938  
FXUS02 KWBC 101559  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1059 AM EST FRI NOV 10 2017  
 
VALID 12Z MON NOV 13 2017 - 12Z FRI NOV 17 2017  
   
..PATTERN OVERVIEW
 
 
THE LARGE SCALE PATTERN WILL REMAIN FAIRLY STABLE THROUGH THE  
MEDIUM RANGE. A PERSISTENT AND STRONG REX BLOCK ACROSS THE  
CENTRAL/NORTHERN PACIFIC WILL CONTINUE TO FAVOR WEAK RIDGING  
ACROSS THE SOUTHERN TIER WITH PROGRESSIVE FLOW LIKELY TO EXTEND  
ACROSS THE REST OF THE LOWER 48. THIS PATTERN WILL PROMOTE  
POTENTIALLY HEAVY PRECIPITATION FOR THE PACIFIC NORTHWEST, AN  
OCCASIONAL PUSH OF CHILLY CANADIAN AIR INTO THE NORTHERN TIER  
STATES, ESPECIALLY FROM THE NORTHERN PLAINS TO THE GREAT LAKES,  
AND GENERALLY WARM CONDITIONS OVER THE REST OF THE CENTRAL  
U.S./FOUR CORNERS STATES.  
 
   
..GUIDANCE/UNCERTAINTY ASSESSMENT
 
 
FOR THE FIRST HALF OF THE PERIOD (EARLY DAY 3 MON INTO EARLY DAY 5  
WED) THERE IS REASONABLE AGREEMENT AND CONTINUITY FOR INDIVIDUAL  
FEATURES, WITH RELATIVELY MODEST DETAIL DIFFERENCES. THIS  
CONSENSUS FAVORS STARTING WITH A BLEND OF OPERATIONAL GUIDANCE  
WITH GREATER 00Z-06Z GFS/00Z ECMWF WEIGHT RELATIVE TO THE 00Z  
UKMET/CMC. A LEADING SHORTWAVE WILL REACH THE EAST COAST LATE MON  
AND THEN FLOW IMMEDIATELY UPSTREAM WILL AMPLIFY INTO ANOTHER  
TROUGH THAT PASSES INTO THE WESTERN ATLANTIC. LATEST GUIDANCE HAS  
STABILIZED IN KEEPING ASSOCIATED SURFACE DEVELOPMENT WELL  
OFFSHORE. FARTHER WEST A FAIRLY STRONG SYSTEM OFF  
WASHINGTON/VANCOUVER ISLAND WILL TRACK INLAND WITH LOW PRESSURE  
CROSSING CANADA AND THE TRAILING FRONT LIKELY REACHING NEAR THE  
WESTERN GREAT LAKES/MS VALLEY/SOUTHERN PLAINS BY WED. UPSTREAM  
ENERGY DROPPING INTO THE NORTHEAST PACIFIC MEAN TROUGH SHOULD  
BRING ANOTHER SURFACE LOW NEAR VANCOUVER ISLAND BY WED.  
 
FROM LATER WED ONWARD INDIVIDUAL MODELS/ENSEMBLES RAPIDLY DIVERGE  
IN RESPONSE TO DIFFERENCES THAT DEVELOP WITH DETAILS OF NORTHEAST  
PACIFIC FLOW AND APPROACHING NORTHERN PACIFIC/ALEUTIANS/BERING SEA  
ENERGY. THIS LEADS TO QUICKLY TRENDING THE FORECAST TOWARD THE  
LATEST GEFS/ECMWF ENSEMBLE MEANS BY DAYS 6-7 THU-FRI. IN TERMS OF  
THE OPERATIONAL MODELS THE RESULT OF PACIFIC DIFFERENCES IS THE  
00Z-06Z GFS AND 00Z ECMWF BECOMING ABOUT 180 DEGREES OUT OF PHASE  
WITH THE ENERGETIC EASTERN PACIFIC UPPER TROUGH THAT EJECTS ACROSS  
THE CONUS AND SURROUNDING RIDGES. THE 00Z ECMWF IS SLOWER THAN  
PREVIOUS RUNS BY VARYING DEGREES WHILE THE GFS HAS TRENDED FASTER  
AND STRONGER OVER THE LAST DAY. THE 00Z CMC IS MORE SIMILAR TO  
THE GFS BUT WEAKER. LOOKING AT ENSEMBLE GUIDANCE, A MAJORITY OF  
GEFS/CMC MEMBERS OFFER SUPPORT FOR A MORE SUBDUED VERSION OF THE  
GFS TIMING WHILE ECMWF MEMBERS ARE MORE BROADLY DISTRIBUTED AMONG  
SOLUTIONS CLOSER TO THE 00Z ECMWF, LESS EXTREME VERSIONS OF THE  
GFS, AND OTHER POSSIBILITIES. THUS THE UPPER TROUGH IN THE ECMWF  
MEAN IS SOMEWHAT SLOWER/FLATTER THAN THE OTHER MEANS. HOWEVER IT  
HAS BEEN CONSISTENT, ALONG WITH THE OTHER MEANS, IN BRINGING  
SURFACE LOW PRESSURE TO NEAR LAKE SUPERIOR BY EARLY DAY 7 FRI WITH  
A FRONT EXTENDING INTO THE SOUTHERN PLAINS. TELECONNECTIONS  
RELATIVE TO THE VERY STRONG CORE OF POSITIVE HEIGHT ANOMALIES JUST  
SOUTH OF THE ALEUTIANS NEAR 180 LONGITUDE SUGGEST THAT THE 00Z  
ECMWF MAY BE KEEPING HEIGHTS TOO HIGH OVER THE NORTHEAST PACIFIC  
WHERE OTHER GUIDANCE SHOWS DEEPER TROUGHING. THIS IS FURTHER  
SUPPORT FOR LEANING AWAY FROM 00Z ECMWF SPECIFICS DURING THIS PART  
OF THE FORECAST. IT WILL TAKE TIME TO GAIN SOME DEGREE OF  
CONFIDENCE IN HOW STRONG THE LATE WEEK UPPER GREAT LAKES SYSTEM  
MAY BECOME. EVEN IF NOT AS STRONG AS RECENT GFS/ECMWF RUNS,  
SUPPORTING ENERGY ALOFT IS FORECAST TO BE DEEPER THAN FOR  
PRECEDING PACIFIC SYSTEMS. THUS WHILE THE MEANS PROVIDE THE BEST  
STARTING POINT GIVEN CURRENT UNCERTAINTY, FUTURE TRENDS ARE MORE  
LIKELY TO BE SOMEWHAT DEEPER. FARTHER EAST, THE ENSEMBLE MEAN  
PREFERENCE DOWNPLAYS THE GFS RUNS THAT BECOME MORE AMPLIFIED THAN  
THE GUIDANCE MAJORITY WITH THE UPPER TROUGH REACHING THE EAST  
COAST AROUND EARLY THU.  
 
   
..SENSIBLE WEATHER HIGHLIGHTS/THREATS
 
 
THROUGH MUCH OF NEXT WEEK EXPECT PERIODS OF STRONG WINDS ALONG  
WITH HEAVY RAIN AND MOUNTAIN SNOW ACROSS THE PACIFIC  
NORTHWEST/NORTHERN CALIFORNIA AND TO SOME EXTENT INTO THE NORTHERN  
ROCKIES, AIDED BY PREVAILING ONSHORE FLOW AND A SERIES OF UPPER  
SHORTWAVES AND SURFACE LOW PRESSURE SYSTEMS/FRONTS. AN INITIAL  
WEST COAST SYSTEM WILL BRING A SURFACE FRONT ACROSS THE CENTRAL  
U.S. AND OH VALLEY TUE-WED ALONG WITH A ROUND OF PRECIPITATION TO  
THOSE REGIONS. MOST OF THE PRECIP WITH THIS FRONT SHOULD BE IN  
THE FORM OF RAIN. AS THE FRONT STALLS AND ANOTHER WAVE OF LOW  
PRESSURE DEVELOPS ACROSS THE NORTHERN PLAINS THU-FRI A SECOND  
EPISODE OF RAIN IS POSSIBLE WITH PERHAPS SOME THUNDERSTORMS FROM  
THE MID-MS VALLEY TO THE OH VALLEY, WITH AT LEAST MODERATE TOTALS  
FROM THESE REGIONS INTO THE GREAT LAKES. DEPENDING ON HOW THIS  
LATE WEEK SYSTEM DEVELOPS, SOME AREAS MAY SEE BRISK WINDS AND COLD  
SECTOR SNOW.  
 
BELOW AVERAGE TEMPERATURES (5-10 DEG F BELOW AVERAGE FOR MAX  
TEMPS) WILL PERSIST ACROSS THE EASTERN THIRD OF THE CONUS FROM  
EARLY-MID NEXT WEEK, BUT TEMPS SHOULD GRADUALLY MODERATE AS WARM  
ADVECTION TAKES HOLD AHEAD OF THE STRENGTHENING LOW PRESSURE  
SYSTEM ACROSS THE CENTRAL U.S. BY LATE IN THE WEEK. MEANWHILE THE  
CENTRAL/SOUTHERN ROCKIES AND MOST OF THE PLAINS SHOULD SEE  
MULTIPLE DAYS OF WELL ABOVE AVERAGE TEMPERATURES (PLUS 10-20F  
ANOMALIES) EARLY-MID WEEK. PROGRESSION OF PACIFIC FRONTS WILL  
GRADUALLY ERODE THIS WARMTH AND AN ARCTIC COLD FRONT WILL BRING  
SOME BELOW NORMAL TEMPS INTO THE NORTHERN PLAINS BY THU-FRI.  
 
RAUSCH/RYAN  
 

 
 
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