312
FXUS21 KWNC 091820
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT AUGUST 09 2023
SYNOPSIS: MID-LEVEL HIGH PRESSURE IS ANTICIPATED TO PERSIST OVER THE SOUTHERN
CONTIGUOUS U.S. (CONUS) DURING WEEK-2, LEADING TO THE INCREASED POTENTIAL FOR
EXCESSIVE HEAT FOR THE SOUTHWESTERN AND SOUTH-CENTRAL WESTERN CONUS. SURFACE
LOW PRESSURE OVER SOUTHERN ARIZONA AND HIGH PRESSURE OVER COLORADO RESULTS
ENHANCED RISK FOR HIGH WINDS OVER THE DESERT SOUTHWEST. A POTENTIAL MOISTURE
SURGE FROM TROPICAL ACTIVITY FAVORED IN THE EAST PACIFIC INCREASES THE RISK FOR
FLASH FLOODING ACROSS SOUTHERN ARIZONA. ABNORMALLY DRY CONDITIONS FROM ARIZONA
EAST ACROSS THE SOUTHERN CONUS TO LOUISIANA SUPPORTS ELEVATED POTENTIAL FOR
RAPID ONSET DROUGHT (ROD) ACROSS THE REGION.
HAZARDS
MODERATE RISK FOR EXCESSIVE HEAT FOR PORTIONS OF THE DESERT SOUTHWEST, SOUTHERN
PLAINS, AND LOWER MISSISSIPPI VALLEY, THU-FRI, AUG 17-18.
SLIGHT RISK FOR EXCESSIVE HEAT FOR MUCH OF THE WESTERN CONUS, THU-FRI, AUG
17-18.
SLIGHT RISK FOR EXCESSIVE HEAT FOR MUCH OF THE SOUTHERN CONUS, THU-TUE, AUG
17-22.
SLIGHT RISK FOR HIGH WINDS FOR MUCH OF THE DESERT SOUTHWEST AND PORTIONS OF THE
SOUTHERN ROCKIES AND THE SOUTHERN GREAT BASIN, THU-WED, AUG 17-23.
FLASH FLOODING POSSIBLE FOR PORTIONS OF SOUTHERN ARIZONA.
RAPID ONSET DROUGHT RISK ACROSS PORTIONS OF THE DESERT SOUTHWEST, SOUTHERN
PLAINS, AND LOWER MISSISSIPPI VALLEY.
DETAILED SUMMARY
FOR SATURDAY AUGUST 12 - WEDNESDAY AUGUST 16:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY AUGUST 17 - WEDNESDAY AUGUST 23: ENSEMBLE MODEL SOLUTIONS FROM THE
GEFS, ECMWF, AND CMCE ALL DEPICT POSITIVE 500-HPA HEIGHT ANOMALIES CENTERED
OVER THE DESERT SOUTHWEST IN EXCESS OF 595 DM AT THE ONSET OF THE WEEK-2
PERIOD. TOWARDS THE SECOND HALF OF THE WEEK THE RIDGE WEAKENS SOMEWHAT BUT
HEIGHT MAXIMA REMAINS ABOVE 590 DM. THIS PATTERN FAVORS CONTINUED ANOMALOUSLY
WARM TEMPERATURES ACROSS THE SOUTHERN CONUS, LEADING TO THE INCREASED POTENTIAL
FOR EXCESSIVE HEAT. THE PROBABILISTIC EXTREMES TOOL (PET) FROM ALL THREE OF
THE AFOREMENTIONED ENSEMBLES GENERALLY AGREE ON AT LEAST A 40% PROBABILITY OF
MAXIMUM TEMPERATURES EXCEEDING THE 85TH CLIMATOLOGICAL PERCENTILE FOR A BROAD
SWATH EXTENDING FROM INTERIOR SOUTHERN CALIFORNIA TO THE LOWER MISSISSIPPI
VALLEY FOR AUG 17-18. THEREFORE A MODERATE RISK FOR EXCESSIVE HEAT IS POSTED
FOR THESE REGIONS. ADDITIONALLY, THE PETS INDICATE AT LEAST A 20% PROBABILITY
OF MAXIMUM TEMPERATURES EXCEEDING THE 85TH PERCENTILE FOR MUCH OF THE WESTERN
AND SOUTHERN CONUS DURING THE WEEK-2 PERIOD, AND A SLIGHT RISK FOR EXCESSIVE
HEAT IS POSTED FOR THESE REGIONS. THIS SLIGHT RISK IS SPLIT INTO TWO AREAS, ONE
COVERING THE WESTERN CONUS FOR AUG 17-18, AND THE OTHER COVERING THE SOUTHERN
CONUS, AUG 17-22. A FINAL NOTE ABOUT THE EXCESSIVE HEAT FOR THE SOUTHERN CONUS:
THE NATIONAL BLEND OF MODELS INDICATES THAT ALONG THE GULF COAST FORECAST
NIGHTTIME LOW TEMPERATURES HAVE THE POTENTIAL TO BREAK RECORDS FOR WARMEST LOW
TEMPS ON RECORD, FURTHER EXACERBATING THE POTENTIAL IMPACTS OF THIS HEAT WAVE.
ANOTHER PROMINENT FEATURE IN THE WEEK-2 SYNOPTIC PICTURE IS A THERMAL LOW OVER
THE MOUTH OF THE COLORADO RIVER AND SURFACE HIGH PRESSURE OVER COLORADO,
RESULTING IN AN ENHANCED PRESSURE GRADIENT OVER THE DESERT SOUTHWEST. THIS
RESULTS IN THE INCREASED POTENTIAL FOR HIGH WINDS THROUGHOUT THE FORECAST
PERIOD. THE ECMWF AND CMCE PETS SHOW THIS WELL, ALTHOUGH THE GEFS DOES NOT
SHARE THIS FEATURE. HOWEVER, THE GEFS PET TENDS TO UNDERESTIMATE EXTREME WIND
POTENTIAL, SO A SLIGHT RISK FOR HIGH WINDS IS POSTED FOR MUCH OF THE SOUTHWEST
CONUS FOR THE WHOLE WEEK-2 PERIOD.
TROPICAL CYCLONE ACTIVITY IN THE EASTERN PACIFIC IS FORECAST TO INCREASE IN THE
COMING WEEKS, BRINGING INCREASING THE LIKELIHOOD FOR A MOISTURE SURGE FROM THE
GULF OF CALIFORNIA INTO THE FOUR CORNERS REGION LATER IN THE FORECAST PERIOD.
MODEL DEPICTIONS OF THIS SURGE CURRENTLY LIMIT ITS NORTHERN EXTENT AND FORECAST
RAINFALL TOTALS WHICH DOES NOT MEET PREDETERMINED HAZARDS CRITERIA PRECLUDING A
DESIGNATED RISK FOR HEAVY PRECIPITATION. HOWEVER, GIVEN THE DRY ANTECEDENT
CONDITIONS AND THE POTENTIAL FOR LOCALIZED HEAVY RAINFALL, A RISK FOR FLASH
FLOODING IS POSTED FOR SOUTHERN ARIZONA.
DROUGHT CONCERNS ARE FORECAST TO INCREASE ACROSS PORTIONS OF THE SOUTHERN CONUS
FROM ARIZONA EAST TO LOUISIANA AS THE HEAT OF SUMMER CONTINUES AND A
PERSISTENCE OF BELOW-NORMAL PRECIPITATION IS FORECAST FOR THE REGION. WHILE
SOME PRECIPITATION IS PREDICTED FOR PORTIONS OF LOUISIANA AND THE MONSOON
REGION OF THE DESERT SOUTHWEST IN THE COMING WEEK, ACCUMULATIONS ARE NOT
EXPECTED TO SIGNIFICANTLY IMPACT SOIL MOISTURE SO NO CHANGES ARE MADE TO THE
ROD OUTLOOK.
FORECASTER: DANNY BARANDIARAN
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