025  
FXUS02 KWBC 131600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1100 AM EST SAT JAN 13 2018  
 
VALID 12Z TUE JAN 16 2018 - 12Z SAT JAN 20 2018  
 
...WINTER COASTAL STORM THREAT FOR THE ERN MID-ATLANTIC AND  
ESPECIALLY NEW ENGLAND THIS WEEK...  
...EARLY-MIDWEEK WET/UNSETTLED FLOW INTO THE NWRN U.S. SPREADS  
DOWN ACROSS THE WEST LATER WEEK...  
   
..PATTERN OVERVIEW
 
 
THE FLOW PATTERN EARLY-MIDWEEK WILL FEATURE A HIGHLY AMPLIFIED  
E-CENTRAL U.S. TROUGH ALOFT AND AN EXPANSIVE ARCTIC SURFACE HIGH  
SETTLING WELL SOUTH ACROSS THE CENTRAL AND ERN US...DUG TO THE LEE  
OF A SHARP INTERMOUNTAIN WEST/ROCKIES MID-UPPER LEVEL RIDGE. THIS  
RIDGE IS FORECAST TO BREAK DOWN MID-LATE WEEK AS SEVERAL PACIFIC  
SHORTWAVES PUNCH INLAND. THE SURFACE HIGH WILL STEADILY MODERATE  
AS THE PATTERN BECOMES LESS AMPLIFIED TO CLOSE OUT THE WEEK AS THE  
ERN TROUGH LIFTS OUT ACROSS THE ATLANTIC...RIDGING ALOFT WORKS  
OVER THE N-CENTRAL US...AND SRN STREAM SHORTWAVE TROUGHING MOVES  
TO THE SRN/SERN US. MUCH STRONGER TROUGH/HEIGHT FALLS MEANHWILE  
SETTLES IN OVER THE WEST THU-NEXT SAT.  
 
   
..GUIDANCE ASSESSMENT/PREFERENCES
 
 
MEDIUM RANGE MODEL AND ENSEMBLE FORECAST SPREAD AND UNCERTAINTY  
SEEM LESS THAN NORMAL. OVERALL...THE 06 UTC GFS/GEFS AND 00 UTC  
ECMWF/ECMWF ENSEMBLE MEAN SEEMS FAIRLY WELL CLUSTERED FOR THE MOST  
PART THIS WEEK. THAT SAID...PERHAPS THE BIGGEST DIFFERENCE IS WITH  
RESPECT TO THE PROXIMITY AND ENHANCED THREAT POTENTIAL FOR THE  
NERN US. THE CLOSER TRACK TO THE COAST OF THE ECMWF AND ECMWF  
ENSEMBLES OFFERS BETTER RUN TO RUN CONTINUITY AND SEEM A BIT MORE  
LIKELY GIVEN THE AMPLITUDE OF THE UPSTREAM RIDGE LEADING INTO  
DEVELOPMENT. THE WPC MEDIUM RANGE PRODUCT SUITE WAS ACCORDINGLY  
PRIMARILY DERIVED FROM A BLEND OF THESE GUIDANCE PIECES...BUT THE  
ECMWF AND ECMWF ENSEMBLES WERE MORE HEAVILY WEIGHTED.  
 
   
..WEATHER/THREATS HIGHLIGHTS
 
 
A WELL DEVELOPED CLIPPER SYSTEM IS FORECAST TO DELIVER ANOTHER  
ROUND OF SNOWFALL TO THE GREAT LAKES, FOLLOWED BY A FRESH SURGE OF  
ARCTIC AIR BEHIND A REINFORCING COLD FRONT. FRIGID CONDITIONS ARE  
EXPECTED ACROSS THE UPPER MIDWEST AND EXTENDING SOUTHEAST TO THE  
OHIO VALLEY ON TUESDAY, WITH HIGHS 20 TO 30 DEGREES BELOW NORMAL  
FOR MID JANUARY. OVERNIGHT LOWS COULD EASILY REACH THE MINUS 20S  
ACROSS PARTS OF NORTH DAKOTA AND MINNESOTA, AND SOME RECORD LOW  
TEMPERATURES WILL BE POSSIBLE WHERE RADIATIONAL COOLING IS  
MAXIMIZED UNDER THE SURFACE HIGH.  
 
ABOVE AVERAGE TEMPERATURES ARE EXPECTED NEXT WEEK FOR THE  
SOUTHWESTERN U.S. AND EXTENDING INTO THE GREAT BASIN.  
PRECIPITATION INCREASES AGAIN OVER THE PACIFIC NORTHWEST AND  
NORTHERN CALIFORNIA TUESDAY WITH MULTIPLE ROUNDS OF UNSETTLED  
CONDITIONS FOR THE COAST THROUGH FRIDAY. EAST OF THE CASCADES,  
THERE SHOULD BE AT LEAST SOME RESPITE BETWEEN THE FIRST AND SECOND  
SYSTEMS. THE SYSTEM TOWARDS THE END OF THE WEEK ADVECTS MORE  
MOISTURE INTO THE REGION WITH SOME LOCATIONS POSSIBLY RECEIVING A  
FEW INCHES OF RAIN AND OVER A FOOT OF MOUNTAIN SNOW.  
 
D. HAMRICK  
 

 
 
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