293  
FXUS02 KWBC 140657  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
257 AM EDT SAT OCT 14 2017  
 
VALID 12Z TUE OCT 17 2017 - 12Z SAT OCT 21 2017  
 
...A COOLING AND STORMY WEATHER PATTERN NEXT WEEK TO DEVELOP OVER  
THE WEST...  
   
..OVERALL FLOW PATTERN AND GUIDANCE/UNCERTAINTY ASSESSMENT
 
 
MODELS AND ENSEMBLES SHOW A PROGRESSIVE AND WAVY FLOW PATTERN IN  
THE BEGINNING OF NEXT WEEK TRANSITIONING TO ONE OF INCREASED WRN  
U.S. TROUGHING AND BUILDING HEIGHTS OVER THE ERN STATES. THERE IS  
NOW GOOD AGREEMENT AND ABOVE NORMAL CONFIDENCE WITH THE OVERALL  
FLOW PATTERN FROM THE 18/00 UTC GFS/GEFS...12/00 UTC ECMWF AND 12  
UTC ECMWF ENSEMBLE MEAN. THE LATEST FEW GFS/GEFS RUNS HAVE TRENDED  
TOWARD WRN U.S. MID-UPPER LEVEL TROUGH TIMINGS AND AMPLITUDE LATER  
NEXT WEEK MORE IN LINE WITH THE ECMWF/ECMWF ENSEMBLES. LINGERING  
MODEL DIFFERENCES ARE MAINLY RELATED TO THE LESS PREDICTABLE  
TIMING AND STRENGTH OF EMBEDDED SHORTWAVES. THE CANADIAN REMAINS  
AN UNLIKELY AND OUT OF PHASE OUTLIER THAT HAS MINIMAL ENSEMBLE  
SUPPORT...EVEN FROM CANADIAN ENSEMBLES.  
 
ACCORDINGLY...WPC SURFACE FRONTS/PRESSURES AND 500 MB  
PROGS...QPF...AND SENSIBLE WEATHER GRIDS HAVE BEEN PRIMARILY  
DERIVED FROM A COMPOSITE BLEND OF THE WELL CLUSTERED GFS/ECMWF AND  
GEFS/ECMWF ENSEMBLE MEANS ALONG WITH THE NATIONAL BLEND OF MODELS  
AND WPC CONTINUITY.  
 
   
..SENSIBLE WEATHER HIGHLIGHTS/THREATS
 
 
LEAD SYSTEM ENERGIES PUSH INCREASINGLY OVER THE WRN ATLANTIC EARLY  
NEXT WEEK...LEAVING THE ERN THIRD OF THE US MAINLY UNDER THE  
INFLUENCE OF COOLED/DRIED HIGH PRESSURE. HOWEVER...A SWWD TRAILING  
FRONT FROM THE ATLANTIC STALLS TO KEEP RAIN CHANCES IN THE  
FORECAST THROUGH NEXT WEEK ACROSS FLORIDA AND THE GULF COAST IN  
EASTERLY POST-FRONTAL FETCH.  
 
MEANWHILE...AN ENERGETIC NERN PACIFIC STORM TRACK WORKS SOUTHWARD  
TO BRITISH COLUMBIA AND PROGRESSIVELY EASTWARD ACROSS SRN CANADA  
AND THE FAR NRN US TIER STATES EARLY-MID NEXT WEEK...ALONG WITH  
SOME SWATHS OF PCPN HOLDING MAINLY NORTH OF THE BORDER.  
SUBSTANTIAL UPSTREAM FLOW THOUGH THEN DIGS DOWN ACROSS THE PACIFIC  
NORTHWEST INTO CA BEFORE TRAVERSING THE INTERMOUNTAIN  
WEST/SOUTHWEST TO THE ROCKIES THU-SAT. EXPECT A RATHER STORMY/WET  
PERIOD FOR THE NWRN US/CA THEN INLAND ACROSS THE WEST AS MAINLY  
POWERED BY HEIGHT FALLS/DYNAMIC AND TOPOGRAPHIC LIFT. A SERIES OF  
EMBEDDED SHORTWAVES TAP AVAILABLE PACIFIC MOISTURE TO PRODUCE  
WIDESPREAD PRECIPITATION INCLUDING SOME HEAVY TERRAIN ENHANCED  
PRECIPITATION. POST-FRONTAL COLD SURGES DOWN THROUGH THE WRN  
STATES WILL INCLUDE A THREAT FOR HEAVY MOUNTAIN SNOWS WITH  
LOWERING SNOW LEVELS...SO PLEASE SEE THE WPC MEDIUM RANGE WINTER  
WEATHER OUTLOOK PROBABILITIES FOR ADDITIONAL DETAILS. AMPLE ENERGY  
EJECTION INTO THE PLAINS HEADING THROUGH NEXT WEEKEND WOULD SPAWN  
CYCLOGENESIS AND FRONTOGENESIS WITH INITIALLY SLUGGISH RETURN GULF  
MOISTURE INFLOW KICKING MORE IN ERNEST LATE PERIOD. THIS MAY FUEL  
RAINFALL/CONVECTIVE POTENTIAL EXPANSION LATER SAT INTO NEXT SUN  
OVER THE CENTRAL US.  
 
SCHICHTEL  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page