715  
FXUS02 KWBC 070453  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1252 AM EDT TUE AUG 07 2018  
 
VALID 12Z FRI AUG 10 2018 - 12Z TUE AUG 14 2018  
   
..RECORD HEAT FOR THE INTERIOR NORTHWEST FRIDAY
 
 
   
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
LATEST 12Z/18Z MODELS AND ENSEMBLES SHOWED GOOD CLUSTERING THROUGH  
THE PERIOD WITH THE UPPER FLOW ACROSS THE CONUS. THIS WILL TAKE AN  
UPPER LOW INITIALLY JUST OFF THE PACIFIC NORTHWEST COAST  
NORTHEASTWARD INTO SOUTHERN BRITISH COLUMBIA THEN INTO SOUTH  
CENTRAL CANADA AS ANOTHER UPPER LOW SINKS SOUTHWARD TOWARD THE  
OHIO VALLEY SUN/MON NEXT WEEK. BY NEXT TUESDAY, ATLANTIC RIDGING  
WILL PUSH WESTWARD WHICH SHOULD BUMP THE UPPER LOW TO THE  
NORTHEAST THROUGH THE EASTERN GREAT LAKES AS TROUGHING SETTLES  
INTO THE PACIFIC NORTHWEST. USED A DETERMINISTIC BLEND TO START  
WITH LESS EMPHASIS ON THE CANADIAN (TOO SLOW WITH HURRICANE JOHN)  
THEN THE ECMWF (TOO QUICK TO LIFT THE EASTERN UPPER LOW NORTHWARD  
AND TOO QUICK WITH WESTERN CANADIAN TROUGHING BY MONDAY COMPARED  
TO THE ENSEMBLES). THE RECENT GFS RUNS WERE MAINTAINED AND SHOWED  
GOOD CONTINUITY. A COUPLE OF SURFACE BOUNDARIES IN THE EAST WILL  
EVENTUALLY COALESCE AROUND THE UPPER LOW BY NEXT WEEK. THE UPPER  
LOW OFF THE WEST COAST WILL DRAG A COLD FRONT EASTWARD ACROSS THE  
HIGH PLAINS.  
 
   
..WEATHER HIGHLIGHTS AND HAZARDS
 
 
EXPECT NEAR OR ABOVE RECORD HIGH TEMPERATURES OVER MUCH OF THE  
INTERIOR NORTHWEST FRIDAY AHEAD OF THE EASTERN PACIFIC UPPER LOW  
WITH 100S WIDESPREAD EAST OF THE CASCADES AND THROUGH THE SNAKE  
VALLEY IN IDAHO AS WELL AS THE MISSOURI RIVER VALLEY IN MONTANA.  
LIGHT PRECIPITATION WILL BE CONFINED TO COASTAL/NORTHERN/HIGHER  
ELEVATION AREAS OF WASHINGTON AS THE BEST UPPER SUPPORT TRAVELS  
THROUGH CANADA, THOUGH THAT MAY DIP SOUTH AGAIN IN EASTERN MONTANA  
TO THE DAKOTAS AS SOME MOISTURE FLOWS NORTHWARD EAST OF THE  
ROCKIES. HEAVIER CONVECTIVE PRECIPITATION IS LIKELY IN THE DEEPER  
MOISTURE ON THE EASTERN SIDE OF THE WESTERN U.S. UPPER HIGH, FROM  
NM/CO/AZ EASTWARD TO THE SOUTHERN PLAINS. IT IS LIKELY THAT SOME  
LOCATIONS WILL SEE SEVERAL INCHES OF RAIN OVER A FEW DAYS WHICH  
MAY LEAD TO LOCALIZED FLOODING. ENSEMBLES HAVE BEEN TARGETING  
TEXAS FOR A FEW RUNS THOUGH THE FAVORED LOCATION MAY SHIFT FROM  
DAY TO DAY. CLOUDS/RAINFALL SHOULD PROMOTE BELOW NORMAL HIGH  
TEMPERATURES OVER THIS REGION FOR MOST OF THE PERIOD.  
 
PRECIPITATION WILL ACCOMPANY AND PRECEDE A FRONTAL BOUNDARY AS IT  
PUSHES THROUGH THE GREAT LAKES AND INTO THE NORTHEAST VIA  
AFTERNOON STORMS. ANOTHER FRONT WILL LINGER ACROSS THE U.S.  
SOUTHERN TIER DURING THE PERIOD WHICH WILL HELP SPARK AFTERNOON  
SHOWERS/STORMS AND LOCALLY HEAVY RAINFALL IN THE WARM/HUMID  
AIRMASS. AS THE UPPER TROUGH DIGS/SHARPENS OVER THE EAST-CENTRAL  
U.S., MORE WIDESPREAD PRECIPITATION MAY BE FAVORED TO ITS EAST  
ALONG THE APPALACHIANS TO THE I-95 CORRIDOR.  
DISTRIBUTION/INTENSITY OF RAINFALL WILL BE SENSITIVE TO THE EXACT  
EVOLUTION OF THE UPPER TROUGH AND POSSIBLE CLOSED LOW. HUMID  
AIRMASS WILL REMAIN IN PLACE TO ITS EAST UP TOWARD THE NORTHEAST.  
 
FRACASSO  
 
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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