197  
FXUS02 KWBC 041600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1100 AM EST MON DEC 04 2017  
 
VALID 12Z THU DEC 07 2017 - 12Z MON DEC 11 2017  
   
..OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES
 
 
LATEST GUIDANCE REMAINS IN EXCELLENT AGREEMENT ON THE MAINTENANCE  
OF AN AMPLIFIED AND STABLE LONGWAVE PATTERN FEATURING A WEST COAST  
RIDGE AND EASTERN NORTH AMERICA TROUGH. THE PRIMARY FORECAST  
ISSUES WILL BE WITH EMBEDDED SHORTWAVES AND ASSOCIATED SURFACE  
WAVES/FRONTS, WHICH DUE TO THEIR SCALE AND FAST SUPPORTING FLOW  
ALOFT MAY BE DIFFICULT TO RESOLVE SATISFACTORILY UNTIL THE SHORT  
RANGE TIME FRAME.  
 
THE UPDATED FORECAST STARTED WITH A MOSTLY OPERATIONAL BLEND  
(00Z-06Z GFS AND 00Z ECMWF/UKMET) FOR DAYS 3-5 THU-SAT TO REFLECT  
THE MOST COMMON IDEAS OF GUIDANCE WHILE ACCOUNTING FOR SPREAD IN  
THE SPECIFICS. THEN THE FORECAST INCORPORATED SLIGHTLY MORE 06Z  
GEFS/00Z ECMWF MEAN INPUT RELATIVE TO THE GFS/ECMWF RUNS BY DAYS  
6-7 SUN-MON DUE TO DECREASING CONFIDENCE IN DETAILS.  
 
LATE WEEK INTO EARLY WEEKEND THERE WILL LIKELY BE MULTIPLE WAVES  
ALONG A WESTERN ATLANTIC/GULF OF MEXICO FRONT, WITH GUIDANCE  
VARYING IN SPECIFICS. AN OPERATIONAL MODEL COMPROMISE FOR TIMING  
OF BEST DEFINED LOW PRESSURE HAS REASONABLE SUPPORT FROM THE  
ENSEMBLE MEANS. UPSTREAM, GFS RUNS HAD BEEN ON THE STRONG SIDE  
WITH ENERGY ALOFT/SURFACE LOW PRESSURE DIVING INTO THE EAST BY  
SAT. LATEST RUNS MAY STILL BE A TAD STRONG BUT SEEM TO BE  
TRENDING TOWARD CONSENSUS. THE 00Z CMC IS THE DEEP EXTREME WITH  
ITS SYSTEM REACHING THE GREAT LAKES. THE EASTERN U.S. SYSTEM ON  
SAT SHOULD TRANSLATE EAST/NORTHEAST THEREAFTER WITH LOW PRESSURE  
IN THE VICINITY OF THE CANADIAN MARITIMES OR NORTHERN NEW ENGLAND  
BY SUN. THERE IS A DECENT SIGNAL FOR ANOTHER SYSTEM OR TWO  
DROPPING SOUTH FROM CANADA INTO THE NORTHERN TIER SUN-MON WITH THE  
EXPECTED DIFFERENCES IN DETAILS/TIMING.  
   
..WEATHER HIGHLIGHTS
 
 
THE LARGE SCALE PATTERN WILL FAVOR WARM DAYTIME TEMPS OVER MOST OF  
THE WEST 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 THE PLAINS, SOME MAX TEMP ANOMALIES SHOULD REACH AT  
LEAST PLUS 10-15F AT SOME LOCATIONS. SOME READINGS OVER THE EAST  
MAY BE BELOW NORMAL BY A SIMILAR MAGNITUDE. FOR THE 5-DAY PERIOD  
AS A WHOLE THE LOWEST ANOMALIES SHOULD EXTEND FROM THE OH  
VALLEY/CENTRAL APPALACHIANS SOUTHWARD. EXPECT AN EXTENDED PERIOD  
OF LAKE EFFECT SNOW WITH SIGNIFICANT TOTALS POSSIBLE AT SOME  
LOCATIONS. ON THE NORTHWEST SIDE OF GULF/ATLANTIC WAVINESS, LATE  
WEEK PRECIP WILL EXTEND FROM THE SOUTHERN TIER NORTHEASTWARD WITH  
SOME ACTIVITY POSSIBLY REACHING BACK TO THE MID  
ATLANTIC/NORTHEAST. HIGHEST AMOUNTS ARE MOST LIKELY ALONG THE  
NC/SC COAST. OVER THE EAST COAST STATES THERE MAY BE SOME SNOW IN  
THE NORTHWEST FRINGE OF THE MOISTURE SHIELD. FINALLY, LOCATIONS  
FROM THE NORTHERN PLAINS INTO THE APPALACHIANS MAY SEE ONE OR MORE  
PERIODS OF GENERALLY LIGHT PRECIP (MOSTLY SNOW) WITH FAST MOVING  
WAVES/FRONTS. WESTERN SLOPES OF THE APPALACHIANS MAY SEE SOME  
ENHANCEMENT OF SNOWFALL.  
 
RAUSCH  
 

 
 
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