSUED OVER MUCH OF THE
SOUTHWESTERN CONUS AND IS NOW VALID FOR THE ENTIRETY OF WEEK-2 DUE TO THE
ANOMALOUSLY HIGH TEMPERATURES AND BELOW NORMAL PRECIPITATION FAVORED. PET
GUIDANCE CONTINUES TO SHOW AT LEAST A 20% CHANCE OF WIND SPEEDS EXCEEDING THE
85TH PERCENTILE FOR PART OF THE PERIOD. 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.
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.
COUPLED WITH AMPLIFIED TROUGHING CENTERED OVER THE ALEUTIANS, THE
AFOREMENTIONED BUILDING OF MID-LEVEL HEIGHTS OVER WESTERN NORTH AMERICA IS
SUPPORTIVE OF ENHANCED ONSHORE FLOW AND ABOVE-NORMAL PRECIPITATION OVER
SOUTHERN MAINLAND ALASKA AND THE SOUTHEAST. RELATIVE TO YESTERDAY, THE GEFS AND
ECMWF PETS ARE MORE SUPPORTIVE OF INCREASED HEAVY PRECIPITATION RISK, THOUGH
THERE IS SOME UNCERTAINTY IN THE VOLATILITY OF THE MID-LEVEL HEIGHT PATTERN IN
THE GUIDANCE. NO PRECIPITATION HAZARDS ARE POSTED, BUT WILL CONTINUE TO BE
MONITORED IN UPCOMING OUTLOOKS.
FORECASTER: NICK NOVELLA
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