222  
FXUS02 KWBC 160701  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
300 AM EDT MON OCT 16 2017  
 
VALID 12Z THU OCT 19 2017 - 12Z MON OCT 23 2017  
 
...A COOLING AND STORMY WEATHER PATTERN TO DEVELOP OVER THE WRN TO  
CENTRAL...  
   
..PATTERN AND GUIDANCE/UNCERTAINTY ASSESSMENT
 
 
IT REMAINS THE CASE THAT MODELS AND ENSEMBLES SHOW A PATTERN  
TRANSITION TO ONE WITH AN AMPLIFIED TROUGH MOVING ONSHORE OF THE  
WEST COAST LATER THIS WEEK THAT PROGRESSES INLAND TO THE CENTRAL  
US NEXT WEEKEND. THE NRN PORTION OF THIS TROUGH IS EXPECTED TO  
WORK OVER THE E-CENTRAL U.S. INTO ABOUT A WEEK...BUT VARIED  
GUIDANCE SOLUTIONS SHOW POTENTIAL FOR FLOW SEPARATION TRENDING TO  
A CLOSED TROUGH/LOW SOMEWHERE NEAR THE SRN PLAINS BY DAY 7.  
DOWNSTREAM FROM THESE FEATURES...A WARMING HIGH AMPLITUDE ERN US  
RIDGE BUILDS THIS WEEK.  
 
THERE IS GENERALLY GOOD AGREEMENT WITH ABOVE NORMAL CONFIDENCE AND  
CONTINUITY FOR THE OVERALL FLOW PATTERN THROUGH MUCH OF THE NEXT  
WEEK. HOWEVER...FORECAST SPREAD AND UNCERTAINTY DOES INCREASE WITH  
THE EXTENT OF FLOW SEPARATION AND POTENTIAL CLOSED LOW DEVELOPMENT  
IN VICINITY OF THE SRN PLAINS IN ABOUT A WEEK THAT WOULD PRESENT  
AN EMERGING LOCAL HEAVY RAINFALL AND RUNOFF RISK.  
 
WPC SURFACE FRONTS/PRESSURES AND 500 MB PROGS...QPF...AND SENSIBLE  
WEATHER GRIDS WERE PRIMARILY DERIVED FROM A COMPOSITE BLEND OF WPC  
CONTINUITY AND REASONABLY WELL CLUSTERED AND COMPATABLE GUIDANCE  
FROM THE 18/00 UTC GFS/GEFS MEAN...THE 12 UTC NAEFS MEAN...AND THE  
12 UTC ECMWF/ECMWF ENSEMBLE MEAN. THE DETERMINISTIC CANADIAN WAS  
AGAIN NOT USED IN THE WPC FORECAST BLEND AS A FASTER OUTLIER THAT  
IS COUNTERED BY SLOWER CANADIAN ENSEMBLES THAT ARE NOW MORE IN  
LINE WITH THE WPC COMPOSITE BLEND THAN YESTERDAYS RUNS.  
 
   
..SENSIBLE WEATHER HIGHLIGHTS/THREATS
 
 
EXPECT A RATHER STORMY/WET PERIOD FOR THE NWRN US/CA WITH LESSER  
AMOUNTS OF PRECIP SPREADING INLAND ACROSS THE WEST...SUPPORTED BY  
SYNOPTIC SCALE ASCENT IN THE VICINITY OF THE UPPER JET AUGMENTED  
BY TOPOGRAPHIC LIFT. A SERIES OF EMBEDDED SHORTWAVES TAP AVAILABLE  
PACIFIC MOISTURE TO PRODUCE WIDESPREAD PRECIPITATION INCLUDING  
SOME HEAVY TERRAIN ENHANCED PRECIPITATION IN THE PACIFIC  
NORTHWEST...ESPECIALLY THE RANGES OF WA STATE. POST-FRONTAL COLD  
SURGES DOWN THROUGH THE WRN STATES WILL LEAD TO LIKELY MOUNTAIN  
SNOWS WITH LOWERING SNOW LEVELS.  
 
THE UPPER TROUGH MOVING INTO THE PLAINS NEXT WEEKEND INTO EARLY  
NEXT WEEK DRIVES A COLD FRONT ACROSS THE REGION. EAST OF THE  
FRONT...MOISTURE RETURN GRADUALLY INCREASES. THE INCREASE IN  
MOISTURE AND STRENGTH OF THE LOW LEVEL JET MAY FUEL  
RAINFALL/CONVECTIVE POTENTIAL EXPANSION LATER SAT INTO SUN OVER  
THE CENTRAL TO SRN PLAINS AND MID MS VALLEY. A BIGGER THREAT FOR  
HEAVIER RAINFALL MAY BE INTO NEXT MON OVER THE SRN PLAINS/LOWER MS  
VALLEY.  
 
MOST OF THE ERN THIRD OF THE COUNTRY WILL BE DRIER THAN NORMAL  
UNDER THE INFLUENCE OF HIGH PRESSURE. HOWEVER...PERSISTING  
MOISTURE AND COASTAL CONVERGENCE PRODUCES THE LIKELIHOOD OF  
SHOWERS ALONG THE EAST COAST OF FLORIDA...WITH AN INVERTED TROUGH  
PRODUCING SHOWERS ALONG THE TEXAS/LA COASTS.  
 
THE UPPER RIDGE LEADS TO WARMER THAN NORMAL CONDITIONS ACROSS MOST  
OF THE ERN US...INCLUDING HIGH TEMPERATURES 10-15 DEGREES ABOVE  
NORMAL IN THE UPPER MS VALLEY...GREAT LAKES...AND OH VALLEY LATE  
THIS WEEK INTO THE WEEKEND...WHEN THE ANOMALOUS WARMTH SPREADS  
INTO THE APPALACHIANS AND NORTHEAST.  
 
SCHICHTEL  
 

 
 
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