The 29-30 January 2005 southeast Colorado snowstorm

On 2005 January 29-30, unseasonably large precipitation and snowfall amounts fell over portions of the southeast mountains and nearby plains of southeast Colorado. While, heavy orographic precipitation/snowfall events are not unprecedented in this region, this event was unique in that: 1) it occurred during the typically dry winter period, and 2) this event had very modest low level upslope flow.

Walsenburg, Colorado had a storm precipitation total around 60 mm, which is the second largest three day precipitation total in the period from November 1 to February 29 since 1934. In Rye, Colorado, precipitation totals for this event was 97 mm with snowfall total around 85 cm. During the event, the winds below 60hPa were almost always less than 7.5ms-1 and the wind direction was mainly from the southeast. Typically, heavy snowfall events at these sites have deep and strong northeast flow, which is perpendicular to the mountains.

Throughout much of the event, weak southeast flow brought moist (for the winter season) low level air against the eastern slopes of the southeast mountains of Colorado. During the day, on 29 January an upper low moved across New Mexico. Heavy snow started when the northeast quadrant of this upper low moved over the region of modestly unstable air. RUC fields show that a region of diffluence at and above 50 hPa moved over the modestly unstable air. Cloud tops rapidly cooled with satellite infrared temperatures indicating cloud tops at the tropopause. The NCEP guidance did not indicate heavy precipitation totals, but the staff of NOAA/NWS Pueblo issued the appropriate warnings recognizing the pool of unstable air near the mountains.

This event will also be utilized to evaluate the WSR-88D snow algorithm. The Pueblo WSR-88D had a clear view of much of the area which received heavy precipitation. Paul Schlatter from NOAA/WDTB will provide snow algorithm output for this event. The output will be compared to NWS COOP data as well as CoCoRaHS observations. CoCoRaHS is a volunteer rain, snow and hail observing network with data density significantly greater than the NWS COOP network.