337  
FXUS02 KWBC 180709  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
305 AM EDT THU AUG 18 2022  
 
VALID 12Z SUN AUG 21 2022 - 12Z THU AUG 25 2022  
 
...MONSOONAL RAINFALL THREAT FOR THE SOUTHWEST AND SOUTH-CENTRAL  
GREAT BASIN/ROCKIES TO RELAX EARLY NEXT WEEK AS A SIGNIFICANT  
EXCESSIVE RAINFALL/FLASH FLOODING THREAT SETTLES INTO THE SOUTHERN  
PLAINS/LOWER MISSISSIPPI VALLEY...  
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
OVERALL, THE LATEST MODELS CONTINUE TO HANDLE THE MID-LARGER SCALE  
FEATURES AND GENERALLY PATTERN EVOLUTION OVER THE LOWER 48 AND  
VICINITY FAIRLY CONSISTENTLY. THE WPC MEDIUM RANGE PRODUCT SUITE  
WAS PRIMARILY DERIVED FROM A COMPOSITE MODEL BLEND DAYS 3-5  
(SUNDAY-TUESDAY) BEFORE SWITCHING BY MID-LATER NEXT WEEK FOR DAY  
6/7 INTO A BLEND OF THE GEFS/ECMWF ENSEMBLE MEANS ALONG WITH BEST  
CLUSTERING MODEL GUIDANCE FROM THE GFS/ECMWF ALONG WITH THE  
NATIONAL BLEND OF MODELS AND SOME WPC CONTINUITY TO EASE RUN TO  
RUN VARIANCES, BUT MUCH OF RECENT TRENDS SEEM PRETTY REASONABLE.  
   
..PATTERN OVERVIEW AND WEATHER/HAZARDS HIGHLIGHTS
 
 
A WEEKEND PATTERN WITH AMPLE MONSOONAL THUNDERSTORMS AND RAINFALL  
OVER THE SOUTHWEST AND SOUTH-CENTRAL GREAT BASIN/ROCKIES WILL  
RELAX AFTER THE WEEKEND, BUT LINGERING MOISTURE AND INSTABILITY  
ALONG WITH TERRAIN FORCING WILL CONTINUE TO FUEL SCATTERED  
ACTIVITY. HOWEVER, THE SUBSTANTIAL HEAVY RAIN AND FLOODING THREAT  
WILL SHIFT TO THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY FOR  
MUCH OF NEXT WEEK. THE MULTI-DAY THREAT SEEMS FORMIDABLE AS  
MOISTURE AND INSTABILITY POOL WITH RETURN FLOW INTO SLOW  
MOVING/WAVY FRONTS IN FAVORABLE UPPER FLOW AS UPPER TROUGH  
ENERGIES EJECT OUT FROM THE WEST/ROCKIES. LATEST GUIDANCE TRENDS  
CONTINUE TO SHIFT THE MAIN QPF AXIS SOUTHWARD FROM PREVIOUS RUNS  
WHICH IS OFTEN THE CASE WITH CONVECTIVE EPISODES. WPC HAS  
EXPERIMENTAL DAY 4/5 SLIGHT RISKS FOR EXCESSIVE RAINFALL SPANNING  
FROM EASTERN NEW MEXICO THROUGH OKLAHOMA AND TEXAS INTO THE LOWER  
MISSISSIPPI VALLEY FROM SUNDAY INTO TUESDAY SO FAR.  
 
SHOWERS AND THUNDERSTORMS ARE EXPECTED TO LINGER ALL NEXT WEEK  
ALONG A SLOW-MOVING, WAVY/PESKY FRONTAL BOUNDARY OVER THE  
SOUTH/SOUTHEAST/MID-ATLANTIC. THERE MAY BE LOCAL AREAS THAT HAVE  
HEAVY DOWNPOURS THANKS FOR MOIST POOLED AIR. MEANWHILE FARTHER  
NORTH, CONVECTION WILL GRADUALLY SPREAD ACROSS THE GREAT  
LAKES/OHIO VALLEY STATES THEN NORTHEAST THROUGH THE PERIOD WITH  
SLOW PROGRESSION AND DEMISE OF A CLOSED UPPER TROUGH/LOW AND  
SURFACE FRONTAL SYSTEM. SLOW CELL MOTIONS/INSTABILITY NEAR THE  
CLOSED FEATURE OFFER POTENTIAL FOR LOCAL DOWNPOURS WITH RUNOFF  
ISSUES.  
 
THERE IS A STRONGER SIGNAL TO BRING AN ENERGETIC PACIFIC UPPER  
TROUGH AND ASSOCIATED FRONTAL SYSTEM WITH LIMITED SUMMER RAINFALL  
POTENTIAL INLAND ACROSS THE PACIFIC NORTHWEST EARLY NEXT WEEK, BUT  
ACTIVITY MAY BECOME MORE ORGANIZED INTO FAVORED TERRAIN DOWNSTREAM  
OVER THE NORTHERN GREAT BASIN/ROCKIES THROUGH NEXT MIDWEEK.  
 
SCHICHTEL  
 
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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