205  
FXUS02 KWBC 211600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1159 AM EDT SAT JUL 21 2018  
 
VALID 12Z TUE JUL 24 2018 - 12Z SAT JUL 28 2018  
   
..SOUTHERN PLAINS HEAT WAVE SHIFTS INTO THE SOUTHWEST NEXT WEEK
 
 
...WIDESPREAD HEAVY RAIN AND FLOODING THREAT CONTINUES OVER THE  
EASTERN U.S...  
...ROCKIES TO CENTRAL PLAINS/MID-MISSISSIPPI VALLEY LOCALIZED  
HEAVY RAIN THREAT POSSIBLE...  
   
..GUIDANCE/UNCERTAINTY ASSESSMENT AND WEATHER THREATS
 
 
THE MEDIUM RANGE PERIOD CONTINUES TO ADVERTISE THAT AN AMPLIFIED  
MID TO UPPER LEVEL TROUGH WILL LINGER THROUGH EARLY NEXT WEEK WITH  
AN AXIS ANCHORED ACROSS THE OHIO VALLEY AND INTO THE DEEP SOUTH.  
DEEP MOISTURE AND ANOMALOUS PRECIPITABLE WATER FEEDING INTO/AHEAD  
OF THE SYSTEM AND ITS ASSOCIATED SURFACE FRONT AND INSTABILITY  
AXIS WILL PROLONG A PATTERN FAVORABLE FOR CELL TRAINING/REPEAT  
ACTIVITY. THIS SHOULD CONTINUE A THREAT FOR LOCALLY  
HEAVY/EXCESSIVE RAINFALL WITH THE AXIS FOR HEAVIEST QPF CENTERED  
UP THE APPALACHIANS AND EASTERN SEABOARD. THIS LEAD SYSTEM WILL  
EVENTUALLY BE REPLACED BY A WELL DEFINED UPSTREAM TROUGH WORKING  
ACROSS THE GREAT LAKES AND NORTHEASTERN STATES WEDNESDAY INTO NEXT  
WEEKEND. THE DEVELOPMENT OF THIS TROUGH WILL FOCUS THE WIDESPREAD  
HEAVY RAINFALL THREAT MORE INTO THE NORTHEAST AND THE EASTERN  
MID-ATLANTIC ALONG A TRAILING AND EVENTUALLY DOMINANT COLD FRONT.  
A FLASH FLOOD AND LONGER TERM/LARGER SCALE FLOODING (E.G. RIVER  
FLOODING) THREAT IS POSSIBLE.  
 
MEANWHILE, A POTENT MID TO UPPER LEVEL RIDGE FOCUSED OVER THE  
SOUTHERN PLAINS AND BACK INTO THE SOUTHWEST EARLY NEXT WEEK, WILL  
EVENTUALLY SHRINK BACK AND SETTLE OVER THE SOUTHWEST THE REMAINDER  
OF THE WEEK. UNDERNEATH THIS RIDGE, RECORD HEAT IS EXPECTED TO  
CONTINUE AS HEIGHTS PEAK SEVERAL STANDARD DEVIATIONS ABOVE NORMAL.  
FORECAST HIGHS ACROSS MUCH OF THE SOUTHWEST ARE IN THE 110 TO 120  
RANGE FOR THE DESERT AREAS (INCLUDING PHOENIX AND LAS VEGAS) FOR  
SEVERAL CONSECUTIVE DAYS. OVERNIGHT LOW TEMPERATURES IN THE UPPER  
80S TO MAYBE EVEN 90 WILL ONLY AMPLIFY THE HAZARDOUS IMPACTS OF  
THE HEAT. IN ADDITION, A SERIES OF LESS PREDICTABLE UPPER LEVEL  
IMPULSES ROTATING OVERTOP THE RIDGE INTERACTING WITH POOLING  
MOISTURE ALONG SURFACE CONVERGENCE BOUNDARIES MAY FUEL STRONG  
CONVECTION AND A POSSIBLY HEAVY TO LOCALLY EXCESSIVE RAINFALL  
THREAT ACROSS PORTIONS OF THE CENTRAL ROCKIES/PLAINS AND INTO THE  
MIDDLE MISSISSIPPI VALLEY.  
 
THE FORECAST CONFIDENCE FOR THIS MEDIUM RANGE PERIOD REMAINS ABOVE  
AVERAGE, WITH STRONG AGREEMENT AND CLUSTERING AMONGST THE MODELS  
AND ENSEMBLES FOR THE LARGER/SYNOPTIC SCALE FEATURES. THIS SUITE  
OF THE WPC MEDIUM RANGE PRODUCTS WAS BASED HEAVILY ON A BLEND OF  
THE GFS/ECMWF/UKMET THROUGH DAY 5, WITH LESS THAN MAJORITY  
CONTRIBUTION FROM THE LATEST GEFS/EC ENSEMBLE MEANS BY THE END OF  
THE PERIOD. THIS FITS VERY WELL WITH PREVIOUS SHIFT CONTINUITY.  
 
SANTORELLI  
 
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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