867  
FXUS02 KWBC 181552  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1052 AM EST SAT NOV 18 2017  
 
VALID 12Z TUE NOV 21 2017 - 12Z SAT NOV 25 2017  
   
..RECORDS HIGHS LIKELY IN THE SOUTHWEST LATER NEXT WEEK
 
 
   
..OVERVIEW
 
 
A VERY STRONG UPPER HIGH NEAR THE DAVIS STRAIT AND A SECONDARY  
UPPER HIGH NEAR SOUTHERN CALIFORNIA WILL CONTINUE TO FAVOR  
TROUGHING IN THE EASTERN CONUS NEXT WEEK. A LEAD SYSTEM WILL PUSH  
THROUGH THE EAST ON TUESDAY AND OFF THE COAST ON WEDNESDAY EXCEPT  
FOR FLORIDA WHERE THE FRONT WILL LINGER THROUGH THE WEEK. ANOTHER  
SYSTEM WILL ENTER THE PACIFIC NORTHWEST BY THURSDAY/THANKSGIVING  
AND MOVE EASTWARD THROUGH THE HIGH PLAINS ON FRIDAY AND INTO THE  
GREAT LAKES NEXT SATURDAY.  
 
   
..GUIDANCE/UNCERTAINTY PREFERENCES...
 
 
THE MODELS/ENSEMBLES REMAIN IN GOOD AGREEMENT ON THE LARGE SCALE  
PATTERN BUT HAVE LINGERING ISSUES WITH THE DETAILS. THE 00Z UKMET  
WAS STILL APART FROM THE BETTER CONSENSUS OF THE 00Z/06Z GFS AND  
00Z ECMWF/CANADIAN AS IT REMAINED A BIT SLOWER THAN THE ENSEMBLES.  
BASED THE FORECAST ON THAT LARGER CONSENSUS WITH INCREASED  
ENSEMBLE WEIGHTING FOR THE LATER PERIODS.  
 
00Z ECMWF MAY BE TOO AGGRESSIVE IN THE NORTHEAST BY LATE WEDNESDAY  
NEAR NEW ENGLAND WITH A DEEPER SYSTEM THAN THE REST OF THE  
GUIDANCE AS IT LIFTS NORTHWARD INTO NEW BRUNSWICK/NOVA SCOTIA  
AROUND 00Z/23. ENSEMBLES CONTINUE TO WAVER ON HOW MUCH TO SEPARATE  
THE FLOW OVER THE GULF OF MEXICO BY THE SAME TIME BUT DISMISSED  
THE 06Z GFS FOR LIKELY BEING TOO QUICK AND RATHER FAVORED THE 00Z  
GFS/ECMWF/CANADIAN THURSDAY AND THE ENSEMBLE MEANS THEREAFTER  
(WITH THE ECMWF/CANADIAN CLOSEST) TO LINGER THE TROUGH OR WEAK  
CLOSED LOW THROUGH SOUTHERN FLORIDA.  
 
FARTHER WEST, TREND HAS BEEN TOWARD A STRONGER UPPER HIGH NEAR  
SOUTHERN CALIFORNIA WHICH SHOULD PREVENT ANY SYSTEM FROM SLIDING  
EASTWARD OUT OF THE EAST-CENTRAL PACIFIC AND KEEP A SURFACE FRONT  
THROUGH NORTHERN CALIFORNIA FRI/SAT. NORTHEAST PACIFIC HAS BEEN  
QUITE UNCERTAIN IN THE DETAILS EVEN IN THE SHORT RANGE BUT  
ENSEMBLE AGREEMENT IS HIGH THAT ANOTHER TROUGH WILL DIG SOUTH OF  
THE GULF OF ALASKA LATE NEXT WEEK.  
 
   
..WEATHER HIGHLIGHTS
 
 
WET FLOW CONTINUES FOR THE PACIFIC NW WITH OCCASIONALLY HEAVY  
DAILY RAINS AND LOCALLY HEAVY ELEVATION SNOWS. UPPER RIDGING WILL  
SUPPORT WELL ABOVE AVERAGE TEMPERATURES IN THE SOUTHWEST WHERE  
RECORD HIGHS ARE LIKELY WED-SAT OVER PARTS OF CA/NV/AZ/UT. MILD  
TEMPERATURES WILL EXTEND EASTWARD THROUGH THE CENTRAL/SOUTHERN  
ROCKIES INTO PLAINS AHEAD OF A COLD FRONT THU/FRI. COOLER THAN  
AVERAGE TEMPERATURES ARE EXPECTED IN THE EASTERN US BEHIND THE  
INITIAL COLD FRONT WEDNESDAY. THERE IS A GOOD CHANCE FOR  
APPRECIABLE PRECIPITATION ALONG THE GULF COAST AS LOW PRESSURE  
MEANDERS ALONG A SLOW MOVING FRONT. EXPECT SOME RAIN/SNOW AROUND  
THE GREAT LAKES BUT GENERALLY NO PRECIPITATION FROM THE SOUTHWEST  
TO THE PLAINS AND MS VALLEY.  
 
   
..THANKSGIVING FORECAST
 
 
GENERALLY QUIET FOR MOST OF THE LOWER 48. PRECIPITATION WILL BE  
MOST CONCENTRATED IN THE COASTAL PACIFIC NORTHWEST INTO NORTHERN  
CALIFORNIA AS WELL AS NORTHERN IDAHO/WESTERN MONTANA/NW WYOMING.  
RAIN IS ALSO QUITE POSSIBLE THROUGH FLORIDA AND THE COASTAL  
SOUTHEAST DEPENDING ON HOW THE SURFACE SYSTEM EVOLVES. RECORD HIGH  
TEMPS ARE POSSIBLE IN THE SOUTHWEST WITH WIDESPREAD 80S AND SOME  
90S BUT COOLER 30S/40S IN THE UPPER MIDWEST/GREAT  
LAKES/NORTHEAST/MID-ATLANTIC.  
 
FRACASSO/SCHICHTEL  
 

 
 
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