Blowdown in the Tobacco Roots of Southwestern Montana – Big Sky Walker

A scary experience.
On Sunday afternoon, August 11, 2019, a micro-eruption occurred in the Tobacco Root Mountains of southwest Montana, downing an estimated 200 to 250 acres of trees shown in the photo above. This flood resulted in the trails leading back to Granite Lake being blocked and four people stranded in the backcountry because trees blocked the trails leading out of the area. Personnel from Madison County Search and Rescue and a National Forest Service fire team were dispatched to rescue those stranded, and two military helicopters were sent to see if anyone else was in the area.

Four years later.
I didn’t have any big adventures planned this summer – I just wanted to enjoy being home and do a few day hikes in the Helena area before returning to Hays for my final (42nd) year of teaching. One thing I really wanted to do this summer was to hike into Tobacco Roots, look at the precipitation, take some drone photos, and then use this blog post (#100) to explain microbursts. I left Helena at 6:30am on 7/14/23, made the 100 mile drive to an ATV trail near Pony and started running. Since I was in the area, I decided to climb Granite Peak as well. Not to be confused with Granite Peak in the Beartooths (Montana’s highest mountain). This Granite Peak (10,580 feet) is impressive in its own right – the second highest in the Tobacco Roots, not far behind Hollowtop, which stands 10,604 feet above sea level.

Hiking 9 a.m. to 5 p.m.
The hike ended up being 15 miles round trip. All but the last few hundred feet to the summit of Granite Peak were on a rocky trail best suited to off-road vehicles. I started the hike at 9am and finished at 5pm. Despite the poor trail conditions, it was a pleasant day – the weather was perfect, the rain didn’t disappoint and the views from the top of Granite were breathtaking due to the exceptionally clear skies. For details about the hike, including maps and photos, see the photo tour (link below). If you want to learn more about microbursts, read on.

The sky is falling!
So why do microbursts happen? Microbursts, like tornadoes, lightning, hail and flash floods, are associated with severe thunderstorms. One of the main causes is evaporative cooling – the same process that occurs when sweat evaporates from the skin. As sweat evaporates, it cools your body because the water molecules absorb (and dissipate) heat as they change from liquid to vapor. The same thing can happen within a thunderstorm. When rain or hail falls through very dry air, or the thunderstorm sucks in dry air, much (or all) of the precipitation can evaporate (called sublimation, when hail turns into vapor). Water molecules absorb heat from the surrounding air to cause this phase change, making the air significantly colder. The more evaporation, the colder the air becomes. Anyone who has ever opened a refrigerator door knows that colder air is heavier than warmer air. As this air (cooled by the evaporation of rain or the sublimation of hail) becomes heavier, it crashes to the ground like a lead weight. When the microburst reaches the ground surface, wind speeds can exceed 150 mph – strong enough to blow over mature pine trees. Interestingly, the opposite phase change (steam to snow) releases heat, contributing to the warming effect that causes Chinook winds.

Mr. Tornado.
Microbursts were discovered in the 1970s by tornado researcher Ted Fujita, who developed the famous Fujita scale for rating tornado intensity. No doubt you’ve heard of an F5 tornado – the “F” stands for Fujita. The scale was revised a few years ago – it is now called the “Enhanced Fujita Scale” (EF0 – EF5). Fujita suspected that micro-explosions did indeed exist and suspected that they were responsible for a number of mysterious plane crashes that had occurred in the past during takeoffs or landings during thunderstorms. Confirmation of his hypothesis ultimately led to a reduction in aviation accidents and saving lives.

Icing on the cake.
The sight of the flood disaster totally enriched my day, leaving me full of energy and ready for the second half of my hike. I followed the ATV trail another 3 miles to a pass and then scampered up the north slope to the summit of Granite Peak. I was pleasantly surprised at how far I could see – even on clear days this summer, visibility seemed to be somewhat limited. I spent about 45 minutes enjoying the views and taking photos (some with my drone) before heading back. For me it was a fun trip, but if seeing the microburst damage isn’t important to you, I recommend climbing Hollowtop instead. Although there is no trail, the extremely steep route I took up to Hollowtop was much more pleasant and the peak itself is more interesting – plus it’s the highest in the range. For more information, see my blog post (link below). Happy Trails!

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