Tornado and Heavy Snow in Montana, November 2 to 4, 2013

Heavy mountain snowfall developed on Saturday Nov. 2nd across northwest Montana. The Hawkins Lake SNOTEL at 6,450 ft. located in extreme northwest Lincoln County reported 1 per hour snowfall rates on the 2nd from 2 to 11 pm MDT with 9 inches of snowfall. This sensor reported 13 total storm snowfall with 1.60 of precipitation through 4 am MST on Nov. 4th. The COOP observer located 9 miles north-northeast of Yaak reported a storm total snowfall of 2.4 with 1.04 of precipitation. On Sunday Nov. 3rd at 7:17 pm MST, a weather spotter reported moderate snow with visibilities less than one half mile from Marion to North Star Meadows and slick conditions on US-2.

The COOP observer in West Glacier reported a storm total snowfall of 7.3 between Nov. 2nd and Nov. 4th with 0.85 of precipitation. The COOP observer at the Hungry Horse Dam reported 4 of snow with 1.07 of precipitation while a citizen in the town of Hungry Horse measured 6 of snow by 10:30 am MST on Monday, Nov. 4th. A person from the public located 1 mile southeast of Swan Lake estimated that 4 inches had fallen by 10:24 am MST on the 4th. They reported that MT-83 was snow-covered. This snowfall was most likely connected with the snow band that developed over Flathead Lake just southwest of Wood's Bay.

The Montana DOT at Lookout Pass on I-90 reported a storm total snowfall of 8 inches from Saturday evening Nov. 2nd through Monday morning the 4th. No accidents were reported, but road surfaces were reported to be slick especially by late evening on the 2nd when road temperatures cooled to freezing and below. The nearby Lookout SNOTEL reported 1.00 of total precipitation during the event. The COOP station 1 mile west of Haugan reported a storm total snowfall of 2 with 0.75 of precipitation.

The Montana DOT reported heavy snow Sunday afternoon Nov. 3rd through the morning hours of Monday Nov. 4th on US-2. The snowfall was especially heavy between Essex (mile-marker 180) and Stanton Creek (mile-marker 192) along US-2. They estimated that up to 2 feet of snow fell during the storm in these areas. The Marias Pass HADS weather sensor at 5233 ft. reported 0.50 of precipitation with temperatures falling into the lower 20's. Using a 20:1 average snow to liquid ratio Marias Pass could have seen a foot of snow.

An avalanche forecaster measured 16 inches of total storm snowfall in Essex by Monday afternoon Nov. 4th, 12 hours after the snowfall ended. The BNSF Shed 4 weather sensor (4520 ft.) located approximately 10 miles southwest of Marias Pass just off of US-2, reported 12 of snow with 0.90 of precipitation 32 hours ending at 7 am MST on Monday Nov. 4th. It reported heavy snowfall rates between 1 to 1.8 per hour from 1 and 8 pm MST on Sunday Nov. 3rd. The Shed 7 weather station at 6363 ft. and 11.5 miles southwest of Marias Pass, reported 25 of snow from this storm. On Nov. 3rd, the arctic front pushed through Marias Pass by 3 pm MST and into Essex by 5:16 pm MST.

Snow showers developed on the back side of an exiting upper level trough across northwest Montana by Sunday afternoon November 3rd. With warm temperatures initially the showers were not much of an impact, but as they grew in size, visibilities dropped down to less than one half mile or less at times, air & road temperatures fell to near freezing and roads became snow-covered and slick. A weather spotter in Columbia Falls reported 4 of total snow with a majority of falling as moderate to heavy snow from 3:37 to 7:37 pm MST on the 3rd. Other snowfall amounts include: 2 5 miles north-northwest of Creston, 3 at the Glacier Park Int. Airport and 2.2 at Bigfork/Ferndale.

A local newspaper reporter tweeted at 7:57 am MST on November 4th that slick roads had caused several accidents from Frenchtown to just east of US-93 in Missoula, or between mile markers 92 and 98 on Interstate 90. The MT DOT Ninemile sensor reported snow falling continuously from 6 pm MST on Sunday evening Nov. 3rd through 11:45 am MST on Monday Nov. 4th with road temperatures ranging between 28 and 32 degrees F. Nearby snowfall amounts include: 1.5 Evaro Hill, 1.3 2 mi. west of Bonner, 3 Arlee, 0.3 Missoula Int. Airport, and 1.5 Seeley Lake.

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.