031   
FXUS21 KWNC 181822  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EDT JULY 18 2024  
  
SYNOPSIS: AN EASTWARD SHIFTING AREA OF MID-LEVEL HIGH PRESSURE DURING WEEK-2 IS   
EXPECTED TO SUSTAIN AN INCREASED RISK FOR EXCESSIVE HEAT OVER MANY PARTS OF THE   
WESTERN CONTIGUOUS U.S. (CONUS) EARLY IN THE PERIOD, WITH INCREASING CHANCES   
FOR HEAT ACROSS THE NORTHERN GREAT PLAINS AND EXPANDING OVER THE NORTHERN TIER   
OF THE CONUS LATER IN JULY. MID-LEVEL LOW PRESSURE FOCUSED OVER THE LOWER   
PLAINS AND MISSISSIPPI VALLEY IS LIKELY TO PROMOTE COOLER AND WETTER CONDITIONS   
EARLY IN WEEK-2, WITH INCREASED CHANCES FOR HEAVY PRECIPITATION IN THE SOUTHERN   
PLAINS AND LOWER MISSISSIPPI VALLEY. WITH HOTTER AND DRIER THAN NORMAL   
CONDITIONS PREDOMINATELY FAVORED, AN EXPANDED RAPID ONSET DROUGHT (ROD) RISK   
AREA IS ISSUED FOR PARTS OF THE NORTHERN AND CENTRAL PLAINS.    
  
HAZARDS  
  
MODERATE RISK OF EXCESSIVE HEAT FOR PARTS OF THE NORTHERN PLAINS AND UPPER   
MISSISSIPPI VALLEY, FRI-SUN, JUL 26-28.   
  
SLIGHT RISK OF EXCESSIVE HEAT FOR PARTS OF CALIFORNIA, DESERT SOUTHWEST, GREAT   
BASIN, ROCKIES AND NORTHERN INTERMOUNTAIN, FRI, JUL 26.  
  
SLIGHT RISK OF EXCESSIVE HEAT FOR PARTS OF THE NORTHERN ROCKIES, NORTHERN AND   
CENTRAL PLAINS, UPPER MISSISSIPPI VALLEY, GREAT LAKES, AND THE NORTHEAST,   
FRI-THU, JUL 26-AUG 1.  
  
SLIGHT RISK OF EPISODIC HIGH WINDS FOR MUCH OF THE WESTERN CONUS, FRI-SUN, JUL   
26-28.  
  
SLIGHT RISK OF HEAVY PRECIPITATION FOR PARTS OF THE SOUTHERN PLAINS, LOWER   
MISSISSIPPI AND TENNESSEE VALLEYS, AND THE SOUTHEAST, FRI-SAT, JUL 26-27.    
  
RAPID ONSET DROUGHT RISK FOR PORTIONS OF THE NORTHERN AND CENTRAL PLAINS.  
  
DETAILED SUMMARY  
  
FOR SUNDAY JULY 21 - THURSDAY JULY 25:   
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP  
  
FOR FRIDAY JULY 26 - THURSDAY AUGUST 01: DYNAMICAL MODEL GUIDANCE APPEARS TO   
REMAIN ON TRACK OVER THE PAST FEW DAYS. BOTH THE GEFS AND ECMWF CONTINUE TO   
FAVOR A WEAKENING 500-HPA RIDGE OVER THE WESTERN CONUS WITH COOLING   
TEMPERATURES TO ALLEVIATE THE EXCESSIVE HEAT RISK OVER MANY PARTS OF WEST FOR   
LATE NEXT WEEK.  ANOMALOUS MID-LEVEL TROUGHING DEVELOPING OVER WESTERN CANADA   
AND INTO THE WEST COAST IS EXPECTED TO LEAD TO EASTWARD PROGRESSION OF THE   
AMPLIFIED RIDGE CENTER TO THE SOUTH OF HUDSON BAY WHERE THERE IS BETTER   
AGREEMENT BETWEEN THE GEFS AND ECMWF ENSEMBLES IN THE TIMING, LOCATION, AND   
STRENGTH OF THIS MID-LEVEL FEATURE. AS A RESULT, THERE IS ADDED CONFIDENCE FOR   
ABOVE-NORMAL TEMPERATURES TO OVERSPREAD THE NORTHERN TIER, AND INTO PARTS OF   
THE EASTERN CONUS LATER IN JULY, WITH A RENEWED RISK OF EXCESSIVE HEAT FOR   
PARTS OF THE GREAT PLAINS AND UPPER MIDWEST. ACROSS THE SOUTHERN TIER OF THE   
U.S., MUCH OF THE TROUGHING THAT IS FAVORED TO LINGER OVER THE LOWER PLAINS AND   
MISSISSIPPI VALLEY DURING WEEK-1 LOOKS TO BE FINALLY LIFTING OUT LATE NEXT   
WEEK, BUT NOT BEFORE ANOTHER ROUND OF POTENTIALLY HEAVY PRECIPITATION COULD BE   
FELT OVER PARTS OF THE PLAINS, MISSISSIPPI AND TENNESSEE VALLEYS EARLY IN THE   
PERIOD.      
  
A SLIGHT RISK OF EXCESSIVE HEAT REMAINS POSTED FOR PARTS OF CALIFORNIA AND THE   
INTERIOR WEST FOR DAY 8 (JUL 26), WHERE THERE ARE RESIDUAL HEAT SIGNALS IN THE   
PROBABILISTIC EXTREMES TOOLS (PETS) TIED TO THE WEAKENING RIDGE ALOFT. MUCH OF   
THE SLIGHT RISK COVERAGE HAS BEEN WITHDRAWN OVER THE NORTHERN INTERMOUNTAIN   
REGION IN THE UPDATED OUTLOOK DUE TO THE ENCROACHING MID-LEVEL TROUGH FAVORED   
OVER THE NORTHWESTERN CONUS. ACROSS THE NORTHERN TIER OF THE CONUS, THERE IS   
BETTER AGREEMENT BETWEEN THE GEFS AND ECMWF PETS DEPICTING AN EXPANSIVE AREA   
WITH AT LEAST 20% CHANCES OF MAXIMUM TEMPERATURES EXCEEDING THE 85TH   
PERCENTILE. HIGHER PROBABILITIES (30-40%) ARE INDICATED ACROSS NORTHERN PARTS   
OF EASTERN MONTANA, NORTH DAKOTA, AND MINNESOTA AND WHILE CHANCES FOR ACTUAL   
TEMPERATURES EXCEEDING 95 DEG F APPEAR RATHER WEAK IN THE PETS, RAW TEMPERATURE   
TOOLS ARE MORE ROBUST IN EXCEEDING THIS THRESHOLD, WITH THE POTENTIAL FOR   
ENHANCED HEAT INDEX VALUES. THEREFORE, A MODERATE RISK OF EXCESSIVE HEAT IS   
ADDED FOR THE REGION (JUL 26-28) AND A BROADER SLIGHT RISK AREA FOR EXCESSIVE   
HEAT IS CONTINUED FOR JUL 27-AUG 1. THE SLIGHT RISK AREA IS EXPANDED EASTWARD   
TO INCLUDE NORTHERN PORTIONS OF THE GREAT LAKES, AND THE NORTHEAST, WHERE PETS   
SHOW BUILDING WARM SIGNALS LATER IN THE PERIOD IN PROXIMITY TO THE AMPLIFIED   
RIDGING OVER SOUTHERN CANADA.  OF NOTE, THE GEFS PET CONTINUES TO FAVOR   
INCREASED CHANCES FOR EXCESSIVE HEAT FURTHER SOUTH INTO THE MIDDLE MISSISSIPPI,   
OHIO AND TENNESSEE VALLEYS TOWARDS THE MIDDLE OF WEEK-2, THOUGH THE ECMWF PET   
AS WELL AS RAW TEMPERATURE TOOLS ARE MUCH LESS SUPPORTIVE OF THIS REALIZATION,   
AS MUCH OF THE COLDER AIR ESTABLISHED OVER THE CENTRAL U.S. EARLY IN WEEK-2 MAY   
TAKE SOME TIME TO MIX OUT.   
  
THE COMBINATION OF CONTINUED ABOVE-NORMAL TEMPERATURES AND BELOW-NORMAL   
PRECIPITATION SUPPORTS THE CONTINUATION OF A RAPID ONSET DROUGHT (ROD) RISK   
OVER PARTS OF EASTERN MONTANA, WYOMING AND THE DAKOTAS. BASED ON SOIL MOISTURE   
TRENDS, RAINFALL REGISTERED DURING THE PAST MONTH AND IN THE NEXT TWO WEEKS,   
THE ROD RISK HAS BEEN EXPANDED TO INCLUDE PARTS OF THE WESTERN DAKOTAS,   
NEBRASKA, NORTHEASTERN COLORADO AND KANSAS IN THE UPDATED OUTLOOK. 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.   
  
AT THE BASE OF THE TROUGHING ALOFT OVER THE NORTHWESTERN CONUS, LEE SIDE   
SURFACE TROUGHING IS FAVORED OVER THE NORTHERN AND CENTRAL PLAINS WHERE   
ENSEMBLES CONTINUE TO SHOW PERIODS OF STRENGTHENING PRESSURE GRADIENTS IN THE   
REGION, AS WELL AS FURTHER SOUTH IN THE DESERT SOUTHWEST. BASED ON CONTINUED   
SUPPORT FROM THE ECMWF PET FAVORING INCREASED CHANCES FOR WIND SPEEDS EXCEEDING   
THE 85TH PERCENTILE, A SLIGHT RISK OF HIGH WINDS REMAINS ISSUED FOR JUL 26-28   
BEFORE THE PATTERN DEAMPLIFIES OVER THE WESTERN CONUS. HOT, DRY AND WINDY   
CONDITIONS ARE LIKELY TO LEAD TO ENHANCED RISK OF WILDFIRES IN THE HIGHLIGHTED   
REGION, AND INHIBIT EFFORTS TO CONTAIN ANY ACTIVE WILDFIRES.   
  
WITH MUCH OF THE TROUGHING FAVORED TO LIFT OUT OVER THE LOWER PLAINS AND   
MISSISSIPPI VALLEY, RAW TOOLS HAVE BEGUN TO BACK OFF ON THE CONTINUED   
ENHANCEMENT OF DAILY PRECIPITATION AMOUNTS. NOTWITHSTANDING, RETURN FLOW FROM   
THE GULF OF MEXICO AND A STALLED FRONTAL BOUNDARY THAT IS EXPECTED TO LINGER   
LATE NEXT WEEK SUSTAINS A HEAVY PRECIPITATION RISK EARLY IN WEEK-2. THERE   
REMAINS GOOD AGREEMENT IN THE PETS SHOWING INCREASED CHANCES FOR 3-DAY AMOUNTS   
EXCEEDING THE 85TH PERCENTILE, AND A CORRESPONDING SLIGHT RISK REMAINS POSTED   
FOR JUL 26-27. A KEY CHANGE IN THE PETS IS THE REDUCTION OF THE WET SIGNALS   
OVER THE EASTERN U.S., AND THE SLIGHT RISK COVERAGE IS REMOVED OVER THIS PART   
OF THE COUNTRY. AS A RESULT OF THE REDUCED POTENTIAL FOR HEAVY PRECIPITATION   
FURTHER EAST, AS WELL AS A LOWERED RISK IN OWPS LATEST EXPERIMENTAL FLOOD   
HAZARD OUTLOOK, THE POSSIBLE FLOODING IS LIKEWISE REMOVED OVER THE EASTERN   
CAROLINAS AND SOUTHEASTERN VIRGINIA IN THE UPDATED OUTLOOK. IT SHOULD BE NOTED   
HOWEVER, THAT ABOVE-NORMAL PRECIPITATION PREDOMINATELY FAVORED DURING WEEK-2   
MAY STILL LEAD TO LOCALIZED FLOODING IN THE REGION.   
  
FORECASTER: NICK NOVELLA   
  
  
 
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