The One and Done Storm

Source: ESPN

Given that it is Final Four weekend, I'm naming our pending storm "One and Done," as in one monsterous airmass change.

The latest GFS calls for tomorrow to be warm and windy.  Crest level (700-mb) temperatures tomorrow are forecast to be near +6C at Salt Lake City, which would be the warmest airmass we've seen thusfar this Spring.

We'll probably see a high temperature at the Salt Lake City airport near 78ºF, which is the all-time record high temperature for the month of March.  Time will tell if we go into uncharted territory.  Blowing dust is likely, although we'll have to see if the trajectory is right for Salt Lake and the central Wasatch to get hit.

The GFS brings the surface front between midnight and 6 am on Sunday.  Should that verify the temperature change will likely still be impressive, but not as large as it would be if it came through in the afternoon.  You can't have everything!

By noon Saturday, the forecast crest-level temperatures have dropped to -10ºC, cold enough for snow down to the valley floor.

So, shorts Saturday, flakes Sunday.  I suspect we won't see much precipitation ahead of the front, but I like 6-12 inches at Alta by the end of the day Sunday and perhaps 1–3 inches on colder surfaces on the east bench as well.  I emphasize colder surfaces because the ground is so warm and likely to be warmer after Saturday's heat.

How quickly it gets cold behind the front is a critical factor in the snow forecast for the valley. The heaviest precipitation will likely come following frontal passage.  If the colder air lags the surface front, that precipitation may fall as rain or slushy snow and accumulations will be limited.  If temperatures fall quickly to near or below freezing, and precipitation rates are high so that ground temperatures can drop, accumulations will be greater.  Even in this case, we'll see major differences in accumulations depending on the surface.