462  
FXUS02 KWBC 060456  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1155 PM EST TUE DEC 05 2017  
 
VALID 12Z SAT DEC 09 2017 - 12Z WED DEC 13 2017  
   
..OVERVIEW
 
 
RESILIENT RIDGE/TROUGH PATTERN SHOWS NO SIGN OF BREAKING DOWN INTO  
THE MIDDLE OF NEXT WEEK. THIS WILL CONTINUE THE STABLE SYNOPTIC  
PATTERN OF MILD/DRY IN THE WEST, A TRANSITION ZONE OF TEMPERATURES  
IN THE CENTRAL STATES (PLAINS TO MISSISSIPPI VALLEY), AND COLD IN  
THE EAST WITH PRECIPITATION FOCUSED IN THE GREAT LAKES.  
 
...GUIDANCE AND PREDICTABILITY ASSESSMENTS AND WEATHER  
HIGHLIGHTS...  
 
THE DETERMINISTIC MODELS HAVE WAVERED GENERALLY WITHIN THE  
MULTI-CENTER ENSEMBLE SPREAD FOR THE PAST SEVERAL DAYS WITH NO  
MODEL SINGLY THE BEST OVER ALL THE CONUS. PREFER TO MAINTAIN THE  
WESTERN RIDGE WITH NO INVASIONS OF PACIFIC SHORTWAVES (PER  
PREVIOUS GFS/ECMWF RUNS) WHILE FOLLOWING THE LEAD OF THE ENSEMBLE  
CONSENSUS IN THE EAST WITH RESPECT TO TIMING/TRACK OF EMBEDDED  
SHORTWAVES IN THE BROAD CYCLONIC FLOW. GIVEN THE RELATIVELY WEAK  
SURFACE REFLECTION, OPTED TO USE A DETERMINISTIC CONSENSUS TO  
START WITH A TRANSITION TOWARD THE ENSEMBLE MEANS FOR NEXT  
TUE/WED. SEVERAL CLIPPERS WILL SWING THROUGH THE EAST WITH A  
RENEWED COLD SHOT OF CANADIAN AIR BUT GENERALLY LIGHT PRECIP --  
THE EXCEPTION WILL BE AROUND THE GREAT LAKES. TEMPERATURES WILL BE  
ABOUT 5-15 DEGREES ABOVE AVERAGE IN THE WEST (OUTSIDE THE INTERIOR  
VALLEY AREAS OF WA/OR UNDER AN INVERSION) AND ABOUT 5-15 DEGREES  
BELOW AVERAGE IN THE EAST.  
 
THERE REMAINS THE CHANCE FOR A MORE ROBUST NORTHERN STREAM SYSTEM  
TO TAKE THE LONG WAY THROUGH THE EAST (INTO THE DEEP SOUTH) NEXT  
WEEK AND PERHAPS AMPLIFY OFF THE EAST COAST, BUT THIS HAS BEEN  
ADVERTISED FOR A FEW DAYS RUNNING AT THE DAY 6-8 LEAD TIME.  
HOWEVER, THE ENSEMBLES ARE IN GOOD AGREEMENT AND HAVE BEEN  
CONSISTENT CONSIDERING THE PATTERN BY NEXT WEDNESDAY WITH LOW  
PRESSURE NEAR THE GULF OF MAINE.  
 
FRACASSO  
 

 
 
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