Weekend Weather Blog: Where’s all the warm weather been?

Published: May. 21, 2022 at 4:37 PM MDT
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TWIN FALLS, Idaho (KMVT/KSVT) — It’s been cold over the last jumble of Months. In fact, the region hasn’t seen monthly above normal temperatures since December, where a very warm pattern skewed the average high temperatures to just a touch above average for the month. There are numerous reasons our temperatures haven’t been able to climb back to being warmer than normal within the last 5 months or so. Let’s break down why this is.

December/March/April/May pattern
December/March/April/May pattern(WeatherModels.com)

The above image shows the basic pattern in the jet stream. Remember, when the jet stream (or the high concentration of the black lines on the image) is to the north, warmer temperatures are permitted to surge up into the region from the south. On the contrary, if the jet stream is to the south, cooler temperatures from near the poles are allowed to surge their way on down into the mid-latitudes.

This pattern is what the current jet stream looks like - very far to the south of the region, allowing some cooler air to move its way in. This was our pattern for much of the second half of December through the first half of January. We also saw this pattern from about mid-March through now.

This pattern essentially keeping all of the warm weather confined to the eastern half of the lower 48. Back in the second half of January and through all of February, we saw something really unique though. The pattern I talked about above wasn’t actually in place. Instead, a much warmer pattern made itself present.

Jan/Feb/early March pattern
Jan/Feb/early March pattern(WeatherModels.com)

This is that warmer pattern I was talking about. Why did we see such cold temperatures then? A process called cold air damming. When the snowpack was present, incoming solar radiation from the sun bounced off of the snow, which allowed the ground to remain cool. On top of this, moisture from the snow itself would evaporate into the atmosphere.

Overnight, the nocturnal inversion develops. This basically occurs due to all of the heat from the sun that hit the earth’s surface escaping out into space. The moisture from the snow is still able to evaporate out into the air above it, but becomes trapped beneath the inversion. All of this fog keeps the sun from warming up the earth’s surface, and the mountains trap the air below the inversion from being able to go anywhere.

This fog caused January and February temperatures to remain very chilly, despite the warmer pattern.

there is much warmer weather headed our way toward the middle of this week, as the above pattern is expected to develop in by Tuesday. Tune in tonight on KMVT to find out just how warm we’ll get.

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