189
FXUS21 KWNC 071913
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT AUGUST 07 2023
SYNOPSIS: MID-LEVEL HIGH PRESSURE PERSISTS OVER THE SOUTHERN CONTIGUOUS U.S.
(CONUS) DURING WEEK-2, LEADING TO THE POTENTIAL FOR EXCESSIVE HEAT FOR THE
SOUTHERN AND WESTERN CONUS. SURFACE LOW PRESSURE OVER SOUTHERN ARIZONA AND HIGH
PRESSURE OVER COLORADO RESULTS IN THE POTENTIAL FOR HIGH WINDS OVER THE DESERT
SOUTHWEST, AND LOW PRESSURE BOTH AT THE SURFACE AND ALOFT OVER THE ALEUTIAN
ISLANDS LEADS TO A CHANCE FOR HIGH WINDS ALONG THE SOUTHERN ALASKAN COAST.
ABNORMALLY DRY CONDITIONS FROM ARIZONA EAST ACROSS THE SOUTHERN CONUS TO
LOUISIANA RESULT IN THE POTENTIAL FOR RAPID ONSET DROUGHT (ROD).
HAZARDS
MODERATE RISK FOR EXCESSIVE HEAT FOR PORTIONS OF THE DESERT SOUTHWEST, SOUTHERN
PLAINS, AND LOWER MISSISSIPPI VALLEY, TUE-THU, AUG 15-17.
MODERATE RISK FOR EXCESSIVE HEAT FOR PORTIONS OF THE NORTHWEST CONUS, TUE-WED,
AUG 15-16.
SLIGHT RISK FOR MUCH OF THE WESTERN AND SOUTHERN CONUS, TUE-SAT, AUG 15-19.
SLIGHT RISK FOR HIGH WINDS FOR MUCH OF THE DESERT SOUTHWEST AND PORTIONS OF THE
SOUTHERN ROCKIES AND THE SOUTHERN GREAT BASIN, TUE-MON, AUG 15-21.
SLIGHT RISK FOR HIGH WINDS FOR PORTIONS OF THE SOUTHERN COAST OF ALASKA,
TUE-WED, AUG 15-16.
RAPID ONSET DROUGHT RISK ACROSS PORTIONS OF THE DESERT SOUTHWEST, SOUTHERN
PLAINS, AND LOWER MISSISSIPPI VALLEY.
DETAILED SUMMARY
FOR THURSDAY AUGUST 10 - MONDAY AUGUST 14:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY AUGUST 15 - MONDAY AUGUST 21: 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 REMAIN ABOVE 590 DM. THIS FAVORS CONTINUED ANOMALOUSLY WARM
TEMPERATURES ACROSS THE SOUTHERN CONUS, LEADING TO THE INCREASED POTENTIAL FOR
EXCESSIVE HEAT. THE PROBABILISTIC EXTREMES TOOL (PET) OF ALL THREE ENSEMBLES
AFOREMENTIONED 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 15-17. THEREFORE A MODERATE RISK FOR EXCESSIVE HEAT IS POSTED FOR THESE
REGIONS.
A MODERATE RISK FOR EXCESSIVE HEAT IS ALSO POSTED FOR PORTIONS OF THE NORTHWEST
CONUS FOR AUG 15-16. AT THE BEGINNING OF THE WEEK-2 PERIOD THE ANOMALOUS
SUBTROPICAL RIDGE FEATURES A NORTHWARD EXTENSION ALONG THE WEST COAST,
RESULTING IN A 40% PROBABILITY PER THE PETS OF HIGH TEMPERATURES EXCEEDING THE
85TH PERCENTILE. THIS FEATURE IS SHORT-LIVED HOWEVER, SO THIS MODERATE RISK
AREAIS ONLY FOR AUG 15-16. ADDITIONALLY, THE PETS INDICATE AT LEAST A 20%
PROBABILITY OF EXCEEDING THE 85TH PERCENTILE FOR MUCH OF THE WESTERN AND
SOUTHERN CONUS FOR AUG 15-19, THUS A SLIGHT RISK FOR EXCESSIVE HEAT IS POSTED
FOR THESE REGIONS. A FINAL NOTE ABOUT THE EXCESSIVE HEAT FOR THE SOUTHERN
CONUS: THE NATIONAL BLEND OF MODELS INDICATES THAT ALONG THE GULF COAST
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 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.
AT THE ONSET OF WEEK-2 A SIMILAR PRESSURE GRADIENT IS DEPICTED IN ENSEMBLE
MODEL SOLUTIONS WITH TROUGHING OVER THE ALEUTIANS AND ANOMALOUS RIDGING OVER
THE NORTH PACIFIC, RESULTING IN A STRONG ONSHORE FLOW FOR THE SOUTHERN ALASKAN
COAST. THIS GRADIENT WEAKENS QUICKLY THOUGH, SO A SLIGHT RISK FOR HIGH WINDS IS
POSTED ALONG THE SOUTHERN ALASKAN COAST FOR AUG 15-16 ONLY.
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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