Tuesday, October 2, 2012

Topographic Effects during Tomorrow's Cold-Air Surge

Cold air will be moving into northern Utah tomorrow, with temperatures falling to levels unseen in many months (hooray!).  The cold air is fairly shallow, however, and this means the topography is going to have a strong influence on its penetration into the Great Salt Lake Basin.

Recently, we've gained new appreciation for how the Raft River Range of northwest Utah and Albion Mountains of southern Idaho can influence the weather of northern Utah.  These two ranges are high barriers that form a formidable obstacle for airmasses attempting to penetrate into Utah from the Snake River Plain.

Low-level airmasses can be blocked and flow around the Albion and Raft River Mountains.  Indeed this is forecast to occur tomorrow by a high-resolution (3.33 km) modeling system run here at the University of Utah by Prof. Zhoaxia Pu.  In particular, the forecast for 1800 UTC (1200 MDT) tomorrow shows a pronounced wake (i.e., area of weak winds) extending downstream of the Raft River Range.

Note how strong flow into northern Utah to the south of the Raft River Mountains surges rapidly southward into the Dugway Proving Ground area (see the G).

Time will tell if this forecast verifies, but we have documented similar features downstream of the Raft River Range during lake-effect events.  In fact, if you look carefully at the forecast above, you can see a convergence zone within the wake.  When such convergence is oriented so that it moves over the Great Salt Lake, it can contribute to the initiation of "lake-effect" bands in some events.

So, the next time you drive I-84 to Idaho, look at the Raft River Mountains with admiration and respect!

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