Historically, there has been snow on the ground in the Red River Valley on Thanksgiving Day roughly half the time. Thanksgiving in the United States happens on the fourth Thursday in November and so ranges from Nov. 22-28. Snow depth in the climate record is always rounded off to the nearest inch, so the lower threshold for there being "measurable" snow on the ground is one inch.
The climate records of these dates for Fargo and Grand Forks indicate a 42% likelihood of there being at least one inch of snow on the ground in Fargo and about a 50% likelihood in Grand Forks. The odds are slightly higher when the holiday occurs later in its possible range and slightly lower when the holiday occurs earlier. For Thanksgiving days on today's date, Nov. 26, the historical percentage has been 47% for Fargo and 53% for Grand Forks.