872  
FXUS02 KWBC 210701  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
300 AM EDT THU JUL 21 2022  
 
VALID 12Z SUN JUL 24 2022 - 12Z THU JUL 28 2022  
 
...DANGEROUS HEAT OVER THE CENTRAL U.S. TO PERSIST OVER SOME AREAS  
INTO MIDWEEK...  
 
...HEAT WAVE OVER THE MID-ATLANTIC AND PARTS OF THE NORTHEAST  
LIKELY TO PEAK THIS WEEKEND...  
   
..HEAT EXPECTED TO BUILD OVER THE NORTHWEST NEXT WEEK
 
 
   
..OVERVIEW
 
 
GUIDANCE SHOWS SOME TRANSITION OF THE LARGE SCALE PATTERN OVER THE  
COURSE OF THE PERIOD. INITIALLY EXPECT STRONG RIDGING TO STRETCH  
ACROSS MOST OF THE SOUTH-CENTRAL U.S. WITH PROGRESSIVE FLOW TO THE  
NORTH, ALONG WITH WEAK TROUGHING ALONG THE NORTHERN HALF OF THE  
WEST COAST. DURING NEXT WEEK AN UPPER RIDGE BUILDING OVER THE  
NORTHEASTERN PACIFIC/WESTERN CANADA SHOULD SUPPORT AN AMPLIFYING  
TROUGH OVER CENTRAL CANADA AND THE NORTHERN PLAINS THROUGH GREAT  
LAKES. AT THE SAME TIME, WESTERN U.S. RIDGING WILL EXTEND MORE  
INTO THE NORTHWEST WHILE STRONGEST SOUTHERN TIER RIDGING SHOULD  
GRAVITATE TOWARD THE SOUTHEAST COAST (VIA POTENTIAL MERGING OF A  
RETROGRADING ATLANTIC RIDGE AND EASTWARD-MOVING PLAINS/MISSISSIPPI  
VALLEY UPPER HIGH). THIS PATTERN TRANSITION SHOULD REDUCE THE  
COVERAGE OF INTENSE HEAT FROM THE CENTRAL/SOUTHERN PLAINS INTO THE  
EAST AFTER SUNDAY (WHEN MANY AREAS SHOULD SEE HIGHS 7-15F ABOVE  
NORMAL) WHILE ESTABLISHING A MULTI-DAY PERIOD OF HOT WEATHER OVER  
THE NORTHWEST (SOME HIGHS 10-15F ABOVE NORMAL) WHICH MAY EXTEND  
BEYOND NEXT THURSDAY PER CLIMATE PREDICTION CENTER FORECAST. TWO  
PROMINENT SURFACE FRONTS WILL LIKELY FOCUS AREAS OF LOCALLY HEAVY  
SHOWERS AND STORMS OVER PARTS OF THE CENTRAL/EASTERN U.S. AND  
SUPPORT THE MODERATING TEMPERATURE TREND EAST OF THE ROCKIES.  
AFTER A RELATIVE LULL IN ACTIVITY DURING THE SHORT RANGE PERIOD,  
GUIDANCE CONTINUES TO SHOW A PERIOD OF ENHANCED MONSOONAL MOISTURE  
FROM ABOUT SUNDAY-MONDAY ONWARD, PROMOTING DAILY CHANCES OF  
SHOWERS AND STORMS THAT MAY PRODUCE SOME INSTANCES OF FLASH  
FLOODING.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
IN GENERAL THE GUIDANCE SEEMS TO BE CONTINUING ON ITS PATH TOWARD  
BETTER OVERALL AGREEMENT, THOUGH WITH SOME CONTINUED DIFFERENCES  
FOR LOW-PREDICTABILITY SHORTWAVE DETAILS WITHIN NORTHERN  
U.S./SOUTHERN CANADA FLOW DURING THE FIRST HALF OF THE PERIOD. THE  
NEW 00Z UKMET APPEARS TO BE LESS COMPARABLE TO OTHER GUIDANCE WITH  
A NORTHERN TIER SHORTWAVE AND RESULTING FLATTER FLOW REACHING THE  
GREAT LAKES/NORTHEAST. A MODEL/MEAN CONSENSUS APPROACH MAINTAINS A  
FAIRLY STABLE SOLUTION FOR THE DEVELOPING CENTRAL CANADA INTO U.S.  
UPPER TROUGH AND ITS LEADING SURFACE LOW PRESSURE/FRONTAL SYSTEM,  
WITH NO SOLUTIONS THROUGH 18Z EXTREME ENOUGH TO EXCLUDE FROM A  
COMPROMISE. THE NEW 00Z ECMWF HAS MADE SOME SIGNIFICANT DETAIL  
CHANGES FROM ITS PRIOR RUN, DECREASING CONFIDENCE A LITTLE.  
OVERALL THE MAJORITY CLUSTER LOOKS GOOD FOR UPPER RIDGING THAT  
PERSISTS OVER THE SOUTHERN TIER AND EXPANDS OVER THE WEST. THE  
UPDATED FORECAST INCORPORATING THE 12Z/18Z GUIDANCE STARTED WITH  
AN OPERATIONAL MODEL BLEND EARLY (MORE GFS/ECMWF THAN UKMET/CMC)  
AND THEN TRANSITIONED TO 40 PERCENT TOTAL 18Z GEFS/12Z ECMWF MEANS  
BY LATE IN THE PERIOD, WITH VARIOUS GFS/ECMWF/CMC WEIGHTS MAKING  
UP THE OTHER 60 PERCENT.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
BROAD COVERAGE OF HOT TEMPERATURES FROM THE SOUTHERN HALF OF THE  
PLAINS THROUGH THE EAST WILL EXTEND THROUGH SUNDAY, WITH MANY  
AREAS FROM THE CENTRAL PLAINS THROUGH THE MID-ATLANTIC/NEW ENGLAND  
SEEING HIGHS 10-15F ABOVE NORMAL (PERHAPS A BIT LOWER IN THE OHIO  
VALLEY). EXPECT A FAIRLY BROAD AREA OF 100+F HIGHS OVER THE  
SOUTHERN HALF OF THE PLAINS AND POSSIBLY EXTENDING INTO PARTS OF  
THE MISSISSIPPI VALLEY, AND AREAS ALONG THE EAST COAST COULD REACH  
THE MID 90S TO AROUND 100. HEAT INDICES COULD BE 105-110F IN MANY  
AREAS, AND VERY WARM LOWS WILL PROVIDE LITTLE NIGHTTIME RELIEF.  
THIS HEAT WAVE SHOULD BRING SCATTERED DAILY RECORDS FOR HIGHS AND  
WARM LOWS AS WELL. A COLD FRONT MOVING INTO THE CENTRAL/EASTERN  
U.S. SHOULD ERODE THE HEAT FROM THE NORTH BY MONDAY-TUESDAY BUT  
NOT REACH FAR ENOUGH SOUTH TO LOWER TEMPERATURES MUCH OVER AND  
NEAR THE SOUTHERN HALF OF THE PLAINS. THE NEXT FRONT THAT REACHES  
THE NORTHERN PLAINS EARLY NEXT WEEK SHOULD HAVE A STRONGER  
SOUTHWARD PUSH, BRINGING MODERATELY BELOW NORMAL HIGHS TO THE  
NORTHERN-CENTRAL PLAINS TUESDAY ONWARD AND POSSIBLY NEAR-NORMAL  
READINGS FARTHER SOUTH BY THURSDAY. BOTH FRONTS WILL FOCUS  
EPISODES OF SHOWERS AND STORMS, WITH SOME SEVERE WEATHER AND HEAVY  
RAINFALL POSSIBLE. THE LEADING FRONT HEADING INTO THE EAST MAY  
INITIALLY FAVOR HIGHEST RAINFALL TOTALS FROM THE EASTERN GREAT  
LAKES/OHIO VALLEY INTO THE NORTHEAST/MID-ATLANTIC BUT COULD ALSO  
FOCUS REPEAT ACTIVITY AS FAR WEST AS THE PLAINS AS IT STALLS  
BEFORE LIFTING BACK AS A WARM FRONT. THE SECOND FRONT SHOULD  
PRODUCE NORTHERN PLAINS CONVECTION THAT EXTENDS SOUTH/EAST WITH  
TIME.  
 
OVER THE WEST, PERSISTENT MONSOONAL MOISTURE AND VARIOUS SHORTWAVE  
IMPULSES WILL SUPPORT DIURNALLY FAVORED SHOWERS/STORMS WITH SOME  
LOCALLY HEAVY RAINFALL OVER THE FOUR CORNERS/GREAT BASIN REGION  
FROM SUNDAY THROUGH AT LEAST THURSDAY. GUIDANCE CONTINUES TO  
SUGGEST THAT THE PATTERN EVOLUTION WILL SUPPORT A MORE ACTIVE  
PERIOD WITH GREATER COVERAGE AND INTENSITY OF RAINFALL VERSUS THE  
SHORT RANGE TIME FRAME. POTENTIAL STILL EXISTS FOR SOME OF THIS  
MOISTURE TO INTERACT WITH CENTRAL PLAINS FRONTS (ONE DURING  
SUNDAY/EARLY NEXT WEEK AND THE SECOND ARRIVING AROUND MIDWEEK) TO  
ENHANCE RAINFALL TOTALS. UPPER RIDGING THAT BUILDS OVER THE  
NORTHWEST NEXT WEEK WILL BRING MULTIPLE DAYS OF HOT WEATHER TO  
THAT REGION, WITH SOME LOCATIONS LIKELY TO SEE HIGHS REACH UP TO  
10-15F OR SO ABOVE NORMAL. SOME DAILY RECORDS FOR HIGHS/WARM LOWS  
WILL BE POSSIBLE.  
 
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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