447  
FXUS02 KWBC 230658  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
257 AM EDT TUE AUG 23 2022  
 
VALID 12Z FRI AUG 26 2022 - 12Z TUE AUG 30 2022  
   
..OVERVIEW
 
 
MOST GUIDANCE CONTINUES TO ADVERTISE DEPARTURE OF THE EASTERN  
NORTH AMERICAN MEAN TROUGH ALOFT AFTER FRIDAY AND THEN DEVELOPMENT  
OF A MEAN TROUGH OVER THE CENTRAL U.S. DURING THE WEEKEND/EARLY  
NEXT WEEK, WITH THIS TROUGH LIKELY REACHING THE MISSISSIPPI  
VALLEY/GREAT LAKES BY NEXT TUESDAY. THE CENTRAL U.S. TROUGH WILL  
BE SUPPORTED BY A QUICKLY AMPLIFYING TROUGH/RIDGE PATTERN OVER THE  
EASTERN PACIFIC AND WESTERN NORTH AMERICA RESPECTIVELY. THE  
WESTERN PERIPHERY OF ATLANTIC UPPER RIDGING SHOULD BUILD WESTWARD  
TO COVER AN INCREASING PORTION OF THE EAST/SOUTH DURING THE  
WEEKEND AND EARLY NEXT WEEK. THE BRIEF PERIOD OF MORE PACIFIC  
INFLUENCE ON MEAN FLOW ALOFT OVER THE WEST INTO THE WEEKEND SHOULD  
LEAD TO A SOMEWHAT DRIER TREND OVER THE FOUR CORNERS STATES WHILE  
POTENTIALLY ADDING SOME MOISTURE TO AN EXPANDING AREA OF PLAINS  
INTO MISSISSIPPI VALLEY/GREAT LAKES RAINFALL AHEAD OF THE  
DEVELOPING CENTRAL U.S. MEAN TROUGH AND LEADING SURFACE SYSTEM.  
SOME AREAS OF RAINFALL SHOULD PERSIST OVER THE SOUTH AND NEARBY  
AREAS DURING THE PERIOD BUT WITH ANY HEAVY TOTALS TENDING TO BE  
FAIRLY LOCALIZED. ABOVE NORMAL TEMPERATURES WILL TEND TO BE  
CONFINED TO THE NORTHWEST (FRIDAY AND MONDAY-TUESDAY) AND  
NORTHEAST/NEARBY AREAS (SUNDAY-TUESDAY) WHILE NEAR OR SLIGHTLY  
BELOW NORMAL HIGHS SHOULD PREVAIL OVER THE SOUTH, ROCKIES, AND  
NORTHERN PLAINS.  
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
MODELS/ENSEMBLES ARE STABLE WITH THE LEADING WEAK SHORTWAVE  
REACHING THE NORTHERN PLAINS BY SATURDAY. HOWEVER THEY CONTINUE  
TO VARY WITH THE DETAILS OF INCOMING NORTHEAST PACIFIC SHORTWAVE  
ENERGY THAT SHOULD ULTIMATELY FEED INTO THE DEVELOPING MEAN  
TROUGH, AND TO SOME DEGREE WITH THE LARGER SCALE PACIFIC/WESTERN  
NORTH AMERICA PATTERN EARLY NEXT WEEK. ONE POSITIVE AT THIS POINT  
IS THAT THE ENSEMBLE SPREAD OVER THE NORTHWEST VALID EARLY  
SATURDAY HAS NARROWED QUITE A BIT FROM 24 HOURS AGO, TOWARD A  
MODERATE SHORTWAVE TROUGH, BUT THERE IS STILL MEANINGFUL SPREAD  
FOR AMPLITUDE. BEYOND THEN THE SPAGHETTI PLOTS STILL BECOME  
RATHER CHAOTIC BUT WITH THE GREATEST DENSITY OF SOLUTIONS  
GRAVITATING TOWARD A TROUGH-RIDGE-TROUGH CONFIGURATION OVER THE  
EASTERN PACIFIC THROUGH EAST-CENTRAL NORTH AMERICA BY NEXT  
TUESDAY. OPERATIONAL MODELS DIFFER SIGNIFICANTLY AS WELL. FOR  
EXAMPLE, LATEST GFS RUNS ARE ON THE DEEP/SOUTH SIDE WITH A COMPACT  
CLOSED LOW. THE CMC HAS SWITCHED FROM A PROGRESSIVE OPEN WAVE  
(FASTER THAN CONSENSUS) IN THE 12Z RUN TO A SLOW CLOSED LOW  
(WEAKER THAN THE GFS) IN THE 00Z RUN. LATER IN THE PERIOD THERE  
ARE SOME DIFFERENCES WITH THE LARGER SCALE EVOLUTION THAT COME  
INTO PLAY. IN PARTICULAR THE GFS HAS SPORADICALLY BEEN SHIFTING  
ITS PATTERN OUT OF PHASE WITH CONSENSUS, SUCH AS IN THE 12Z RUN  
THAT HAD ITS PACIFIC/NORTH AMERICA PATTERN FARTHER WEST. 18Z AND  
NEW 00Z RUNS ARE CLOSER. STILL, ALL OF THOSE GFS RUNS ULTIMATELY  
END UP SOMEWHAT ON THE DEEP/SLOW SIDE WITH THE UPPER TROUGH  
REACHING THE MISSISSIPPI VALLEY BY NEXT WEEK.  
 
THE UPDATED FORECAST PRIMARILY FOCUSED ON 12Z/18Z OPERATIONAL  
MODELS DURING THE FIRST HALF OF THE PERIOD BUT ALREADY WITH A  
SMALL ENSEMBLE COMPONENT GIVEN THE GREATER THAN USUAL DETAIL  
SPREAD. THEN THE BLEND TRENDED TOWARD HALF MODELS/HALF MEANS BY  
DAY 7 TUESDAY, WITH MORE 12Z ECMWF THAN 18Z GFS/12Z CMC FOR THE  
MODEL COMPONENT AND THE 18Z GEFS/12Z ECENS COMPRISING THE ENSEMBLE  
PORTION. THIS APPROACH YIELDED GOOD CONTINUITY OVERALL.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
THE BRIEF TRANSITION TO MORE PROGRESSIVE FLOW ALOFT OVER THE WEST  
DURING THE WEEKEND SHOULD PROMOTE A LIGHTER AND MORE SCATTERED  
TREND FOR RAINFALL OVER THE FOUR CORNERS STATES AFTER FRIDAY.  
SOME OF THE WESTERN U.S. DEEP MOISTURE THAT IS PUSHED EASTWARD MAY  
CONTRIBUTE TO THE EXPANDING AREA OF RAINFALL FORECAST TO SPREAD  
ACROSS THE PLAINS AND EVENTUALLY INTO THE MISSISSIPPI VALLEY/GREAT  
LAKES. A LEADING WARM FRONT FOLLOWED BY A SURFACE TROUGH AND COLD  
FRONT, AS WELL AS NORTHERN TIER UPPER DYNAMICS, WILL ALL PROVIDE  
VARYING DEGREES OF FOCUS FOR WHAT COULD BE MULTIPLE AREAS OF  
LOCALLY MODERATE TO HEAVY RAINFALL WITHIN THE BROAD MOISTURE  
SHIELD. IT WILL TAKE ADDITIONAL TIME TO RESOLVE WHERE THE MOST  
FAVORED AREAS FOR HIGHEST TOTALS WILL BE. SHOWERS/THUNDERSTORMS  
WILL LIKELY CONTINUE OVER THE SOUTH AND FLORIDA PENINSULA THROUGH  
THE PERIOD BUT WITH ANY AREAS OF ENHANCED TOTALS LIKELY TO BE MORE  
LOCALIZED AND UNCERTAIN ON A DAY-TO-DAY BASIS. A WEAKENING FRONT  
REACHING THE GULF/SOUTHEAST COASTS MAY STILL PROVIDE SOME FOCUS  
LATE THIS WEEK INTO THE FIRST PART OF THE WEEKEND. A COLD FRONT  
DROPPING SOUTHWARD THROUGH THE EAST FROM FRIDAY THROUGH THE  
WEEKEND MAY PRODUCE AREAS OF RAINFALL WITH VARYING INTENSITY.  
WAVINESS ALONG THE FRONT COULD ENHANCE TOTALS OVER NORTHERN NEW  
ENGLAND ON FRIDAY.  
 
THE PRIMARY AREAS OF ABOVE NORMAL TEMPERATURES DURING THE PERIOD  
WILL BE OVER THE NORTHWEST AS WELL AS THE NORTHEAST AND VICINITY.  
THE NORTHWEST WILL BE MODESTLY ABOVE NORMAL FRIDAY, FOLLOWED BY A  
COOLER WEEKEND AND THEN REBOUND TO PLUS 5-10F OR SO ANOMALIES NEXT  
MONDAY-TUESDAY. MEANWHILE PARTS OF THE NORTHEAST/NORTHERN  
MID-ATLANTIC WILL SEE MODERATELY ABOVE NORMAL READINGS ON FRIDAY.  
THEN A LARGER AREA OF WARM TEMPERATURES SHOULD SPREAD ACROSS THE  
GREAT LAKES THROUGH NORTHEAST/NORTHERN MID-ATLANTIC  
SUNDAY-TUESDAY. HIGHS COULD LOCALLY REACH 10-15F ABOVE NORMAL  
EARLY NEXT WEEK. NEAR TO SOMEWHAT BELOW NORMAL HIGH TEMPERATURES  
(SINGLE-DIGIT ANOMALIES) WILL PREVAIL ACROSS MUCH OF THE SOUTHERN  
TIER THROUGH THE ROCKIES AND NORTHERN PLAINS.  
 
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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