644  
FXUS02 KWBC 140701  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
200 AM EST THU DEC 14 2017  
 
VALID 12Z SUN DEC 17 2017 - 12Z THU DEC 21 2017  
   
..OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
MODELS AND ENSEMBLES OFFER GREATER THAN NORMAL FORECAST SPREAD AND  
UNCERTAINTY FOR THE 3-7 DAY FORECAST PERIOD. THERE ARE TWO MAIN  
FORECAST CLUSTER SCENARIOS EVIDENT. THE MAIN FORECAST PROBLEM  
EMINATES FROM THE DIFFERENT HANDLING OF SHORT RANGE BASED TROUGH  
ENERIES DIGGING ALOFT OVER THE WRN US. RECENT GFS/CANADIAN RUNS  
AND TO A LESSER EXTENT GEFS/NAEFS MEANS DEVELOP A PHASED/AMPLIFIED  
SWRN US UPPER TROUGH THIS WEEKEND. THIS SRN STREAM SPLIT FEATURE  
AND ASSOCIATED SURFACE SYSTEM EJECTS ACROSS THE US SRN TIER  
MON-FRI TO FOCUS MODERATE TO HEAVY RAINS/THUNDERSTORMS OVER THE  
GULF COAST STATES/SERN US/SRN MID-ATLANTIC AS GULF MOISTURE IS  
ADVECTS INLAND. MEANWHILE IN THIS SCENARIO...SEPARATE NRN STREAM  
FLOW MID-UPPER LEVEL TROUGH ENERGIES AND ASSOCIATED AND PCPN  
SWATHS WITH MORE COLD AIR TO WORK WITH PROGRESS OVERTOP THEN TEND  
TO REMERGE TO SOME DEGREE WITH EJECTING SRN STREAM FLOW OVER THE  
E-CENTRAL STATES EARLY-MID NEXT WEEK BEFORE FULLY REDOMINATING  
LATER WEEK. IN STARK CONTRAST...RECENT ECMWF RUNS AND TO A LESSER  
EXTEND ECMWF ENSEMBLE MEANS SHOW MORE WEEKEND SPLIT FLOW OVER THE  
WEST AND SPLIT SOME TROUGHING BACK OVER THE ERN PACIFIC AND ALLOWS  
MORE PROGRESSIVE TROUGHING/PCPN SWATH SPLIT RAPIDLY EASTWARD  
CENTRAL AND ERN US MID-LATITUDES MON-TUE. IT DOES NOT SEEM  
REASONABLE AMID UNCERTAINTY TO FAVOR EITHER CAMP OF THOUGHT. A  
BLEND OF SOMEWHAT MORE COMPATABLE GEFS/NAEFS/ECMWF ENSEMBLES  
PROVIDES A COMPROMISE SOLUTION THAT SEEMS TO TAKE INTO ACCOUNT  
SOME OF EACH CAMP AND MAINTAINS MAX WPC FORECAST CONTINUITY. THE  
WPC PRODUCT SUITE WAS DERIVED FROM THAT BLEND. GUIDANCE DOES SEEM  
TO BETTER CONVERGE LATER WEEK AND SHOWS A MORE COMMON WETTER  
TROUGH SOLU SOLUTION AND  
 
SCHICHTEL  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page