006
FXUS02 KWBC 211815
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
215 PM EDT MON SEP 21 2009
VALID 12Z THU SEP 24 2009 - 12Z MON SEP 28 2009
TELECONNECTIONS WITH A NEGATIVE ANOMALY OVER GREENLAND FAVOR
TROUGHING OVER THE GREAT LAKES...WHICH THE MODELS ESTABLISH LATE
IN THE PERIOD. LARGE SCALE MODEL AGREEMENT THIS CYCLE IS QUITE
GOOD...WITH THE CUTOFF LOW OVER THE PLAINS ON THURSDAY LIFTING
NORTHEASTWARD IN RESPONSE TO A FLATTENING/BRIEFLY ZONAL FLOW
PATTERN DEVELOPING TO ITS NORTHWEST AND NORTH. IN AN UNUSUAL
SITUATION...THE 00Z GEFS MEAN/06Z GFS ARE SLOWER WITH THE
MIDWESTERN SYSTEMS EJECTION THAN THE 00Z ECMWF/ITS ENSEMBLE
MEAN/12Z GFS/12Z CANADIAN. HOWEVER...THE 00Z MULTI-MODEL ENSEMBLE
SPREAD IS BROADER IN SCOPE THE DIFFERENCES SEEN OVERNIGHT. WITH
THE MODELS HAVING EXCEPTIONAL DIFFICULTY IN HANDLING DEEP CYCLONES
IN THE PLAINS AND THEIR EJECTION INTO THE WESTERLIES OVER THE PAST
FEW WEEKS DURING THE MEDIUM RANGE PERIOD...CHOSE TO COMPROMISE
BETWEEN THE 00Z ECMWF/06Z GFS TO ACCOUNT FOR THE
UNCERTAINTY...SUBSTITUTING THE 00Z GEFS MEAN FOR THE 06Z GFS NEXT
MONDAY. THIS SOLUTION KEPT GOOD CONTINUITY WITH THE PREVIOUS
ISSUANCE. THIS PATTERN SHOULD BE A WET ONE FROM THE PLAINS
EASTWARD...WITH THE HEAVIEST RAINFALL PRIMARILY ACROSS THE
SOUTHEAST AND MISSISSIPPI VALLEY.
ROTH
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