272  
FXUS02 KWBC 100709  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
309 AM EDT TUE JUL 10 2018  
 
VALID 12Z FRI JUL 13 2018 - 12Z TUE JUL 17 2018  
   
..OVERVIEW, GUIDANCE EVALUATION AND PREFERENCES
 
 
MODEL GUIDANCE THIS EVENING SHOWS GOOD OVERALL AGREEMENT ON THE  
EVOLUTION OF THE SYNOPTIC PATTERN THROUGH NEXT TUESDAY ALTHOUGH  
THE SPREAD HAS INCREASED SINCE YESTERDAY. THE MAIN UNCERTAINTY  
WILL BE ACROSS THE PACIFIC NORTHWEST EASTWARD INTO THE NORTHERN  
PLAINS THIS WEEKEND INTO EARLY NEXT WEEK AS A SHORTWAVE TROUGH IS  
FORECAST TO MOVE ALONG OR JUST NORTH OF THE U.S.-CANADIAN BORDER.  
THE GFS HAS INTRODUCED A DIGGING AND HIGHER AMPLITUDE SHORTWAVE IN  
THE LAST FEW RUNS WHILE THE ECMWF KEEPS A LESS-AMPLIFIED  
POSITIVELY-TILTED TROUGH MAINLY NORTH OF THE BORDER. THE GEFS ON  
THE OTHER HAND SHOWS A LESS-AMPLIFIED MEAN SOLUTION COMPARABLE TO  
THE EC MEAN. THE ECMWF HAS ACTUALLY SHOWN A TENDENCY FOR  
INCREASING THE 500 MB HEIGHT OVER THE NORTHWESTERN U.S. WHILE THE  
GFS SHOWS THE OPPOSITE. A GENERAL COMPROMISE BETWEEN THE 18Z GEFS  
AND THE 12Z EC MEAN MIXING IN WITH THEIR DETERMINISTIC SOLUTIONS  
WAS USED TO HANDLE THIS AREA FROM DAY 5 THROUGH DAY 7  
(SUNDAY-TUESDAY), WHICH MAINTAINS GOOD CONTINUITY WITH THE  
PREVIOUS WPC PACKAGE.  
 
OTHERWISE, MODELS CONTINUE TO SHOW EXCELLENT AGREEMENT ON A  
SUBTROPICAL HIGH DOMINATING THE LOWER 48 LATER THIS WEEK INTO NEXT  
WEEK.  
   
..WEATHER HIGHLIGHTS
 
 
ALTHOUGH THE DOMINATING SUBTROPICAL HIGH WILL BRING HEAT ACROSS A  
LARGE PORTION OF THE COUNTRY THROUGH EARLY NEXT WEEK, THERE WILL  
BE BOUTS COOL AIR INTRUSION FROM CANADA FOLLOWING OCCASIONAL  
FRONTAL PASSAGES ACROSS THE NORTHERN TIER STATES. A COLD FRONT  
WILL INITIALLY BRING SHOWERS AND THUNDERSTORMS ACROSS THE NORTHERN  
PLAINS INTO THE GREAT LAKES FRIDAY BUT AS THE FRONT IS FORECAST TO  
BECOME MORE DIFFUSED WITH TIME, MORE ISOLATED COVERAGE IN THE  
NORTHEAST WILL BE THE RESULT DURING THE WEEKEND. MEANWHILE, THE  
NEXT FRONT WILL MOVE OUT OF CANADA THIS WEEKEND WITH SCATTERED  
SHOWERS AND THUNDERSTORMS ALONG/AHEAD OF ITS BOUNDARY. COOL AIR  
IN ITS WAKE WILL BREAK THE HEAT WAVE ACROSS THE NORTHERN ROCKIES  
AND IS FORECAST TO DROP TEMPERATURES MORE THAN 10 DEGREES BELOW  
NORMAL ACROSS THE NORTHERN PLAINS EARLY NEXT WEEK. AHEAD OF THE  
FRONT, TEMPERATURES WILL BE ABOUT 5-10 DEGREES ABOVE AVERAGE (80S  
AND MANY 90S), AND INITIALLY NEAR OR ABOVE 100 OVER PORTIONS OF  
THE INTERIOR PACIFIC NORTHWEST/GREAT BASIN ON FRIDAY. BUT  
TRIPLE-DIGIT HEAT IS EXPECTED TO CONTINUE IN PARTS OF INTERIOR  
CALIFORNIA.  
 
FROM THE SOUTHEASTERN U.S. WESTWARD ALONG THE GULF COAST, A  
DISSIPATING FRONT WILL KEEP A CHANCE OF SHOWERS AND THUNDERSTORMS  
IN THE VICINITY THROUGH THE WEEKEND. MONSOONAL MOISTURE WILL  
LINGER ACROSS THE FOUR CORNERS AREA WHERE LOCALLY HEAVY DOWNPOURS  
ARE POSSIBLE THROUGH EARLY NEXT WEEK. TEMPERATURES WILL GENERALLY  
BE NEAR OR BELOW AVERAGE IN THE SOUTHWEST UNDER LIMITED SOLAR  
INSOLATION AND A DAILY CHANCE OF SHOWERS/STORMS.  
 
KONG/FRACASSO  
 
WPC MEDIUM RANGE 500 MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDEXES ARE 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  
HTTP://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML  
 

 
 
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