1. Ogden Supercell?: Yesterday afternoon, a long-lived thunderstorm with supercell-like characteristics developed near Dugway Proving Ground and tracked to the Ogden Area over about a 2.5-hour period. It was a right-moving storm, in that it was moving somewhat to the right of the steering-layer flow and the tracks of other convective cells. This is common characteristic of supercell thunderstorms, which are long-lived thunderstorms with rotating updrafts (note: there are also left-moving storms, but they are less common). The Doppler velocity signature of the storm, however, wasn't especially pronounced, so I'll leave it to the severe convective storms experts to ascertain whether or not the storm qualifies for Supercell status.
2. Severe straight-line winds. The storm brought strong straight-line winds to the Ogden area and the northern Wasatch Front. Here's a remarkable video of the straight-line winds from Antelope Island:Long-lived svr t-strm tracked from Dugway to Ogden area this aft. 75 mph gust at Hill AFB. Warnings up for Box Elder/Cache. Check w/ NWS pic.twitter.com/KnzSvlH2FA— Jim Steenburgh (@ProfessorPowder) September 22, 2016
— Antelope Island SP (@AntelopeSP) September 22, 2016
Colleagues here in our mountain meteorology group installed a sensor on the playa just east of Antelope Island earlier this summer that collects data every minute. The passage of the storm's gust front was accompanied by a nearly instantaneous drop in temperature of more than 20ºF, wind shift from SSE to W, and a wind gust of 75 mph.
3. Ogden tornado. The storm also spawned a tornado south of Ogden, which was captured in a video posted by Neil Essig on YouTube.
3. Tornado Damage Scale. I have been asked by a few people how strong the tornado was. Tornadoes today are classified using the Enhanced Fujita (EF) Scale, which is an updated version of the Fujita Scale originally developed by Ted Fujita, a meteorological pioneer in many areas, including forensic investigations of tornadoes and severe storms.
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| Source: NWS |
5. Try to avoid saying it was "only" and EF-0, EF-1, or EF-2 tornado. I used to tell people that I really wanted to see a tornado, and then I saw the August 11, 1999 tornado move through the Avenues. I was completely naive about the damage that a "small" tornado could do. Like a surgical knife, it cut through the neighborhood, doing considerable damage along a path one or two houses wide, with nearby homes mostly unscathed. For those impacted, "only" and EF-0, EF-1, or EF-2 makes little sense. Their homes and lives have been upended.
6. Overnight snow. Yup, the white stuff has arrived in the upper elevations of the Wasatch Range.
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| Source: Alta |
7. Future snow. The circulation center for the system is currently moving over us and precipitation is occurring mainly to the north and west of the Salt Lake Valley.
If you feel disappointed, don't despair, we will see more snow today and tonight. I'm going to go for another 5-10 inches through 6 am tomorrow morning at Alta-Collins. There's a chance for more, and indeed there were 2 members of last night's NCAR ensemble that pumped out more than 1.5" of water today and tonight for that area (which would probably give us something like 12-18" given the high densities we are dealing with), but 5-10" is the most likely range.
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ReplyDeleteFrom your blog post the day prior: "Over the years, I've learned to pay careful attention to weather situations that involve the interaction of upper-level troughs in the midlatitude westerlies with monsoon moisture as this often leads to the development of severe convective storms. The pattern through Thursday night fits this description and demands this careful attention." Pretty fortuitous statement Jim!
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