605  
FXUS02 KWBC 300658  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
257 AM EDT TUE AUG 30 2022  
 
VALID 12Z FRI SEP 02 2022 - 12Z TUE SEP 06 2022  
 
...PROLONGED AND POTENTIALLY DANGEROUS HEAT WAVE FOR PORTIONS OF  
THE WESTERN U.S. THIS HOLIDAY WEEKEND...  
   
..HEAVY RAIN THREAT ALONG PORTIONS OF THE GULF COAST
 
 
   
..OVERVIEW
 
 
ANOMALOUSLY STRONG UPPER RIDGING IS EXPECTED TO BE ONGOING AT THE  
START OF THE MEDIUM RANGE PERIOD AND PERSIST THROUGH EARLY NEXT  
WEEK. THIS WILL SUPPORT VERY WARM TO HOT TEMPERATURES IN THAT  
REGION, WITH POTENTIALLY RECORD BREAKING AND DANGEROUS HIGH  
TEMPERATURES. THE OTHER FOCUS FOR SIGNIFICANT WEATHER WILL BE  
FOUND ACROSS THE GULF COAST AND SOUTH WHERE INTERACTIONS WITH A  
STALLING FRONTAL BOUNDARY AND DEEPER GULF MOISTURE COULD SPELL A  
MULTI-DAY HEAVY RAINFALL PERIOD LEADING TO SOME FLASH FLOODING,  
INITIALLY OVER PORTIONS OF THE FLORIDA PANHANDLE THEN MOVING  
WESTWARD TOWARD THE TEXAS GULF COAST THIS WEEKEND. SOME OF THAT  
MOISTURE AND POTENTIAL HEAVY RAIN MAY LIFT NORTHWARD THROUGH THE  
LOWER MISSISSIPPI VALLEY BY LATE IN THE WEEKEND. MEANWHILE,  
SHORTWAVE TROUGHING WILL WORK THROUGH THE GREAT LAKES AND  
NORTHEAST THIS WEEKEND INTO EARLY NEXT WEEK, BRINGING ANOTHER COLD  
FRONT THROUGH THE EAST. SOME UNSETTLED WEATHER MAY DEVELOP ALONG  
THAT FRONT FOR LABOR DAY ACROSS THE MID-ATLANTIC AND NORTHEAST,  
BUT THERE REMAINS SOME UNCERTAINTY.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
THE INITIAL SYNOPTIC MODEL DIFFERENCES THIS CYCLE REMAIN WITH THE  
EASTERN PACIFIC UPPER LOW AND THE STRENGTH/AMPLITUDE OF THE ENERGY  
THAT BRUSHES UP THE NORTHWEST EARLY ON IN THE FORECAST PERIOD. BY  
FRIDAY, A SHARP SHORTWAVE TROUGH AXIS CENTERED NEAR 35N/135W  
QUICKLY LIFTS NORTHEAST AS IT OPENS UP OVER BRITISH COLUMBIA.  
WHILE EARLIER RUNS OF THE DETERMINISTIC GUIDANCE SHOWED A BIT OF  
TIMING VARIABILITY, IT SEEMS THIS CYCLE THINGS HAVE CLUSTERED  
BETTER, ASIDE FROM THE CMC WHICH CONTINUES TO BE A SLOWER  
SOLUTION. THIS ENERGY ROUNDS THE TOP OF THE WESTERN U.S. RIDGE AND  
THEN EVENTUALLY HELPS TO CARVE OUT A DEEPER TROUGH OVER THE GREAT  
LAKES BY LABOR DAY. HERE, THE MODEL DIFFERENCES ARE MORE NOTABLE  
WITH GREATER UNCERTAINTY IN THE SENSIBLE WEATHER. THE LATEST  
DETERMINISTIC HAVE TRENDED TOWARD A DEEPER TROUGH OVER THE EAST  
COAST BY 12Z TUESDAY THOUGH VARY ON THE DEPTH AND POSITION OF THAT  
TROUGH.  
 
THE FORECAST CHALLENGES NEAR THE GULF COAST ARE MORE SUBTLE WITH  
LESS SYNOPTIC FORCING AND MORE CONVECTIVE/MESOSCALE DRIVEN  
INFLUENCE ON THE AREAS OF SIGNIFICANT RAINFALL. A DISTURBANCE AND  
INTERACTIONS WITH THE STALLING FRONTAL BOUNDARY IN THE AREA SHOULD  
FOCUS THE GREATEST THREAT OF HEAVY RAINFALL INITIALLY OVER THE  
CENTRAL GULF COAST TO FLORIDA PANHANDLE FRIDAY THEN THE DEEPER  
MOISTURE MOVING WESTWARD AND EASTERLY FLOW PUSHES THE THREAT  
TOWARD THE TEXAS GULF COAST BY THIS WEEKEND. BEYOND THAT, SOME  
INDICATIONS THAT A WEAK JET STREAK OVER THE SOUTH AND SOUTHERLY  
FLOW MAY PULL SOME OF THIS DEEPER MOISTURE THROUGH THE LOWER  
MISSISSIPPI VALLEY AND POTENTIALLY AS FAR NORTH AS THE OHIO VALLEY  
INTO MID-ATLANTIC BY LABOR DAY AND TUESDAY NEXT WEEK. THE ECMWF  
HAS BEEN MORE AGGRESSIVE PULLING MOISTURE NORTHWARD THROUGH MUCH  
OF THE EASTERN U.S. EARLY NEXT WEEK WHILE THE GFS HAD BEEN ON THE  
DRIER SIDE, THOUGH THE LATEST 00Z RUN SEEMS TO BE TRENDING TOWARD  
THE ECMWF. FOR THE WPC BLEND OVERALL, A SPLIT BETWEEN THE  
ECMWF/GFS WAS GENERALLY USED WITH SOME INCLUSION OF THE UKMET/CMC  
EARLY ON THEN TRANSITIONED TOWARD THE ECENS/GEFS MEANS BY DAY 6-7  
GIVEN SOME OF THE MODEL UNCERTAINTY AND SPREAD.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
AN ANOMALOUSLY STRONG UPPER RIDGE FOR EARLY SEPTEMBER POSITIONED  
OVER THE WESTERN U.S. WILL SUPPORT MUCH ABOVE NORMAL TEMPERATURES  
FRIDAY THROUGH EARLY NEXT WEEK, WITH THE GREATEST DEPARTURES FROM  
NORMAL EXPECTED FROM CALIFORNIA THROUGH THE PACIFIC NORTHWEST,  
GREAT BASIN, AND THE NORTHERN ROCKIES. DAYTIME HIGHS BETWEEN  
10-20F ABOVE NORMAL AND NIGHTTIME LOWS BETWEEN 15-20F ABOVE NORMAL  
ARE LIKELY. THE HOLIDAY WEEKEND LOOKS PARTICULARLY HOT WITH HIGHS  
FROM THE DESERT SOUTHWEST THROUGH THE CALIFORNIA CENTRAL VALLEY  
WELL ABOVE 100 WITH SOME READINGS GREATER THAN 110 WHILE MID TO  
UPPER 90S LIKELY FOR PORTIONS OF THE NORTHERN ROCKIES. WIDESPREAD  
DAILY RECORDS ARE POSSIBLE EACH DAY AND FOR PORTIONS OF DESERT  
SOUTHWEST THROUGH CALIFORNIA, A POTENTIALLY DANGEROUS AND RECORD  
BREAKING HEAT WAVE IS POSSIBLE.  
 
A RESIDUAL FRONTAL BOUNDARY DRAPED ACROSS THE GULF COAST  
INTERACTING WITH FAVORABLE GULF MOISTURE TRANSPORT AND A WEAK  
UPPER LEVEL DISTURBANCE WILL HELP FOCUS WIDESPREAD SHOWERS AND  
THUNDERSTORMS THROUGH THE WEEKEND INTO EARLY NEXT WEEK. FOR  
FRIDAY, THE BEST FOCUS LOOKS TO BE OVER THE FLORIDA PANHANDLE THEN  
THE MOISTURE/DISTURBANCE MOVES WESTWARD TOWARD THE TEXAS GULF  
COAST BY THIS WEEKEND INTO EARLY NEXT WEEK. SOME OF THIS ENERGY  
MAY GET DRAWN NORTHWARD ACROSS THE LOWER MISSISSIPPI VALLEY,  
BRINGING THE THREAT FOR HEAVY RAINFALL NORTHWARD ACROSS PORTIONS  
OF MISSISSIPPI AND ALABAMA THROUGH THE HOLIDAY WEEKEND. OVER THE  
ENTIRE PERIOD, THE GREATEST THREAT FOR MULTI-DAY TOTALS REACHING  
SEVERAL INCHES LOOKS TO BE ACROSS THE TEXAS GULF COAST AND THE  
CENTRAL GULF COAST WITH SLIGHTLY LESS CONFIDENCE FURTHER  
INLAND/NORTH ACROSS THE LOWER MISSISSIPPI VALLEY. A SLIGHT RISK IN  
THE DAY 5 (12Z SAT - 12Z SUN) EXPERIMENTAL EXCESSIVE RAINFALL  
OUTLOOK WAS INTRODUCED GIVEN THE POTENTIAL FOR BOTH INTENSE RAIN  
RATES AND LONGER DURATION HEAVY RAIN THAT COULD LEAD TO FLASH  
FLOODING. SOME OF THESE AREAS HAVE SEEN RECENT HEAVY RAINFALL WITH  
THE LATEST SOIL MOISTURE ANOMALIES WELL ABOVE 90 PERCENT,  
PARTICULARLY ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY.  
THERE DOES REMAIN SOME MEANINGFUL MODEL DIFFERENCES, SO OVERALL  
CONFIDENCE IN SPECIFIC DETAILS AND LOCATIONS OF HEAVY RAIN/FLASH  
FLOODING IS A BIT LOWER NOW, BUT THE ENVIRONMENTAL INGREDIENTS DO  
SUPPORT THE POTENTIAL SOMEWHERE IN THE REGION.  
 
ELSEWHERE, THE COMBINATION OF A WEAKENING WARM FRONT CROSSING THE  
PLAINS AND COLD FRONT PUSHING INTO THE NORTHERN TIER LATE THIS  
WEEK MAY PRODUCE SHOWERS/THUNDERSTORMS OF VARYING INTENSITY FROM  
THE UPPER GREAT LAKES SOUTHWESTWARD WITH SOME THREAT OF LOCALIZED  
HEAVY RAINFALL ACROSS THE UPPER PENINSULA OF MICHIGAN ON FRIDAY  
WHERE SLIGHTLY HIGHER MOISTURE POOLS AHEAD OF THE ADVANCING FRONT.  
AFTER STARTING METEOROLOGICAL FALL WITH A DRIER AIRMASS, THERE  
REMAINS UNCERTAINTY IN THE FORECAST FOR THE EAST COAST BY LATE IN  
THE WEEKEND AND LABOR DAY AS MODEL GUIDANCE HAS TRENDED WETTER  
OVER THE LAST COUPLE OF CYCLES. DEEPER MOISTURE BEING PULLED  
NORTHWARD INTO THE REGION FROM THE GULF BY LABOR DAY INTERACTING  
WITH FAVORABLE UPPER LEVEL DYNAMICS COULD BRING GREATER CHANCES OF  
SHOWERS AND THUNDERSTORMS.  
 
TAYLOR/RAUSCH  
 
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC  
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP  
 
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, EXPERIMENTAL EXCESSIVE RAINFALL  
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES ARE  
AT:  
 
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=ERO  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML  
 

 
 

 
 
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