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HMT wx forecast discussion: 13 February 2008 at 1945 UTC

A NE-SW band of enhanced cold cloud tops in the IR satellite imagery is clearly evident diving SSEward across NV and SEern CA this morning in association with the now sharply digging S/W trough. The Reno 88D radar shows a precip band beneath the IR cloud enhancement, although the echoes are remaining mostly E of the Sierra Crest. The Sacramento 88D has tagged only a few scant echoes near the Crest midmorning. As the upward-motion forcing with the S/W quickly propagates into the Great Basin, the ARB will transition into strong subsidence this afternoon in a post-cold-frontal environment. Hence, what little precip may fall across the ARB today will be minimal at best and only short-lived.

As the S/W circulation intensifies over the Great Basin later today into tomorrow, brisk N to NE winds will blow on its back side across the ARB, partly due to a developing large-scale pressure gradient of significant magnitude. W should also expect a period of downslope mountain-wave dynamics tonight into tomorrow, which should further intensify the NEerlies along the western slope of the Sierra. No precip will fall tonight or tomorrow, although temperatures will be cooler than the last couple of days.

Temperatures will quickly rebound by Friday and the weekend, as high-amplitude ridging aloft will once again take hold across CA. It will remain dry. Thereafter, the picture has not changed appreciably for the long range. S/W troughs propagate into the diffluent upper-level flow across the EPAC, weaken, and make landfall in BC, the PacNW, or perhaps as far S as N CA through the middle of next week (~20 Feb). These systems will likely not yield much (or any) precip for the ARB. Thereafter, perhaps zonal wave energy will finally reach CA to provide moisture to the ARB. We shall see.

Paul Neiman
NOAA/PSD