998  
FXUS02 KWBC 071600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1200 PM EDT TUE AUG 07 2018  
 
VALID 12Z FRI AUG 10 2018 - 12Z TUE AUG 14 2018  
 
...RECORD HEAT LINGERS FOR THE INTERIOR NORTHWEST TO NORTHERN HIGH  
PLAINS AND SOUTHERN CALIFORNIA INTO SATURDAY...  
   
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
MODELS AND ENSEMBLES SHOW REASONABLY GOOD CLUSTERING THROUGH MUCH  
OF 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 TO THE OH  
VALLEY EARLY NEXT WEEK.  
 
WESTERN PACIFIC TYPHOON SHANSHAN IS FORECAST TO BECOME  
EXTRATROPICAL AND TRACK TO ALASKA LATER THIS WEEK. PREFER A  
SOLUTION THAT MAINTAINS A DEEPENED SURFACE LOW AND LEAD AMPLIFYING  
FLOW ALOFT. THE 00 UTC GFS/CANADIAN AND EXPERIMENTAL FV3 OFFER THE  
MOST DOWNSTREAM AMPLITUDE AND THE 00 UTC GEFS/NAEFS OFFER THE MOST  
ENSEMBLE MEAN AMPLITUDE. DISCOUNTED LESS AMPLIFIED 00 UTC  
ECMWF/ECMWF ENSEMBLE SOLUTIONS.  
   
..WEATHER HIGHLIGHTS AND HAZARDS
 
 
EXPECT NEAR OR ABOVE RECORD HIGH TEMPERATURES FROM OVER THE  
INTERIOR NORTHWEST INTO THE NORTHERN ROCKIES/HIGH PLAINS FRIDAY  
INTO SATURDAY 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 INTO A LEAD FRONT TO FOCUS CONVECTION. EXPECT HEAVY  
CONVECTIVE PRECIPITATION IN 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.  
 
PRECIPITATION WILL ACCOMPANY AND PRECEDE FRONTAL BOUNDARIES OVER  
THE OH VALLEY AND NORTHEAST. A LEAD WAVY 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. THIS COULD  
DEVELOP INTO A MORE WIDESPREAD HEAVY RAINFALL THREAT CONSIDERING  
SLOW SYSTEM TRANSLATION AND AMPLITUDE. DISTRIBUTION/INTENSITY OF  
RAINFALL WILL BE SENSITIVE TO THE EXACT EVOLUTION OF THE UPPER  
TROUGH AND POSSIBLE CLOSED LOW. THE HUMID AIRMASS WILL REMAIN IN  
PLACE TO ITS EAST.  
 
FRACASSO/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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