385  
FXUS02 KWBC 170655  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
254 AM EDT SUN JUN 17 2018  
 
VALID 12Z WED JUN 20 2018 - 12Z SUN JUN 24 2018  
 
...HEAVY RAIN THREAT FOR SOUTHERN TEXAS AND THE NORTH-CENTRAL  
U.S...  
   
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
SHORT RANGE WESTERN U.S. CLOSED LOW ENERGY AND HEIGHT FALLS EJECT  
TO THE PLAINS MIDWEEK AND MISSISSIPPI VALLEY LATE WEEK. STRONG  
PACIFIC NORTHWEST RIDGING SHIFTS EASTWARD AS A SHORTWAVE TROUGH  
BREACHES THE NORTHWEST FRIDAY. MEANWHILE, THE NORTHERN PERIPHERY  
OF DOWNSTREAM RIDGING OVER THE EAST/SOUTHEAST IS ERODED BY  
NORTHERN STREAM CYCLONIC FLOW OVER THE GREAT LAKES AND THE  
NORTHEAST, WHICH SHOULD SUPPRESS THE OPPRESSIVE HEAT AND HUMIDITY  
EXPECTED EARLY THIS WEEK.  
 
OVERALL, THE MODELS AND ENSEMBLES SHOW A REASONABLY SIMILAR LARGER  
SCALE PATTERN OVER THE NEXT WEEK, BUT SMALLER MID-SCALE EMBEDDED  
FEATURES STILL OFFER A BIT OF FORECAST SPREAD. THIS CYCLE OF THE  
WPC MEDIUM RANGE SUITE WAS MAINLY DERIVED FROM A BLEND OF THE  
LATEST RUNS OF THE GFS/ECMWF WITH THEIR ENSEMBLE MEANS. LEANED  
WEIGHTING IN THIS COMPOSITE IN FAVOR OF THE ENSEMBLE MEANS TO  
DE-EMPHASIZE THE LESS PREDICTABLE SMALLER SCALE FEATURES WHICH  
STILL REMAIN HIGHLY UNCERTAIN. THIS FORECAST METHODOLOGY MAINTAINS  
GOOD WPC CONTINUITY.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
A MAIN AND PERSISTENT/WAVY FRONTAL BOUNDARY REMAINS  
QUASI-STATIONARY THIS WEEK FROM THE PLAINS TO THE OHIO VALLEY AND  
MID-ATLANTIC. PERIODS OF LOCALLY EXCESSIVE CONVECTION WILL FOCUS  
ALONG THIS BOUNDARY AND IN THE WARM SECTOR AIDED BY EARLY PERIOD  
TROPICAL MOISTURE INFLUX FROM THE GULF OF MEXICO. WPC MEDIUM RANGE  
QPF FORECASTS SHOW THE HEAVIEST POTENTIAL OVER SOUTHERN TX DUE TO  
A POTENTIAL TROPICAL WAVE/DISTURBANCE NOW FOLLOWED BY NHC.  
MOISTURE STREAMING INLAND INTERSECTS THE WAVY BOUNDARY TO THE  
NORTH TO FUEL STRONG/SEVERE CONVECTION AS PER SPC AND PERIODS OF  
POTENTIALLY EXCESSIVE RAINFALL CENTERED OVER THE N-CENTRAL U.S. AS  
THE TROUGH AND FRONT SHIFTS SLOWLY EASTWARD INTO LATER WEEK, THE  
HEAVIEST RAINFALL MAY INCREASINGLY SPREAD ALONG THE SURFACE  
BOUNDARY AS ENHANCED BY ANY POTENTIAL WAVE DEVELOPMENTS/CONVECTIVE  
SYSTEM PROPAGATIONS INTO THE MIDWEST/OHIO VALLEY STATES AND  
MID-ATLANTIC.  
 
SCHICHTEL  
 
WPC MEDIUM RANGE FORECASTS OF 500 MB HEIGHTS, SURFACE SYSTEMS,  
WEATHER GRIDS, QUANTITATIVE PRECIPITATION, AND WINTER WEATHER  
OUTLOOK PROBABILITIES CAN BE FOUND AT:  
 
HTTP://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF  
HTTP://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF  
HTTP://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML  
HTTP://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML  
HTTP://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page