Research on Lake-Effect Snow
Lake-effect snow, produced when cold winter winds move across warm lake water, brings joy to skiers, headaches to commuters, and ulcers to meteorologists. Utah meteorologists call it the "dreaded" lake-effect because it remains difficult to predict despite dramatic advances over the past few decades in numerical weather prediction. Funded by the National Science Foundation and supported by CHPC, Professor Jim Steenburgh, Atmospheric Sciences, heads a new research project that aims to make the lake-effect less dreaded and better anticipated. University of Utah graduate students Trevor Alcott and Kristen Yeager, along with faculty and students at Weber State University and Hobart and William Smith Colleges in upstate New York are also contributing.
The Great Salt Lake, with its widely varying surface area ranging from 2800 to 4700 km2, is approximately 1/25th the size of Lake Superior. It is quite shallow, with a mean depth of only three meters, and is surrounded by tall mountains and a highly heterogeneous land surface. Forecasting the Great Salt Lake effect is complicated by the lake's small size, which increases sensitivity to small changes in the upstream flow, and the difficulties in specifying the temperature of the lake and the surrounding land-surface conditions, which include the flat desert of the Great Basin and the mountainous terrain of the Wasatch, Oquirrh and Stansbury ranges. Satellite imagery can help specify lake-temperature and land-surface conditions, but only if cloud-free conditions exist prior to a potential storm. The Great Salt Lake lake-effect storms also come in a number of "flavors" or modes. Organized bands produce heavy snowfall over a narrow area, but non-banded events are widespread and less intense. The processes responsible for these different lake-effect morphologies have yet to be identified.
The U's research project involves three major components: (1) a radar-based climatology, (2) an observational field program, and (3) numerical modeling. The radar-based climatology has identified 177 lake-effect events since 1997 with data from several sources, including the KMTX radar station located at Promontory Point and North American Regional Reanalysis, which provides gridded atmospheric and land-surface analyses for the western United States. The data are being mined statistically to better understand the environmental conditions that control lake-effect initiation, mode, and intensity. The project is also examining how much the lake effect contributes to snowfall and the hydrologic cycle of the Great Salt Lake basin.
The observational field program is called the Sounding Observations of Lake-Effect Precipitation Experiment (SOLPEX). The objectives of SOLPEX are: (1) to identify the upstream and near-lake environmental conditions that control the initiation, mode, and intensity of lake-effect precipitation, (2) to determine the strength and depth of east-side land breezes and their role in lake-effect events, and (3) to obtain the upper-air data needed to better initialize and validate numerical simulations of lake-effect storms.
SOLPEX will observe several lake-effect storms this winter. Two teams of scientists comprised of University of Utah graduate and undergraduate students will be deployed during potential lake-effect snowstorms, one to the immediate north of the Great Salt Lake near the ghost town of Kelton and the other to the east shore of the Great Salt Lake near the Antelope Island causeway. These two teams will brave snow, wind and cold to launch weather balloons that will provide profiles of wind and temperature during lake-effect storms. The group will study the data to determine lake-effect sensitivity to upstream flow conditions and to improve knowledge of how land breezes and downslope flows from east of the Great Salt Lake affect the initiation and mode of lake-effect storms.
CHPC's computational resources and support play a central role in the field program. Vital to SOLPEX are numerical forecasts produced on CHPC-supported infrastructure using the Advanced Research Weather Research and Forecasting model (WRF-ARW). Current operational weather prediction models used for weather prediction in the United States are run with a12-km grid spacing, which is insufficient to adequately resolve lake-effect storms. WRF-ARW forecasts will be produced for SOLPEX at 1.3 km grid spacing, which permits the explicit prediction of lake-effect snow bands and improves representation of topographic and lake-surface processes. These forecasts will be used to plan observing efforts, with SOLPEX data ultimately used to validate their accuracy and reliability.
Numerical simulations by the WRF-ARW will also be used to better understand the physics and predictability of lake-effect events. Of particular interest is the role of topography in event initiation and intensity. Preliminary work shows that flow splitting around the Raft River range of northwest Utah influences lake-effect band development and intensity over the Great Salt Lake. Such effects are not presently incorporated in numerical operational weather prediction.