692  
FXUS02 KWBC 210634  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
233 AM EDT SAT JUL 21 2018  
 
VALID 12Z TUE JUL 24 2018 - 12Z SAT JUL 28 2018  
   
..SOUTHERN PLAINS HEAT WAVE SHIFTS ACROSS THE SOUTHWEST/WEST
 
 
...WIDESPREAD HEAVY RAIN AND FLOODING THREAT OVER THE EASTERN  
U.S...  
...ROCKIES TO CENTRAL PLAINS/MID-MS VALLEY STRONG CONVECTION AND  
LOCALIZED HEAVY RAIN THREAT...  
   
..GUIDANCE/UNCERTAINTY ASSESSMENT AND WEATHER THREATS
 
 
FORECAST PREDICTABILITY REMAINS MUCH ABOVE NORMAL IN SHOWING THAT  
AN AMPLIFIED/CLOSED MID-UPPPER LEVEL TROUGH WILL LINGER WITH AN  
AXIS ROUGHLY ALONG 85W EARLY EARLY-MID NEXT WEEK. DEEP MOISTURE  
WITH POOLED PRECIPITABLE WATER VALUES UPWARDS OF 2" FEEDING  
INTO/AHEAD OF THE SYSTEM AND ASSOCIATED/SLOW MOVING SURFACE  
FRONTS/INSTABILITY WILL FUEL A PROLONGED PATTERN FAVORABLE FOR  
CELL TRAINING/REPEAT ACTIVITY THAT WILL LEAD TO A THREAT OF  
LOCALLY HEAVY/EXCESSIVE RAINFALL CENTERING UP ACROSS THE  
APPALACHIANS AND EASTERN SEABOARD. THIS LEAD SYSTEM WILL BE  
EVENTUALLY SURPLANTED BY A WELL DEFINED UPSTREAM TROUGH WORKING  
ACROSS THE GREAT LAKES AND NORTHEASTERN STATES WED INTO NEXT  
WEEKEND WHOSE DEVELOPMENT WILL FOCUS THE WIDESPREAD HEAVY RAINFALL  
THREAT MORE INTO THE NORTHEAST AND ERN MID-ATLANTIC CONSISTENT  
WITH DYNAMIC SUPPORT/FRONTAL PROGRESSION. FLASH FLOODING AND  
LONGER TERM/LARGER SCALE FLOODING (E.G., RIVER FLOODING) IS  
POSSIBLE.  
 
MEANWHILE, A POTENT MID-UPPER LEVEL RIDGE SETTLES OVER THE  
SOUTHWEST AND GRADUALLY EXPANDS UP OVER THE WEST NEXT WEEK.  
UNDERNEATH THE RIDGE, SOME RECORD HOT TEMPERATURES ARE EXPECTED AS  
HEIGHTS PEAK SEVERAL STANDARD DEVIATIONS ABOVE CLIMATOLOGY.  
FORECAST HIGHS ARE IN THE UPPER 100S AND TEENS (110-119+) IN THE  
DESERT AREAS (INCLUDING PHOENIX, VEGAS) FOR SEVERAL CONSECUTIVE  
DAYS. LOW TEMPERATURES UPWARDS TO 90 DEG IN SOME DESERT LOCALS  
WILL AMPLIFY THE HAZARDOUS IMPACTS OF THE HEAT. A SERIES OF  
IMPULSES ROTATING WITHIN AND OVERTOP THE RIDGE OFFER LESS  
PREDICTABLE TIMINGS INDIVIDUALLY, BUT EACH WILL PROVIDE ENHANCED  
LIFT. THIS MAY BE ESPECIALLY PROBLEMATIC IN UPPER DIFFLUENT  
FLOW/BOUNDARY CONVERGENCE FROM THE CENTRAL ROCKIES/PLAINS INTO THE  
MID-MS VALLEY WHERE CONVECTIVE COMPLEXES/THUNDERSTORMS WILL BE  
FUELED BY INFLOW POOLING MOISTURE AND HEAVY/REPEAT CELLS MAY LEAD  
TO A LOCAL EXCESSIVE RAINFALL THREAT.  
 
MUCH OF THIS MEDIUM RANGE FORECAST REMAINS OF HIGH CONFIDENCE  
DURING THIS CYCLE, WITH STRONG AGREEMENT AND CLUSTERING AMONG THE  
MODELS AND ENSEMBLES REGARDING THESE WELL DEFINED AND  
SLOWLY/STEADILY EVOLVING FEATURES. ACCORDINGLY, THE WPC MEDIUM  
RANGE FORECAST SUITE WAS PRIMARILY DERIVED FROM A COMPOSITE BLEND  
OF THE LATEST GFS/ECMWF, GEFS AND ECMWF ENSEMBLE MEANS, THE NBM,  
AND WPC CONTINUITY.  
 
SCHICHTEL  
 
WPC MEDIUM RANGE 500 MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDEXES ARE FOUND 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/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML  
 

 
 
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