Nancy's Almanac, Feb. 12, 2014: Why do this weekend's temperature forecasts vary so widely? -
Published Wednesday, February 12, 2014 at 1:00 am / Updated at 6:59 am
Nancy's Almanac, Feb. 12, 2014: Why do this weekend's temperature forecasts vary so widely?

Forecasts for high temperatures in Omaha this weekend varied by as much as 10 degrees, depending on the source Tuesday morning.

Some forecasts projected Omaha highs in the low to mid-50s, while others limited the highs to the mid-40s.

The reason for such a wide difference?

Our weekend weather will be affected by a Canadian Clipper dipping down from the north and warm air moving up from the southwest, said Cathy Zapotocny, a meteorologist with the National Weather Service.

The paths and timing of these two air masses is subject to change, especially since the weekend is so far away (the Canadian Clipper was still “at sea” on Tuesday).

As Zapotocny explains it:

Cold air

The Canadian Clipper, traveling along a northwest-to-southeast path, will usher cold air into the northern United States this weekend. Eastern Nebraska and western Iowa are along the edge of that clipper, so our temperatures will vary significantly.

In the space of 100 miles, there's a 10-degree difference in the highs forecast for Saturday. Lincoln's high was projected at 50 degrees, while Atlantic, Iowa, wasn't expected to rise above 41.

Forecasts that have Omaha in the 40s on Saturday are based on the Clipper dipping far enough south for more of the Midlands to catch a taste of that cold air.

Warm air

Clippers rotate in a counterclockwise motion as they travel across the continent (think of a top spinning across the floor). The front edge of the rotation pulls warmth up from the south, while the back edge brings cold down from the north.

The timing of the arrival of the front edge of the clipper will determine Saturday's temperatures, Zapotocny said.

Ideally, the clipper will pull warm air into our region Saturday afternoon as normal daytime warming occurs. If these two happen together, temperatures will rise higher.

If the warmth arrives earlier — overnight Friday — its effect could weaken by Saturday afternoon and temperatures might not climb into the 50s.

Sunday's high will depend on how quickly the clipper heads east as it leaves this area. If it departs quickly, warm air from the southwest could linger another day.

Other factors also affect temperatures, Zapotocny said.

As an example of the complexity of weather, she pointed to the snow cover in Kansas. A blanket of snow absorbs warmth from the air, so the snow in Kansas will remove some heat from southwesterly winds blowing into Nebraska. If that snow melts quickly, more warmth will reach Nebraska sooner.

Brian Edwards, a meteorologist with AccuWeather Inc., said it's possible that the warm air arriving Friday night into Saturday will bring some rain with it.

He said the weekend will be breezy, given the jockeying between warm and cold air masses.

Sources: National Weather Service, AccuWeather Inc.

Current conditions and forecast

Contact the writer: Nancy Gaarder    |   402-444-1102    |  

Nancy writes about weather, including a blog, Nancy's Almanac. She enjoys explaining the science behind weather and making weather stories relevant in daily life.

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