592  
FXUS02 KWBC 060646  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
145 AM EST MON NOV 06 2017  
 
VALID 12Z THU NOV 09 2017 - 12Z MON NOV 13 2017  
   
..PATTERN OVERVIEW/MODEL GUIDANCE/UNCERTAINTIES/PREFERENCES
 
 
AN ACTIVE PATTERN AHEAD WITH A SPLIT FLOW REGIME IN PLACE.  
SOUTHERN STREAM SHORTWAVE ENERGY WILL BE TRAVERSING THROUGH THE  
MID-SOUTH ON THURSDAY MORNING WITH AN ACCOMPANYING WEAK AREA OF  
LOW PRESSURE EVENTUALLY EXITING THE SOUTHEASTERN U.S. COAST. TO  
THE NORTH...AN IMPRESSIVE LONGWAVE TROUGH DESCENDS FROM HUDSON BAY  
TOWARD THE GREAT LAKES/NORTHEASTERN U.S. ON THURSDAY/FRIDAY. THIS  
WILL DRAW THE FIRST SIGNIFICANT SHOT OF MODIFIED ARCTIC AIR TO THE  
CENTRAL/EASTERN STATES. A RATHER DEEP SURFACE CYCLONE WILL FORM AS  
AN EMBEDDED SHORTWAVE ATTAINS A NEGATIVE TILT OVER SOUTHERN QUEBEC  
ON THURSDAY NIGHT. IN THE WAKE OF THIS SYSTEM...THE GUIDANCE SHOWS  
SURFACE PRESSURES NEARING 1040-MB FROM THE UPPER MIDWEST TO NEW  
ENGLAND. LOOKING BACK TOWARD THE WESTERN U.S...A DEEP UPPER LOW  
SHOULD BE APPROACHING THE NORTHERN CA/PACIFIC NORTHWEST COAST  
EARLY THURSDAY. THIS WILL QUICKLY EVOLVE INTO AN OPEN WAVE WHICH  
SLIDES DOWNSTREAM TOWARD THE GREAT PLAINS/MS RIVER VALLEY BY  
SATURDAY. DEPENDING ON THE DEGREE OF AMPLIFICATION...A COASTAL LOW  
MAY EMERGE OVER THE COASTAL ATLANTIC BY THE DAY 6/7...NOVEMBER  
12/13 TIME PERIOD. EVENTUALLY ANOTHER SYSTEM MOVES ONTO THE MAP  
LATE IN THE FORECAST AS HEIGHTS BEGIN TO LOWER OVER THE EASTERN  
PACIFIC BY LATE NEXT WEEKEND. WHILE MUCH OF THE COUNTRY SEES AN  
ACTIVE PERIOD AHEAD...UPPER RIDGING SHOULD DOMINATE THE RIO GRANDE  
RIVER VALLEY DOWN INTO MX.  
 
REGARDING THE AVAILABLE MODEL GUIDANCE...THERE HAS BEEN A FASTER  
TREND NOTED IN THE 00Z CMC/UKMET WITH THE SHORTWAVE TRACKING  
THROUGH THE MID-SOUTH ON THURSDAY. THIS SHIFT IN THE 00Z UKMET IS  
AN ADJUSTMENT TO ITS PREVIOUSLY OUTLYING MORE WESTWARD DISPLACED  
SOLUTION. SOME WEAK WAVES ARE EXPECTED TO DEVELOP ALONG THE WAVY  
FRONT AS IT SLIDES SOUTH AND EAST. TO THE NORTH...THE EXPECTED  
AMPLIFICATION STILL REMAINS THE MOST CONTENTIOUS AREA ON THE MAP.  
ENSEMBLE SPAGHETTI PLOTS CONTINUE TO SHOW A GREAT DEAL OF MOVEMENT  
BETWEEN MODEL RUNS AND AMONG THE GLOBAL GUIDANCE. MULTI-DAY  
COMPARISONS INDICATE THE ECMWF/ECMWF ENSEMBLE MEAN HAVE BEEN THE  
MOST STABLE SOLUTIONS. THE 00Z/12Z CMC HAVE BEEN SHOWING SUPPORT  
FOR THIS ECMWF SCENARIO WHICH IS MORE AGGRESSIVE WITH THE ARCTIC  
PUSH. TRENDS IN THE GFS HAVE ALSO BEEN MOVING IN THAT DIRECTION  
ALTHOUGH IT WAS NOT TOO LONG AGO WHERE IT REMAINED MORE  
SUPPRESSED. THE 12Z UKMET APPEARED TO BE THE LARGER OUTLIER BEING  
SLOW BUT THE NEWER RUN HAS MADE SOME POSITIVE ADJUSTMENTS.  
ELSEWHERE...GENERAL AGREEMENT EXISTS WITH THE POSITION/STRENGTH OF  
THE UPPER LOW MOVING INTO THE WEST COAST ON THURSDAY. THEY DIFFER  
MORE GREATLY ON HOW QUICKLY TO EJECT THE STACK OF SHORTWAVES  
TOWARD THE CENTRAL U.S. OPERATIONAL RUNS OF THE GFS AS WELL AS  
MANY OF THE ENSEMBLE MEMBERS HAVE FAVORED A QUICKER/FLATTER  
EVOLUTION RELATIVE TO PRIOR RUNS OF THE ECMWF. AN AREA OF LOW  
PRESSURE IS LIKELY TO DEVELOP BY THE DAY 6/7...NOVEMBER 12/13  
WINDOW ALTHOUGH ENSEMBLE LOW PLOTS SHOW A LOT OF SPREAD IF IT  
INDEED FORMS. BACK WEST...MODELS ARE VARIABLE WITH THE EVOLUTION  
OF THE RENEWED TROUGHING LATE IN THE PERIOD. HOWEVER...ENSEMBLE  
MEANS AGREE AS A WHOLE WITH THE 18Z/12Z GEFS MEAN BEING SLIGHTLY  
WEST OF THE 12Z ECMWF ENSEMBLE MEAN.  
 
AS GENERAL SYNOPTIC-SCALE AGREEMENT HAS IMPROVED...WAS ABLE TO  
UTILIZE A STEADY DOSE OF OPERATIONAL MODELS THROUGHOUT THE PERIOD.  
DID NOT INCORPORATE ANY ENSEMBLE MEANS UNTIL SATURDAY AS THE  
MODELS VARY WITH THE LONGWAVE TROUGH PUSHING INTO THE GREAT  
LAKES/NEW ENGLAND. BEFORE THIS...FAVORED AN EQUAL BLEND OF THE 18Z  
GFS/12Z ECMWF WITH SOME MINOR CONTRIBUTIONS FROM THE 12Z CMC.  
THEREAFTER...KEPT AN APPRECIABLE AMOUNT OF THE 18Z GFS/12Z ECMWF  
IN THE PICTURE WITH A MIX OF THE USUAL TRIO OF ENSEMBLE  
MEANS...GEFS/ECMWF/NAEFS. TOOK A SLIGHTLY HIGHER WEIGHT OF THE 12Z  
ECMWF/ECMWF ENSEMBLE MEAN GIVEN STRONGER MODEL CONSISTENCY.  
 
   
..SENSIBLE WEATHER HIGHLIGHTS/THREATS
 
 
WHILE AN IMPRESSIVE SHOT OF MODIFIED ARCTIC AIR ENTERS THE PICTURE  
DURING THE THURSDAY THROUGH SATURDAY TIMEFRAME...NO DAILY  
TEMPERATURE RECORDS ARE LIKELY TO BE BROKEN. HOWEVER...EXPECT  
DEPARTURES FROM NORMAL ON THE ORDER OF 10 TO 20 DEGREES BELOW  
AVERAGE TO BE THE NORM FROM THE NORTHERN PLAINS THROUGH THE UPPER  
MIDWEST AND INTO THE GREAT LAKES/OH VALLEY/NORTHEASTERN U.S. SOME  
OVERNIGHT LOWS MAY PUSH BELOW ZERO DEGREES ON FRIDAY MORNING  
ACROSS ND/MN. THIS WILL BE THE NIGHT OF EFFICIENT RADIATIONAL  
COOLING AS A 1036-MB ANTICYCLONE SITS OVERHEAD. THE AIR MASS WILL  
MODIFY IN TIME WHILE ADVANCING EASTWARD BUT MAY BRING THE FIRST  
FREEZE TO MANY LOCATIONS FARTHER EAST. GRADUALLY TEMPERATURES  
ACROSS THE COUNTRY WILL MODERATE SOME AS THE FLOW TURNS A BIT MORE  
ZONAL IN NATURE BY THE END OF THE WEEKEND.  
 
REGARDING PRECIPITATION...UNSETTLED CONDITIONS ARE LIKELY FROM  
NORTHERN CA UP INTO WESTERN OR/WA GIVEN STRONG DYNAMICAL  
LIFT...AMPLE ONSHORE FLOW...AND UPSLOPE TRAJECTORIES. THROUGH  
EARLY FRIDAY...MODERATE TO LOCALLY HEAVY PRECIPITATION IS LIKELY  
FROM THE SHASTA/NORTHERN SIERRA NEVADA RANGES NORTHWARD TO THE  
OLYMPICS/CASCADES. SOME OF THIS WILL FALL IN THE FORM OF SNOWFALL  
ACROSS THE HIGHER ELEVATIONS AS WELL AS MORE INLAND LOCALES LIKE  
THE BITTERROOTS...SAWTOOTH...AND TETONS. THE WEST COAST WILL  
BRIEFLY DRY OUT OVER THE WEEKEND BEFORE THE NEXT TROUGH BRINGS A  
BOUT OF RAIN/SNOW BY LATE IN THE PERIOD. ACROSS THE EASTERN  
U.S...LINGERING SHOWERS ARE LIKELY ACROSS THE CENTRAL/EASTERN GULF  
COAST ON THURSDAY WHILE SOME CONVECTIVELY FORCED ACTIVITY IS  
POSSIBLE OVER THE GREAT LAKES GIVEN STEEPENING LAPSE RATES  
ACCOMPANYING THE STRONG UPPER TROUGH. SOME SNOW IS POSSIBLE OVER  
THE INTERIOR NORTHEAST ALTHOUGH MOISTURE SHOULD BE SOMEWHAT SCANT.  
EVENTUALLY SOME WARM ADVECTION ACTIVITY IS POSSIBLE BY SATURDAY  
ACROSS THE GREAT PLAINS/MS RIVER VALLEY WITH THE PROGRESSIVE  
SHORTWAVE MOVING THROUGH. IF ENOUGH COLD AIR LINGERS ACROSS THE  
UPPER MIDWEST/GREAT LAKES...SOME PRECIPITATION MAY FALL AS SNOW  
OVER THE WEEKEND. EVENTUALLY ALL OF THE UNSETTLED WEATHER WILL  
MOVE TOWARD THE EASTERN SEABOARD BY NOVEMBER 12/13 WITH ANY  
DISCERNIBLE COASTAL WAVE AUGMENTING LOCAL AMOUNTS.  
 
RUBIN-OSTER  
 

 
 
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