Wednesday, February 3, 2016

Flirtin' with Disaster

As far as inversions and air pollution go, we've had a pretty good run this year.  Although November and the first half of December did not bring a lot of precipitation, a number of weak storms moved through northern Utah to keep things stirred up.  Since then, a progression of storms has also prevented persistent inversion events, limiting the severity and duration of poor air quality episodes.

That's all about to change.

The loop below tells the story well and covers analyses and forecasts for a one week period from 1200 UTC 1 Feb (0500 MST Monday 1 Feb) through 1200 UTC 8 Feb (0500 MST Monday 8 Feb).  At the beginning of the look, you can see the deep trough associated with last weekend's storm existing the state.  Then, we have another trough move through on the 4th (tomorrow), which will probably give us our last gasp of snow for a while (2-4 inches in the mountains).  Although there is a brush-by trough on the 6th and 7th, the long-term trend is for ridging along the west coast and, as far as ridges go, this one is a big one.

With snow on the ground in the valley, as far as air quality is concerned, we will be flirtin' with disaster.

The severity of the event will probably depend on two things.  The first is the strength of the brush-by on the 6th and 7th.  If we are fortunate, that brush-by will give a clean flush to the valley even if it doesn't bring much snow to the mountains.  If we're unfortunate, it will pass too far to the north.  The second is how long the high amplitude ridge will be around.  Although we have confidence in the development of the ridge, forecasts of its potential demise are far enough in the future that I don't want to speculate.  I suspect a best-case scenario is that we have a 4 day inversion event and just begin to flirt with values at or above the EPA clean-air act standard.

In the mountains next week, the ridge should produce the first extended period of warm weather and blue skies we've had in a while.  Conditions should be ideal for high-speed cruising at the resorts as it will be warm, but the sun still isn't high enough to trash the north aspects.  The backcountry snowpack, however, remains tricky, and will probably need to be treated as "guilty until proven innocent", as the Utah Avalanche Center said a few days ago.

One quick comment on the backcountry.  There are more people out than ever before.  Spooning is hard these days due to the great diversity of skis people are on, but keeping your tracks tight with your partner conserves the hill and leaves more powder for others to enjoy during dry spells.  A conserved hill is a happy hill.

Photo: "Steve the Cook"

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