135   
FXUS21 KWNC 191841  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EDT JULY 19 2024  
  
SYNOPSIS: AN EASTWARD SHIFTING AREA OF STRONG MID-LEVEL HIGH PRESSURE DURING   
WEEK-2 LEADS TO AN INCREASED RISK FOR EXCESSIVE HEAT OVER PARTS OF THE   
NORTH-CENTRAL AND NORTHEASTERN CONTIGUOUS U.S. (CONUS) LATER IN JULY. WITH   
HOTTER AND DRIER THAN NORMAL CONDITIONS PREDOMINATELY FAVORED OVER THE INTERIOR   
WEST AND GREAT PLAINS, AN EXPANDED RAPID ONSET DROUGHT (ROD) RISK AREA IS   
ISSUED FOR PARTS OF THE NORTHERN AND CENTRAL PLAINS WHERE POOR SOIL MOISTURES   
AND BELOW-NORMAL RAINFALL AMOUNTS HAVE BEEN REGISTERED.     
  
HAZARDS  
  
MODERATE RISK OF EXCESSIVE HEAT FOR PARTS OF THE NORTHERN PLAINS AND UPPER   
MISSISSIPPI VALLEY, SAT-SUN, JUL 27-28.   
  
MODERATE RISK OF EXCESSIVE HEAT FOR PARTS OF THE NORTHERN GREAT LAKES AND THE   
NORTHEAST, SUN-TUE, JUL 28-30.    
  
SLIGHT RISK OF EXCESSIVE HEAT FOR PARTS OF THE NORTHERN ROCKIES, NORTHERN AND   
CENTRAL PLAINS, UPPER MISSISSIPPI VALLEY, GREAT LAKES, OHIO VALLEY,   
MID-ATLANTIC, AND THE NORTHEAST, SAT-FRI, JUL 27-AUG 2.  
  
SLIGHT RISK OF EPISODIC HIGH WINDS FOR MUCH OF THE WESTERN CONUS, SAT-MON, JUL   
27-29.  
  
RAPID ONSET DROUGHT RISK FOR PORTIONS OF THE NORTHERN AND CENTRAL PLAINS.  
  
DETAILED SUMMARY  
  
FOR MONDAY JULY 22 - FRIDAY JULY 26:   
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP  
  
FOR SATURDAY JULY 27 - FRIDAY AUGUST 02: BY LATE NEXT WEEK AND INTO THE   
FOLLOWING WEEKEND, 500-HPA HEIGHT FORECASTS FROM THE GEFS AND ECMWF ENSEMBLES   
CONTINUE TO FEATURE AN AMPLIFYING TROUGH OVER WESTERN CANADA AND THE WEST   
COAST, AND AN EASTWARD PROGRESSION OF A STRONG RIDGE CENTER WITH POSITIVE   
HEIGHT DEPARTURES OVERSPREADING MUCH OF SOUTHERN CANADA AND THE NORTHEASTERN   
CONUS. LATER IN WEEK-2, DYNAMICAL MODELS GENERALLY AGREE ON THE MID-LEVEL   
PATTERN EVOLUTION OVER EASTERN NORTH AMERICA, FAVORING THE CONTINUATION OF THE   
ANOMALOUS RIDGING (ALBEIT SOME DIFFERENCES IN STRENGTH) OVER THE CANADIAN   
MARITIMES WITH MORE SUBTROPICAL RIDGING DEVELOPING IN THE SOUTHEAST, BUT   
DIVERGE IN REGARDS TO THE EVOLUTION OF TROUGHING UPSTREAM OVER THE WEST. THE   
GEFS MAINTAINS A MORE PERSISTENT SOLUTION OF THE TROUGH, WHEREAS THE ECMWF IS   
QUICK TO BUILD MORE RIDGING BACK IN OVER THE FOUR CORNERS. GIVEN THIS, OUTLOOK   
CONFIDENCE IS HIGHER EAST OF THE ROCKIES, FAVORING WARMING TEMPERATURES AND THE   
POTENTIAL FOR EXCESSIVE HEAT ACROSS THE NORTHERN TIER OF THE CONUS, WITH THE   
HAZARDS PICTURE BECOMING LESS CLEAR OUT WEST THROUGH THE END OF JULY AND   
HEADING INTO AUGUST.   
  
TIED TO THE AMPLIFYING TROUGH AND THE ASSOCIATED NORTHWESTERLY FLOW TO BRING   
COOLER TEMPERATURES OVER PARTS OF THE WESTERN CONUS LATE NEXT WEEK, THE SLIGHT   
RISK OF EXCESSIVE HEAT IS DISCONTINUED IN TODAY'S OUTLOOK AS THE PREDICTED HEAT   
EVENT OVER THE WEST NOW APPEARS TO BE LARGELY WITHIN THE WEEK-1 TIMEFRAME. BUT   
IN RESPONSE TO THE ENHANCED SOUTHWESTERLY FLOW UPSTREAM OF THE AMPLIFIED RIDGE   
CENTER TO THE SOUTH OF HUDSON BAY, THERE CONTINUES TO BE INCREASED ODDS FOR   
ABOVE-NORMAL TEMPERATURES MAINLY OVER THE NORTH-CENTRAL CONUS EARLY IN THE   
PERIOD. GOOD AGREEMENT EXISTS BETWEEN THE GEFS AND ECMWF PROBABILISTIC EXTREMES   
TOOLS (PETS) SHOWING ELEVATED CHANCES (30-40%) FOR MAXIMUM TEMPERATURES   
EXCEEDING THE 85TH PERCENTILE TO SUPPORT THE CONTINUATION OF THE MODERATE RISK   
OF EXCESSIVE HEAT OVER THE NORTHERN HIGH PLAINS AND UPPER MISSISSIPPI VALLEY   
THROUGH DAY 9 (JUL 28).    
  
AS THE TROUGHING OVER THE NORTHWESTERN CONUS WEAKENS, AND THE ANOMALOUS RIDGE   
CENTER SHIFTS EASTWARD INTO SOUTHEASTERN CANADA TOWARDS THE MIDDLE OF WEEK-2,   
PETS SHOW AN EXPANSION OF THE HEAT SIGNALS INTO PORTIONS OF THE GREAT LAKES,   
OHIO VALLEY, MID-ATLANTIC AND THE NORTHEAST. GIVEN INCREASED SUPPORT IN THE RAW   
TEMPERATURE TOOLS AND THE BETTER AGREEMENT IN THE PETS DEPICTING 30-50% CHANCES   
FOR MAXIMUM TEMPERATURES EXCEEDING THE 85TH PERCENTILE, A MODERATE RISK OF   
EXCESSIVE HEAT IS ISSUED FOR THE REGION FROM JUL 28-30.  A BROAD SLIGHT RISK OF   
EXCESSIVE HEAT REMAINS ISSUED ALONG THE NORTHERN TIER OF THE CONUS, EAST OF THE   
ROCKIES, IN PROXIMITY TO THE PREVAILING POSITIVE HEIGHT ANOMALIES OVER SOUTHERN   
CANADA AND REMAINS VALID FOR ALL OF WEEK-2.  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, HOWEVER   
THE ECMWF PET, AS WELL AS RAW TEMPERATURE TOOLS ARE LESS SUPPORTIVE OF THIS   
REALIZATION. EXCESSIVE HEAT CONDITIONS MAY BE FELT ACROSS PARTS OF THE CORN   
BELT AND LOWER GREAT LAKES AS THE HEAT SIGNALS BEGIN TO SHIFT SOUTH, BUT THERE   
REMAINS UNCERTAINTY AS TO HOW LONG THE COLDER AIR ESTABLISHED OVER THE CENTRAL   
U.S. EARLY IN WEEK-2 TAKES TO MODERATE. THERE ARE ALSO QUESTIONS AS TO   
RELIABILITY AND BIAS OF THE GEFS PET IN THIS PART OF THE COUNTRY DURING THE   
WARM SEASON.    
  
THE COMBINATION OF CONTINUED ABOVE-NORMAL TEMPERATURES AND BELOW-NORMAL   
PRECIPITATION SUPPORTS THE CONTINUATION OF A RAPID ONSET DROUGHT (ROD) RISK   
OVER MANY PARTS OF THE NORTHERN AND CENTRAL HIGH PLAINS. 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.   
  
LEE SIDE SURFACE TROUGHING REMAINS 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 27-29 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.   
  
FOR PRECIPITATION, THE THREAT OF HEAVY RAINFALL LOOKS TO HAVE TIMED OFF OVER   
THE LOWER PLAINS AND MISSISSIPPI VALLEY, WITH MUCH OF THE TROUGHING FAVORED TO   
LIFT OUT LATE NEXT WEEK, AND MORE SUBTROPICAL RIDGING OVERSPREADING THE   
SOUTHEAST FROM THE WESTERN ATLANTIC. WHILE THERE CONTINUES TO BE MODEST SUPPORT   
IN THE PETS FOR 3-DAY AMOUNTS EXCEEDING THE 85TH PERCENTILE EARLY IN WEEK-2,   
RAW PRECIPITATION AMOUNTS FROM THE ENSEMBLES HAVE BECOME TENUOUS, AND THE   
SLIGHT RISK OF HEAVY PRECIPITATION IS REMOVED IN THE UPDATED OUTLOOK. IT SHOULD   
BE NOTED HOWEVER, THAT ABOVE-NORMAL PRECIPITATION PREDOMINATELY FAVORED IN THE   
NEXT TWO WEEKS OVER PORTIONS OF SOUTHERN TEXAS AND THE EASTERN CAROLINAS MAY   
LEAD TO LOCALIZED FLOODING IN THESE REGIONS DURING THE PERIOD.   
  
OVER ALASKA, A HIGHLY AMPLIFIED TROUGH/RIDGE COUPLET IS FAVORED OVER THE BERING   
SEA AND NORTHERN PACIFIC DURING WEEK-2. THE RESULTANT ENHANCED ONSHORE FLOW IS   
EXPECTED TO LEAD TO PERIODS OF ELEVATED WIND SPEEDS AND ENHANCED PRECIPITATION   
OVER PARTS OF THE MAINLAND, HOWEVER, PETS SHOW NEITHER WIND NOR PRECIPITATION   
AMOUNTS EXCEEDING HAZARD THRESHOLDS, AND NO CORRESPONDING HAZARDS ARE ISSUED.   
LOCALIZED FLOODING MAY BE A CONCERN ASSOCIATED WITH THE GLACIAL OUTBURST FLOOD   
FOR THE MENDENHALL RIVER.  
  
FORECASTER: NICK NOVELLA   
  
  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.


The Nexlab HPC Page

Main Text Page