Water Resources Research Act Program

Details for Project ID 2006WY33B

Precipitation Measurement and Growth Mechanisms in Orographic Wyoming Snowstorms

Institute: Wyoming
Year Established: 2006 Start Date: 2006-03-01 End Date: 2009-02-28
Total Federal Funds: $20,709 Total Non-Federal Funds: $318,466

Principal Investigators: Jefferson Snider, Bart Geerts

Project Summary: Much of Wyomings water supply originates as winter snow, mainly over the state's numerous mountain ranges. Snowrate and snow accumulation measurements are complicated by strong winds. A consequence is that springtime runoff estimates have limited accuracy and this uncertainty impacts our ability to assess the efficacy of water management practices. This proposal has two related objectives: (a) to advance techniques for measuring regional snowrates based on a newly designed Hotplate snowrate sensor and operational weather radar data; and (b) to improve understanding of atmospheric processes leading to snow generated in clouds forming over the Wyoming high country. Such research is fundamental to snow measurement and to its augmentation by artificial means (i.e., cloud seeding). The studies proposed here will build on coupled airborne and ground-based field work already planned by the University of Wyoming Department of Atmospheric Science through a grant from NASA. The airborne data will be collected by the University of Wyoming King Air, a state-of-the-art cloud physics platform equipped with a millimeter-wave radar, the Wyoming Cloud Radar (WCR). The WCR measures cloud, precipitation, and air motion fields with high spatial resolution. Extra flight hours are requested under this proposal as an add-on to the NASA-sponsored field work scheduled for early 2006. We plan to acquire data by conducting flight transects across the Laramie Range and Snowy Range and to study how cloud depth, horizontal and vertical wind speed, thermal stability and properties of the aerosol ingested by winter orographic storms influence snow formation. We will also contrast precipitation development in storms moving in from the west against those coming from the Great Plains. We are also proposing to instrument ground-based sites with a Hotplate and a multi-frequency radiometer for studies concentrated on the accuracy of surface snowrate measurements. In Year 1 the surface measurements will be conducted near the Cheyenne weather surveillance radar (WSR) in partial coordination with the King Air overflights. Values of WSR radar reflectivity (Z) will also used to derive snowrates (S); however, the Z-to-S parameterization necessary for this is poorly constrained. In Year 2, both low- and high-altitude sites in the Snowy Range will be equipped with Hotplate sensors. Hotplate data will be collected, and analyzed, with snow accumulations recorded by co-located Snowpack Telemetry (SNOTEL) sensors. Objectives of these ground-based studies are 1) refinement of the Z-to-S parameterization applied to WSR measurements of Z acquired in shallow winter upslope snow storms, 2) intercomparison studies of snowrate data from two Hotplates leading to quantification of Hotplate measurement uncertainties, 3) evaluations of the consistency among Hotplate and SNOTEL snow accumulation measurements, and 4) quantification of orographic precipitation enhancement, in the Snowy Range, over time intervals shorter than that measurable by SNOTEL. This work will aid Wyomings operational cloud seeding initiative. It will also be instrumental in laying the ground work for an international orographic precipitation experiment we will propose separately for 2008. One Ph.D. student will be supported by this project, at least one other graduate student will be trained in field data collection, and the M.S. student funded through the NASA project will benefit from the airborne measurements proposed herein.