693  
FXUS02 KWBC 221537  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1136 AM EDT SUN JUL 22 2018  
 
VALID 12Z WED JUL 25 2018 - 12Z SUN JUL 29 2018  
 
...HEAVY RAIN AND FLOODING POTENTIAL CONTINUING FOR PARTS OF THE  
EAST...   
..SOUTHWEST/WEST HEAT WAVE LASTING INTO MID-LATE WEEK
 
 
...CENTRAL ROCKIES/PLAINS TO MID-MS VALLEY HEAVY RAINFALL  
POTENTIAL...  
   
..GUIDANCE/UNCERTAINTY ASSESSMENT AND WEATHER THREATS
 
 
FORECAST PREDICTABILITY IN THE MEDIUM RANGE PERIOD REMAINS MUCH  
ABOVE NORMAL IN SHOWING AN AMPLIFIED MID-UPPER LEVEL TROUGH  
LINGERING ACROSS THE EAST WITH AN AXIS ACROSS THE OHIO VALLEY AND  
INTO THE DEEP SOUTH. DEEP MOISTURE WITH POOLED PRECIPITABLE WATER  
VALUES OF 2+ INCHES FEEDING INTO/AHEAD OF THE SYSTEM AND  
ASSOCIATED/SLOW MOVING SURFACE FRONTS/INSTABILITY WILL PROLONG A  
PATTERN FAVORABLE FOR CELL TRAINING/REPEAT ACTIVITY. THIS WILL  
CONTINUE A THREAT OF LOCALLY HEAVY/EXCESSIVE RAINFALL FOR PORTIONS  
OF THE EASTERN SEABOARD. MID TO LATE WEEK, THIS SYSTEM GETS  
REPLACED BY A WELL DEFINED UPSTREAM TROUGH/HEIGHT FALLS WORKING  
ACROSS THE GREAT LAKES/MIDWEST AND INTO THE NORTHEAST. THIS SHOULD  
FOCUS LINGERING HEAVY RAINFALL MORE INTO THE NORTHEAST/COASTAL  
MID-ATLANTIC AND TRAILING TO FL ALONG AND AHEAD OF A COLD FRONT.  
FLASH FLOODING AND LONGER TERM/LARGER SCALE FLOODING REMAINS  
POSSIBLE IN THE WAKE OF RECENT HEAVY RAINS.  
 
MEANWHILE, A HOT MID-UPPER LEVEL RIDGE SETTLED OVER THE SOUTHWEST  
AND UP INTO THE WEST ALONG WITH POTENTIAL FOR RECORD MAXIMUM  
TEMPERATURES WILL GRADUALLY EASE THROUGH MID-LATER THIS WEEK, BUT  
MONSOONAL MOISTURE COULD ALLOW FOR MORE RECORD HIGH MINIMUM  
TEMPERATURES. A SERIES OF LESS PREDICTABLE IMPULSES ROTATING  
WITHIN AND OVERTOP THE RIDGE INTERACTING WITH SURFACE CONVERGENCE  
BOUNDARIES SHOULD PROVIDE ADDITIONAL LIFT FOR HEAVY CONVECTION TO  
DEVELOP FROM THE CENTRAL ROCKIES/PLAINS INTO THE MID-MISSISSIPPI  
VALLEY. ITS HERE WHERE POTENTIAL 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 MAJORITY BLEND  
OF THE LATEST GFS/ECMWF DETERMINISTIC RUNS, WITH SMALLER  
CONTRIBUTIONS FROM THE GEFS/EC ENSEMBLE MEANS.  
 
SANTORELLI/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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