705  
FXUS02 KWBC 190700  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
300 AM EDT THU OCT 19 2017  
 
VALID 12Z SUN OCT 22 2017 - 12Z THU OCT 26 2017  
 
...HEAVY RAINFALL POTENTIAL IN THE ERN U.S. WITH RECORD HEAT IN  
THE SOUTHWEST...  
 
   
..PATTERN OVERVIEW AND GUIDANCE/UNCERTAINTY ASSESSMENTS
 
 
MODELS AND ENSEMBLES AGREE TO DEVELOP AN AMPLIFIED FLOW PATTERN  
OVER THE LOWER 48 NEXT WEEK. A LEAD CLOSED LOW POTENTIALLY PEELING  
OFF FROM THE FLOW MAY AFFECT THE GULF COAST EARLY NEXT WEEK AS  
DEEPENED MOISTURE FROM THE GULF OF MEXICO THEN ATLANTIC FEEDS  
INCREASINGLY INLAND. GIVEN SUBSEQUENT PHASING WITH A DIGGING NRN  
STREAM TROUGH...A RESULTANT NEGATIVELY-TILTED TROUGH LEADS TO  
500MB HEIGHT DEPARTURES UPWARDS OF 3 STANDARD DEVIATIONS BELOW  
NORMAL BY THE MIDDLE OF NEXT WEEK OVER THE EAST. THIS SCENARIO  
OFFERS WIDESPREAD HEAVY RAIN POTENTIAL OVER THE E-CENTRAL TO ERN  
US. PREFER A COMPOSITE 12 UTC GFS/ECMWF AND GEFS/ECMWF ENSEMBLE  
MEAN GIVEN RECENT MODEL UNCERTAINTY.  
 
AS A SHARP NEGATIVE HEIGHT ANOMALY ENCOMPASSES THE ERN THIRD OF  
THE NATION...PRONOUNCED UPSTREAM RIDGING OVER THE WEST WILL USHER  
IN WARM/DRY CONDITIONS TO THE REGION. A COMPOSITE GUIDANCE  
SOLUTION SEEMS REASONABLE INTO TUE...BUT PREFER TO LEAN WEIGHTING  
TOWARD THE MORE AMPLIFIED/LESS PROGRESSIVE ECMWF AND ECMWF  
ENSEMBLE MEAN UPSTREAM OVER THE PACIFIC TO THE WEST COAST BY LATER  
NEXT WEEK WITH THE ANTICIPATION OF WELL DOWNSTREAM EFFECTS FROM  
THE ENTRAINMENT OF WRN PACIFIC TYPHOON LAN INTO THE WESTERLIES.  
 
   
..SENSIBLE WEATHER HIGHLIGHTS/THREATS
 
 
ZONAL FLOW OVER THE NWRN US SUPPORTS SOME HEAVY PRECIPITATION OVER  
THE OROGRAPHICALLY FAVORED LOCATIONS OF THE OLYMPICS AND CASCADES  
THIS WEEKEND. THIS WESTERLY FLOW REGIME SHOULD BE DEVOID OF  
APPRECIABLE COLD AIR WHICH MAINTAINS SNOW OVER THE HIGHER  
ELEVATIONS. WITH HEIGHTS BUILDING IN TIME...THE ACTIVE STORM TRACK  
WILL LIFT UP INTO BRITISH COLUMBIA NEXT WEEK. FARTHER  
EAST...WIDESPREAD RAINFALL SHOULD BE ONGOING WITH A WAVY COLD  
FRONT MOVING THROUGH THE E-CENTRAL U.S. SUN/MON. ACTIVITY WILL  
PICK UP IN COVERAGE AND INTENSITY AS THE SRN STREAM SHORTWAVE  
DEVELOPS WITH HEAVIER AMOUNTS POSSIBLE IF THE SYSTEM SLOWS. A  
HEAVY RAINFALL SIGNAL THEN EXISTS FOR THE ENTIRE ERN SEABOARD  
OCTOBER 23-25 ONCE THE UPPER TROUGH STRENGTHENS AND A SERIES OF  
SURFACE LOWS FORM. THERE IS A THREAT OF RUNOFF ISSUES.  
 
SCHICHTEL  
 

 
 
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