009  
FXUS02 KWBC 111600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1059 AM EST SAT NOV 11 2017  
 
VALID 12Z TUE NOV 14 2017 - 12Z SAT NOV 18 2017  
   
..PATTERN OVERVIEW
 
 
GUIDANCE AGREES THAT A STRONG CENTRAL PACIFIC INTO BERING SEA MEAN  
RIDGE WILL ENCOURAGE AMPLIFICATION OF NORTHEAST/EAST-CENTRAL  
PACIFIC MEAN TROUGHING. AS THIS OCCURS, RELATIVELY PROGRESSIVE  
AND LOW AMPLITUDE FLOW ACROSS THE LOWER 48 WILL GRADUALLY  
TRANSITION TOWARD A WESTERN RIDGE/EASTERN TROUGH CONFIGURATION.  
TELECONNECTIONS RELATIVE TO THE RIDGE (SPECIFICALLY THE PRONOUNCED  
POSITIVE HEIGHT ANOMALY CENTER NEAR THE ALEUTIANS) PROVIDE  
REASONABLE SUPPORT FOR THE EXPECTED PATTERN EVOLUTION ASIDE FROM  
SUGGESTING THAT EASTERN PACIFIC-NORTH AMERICAN FEATURES MAY SET UP  
A TAD FARTHER WESTWARD THAN FORECAST BY CURRENT CONSENSUS. FROM  
THE SENSIBLE WEATHER PERSPECTIVE THE MOST PROMINENT ASPECTS OF THE  
FORECAST WILL BE THE SERIES OF SYSTEMS AFFECTING THE NORTHWEST  
STATES, AND BY LATE IN THE WEEK ONE OF THE EJECTING WESTERN  
SYSTEMS THAT MAY SHOW STRONG DEVELOPMENT AS IT REACHES THE EASTERN  
U.S./EXTREME SOUTHERN CANADA.  
 
   
..GUIDANCE/UNCERTAINTY ASSESSMENT
 
 
AS HAS BEEN THE CASE RECENTLY, GUIDANCE SHOWS REASONABLE AGREEMENT  
THROUGH AT LEAST THE FIRST COUPLE DAYS OF THE FORECAST PERIOD  
(TUE-WED), ALLOWING FOR GREATER EMPHASIS OF THE OPERATIONAL  
00Z-06Z GFS/00Z ECMWF RELATIVE TO THE 06Z GEFS/00Z ECMWF MEANS.  
SOME 00Z UKMET/CMC DETAILS DIFFERED ENOUGH TO FAVOR EXCLUSION FROM  
THE BLEND.  
 
BY MID-PERIOD GUIDANCE BEGINS TO DIVERGE WITH THE ENERGETIC UPPER  
TROUGH ENTERING THE WESTERN STATES, IN RESPONSE TO DIFFERENCES IN  
HANDLING OF APPROACHING NORTHERN PACIFIC/BERING SEA FLOW. THERE  
HAVE BEEN SOME ATTEMPTS AT CONVERGENCE IN THE LATEST CYCLE OF  
GUIDANCE THOUGH. THE 00Z ECMWF IS STILL SLOWER THAN GFS RUNS BUT  
HAS TRENDED NOTABLY FASTER THAN ITS PRIOR TWO RUNS, AND IN FACT BY  
12Z DAY 7 SAT FULLY CATCHES UP TO THE 00Z GFS AND LATEST ENSEMBLE  
MEANS FOR THE STRONG SURFACE LOW THAT REACHES THE GREAT  
LAKES/SOUTHEAST ONTARIO AT THAT TIME. THE 06Z GFS TRENDED A BIT  
FASTER BUT OTHERWISE GFS/GEFS GUIDANCE HAS NUDGED A BIT SLOWER  
OVER THE PAST DAY ESPECIALLY AROUND DAY 6 FRI. THIS REFLECTS  
RECENT ADJUSTMENTS TOWARD TAKING A LITTLE LONGER TO WRAP UP THE  
SYSTEM, WITH POTENTIAL FOR A COUPLE SURFACE WAVES TO EXIST INTO  
EARLY FRI BEFORE CONSOLIDATION/STRONGER DEEPENING OCCUR SHORTLY  
THEREAFTER. ENSEMBLE MEANS SHOW THIS TREND AS WELL. LIKE THE  
OPERATIONAL RUNS, ENSEMBLE MEMBERS GENERALLY SHOW A TREND TOWARD  
SOME INTERMEDIATE TIMING, WITH GEFS MEMBERS ADJUSTING A LITTLE  
SLOWER AND SPREAD IN ECMWF MEMBERS DECREASING SOMEWHAT. HOWEVER  
THERE ARE STILL SOME SLOWER ECMWF MEMBERS THAT PERSIST IN THE 00Z  
CYCLE. THE DEVELOPING AMPLITUDE OF THE OVERALL PATTERN AND  
TELECONNECTION CONSIDERATIONS COULD SUPPORT LEANING AWAY FROM THE  
FAST SIDE OF THE SPREAD LATER IN THE PERIOD, BUT THE PROGRESSIVE  
NATURE OF FLOW UP TO THAT POINT WOULD STILL FAVOR LEANING FASTER  
THAN THE SLOW SIDE OF THE ENVELOPE AT LEAST INTO THU-FRI. THUS  
THE FORECAST BLEND MAINTAINS AN INTERMEDIATE APPROACH THAT  
INCREASES 00Z NAEFS/06Z GEFS/00Z ECMWF MEAN WEIGHT RELATIVE TO THE  
00Z GFS/ECMWF FARTHER OUT IN TIME. THE RESULT IS CLOSE TO  
CONTINUITY ASIDE FROM REFLECTING CONSENSUS THAT NOW SHOWS HIGHER  
PROBABILITY OF DELAYED MS VALLEY/GREAT LAKES SURFACE LOW  
CONSOLIDATION AS OF EARLY DAY 6 FRI.  
 
   
..SENSIBLE WEATHER HIGHLIGHTS/THREATS
 
 
EXPECT A SERIES OF PACIFIC SYSTEMS TO BRING PERIODS OF ENHANCED  
WINDS AND HEAVY RAIN/MOUNTAIN SNOW ACROSS THE PACIFIC  
NORTHWEST/NORTHERN CA AND TO SOME EXTENT INTO THE NORTHERN  
ROCKIES. HIGHEST 5-DAY TOTALS ARE MOST LIKELY OVER THE COASTAL  
RANGES AND WA CASCADES. A FRONTAL SYSTEM EMERGING OVER THE PLAINS  
TUE WILL BRING AN EPISODE OF MOSTLY RAIN TO THE MIDWEST/GREAT  
LAKES/OH VALLEY AROUND MIDWEEK, WITH PRECIP LIKELY TRENDING  
LIGHTER FARTHER EAST AS THE FRONT WEAKENS. THE COMBINATION OF THE  
TRAILING PART OF THE FRONT STALLING/RETURNING NORTH AS A WARM  
FRONT AND UPSTREAM LOW PRESSURE WILL GENERATE ANOTHER PRECIP AREA  
FROM NEAR THE MS VALLEY TO THE EAST COAST APPROXIMATELY THU NIGHT  
ONWARD. THUNDER MAY BE POSSIBLE IN PARTS OF THE WARM SECTOR.  
THERE ARE STILL DECENT SIGNALS THAT THE LATE WEEK SYSTEM MAY  
BECOME FAIRLY STRONG/WINDY AND COULD SUPPORT SNOW OVER EXTREME  
NORTHERN LOCATIONS. THE MOST EXTREME TEMPERATURE ANOMALIES OF  
PLUS 10-20F SHOULD EXTEND FROM THE FOUR CORNERS STATES INTO  
PORTIONS OF THE PLAINS TUE-THU AHEAD OF TWO SEPARATE PACIFIC  
FRONTS TRACKING OUT OF THE WEST. PARTS OF THE SOUTHWEST MAY  
REMAIN SOMEWHAT ABOVE NORMAL WITH A TENDENCY TOWARD MEAN RIDGING  
ALOFT LATE IN THE PERIOD. MEANWHILE THE EAST WILL BE SEVERAL  
DEGREES BELOW NORMAL EARLY IN THE PERIOD AND THE STRENGTHENING LOW  
PRESSURE LATER IN THE WEEK WILL PULL DOWN CHILLY CANADIAN AIR  
THROUGH THE NORTHERN TIER INTO THE GREAT LAKES/OH VALLEY.  
 
RAUSCH  
 

 
 
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