175  
FXUS02 KWBC 070655  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
154 AM EST TUE NOV 07 2017  
 
VALID 12Z FRI NOV 10 2017 - 12Z TUE NOV 14 2017  
   
..PATTERN OVERVIEW/MODEL GUIDANCE/UNCERTAINTIES/PREFERENCES
 
 
AN ACTIVE PROGRESSIVE MID-LATITUDE FLOW WILL BE FEATURED  
THROUGHOUT THE PERIOD. ON FRIDAY MORNING...A STRONG UPPER LOW  
SHOULD BE LIFTING AWAY FROM SOUTHERN QUEBEC WITH 500-MB HEIGHT  
ANOMALIES ON THE ORDER OF 2 TO 2.5 STANDARD DEVIATIONS BELOW  
CLIMATOLOGY. AS THIS SYSTEM MIGRATES DEEPER INTO NORTHERN  
QUEBEC...A PRONOUNCED SURFACE ANTICYCLONE SETS UP FROM THE GREAT  
LAKES INTO NEW ENGLAND WITH PRESSURES POSSIBLY APPROACHING 1040-MB  
ON FRIDAY. ONCE THIS RIDGE SHIFTS INTO THE WESTERN ATLANTIC ON  
SUNDAY...INCREASING WARM ADVECTION WILL TAKE SHAPE IN ADVANCE OF  
THE NEXT ARRAY OF SHORTWAVES. SPLIT FLOW IS EVIDENT WITH THE  
FEATURES GENERALLY OF LOWER AMPLITUDE. MODELS VARY ON WHETHER TO  
KEEP THE PAIR OF SHORTWAVES SEPARATE OR SOME SORT OF PHASING  
PROCESS TAKES SHAPE. SURFACE CYCLOGENESIS IS LIKELY TO TAKE PLACE  
OVER THE WESTERN ATLANTIC BY LATE SUNDAY/EARLY MONDAY ALTHOUGH THE  
CYCLONE SHOULD ACCELERATE AWAY FROM THE COAST THEREAFTER.  
EVENTUALLY THE ACTION TURNS BACK TO THE WEST COAST AS A PAIR OF  
SYSTEMS IMPACT THE PACIFIC NORTHWEST DURING THE DAY 6/7...NOVEMBER  
13/14 TIMEFRAME. WHILE THE PATTERN IS ACTIVE OVER A MAJORITY OF  
THE COUNTRY...A STAGNANT CLOSED UPPER RIDGE SHOULD REMAIN IN PLACE  
OVER MX POSSIBLY EXTENDING INTO THE RIO GRANDE RIVER VALLEY.  
 
COMPARED TO PREVIOUS DAYS OF GUIDANCE...THERE IS NOT AS MUCH  
VOLATILITY NOTED AMONG THE AVAILABLE SOLUTIONS. MULTI-DAY ENSEMBLE  
SPAGHETTI COMPARISONS INDICATE THE ECMWF ENSEMBLES HAVE BEEN  
RATHER CONSISTENT WITH THE MORE AMPLIFIED SCENARIO OVER THE  
NORTHEASTERN U.S. OTHER GLOBAL MODELS HAVE EVENTUALLY MOVED IN  
THAT DIRECTION. THE LARGEST OUTLIER EARLY ON IS THE 12Z UKMET  
WHICH FAVORS A SLOWER MORE AMPLIFIED SOLUTION WITH LITTLE CHANGE  
NOTED IN THE MORE RECENT 00Z RUN. THE UPPER LOW AND ITS  
ACCOMPANYING DEEP SURFACE LOW SHOULD BE IN THE PROCESS OF EXITING  
INTO QUEBEC AT THE START OF THE PERIOD WHILE PRESSURES RAPIDLY  
RISE GIVEN THE INTRUSION OF MODIFIED ARCTIC AIR. FARTHER  
UPSTREAM...MODELS STILL HAVE NOT FOUND AN AGREED UPON SOLUTION  
WITH THE PROGRESSIVE SPLIT FLOW PUSHING THROUGH THE CENTRAL U.S.  
ON SATURDAY. UNCERTAINTY LOOMS WITH WHETHER THE TWO STREAMS WILL  
PHASE OR REMAIN SEPARATE AS INDIVIDUAL MODELS MEANDER BETWEEN THE  
PAIR OF SCENARIOS. TIMING DIFFERENCES ARE PROMINENT AMONG THE  
GUIDANCE WITH THE PREVIOUS FEW GFS RUNS BEING QUICKER THAN THE  
12Z/00Z ECMWF. THE 12Z CMC IS MORE IN LINE WITH THE FASTER GFS AS  
ENSEMBLE SPAGHETTI PLOTS HAVE DICTATED. THIS TEMPORAL UNCERTAINTY  
IS REFLECTED WITH THE EVENTUAL CYCLOGENESIS PROCESS OCCURRING OFF  
THE EASTERN SEABOARD BY LATE SUNDAY/EARLY MONDAY. ENSEMBLE LOW  
PLOTS SUGGEST A GREAT DEAL OF SPREAD BUT IT APPEARS MOST MEMBERS  
TAKE THE SYSTEM HARMLESSLY OUT TO SEA. SHIFTING FOCUS TO THE  
EASTERN PACIFIC...A PAIR OF SYSTEMS ARE PRIMED TO IMPACT NORTHERN  
CA/PACIFIC NORTHWEST INTO THE ADJACENT INTERMOUNTAIN WEST BY DAY  
5/SUNDAY INTO EARLY NEXT WEEK. THE LEAD LONGWAVE TROUGH HAS BEEN  
WELL ADVERTISED FOR DAYS NOW WITH MODEL UNCERTAINTY ON THE LOWER  
SIDE. THE 12Z ECMWF/CMC ARE A BIT QUICKER TO BRING HEIGHT FALLS  
INTO THE PACIFIC NORTHWEST ON MONDAY MORNING COMPARED TO THE  
00Z/18Z GFS. GRADUALLY THIS SYSTEM WILL ACCELERATE TOWARD THE HIGH  
PLAINS BY DAY 7/NOVEMBER 14 WHILE ANOTHER UPPER LOW FROM THE GULF  
OF AK PEELS DOWN AND APPROACHES THE BRITISH COLUMBIA COAST. AS A  
WHOLE...THIS SCENARIO IS WELL AGREED UPON WITH ONLY MINOR  
DIFFERENCES BETWEEN THE OPERATIONAL MODELS.  
 
THROUGH DAY 4/SATURDAY...PRIMARILY USED A COMBINATION OF THE 18Z  
GFS WITH THE 12Z ECMWF/CMC GIVEN ABOVE AVERAGE AGREEMENT AMONG  
THESE SOLUTIONS. GRADUALLY SAW THE 12Z CMC BECOMING TOO  
PROGRESSIVE WITH THE SPLIT FLOW OVER THE CENTRAL U.S. SO REMOVED  
ITS INFLUENCES TOWARD THE END OF THE WEEKEND. ENSEMBLE MEANS...THE  
18Z GEFS AND 12Z ECMWF/NAEFS WERE ADDED TO THE MIX FROM DAYS  
5-7...NOVEMBER 12-14 AS SPREAD INCREASED ACROSS THE BOARD.  
HOWEVER...FELT CONFIDENCE ENOUGH TO KEEP ABOUT 30-40 PERCENT OF  
THE BLEND DEDICATED TO THE 18Z GFS/12Z ECMWF OUT TO THE END OF THE  
PERIOD. REGARDING RATIOS OF THESE MODELS...TOOK AN EQUAL SPLIT OF  
THE GFS/ECMWF WITH MINOR CONTRIBUTIONS FROM THE 12Z NAEFS MEAN.  
 
   
..SENSIBLE WEATHER HIGHLIGHTS/THREATS
 
 
IT WILL BE A COLD START TO THE PERIOD ACROSS MOST LOCATIONS EAST  
OF THE ROCKIES GIVEN THE AMPLIFIED FLOW SWEEPING THROUGH THE GREAT  
LAKES/NORTHEASTERN U.S. IT SHOULD BE QUITE COOL AND AT TIMES  
BREEZY ON FRIDAY/SATURDAY WITH A STRONG SURFACE RIDGE SETTING UP  
OVER THE REGION AS THE DEEP CYCLONE EXITS INTO EASTERN CANADA. THE  
LARGEST DEPARTURES FROM NORMAL WILL BE ACROSS THE GREAT LAKES/OH  
VALLEY/MID-ATLANTIC/NEW ENGLAND WITH 10 TO 20 DEGREES BELOW  
AVERAGE BEING LIKELY. HIGH TEMPERATURES IN THE 40S WILL BE LIKELY  
AS FAR SOUTH AS UPSTATE NC WHILE BELOW FREEZING OVERNIGHT  
TEMPERATURES COULD REACH DOWN INTO THE INTERIOR CAROLINAS. WHILE  
NO DAILY TEMPERATURE RECORDS SHOULD BE BROKEN DOWN IN THE  
CAROLINAS...EXPECT SOME RECORD LOWS POSSIBLE ON SATURDAY MORNING  
OVER THE MID-ATLANTIC INTO LOWER NEW ENGLAND. FOR THE REST OF THE  
COUNTRY...TEMPERATURES SHOULD BE ON THE MILDER SIDE GIVEN THE  
LOWER AMPLITUDE FLOW REGIME. EXPECT READINGS CLOSER TO CLIMATOLOGY  
TO ABOVE BY AROUND 5 TO 10 DEGREES FROM THE FOUR CORNERS EASTWARD  
INTO THE GREAT PLAINS. COOLER WEATHER CAN BE EXPECTED LATER IN THE  
FORECAST ACROSS THE PACIFIC NORTHWEST GIVEN THE RETURN OF MULTIPLE  
SHORTWAVES.  
 
ACROSS THE GREAT PLAINS/MS RIVER VALLEY/GREAT LAKES...WARM  
ADVECTION PRECIPITATION WILL LIKELY BE EXPANDING IN COVERAGE OVER  
THE WEEKEND. THE BEST FORCING WILL RESIDE ACROSS THE NORTHERN TIER  
STATES WHERE A SURFACE WAVE WILL ACCELERATE TOWARD THE GREAT  
LAKES. REMNANT COLD AIR FROM THE ARCTIC BLAST MAY KEEP SURFACE  
TEMPERATURES COLD ENOUGH FOR SNOW OVER THE GREAT LAKES THIS  
WEEKEND WITH FURTHER CHANCES DOWNSTREAM OVER THE INTERIOR  
NORTHEASTERN U.S. OUT WEST...IT SHOULD BE QUITE UNSETTLED  
THROUGHOUT MUCH OF THE FORECAST ALTHOUGH THERE WILL BE A BRIEF  
LULL IN THE ACTIVITY IN BETWEEN SYSTEMS. THE LONGWAVE TROUGH  
APPROACHING ON SUNDAY HAS AN IMPRESSIVE HEAVY PRECIPITATION SIGNAL  
FROM NORTHERN CA UP INTO THE PACIFIC NORTHWEST WITH OROGRAPHICALLY  
FAVORED LOCATIONS SEEING A BRUNT OF THE RAIN/SNOW. EVENTUALLY THE  
ACTIVITY WILL SHIFT INTO THE UPPER INTERMOUNTAIN WEST WITH  
RAIN/SNOW EXPECTED INTO THE BITTERROOTS...SAWTOOTH...AND TETONS.  
 
RUBIN-OSTER  
 

 
 
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