089  
FXUS02 KWBC 291900  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
259 PM EDT MON AUG 29 2022  
 
VALID 12Z THU SEP 01 2022 - 12Z MON SEP 05 2022  
 
...MUCH ABOVE NORMAL TEMPERATURES AND SOME RECORD HIGHS POSSIBLE  
OVER A LARGE PORTION OF THE WEST FOR MULTIPLE DAYS...  
   
..HEAVY RAIN THREAT ALONG PORTIONS OF THE GULF COAST
 
 
   
..OVERVIEW
 
 
THE MOST STABLE FEATURE DURING THE THURSDAY-MONDAY PERIOD SHOULD  
BE A STRONG WESTERN U.S. UPPER RIDGE THAT WILL PROMOTE VERY WARM  
TO HOT TEMPERATURES OVER A MAJORITY OF THE REGION, WITH DAILY  
RECORDS FOR HIGHS AND WARM LOWS POSSIBLE EACH DAY. THE OTHER FOCUS  
FOR SIGNIFICANT WEATHER WILL BE OVER THE SOUTH AND GULF COAST  
AREAS WHERE THE INTERACTION OF A FRONT SETTLING OVER THE REGION  
AND SOUTHEASTERLY TO EASTERLY LOW LEVEL FLOW FROM THE GULF, ALONG  
WITH ONE OR MORE UPPER LEVEL IMPULSES/CIRCULATIONS, COULD PRODUCE  
SEVERAL DAYS OF HEAVY RAINFALL AND POTENTIAL FOR SOME FLASH  
FLOODING. CURRENTLY EXPECT HIGHEST TOTALS TO SHIFT WESTWARD FROM  
NEAR THE FLORIDA PANHANDLE TO THE TEXAS GULF COAST OVER THE COURSE  
OF THE PERIOD. MEANWHILE ONE UPPER TROUGH DEPARTING FROM THE  
NORTHEAST LATE THIS WEEK WILL BE REPLACED BY ANOTHER ONE THAT  
REACHES THE AREA BY SUNDAY-MONDAY. THE LATTER TROUGH SHOULD PUSH A  
COLD FRONT FROM THE NORTHERN TIER INTO THE EAST.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
THE FIRST GUIDANCE DIFFERENCE OF NOTE INVOLVES THE DETAILS OF AN  
EASTERN PACIFIC UPPER LOW WHOSE ENERGY BRUSHES THE NORTHWEST AS  
UPSTREAM TROUGHING AMPLIFIES TO THE SOUTH OF ALASKA. THUS FAR THE  
OPERATIONAL MODELS HAVE VARIED AMONG EACH OTHER AND FROM RUN TO  
RUN FOR TIMING. SLOWER 12Z CMC TREND TO THE 00Z ECMWF HAS LEFT AN  
EVEN SPLIT BETWEEN THAT CLUSTER AND THE FASTER GFS/UKMET (THOUGH  
WITH THE 12Z UKMET SLOWER THAN ITS PRIOR RUN). LARGER SCALE  
DIFFERENCES DEVELOP FROM THE PACIFIC EASTWARD BY THE LATTER HALF  
OF THE PERIOD AS GFS/GEFS MEAN RUNS CONTINUE THEIR RECENT TENDENCY  
TO BRING IN PACIFIC TROUGHING MORE QUICKLY THAN OTHER GUIDANCE AND  
IN TURN BEGIN TO SHIFT THE DOWNSTREAM RIDGE/TROUGH CONFIGURATION  
OVER SOUTHERN CANADA AND INTO THE LOWER 48 FARTHER EASTWARD. THE  
12Z GFS NUDGED A LITTLE SLOWER THAN THE 06Z RUN BUT IS STILL  
SOMEWHAT OUT OF PHASE WITH THE MAJORITY. ASSOCIATED WITH THIS  
DIFFERENCE, BY LATE IN THE PERIOD THE GFS/GEFS MEAN WEAKEN THE  
WESTERN UPPER RIDGE VERSUS THE ECMWF/CMC AND THEIR MEANS, ALL OF  
WHICH STILL SHOW A 594+ DM RIDGE CENTERED OVER CALIFORNIA AND/OR  
NEVADA AS OF EARLY MONDAY. OVERALL PREFERENCE IS TO MAINTAIN A  
FORECAST THAT TILTS AT LEAST TWO-THIRDS TOWARD THE ECMWF/CMC  
CLUSTER. FAVORING THIS SCENARIO SHOULD IN TURN RESULT IN THE  
LEADING FEATURE EJECTING A LITTLE SLOWER THAN FORECAST BY THE GFS.  
 
THE FORECAST NEAR THE GULF COAST SHOWS LOWER THAN DESIRED  
PREDICTABILITY FOR SPECIFICS, GIVEN THE SHORT-TERM  
CONVECTIVE/MESOSCALE INFLUENCE ON AREAS OF SIGNIFICANT RAINFALL AS  
WELL AS THE MEDIUM TO SMALLER SCALE OF UPPER FEATURES THAT MAY BE  
INVOLVED. HOWEVER THERE ARE SOME GENERAL SIGNALS. THESE INCLUDE A  
STALLING GULF COAST FRONTAL BOUNDARY THAT SHOULD INTERACT WITH  
GULF MOISTURE CARRIED BY SOUTHEASTERLY TO EASTERLY LOW LEVEL  
WINDS, AND A GENERAL WESTWARD SHIFT IN RAINFALL EMPHASIS FROM THE  
FLORIDA PANHANDLE LATE THIS WEEK TOWARD THE TEXAS GULF COAST BY  
THE WEEKEND AND EARLY NEXT WEEK. GUIDANCE DISAGREES WITH THE  
MAGNITUDE OF ANOMALOUSLY HIGH PRECIPITABLE WATER VALUES, WITH THE  
ECMWF/ECMWF MEAN SUGGESTING MOISTURE COULD REACH UP TO 2-3  
STANDARD DEVIATIONS ABOVE NORMAL OVER/NEAR THE CENTRAL/WESTERN  
GULF COAST.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
THE PERSISTENT UPPER RIDGE OVER THE WEST WILL SUPPORT A BROAD AREA  
OF MUCH ABOVE NORMAL TEMPERATURES, WITH THE HIGHEST ANOMALIES  
LIKELY TO EXTEND FROM CALIFORNIA INTO THE INTERIOR  
NORTHWEST/NORTHERN ROCKIES AND AT TIMES INTO THE NORTHERN HIGH  
PLAINS. EXPECT MOST DAYS TO SEE PLUS 10-20F ANOMALIES WHICH COULD  
CHALLENGE DAILY RECORDS FOR BOTH HIGHS AND WARM LOWS. MEANWHILE  
THE OTHER PRIMARY WEATHER FOCUS WILL BE WITH SHOWERS AND  
THUNDERSTORMS ACROSS THE SOUTHERN TIER DUE TO A STALLING FRONT  
LIKELY INTERACTING WITH AMPLE INSTABILITY AND MOISTURE AS WELL AS  
ONE OR MORE UPPER LEVEL IMPULSES/CIRCULATIONS BETWEEN THE CENTRAL  
U.S. AND THE SOUTH. INITIAL MOISTURE/ENERGY COULD PRODUCE RAINFALL  
OVER PARTS OF TEXAS. OTHERWISE THE BEST SURGE OF MOISTURE SHOULD  
GENERALLY TRANSLATE WESTWARD WITH TIME, FROM NEAR THE FLORIDA  
PANHANDLE LATE THIS WEEK AND THEN CONTINUING THROUGH THE CENTRAL  
GULF COAST AND WESTERN GULF COAST/TEXAS DURING THE WEEKEND INTO  
EARLY NEXT WEEK. SOME OF THIS RAINFALL MAY BE HEAVY WITH MULTIPLE  
DAYS OF SUCH ACTIVITY LEADING TO CONCERNS FOR FLASH FLOODING AND  
AT LEAST LOCALIZED RAINFALL ACCUMULATIONS OF SEVERAL INCHES. NOTE  
THAT THERE ARE STILL MEANINGFUL GUIDANCE DIFFERENCES FOR SPECIFICS  
SO DETAIL CONFIDENCE IS LOWER THAN DESIRED AT THIS TIME.  
 
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. HOW MUCH RAINFALL THE COLD  
FRONT PRODUCES AS IT CONTINUES FARTHER EASTWARD IS STILL UP FOR  
DEBATE. THE START OF METEOROLOGICAL FALL WILL INDEED FEEL  
FALL-LIKE FOR PARTS OF THE EASTERN U.S. PORTIONS OF THE GREAT  
LAKES/NORTHEAST COULD SEE HIGHS AND/OR LOWS UP TO 5-10F BELOW  
NORMAL THURSDAY-FRIDAY. EASTERN U.S. TEMPERATURES SHOULD TREND TO  
NEAR OR SOMEWHAT ABOVE NORMAL AFTER FRIDAY. CLOUDS AND RAINFALL  
WILL LIKELY KEEP HIGHS NEAR TO BELOW NORMAL ACROSS THE FAR  
SOUTHERN TIER.  
 
RAUSCH/TAYLOR  
 
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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