333  
FXUS02 KWBC 080533  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1232 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
 
 
THE WESTERN RIDGE/EASTERN TROUGH PATTERN WILL FALL INTO PLACE BY  
THIS WEEKEND AS A BIG WARMUP IN THE EAST BECOMES JUST A MEMORY BY  
NEXT WEEK. A FRONTAL SYSTEM IN THE CENTRAL US THURSDAY WILL MOVE  
EASTWARD AS A SOUTHERN LOW PRESSURE LIFTS NORTHEASTWARD THROUGH  
THE MID-ATLANTIC ON SATURDAY AND INTO NEW ENGLAND BY SUNDAY. HIGH  
PRESSURE IN ITS WAKE WILL BRING A MUCH DRIER (AND COLDER) AIRMASS  
BACK INTO THE EAST FOR NEXT MONDAY. THE WEST WILL SEE ONE SYSTEM  
MOVE INTO WA/OR AND THE INTERIOR NORTHWEST ON THURSDAY BEFORE  
UPPER RIDGING BRINGS A QUIETER PERIOD TO THE REGION. PRECIPITATION  
MAY TRY TO PUSH INTO COASTAL WA/OR NEXT WEEK.  
 
   
..GUIDANCE ASSESSMENT AND PREFERENCES
 
 
MODELS REMAIN FAIRLY WELL-CLUSTERED FOR THE FIRST FEW DAYS OF THE  
PERIOD, THOUGH THE GFS/UKMET WAS QUICKER THAN THE ENSEMBLE MEANS  
WITH THE PACIFIC SYSTEM THURSDAY. BLENDED POSITION WAS IN LINE  
WITH THE ENSEMBLES. ON FRIDAY, QUESTION HAS BEEN HOW THE SOUTHERN  
PART OF THE SYSTEM (COMBINATION OF PACIFIC SYSTEM MOVING THROUGH  
CALIFORNIA IN THE SHORT TERM AND AN ARCTIC FRONT DIVING OUT OF THE  
HIGH PLAINS) WILL EVOLVE AND THEN WHERE IT WILL TRACK AS IT HEADS  
NORTHEASTWARD. 12Z ECMWF REMAINED WELL NORTHWEST OF ITS ENSEMBLE  
MEAN (AND THE GEFS/CANADIAN MEANS) WHILE THE 18Z/12Z GFS WERE  
QUICKER THAN THE MEANS (WHICH IT CAN OFTEN BE). 12Z CANADIAN/UKMET  
REPRESENTED A GOOD MIDDLE GROUND THAT HAS BEEN NEAR THE ONGOING  
ENSEMBLE CONSENSUS. USED THE CANADIAN AS THE DETERMINISTIC WEIGHT  
(AFTER THE UKMET STOPPED AT F144) TO TAKE THE SFC LOW TOWARD THE  
GULF OF MAINE SUNDAY AND THEN OUT THROUGH THE CANADIAN MARITIMES.  
12Z ECMWF ENSEMBLE MEAN AND NAEFS MEAN FORMED THE MAJORITY  
ENSEMBLE WEIGHTING NEXT SUN/MON.  
 
   
..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). RAIN WILL INCREASE IN COVERAGE IN THE LOWER MISSISSIPPI  
VALLEY INTO THE SOUTHEAST AS THE SOUTHERN SFC LOW ORGANIZES AND  
LIFTS NORTHEASTWARD LATE FRIDAY INTO SATURDAY. ON ITS FORECAST  
TRACK THROUGH THE CENTRAL APPALACHIANS, THE POTENTIAL EXISTS FOR  
ICING JUST NORTH OF THIS LOW AND ATTENDANT FRONTAL BOUNDARY TO ITS  
NORTHEAST. THERE HAS BEEN A SIGNAL FOR APPRECIABLE ICING IN THE  
ZONE BETWEEN PLAIN RAIN AND JUST SNOW FARTHER NORTH NEAR THE  
US/CANADIAN BORDER, BUT WHERE THAT MAY SET UP IS VERY MUCH IN  
QUESTION DUE TO THE UNCERTAINTY IN THE TRACK OF THE MAIN LOW.  
 
TEMPERATURES WILL BE A BIT VARIABLE OVER THE CONUS BUT GENERALLY  
10-20 DEGREES BELOW AVERAGE BEHIND THE ARCTIC FRONT (STARTING IN  
MONTANA/NORTH DAKOTA ON WEDNESDAY) BUT 10-20 DEGREES ABOVE AVERAGE  
AHEAD OF THE FRONT. SOME AREAS IN THE NORTHEAST/MID-ATLANTIC WILL  
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 RETURN TO BELOW AVERAGE  
NEARLY EVERYWHERE EAST OF THE ROCKIES.  
 
FRACASSO  
 

 
 
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