Monday, February 13, 2012

The Tonopah Low

A somewhat unusual occurrence that becomes more common in Spring is the development of the so-called Tonopah or Nevada Low ( ). These aptly named systems tend to form in the lee of the Sierra Nevada mountains, in the vicinity of Tonopah, NV. These systems can produce heavy precipitation on the east-facing slopes of the Sierra and in other regions that experience the typical rain shadow associated with approaching Pacific storms.

The document linked above states that the development of these systems is typically preceded by the flow of cold air from Canada towards a warmer airmass over the Great Basin, creating unstable conditions. Indeed, The 18z GFS indicates a pronounced flow of cold air at 850mb from British Columbia into Nevada in the wake of an upper-level trough.

The same page goes on to list three other conditions that may contribute to the strengthening of the Tonopah Low:

1. A wave on a west-east oriented front.
2. A secondary low in an unstable air mass follows the passage of a frontal low.
3. Beneath a cut-off low, or at the tip of a long wave trough, which has a jet maximum over the area.

I don't see much in the way of the first two today, but note the intense jet max rounding the base of the upper-level cut-off low centered over the Sierra at 500mb.

These conditions have led to the development of a low pressure system in south/central Nevada today, which is forecast to move east overnight...

...spawning the issuance of winter storm warnings from central Nevada through the southern Wasatch, where 6-12" of snow is expected at higher elevations. As for those east-facing slopes of the Sierra, a few inches are in the forecast, but nothing big this time.

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