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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