286  
FXUS02 KWBC 090657  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
156 AM EST THU NOV 09 2017  
 
VALID 12Z SUN NOV 12 2017 - 12Z THU NOV 16 2017  
   
..PATTERN OVERVIEW/MODEL EVALUATION/UNCERTAINTIES/PREFERENCES
 
 
THE SYNOPTIC-SCALE PATTERN ACROSS THE NATION WILL MAINTAIN A  
PERSISTENT UPPER RIDGE ACROSS MX POSSIBLY EXTENDING INTO THE RIO  
GRANDE RIVER VALLEY. BOUNDED TO THE NORTH...A SERIES OF PACIFIC  
SYSTEMS OF VARIABLE AMPLITUDES WILL CHURN EASTWARD KEEPING THE  
WEATHER ON THE MORE ACTIVE SIDE...PARTICULARLY OVER THE PACIFIC  
NORTHWEST INTO NORTHERN CA. IT APPEARS A RATHER REPEATABLE PATTERN  
IS IN PLACE AS A MEAN UPPER RIDGE LOOMS LARGE ACROSS THE CENTRAL  
PACIFIC WHICH FAVORS LOWER HEIGHTS ACROSS THE EASTERN  
PACIFIC/ADJACENT WEST COAST. THE LEAD SHORTWAVE IN THE VICINITY OF  
THE MIDDLE MS VALLEY...DEPENDING ON THE MODEL...SHOULD HAVE A  
GRADUAL TENDENCY TO AMPLIFY WHILE APPROACHING THE  
CAROLINAS/MID-ATLANTIC EARLY MONDAY. THIS SHOULD INDUCE A WAVE OF  
LOW PRESSURE OFF THE MID-ATLANTIC COAST WITH SOLUTIONS QUITE  
VARIABLE WITH REGARD TO FORWARD PROGRESSION AND STRENGTH. IN ITS  
WAKE...BROAD LOW-AMPLITUDE LONGWAVE RIDGING WILL SET UP FROM THE  
INTERMOUNTAIN WEST EASTWARD TO THE MS RIVER VALLEY ON MONDAY.  
FARTHER UPSTREAM...A CONVEYOR BELT OF SHORTWAVES EMANATING FROM  
THE GULF OF AK WILL CONTINUE TO RACE THROUGH THE PACIFIC NORTHWEST  
WHILE MAINTAINING A GENERAL EASTWARD TRACK ALONG THE NORTHERN TIER  
STATES. MANY MODELS SHOW THREE DISTINCT SYSTEMS TRACKING WITHIN  
THIS WAVE TRAIN OF SHORTWAVES...THUS KEEPING CONDITIONS QUITE WET  
FROM NORTHERN CA/PACIFIC NORTHWEST EASTWARD INTO THE UPPER  
INTERMOUNTAIN WEST AND NORTHERN ROCKIES.  
 
ONE OF THE MORE UNCERTAIN ASPECTS OF THE FORECAST WILL BE THE  
ULTIMATE FATE OF THE MENTIONED SHORTWAVE PUSHING THROUGH THE  
MIDDLE MS VALLEY LATE IN THE WEEKEND. THE PAST FEW RUNS OF THE  
GFS/ECMWF HAVE BEEN FAIRLY CONSISTENT WITH THE INITIAL PLACEMENT  
OF THE SHORTWAVE ON 12/1200Z WHILE THE 12Z CMC/UKMET HAVE BEEN  
MORE WILDLY VARIABLE. IT APPEARS THE 12Z UKMET EACH DAY HAS COME  
IN THE SLOWEST IN THE PACK WHILE THE 00Z COMES IN AND ALWAYS MAKES  
THE EASTWARD ADJUSTMENT. WHERE THE FORECAST REALLY BEGINS TO BREAK  
DOWN IS ON MONDAY/TUESDAY WHERE THE GUIDANCE IS UNCERTAIN WITH HOW  
AMPLIFIED THE WAVE WILL BECOME AND WHETHER IT COULD EVEN CUT OFF.  
THE 00Z/18Z/12Z GFS RUNS ARE CONSISTENTLY QUICKER THAN THE  
CONSENSUS GIVEN THE WAVE IS ON THE MORE PROGRESSIVE SIDE. BY  
14/0000Z...THE 570-DM ENSEMBLE SPAGHETTI PLOTS DEPICT A WIDE  
VARIETY OF SOLUTIONS...PARTICULARLY AMONG THE OPERATIONAL MODELS.  
COMPARED TO THE QUICKER TRIO OF GFS RUNS...THE 00Z UKMET/12Z ECMWF  
AS WELL AS THE LAST TWO CMC RUNS SHOW A MUCH MORE DEFINED  
SHORTWAVE WHICH THE 12Z ECMWF SHOWS CUTTING OFF AND MIGRATING  
SLOWLY THROUGH THE LOWER MID-ATLANTIC ON TUESDAY/WEDNESDAY. THE  
00Z UKMET FOLLOWS THIS SOLUTION TO SOME DEGREE BUT IN A MUCH LESS  
DRAMATIC FASHION. LOOKING TO THE ACTIVE PACIFIC STORM TRACK...THIS  
WELL ADVERTISED SYSTEM ENTERING THE PICTURE LATE SUNDAY/EARLY  
MONDAY IS STILL WELL RESOLVED. THERE REMAIN SOME RUN-TO-RUN  
CHANGES IN THE GUIDANCE BUT THE BIG PICTURE DOES NOT CHANGE  
SIGNIFICANTLY. THE ECMWF HAS ROUTINELY BEEN A HAIR QUICKER THAN  
THE GFS BUT THE DIFFERENCES HAVE NOT BEEN REMARKABLY ROBUST. THE  
STRONGEST HEIGHT FALLS SEEM TO BE RESTRICTED TO ALONG THE  
INTERNATIONAL BORDER WITH CANADA AND NORTHWARD. IN ITS  
WAKE...ANOTHER POWERFUL PACIFIC CYCLONE APPROACHES THE WA COAST BY  
EARLY WEDNESDAY WITH ADDITIONAL SHORTWAVE ENERGY POSSIBLY  
FOLLOWING ITS PATH THE DAY AFTER. ENSEMBLE MEANS TEND TO MERGE THE  
FEATURES INTO ONE BUT THE WAVELENGTH BETWEEN THE SHORTWAVES IS ON  
THE SMALLER SIDE.  
 
GIVEN THE EXTREME NATURE OF THE 12Z ECMWF ACROSS THE EASTERN  
SEABOARD EARLY NEXT WEEK...DISCARDED ITS SOLUTION AS AN OUTLIER.  
THUS...LEANED ON THE FORMER 00Z SOLUTION WHICH ACTUALLY LOOKS  
RATHER SIMILAR TO THE LATEST 00Z ECMWF WHICH JUST ARRIVED.  
THROUGHOUT THE PERIOD...TOOK AN EVEN SPLIT OF THE 12Z GFS/GEFS  
MEAN WITH THE PREVIOUS 00Z ECMWF/ECMWF ENSEMBLE MEAN. GRADUALLY  
INCORPORATED ENSEMBLE MEANS INTO THE FORECAST BY DAY 5/TUESDAY  
WHILE STILL KEEPING AROUND 30 PERCENT OF AN OPERATIONAL COMPONENT  
INTO THE END OF THE PERIOD. CONFIDENCE IN THE WESTERN U.S. IS  
ABOVE AVERAGE GIVEN THE DECENT MODEL AGREEMENT WHILE IT REMAINS  
CLOSER TO AVERAGE OVER THE EAST GIVEN EARLIER MENTIONED SHORTWAVE  
DETAIL ISSUES.  
 
   
..SENSIBLE WEATHER HIGHLIGHTS/THREATS
 
 
DURING MUCH OF THE PERIOD...ABOVE NORMAL TEMPERATURES FOR  
MID-NOVEMBER ARE EXPECTED FROM THE ROCKIES EASTWARD TO THE MS  
RIVER VALLEY. THE DOMINANCE OF PACIFIC ORIGIN SYSTEMS WITH THE  
FLOW DE-AMPLIFYING WHILE MOVING INLAND WILL KEEP A STRONGER  
WESTERLY COMPONENT TO THE SYNOPTIC FLOW. BY TUESDAY...HIGH  
TEMPERATURES AROUND 10 TO 15 DEGREES ABOVE CLIMATOLOGY CAN BE  
EXPECTED FROM THE FOUR CORNERS INTO THE GREAT PLAINS WHICH WILL  
SPREAD 60S AS FAR NORTH AS WESTERN NEB. REGARDING THE COOLER  
SPOTS...IT SHOULD BE A CHILLY DAY OVER THE EASTERN THIRD OF THE  
COUNTRY ON SUNDAY GIVEN A SURFACE RIDGE SPRAWLING DOWN ALONG THE  
EASTERN SEABOARD. EXPECT NEAR FREEZING OVERNIGHT TEMPERATURES DOWN  
INTO THE INTERIOR CAROLINAS WHILE LOW/MID 20S BLANKET MUCH OF NEW  
ENGLAND. ACROSS THE PACIFIC NORTHWEST...THE PERSISTENCE OF CLOUD  
COVER AND RAIN CHANCES WILL KEEP CONDITIONS COOL AND DAMP  
THROUGHOUT A MAJORITY OF THE PERIOD.  
 
CONDITIONS WILL REMAIN UNSETTLED FROM NORTHERN CA UP TO THE  
PACIFIC NORTHWEST/UPPER INTERMOUNTAIN WEST GIVEN THE ACTIVE STORM  
TRACK. THE INITIAL SYSTEM SHOULD SPREAD COASTAL RAIN FROM NORTHERN  
CA UP TO THE INTERNATIONAL BORDER WHILE SNOW HITS THE HIGHER  
ELEVATIONS OF THE CASCADES INTO THE SAWTOOTH/BITTERROOTS/TETONS.  
ON ITS HEELS...THE NEXT SHORTWAVE SHOULD FOCUS MORE OF THE  
ACTIVITY FROM THE CA/OR BORDER UP TO BRITISH COLUMBIA WITH SOME 2  
TO 3 INCH 24-HOUR AMOUNTS ARE NOTED IN THE GUIDANCE ACROSS WESTERN  
OR/WA. ADDITIONAL SNOW IS LIKELY ACROSS THE INTERIOR HIGHER  
ELEVATIONS AS WELL. OVER THE CENTRAL/EASTERN U.S...FRONTAL  
PRECIPITATION WILL BE COMMONPLACE ON SUNDAY/MONDAY WITH AMOUNTS ON  
THE LIGHTER END GIVEN SCANT MOISTURE RETURN. EVENTUALLY SOME HEAVY  
RAINFALL IS POSSIBLE IF SOME OF THE MORE INTENSE SOLUTIONS VERIFY  
OVER THE COASTAL MID-ATLANTIC/NEW ENGLAND ON MONDAY/TUESDAY. THE  
NEXT SYSTEM WHICH MOVES OUT OF THE PACIFIC NORTHWEST ON MONDAY  
SHOULD BRING INCREASING PRECIPITATION CHANCES OVER THE MIDDLE MS  
VALLEY/GREAT LAKES WHERE THE BETTER DYNAMICS WILL RESIDE. THE MAIN  
THREAT FOR SNOW EAST OF THE ROCKIES WOULD BE ACROSS THE INTERIOR  
NORTHEAST WHERE TEMPERATURES MAY BE COLD ENOUGH.  
 
RUBIN-OSTER  
 

 
 
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