495  
FXUS02 KWBC 180701  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
300 AM EDT MON JUN 18 2018  
 
VALID 12Z THU JUN 21 2018 - 12Z MON JUN 25 2018  
 
...GUIDANCE/PREDICTABILITY ASSESSMENT AND WEATHER  
HIGHLIGHTS/THREATS...  
 
MODELS AND ENSEMBLES ARE IN CLOSER AGREEMENT WITH OVERALL PATTERN  
TIMING AND EVOLUTION, BOLSTERING FORECAST CONFIDENCE, WITH A  
COMPOSITE TRENDING SLIGHTLY MORE PROGRESSIVE WITH MID-LATITUDE  
FLOW AND MORE AMPLIFIED NORTHERN STREAM FLOW OVER CANADA. CENTRAL  
PLAINS CLOSED TROUGH/LOW ENERGY THURSDAY SLIDES EAST-NORTHEASTWARD  
OVER THE EAST-CENTRAL U.S. THEN THE NORTHEAST LATE WEEKEND. THIS  
OCCURS AS A KICKER SHORTWAVE TROUGH PUSHES INLAND OVER THE NWRN  
U.S. FRIDAY AND THROUGH THE ROCKIES INTO THE CENTRAL STATES.  
GUIDANCE HAS ALSO TRENDED TO PRODUCE A MORE DEVELOPED SERIES OF  
SURFACE LOWS TO RUN ALONG A MAIN FRONTAL BOUNDARY FROM THE PLAINS  
TO THE OHIO VALLEY AND MID-ATLANTIC. EXPECT PERIODS OF LOCALLY  
EXCESSIVE CONVECTIVE COMPLEXES/RAINS TO FOCUS ALONG THIS BOUNDARY  
AND IN THE WARM SECTOR AIDED TROPICAL MOISTURE INFLUX FROM THE  
GULF OF MEXICO. GUIDANCE DIFFERENCES ARE INDEED MORE STARK  
UNDERNEATH WITH THE SHORT AND MEDIUM RANGE HEAVY RAIN THREAT OVER  
TEXAS ASSOCIATED WITH A TROPICAL DISTURBANCE NOW OVER THE GULF OF  
MEXICO. THIS SYSTEM IN SOME FORM IS EXPECTED TO LIFT OVER TEXAS  
WITH PARTS LINGERING BACK TOWARD THE RIO GRANDE VALLEY. THE  
OPERATIONAL ECMWF AND UKMET STILL BOTH SHOW A MUCH BETTER DEFINED  
SYSTEM AND EXTREMELY HEAVY RAINFALL, WHILE THE GFS AND ENSEMBLE  
MEANS OFFER MUCH LESS. TROPICAL NATURE AND SLOW TRANSLATION SHOULD  
COMBINE TO POSE A HEAVY/EXCESSIVE RAINFALL THREAT, LEANING WPC QPF  
IN THE DIRECTION OF THE WETTER LINGERING SCENARIOS. OTHERWISE, THE  
WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARITY DERIVED FROM A  
COMPOSITE MODEL BLEND ACROSS THE MID-LATITUDES.  
 
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  
 

 
 
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