695
FXUS21 KWNC 091809
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JULY 09 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, WED-TUE, JUL 17-23.
SLIGHT RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE MID-ATLANTIC AND SOUTHEAST
U.S., WED-THU, JUL 17-18.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE DESERT SOUTHWEST AND
SOUTHERN ROCKIES, WED-SUN, JUL 17-21.
SLIGHT RISK OF HIGH WINDS FOR PORTIONS OF CALIFORNIA AND THE PACIFIC NORTHWEST,
WED-SUN, JUL 17-21.
RAPID ONSET DROUGHT RISK FOR PORTIONS OF THE SOUTHEAST U.S., OHIO AND TENNESSEE
VALLEYS, AND NORTHERN PLAINS.
DETAILED SUMMARY
FOR FRIDAY JULY 12 - TUESDAY JULY 16:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY JULY 17 - TUESDAY JULY 23: AN AMPLIFIED MID-LEVEL RIDGE IS
FORECAST TO BE CENTERED OVER THE INTERIOR WEST AT THE BEGINNING OF WEEK-2,
GRADUALLY EXPANDING EASTWARD 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 17-18, WHERE THE
GREATEST AGREEMENT BETWEEN THE MODELS IS FOUND. TODAY’S MODEL SOLUTIONS ALSO
HIGHLIGHT THE POTENTIAL FOR EXCESSIVE HEAT LATE IN WEEK-1 AND POSSIBLY INTO
WEEK-2 FOR EASTERN PORTIONS OF KANSAS AND OKLAHOMA. THE HIGHEST CHANCES FOR
IMPACTFUL HEAT FOR THIS REGION ARE CONFINED TO WEEK-1 AND THERE IS CONSIDERABLE
DISAGREEMENT BETWEEN THE ECMWF AND GEFS WITH REGARD FOR THIS HEAT SIGNAL TO
CARRY OVER INTO THE WEEK-2 PERIOD 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 17-21. 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. TODAY’S MODEL SOLUTIONS MAINTAIN THIS FAVORABLE
RIDGE ORIENTATION FURTHER INTO WEEK-2 THAN YESTERDAY, RESULTING IN A LONGER
DURATION OF ENHANCED MONSOON-RELATED PRECIPITATION. THE PETS INDICATE
PROBABILITIES ABOVE 20 PERCENT FOR 3-DAY PRECIPITATION TOTALS EXCEEDING THE
85TH CLIMATOLOGICAL PERCENTILE AND 0.5 INCHES THROUGH THE MIDDLE OF THE PERIOD.
THEREFORE, A SLIGHT RISK OF PERIODIC HEAVY PRECIPITATION IS POSTED ACROSS
PORTIONS OF ARIZONA, NEW MEXICO, AND SOUTHERN COLORADO, JUL 17-21. LOCALIZED
FLOODING IS POSSIBLE ACROSS THIS AREA, ALTHOUGH THERE IS TOO MUCH UNCERTAINTY
AT THIS TIME TO DESIGNATE A FLOOD RISK. THE ECMWF PET ALSO INDICATES 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.
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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