A forecaster and microphysical perspective on the 24 February 2007 snow event over the Park Range of northern Colorado

Cloud microphysical processes play an active role in the development of precipitation, but to what extent? In the operational forecasting environment, dynamical meteorology is given considerable attention before cloud microphysics is considered. In complex terrain, orographical lift complicates the forecast process and cloud microphysical processes may be ignored. However, cloud microphysical processes may dominate and dramatically enhance snowfall amounts. This poster presentation will look at the 24 February 2007 event that occurred over the Park Range near Steamboat Springs, Colorado, where more than 50 cm of snow occurred during a 24 hour period. Dynamics and orographics were contributing factors to the heavy snow, but a closer examination suggests that cloud microphysical processes accounted for much of the snowfall. The synoptic scale pattern did not support heavy snow; quasi-geostrophic forcing was moving away from Steamboat Springs during the period of heavy snow. Mountain top winds were from the northwest, ideal orographic flow for the Park Range, but the forcing was weak as wind speeds were in the 5 to 10 m s-1 range. NCEP models, such as the NAM12, missed the heavy snow as model data depicted light precipitation during the period of heavy snow. Microphysical observations made during this event indicated there was plenty of ice and very little liquid water. Orographic clouds were shallow and the Bergeron process was active, efficient and depleting most of the available liquid water. Riming was not a factor in this particular event. The microphysical processes were the primary reason for the heavy snow, while orographics and dynamical forcing were secondary.