606  
FXUS02 KWBC 201901  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
259 PM EDT MON JUN 20 2022  
 
VALID 12Z THU JUN 23 2022 - 12Z MON JUN 27 2022  
 
...EXPANSIVE AREA OF EXCESSIVE HEAT LIKELY TO PERSIST ACROSS THE  
SOUTH INTO THE WEEKEND...  
 
   
..OVERVIEW
 
 
A BROAD UPPER LEVEL RIDGE PARKED OVER THE SOUTHERN U.S. THROUGH  
THE WEEKEND WILL BRING AN EXTENDED PERIOD OF EXCESSIVE HEAT AND  
RECORD TEMPERATURES TO MANY LOCATIONS ACROSS THE REGION. TO THE  
NORTH, A MODEST TROUGH INITIALLY ANCHORED BY A SOUTHERN BRITISH  
COLUMBIA UPPER LOW WILL RIDE AROUND THE TOP OF THE RIDGE FROM THE  
NORTHWEST TO THE MIDWEST, EVENTUALLY AMPLIFYING AS IT REACHES THE  
GREAT LAKES/NORTHEAST LATER IN THE PERIOD. THIS AMPLIFICATION  
SHOULD FINALLY HELP TO BREAK DOWN THE MASSIVE SOUTHERN HEAT DOME.  
MONSOONAL MOISTURE WILL LIKELY PERSIST OVER THE FOUR CORNERS  
REGION THROUGH MUCH OF THE PERIOD AND COULD CONTRIBUTE TO HEAVIER  
RAINFALL ALONG THE SOUTHERN HALF OF THE ROCKIES BY THE WEEKEND  
WITH THE ARRIVAL OF A SURFACE FRONT AND TRAILING LOW LEVEL UPSLOPE  
FLOW.  
   
..GUIDANCE/PREDICTABILITY EVALUATION
 
 
THERE IS DECENT AGREEMENT ON THE OVERALL PATTERN IN THE LATEST  
MODEL GUIDANCE, ESPECIALLY REGARDING A PERSISTENT AND EXPANSIVE  
UPPER RIDGE OVER THE SOUTHERN U.S. THE MOST UNCERTAIN PARTS OF THE  
FORECAST CONTINUE TO BE WITH THE OVERALL TROUGH ROUNDING THE TOP  
OF THE UPPER RIDGE (LEADING TO TIMING DIFFERENCES WITH THE LEADING  
FRONTAL SYSTEM) AND DETAILS WITHIN THE AREA OF MEAN TROUGHING FROM  
NEW ENGLAND AND THE CANADIAN MARITIMES THROUGH THE WESTERN  
ATLANTIC. FOR THE NORTHERN STREAM TROUGH, GUIDANCE THROUGH THE  
00Z/06Z CYCLES WAS SPLIT BETWEEN THE SLOWER GFS/CMC AND FASTER  
ECMWF/UKMET. THE GEFS MEAN HAS TRENDED SOMEWHAT FASTER OVER THE  
PAST DAY OR SO, CLOSER TO THE ECMWF MEAN, SO THAT HINTS TOWARD  
NUDGING A LITTLE MORE TOWARD THE ECMWF CLUSTER. AMONG THE NEW 12Z  
RUNS, THE CMC HAS ADJUSTED A LITTLE FASTER TO LEAVE THE GFS MORE  
IN THE MINORITY. HOWEVER THE 12Z ECMWF HAS ADJUSTED A BIT SLOWER.  
MEANWHILE THE MODELS ALREADY DIVERGE SIGNIFICANTLY OVER THE  
CANADIAN MARITIMES/EAST COAST/WESTERN ATLANTIC AREA IN THE SHORT  
RANGE, WITH CONSIDERABLE SPREAD AND RUN-TO-RUN VARIABILITY FOR  
WHERE ONE OR MORE EMBEDDED UPPER LOWS MAY BE FROM THE START OF THE  
PERIOD (EARLY THURSDAY) ONWARD. NEEDLESS TO SAY, PREDICTABILITY IS  
QUITE LOW OVER THIS REGION AND CONFIDENCE IN ANY SPECIFIC SOLUTION  
IS LIKEWISE VERY LOW, THUS FAVORING A CONSERVATIVE BLEND APPROACH.  
FINALLY, A MODEL/ENSEMBLE MEAN COMPROMISE APPEARS BEST FOR THE  
UPPER LOW THAT MAY APPROACH THE PACIFIC NORTHWEST AND SOUTHERN  
BRITISH COLUMBIA BY EARLY NEXT WEEK. THE UPPER LOW MOVES ALONG  
RATHER SLOWLY FOR MOST OF THE PERIOD UNDER ALASKA/NORTHWESTERN  
CANADA RIDGING, SO THE LATEST GFS RUNS AND 00Z ECMWF COULD BECOME  
A TAD FAST BY THE END OF THE PERIOD. CMC/GEFS MEAN RUNS THROUGH  
THE 12Z CYCLE AND THE 00Z ECMWF MEAN FAVOR SOMEWHAT SLOWER  
PROGRESSION. CONSIDERATIONS FOR VARIOUS FEATURES LED TO STARTING  
THE FIRST HALF OF THE FORECAST WITH A MOSTLY 00Z/06Z OPERATIONAL  
MODEL BLEND INCORPORATING THE ECMWF/GFS/UKMET/CMC FROM HIGHEST TO  
LOWEST WEIGHT AND A LITTLE 06Z GEFS/00Z ECENS INPUT. THEN THE  
STARTING BLEND QUICKLY TRANSITIONED TO HALF MODELS/HALF MEANS BY  
DAYS 6-7 SUNDAY-MONDAY.  
   
..SENSIBLE WEATHER/THREAT HIGHLIGHTS
 
 
ANOMALOUSLY HIGH MONSOONAL MOISTURE FOR THIS TIME OF YEAR, LIKELY  
TIED AT LEAST IN PART TO EASTERN PACIFIC TROPICAL SYSTEMS, WILL  
CONTINUE STREAMING INTO THE FOUR CORNERS STATES INTO THE WEEKEND.  
LOCALLY HEAVY TO EXCESSIVE RAINFALL IS POSSIBLE, PARTICULARLY OVER  
SENSITIVE BURN SCAR AREAS AND CONSIDERING THE MULTIPLE DAY  
REPEATING NATURE OF THIS ACTIVITY. RAINFALL MAY TREND HEAVIER OVER  
PARTS OF COLORADO/NEW MEXICO BY THE WEEKEND AS A FRONT DROPPING  
SOUTH THROUGH THE REGION AND TRAILING LOW LEVEL UPSLOPE FLOW COULD  
INTERACT WITH THE MOISTURE ALREADY IN PLACE. A SHOWERY/STORMY  
PATTERN COULD ALSO SET UP THROUGH FRIDAY IN PARTS OF THE NORTHERN  
HALF OF THE PLAINS/MISSISSIPPI VALLEY WITH THE COMBINATION OF A  
COLD FRONT PUSHING INTO THE AREA FROM THE WEST AND LEADING WARM  
FRONT LIFTING NORTHEASTWARD. RAINFALL TOTALS WILL DEPEND IN PART  
ON STILL UNCERTAIN FRONTAL TIMING. PROGRESSION OF THE PLAINS COLD  
FRONT SHOULD INCREASE COVERAGE OF RAIN/THUNDERSTORMS OVER THE EAST  
BY THE START OF NEXT WEEK. AHEAD OF THIS FEATURE, THE EAST MAY  
ALSO SEE EPISODES OF RAIN/STORMS OF VARYING INTENSITY LATE THIS  
WEEK WITH A LEADING WAVY FRONT AS WELL AS A SURFACE TROUGH TO ITS  
SOUTH. EAST COAST RAINFALL DETAILS WILL DEPEND ON UNCERTAIN  
SPECIFICS OF FEATURES WITHIN THE NEARBY MEAN TROUGH ALOFT.  
 
LIKELY THE BIGGEST THREAT OF THE MEDIUM RANGE PERIOD WILL BE A  
BROAD AREA OF POTENTIALLY RECORD-BREAKING HEAT ACROSS SOUTHERN  
PARTS OF THE PLAINS INTO THE SOUTHEAST. EXPECT DAILY RECORD MAX OR  
MIN TEMPERATURES BE SET WITHIN THIS AREA, INCLUDING HIGHS  
EXCEEDING 100F AND LOWS WELL INTO THE 70S MEANING LITTLE RELIEF  
OVERNIGHT IN MANY AREAS. TEMPERATURES 10-15F ABOVE NORMAL COULD  
STRETCH FARTHER NORTH INTO MUCH OF THE PLAINS AND MISSISSIPPI AND  
OHIO VALLEYS, MAINLY THURSDAY INTO SATURDAY. THE SOUTH SHOULD  
FINALLY SEE A MODERATING TREND BY THE WEEKEND AND ESPECIALLY EARLY  
NEXT WEEK AS A LEADING FRONT DIPS INTO THE SOUTHEAST AND THEN THE  
LATE WEEK PLAINS FRONT REACHES INTO THE SOUTH AND EAST.  
TEMPERATURES ALONG THE EAST COAST SHOW THE MOST FORECAST SPREAD,  
AND WILL BE DEPENDENT ON THE UPPER PATTERN. RELATIVELY COOLER  
TEMPERATURES WITH WELL BELOW NORMAL HIGHS ARE LIKELY TO BE MOST  
PERSISTENT OVER NEW MEXICO GIVEN THE MONSOONAL CLOUDS AND RAIN  
COVERAGE. THE NORTHERN HIGH PLAINS MAY ALSO SEE COOL HIGHS FROM  
FRIDAY INTO THE WEEKEND, DROPPING INTO COLORADO FROM THE WEEKEND  
INTO EARLY NEXT WEEK WITH SOUTHWARD COLD FRONT PROGRESSION. THE  
WEST COAST STATES SHOULD SEE HIGHS 5-15F ABOVE AVERAGE.  
 
RAUSCH/SANTORELLI  
 
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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