Today is the date, on average, that Omaha sees its final night of 32-degree temperatures, according to the National Weather Service.
Half the years between 1981 and 2010 there was no 32-degree night after April 24, but half the time there was.
To mark the occasion, temperatures were forecast to drop this morning well below 32 degrees into a hard freeze — record territory. Another hard freeze is possible Wednesday night into Thursday morning.
The 30-year time period of 1981-2010 is simply an artifact of weather data.
The National Weather Service bases its definition of “normal” on 30 years of weather and on the supposition that it's more reflective of current climate than the full period of record, which dates to the 1800s.
Later this week, temperatures are forecast to warm considerably, so maybe we'll be able to say goodbye to freezing temperatures after that.
Source: National Weather Service