Winter Storm — Southern Lewis and Clark, Montana

2021-05-20 · Southern Lewis and Clark, Montana

Event narrative

Northwest Energy reports scattered power outages due to snow and wind near the Bowman's Corner area.

Wider weather episode

On Wednesday May 19, 2021, an upper level Pacific trough dove south through the Pacific Northwest into the Great Basin and then became nearly stationary for a couple of days. The southerly flow ahead of this system transported middle and upper level moisture into the state, while an upslope east to northeast flow developed at the lower levels in response to relatively strong surface high and low pressure systems respectively set up over Alberta Canada and Utah. The upslope flow eventually led to cold air damming and the development of a low level barrier jet along the Divide. This resulted in strong northerly surface winds along eastern slopes adjacent to the Rocky Mountain Front for periods of near blizzard conditions and subsequently sent the unseasonably cold air into the southwestern portion of the state. Locations from Roger's Pass northward into the East Glacier and Browning areas observed the worst conditions due to the combination of falling snow and gusty northerly winds. The impacts ranged from severe driving conditions on area roadways to isolated power outages. By Thursday morning, the rain began to change to snow at lower elevations over North-central Montana and this transition eventually reached the southwest valleys later that evening.

Source: NOAA Storm Events Database, event_id 963219. Narrative written by the NWS forecast office that issued the report.