188   
FXUS21 KWNC 191923  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EDT AUGUST 19 2024  
  
SYNOPSIS: MODEL ENSEMBLES DEPICT HIGH PRESSURE BOTH AT THE SURFACE AND   
MID-LEVELS ACROSS MUCH OF THE CONTIGUOUS U.S. (CONUS) THROUGHOUT THE WEEK-2   
PERIOD, LEADING TO THE POTENTIAL FOR EXCESSIVE HEAT FOR PORTIONS OF THE GREAT   
PLAINS AND THE OHIO AND MISSISSIPPI VALLEYS. PROLONGED RAINFALL DEFICITS AND   
CONTINUED HEAT RESULTS IN THE POTENTIAL FOR RAPID ONSET DROUGHT FOR PARTS OF   
THE SOUTHERN PLAINS AND MISSISSIPPI VALLEY.  
  
HAZARDS  
  
SLIGHT RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE MISSISSIPPI, TENNESSEE, AND   
OHIO VALLEYS, GREAT LAKES, AND CENTRAL PLAINS, TUE-FRI, AUG 17-30.  
  
RISK FOR RAPID ONSET DROUGHT FOR PORTIONS OF THE SOUTHERN PLAINS, AND LOWER AND   
MIDDLE MISSISSIPPI VALLEY.  
  
DETAILED SUMMARY  
  
FOR THURSDAY AUGUST 22 - MONDAY AUGUST 26:   
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP  
  
FOR TUESDAY AUGUST 27 - MONDAY SEPTEMBER 02: TODAY’S MODEL SOLUTIONS FOR 500   
HPA HEIGHTS AND ANOMALIES DEPICT GENERALLY ZONAL FLOW AND BROAD RIDGING OVER   
THE CONUS AT THE OUTSET OF WEEK-2 WITH A 594 DM MAXIMUM OVER THE DESERT   
SOUTHWEST. THIS RIDGE WEAKENS GRADUALLY THROUGHOUT THE FORECAST PERIOD AS A   
WEAK TROUGH BEGINS TO TAKE SHAPE OVER THE GREAT LAKES REGION. THE EARLY RIDGING   
LEADS TO THE POTENTIAL FOR EXCESSIVE HEAT FOR PORTIONS OF THE CENTRAL CONUS.   
THE GEFS AND ECMWF PROBABILISTIC EXTREMES TOOLS (PETS) BOTH INDICATE AT LEAST A   
20% PROBABILITY OF MAXIMUM TEMPERATURES EXCEEDING THE 90TH PERCENTILE AND 90F   
AS FAR NORTH AS CHICAGO AND GRAND RAPIDS, AND POSSIBLY OVER 100F FOR PORTIONS   
OF NORTH TEXAS AT THE OUTSET OF WEEK-2. A DEVELOPING TROUGH OVER THE GREAT   
LAKES REDUCES POTENTIAL FOR EXCESSIVE HEAT BY DAY-11 SO A SLIGHT RISK FOR   
EXCESSIVE HEAT IS POSTED FOR PORTIONS OF THE MISSISSIPPI, TENNESSEE, AND OHIO   
VALLEYS, GREAT LAKES, AND CENTRAL PLAINS FOR AUG 27-30. THE PETS ALSO INDICATE   
A 20% PROBABILITY OF MAXIMUM TEMPERATURES EXCEEDING THE 90TH PERCENTILE OVER   
PORTIONS OF THE DESERT SOUTHWEST BUT ABSOLUTE TEMPERATURES ARE NOT EXPECTED TO   
EXCEED HAZARDOUS THRESHOLDS FOR THE REGION, THUS NO ASSOCIATED HAZARD IS POSTED   
AT THIS TIME.  
  
ZONAL MID-LEVEL FLOW OVER THE CONUS GENERALLY DECREASES THE POTENTIAL FOR HEAVY   
PRECIPITATION. THE PETS DO INDICATE A 20% CHANCE OF 3-DAY TOTAL PRECIPITATION   
EXCEEDING THE 85TH PERCENTILE FOR PORTIONS OF THE GULF COAST DUE TO AN   
INCREASED POTENTIAL FOR TROPICAL CONVECTION, BUT ABSOLUTE RAINFALL TOTALS ARE   
NOT EXPECTED TO EXCEED HAZARDOUS THRESHOLDS SO NO HEAVY PRECIPITATION HAZARD IS   
POSTED AT THIS TIME. THE ECMWF PET ALSO INDICATES A SIMILAR POTENTIAL FOR HEAVY   
PRECIPITATION FOR PORTIONS OF ALASKA, BUT SIMILAR TO THE GULF COAST,   
PRECIPITATION TOTALS ARE NOT EXPECTED TO EXCEED HAZARDOUS THRESHOLDS SO NO   
ASSOCIATED HAZARD IS DESIGNATED.  
  
BELOW-NORMAL RAINFALL ANTICIPATED OVER MUCH OF THE SOUTHERN PLAINS AND   
MISSISSIPPI VALLEY DURING WEEK-2  COMBINED WITH AN  INCREASED LIKELIHOOD OF   
EXCESSIVE HEAT AND BELOW-NORMAL 30-DAY ACCUMULATED PRECIPITATION, RESULTS IN AN   
ELEVATED RISK OF RAPID ONSET DROUGHT (ROD) ACROSS PORTIONS OF THE SOUTHERN   
PLAINS AND MISSISSIPPI VALLEY FURTHER SUPPORTED BY DECLINING SOIL MOISTURE   
VALUES AND DRY CONDITIONS FAVORED OVER THE NEXT TWO WEEKS. WITH RECENT AND   
CONTINUING HOT AND DRY CONDITIONS, THE ROD RISK AREA HAS BEEN SLIGHTLY EXPANDED   
SOUTHWARD, AS WELL AS NORTHWARD ALONG THE MISSISSIPPI VALLEY INTO SOUTHERN   
ILLINOIS AND INDIANA.  
  
FORECASTER: DANNY BARANDIARAN   
  
  
 
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