385  
FXUS02 KWBC 180700  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
259 AM EDT TUE SEP 18 2018  
 
VALID 12Z FRI SEP 21 2018 - 12Z TUE SEP 25 2018  
 
***PATTERN OVERVIEW AND MODEL GUIDANCE***  
 
UPPER RIDGING NEAR THE ALEUTIANS AND THE SOUTH-CENTRAL U.S. WILL  
TEND TO FAVOR LARGE SCALE TROUGHING CENTERED NEAR THE PACIFIC  
NORTHWEST COAST THIS WEEKEND. A LEAD STORM SYSTEM WILL LIFT INTO  
SOUTHEASTERN CANADA LATE THIS WEEK AND SETTLE ITS COLD FRONT  
ACROSS THE MID-ATLANTIC REGION AND OHIO VALLEY AS A WESTERN FRONT  
PUSHES THROUGH THE INTERIOR. THE NATIONAL HURRICANE CENTER IS  
MONITORING AN AREA OF DISTURBED WEATHER SOUTH OF BAJA CALIFORNIA  
THAT HAS THE POTENTIAL FOR TROPICAL DEVELOPMENT. THIS FEATURE IS  
PROGGED TO LIFT NORTHWARD AND SPREAD RAINFALL INTO PORTIONS OF  
SOUTHERN ARIZONA AND NEW MEXICO LATER THIS WEEK AND ENHANCE  
RAINFALL ACROSS THE SOUTHERN PLAINS.  
 
THE DETERMINISTIC MODELS AND THEIR RESPECTIVE ENSEMBLE MEANS WERE  
IN RELATIVELY GOOD AGREEMENT SYNOPTICALLY AT THE BEGINNING OF THE  
FORECAST PERIOD FRIDAY, SO MAINLY A BLEND OF THE ECMWF/GFS/CMC WAS  
USED THROUGH SATURDAY. THE FORECAST BECOMES MORE UNCERTAIN FOR  
THE WESTERN U.S. REGARDING THE EVOLUTION OF THE UPPER LEVEL TROUGH  
AXIS AND THE RESULTING SURFACE LOW DEVELOPMENT OVER THE  
INTERMOUNTAIN WEST. THE 12Z ECMWF WAS CONSIDERABLY MORE  
PROGRESSIVE THAN THE MODEL CONSENSUS, INCLUDING THE EC MEAN, SO  
THE SECOND HALF OF THE FORECAST INCORPORATED MORE GFS ALONG WITH  
GREATER PERCENTAGES OF THE EC AND GEFS MEANS.  
 
***SENSIBLE WEATHER AND HAZARDS***  
 
THE NEXT HEAVY RAINFALL EVENT DURING THE MEDIUM RANGE PERIOD IS  
EXPECTED ACROSS THE SOUTH-CENTRAL PLAINS FOR THE UPCOMING WEEKEND  
AS TROPICAL MOISTURE SURGES NORTHWARD FROM MEXICO AND THE WESTERN  
GULF. THE POTENTIAL EXISTS FOR A FEW INCHES OF RAIN ACROSS  
PORTIONS OF TEXAS AND OKLAHOMA, AND LESSER AMOUNTS EXTENDING  
EASTWARD ACROSS THE MIDWEST AND THE OHIO VALLEY REGION IN THE  
VICINITY OF A FRONTAL BOUNDARY. ANOTHER AREA OF MODERATE TO  
LOCALLY HEAVY RAINFALL WILL BE POSSIBLE ACROSS THE UPPER MIDWEST  
TOWARDS THE BEGINNING OF NEXT WEEK AS A SURFACE LOW DEVELOPS OVER  
THE NORTHERN PLAINS.  
 
EXPECT TEMPERATURES TO BE WELL ABOVE AVERAGE ON FRIDAY ACROSS MUCH  
OF THE EASTERN U.S. AHEAD OF THE COLD FRONT, WITH SOME PLACES  
CLOSE TO 15 DEGREES ABOVE NORMAL. MORE SEASONAL READINGS ARE  
FORECAST TO RETURN FOR THE WEEKEND FOLLOWED BY MORE ABOVE NORMAL  
VALUES OVER THE CENTRAL AND SOUTHERN U.S. BY NEXT TUESDAY. COOLER  
THAN NORMAL CONDITIONS ARE LIKELY FOR THE NORTHERN TIER OF THE  
NATION FROM THE NORTHERN ROCKIES TO MINNESOTA WITH THIS REGION  
UNDER MORE OF AN INFLUENCE FROM CANADIAN AIRMASSES.  
 
D. HAMRICK  
 
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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