On average, Omaha sees its first 32-degree day on Oct. 12, according to the National Weather Service.
So far, Omaha is about a week behind average. But with cold air shoving south out of Canada, temperatures could drop to freezing anytime soon.
Any night next week is vulnerable to a freeze, said Rick Chermok meteorologist with the National Weather Service.
All that's needed is for overnight skies to clear and winds to die down, he said. When skies are clear, warm air lifts skyward and cold air sinks to the ground. And when winds are light, the warm and cool air isn't mixed together, allowing that cool air to sink.
The weather service defines “average” according to 30-year periods, and updates those averages, or normals as they're sometimes called, every 10 years. Current averages are based upon the period 1981 to 2010.
There's nothing magic about a 30-year period, it is simply the time period selected to take into account evolving climate patterns.
Some areas near Omaha have seen a drop to freezing, but many haven't. Lincoln recorded its first 32-degree temperature Thursday morning.
Last year, due in part to the drought, Omaha skipped past an early light freeze and instead had a hard freeze for its first 32-degree or lower night. On Oct. 6, 2012, temperatures plunged to 26 degrees. When the landscape is dry, it releases heat easier. When it's wet, as it has been recently, it holds onto heat.
The average date of Omaha's first hard freeze is Oct. 26, according to the weather service.
Temperatures have gotten cool enough, overall, that a hard freeze, when it arrives, will not shock native vegetation.
Who has had afirst freeze so far this fall?
What is “average” for this area?