749  
FXUS02 KWBC 051559  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1058 AM EST TUE DEC 05 2017  
 
VALID 12Z FRI DEC 08 2017 - 12Z TUE DEC 12 2017  
   
..GUIDANCE AND PREDICTABILITY ASSESSMENTS
 
 
THERE REMAINS ABOVE AVERAGE CONFIDENCE IN THE LONGWAVE PATTERN  
HIGHLIGHTED ALOFT BY A HIGHLY AMPLIFIED RIDGE IN THE WEST AND  
TROUGH IN THE EAST...BUT BELOW AVERAGE IN THE EMBEDDED SMALL-MID  
SCALE WEAKER/QUICK SYSTEMS MOVING THROUGH THE FLOW. THE MODELS  
HAVE WAVERED ON WHICH ONE MAY OR MAY NOT DEVELOP. IN ORDER TO  
LIMIT MODEL CHASING...OPT TO MAINTAIN AS MUCH WPC CONTINUITY AS  
FEASIBLE WITH USE OF A CONSENSUS OF THE MOST RECENT AND REASONABLY  
WELL CLUSTERED FORECAST SOLUTIONS OF THE 06 UTC GFS/GEFS MEAN AND  
00 UTC ECMWF/ECMWF ENSEMBLE MEAN.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
THE LARGE SCALE PATTERN WILL FAVOR WARM DAYTIME TEMPS OVER MOST OF  
THE WEST (OUTSIDE AREAS CAUGHT UNDER LOW ELEVATION INVERSIONS) AND  
CHILLY READINGS OVER THE EAST. THE PLAINS WILL BE THE DIVIDING  
LINE BETWEEN THESE TWO REGIMES...WITH SOME OSCILLATION IN RESPONSE  
TO SHORTWAVES ALOFT/FRONTAL SYSTEMS. OVER THE WEST AND AT TIMES  
INTO THE PLAINS...SOME MAX TEMP ANOMALIES SHOULD REACH AT LEAST  
PLUS 10-15F AT SOME LOCATIONS...ESPECIALLY OVER THE NRN HIGH  
PLAINS. MEANWHILE...SOME READINGS OVER THE EAST MAY BE BELOW  
NORMAL BY A SIMILAR MAGNITUDE...ESPECIALLY IN THE SOUTH.  
 
THERE WILL BE AN EXTENDED PERIOD OF LAKE EFFECT SNOW WITH  
SIGNIFICANT TOTALS POSSIBLE AT SOME LOCATIONS. DOWNSTREAM ON THE  
NW SIDE OF GULF OF SEVERAL POTENTIAL GULF OF MEXICO/ATLANTIC  
COASTAL WAVES...THERE IS ALSO SOME THREAT FOR ORGANIZED PRECIP TO  
EXTEND FROM THE SRN/SERN US/FL NORTHEASTWARD WITH SOME ACTIVITY  
REACHING BACK INTO THE MID-ATLANTIC AND NORTHEAST. THIS WOULD BE  
MAXIMIZED IF DYNAMIC SUPPORT COMES TOGETHER TO FOCUS DEEPENING OF  
ANY OF THE LOWS MORE THAN DEPICTED IN WPC PROGS. A FEW ENSEMBLE  
MEMBERS OFFER THIS HIGHLY UNCERTAIN POTENTIAL. OVER THE EAST COAST  
STATES THERE MAY ALSO BE SOME SNOW IN THE NW FRINGE OF THE  
MOISTURE SHIELD. UPSTREAM...LOCATIONS FROM THE NRN PLAINS INTO THE  
APPALACHIANS MAY SEE ONE OR MORE PERIODS OF GENERALLY LIGHT PRECIP  
(MOSTLY SNOW) WITH FAST MOVING AND COLD AIR REINFORCING  
WAVES/FRONTS. THIS WOULD FAVOR THE WESTERN SLOPES OF THE  
APPALACHIANS WHICH MAY SEE SOME ENHANCEMENT OF SNOWFALL.  
 
SCHICHTEL  
 

 
 
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