061  
FXUS02 KWBC 081601  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1100 AM EST MON JAN 08 2018  
 
VALID 12Z THU JAN 11 2018 - 12Z MON JAN 15 2018  
   
..WINTRY MIX FOR THE NORTHEAST THIS WEEKEND
 
 
   
..OVERVIEW
 
 
A SHORTWAVE ENTERING THE PACIFIC NORTHWEST EARLY IN THE PERIOD  
SHOULD PHASE WITH SOUTHERN STREAM ENERGY LIFTING OUT OF THE LOWER  
MISSISSIPPI VALLEY BY THE WEEKEND. AT THE SURFACE THIS TRANSLATES  
TO A FRONTAL SYSTEM IN THE CENTRAL US ON THURSDAY MOVING EASTWARD  
WHILE AT THE SAME TIME A SURFACE LOW LIFTS NORTHEASTWARD THROUGH  
THE MID-ATLANTIC AND INTO NEW ENGLAND THIS WEEKEND. IN THE WAKE OF  
THIS...RIDGING SHOULD BUILD OUT WEST AS BROAD TROUGHING ONCE AGAIN  
BUILDS ACROSS THE EAST.  
 
   
..GUIDANCE ASSESSMENT AND PREFERENCES
 
 
MODELS CONTINUE TO REMAIN FAIRLY WELL-CLUSTERED FOR THE FIRST FEW  
DAYS OF THE MEDIUM RANGE PERIOD, ALTHOUGH THE ECMWF WAS SLOWER  
WITH THE SHORTWAVE ENTERING THE PACIFIC NORTHWEST ON THURSDAY. A  
BLEND BETWEEN THE SLOWER 00Z ECMWF AND SLIGHTLY FASTER 06Z GFS  
PROVIDED A GOOD POSITION IN LINE WITH THE ENSEMBLES. BY FRIDAY,  
THE BIG QUESTION CONTINUES TO BE HOW A SOUTHERN STREAM SURFACE LOW  
EVOLVES AND EXACTLY HOW IT TRACKS AS IT HEADS NORTHEASTWARD THIS  
WEEKEND. NEW MODEL GUIDANCE PROVIDED LITTLE CHANGE FROM THE  
PREVIOUS SHIFT THINKING WITH THE 00Z ECMWF REMAINING WELL  
NORTHWEST OF ITS ENSEMBLE MEAN, WHILE THE 06Z GFS IS OFF TO THE  
EAST OF ITS MEAN (WHICH IT OFTEN CAN BE). THE 00Z CMC/UKMET  
CONTINUED TO REPRESENT A MIDDLE GROUND WHICH IS NEAR THE ONGOING  
ENSEMBLE CONSENSUS. THUS THE WPC BLEND FOR THIS SYSTEM USED A 00Z  
CMC/UKMET BLEND (JUST CMC AFTER 144 HOURS WHEN THE UKMET DROPS  
OFF) WITH THE ENSEMBLE MEANS TO TAKE THE SURFACE LOW TOWARDS THE  
GULF OF MAINE ON SUNDAY AND THEN INTO THE CANADIAN MARITIMES. BY  
MONDAY, A MAJORITY ENSEMBLE MEAN GUIDANCE BLEND WAS USED. THIS  
FORECAST REMAINS VERY CLOSE TO PREVIOUS SHIFT CONTINUITY.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
LOW PRESSURE NEARING THE WESTERN GREAT LAKES ON THURSDAY WILL  
CONTINUE TO FOCUS MODEST TO PERHAPS LOCALLY HEAVY SNOW TO THE  
NORTH AND NORTHWEST OF ITS TRACK (STRADDLING THE SHORT AND MEDIUM  
RANGE). MEANWHILE, RAIN WILL INCREASE IN COVERAGE IN THE DEEP  
SOUTH AND EVENTUALLY THE MID-ATLANTIC AS THE SOUTHERN SURFACE LOW  
ORGANIZES AND LIFTS NORTHEASTWARD LATE FRIDAY INTO SATURDAY. THERE  
CONTINUES TO BE A SIGNAL FOR APPRECIABLE ICING IN THE TRANSITION  
ZONE BETWEEN PLAIN RAIN AND JUST SNOW TO THE NORTH AND NORTHEAST  
OF THE LOW, ALONG THE ATTENDANT FRONTAL BOUNDARY. BUT WHERE THIS  
MAY SET UP EXACTLY IS VERY MUCH IN QUESTION DUE TO THE UNCERTAINTY  
IN THE TRACK OF THE MAIN LOW. OUT WEST, MODERATE TO HEAVY COASTAL  
RAINS LATE THIS WEEK WILL LEAD TO A MOSTLY DRY PERIOD TO FOLLOW,  
WITH ANOTHER ROUND OF PRECIPITATION POSSIBLY TRYING TO MAKE ITS  
WAY ONSHORE BY EARLY NEXT WEEK.  
 
TEMPERATURES WILL BE A BIT VARIABLE OVER THE CONUS BUT GENERALLY  
10-20 DEGREES BELOW AVERAGE BEHIND THE ARCTIC FRONT ACROSS THE  
PLAINS BUT 10-20 DEGREES ABOVE AVERAGE AHEAD OF THE FRONT IN THE  
EAST. SOME AREAS IN THE NORTHEAST/MID-ATLANTIC COULD SEE HIGH  
TEMPERATURES 40-50 DEGREES WARMER THAN WHAT WAS OBSERVED THIS PAST  
WEEKEND. AFTER THE FRONT AND SECONDARY BOUNDARY CLEAR THE COAST  
THIS WEEKEND, TEMPERATURES WILL AGAIN RETURN TO BELOW AVERAGE  
NEARLY EVERYWHERE EAST OF THE ROCKIES.  
 
SANTORELLI  
 

 
 
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