Could this be the reason??

EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
137 PM EDT TUE JUL 20 2010

VALID 12Z FRI JUL 23 2010 - 12Z TUE JUL 27 2010

FINAL...

THE 12Z GUIDANCE CONTINUES TO SHOW A MODERATE DEGREE OF SPREAD
WITH BOTH THE TIMING AND INTENSITY OF SHORTWAVES ALONG THE
CANADIAN BORDER THIS PERIOD. THE LATEST GEFS MEAN AND UKMET ARE
CLOSEST TO THE 00Z ECENS MEAN...USED FOR THE UPDATE PACKAGE...WITH
THIS 12Z GUIDANCE SLIGHTLY FASTER WITH THE PROGRESSION OF POLAR
CYCLONES. THE GFS AND PARALLEL GFS STILL DO NOT CLUSTER WELL
ENOUGH WITH THE BULK OF THE OTHER GUIDANCE TO BE VERY RELIABLE.
CHANGED THE GULF TROPICAL WAVE TROUGH TO A LOW CENTER...AS PER
COORDINATION WITH TPC. NONE OF THE NEW MODELS DEVELOP THIS SYSTEM
TO A SUBSTANTIAL DEGREE. OTHERWISE...MADE ONLY MINIMAL CHANGES
FOR THE FINAL ISSUANCE.
(emphasis added by danielw)
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