215  
FXUS02 KWBC 101916  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
215 PM EST WED JAN 10 2018  
 
VALID 12Z SAT JAN 13 2018 - 12Z WED JAN 17 2018  
   
..A SIGNIFICANT WINTER STORM EXITS THE NERN US SATURDAY
 
   
..A WET PATTERN TRANSITION NEXT WEEK FOR THE NWRN US/NRN CA
 
 
   
..OVERVIEW
 
 
A COMPLEX/DYNAMIC SYSTEM WITH A HIGHLY LIKELY THREAT OF HEAVY  
ICE/SNOW/RAIN AND UNSETTLED WEATHER OVERALL IN THE EAST ON  
SATURDAY WILL EXIT INTO THE CANADIAN MARITIMES BY SUNDAY AS THE  
WEATHER TURNS QUIET FOR A COUPLE DAYS OVER THE LOWER 48. A CLIPPER  
SYSTEM WILL WHISK DOWN THROUGH THE GREAT LAKES NEXT WEEK AND A  
WETTENED PACIFIC SYSTEM WILL PUSH INTO WA/OR/NRN CA TUESDAY THEN  
INLAND AS THE UPPER RIDGE YIELDS TO STRONG ONSHORE FLOW/PACIFIC  
ENERGY. THIS SCENARIO TRANSITIONS TO SUPPORT A PERIOD WITH SOME  
HEAVY NW US COASTAL PCPN.  
 
   
..UPDATED GUIDANCE ASSESSMENT/PREFERENCES
 
 
MUCH OF THE IMPLIED UNCERTAINTY SEEMS TO UNCHARACTERISTICALLY  
EXIST INTO THE BEGINNING OF THE MEDIUM RANGE FORECAST PERIOD THIS  
WEEKEND AS SEVERAL COMPLEX INTERACTIONS EFFECT THE DEVELOPMENT OF  
THE AFOREMENTIONED WEEKEND ERN US STORM. THE INHERENT ISSUES WITH  
THIS FEATURE HAS DEPENDENCY ON THE FLOW OVER THE DATA SPARSE ERN  
PACIFIC WHERE DOWNSTREAM FLOW EVOLUTIONS SEEMS QUITE SENSITIVE TO  
SUBTLE SYSTEM WAVELENGTH AND AMPLITUDE INITIALIZATION  
VARIANCE...EVEN THOUGH GOES-16 LOOPS OVER THE REGION TEND TO  
SUPPORT DECENT TROUGH/RIDGE AMPLITUDES ALOFT AND REASONABLE  
SPACING. WPC HAS REQUESTED A RECON FLIGHT...BUT THAT ADDITIONAL  
SAMPLING WOULD ONLY BE OVER THE GULF OF MEXICO WELL LATER IN THE  
PROCESS FRIDAY MORNING. THIS STORM HAS SOME ANALOG SIMILARITIES TO  
A SYSTEM JAN 30-FEB 1 1982 THAT PROVIDED A SIGNIFICANT  
MIDWEST/GREAT LAKES TO INTERIOR NERN US ICE/SNOW THREAT...BUT THAT  
STORM OFFERRED MORE SRN STREAM AMPLITUDE AND SEPARATION THAN MOST  
OF THE LATEST MODELS SHOW FOR THE UPCOMING SYSTEM. THE LATEST  
MODELS HAVE OVERALL TRENDED SLIGHTLY MORE SHEARED AND  
PROGRESSIVE...INCLUDING 12 UTC GUIDANCE EXCEPT FOR THE ECMWF. WPC  
MORNING PROGS DID NOT MAKE TOO MUCH OF A CONTINUITY LOW TRACK  
GIVEN THE UNCERTAINTY. WPC UPDATED AFTERNOON SURFACE  
FRONTS/PRESSURE PROGS TRENDED A BIT MORE TOWARD PROGRESSION AND  
THIS WAS CONSIDERED IN DERIVING THE DAYS 4-7 QPF AND WINTER  
WEATHER OUTLOOK PROBABILITIES.  
 
FORECAST CLUSTERING AND UNCERTAINTY SEEM MUCH REDUCED BY LATER  
WEEKEND INTO EARLY-MID NEXT WEEK FROM THE ERN PACIFIC INTO/ACROSS  
THE LOWER 48. ACCORDINGLY...A COMPOSITE BLEND OF THE QUITE  
COMPATABLE 06 UTC GFS/GEFS AND 00 UTC ECMWF/ECMWF ENSMEBLE MEAN  
SEEMS TO PROVIDE A SOLID BASIS FOR THIS PERIOD...ALBIET WITH  
GROWING VARIANCE INTO DAYS 6/7.  
 
   
..WEATHER HIGHLIGHTS
 
 
WELL ABOVE AVERAGE TEMPERATURES AND DEEPENED MOISTURE WILL BE  
SHUNTED OUT TO SEA AS THE SYSTEM MOVES THROUGH NEW ENGLAND ON  
SATURDAY...ENDING THE BRIEF WARM SPELL. HIGH PRESSURE WILL RETURN  
TEMPERATURES TO BELOW AVERAGE BY ABOUT 10-20 DEGREES. A CLIPPER  
SYSTEM WILL THEN BRING LIGHT SNOW TO THE GREAT LAKES (WITH LOCAL  
ENHANCEMENT) AND ANOTHER PUSH OF COLDER AIR (SUB-ZERO HIGHS FOR  
MUCH OF THE DAKOTAS AND MINNESOTA ON MONDAY). FOR MUCH OF THE  
WEST...ABOVE AVERAGE TEMPERATURES WILL RULE INTO AT EARLY NEXT  
WEEK THANKS TO THE UPPER RIDGE. PRECIPITATION CHANCES WILL  
INCREASE ALONG THE COAST STARTING MONDAY AND THEN WORK THEIR WAY  
INLAND NEXT TUE-WED THROUGH THE CENTRAL AND NRN INTERMOUNTAIN WEST  
AND ROCKIES. SNOW LEVELS WILL BE ON THE HIGHER SIDE TO START...BUT  
THEN DROP BEHIND THE ASSOCIATED FRONT.  
 
SCHICHTEL  
 

 
 
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