534
FXUS21 KWNC 191807
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JULY 19 2023
SYNOPSIS: STRONG MID-LEVEL HIGH PRESSURE IS FORECAST THROUGHOUT MUCH OF THE
WESTERN AND CENTRAL CONTIGUOUS U.S. (CONUS), WHICH IS EXPECTED TO SUSTAIN AN
ELEVATED EXCESSIVE HEAT RISK THROUGHOUT THE SOUTHWEST AND SOUTH-CENTRAL CONUS,
WITH INCREASED CHANCES FOR EXCESSIVE HEAT OVER PARTS OF THE MIDWEST EARLY IN
WEEK-2. THE COMBINATION OF RECENT DRYNESS AND ABOVE-NORMAL TEMPERATURES
FORECAST ACROSS THE GREAT PLAINS SUPPORTS A CONTINUED RAPID ONSET DROUGHT (ROD)
RISK OVER PARTS OF WESTERN TEXAS.
HAZARDS
HIGH RISK OF EXCESSIVE HEAT FOR THE SOUTHWEST, SOUTHERN ROCKIES, AND SOUTHERN
HIGH PLAINS, THU-FRI, JUL 27-28.
MODERATE RISK OF EXCESSIVE HEAT FOR PARTS OF SOUTHWEST, GREAT BASIN, ROCKIES,
GREAT PLAINS, MISSISSIPPI AND OHIO VALLEYS, AND THE GREAT LAKES, THU-SUN, JUL
27-30.
SLIGHT RISK OF EXCESSIVE HEAT FOR MUCH OF THE CONUS EXCLUDING THE NORTHEAST,
AND PORTIONS OF THE MID-ATLANTIC AND PACIFIC NORTHWEST, THU-WED, JUL 27-AUG 2.
RAPID ONSET DROUGHT RISK ACROSS PORTIONS OF SOUTHERN TEXAS AND INTO LOUISIANA.
DETAILED SUMMARY
FOR SATURDAY JULY 22 - WEDNESDAY JULY 26:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY JULY 27 - WEDNESDAY AUGUST 02: ONE OF THE HALLMARKS ASSOCIATED
WITH THE ONGOING HEAT EVENT AFFECTING THE SOUTHERN TIER OF THE U.S. THIS SUMMER
HAS BEEN ITS ENDURANCE, AND UNFORTUNATELY THAT ASPECT LOOKS TO CHANGE VERY
LITTLE HEADING INTO LATE JULY. 500-HPA HEIGHT FORECASTS FROM THE 0Z GEFS AND
ECMWF ENSEMBLES CONTINUE TO REFLECT AN ELEVATED EXCESSIVE HEAT RISK, AND EVEN
SUGGEST STRONGER RIDGING (>597 DM MEAN HEIGHTS) RELATIVE TO PREVIOUS GUIDANCE
OVER THE SOUTHWESTERN CONUS AT THE START OF THE PERIOD. THE ECMWF IN
PARTICULAR, MAINTAINS THESE MID-LEVEL HEIGHTS INTO NEXT WEEKEND WHICH IS NOT
WELCOME NEWS FOR AREAS DEALING WITH THE STIFLING TEMPERATURES IN THE SOUTH. IN
ADDITION, THERE ARE STRONGER INDICATIONS IN THE MID-LEVEL GUIDANCE TO INCREASE
CONFIDENCE FOR A HEATWAVE EXPANDING EASTWARD AND POSSIBLY GRIPPING THE MIDWEST
DURING THE PERIOD.
WHILE THE PROBABILISTIC EXTREMES TOOLS (PETS) HAD SUGGESTED A GRADUAL EASING OF
THE EXCESSIVE HEAT POTENTIAL OVER THE SOUTHWESTERN CONUS BY LATE NEXT WEEK, THE
LATEST TOOLS MAINTAIN 50-60% CHANCES OF MAXIMUM TEMPERATURES EXCEEDING THE 85TH
PERCENTILE FROM THE DESERT SOUTHWEST TO THE SOUTHERN PLAINS. GIVEN THE TREND OF
HIGH HEAT SIGNALS PERSISTING IN THE REGION, A HIGH RISK OF EXCESSIVE HEAT IS
CONTINUED THROUGH DAYS 8-9 (JUL 27-28). IN THE HIGHLIGHTED HIGH RISK AREA,
THERE REMAINS ELEVATED CHANCES FOR DAYTIME TEMPERATURES EXCEEDING 110 DEG F
ACROSS THE SONORAN DESERT, 100 DEG F EASTWARD ALONG THE U.S./MEXICO BORDER INTO
WESTERN TEXAS, AND 95 DEG F IN THE HIGHER ELEVATIONS FURTHER NORTH. TIED TO THE
STRONGLY POSITIVE ANOMALOUS MID-LEVEL HEIGHT DEPARTURES FURTHER NORTH, THE PETS
HAVE COME INTO BETTER AGREEMENT REGARDING THE CONVERGENCE OF MODERATE RISK
LEVEL HEAT SIGNALS OVER PARTS OF THE GREAT PLAINS AND MISSISSIPPI VALLEY. AS A
RESULT, THE SEPARATE MODERATE RISK AREAS OF EXCESSIVE HEAT IN THE PREVIOUS
HAZARD OUTLOOKS ARE COMBINED WHERE THERE IS BETTER SPATIAL CONTINUITY
INDICATING 30-40% CHANCES OF MAXIMUM TEMPERATURES EXCEEDING THE 85TH
PERCENTILE. HOWEVER, THERE IS UNCERTAINTY REGARDING THE EASTERN EXTENT AND
TIMING OF THE MODERATE RISK AREA DUE TO MODEL DIFFERENCES WITH THE EVOLUTION OF
MID-LEVEL HEIGHT PATTERN. WHILE DYNAMICAL MODELS FAVOR THE RIDGING OVER THE
SOUTHWEST TO EASE, THE GEFS AND CANADIAN BRING IN MORE TROUGHING EARLIER OVER
THE EASTERN CONUS TO HELP QUELL THE EXCESSIVE HEAT RISK BY THE MIDDLE OF WEEK-2
WHICH IS LESS SUPPORTED IN THE ECMWF. TO RECONCILE THESE DIFFERENCES, THE
EASTERN EXTENT OF THE MODERATE RISK AREA IS MAINTAINED OVER PARTS OF THE GREAT
LAKES AND OHIO VALLEY, AND IS NOW VALID THROUGH DAY 11 (JUL 30) IN THE UPDATED
OUTLOOK. THE SLIGHT RISK OF EXCESSIVE REMAINS POSTED FOR MUCH OF THE CONUS (JUL
27-AUG 2), AND IS EXPANDED OVER THE SOUTHEAST TO ACCOUNT FOR THE INCREASED HEAT
SIGNALS IN THE PETS DURING WEEK-2
FOR PRECIPITATION, SIGNALS FOR ABOVE-NORMAL RAINFALL CONTINUE TO BE QUITE
TENUOUS THROUGHOUT MUCH OF THE U.S. DURING THE PERIOD. FOR THE NORTH AMERICAN
MONSOON REGION, THE ECMWF CONTINUES TO FAVOR A SLIGHTLY SUPPRESSED RIDGE AXIS,
TRANSLATING INTO LOWER PRECIPITATION AMOUNTS IN THE UNCALIBRATED GUIDANCE
COMPARED TO THE GEFS. WHILE LOCALLY HEAVY AMOUNTS ARE POSSIBLE DURING WEEK-2,
THERE IS INSUFFICIENT SUPPORT IN THE TOOLS TO INCLUDE A CORRESPONDING HEAVY
PRECIPITATION OR FLOODING HAZARD AT THIS TIME.
DUE TO LITTLE TO NO RAINFALL FORECAST AND THE ONGOING EXCESSIVE HEAT CONDITIONS
FAVORED TO PERSIST ACROSS THE SOUTHERN TIER, THERE CONTINUES TO BE AN ELEVATED
RISK OF RAPID ONSET DROUGHT (ROD) DEVELOPMENT FOR PARTS OF THE SOUTHERN PLAINS
AND LOWER MISSISSIPPI VALLEY GIVEN THE INCREASED EVAPOTRANSPIRATION RATES. OVER
PARTS OF THE NORTHWESTERN CONUS, A SEPARATE ROD AREA MAY BE ADDED IN UPCOMING
HAZARD OUTLOOKS BASED ON ABOVE(BELOW)-NORMAL TEMPERATURES (PRECIPITATION) BEING
FAVORED WITH SOIL MOISTURE CONTENT REGISTERING IN THE LOWEST PERCENTILES.
NO HAZARDS ARE POSTED FOR ALASKA DURING WEEK-2. ABOVE NORMAL TEMPERATURES ARE
FAVORED FOR MOST OF EASTERN ALASKA, WHILE NEAR NORMAL TEMPERATURES ARE
INDICATED FOR PARTS OF THE WESTERN MAINLAND AND ALEUTIANS.
FORECASTER: NICK NOVELLA
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page