EF0 Tornado — Flathead, Montana

2013-11-04 · near Bigfork, Flathead, Montana

Event narrative

A cold core upper level trough dropped out of British Columbia providing the necessary lift and instability to trigger showers across western Montana early on November 4th. The unstable atmosphere saw a 24 degree difference between Flathead Lake water temperatures(8.9 deg. C) and at 9,665 ft. MSL(700 millibars) -15 deg. C. A convergent boundary set up southwest of Wood's Bay with cool northerly winds coming out of the Flathead Valley and relatively mild southerly winds moving across the lake. This boundary provided the vertical lift to develop the band of graupel and snow showers. A waterspout was spotted by passers-by traveling on MT-83 near mile-marker 24. Viewing the photos and video that Mike and Dana Marchetti took, it appears that there could have been multiple vortices based on darkened shadows in the vicinity of the main vortex. The waterspout remained over Flathead Lake and no damage was reported.

Wider weather episode

A vigorous moist Pacific system brought snow to the higher elevations of western Montana impacting mountain passes including Lookout and Lost Trail. Impacts such as slick roads were reported at pass level by late evening Saturday November 2nd and continued through Monday the 4th. The frontal system brought heavy precipitation (up to 1.60) across the higher elevations of western Montana. Anywhere from 8 to 12 inches of snow were reported in the mountains while valley locations received a trace to 4 inches. A stalled out arctic front brought heavy snow to US-2 from Essex to Marias Pass between Nov. 3 & 4. A second cold-core upper level trough provided strong unstable conditions that helped to trigger winter waterspouts on Flathead Lake and intense valley-level snow showers on Nov. 4th.

View location on OpenStreetMap → (47.9710, -114.0720)

Source: NOAA Storm Events Database, event_id 483062. Narrative written by the NWS forecast office that issued the report.