Fresh snow cover in Montana and Alberta

September 30th, 2019 |

GOES-16 Day Cloud Phase Distinction RGB images [click to play animation | MP4]

GOES-16 Day Cloud Phase Distinction RGB images [click to play animation | MP4]

Through breaks in the cloud cover, GOES-16 (GOES-East) Day Cloud Phase Distinction Red-Green-Blue (RGB) images on 30 September 2019 (above) showed the bright green signature of fresh snow cover across northern Montana and southern Alberta in the wake of a record-setting snowfall event that occurred during the previous 2-3 days (NWS Great Falls summary). Note that the surface air temperatures over the areas of fresh snow cover only rose into the upper 20s and low 30s F, in contrast to 40s F in adjacent areas with minimal or no snow cover — in fact, many locations set daily record low maximum temperatures.


GOES-16 Mid-level Water Vapor (6.9 µm) images from 0001 UTC on 28 September to 0901 UTC on 30 September (below) covered the duration of the winter storm — the circulation of an anomalously-deep mid-tropospheric low over the Pacific Northwest was evident, in addition to a long fetch of middle/high-level moisture from the southwestern US toward Montana. Another notable feature included widespread mountain waves over Colorado beginning on 29 September, which eventually extended downwind over western Nebraska/Kansas; Colorado had a peak wind gust of 81 mph during this event (WPC storm summary).

GOES-16 Mid-level Water Vapor images, with hourly plots of precipitation type [click to play animation | MP4]

GOES-16 Mid-level Water Vapor (6.9 µm) images, with hourly plots of precipitation type [click to play animation | MP4]

===== 01 October Update =====

GOES-16 Day Cloud Phase Distinction and Day Snow-Fog RGB images [click to play animation | MP4]

GOES-16 Day Cloud Phase Distinction and Day Snow-Fog RGB images [click to play animation | MP4]

With less cloud cover on 01 October, a comparison of GOES-16 Day Cloud Phase Distinction and Day Snow-Fog RGB images (above) provided a better view of the areal coverage of snow cover. Note that while the Day Cloud Phase Distinction RGB (snow=green) produces “sharper” imagery — since it uses the higher spatial resolution of the 0.64 µm Visible data — the Day Snow-Fog RGB (snow=red) does a better job at highlighting thin supercooled cloud features (shades of white) over snow cover.  The combination of fresh snow cover, light winds and minimal cloudiness allowed Cut Bank to record the coldest official temperature in the US at +1ºF (although a couple of sites unofficially dropped below 0ºF).

In a toggle between GOES-16 Day Cloud Phase Distinction RGB and Topography images (below), note the darker blue gaps in snow cover in Montana and Alberta – with easterly/northeasterly winds during the snow event (Cut Bank | Havre | Great Falls), those areas experienced downslope flow which warmed the boundary layer air and minimized snow accumulation.

GOES-16 Day Cloud Phase Distinction RGB and Topography images [click to enlarge]

GOES-16 Day Cloud Phase Distinction RGB and Topography images [click to enlarge]

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