944
FXUS21 KWNC 081833
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JULY 08 2024
SYNOPSIS: MID-LEVEL HIGH PRESSURE IS FORECAST TO CONTINUE OVER MUCH OF THE
CONTIGUOUS U.S. (CONUS) FAVORING CONTINUED CHANCES OF EXCESSIVE HEAT
CONDITIONS, PARTICULARLY OVER PORTIONS OF THE GREAT BASIN AND THE MID-ATLANTIC,
ALTHOUGH THE HIGHEST RISK FOR IMPACTFUL HEAT IS NOW IN WEEK-1. SOUTHERLY MOIST
FLOW INTO THE SOUTHWEST RESULTS IN INCREASED CHANCES FOR LOCALIZED HEAVY
PRECIPITATION IN THE REGION. PERIODS OF POTENTIALLY HIGH WINDS ACROSS THE
CASCADES, SOUTHWESTERN OREGON, AND CENTRAL AND NORTHERN CALIFORNIA MAY INCREASE
THE RISK FOR WILDFIRES IN THE AREA.
HAZARDS
SLIGHT RISK OF EXCESSIVE HEAT ACROSS CENTRAL AND NORTHERN GREAT BASIN, NORTHERN
ROCKIES, AND NORTHERN PLAINS, TUE-MON, JUL 16-22.
SLIGHT RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE MID-ATLANTIC AND SOUTHEAST
U.S., TUE-THU, JUL 16-18.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE DESERT SOUTHWEST AND
SOUTHERN ROCKIES, TUE-THU, JUL 16-18.
SLIGHT RISK OF HIGH WINDS FOR PORTIONS OF CALIFORNIA AND THE PACIFIC NORTHWEST,
TUE-THU, JUL 16-18.
RAPID ONSET DROUGHT RISK FOR PORTIONS OF THE SOUTHEAST U.S., OHIO AND TENNESSEE
VALLEYS, AND NORTHERN PLAINS.
DETAILED SUMMARY
FOR THURSDAY JULY 11 - MONDAY JULY 15:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY JULY 16 - MONDAY JULY 22: AN AMPLIFIED MID-LEVEL RIDGE IS FORECAST
TO BE CENTERED OVER THE INTERIOR WEST AT THE BEGINNING OF WEEK-2, EXPANDING
EASTWARD AND GRADUALLY WEAKENING OVER TIME. MULTIPLE MODEL ENSEMBLE MEANS
INDICATE PERSISTENT WIDESPREAD POSITIVE 500 HPA HEIGHT DEPARTURES OVER THE
NORTHERN ROCKIES AND NORTHERN PLAINS AT THE START OF THE PERIOD, RESULTING IN
CONTINUED CHANCES FOR EXCESSIVE HEAT ACROSS THESE AREAS. THE STRONGEST POSITIVE
HEIGHT ANOMALIES AND ANOMALOUS TEMPERATURES ASSOCIATED WITH THIS EVENT ARE NOW
IN THE WEEK-1 PERIOD BUT A SLIGHT RISK OF EXCESSIVE HEAT IS POSTED FOR PORTIONS
OF THE GREAT BASIN, NORTHERN ROCKIES, AND NORTHERN PLAINS FOR THE ENTIRETY OF
WEEK-2, WHERE THE ECMWF AND GEFS PROBABILISTIC EXTREMES TOOLS (PETS) STILL
INDICATE AT LEAST A 20% CHANCE OF MAXIMUM TEMPERATURES EXCEEDING THE 85TH
PERCENTILE AND 95F. MODEL SOLUTIONS GENERALLY FAVOR A WIDER EASTWARD EXTENT OF
THE RIDGE, SPREADING THE CHANCES FOR EXCESSIVE HEAT INTO PORTIONS OF THE
EASTERN CONUS AS WELL. THE GEFS IS ESPECIALLY BULLISH, INDICATING THE POTENTIAL
FOR EXCESSIVE HEAT OVER MUCH OF THE EAST COAST AND OHIO VALLEY THROUGHOUT THE
WEEK, WHILE THE ECMWF CONFINES THE GREATEST CHANCES OF EXCESSIVE HEAT TO THE
MID-ATLANTIC, AND ONLY FOR THE EARLY PORTION OF WEEK-2. A SLIGHT RISK OF
EXCESSIVE HEAT IS POSTED FOR PORTIONS OF THE SOUTHEAST U.S. AND MID-ATLANTIC
FOR JUL 16-18, WHERE THE GREATEST AGREEMENT BETWEEN THE MODELS IS FOUND. THE
GEFS AND ECMWF PETS ALSO INDICATE THE POTENTIAL FOR 3-DAY ACCUMULATED RAINFALL
TO EXCEED THE 85TH PERCENTILE OVER THE MID-ATLANTIC THROUGHOUT WEEK-2, HOWEVER
THE HEAVIEST PRECIPITATION TOTALS ARE PREDICTED TO REMAIN OVER THE OCEAN, SO NO
ASSOCIATED HAZARD IS POSTED AT THIS TIME.
POSSIBLE SURFACE LOW FORMATION WITH ADJACENT SURFACE HIGH PRESSURE OVER THE
NORTHERN PACIFIC MAY SUPPORT TIGHT PRESSURE GRADIENTS ACROSS THE NORTHWEST AND
CALIFORNIA, THUS A SLIGHT RISK OF EPISODIC HIGH WINDS IS MAINTAINED FOR THE
CASCADES AND NORTHERN AND CENTRAL CALIFORNIA, JUL 16-18. THE GEFS AND ECENS PET
BOTH SHOW A WEAKER SIGNAL THAN LATE LAST WEEK, BUT THE POTENTIAL FOR HIGH WINDS
IS STILL INDICATED BY PROBABILISTIC WIND SPEED FORECASTS FROM BOTH MODELS EARLY
IN WEEK-2 (I.E., NEAR CERTAINTY OF WINDS OVER 10KTS ALONG AND IN THE LEE OF THE
CASCADES AND NORTHERN SIERRAS, >70% CHANCE OF WINDS JUST OFFSHORE EXCEEDING
20KTS). HOT, DRY, AND WINDY CONDITIONS ARE LIKELY TO LEAD TO ENHANCED RISK OF
WILDFIRES ACROSS WEST COAST STATES AND INHIBIT EFFORTS TO CONTAIN ANY ACTIVE
WILDFIRES.
THE INITIAL POSITION OF THE RIDGE AXIS NEAR THE DESERT SOUTHWEST FAVORS A MORE
ACTIVE MONSOON EARLY IN WEEK-2. HOWEVER, THE RIDGE TILTS MORE NORTHWESTERLY AS
WEEK-2 PROGRESSES, WHICH IS LESS FAVORABLE FOR SOUTHERLY MOISTURE FLOW INTO
PARTS OF THE SOUTHWEST. THE PETS INDICATE PROBABILITIES ABOVE 20 PERCENT FOR
3-DAY PRECIPITATION TOTALS EXCEEDING THE 85TH CLIMATOLOGICAL PERCENTILE AND 0.5
INCHES DURING THE EARLY HALF OF THE PERIOD. THEREFORE, A SLIGHT RISK OF
PERIODIC HEAVY PRECIPITATION IS POSTED ACROSS PORTIONS OF ARIZONA, NEW MEXICO,
AND SOUTHERN COLORADO, JUL 16-18. LOCALIZED FLOODING IS POSSIBLE ACROSS THIS
AREA, ALTHOUGH THERE IS TOO MUCH UNCERTAINTY AT THIS TIME TO DESIGNATE A FLOOD
RISK.
THE PERSISTENT WARMER AND DRIER THAN NORMAL CONDITIONS OVER AT LEAST THE PAST
MONTH HAVE LED TO A RISK FOR RAPID ONSET DROUGHT FOR PARTS OF THE NORTHERN
PLAINS, OHIO VALLEY (EASTERN CORN BELT), TENNESSEE VALLEY, AND SOUTHEAST U.S.
THE RECENT HEAT WAVES ACROSS THE EASTERN U.S. HAVE EXACERBATED THE ONGOING
DRYNESS ACROSS THIS AREA, AND HAS LED TO MODERATE DROUGHT (D1) FOR MANY AREAS
IN THE EAST. MUCH OF THE AREAS HIGHLIGHTED FOR RISK OF RAPID ONSET DROUGHT HAVE
SEEN LARGE PRECIPITATION DEFICITS OVER THE PAST TWO WEEKS TO A MONTH AND HAVE
SEEN LARGE REDUCTIONS IN AVAILABLE SOIL MOISTURE. THERE IS ADDITIONAL RISK FOR
HIGH EVAPOTRANSPIRATION RATES WITH ABOVE-NORMAL TEMPERATURES FORECAST ACROSS
MUCH OF THE EASTERN CONUS. PERIODIC, LOCALIZED HEAVY PRECIPITATION CANNOT BE
RULED OUT DUE TO FRONTAL AND/OR DAYTIME THUNDERSTORM ACTIVITY, BUT THIS IS
UNLIKELY TO RESULT IN ANY MEANINGFUL CHANGE IN THE POTENTIAL FOR CONTINUED
DEVELOPMENT OF DROUGHT CONDITIONS. DRY SOILS, STRESSED VEGETATION, AND REDUCED
WATER AVAILABILITY DUE TO LOW PONDS AND STREAMS MAY LEAD TO INCREASED IMPACTS
TO AGRICULTURE AND LIVESTOCK, WITH SEVERAL LOCATIONS ALREADY EXPERIENCING
IMPACTS.
FORECASTER: DANNY BARANDIARAN
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