849  
FXUS02 KWBC 011600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1159 AM EDT WED NOV 01 2017  
 
VALID 12Z SAT NOV 04 2017 - 12Z WED NOV 08 2017  
   
..GUIDANCE/UNCERTAINTY ASSESSMENT AND WEATHER/THREAT HIGHLIGHTS
 
 
THE 06 UTC GFS/GEFS AND 00 UTC ECMWF/ECMWF ENSEMBLES ARE WELL  
CLUSTERED THIS WEEKEND AND DEVELOP AN AMPLIFIED WRN US MEAN TROUGH  
WITH A PROLONGED PERIOD OF WIDESPREAD MODERATE TO TERRAIN ENHANCED  
PRECIPIATION AND LOWERING SNOW LEVEL THREAT. THE PATTERN ALSO  
OFFERS A STEADY FLOW OF LESS PREDICTABLE AND MODERATE  
PRECIPITATION FOCUSING IMPULSES THAT EJECT ENEWD OVER THE CENTRAL  
AND ERN US. THIS PATTERN ALLOWS FOR SEVERAL COLD AIR SURGES. LEAD  
CANADIAN HIGH PRESSURE DIGS THROUGH THE CENTRAL THEN ERN US  
FRI-SUN AND AN UPSTREAM LOWER ATMOSPHERIC COOLING HIGH/RIDGE  
SHOULD DIG THROUGH THE WRN TO EAST-CENTRAL US SUN-NEXT TUE. THIS  
FURTHER SUPPORTS WRN US/ROCKIES HEAVY SNOWS AND OFFERS SOME  
DOWNSTREAM SNOW POTENTIAL OVER THE CENTRAL TO ERN US NRN TIER.  
LEAD WAVY FRONT ENHANCED WARM SECTOR RAINS/CONVECTION ARE ALSO ON  
TAP FOR THE NERN QUARTER OF THE NATION AND WITH THE TRAILING FRONT  
BACK DOWN TO THE EAST-CENTRAL US...BUT THE MECHANISMS TO DEVELOP  
FRONTAL WAVES TO SIGNIFICANTLY FOCUS ACTIVITY STRENGTH AND  
DURATION REMAIN HIGHLY UNCERTAIN. MODEL SPREAD AND CONTINUITY FOR  
THESE POTENTIALLY IMPORTANT FEATURES HAS BEEN LESS THAN  
STELLAR...SO SUGGEST AN ENSEMBLE BASED APPROACH UNTIL GUIDANCE  
PROVIDES BETTER CLUSTERED AND REASONABLE FORECASTS.  
 
THE WPC MEDIUM RANGE PRODUCT SUITE WAS ACCORDINGLY DERIVED FROM A  
COMPOSITE BLEND OF THE 06 UTC GFS/GEFS AND 00 UTC ECMWF/ECMWF  
ENSEMBLES SUNDAY. STEADILY INCREASING FORECAST SPREAD/UNCERTAINTY  
OVER TIME THEN SUPPORTS A GRADUAL TRANSITION TO LESS DETERMINISTIC  
MODEL INPUT DAYS 4-7...
LEANING INCREASINGLY ON ECMWF ENSEMBLES  
THAT SEEM TO HAVE A BETTER HANDLE OF NWRN US MID-UPPER LEVEL  
TROUGH AMPLITUDE BY EARLY NEXT WEEK. THE 06 UTC GEFS SEEMS TO BE  
AT LEAST TRENDING TOWARD THIS DEEPER AMPLITUDE COMPARED TO THE 00  
UTC GEFS. THE HANDLING OF THIS FEATURE SEEMS TO DRIVE LATER PERIOD  
GUIDANCE DIFFERNECES DOWNSTREAM.  
 
SCHICHTEL  
 

 
 
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