321  
FXUS02 KWBC 131529  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1129 AM EDT FRI OCT 13 2017  
 
VALID 12Z MON OCT 16 2017 - 12Z FRI OCT 20 2017  
   
..OVERALL FLOW PATTERN/GUIDANCE EVALUATION/PREFERENCES
 
 
MEDIUM RANGE GUIDANCE CONTINUES TO SHOW A PROGRESSIVE AND WAVY  
FLOW PATTERN IN THE BEGINNING OF NEXT WEEK TRANSITIONING TO ONE OF  
INCREASED WESTERN U.S. TROUGHING AND BUILDING HEIGHTS OVER THE  
EASTERN STATES. THERE IS PRETTY GOOD AGREEMENT ON THIS OVERALL  
FLOW PATTERN BETWEEN THE DETERMINISTIC GFS/ECMWF AND THEIR  
RESPECTIVE ENSEMBLE MEANS...WITH MODEL DIFFERENCES RELATED TO THE  
LESS PREDICTABLE TIMING AND STRENGTH OF EMBEDDED SHORTWAVES. THE  
06Z DETERMINISTIC GFS APPEARS TO BE AN OUTLIER WITH ITS DEPICTION  
OF A NEGATIVELY TILTED SHORTWAVE ACROSS CENTRAL CANADA  
MID-WEEK...AND CONSEQUENTLY A FASTER PROGRESSION OF TROUGHING  
BEHIND IT MOVING INTO THE WESTERN U.S.. THE PREVIOUS RUN (00Z) OF  
THE GFS BETTER SUPPORTS THE REST OF THE GUIDANCE SHOWING A MORE  
PROGRESSIVE/SLIGHTLY AMPLIFIED CANADIAN SHORTWAVE AND SLOWER/LATER  
ARRIVAL OF THE WESTERN U.S. TROUGH. THE 00Z ECMWF/CMC ARE QUITE A  
BIT MORE AMPLIFIED WITH THE CANADIAN SHORTWAVE AS WELL AS IT MOVES  
INTO EASTERN CANADA BY THE END OF THE WEEK. WHILE THE 00Z EC  
ENSEMBLE MEAN ALSO HINTS AT A SLIGHTLY MORE AMPLIFIED SHORTWAVE...  
IT IS STILL IN LINE WITH THE REST OF THE GUIDANCE.  
 
ELIMINATING THE CMC AND ITS ENSEMBLE...THIS CYCLE OF THE WPC  
MEDIUM RANGE PROGS WAS BASED ON A BLEND OF THE 00Z GFS/ECMWF WITH  
THE 06Z GEFS MEAN AND 00Z EC MEAN. THE BLEND FEATURES A MAJORITY  
DETERMINISTIC MODEL WEIGHT IN THE BEGINNING OF THE PERIOD  
TRANSITIONING TO A NEARLY EQUAL BLEND OF THE ENSEMBLES BY THE END  
OF THE PERIOD.  
   
..SENSIBLE WEATHER HIGHLIGHTS/THREATS
 
 
A COLD FRONT MOVING OFF THE EAST COAST ON MONDAY WILL PUSH  
RAINFALL OFF THE COAST AS WELL AS USHER IN A BRIEF RETURN TO  
COOLER MORE FALL-LIKE TEMPERATURES. THE SOUTHERN PORTION OF THIS  
FRONT MAY STALL WHICH SHOULD KEEP RAIN CHANCES IN THE FORECAST  
THROUGH THE WEEK ACROSS FLORIDA AND THE GULF COAST. AN UPPER LOW  
SETTLING INTO ALASKA WILL PUSH THE STORM TRACK SOUTHWARD INTO  
BRITISH COLUMBIA EARLY NEXT WEEK...THEN EVENTUALLY INTO THE  
PACIFIC NORTHWEST AND INTERIOR WEST BY THURSDAY/FRIDAY. THIS WOULD  
START A RATHER STORMY PERIOD FOR THE NORTHWESTERN U.S. BY LATER IN  
THE WEEK AS A SERIES OF SHORTWAVES TAPS INTO AVAILABLE PACIFIC  
MOISTURE TO PRODUCE WIDESPREAD PRECIPITATION WITH SOME MODERATE TO  
HEAVY TERRAIN ENHANCED PRECIPITATION EXPECTED. THIS WILL INCLUDE A  
THREAT FOR HEAVY MOUNTAIN SNOWS...PLEASE SEE THE WPC WINTER  
WEATHER OUTLOOK PROBABILITIES FOR ADDITIONAL DETAILS.  
OTHERWISE...THE REST OF THE COUNTRY NEXT WEEK WILL SEE MAINLY DRY  
CONDITIONS AND NEAR TO ABOVE AVERAGE TEMPERATURES.  
 
SANTORELLI  
 

 
 
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