961  
FXUS02 KWBC 311556  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1055 AM EST WED JAN 31 2018  
 
VALID 12Z SAT FEB 3 2018 - 12Z WED FEB 7 2018  
 
16Z UPDATE:  
 
THE MODELS CONTINUE TO REMAIN IN GOOD AGREEMENT ON THE LARGE SCALE  
SYNOPTIC PATTERN ACROSS NORTH AMERICA THROUGH EARLY NEXT WEEK.  
THERE WERE SOME RELATIVELY MINOR TIMING AND AMPLITUDE DIFFERENCES  
WITH A COUPLE OF SHORTWAVE IMPULSES TRACKING SOUTHEASTWARD AROUND  
THE WEST COAST RIDGE AND THEN TRACKING TOWARDS THE EAST COAST.  
THE UKMET BECOME MORE AMPLIFIED AND SLOWER THAN THE MODEL  
CONSENSUS EARLY IN THE FORECAST PERIOD OVER THE PLAINS WITH THE  
FIRST SHORTWAVE, AND GIVEN ITS LACK OF SUPPORT FROM THE ENSEMBLE  
MEANS, MORE WEIGHTING WAS GIVEN TO THE GFS AND ECMWF. SOME OF THE  
00Z CMC WAS INCORPORATED THROUGH THE WEEKEND WHEN IT WAS IN GOOD  
AGREEMENT WITH THE CONSENSUS. A SMALL PERCENTAGE OF THE GEFS MEAN  
AND EC MEAN WAS INCORPORATED FOR THE TUESDAY AND WEDNESDAY TIME  
PERIOD TO ACCOUNT FOR INCREASING SPREAD IN THE SURFACE PRESSURE  
PATTERN. THE MAIN CHANGE IN THE FORECAST FROM YESTERDAY IS A  
WEAKER SURFACE HIGH SETTLING SOUTHWARD ACROSS THE NORTHERN PLAINS  
ON SUNDAY, AND A STRONGER LOW PRESSURE SYSTEM OFF THE EAST COAST  
BY MONDAY. THE FORECAST REMAINS SIMILAR FOR THE INTERMOUNTAIN  
WEST AND THE WEST COAST.  
 
D. HAMRICK  
 
   
..OVERVIEW AND GUIDANCE PREFERENCES
 
 
MEDIUM RANGE FLOW ALOFT CONTINUES TO FEATURE RIDGING OFF THE WEST  
COAST AND BROAD CYCLONIC FLOW/TROUGHING DOWNSTREAM OVER MUCH OF  
THE REST OF THE LOWER 48. MODELS AND ENSEMBLES OFFER SIMILAR  
LARGER SCALE FLOW PATTERNS AND HAVE BECOME A BIT BETTER CLUSTERED  
WITH LESS PREDICTABLE SMALLER SCALE EMBEDDED FEATURES. THERE  
REMAINS VARIANCE WITH BOTH THE SPECIFICS OF COLD HIGH PRESSURE  
DIGGING INTO THE LOWER 48 AND THE DEVELOPMENT OF PRECIP/WINTER  
WEATHER ASSOCIATED WITH FRONTAL WAVES ON THE LEADING EDGE OF THE  
COLD DOME.  
 
THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED FROM THE  
12 UTC GFS/ECMWF...THE 18 UTC GEFS MEAN AND THE 12 UTC ECMWF  
ENSEMBLE MEAN WHOSE COMPOSITE BLEND MAINTAINS MAX WPC CONTINUITY.  
HOWEVER...LEANED MORE WEIGHT ON THE COLDER SOLUTIONS OF THE  
NATIONAL BLEND OF MODELS...THE GFS/GEFS AND MOS IN AREAS DEEP IN  
THE INFLUENCE OF ARCTIC AIR VERSUS THE WARMER LOW LEVEL  
TEMPERATURES OF THE ECMWF/ECMWF ENSEMBLE MEAN. TEMPS FOR THE  
POTENTIAL WINTRY THREAT OVER THE SRN/SERN AND ERN US WOULD BE MORE  
DEPENDENT ON ANY ULTIMATE COASTAL LOW TRACK AND THE 00 UTC  
GFS/ECMWF HAVE TRENDED SLIGHTLY INLAND OF PREVIOUS RUNS.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
OVER THE NWRN US...IT REMAINS THE CASE THAT A SERIES OF  
PROGRESSIVE IMPULSES RUNNING OVER THE EAST PACIFIC/WEST COAST  
RIDGE WILL SUPPORT ADDITIONAL PERIODS OF MODEST PRECIPITATION.  
HOWEVER...EXPECT LOCALLY HEAVIER TERRAIN-ENHANCED SNOWS ACROSS THE  
NWRN US AND ESPECIALLY THE NRN ROCKIES WITH ADDED NRN STREAM  
IMPULSES OF LESS CERTAIN TIMINGS. EXPECT ADDITIONAL POST-FRONTAL  
UPSLOPE SNOWS UP TO THE DIVIDE. UPSTREAM...THERE REMAINS A DECENT  
MODEL SIGNAL TO BRING ADDITIONAL MODEST ERN PACIFIC SYSTEM  
ENERGY/PCPN TO THE PACIFIC NW EARLY NEXT WEEK.  
 
A WEEKEND CLIPPER SYSTEM WILL SPREAD SNOWS ACROSS THE N-CENTRAL  
US...GREAT LAKES...THEN NORTHEAST. UNDERNEATH...RAINS WILL  
MEANWHILE INCREASE OVER THE GULF COAST BY SUNDAY WITH RETURN FLOW  
TO INCLUDE SOME LOCAL HEAVIER DOWNPOURS. WIDESPREAD MODERATE PCPN  
SHOULD EXPAND NEWD INTO EARLY NEXT WEEK INTO THE MID-SOUTH AND  
ACROSS THE ERN US. THIS WOULD OFFER AN INTERIOR WINTER WEATHER  
THREAT. A COLD HIGH SURGE IN THE WAKE OF THE CLIPPER HAS SOME  
TIMING/STRENGTH VARIANCE IN GUIDANCE BUT BEST CLUSTERING SUGGESTS  
A PATH FROM W-CENTRAL CANADA INTO THE N-CENTRAL US SATURDAY TO  
THEN SPREAD OVER THE REST OF THE CENTRAL AND ERN US SUNDAY INTO  
MONDAY.  
 
SCHICHTEL  
 

 
 
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