Monday, April 13, 2015

Weather's a Changing

It's been a long time since I've seen the state of Utah colored by watches and warning.

Most of the state is covered by high wind warnings, freeze warnings, and a winter storm watch. So what's going on? two words: Cold Front.

Monday (today) will be a warm, clear sunny day with high's in the mid 70s. But don't let today's amazing weather fool you. Just upstream our ridge is a cold, digging trough.
NAM Forecast: April 13, 12:00 PM Mountain Time
By Tuesday afternoon the trough will have moved into Utah, and the cold front will pass in the afternoon, bringing much colder temperatures and snow.
NAM Forecast: April 14, 3:00 PM Mountain Time
The cold front is especially visible in the 700 mb temperature map. The contours are packed together really tight over Utah. The air behind the cold front will be about 20 degrees colder than Monday's temperatures.
NAM Forecast: April 14, 3:00 PM Mountain Time
Another look at the cold front is shown in the Theta-e time heights. (Read this graph from right to left.) The blue line is the freezing level. Looks like the freezing level (thick blue line) reaches the valley surface around 7:00 or 8:00 PM mountain time.

There is a good chance of precipitation along the entire Wasatch Front. In the valley's it will start as rain and then turn to snow. Higher elevations could get several inches of new snow.
NAM Forecast, April 14, 9:00 PM Mountain Time
Now, this forecast is just the NAM solution. Other models show different results, but most agree we'll get some snow. How much snow we'll receive is hard to predict. Below is the "plume" ensemble results from 22 different models for the amount of liquid precipitation in Salt Lake City. Some solutions are wet with nearly an inch of water, others are dry with only a trace. It's best to pick the middle of the road--somewheres around a few tenths of an inches of water is most likely in Salt Lake. That translates to less than two inches of snow, max. In the valley. Tomorrow morning when the storm gets a little closer I'll take another look at how much snow is expected.

Despite uncertainty in the forecast details be aware that the approaching storm will pass through Utah Tuesday afternoon/evening bringing much colder temperatures for Wednesday, high winds, and rain turning to snow. Good news is that by the weekend sunshine and warmer temperatures will return.

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