Investigation of WRF Microphysics Schemes and Dynamics During an Extreme Precipitation Event in East Idaho

Thomas A. Andretta*
Andretta Innovations LLC, Cheyenne, WY, USA

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© 2018 Thomas A. Andretta.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at Andretta Innovations LLC, P.O. Box 21057 Cheyenne, WY 82003, USA; Tel: (307)365-4541; E-mail:



The 26 December 2003 snowstorm was a rare and long-lived weather system that affected east Idaho. Light snow began falling Christmas night, became steadier and heavier during the next day, and tapered off during the morning on the 27th. Snowfall estimates of 20.3-38.1 cm (8.0-15.0 in) were observed over a 24-hour period on 26 December 2003 in the lower part of the Snake River Plain, paralyzing local communities and transportation centers with snowdrifts and poor visibilities.


The Weather Research and Forecasting Unified Environmental Modeling System was used to conduct a sensitivity study of five precipitation microphysics schemes at two grid scales during the event.


A comparison of the model accumulated total grid scale precipitation at 12-km and 4-km scales with the observed precipitation at several stations in the lower plain, indicated small negative biases (underprediction) in all of the schemes. The Purdue-Lin and Weather Research and Forecasting Double-Moment 6-Class microphysics schemes contained the smallest root mean squared errors.


The Purdue-Lin and Weather Research and Forecasting Double-Moment 6-Class schemes provided several insights into the dynamics of the snowstorm. A topographic convergence zone, seeder-feeder mechanism, and convective instability were major factors contributing to the heavy snowfall in the lower plain.

Keywords: Extreme precipitation, Seeder-feeder mechanism, Topographic convergence zone, East Idaho, Snowstorm.