262  
FXUS02 KWBC 021859  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
258 PM EDT TUE AUG 02 2022  
 
VALID 12Z FRI AUG 05 2022 - 12Z TUE AUG 09 2022  
 
...THE SOUTHWEST MONSOON RESUMES A VERY ACTIVE PHASE LATE THIS  
WEEK...  
...HEAVY RAIN LIKELY FROM THE OHIO VALLEY THROUGH THE NORTHEAST  
LATE THIS WORK WEEK...  
 
   
..OVERVIEW
 
 
GUIDANCE EXPECTS A FAIRLY TYPICAL SUMMERTIME PATTERN WITH THE MAIN  
BAND OF WESTERLIES ACROSS SOUTHERN CANADA AND NORTHERN TIER CONUS,  
THOUGH WITH UPPER RIDGING TO THE SOUTH TENDING TO BE SOMEWHAT  
STRONGER THAN THE CLIMATOLOGICAL MEAN. AN UPPER LOW SHOULD LIFT  
VERY SLOWLY NORTHEASTWARD OFFSHORE THE WEST COAST. THE MODELS AND  
ENSEMBLES AGREE ON THE LARGE SCALE PATTERN BUT SIGNIFICANT  
SHORTWAVE DIFFERENCES DEVELOP WITHIN THE WESTERLIES FROM FAIRLY  
EARLY IN THE FORECAST. AS A RESULT CONFIDENCE DECREASES FOR  
SURFACE FRONT/WAVE DETAILS AND IN TURN FOR ASSOCIATED AREAS OF  
RAINFALL WHICH COULD BE HEAVY AT TIMES OVER PORTIONS OF THE  
NORTHERN HALF OF THE CENTRAL/EASTERN U.S. MEANWHILE THE MONSOONAL  
PATTERN OVER THE WEST SHOULD BECOME MORE PRONOUNCED AGAIN LATE  
THIS WEEK AND LIKELY REMAIN FAIRLY ACTIVE THROUGH THE WEEKEND AND  
PERHAPS INTO NEXT WEEK.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
THERE ARE TWO PRIMARY ASPECTS TO THE UNCERTAINTY WITHIN THE  
NORTHERN TIER U.S./SOUTHERN CANADA FLOW. THE FIRST IS WITH WITH  
INITIAL TROUGHING OVER AND NEAR SOUTHWESTERN CANADA. IN THE  
00Z/06Z GUIDANCE THERE WAS A NEARLY EVEN SPLIT BETWEEN THE  
ECMWF/CMC THAT TOOK MOST OF THE TROUGH ENERGY BODILY EASTWARD  
VERSUS THE GFS/UKMET THAT ACCELERATED THE CORE OF THE CANADIAN  
TROUGH ONWARD WHILE LEAVING BEHIND A TRAILING SHORTWAVE THAT  
ULTIMATELY TRACKS ALONG THE U.S.-CANADIAN BORDER. NEEDLESS TO SAY,  
THESE DIFFERENT SCENARIOS LEAD TO SIGNIFICANT REGIONAL DIFFERENCES  
IN FRONT/WAVE DETAILS. IN THE NEW 12Z CYCLE, THE CMC HAS ADJUSTED  
MORE TOWARD THE GFS CLUSTER WHILE THE ECMWF HAS NUDGED TOWARD  
HOLDING BACK A LITTLE MORE TRAILING SHORTWAVE ENERGY. THE SECOND  
ISSUE ARISES WITH UPSTREAM ENERGY ORIGINATING FROM THE  
ALEUTIANS/BERING SEA. THERE IS A GENERAL SIGNAL FOR A DEFINED  
SHORTWAVE TO PROGRESS ACROSS THE WESTERN AND CENTRAL PORTIONS OF  
SOUTHERN CANADA SUNDAY-TUESDAY BUT WITH TIMING/AMPLITUDE  
DIFFERENCES AFFECTING THE PROGRESS OF THE LEADING FRONT THAT MAY  
REACH THE NORTHERN STATES. GFS/GEFS MEAN RUNS HAVE BEEN ON THE  
FLAT SIDE ALOFT WHILE THE PAST COUPLE ECMWF RUNS HAVE BEEN ON THE  
FAST AND/OR AMPLIFIED SIDE. THE 06Z GEFS DID SHOW HINTS OF A TREND  
IN THE ECENS/CMCENS DIRECTION. THE NEW 12Z ECMWF HAS TRENDED  
NOTICEABLY FLATTER AS THE TROUGH ENTERS SOUTHWESTERN CANADA BUT  
THEN TRENDS TOWARD ITS AMPLIFIED TENDENCY THEREAFTER.  
 
BASED ON THE ARRAY OF GUIDANCE, THE UPDATED FORECAST STARTED WITH  
AN OPERATIONAL MODEL COMPOSITE FOR THE FIRST HALF OF THE PERIOD TO  
BALANCE THE POSSIBLE SCENARIOS FOR NORTHERN STREAM SHORTWAVES AND  
RESULTING FRONTS/WAVES. TRENDING TOWARD AN EVEN BLEND OF MODELS  
AND ENSEMBLE MEANS BY LATE IN THE PERIOD (EARLY NEXT WEEK)  
PROVIDED A GOOD INTERMEDIATE STARTING POINT WITHIN THE FULL RANGE  
OF POSSIBILITIES.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
EXPECT HOT TEMPERATURES OVER NORTHERN HALF OF THE PLAINS INTO THE  
MIDWEST LATE THIS WEEK INTO THE WEEKEND, ERODING FROM THE  
NORTHWEST AS A COLD FRONT APPROACHES. SOME HIGHS MAY REACH 10-15F  
ABOVE NORMAL AND A FEW RECORD HIGHS MAY BE POSSIBLE OVER THE HIGH  
PLAINS. VERY WARM CONDITIONS SHOULD EXTEND INTO THE GREAT  
LAKES/NORTHEAST THROUGH THE WEEKEND WITH SOME GRADUAL COOLING  
EARLY NEXT WEEK. OVER THE WEST, MAXIMUM TEMPERATURES WILL TEND TO  
BE SOMEWHAT BELOW NORMAL OVER THE GREAT BASIN/SOUTHWEST AND  
VICINITY DUE TO PERSISTENT CLOUDS AND PERIODS OF RAIN. THE UPPER  
SHORTWAVE INITIALLY OVER THE NORTHWEST SHOULD PROMOTE NEAR TO  
SLIGHTLY BELOW NORMAL HIGHS ON FRIDAY. THEN THE NORTHWEST SHOULD  
TREND MORE ABOVE NORMAL AS SOME DEGREE OF UPPER RIDGING BUILDS.  
HIGHS COULD LOCALLY REACH 10-12F ABOVE NORMAL.  
 
FOR PRECIPITATION, THE MAIN THREATS FOR FLASH FLOODING WILL BE  
ASSOCIATED WITH MONSOONAL MOISTURE OVER THE SOUTHWEST/GREAT  
BASIN/ROCKIES AS WELL AS WITH FRONTS/WAVES OVER NORTHERN AND  
CENTRAL PARTS OF THE U.S. EAST OF THE ROCKIES. THE COMBINED  
SIGNALS FOR RAINFALL AND ALREADY WET CONDITIONS OVER THE DESERT  
SOUTHWEST INTO THE CENTRAL ROCKIES/GREAT BASIN LATE THIS WEEK INTO  
THE WEEKEND SUPPORT SOME SLIGHT RISK AREAS IN THE EXPERIMENTAL  
DAYS 4-5 EXCESSIVE RAINFALL OUTLOOKS. FARTHER EAST, ONE AREA OF  
POTENTIAL FOCUS FOR SIGNIFICANT RAINFALL WILL BE OVER THE OHIO  
VALLEY AND NORTHEAST ALONG A FRONT THAT STALLS AND THEN RETURNS  
NORTH AS A WARM FRONT LATE THIS WEEK INTO THE WEEKEND. A TRAILING  
WAVY FRONT PROGRESSING EASTWARD FROM THE NORTHERN PLAINS MAY ALSO  
GENERATE SOME AREAS OF HEAVY RAINFALL BETWEEN THE NORTHERN HALF OF  
THE PLAINS AND EASTERN U.S. FROM THE WEEKEND INTO NEXT WEEK.  
 
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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