Weekend Weather Blog: Cold air damming

Why the sudden change in weather?
Published: Jan. 8, 2022 at 5:22 PM MST
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TWIN FALLS, Idaho (KMVT/KSVT) — A pattern flip is expected to impact the area with calmer weather entering southern Idaho. After a three-week period of cold and snow just about every day, sunshine is expected to make its return to the area as the jet stream is expected to lift off to the north of the area.

Jet Stream over the next 48 hours (KMVT)
Jet Stream over the next 48 hours (KMVT)(Jet Stream over the next 48 hours (KMVT))

With the jet off to the north, you may be expecting warmer than normal temperatures to begin making themselves present over much of the area. However, this isn’t the case, according to the Climate Prediction Center’s 6-to 10-day outlook.

6 to 10 Day Temperature Outlook (CPC)
6 to 10 Day Temperature Outlook (CPC)(6 to 10 Day Temperature Outlook (CPC))

According to the Climate Prediction Center, much of the region is expecting near average temperatures over the next 6 to 10 days. Why is that? A big part of this is due to very slow winds over much of the region. Another reason is the snowpack.

Refer to the jet stream image above. Notice how the strongest winds are located well to our north? That overall pattern will allow an area of high pressure to form to our southeast, allowing for very slow winds, mainly out of the south. These southerly winds will slope up the terrain of the Snake River Plain as it moves from south to north.

What will happen next? The wind will encounter the mountains of central Idaho. This is where the snowpack will come into the picture.

Snow in Buhl With Explainer On It (From: RJ via Burst)
Snow in Buhl With Explainer On It (From: RJ via Burst)(Snow in Buhl With Explainer On It (From: RJ via Burst))

With how cold the snowpack is, as well as how reflective of a surface is, incoming energy from the sun will be reflected back to space. This will keep much of the surface of the earth relatively cool. Aloft, the southerly winds will continue to blow warm temperatures above this layer of cool air near the surface.

What’s the result? The air higher up in the atmosphere is warmer than the air near the surface. Since air typically cools with height, this is called an ‘inversion’. This prevents air near the surface from rising over the layer of warm air, effectively trapping the cooler air in the lower levels of the atmosphere.

Earlier, I mentioned the central mountains. This is where these come into play. Weak winds out of the south will blow up toward the Wood River Valley, and eventually to the southern edge of the central mountains. Because the winds will be so weak, however, the mountains will block the wind from going any further north. Where can they go from there? Up.

However, remember the warm air located above the cold air near the earth’s surface due to the cold snowpack. What will this do? Prevent the southerly winds from easily rising over the mountains. This will allow for much of the cold air over the region to be trapped in the lower elevations of the region, allowing us to see near-average temperatures, despite the jet stream being located well off to the north.

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