An early season winter storm brought much colder temperatures and widespread snowfall to portions of the eastern Rockies and high plains October 9-10. Analysis of GOES-16 water vapor imagery shows key large scale features associated with the system as it digs south into the Great Basin and WY/CO (Figure 1) through 12Z. Overlaid on the animation are 700-300 mb GFS-derived Quasi-Geostrophic Omega, highlighting regions of greatest ascent and descent, correlating with what is observed in the imagery. The surface cold front is also seen pushing south through the high plains.
Now analyzing GOES-16 IR imagery over the same period and zooming in, the southward progression of the cold front is easily diagnosed in the imagery, including the banking of cold air up against the Colorado front range and Sangre de Cristo Mountains. An overlay of a surface wind analysis confirms the progression of the front. 60 mph winds were measured behind the front across southern Colorado.
Behind the front in northern Colorado during the evening of the 9th, thunderstorms managed to develop, producing heavy graupel and small hail. GLM Flash Extent Density from GOES-16 showed a lightning jump during the development of the strongest storm, which produced up to 3/4″ hail.
The Suomi NPP VIIRS Day Night Band (DNB) Near Constant Contrast (NCC) product provided high resolution “visible” imagery during the night as the front pushed south and low clouds expanded across the plains, thanks to illumination from the moon.
The storm system resulted in widespread snowfall amounts of up to around 5 inches over the portions of the Colorado I-25 corridor and eastern plains. The Day Cloud Phase Distinction RGB can be utilized during winter weather events to diagnose developing bands of snow or track ongoing snow bands during (especially in poor radar coverage areas). Using this event over southeast Colorado as an example, shades of cyan colored clouds (water clouds) transitioning to bright green represent increase of ice in the cloud top and a potential snow producing cloud/band (Fig 5). Multiple snow bands developed in the vicinity of Pueblo and areas south, expanding east through the afternoon in the presence of strong upper forcing and low-level easterly/northeasterly upslope flow.
Overlaying base radar reflectivity, one can see the snow bands as observed in radar imagery match up well with our analysis of the bands in RGB imagery (Fig 6).
NOAA-20 VIIRS DNB NCC imagery from the next evening provided an early view of snow cover over eastern Colorado from the previous day’s storm (Fig 7). Widespread snow cover is observed along the I-25 Corridor from Colorado Springs to Fort Collins, and much of the plains to the east. Further south, snow cover resulting from the banded snowfall is diagnosed near and south of Pueblo. Low clouds are masked with the GOES fog difference (blue).
Bill Line, NWS