Saturday, January 9, 2010

Not So Fast

New data in this morning is indicating that we could be adding on to the "at or below freezing temperature" streak for a while longer.

Forecast models are hinting at a temperature inversion setting up over the area. This happens quite often around here in the winter. Normally, temperature decreases with altitude. Hence, it is colder on the top of a mountain than at its base. A temperature inversion is an increase in temperature with altitude.

The inversion acts as a block to trap the cold air at the surface. It doesn't allow it to mix and can often times help in the creation of a low deck of clouds or fog.

Here is the 12z run of the NAM model. Notice all of the low clouds it keeps over the top of the area?

I have several weather parameters displaying on the image. First, surface air temperature is the red line. Blue vertical bars indicate snow. Orange vertical bars indicate sleet. Yellow lines indicate air temperature at different elevations. The first vertical set of numbers on the right side of the screen indicates the elevation in 1,000's of feet. For example 4k=4,000'.

As long as the inversion is set up, we might have a hard time of getting enough sunshine to warm us above 32°F. Notice the high temperature on Monday is around 30° and in the upper 20°'s on Tuesday.

I find temperatures difficult to forecast when we have inversions setup. Mainly because we don't always get the cloud formation. Sometimes the models will indicate sunny skies, because they have a hard time resolving what is going on in the lower couple hundred feet of the atmosphere, and it will end up being cloudy.

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