919  
FXUS02 KWBC 031900  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
259 PM EDT SUN JUL 03 2022  
 
VALID 12Z WED JUL 06 2022 - 12Z SUN JUL 10 2022  
   
..OVERVIEW
 
 
THE CENTER OF A STRONG UPPER LEVEL RIDGE/HIGH OVER THE SOUTHERN  
TIER OF THE CONTIGUOUS U.S. WILL DRIFT FROM THE MISSISSIPPI VALLEY  
INTO THE FOUR CORNERS/HIGH PLAINS DURING THE LATTER PART OF THIS  
WEEK INTO THE WEEKEND, WHILE EXTENDING RIDGING FARTHER NORTH INTO  
THE ROCKIES/HIGH PLAINS. THIS BROAD AREA OF RIDGING WILL LEAD TO  
HOT TEMPERATURES ACROSS MUCH OF THE CENTRAL CONUS. SURROUNDING THE  
MEAN RIDGE, A RELOADING UPPER LOW/TROUGH JUST OFF THE WEST COAST  
WILL PERSIST UNTIL EJECTING NORTHEASTWARD BY THE WEEKEND WHILE  
LEADING ENERGY SHOULD FLOW ACROSS THE NORTHERN TIER AND FEED INTO  
A BROAD MEAN TROUGH COVERING EASTERN CANADA AND THE NORTHEASTERN  
U.S. THE EASTERN NORTH AMERICA TROUGH SHOULD MAINTAIN FAIRLY  
STABLE AMPLITUDE THROUGH LATE WEEK AND THEN MAY DEEPEN GRADUALLY  
OVER THE WEEKEND. THIS FLOW PATTERN IS FAIRLY TYPICAL FOR SUMMER,  
WITH THE LARGE SCALE FEATURES JUST A LITTLE STRONGER THAN THE  
CLIMATOLOGICAL AVERAGE. A MEAN SURFACE FRONTAL BOUNDARY (POSSIBLY  
REINFORCED BY ONE OR MORE CANADIAN FRONTS) DRAPED FROM THE  
NORTH-CENTRAL PLAINS TO THE MID-ATLANTIC, COMBINED WITH SHORTWAVES  
EMBEDDED IN THE FLOW ALOFT, WILL LIKELY PRODUCE MULTIPLE EPISODES  
OF CONVECTION WITH LOCALLY HEAVY RAINFALL.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
MODEL AND ENSEMBLE GUIDANCE REMAINS IN GOOD AGREEMENT FOR THE  
LARGE SCALE EVOLUTION OF A STRENGTHENING RIDGE BETWEEN AN EASTERN  
PACIFIC TROUGH/LOW EVENTUALLY TRACKING INTO THE NORTHWEST U.S. AND  
SOUTHWESTERN CANADA LATE WEEK INTO THE WEEKEND, AND EASTERN  
CANADA/NORTHEAST U.S. TROUGH THAT MAY AMPLIFY SOMEWHAT NEXT  
WEEKEND. SOLUTIONS CLUSTER REASONABLY WELL IN PRINCIPLE INTO ABOUT  
DAY 5 FRIDAY. THEN THEY DIVERGE FOR DETAILS OF NORTH PACIFIC FLOW  
AS WELL AS THE DISTRIBUTION, STRENGTH, AND TRACK OF PACIFIC TROUGH  
ENERGY AS IT PROGRESSES INLAND. PART OF THE CHALLENGE IN  
FORECASTING THE PACIFIC TROUGH IS THAT MODELS SUGGEST THE FEATURE  
WILL CONSIST OF MULTIPLE IMPULSES, EACH OF WHICH HAS LOW  
PREDICTABILITY ON ITS OWN WITHIN THE MORE CONFIDENT MEAN FEATURE.  
OF PARTICULAR NOTE BY DAY 7 SUNDAY, THE 06Z AND 12Z GFS RUNS LEAN  
SOMEWHAT TO THE FAST/AMPLIFIED SIDE OF THE SPREAD (00Z GFS MUCH  
CLOSER TO CONSENSUS WITH THE OVERALL TROUGH) WITH THE EJECTING  
TROUGH WHILE THE LAST TWO CMC RUNS STRAY TO THE FLAT SIDE WITH ANY  
LINGERING WEST COAST TROUGHING DUE TO BEING FAST WITH THE UPSTREAM  
LOW/TROUGH. MEANWHILE THERE IS FAIR CONSENSUS THAT THE MEAN FRONT  
OVER THE EAST SHOULD PUSH SOUTHWARD BY NEXT WEEKEND AS SUPPORTING  
UPPER TROUGHING SLOWLY AMPLIFIES.  
 
OTHER SMALLER SCALE FEATURES REMAIN CONSIDERABLY UNCERTAIN THROUGH  
THE PERIOD. ONE SUCH MESOSCALE FEATURE IS SHORTWAVE ENERGY THAT  
LOOKS TO BE SOMEWHERE NEAR BAJA CALIFORNIA/NORTHERN  
MEXICO/SOUTHERN ARIZONA AS THE PERIOD BEGINS WEDNESDAY MORNING AND  
TRACKS NORTH-NORTHEAST THURSDAY-FRIDAY, POSSIBLY DISRUPTING  
EVOLUTION OF THE BROAD UPPER HIGH AT TIMES. UNFORTUNATELY THE  
FEATURE IS SMALL ENOUGH TO HAVE FAIRLY LOW PREDICTABILITY AND  
MODELS CONTINUE TO DIFFER WITH WHAT PROPORTION OF INITIAL ENERGY  
REACHES THE FOUR CORNERS STATES. GFS RUNS HAVE TYPICALLY BEEN  
STRONGER WITH THIS FEATURE WITH THE ECMWF AMONG THE WEAKEST (OR  
DIVERTING MORE ENERGY WESTWARD INSTEAD OF NORTHWARD). UKMET RUNS  
HAVE GENERALLY BEEN CLOSER TO THE GFS IN PRINCIPLE WHILE THE 12Z  
CMC SEEMS TO SPLIT BETWEEN THE GFS AND ECMWF IDEAS. WHATEVER  
PROPORTION OF ENERGY THAT LIFTS NORTHWARD WILL PLAY AN IMPORTANT  
ROLE WITH RESPECT TO THE RAINFALL FORECAST OVER THE  
SOUTHWEST/ROCKIES AND THEN THE CONVECTIVE FORECAST AS THIS ENERGY  
BECOMES EMBEDDED IN THE SOUTHERN FRINGE OF THE WESTERLIES AND  
INTERACTS WITH THE SURFACE FRONT TO THE EAST OF THE ROCKIES.  
ADDITIONALLY, SHORTWAVE SPECIFICS AROUND THE NORTHERN PERIPHERY OF  
THE CONUS RIDGE AND INTO THE EASTERN CANADA/NORTHEAST U.S. MEAN  
TROUGH VARY CONSIDERABLY BETWEEN MODELS (THOUGH WITH SOME  
SIMILARITY IN THE 12Z CMC/UKMET) AND THUS CONFIDENCE IS LOW FOR  
THESE FEATURES AND FOR SURFACE FRONT/WAVE DETAILS. STILL EXPECT TO  
WAIT UNTIL THE SHORT RANGE PERIOD TO RESOLVE THESE DETAILS, AND  
EVEN THEN SOME ASPECTS OF THE FORECAST MAY HAVE VERY SHORT LEAD  
TIME GIVEN HOW CHALLENGING IT CAN BE FOR MODELS TO LATCH ONTO  
MESOSCALE FEATURES THAT WILL MATTER GREATLY FOR QPF PLACEMENT AND  
AMOUNTS. CONTINUE TO MONITOR THE FORECAST FOR UPDATES GOING  
FORWARD.  
 
THE ABOVE CONSIDERATIONS LED TO STARTING THE UPDATED FORECAST WITH  
A COMPOSITE OF 00Z/06Z OPERATIONAL MODEL RUNS FOR THE FIRST HALF  
OF THE PERIOD, FOLLOWED BY ADDING SOME 06Z GEFS/00Z ECMWF MEAN  
INPUT WHILE MAINTAINING THE 00Z ECMWF COMPONENT BUT TRANSITIONING  
THE GFS EXCLUSIVELY TO THE 00Z RUN AND REDUCING CMC WEIGHT. THIS  
APPROACH PROVIDED GOOD CONTINUITY ASIDE FROM TYPICAL ADJUSTMENTS  
RESULTING FROM GUIDANCE CHANGES IN SMALLER-SCALE FRONTAL WAVE  
DETAILS.  
 
   
..SENSIBLE WEATHER AND HAZARDS
 
 
SCATTERED SHOWERS AND STORMS ARE LIKELY ACROSS MUCH OF THE U.S.  
FROM THE ROCKIES EASTWARD AT TIMES THIS WEEK, WITH ENHANCED TOTALS  
IN THE VICINITY OF A COUPLE OF FRONTAL BOUNDARIES STRETCHING  
GENERALLY WEST TO EAST ACROSS THE NORTHERN HALF OF THE COUNTRY.  
NORTHWESTERLY FLOW ALOFT AND ABUNDANT MOISTURE AND INSTABILITY  
WILL CREATE A FAVORABLE PATTERN FOR MESOSCALE CONVECTIVE SYSTEMS  
AND HIGH RAINFALL RATES WITHIN A BROAD AREA FROM THE NORTHERN  
PLAINS/MIDWEST/UPPER GREAT LAKES INTO THE OHIO VALLEY AND  
APPALACHIANS TO THE EAST COAST. AREAS OF EXCESSIVE RAINFALL/FLASH  
FLOODING ARE CERTAINLY POSSIBLE THROUGH THE END OF THE WEEK, BUT  
CONSIDERABLE UNCERTAINTY WITH THE PLACEMENT OF HEAVY RAIN AMOUNTS  
PRECLUDES DELINEATING SLIGHT RISK AREAS IN THE EXPERIMENTAL DAY  
4-5 EXCESSIVE RAINFALL OUTLOOK AT THIS POINT. SCATTERED  
THUNDERSTORMS ARE ALSO LIKELY IN THE SOUTHEAST THROUGH THE WEEK,  
AND THE CURRENT FORECAST SHOWS THE EASTERN PART OF THE MAIN FRONT  
SINKING SOUTHWARD FROM MEANDERING OVER THE MID-ATLANTIC INTO THE  
CAROLINAS BY NEXT WEEKEND, LEADING TO MORE FOCUSED RAINFALL IN THE  
SOUTHEAST AND CLEARING FOR THE NORTHEAST BEHIND THE FRONT. AT THE  
SAME TIME A FRONTAL SYSTEM EMERGING INTO THE NORTHERN PLAINS NEXT  
WEEKEND MAY PROVIDE ADDED CONVECTIVE FOCUS OVER THAT REGION.  
MEANWHILE MONSOONAL MOISTURE COULD PERSIST THROUGH MUCH OF THE  
WEEK WITH MOIST SOUTHWESTERLY FLOW/EMBEDDED SHORTWAVES LEADING TO  
MAINLY DIURNALLY DRIVEN SHOWERS AND STORMS OVER THE FOUR CORNERS  
STATES. THE SOUTHERN PLAINS AND CALIFORNIA INTO THE GREAT BASIN  
SHOULD BE THE MOST CONSISTENTLY DRY AREAS DURING THE PERIOD.  
 
THE GREATEST CONCERN FOR TEMPERATURES IS WITH THE HEAT EXPECTED TO  
BUILD ACROSS THE CENTRAL U.S. IN RESPONSE TO A STRENGTHENING UPPER  
LEVEL RIDGE. HIGHS OF 10-15 DEGREES ABOVE NORMAL ARE MOST LIKELY  
OVER THE CENTRAL PLAINS TO MIDDLE MISSISSIPPI VALLEY MID-LATE  
WEEK, EQUATING TO TEMPERATURES IN THE MID 90S TO LOW 100S, WHILE  
PARTS OF THE NORTHERN/NORTH-CENTRAL PLAINS MAY EXPERIENCE  
SIMILARLY HOT WEATHER BY NEXT SATURDAY-SUNDAY. ADDING IN THE  
EFFECT OF HUMIDITY, HIGHEST HEAT INDEX VALUES SHOULD BE FROM THE  
LOWER HALF TO TWO-THIRDS OF THE MISSISSIPPI VALLEY WESTWARD INTO  
THE PLAINS. DAY-TO-DAY TEMPERATURES AROUND THE PERIPHERY OF THIS  
HEAT WILL DEPEND ON UNCERTAIN DETAILS OF A WAVY FRONT AND  
ASSOCIATED CONVECTION. SOUTHERN PLAINS LOCATIONS WILL ALSO SEE HOT  
TEMPERATURES THROUGH THE PERIOD WITH MOSTLY PLUS 5-10F ANOMALIES  
FOR HIGHS. MOST OF THE EAST SHOULD SEE HIGHS WITHIN A FEW DEGREES  
ON EITHER SIDE OF NORMAL FOR MOST OF THE PERIOD WHILE LOWS TEND TO  
BE SOMEWHAT MORE ABOVE NORMAL. SOME DAILY RECORD WARM LOWS WILL BE  
POSSIBLE OVER PARTS OF THE CENTRAL/EASTERN U.S. EASTERN U.S. HIGHS  
MAY TREND SLIGHTLY BELOW NORMAL NEXT SUNDAY AS UPPER TROUGHING  
NEAR THE EAST COAST AMPLIFIES. MEANWHILE THE WEST WILL SEE COOLER  
THAN NORMAL HIGHS THROUGH AT LEAST MIDWEEK DUE TO THE INITIAL  
EASTERN PACIFIC UPPER TROUGH AND LEADING MOISTURE OVER THE FOUR  
CORNERS STATES. THEN TEMPERATURES SHOULD MODERATE CLOSER TO  
NORMAL. HIGHS OVER AND NEAR THE DESERT SOUTHWEST MAY TREND  
SLIGHTLY ABOVE NORMAL BY THE WEEKEND.  
 
RAUSCH/TATE  
 
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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