Has winter begun yet in the area? Well, it depends on how you define "winter"!
For some people, winter depends on the calendar. "Meteorological" winter starts on December 1 and ends on February 28/29. "Astronomical" winter begins with the winter solstice, which is on December 21 at 11:11 AM CST this year, and ends with the vernal equinox, which is on March 20 at 11:57 AM CDT in 2014.
For some of us, though, winter arrives when the weather feels "wintry". That might be when the temperatures don't rise above freezing (maximum temperature at or below 32 °F), when the first measurable snow falls (snowfall at or above 0.1"), or when the first snow stays on the ground (snow depth at or above 1"). In this area, those firsts arrive in November, on average. The table below lists the average (1981-2010) occurrence of each of those "firsts", along with the earliest and latest occurrence of each one.
*Note: For Omaha, temperature data are from 1871-2013, snowfall data are from 1885-2013 (missing 1997-99), and snow depth data are from 1948-2013. For Lincoln, temperature data are from 1887-2013, snowfall data are from 1948-2013, and snow depth data are from 1948-2013 (missing 1996). For Norfolk, temperature data are from 1893-2013 (missing 1887, 1900-02, 1904, and 1939), snowfall data are from 1920-2013 (missing 1924-25 and 1933-43), and snow depth data are from 1946-2013.
As of November 18, none of the three sites has experienced any of these "wintry" conditions. By any definition, winter has not yet started. For snowfall, this is a little later than average. For temperatures and snow depth, we are close to on time right now, heading toward being later than average. Watch out for late this week and this weekend, when the temperatures might stay below freezing for a day!