193
FXUS21 KWNC 041818
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT AUGUST 04 2025
SYNOPSIS: AT THE OUTSET OF THE PERIOD, THE STRONGEST POSITIVE MID-LEVEL HEIGHT
ANOMALIES ARE FORECAST ACROSS THE NORTHWEST AND THE NORTHEAST WHICH FAVOR
INCREASED CHANCES FOR EXTREME HEAT OVER BOTH OF THESE AREAS EARLY IN WEEK-2. A
GENERAL BROADENING OF THE MID-LEVEL HEIGHT PATTERN IS FORECAST ACROSS THE CONUS
THEREAFTER, WITH WEAK POSITIVE HEIGHT ANOMALIES DEVELOPING ACROSS MUCH OF THE
NORTHERN TIER. OVERALL THE WEATHER PATTERN IS ANTICIPATED TO BE TRANQUIL, WITH
MANY AREAS LESS LIKELY TO SEE EXTREME HEAT GIVEN THE DECREASING TEMPERATURE
CLIMATOLOGY IN MID-AUGUST TOWARD THE LATTER PART OF THE PERIOD. THE TROPICAL
ATLANTIC WILL CONTINUE TO BE MONITORED WITH ENHANCED POTENTIAL FOR DISTURBANCES
DEVELOPING BY THE SECOND HALF OF AUGUST, BUT WITH HIGH UNCERTAINTY REGARDING
POTENTIAL U.S. IMPACTS AT THIS LEAD.
HAZARDS
MODERATE RISK OF EXTREME HEAT FOR PORTIONS OF THE PACIFIC NORTHWEST, GREAT
BASIN, AND NORTHERN CALIFORNIA, TUE-WED, AUG 12-13.
MODERATE RISK OF EXTREME HEAT FOR PORTIONS OF THE NORTHEAST, TUE-WED, AUG 12-13.
SLIGHT RISK OF EXTREME HEAT FOR MUCH OF THE WESTERN CONUS, TUE-THU, AUG 12-14.
SLIGHT RISK OF EXTREME HEAT FOR PORTIONS OF THE OHIO VALLEY, EASTERN GREAT
LAKES, NORTHEAST, AND NORTHERN MID-ATLANTIC, TUE-FRI, AUG 12-15.
DETAILED SUMMARY
FOR THURSDAY AUGUST 07 - MONDAY AUGUST 11:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY AUGUST 12 - MONDAY AUGUST 18: AT THE OUTSET OF WEEK-2, MID-LEVEL
RIDGING AND ASSOCIATED POSITIVE 500-HPA HEIGHT ANOMALIES ARE PREDICTED ACROSS
THE EASTERN NORTH PACIFIC EXTENDING INTO THE NORTHWESTERN CONUS. AS A RESULT,
THE GREATEST RISK OF EXTREME HEAT IS FORECAST TO SHIFT NORTHWARD RELATIVE TO
WEEK-1 AND BECOME MORE FOCUSED ACROSS THE NORTHWEST. THE GEFS AND ECENS
PROBABILISTIC EXTREMES TOOLS (PETS) DEPICT 30-50 PERCENT PROBABILITIES FOR
TEMPERATURES EXCEEDING THE 85TH CLIMATOLOGICAL PERCENTILE ON DAY-8 (AUG 12),
AND GRADUALLY DECREASE THEREAFTER. TEMPERATURES IN THE UNCALIBRATED GUIDANCE
PEAK AROUND DAY-7, BUT THE 0Z ECENS CONTINUES TO SHOW MAXIMUM TEMPERATURES IN
THE MID 90S DEG F OVER THE WILLAMETTE VALLEY OF OREGON INCLUDING PORTLAND,
PERSISTING INTO DAY-8, WITH HIGHER TEMPERATURES (UPWARDS OF 95-100 DEG F OVER
THE VALLEYS OF THE GREAT BASIN. THE 0Z GEFS IS ON AVERAGE A FEW DEGREES COOLER
THAN THE ECENS BUT DEPICTS THE SAME GENERAL TEMPERATURE PATTERN. A MODERATE
RISK OF EXTREME HEAT IS HIGHLIGHTED FOR PORTIONS OF THE PACIFIC NORTHWEST,
GREAT BASIN, AND NORTHERN CALIFORNIA, AUG 12-13. A SLIGHT RISK CONTINUES
THROUGH AUG 14 AND ALSO INCLUDES PORTIONS OF THE SOUTHWEST AND FOUR CORNERS.
WHILE THESE AREAS ARE LIKELY TO HAVE COMPARATIVELY HIGHER TEMPERATURES THAN
THOSE FARTHER NORTH, THE TEMPERATURES ARE FORECAST TO BE COOLER COMPARED TO
THOSE FORECAST EARLIER IN WEEK-1.
THE OTHER AREA BEING MONITORED FOR EXTREME HEAT IS OVER PORTIONS OF THE
NORTHEAST UNDERNEATH ANOMALOUS RIDGING PREDICTED OVER NORTHEASTERN NORTH
AMERICA. THE PETS ARE QUITE BULLISH IN PROBABILISTIC SPACE, WITH THE ECENS PET
IN PARTICULAR DEPICTING PARTS OF UPSTATE NEW YORK AND NEW ENGLAND HAVING AT
LEAST A 40 PERCENT CHANCE OF TEMPERATURES EXCEEDING THE 95TH CLIMATOLOGICAL
PERCENTILE. LIKE THE NORTHWEST, PROBABILITIES ARE HIGHEST AT THE START OF THE
PERIOD AND DECREASE BY THE MIDDLE OF THE PERIOD. THE DOWNWARD TREND IN THE
SEASONAL TEMPERATURE CLIMATOLOGY IS LIKELY PLAYING A ROLE IN THE INFLATED
PROBABILITIES IN THE PETS, ALTHOUGH ACTUAL TEMPERATURES IN THE UNCALIBRATED 0Z
ECENS AND GEFS ARE IN THE UPPER 80S TO LOWER 90S DEG F, WITH SOME DAILY RECORDS
BEING DEPICTED IN THE NATIONAL BLEND OF MODELS. ADDITIONALLY, THE CALIBRATED
SKILL-WEIGHTED HEAT RISK GUIDANCE DEPICTS AT LEAST A 50 PERCENT CHANCE OF
TEMPERATURES OR HEAT INDICES EXCEEDING THE 95TH CLIMATOLOGICAL PERCENTILE
ACROSS THE REGION. WHILE FORECAST TEMPERATURES MAY NOT NECESSARILY BE
IMPACTFUL, THEY MAY BE WARM ENOUGH TO TRIGGER HEAT RELATED MESSAGING ACROSS THE
REGION FROM LOCAL NATIONAL WEATHER SERVICE FORECAST OFFICES. THEREFORE, A
MODERATE RISK OF EXTREME HEAT IS POSTED ACROSS PORTIONS OF THE NORTHEAST, AUG
12-13, WITH A SLIGHT RISK EXTENDED FURTHER SOUTH ACROSS THE NORTHERN
MID-ATLANTIC, OHIO VALLEY, AND EASTERN GREAT LAKES THROUGH AUG 15.
BY THE SECOND HALF OF WEEK-2, WEAK BROAD MID-LEVEL RIDGING IS FORECAST TO
SET-UP ACROSS THE CONUS WITH GENERALLY TRANQUIL WEATHER AND DECREASING EXTREME
HEAT SIGNALS. THE BIG STORY WILL LIKELY BE THE UPTICK IN ACTIVITY ACROSS THE
TROPICAL ATLANTIC. IN ADDITION TO TROPICAL STORM DEXTER TRACKING OVER THE
NORTHWEST ATLANTIC, THE NATIONAL HURRICANE CENTER (NHC) IS MONITORING 2 AREAS
FOR POTENTIAL TROPICAL CYCLONE DEVELOPMENT IN THE NEXT 7-DAYS, LOCATED OFF THE
SOUTHEAST COAST AND IN THE CENTRAL ATLANTIC. BOTH THE GEFS AND ECENS INDIVIDUAL
ENSEMBLE MEMBERS DEPICT TROPICAL LOWS APPROACHING THE U.S. COAST DURING WEEK-2,
WITH THE GEFS AND ITS 0Z AND 6Z DETERMINISTIC COUNTERPARTS FAVORING A FASTER
ARRIVAL OF A SYSTEM BY THE END OF NEXT WEEK. HOWEVER, THE ECENS IS A BIT MORE
DELAYED AND ALSO GENERALLY FAVORS MORE SUPPRESSION INTO THE CARIBBEAN. FOR NOW,
NO RELATED PRECIPITATION OR WIND HAZARDS ARE HIGHLIGHTED ALONG THE EAST OR GULF
COASTS GIVEN THE HIGH MODEL SPREAD AT THIS LEAD, BUT THERE IS INCREASING
CONFIDENCE THAT TROPICAL CYCLONE ACTIVITY WILL INCREASE ACROSS THE ATLANTIC BY
MID- TO LATE-AUGUST. INTERESTS ARE ADVISED TO MONITOR NHC FOR THE LATEST
INFORMATION AND TRACK GUIDANCE.
A ZONAL MID-LEVEL FLOW PATTERN IS FORECAST OVER ALASKA, WITH WEAK TROUGHING
ACROSS THE MAINLAND AND RIDGING TO THE SOUTH OVER THE NORTH PACIFIC. ONSHORE
FLOW ACROSS THE SOUTHEAST IS FORECAST TO DIMINISH COMPARED TO WEEK-1 ALLOWING
THE SLIGHT RISK FOR HEAVY PRECIPITATION TO BE DISCONTINUED, ALTHOUGH AN
UNSETTLED PATTERN REMAINS LIKELY THROUGHOUT THE PERIOD.
FORECASTER: THOMAS COLLOW
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