973  
FXUS02 KWBC 281538  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1037 AM EST TUE NOV 28 2017  
 
VALID 12Z FRI DEC 01 2017 - 12Z TUE DEC 05 2017  
   
..OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES
 
 
THE UPCOMING PERIOD WILL MARK THE START OF METEOROLOGICAL  
WINTER...DECEMBER 1...WITH THE SYNOPTIC-SCALE PATTERN ON THE  
DE-AMPLIFIED SIDE. QUASI-ZONAL FLOW IS FORECAST TO BE IN PLACE  
WITH A PAIR OF NOTABLE RIPPLES IN THE JET STREAMS. A SHORTWAVE  
THROUGH WILL BE PUSHING THROUGH NEW ENGLAND ON FRIDAY WHILE THE  
SOUTHERN STREAM FEATURES A SUBTLE PERTURBATION TRACKING OUT OF THE  
SOUTHERN HIGH PLAINS. BY THE WEEKEND...THE LARGE-SCALE PATTERN  
SHOULD ATTAIN MORE AMPLITUDE AS HEIGHT FALLS CARVE OUT A SIZABLE  
TROUGH OVER THE UPPER MIDWEST BY 02/1200Z. DOWNSTREAM PROGRESSION  
IS EXPECTED WITH THE SYSTEM EXITING NEW ENGLAND DURING THE  
SUNDAY/MONDAY TIMEFRAME. DEPENDING ON THE LEVEL OF AMPLIFICATION  
ATTAINED...A WAVE OF LOW PRESSURE WILL LIKELY DEVELOP EAST OF THE  
40N/70W BENCHMARK. SOME ADDITIONAL NORTHERN STREAM ENERGY SHOULD  
BEGIN AFFECTING THE NORTHERN TIER STATES BY EARLY NEXT WEEK  
ALTHOUGH THE CORE OF LOWER HEIGHTS ARE EXPECTED TO STAY IN CENTRAL  
CANADA.  
 
OVER THE EASTERN PACIFIC AND INTO THE WESTERN STATES...AN ACTIVE  
PATTERN IS IN STORE AS A NUMBER OF FEATURES OF INTEREST ARE NOTED.  
WITHIN THE SUBTROPICAL EASTERN PACIFIC...A CLOSED LOW SHOULD  
EVENTUALLY ACCELERATE TOWARD THE BAJA CA COAST OVER THE WEEKEND  
WHILE GRADUALLY SHEARING INTO THE SOUTHERN PLAINS BY THE  
CONCLUSION OF THE WEEKEND. FARTHER NORTH...AMPLIFIED FLOW WILL  
STEER LOWER HEIGHTS INTO THE PACIFIC NORTHWEST WITH SOME VARIANCE  
AMONG THE AVAILABLE GUIDANCE. GRADUALLY THIS WILL LEAD TO A  
PRONOUNCED NEGATIVE HEIGHT ANOMALY OVER THE WESTERN U.S. FOR THE  
DAY 5-7...DECEMBER 3-5 WINDOW. IN ADVANCE OF THIS LONGWAVE  
TROUGH...A SLOW-MOVING...SHARP FRONTAL ZONE SHOULD SET UP OVER THE  
CENTRAL U.S. ALTHOUGH DETAILS ARE RATHER FUZZY GIVEN VAST MODEL  
SPREAD.  
 
DURING THE FIRST COUPLE OF DAYS OF THE PERIOD...MODELS ARE WITHIN  
REASONABLE TOLERANCE OF ONE ANOTHER. THE ONE EXCEPTION WOULD BE  
WITH THE FEATURE OVER THE SUBTROPICAL PACIFIC WITH MODEL TRENDS  
FAVORING A SLOWER EVOLUTION THAN PRIOR DAYS WOULD SUGGEST. THE 00Z  
CMC IS A FAST OUTLIER WHILE THE 06Z/00Z GFS DAMPEN THE SYSTEM  
ENOUGH TO BE OF LITTLE TO NO CONSEQUENCE TO THE SOUTHWESTERN TO  
SOUTH-CENTRAL U.S. REGARDING THE SHORTWAVE TROUGH PASSING THE  
NORTHEASTERN STATES THIS WEEKEND...THE GFS/ECMWF HAVE BEEN  
EXHIBITING OPPOSITE TRENDS WITH THE GFS MOVING TOWARD GREATER  
AMPLIFICATION...MORE CONSISTENT WITH THE 00Z UKMET. IF THE 00Z GFS  
WERE TO VERIFY...A RATHER DEEP SURFACE CYCLONE WOULD FORM OFFSHORE  
OF NEW ENGLAND ON MONDAY MORNING ALTHOUGH ITS EASTWARD TRACK WOULD  
MOVE IT OUT TO SEA. ACROSS THE WESTERN U.S...MODEL SPREAD BECOMES  
A NUISANCE BY AS EARLY AS DAY 5/SUNDAY. FOR MULTIPLE MODEL  
RUNS...IT APPEARED SOLUTIONS WERE LOCKED INTO A SLOW-MOVING  
LONGWAVE TROUGH GENERALLY CENTERED OVER THE SOUTHWESTERN U.S. THIS  
SCENARIO FAVORS A SLOW EASTWARD PROPAGATION OF THE SURFACE FRONT  
AS HEIGHTS BUILD IN ADVANCE. HOWEVER...THE 00Z ECMWF MADE A MARKED  
SHIFT FROM THE CLUSTER FAVORING A QUICK MOVING TROUGH ACCOMPANIED  
BY CONSIDERABLE SURFACE LOW DEVELOPMENT ACROSS THE GREAT LAKES ON  
MONDAY EVENING. THIS SEEMED TO BE IN THE MINORITY HOWEVER WHICH  
CASTS SOME DOUBT IN ITS FORECAST. THE EVOLUTION BETWEEN THE GLOBAL  
MODELS VARY AHEAD OF THESE DIFFERENCES WITH THE 06Z GFS DEPICTING  
A PAIR OF TROUGHS APPROACHING THE WEST COAST WHILE OTHER SOLUTIONS  
FAVOR ONE CONSOLIDATED SYSTEM. ALL AND ALL...THE CONFIDENCE HAS  
DIMINISHED INTO EARLY NEXT WEEK AS MODELS STRAY FROM ONE ANOTHER.  
 
GIVEN THE BUILDING UNCERTAINTY IN THE MOST RECENT MODEL  
CYCLE...DECIDED TO KEEP 40 PERCENT OF CONTINUITY IN THE MIX  
THROUGHOUT. THE REMAINING 60 PERCENT WAS COMPRISED OF AN EVEN  
SPLIT AMONG THE 00Z CMC AND 00Z ECMWF/NAEFS ENSEMBLE MEANS. THIS  
SCENARIO STAYED ON THE SLOWER SIDE WHILE DISREGARDING THE  
CURRENTLY OUTLANDISH 00Z ECMWF.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
THROUGHOUT MUCH OF THE PERIOD...ABOVE AVERAGE TEMPERATURES WILL BE  
THE NORM GIVEN THE ABSENCE OF ANY ARCTIC INTRUSIONS. THE MOST  
ANOMALOUS READINGS SHOULD BE FROM THE ROCKIES EASTWARD TO THE MS  
RIVER VALLEY WITH EXPECTED HIGHS AROUND 10 TO POSSIBLY 20 DEGREES  
ABOVE CLIMATOLOGY THROUGH MONDAY. EVENTUALLY COOLING TEMPERATURES  
CAN BE EXPECTED AS THE UPSTREAM TROUGH MAKES ITS WAY TOWARD THE  
CENTRAL U.S. WIDESPREAD 50S AND 60S ARE LIKELY OVER THE CENTRAL  
PLAINS ALTHOUGH DAILY TEMPERATURE RECORDS ARE NOT EXPECTED TO BE  
BROKEN. THE ONLY COOL SPOT WILL BE ACROSS THE WESTERN STATES  
DURING THE DAY 5-7...DECEMBER 3-5 TIMEFRAME AS HEIGHTS LOWER OVER  
THE REGION.  
 
LOOKING AT PRECIPITATION THREATS...RAIN SHOWERS ARE LIKELY ALONG  
THE TRAILING FRONT OVER THE SOUTHEASTERN U.S. THIS WEEKEND WITH  
SOME SCATTERED ACTIVITY FARTHER NORTH OVER THE GREAT LAKES/NEW  
ENGLAND UNDERNEATH THE UPPER TROUGH ITSELF. ACROSS THE WESTERN  
STATES...LONGWAVE TROUGHING WILL SPREAD A BROAD AREA OF  
PRECIPITATION WITH SNOW ACROSS THE HIGHER ELEVATIONS. LOCAL  
OROGRAPHICS SHOULD DICTATE WHERE HEAVIER AMOUNTS WILL RESIDE WITH  
THE GUIDANCE UNCERTAIN EXACTLY WHAT MOUNTAIN RANGES WILL MAXIMIZE  
THEIR TOTALS. MODEL SPREAD IS ON THE HIGHER SIDE AS THE SYSTEM  
TRACKS TOWARD THE HIGH PLAINS BUT WOULD EXPECT A SHIELD OF  
SHOWERS/THUNDERSTORMS TO BREAK OUT ALONG THE SLOW-MOVING COLD  
FRONT ACROSS THE CENTRAL U.S. UP TOWARD THE GREAT LAKES BY EARLY  
NEXT WEEK.  
 
RUBIN-OSTER  
 

 
 
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