18th Conference on Weather and Forecasting, 14th Conference on Numerical Weather Prediction, and Ninth Conference on Mesoscale Processes

Tuesday, 31 July 2001: 5:15 PM
Orographic precipitation processes associated with the Wasatch Mountains during IPEX IOP3
Justin A. W. Cox, NOAA/CIRP and Univ. of Utah, Salt Lake City, UT; and W. J. Steenburgh, D. E. Kingsmill, and B. A. Colle
Poster PDF (176.4 kB)
This paper will present results from an ongoing investigation of IOP-3 of the Intermountain Precipitation Experiment (IPEX), held in Salt Lake City during February 2000. A major goal of IPEX was to improve the understanding and numerical simulation of orographic precipitation processes over the Intermountain West, with an emphasis on the narrow, steeply sloped Wasatch Mountains of northern Utah. Since present-day numerical models exhibit lower precipitation skill scores in the Intermountain West than in any other region of the United States, quantitative precipitation forecasting of snowfall and snow water equivalent remains a major challenge for numerical weather prediction and operational forecasters.

IOP-3 provided intensive observations of the largest winter storm to strike the Wasatch Mountains in two years, with as much as 80 cm of snow falling near the Wasatch crest in less than 18 h. Observations provided by high-density precipitation gauges will be used to show that orographic precipitation enhancement extended 2030 km upwind of the barrier and reached a maximum on or near the Wasatch crest. To the lee of the barrier, storm-total precipitation decreased by a factor of 4 within 10 km of the crest. Data collected by the NOAA P-3 research aircraft, two mobile Doppler radars, supplemental radiosondes, and a high-density mesonet (MesoWest) will be used to describe how the major kinematic features of the event, including a convergence zone and barrier jet windward of the Wasatch and an intense mountain wave to the lee, contributed to the observed precipitation distribution. Additionally, although the Wasatch are nearly a linear, meridionally-oriented mountain barrier, at one location (Ben Lomond Peak), significant topography extends 5 km normal to the crest towards the west. We will illustrate that the interaction of the barrier jet with this feature resulted in westward deflection of the jet, low-level convergence, and substantial local enhancement of precipitation. An evaluation of high-resolution numerical simulations of the event will also be presented as time allows.

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