565  
FXUS02 KWBC 281526  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1026 AM EST SUN JAN 28 2018  
 
VALID 12Z WED JAN 31 2018 - 12Z SUN FEB 04 2018  
   
..WINTRY WEATHER FOR THE EAST AND ALSO THE NORTHWESTERN US
 
 
   
..OVERVIEW AND GUIDANCE PREFERENCES
 
 
UPPER PATTERN WILL FEATURE WESTERN RIDGING JUST OFF THE PAC NW  
COAST WITH BROAD TROUGHING FOR MOST OF THE LOWER 48 (EAST OF THE  
ROCKIES). MODELS/ENSEMBLES REMAIN IN GOOD AGREEMENT OVERALL AND A  
DETERMINISTIC BLEND OF THE RECENT GFS/ECMWF/CANADIAN/UKMET OFFERED  
A REASONABLE STARTING POINT FOR WED/THU AS A SYSTEM MOVES OUT OF  
THE PLAINS AND INTO THE NORTHEAST AND LOWER MS/OH VALLEY. MODELS  
HAVE THEN BEEN SHOWING VARYING DEGREES OF SFC WAVE DEVELOPMENT OUT  
OF THE LOWER MS VALLEY/SOUTHEAST NORTHEASTWARD THROUGH THE  
MID-ATLANTIC ON FRIDAY THEN INTO THE ATLANTIC SATURDAY OFF THE NEW  
ENG COAST. AS SUCH DEVELOPMENT IS SENSITIVE TO SMALLER SCALE  
FEATURES WITH LONG LEAD TIMES, ENSEMBLE TRENDS WILL REMAIN MORE  
USEFUL FOR THE NEXT COUPLE OF DAYS THAN ANY GIVEN DETERMINISTIC  
RUN. BLENDED/CONSENSUS POSITION TAKES A WEAK WAVE (OR MULTIPLE  
WAVES) THROUGH SE VIRGINIA. CLIPPER SYSTEM OUT OF CANADA WILL DROP  
DOWN NEXT WEEKEND WITH ANOTHER PUSH OF ARCTIC AIR FOR  
CENTRAL/EASTERN MONTANA INTO THE HIGH PLAINS AND UPPER  
MIDWEST/GREAT LAKES. TRENDED TOWARD A MAJORITY ENSEMBLE MEAN  
WEIGHTING BY NEXT WEEKEND AS THE MODELS DIVERGE IN HOW MUCH COLD  
AIR TO PUSH SOUTHWARD (GFS WAS RATHER AGGRESSIVE). UPSTREAM RIDGE  
CONFIGURATION/ORIENTATION/STRENGTH IS UNCERTAIN (SEE THE LATEST  
ALASKA MEDIUM RANGE DISCUSSION) WHICH WILL INFLUENCE THE SHAPE OF  
THE TROUGH OVER THE LOWER 48. FOR NOW, ENSEMBLE MEAN CONSENSUS  
WILL SERVE WELL.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
IN THE WEST, A POTENT LEAD SHORTWAVE TROUGH ENERGY/HEIGHT FALLS  
PUNCHES PROGRESSIVELY OUT FROM THE NWRN US TO THE N-CENTRAL US BY  
MIDWEEK. WEAKER UPSTREAM IMPULSES WILL SUPPORT ADDITIONAL PERIODS  
OF MODEST PRECIPITATION INCLUDING HEAVIER TERRAIN ENHANCED SNOWS  
ACROSS THE NWRN US AND ESPECIALLY THE NRN ROCKIES WITH ADDED NRN  
STREAM IMPULSES OF UNCERTAIN TIMINGS. EXPECT ANOTHER ROUND OF  
PRECIPITATION (MOSTLY SNOW) ALONG THE DIVIDE VIA UPSLOPE FLOW NEXT  
WEEKEND IN THE WAKE OF THE CLIPPER SYSTEM.  
 
DOWNSTREAM...A MAIN FRONT REACHES THE GREAT LAKES  
WED/THU...DRAGGING A TRAILING COLD FRONT THROUGH THE PLAINS AND  
INTO THE LOWER MS/OH VALLEY. THE SFC LOW CENTER WILL TRACK THROUGH  
SRN CANADA WITH MOST OF THE PRECIPITATION TO START...BUT INCREASED  
GULF MOISTURE WILL SUPPORT AN EXPANDED PRECIPITATION AREA  
ALONG/AHEAD OF THE COLD FRONT WED/THU ACROSS THE E-CENTRAL  
STATES/SOUTHEAST. ENOUGH COLD AIR SHOULD BE IN PLACE TO THE NORTH  
OF THE FRONT TO SUPPORT A WIDESPREAD SWATH OF LIGHT/MODERATE AND  
POTENTIALLY HEAVY SNOW PARALLEL TO ANY SFC LOW TRACK OR AT LEAST  
PARALLEL TO THE UPPER TROUGH AXIS PROPAGATION. NEXT WEEKEND,  
CLIPPER SYSTEM WILL SPREAD SOME LIGHT SNOW TO THE CENTRAL STATES  
INTO THE GREAT LAKES WITH RAIN INCREASING ALONG THE NW GULF COAST  
AS SOUTHEASTERLY RETURN FLOW RESUMES.  
 
FRACASSO/SCHICHTEL  
 

 
 
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