272   
FXUS21 KWNC 281814  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EDT AUGUST 28 2024  
  
SYNOPSIS: MODEL ENSEMBLES DEPICT HIGH PRESSURE BOTH AT THE SURFACE AND   
MID-LEVELS ACROSS THE WESTERN AND CENTRAL CONTIGUOUS U.S. (CONUS) DURING   
WEEK-2, LEADING TO THE POTENTIAL FOR EXCESSIVE HEAT FOR PORTIONS OF CALIFORNIA   
FOR THE FIRST HALF OF THE FORECAST PERIOD. A STALLED FRONTAL BOUNDARY OVER THE   
SOUTHEASTERN CONUS IS FAVORED TO COMBINE WITH TROPICAL MOISTURE, POTENTIALLY   
BRINGING HEAVY PRECIPITATION TO PORTIONS OF THE GULF COAST AND MID-ATLANTIC.   
LOW PRESSURE AT THE SURFACE AND MID-LEVELS OVER THE GULF OF ALASKA FAVORS   
STORMY CONDITIONS AND POSSIBLY HAZARDOUS PRECIPITATION TO PORTIONS OF   
SOUTHEASTERN ALASKA. PROLONGED RAINFALL DEFICITS COMBINED WITH CONTINUED   
ABOVE-NORMAL TEMPERATURES RESULTS IN THE POTENTIAL FOR RAPID ONSET DROUGHT FOR   
PARTS OF THE SOUTHERN PLAINS AND THE OHIO, TENNESSEE, AND MISSISSIPPI VALLEYS.  
  
HAZARDS  
  
SLIGHT RISK OF EXCESSIVE HEAT FOR THE CALIFORNIA CENTRAL VALLEY, THU-SAT, SEP   
5-7.  
  
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE GULF COAST, SOUTHEAST   
U.S., AND MID-ATLANTIC, THU-SAT, SEP 5-7.  
  
SLIGHT RISK OF HEAVY PRECIPITATION FOR THE ALASKA PANHANDLE, THU-FRI, SEP 5-6.  
  
RISK FOR RAPID ONSET DROUGHT FOR PORTIONS OF THE SOUTHERN PLAINS, AND THE OHIO,   
TENNESSEE, AND LOWER AND MIDDLE MISSISSIPPI VALLEYS.  
  
DETAILED SUMMARY  
  
FOR SATURDAY AUGUST 31 - WEDNESDAY SEPTEMBER 04:   
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP  
  
FOR THURSDAY SEPTEMBER 05 - WEDNESDAY SEPTEMBER 11: TODAY’S MODEL SOLUTIONS FOR   
500 HPA HEIGHTS AND ANOMALIES DEPICT AN AMPLIFIED RIDGE OVER THE NORTHWESTERN   
CONUS AT THE OUTSET OF WEEK-2, AND TROUGHS OVER THE GULF OF ALASKA AND THE   
GREAT LAKES. MODEL SOLUTIONS TODAY FAVOR HEIGHT ANOMALIES OVER THE WESTERN   
CONUS TO REDUCE QUICKLY AFTER BEING INITIALLY QUITE AMPLIFIED, SO THERE REMAINS   
A POTENTIAL FOR EXCESSIVE HEAT FOR PORTIONS OF THE WESTERN CONUS, THOUGH THE   
RISK IS LIKELY TO BE SHORT-LIVED. THE GEFS AND ECMWF PROBABILISTIC EXTREMES   
TOOLS (PETS) BOTH INDICATE AT LEAST A 20% PROBABILITY OF MAXIMUM TEMPERATURES   
EXCEEDING THE 90TH PERCENTILE AND AT LEAST 100F FOR THE CALIFORNIA CENTRAL   
VALLEY THROUGH DAY-10 (SEP 7), THEREFORE A SLIGHT RISK FOR EXCESSIVE HEAT IS   
POSTED FOR SEP 5-7. THE PETS ALSO INDICATE WIDESPREAD POTENTIAL FOR MAXIMUM   
TEMPERATURES EXCEEDING THE 85TH PERCENTILE FOR THE DESERT SOUTHWEST BUT   
HAZARDOUS CRITERIA ARE NOT EXPECTED TO BE EXCEEDED SO NO HAZARD IS POSTED AT   
THIS TIME.  
  
AN EXTENSION OF THE BERMUDA HIGH OVER THE SOUTHEAST U.S. IS DEPICTED IN TODAY’S   
MODEL SOLUTIONS WHICH WOULD INCREASE RETURN FLOW OFF THE GULF OF MEXICO. A   
STALLED FRONTAL SYSTEM IS DEPICTED OVER THE SOUTHEASTERN CONUS AT THE OUTSET OF   
WEEK-2, WHICH COMBINED WITH INCREASED TROPICAL MOISTURE LEADS TO THE POTENTIAL   
FOR HEAVY PRECIPITATION. THE PETS INDICATE A 20% CHANCE OF 3-DAY TOTAL   
PRECIPITATION EXCEEDING THE 85TH PERCENTILE AND AT LEAST 1 INCH FOR PORTIONS OF   
THE GULF COAST AND EXTENDING NORTHWARD ALONG THE EAST COAST FOR AT LEAST THE   
FIRST HALF OF THE FORECAST PERIOD DUE TO THIS INCREASED RETURN FLOW POTENTIAL.   
THERE HAS BEEN A LOT OF UNCERTAINTY REGARDING THE DURATION OF THIS EVENT, WITH   
MODEL SOLUTIONS CHANGING FROM DAY TO DAY. THE SIGNAL CONTINUES TO BE STRONGEST   
EARLY IN THE WEEK, THEREFORE A SLIGHT RISK FOR HEAVY PRECIPITATION IS POSTED   
FOR PORTIONS OF THE GULF COAST, SOUTHEAST U.S., AND MID-ATLANTIC FOR SEP 5-7,   
AND THE SITUATION WILL BE CLOSELY MONITORED IN THE COMING DAYS.   
  
THE PETS ALSO INDICATE INCREASED CHANCES FOR HEAVY PRECIPITATION FOR   
SOUTHEASTERN ALASKA DUE TO AN AMPLIFIED TROUGH OVER THE GULF OF ALASKA,   
POTENTIALLY ENHANCED BY TROPICAL MOISTURE INFLUXES FROM EXTRATROPICAL SYSTEMS   
EMERGING FROM THE WESTERN PACIFIC. THIS POTENTIAL IS GREATEST AT THE BEGINNING   
OF WEEK-2, WITH THE ECMWF PET INDICATING WIDESPREAD PROBABILITIES OF AT LEAST   
20% OF 3-DAY PRECIPITATION EXCEEDING 2 INCHES, WITH 3 INCHES POSSIBLE IN SOME   
LOCATIONS. THUS A SLIGHT RISK FOR HEAVY PRECIPITATION IS POSTED FOR THE ALASKA   
PANHANDLE FOR SEP 5-6. THE SOIL IN THIS REGION IS ALREADY SATURATED DUE TO   
HEAVY ANTECEDENT RAINFALL AND LANDSLIDES HAVE BEEN AN ONGOING CONCERN, A   
PROBLEM WHICH MAY BE EXACERBATED BY THIS POTENTIALLY HAZARDOUS PRECIPITATION.  
  
NEAR- TO BELOW-NORMAL RAINFALL ANTICIPATED OVER MUCH OF THE NORTH-CENTRAL AND   
EAST-CENTRAL CONUS DURING WEEK-2 COMBINED WITH AN INCREASED LIKELIHOOD OF   
EXCESSIVE HEAT DURING WEEK-1 AND BELOW-NORMAL 30-DAY ACCUMULATED PRECIPITATION,   
RESULTS IN AN ELEVATED RISK OF RAPID ONSET DROUGHT (ROD) ACROSS PORTIONS OF THE   
SOUTHERN PLAINS AND PARTS OF THE MISSISSIPPI, TENNESSEE AND OHIO VALLEYS. THIS   
IS FURTHER SUPPORTED BY DECLINING OBSERVED SOIL MOISTURE VALUES AND DRY   
CONDITIONS FAVORED OVER THE NEXT TWO WEEKS.  
  
FORECASTER: DANNY BARANDIARAN   
  
  
 
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