561  
FXUS02 KWBC 080648  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
148 AM EST WED NOV 08 2017  
 
VALID 12Z SAT NOV 11 2017 - 12Z WED NOV 15 2017  
   
..PATTERN OVERVIEW/MODEL EVALUATION/UNCERTAINTIES/PREFERENCES
 
 
WHILE A BROAD UPPER HIGH REMAINS A FIXTURE IN THE FORECAST ACROSS  
MX AND AT TIMES EXTENDING TOWARD THE RIO GRANDE RIVER VALLEY...AN  
ACTIVE MID-LATITUDE PATTERN IS EXPECTED TO THE NORTH. A CONVEYOR  
BELT OF FEATURES WILL TRANSLATE EASTWARD WITH ONE POWERFUL UPPER  
LOW EXITING TOWARD THE HIGHER LATITUDES OF EASTERN CANADA ON  
SATURDAY MORNING. ON ITS HEELS...A STRONG SURFACE ANTICYCLONE WILL  
INHABIT MUCH OF THE EASTERN SEABOARD BRINGING WELL BELOW NORMAL  
TEMPERATURES TO THE REGION. ACROSS THE GREAT PLAINS...A PACIFIC  
SHORTWAVE SHOULD BE TRACKING EASTWARD WHILE SOME POTENTIAL PHASING  
IS NOTED WITH A WAVE MOVING THROUGH SOUTHERN MANITOBA. DEPENDING  
ON HOW AMPLIFIED THIS SHORTWAVE BECOMES...SOME CYCLOGENESIS WILL  
LIKELY TAKE PLACE EARLY MONDAY OVER COASTAL NEW ENGLAND BEFORE THE  
CYCLONE PUSHES OUT TO SEA. LOOKING TO NEXT WEEK...BROAD LONGWAVE  
RIDGING SHOULD EXTEND FROM THE INTERMOUNTAIN WEST TO THE MS RIVER  
VALLEY WHILE HEIGHTS BEGIN TO LOWER ALONG THE WEST COAST. A PAIR  
OF UPPER TROUGHS ARE FORECAST TO SWING THROUGH NORTHERN CA/PACIFIC  
NORTHWEST...EACH KEEPING CONDITIONS QUITE WET OVER THE REGION. THE  
LEAD SYSTEM IS FORECAST TO ACCELERATE TOWARD THE GREAT PLAINS LATE  
TUESDAY WITH THE STRONGER FORCING LIKELY STAYING NORTH OF THE  
INTERNATIONAL BORDER WITH CANADA. RENEWED HEIGHT FALLS WILL BE  
PUSHING INTO THE PACIFIC NORTHWEST BY DAY 7/NOVEMBER 15 AS THE  
PATTERN SEEMS TO BE RATHER LOCKED IN PLACE.  
 
MODELS STILL CONTINUE TO STRUGGLE WITH WHETHER TO SHOW A MORE  
PHASED SOLUTION EVOLVING THROUGH THE CENTRAL U.S. ON SATURDAY.  
WHILE THE RECENT RUNS OF THE GFS HAVE BEEN ON THE QUICKER  
SIDE...THE 00Z RUN ARRIVED WITH A MUCH SLOWER SOLUTION WHICH IS  
EVEN WEST OF THE 12Z ECMWF. THIS 00Z GFS IS ALSO A BIT MORE SUBTLE  
WITH THE AMPLIFICATION PROCESS WHICH LEADS TO A MORE MODEST WAVE  
OF LOW PRESSURE. THE 18Z GFS/12Z ECMWF WERE STRONGER THAN THE  
REMAINING SOLUTIONS AS THE 00Z/12Z CMC/UKMET CARRY A MUCH FLATTER  
WAVE. EVENTUALLY THE SYSTEM WILL REACH THE EASTERN SEABOARD BY  
LATE SUNDAY/EARLY MONDAY INDUCING AN AREA OF LOW PRESSURE OFF THE  
COAST. MOST MODELS ARE MORE SUBTLE WITH THIS DEVELOPMENT ALTHOUGH  
THE 00Z CMC HAS MOVED TOWARD A MORE EXTREME SOLUTION AS A RAPIDLY  
STRENGTHENING COASTAL STORM TAKES SHAPE ON TUESDAY OFF THE UPPER  
MID-ATLANTIC COAST. TURNING THE FOCUS TOWARD THE ACTIVE PACIFIC  
STORM TRACK...THE LEAD UPPER TROUGH HAS BEEN WELL ADVERTISED FOR  
THE PAST SEVERAL DAYS. SHORT-TERM ENSEMBLE TRENDS SHOW A SLOWING  
WHICH THE 00Z UKMET HAS FOLLOWED AFTER ITS FORMER SOLUTION WAS A  
PROGRESSIVE OUTLIER. BY 14/0000Z...THE 00Z GFS/CMC/UKMET ARE IN  
REMARKABLY CLOSER AGREEMENT WITH HEIGHT FALLS MOVING INTO EASTERN  
WA/OR WHILE THE 12Z ECMWF IS A HAIR QUICKER. THE DIFFERENCES EVEN  
OUT TO DAY 7/NOVEMBER 15 ARE NOT TERRIBLY LARGE WHICH SUGGESTS  
SLIGHTLY ABOVE AVERAGE FORECAST CONFIDENCE. ON THE HEELS OF THIS  
LEAD SYSTEM...STRONG HEIGHT FALLS LOOM OFFSHORE WITH ENSEMBLE  
MEANS IN SOLID AGREEMENT WITH ONE ANOTHER. SOME RUN-TO-RUN CHANGES  
WERE NOTED IN THE GUIDANCE...PARTICULARLY THE CMC.  
HOWEVER...ENSEMBLE SPAGHETTI PLOTS DO NOT SHOW A TREMENDOUS AMOUNT  
OF SPREAD.  
 
GIVEN A DECENT SIGNAL OF ALL RELEVANT SOLUTIONS DURING THE  
PERIOD...WAS ABLE TO KEEP A GOOD CHUNK OF OPERATIONAL GUIDANCE IN  
THE MIX THROUGHOUT. DID NOT INTRODUCE ANY ENSEMBLE MEANS UNTIL  
MONDAY WHILE DEDICATING SLIGHTLY MORE WEIGHTING TOWARD THE 12Z  
ECMWF/ECMWF ENSEMBLE MEAN...60 PERCENT...RELATIVE TO THE 18Z  
GFS/GEFS MEAN. MAINTAINED THIS RATIO FOR THE ENTIRE PERIOD WITH  
THE 12Z ECMWF/ECMWF ENSEMBLE MEAN GIVEN A TAD MORE WEIGHT GIVEN  
ITS STRONGER CONSISTENCY THE PAST FEW DAYS.  
 
   
..SENSIBLE WEATHER HIGHLIGHTS/THREATS
 
 
EXCEPT FOR SATURDAY WHICH WILL BE DOMINATED BY BELOW AVERAGE  
TEMPERATURES...THE HEAVY INFLUENCE OF PACIFIC AIR MASSES SHOULD  
CONTRIBUTE TO READINGS CLOSER TO CLIMATOLOGY OR ABOVE IN SOME  
CASES. BEGINNING IN THE EASTERN THIRD OF THE COUNTRY...STRONG  
SURFACE RIDGING WILL ALLOW FOR ADEQUATE RADIATIONAL COOLING ON  
SATURDAY MORNING. THIS WILL BRING THE FIRST FREEZE TO MANY  
LOCATIONS AS SUCH TEMPERATURES PUSH AS FAR SOUTH AS NASHVILLE TN  
INTO THE INTERIOR CAROLINAS. WHILE NO DAILY TEMPERATURE RECORDS  
ARE EXPECTED TO BE BROKEN...SOME RECORD LOWS ARE POSSIBLE OVER THE  
UPPER GREAT LAKES INTO THE UPPER MID-ATLANTIC/LOWER NEW ENGLAND.  
LOOKING TO AN AREA WHERE ABOVE NORMAL TEMPERATURES WILL BE THE  
NORM...GENERAL WESTERLY FLOW SHOULD KEEP CONDITIONS MILD FROM THE  
ROCKIES EASTWARD TO THE GREAT PLAINS. AT TIMES READINGS 5 TO 10  
DEGREES ABOVE CLIMATOLOGY WILL BE WIDESPREAD BY EARLY NEXT WEEK.  
ACROSS THE PACIFIC NORTHWEST AND INTO NORTHERN CA...AN ACTIVE  
STORM TRACK SHOULD KEEP CONDITIONS COOL GIVEN THE EXPECTATIONS OF  
ABUNDANT CLOUDS AND BANDS OF PRECIPITATION.  
 
WARM ADVECTION PRECIPITATION ALONG THE ADVANCING FRONT IS IN THE  
FORECAST FROM THE ARKLATEX UP TO THE GREAT LAKES. GIVEN STRONGER  
FORCING TO THE NORTH...LOCALLY HEAVIER PRECIPITATION IS POSSIBLE  
OVER THE GREAT LAKES THIS WEEKEND WITH A THREAT FOR SNOW GIVEN  
SOME REMNANT ARCTIC AIR REMAINING IN PLACE. THE CHANCES FOR SNOW  
WILL MOVE TOWARD INTERIOR NEW ENGLAND BY LATE IN THE WEEKEND INTO  
EARLY NEXT WEEK. AS THE COASTAL LOW DEVELOPS...ANY CLOSER TO  
TRAJECTORY TO THE COAST WOULD BRING HIGHER AMOUNTS NEAR FAR  
EASTERN SECTIONS OF THE MID-ATLANTIC/NEW ENGLAND. THE MOST  
CONSISTENT AREA OF UNSETTLED WEATHER WILL BE ACROSS NORTHERN  
CA/PACIFIC NORTHWEST INTO THE UPPER INTERMOUNTAIN WEST WITH  
COASTAL RAIN AND HIGHER ELEVATION SNOWS. THIS MULTI-DAY EVENT  
SHOULD PERSIST INTO THE MIDDLE OF NEXT WEEK WHICH MAINTAINS THE  
FAIRLY WET PATTERN. EVENTUALLY A RETURN OF ADDITIONAL SHOWERS ARE  
POSSIBLE OVER THE MIDDLE MS VALLEY/UPPER MIDWEST/GREAT LAKES BY  
MID-WEEK AS THE LEAD PACIFIC TROUGH TRACKS EASTWARD.  
 
RUBIN-OSTER  
 

 
 
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