Early models are trying to add a Mid Western Storm to the Thankgiving weather.
Disagreement at this time over the exact track and intensity of the LOW that is forecast to develop and move into the Midwest in the Thursday- Friday time frame.
Worse case scenario at this time would put stranded travelers in airports. Waiting for flights to resume.

EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
224 PM EST SAT NOV 17 2007

VALID 12Z TUE NOV 20 2007 - 12Z SAT NOV 24 2007

...LOWER 48...

500MB RIDGING OFF THE WEST COAST WILL DRY OUT LINGERING SN SHOWERS
TUE OVER THE NRN ROCKIES.
THERE ARE ONLY TWO OTHER POSSIBLE
LARGE-SCALE IMPORTANT QPF EVENTS OVER THE LOWER 48 THRU THE MEDIUM
RANGE.
THE FIRST OF THESE WILL BE THE CYCLOGENESIS OVER THE MS/OH VLYS WED/THU AND ITS SUBSEQUENT NE MOVEMENT. THIS SYS COULD LAY DOWN AS BELT OF HVY SNOWFALL ACROSS THE UPPER MIDWEST AND SRN GRT
LAKES MAKING FOR MESSY HOLIDAY TRAVEL IN THOSE AREAS.
SHOWERS AND A FEW TSRA ALONG THE TRAILING COLD FRONT OF THE ASSOCIATED LOW.
IT REMAINS TO BE SEEN HOW QUICKLY OVERRUNNING PCPN DEVELOPS TOWARD THE END OF OUR PERIOD OVER THE GULF COAST STATES IN CONNECTION WITH ANY DEVELOPMENT IN THE GULF OF MEXICO DAY 7.

Latest version of the Extended Forecast at the link below~danielw
http://www.srh.noaa.gov/productview.php?pil=PMDEPD&max=61

(Thread was moved after it drifted off-topic)