Saturday, January 31, 2009

Talks at Denver Storm Chaser Convention 2/14/09 and 2/15/09

I will be doing 2 talks at the Denver convention this year: "Thoughts and Research on Nighttime Tornadoes and Rain-wrapped Tornadoes", and "A Review of Some Recent Tornado Settings from a Chase Forecast Perspective". There will several excellent speakers, including Rich Thompson of SPC talking about tornado forecasting, Dr. Howie Bluestein on VORTEX-II, and also Dr. Steve Lyons and Dr. Greg Forbes from The Weather Channel.

In addition, my wife Shawna will be doing what I think is a very important and down-to-earth talk for chasers, "Beyond the Storm - Chasers Helping with Communities and First Response". See:

I understand there may be live online streaming of convention talks this year. So I hope you can make it to Denver, or at least watch online.

- Jon Davies 1/30/09

Monday, January 12, 2009

EF-1 tornado in Alabama on 1/10/09: a subtle small CAPE setting

A weak tornado occurred shortly after 2300 UTC (5 pm CST) on Saturday, Jan. 10, about 30 miles north of Mobile in southwest Alabama. It wasn't very impressive (1-2 mile path, EF-1 winds around 100 mph), and thankfully no one was hurt, but it did do some damage (see NWS photos above, also click here). Given the subtle setting, it was kind of interesting from an environment standpoint.

Radar reflectivity at 2304 UTC from Mobile above shows the tornadic cell, and NWS Mobile did a good job with tornado warnings that were issued across southern Washington county for more than 45 minutes before the tornado struck the town of McIntosh.

The RUC analysis profile above for Mobile (MOB) at 2300 UTC is somewhat unusual, with small total CAPE (only around 400 J/kg!), and most of the CAPE below 600 mb, very low to the ground. Settings like this can enhance stretching near the ground, and with decent SRH (> 200 m2/s2 in the lowest 1 km), they can occasionally support tornadoes, even with small total CAPE.

The SPC graphics above show a large positive tilt 500 mb trough was heading southeastward, with a cold front (not shown) ahead over central Tennessee into central Mississippi. The Alabama tornadic cell occurred well in advance of this front in a moisture axis of 60s F dew points. In the parameter graphics, the SPC total MLCAPE field over southwest Alabama wasn't impressive (> 250 J/kg), but low-level CAPE was large (near 100 J/kg below 3 km) along with low-level SRH (200-300 m2/s2) overlapping the southwest Alabama moisture axis. These ingredients, combined with the low-to-the-ground vertical CAPE distribution in the RUC analysis above, were just enough to help generate a tornado with the cell north of Mobile.

This case is a reminder that storm environments with CAPE "squeezed" low to the ground certainly aren't limited to cold-core events (for example, see here).

- Jon Davies 1/12/09