Extended Abstract (96K)6.1
Dual-Doppler analysis of the kinematic structure of a Wasatch Mountain winter storm
Justin A. W. Cox, NOAA/CIRP and Univ. of Utah, Salt Lake City, UT; and W. J. Steenburgh and D. E. Kingsmill
The near-mountain kinematic structure of the Wasatch snowstorm of 12-13 February 2000 is examined using data collected during IOP-3 of the Intermountain Precipitation Experiment (IPEX). Similar to many ranges of the United States' Great Basin region, the Wasatch Mountains of northern Utah are narrow [O(10 km)] and steeply sloped, rising 1500-2000 m above the surrounding lowlands in as little as 5 km. Typical of Wasatch Mountain snowstorms, IOP-3 featured large spatial gradients in precipitation both along and across the barrier. Upwind of the Wasatch, stations in the Salt Lake Valley reported less than 10 mm of precipitation (liquid precipitation equivalent, LPE), whereas similar-elevation sites 40 km to the north near Ogden, UT received up to 32 mm. Along the Wasatch crest, only 10-15 km from these low elevation regions, up to 70 mm LPE was observed, while just 10 km downwind of the crest, precipitation decreased by a factor of four.
During IOP-3, observations were collected using two Doppler on Wheels (DOW) radars, a high-density surface mesonet (MesoWest), flight-level data from the NOAA P-3 research aircraft, and three-hourly radiosonde releases by NWS and mobile laboratory sites. The DOWs yielded an excellent dual-Doppler dataset in the windward near-mountain environment, revealing several small-scale circulation features that were produced by the local topography. A windward convergence zone was observed where southwesterly flow from over the Great Salt Lake converged with terrain-parallel southerly flow near the Wasatch Mountains. This windward convergence zone appeared to result in the precipitation enhancement that was observed near Ogden, UT. The terrain-parallel southerly flow varied in magnitude along the Wasatch and was found to be weakest near the mouths of major canyons. Winds veered with height, resulting in increasing cross-barrier flow from mid-mountain to crest level. In this region, flow splitting was observed upwind of higher topographic features, with flow channeling between the peaks. The impact of these flow features on the observed distribution will be discussed, as well as their evolution as a synoptic scale pressure trough moved through the region.
Session 6, Orographic Precipitation I
Tuesday, 18 June 2002, 9:00 AM-10:15 AM
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