Unexpected tornadoes in North Carolina on 3/27/09, while snowstorm raged in the Plains

It was a wild week of weather across the country, with flooding in North Dakota and a blizzard in Kansas (the town of Pratt where I grew up got 28 inches of snow!). Early in the week, there were tornadoes and injuries in Nebraska on Monday 3/23/09, and tornadoes again in Mississippi early Thursday morning with 20 injuries and many homes destroyed in the town of Magee. However, the event that really caught my attention was the tornadoes in North Carolina on Friday 3/27/09. It was unexpected (no severe outlook, watches, or even warnings early on), and involved several tornado reports over a 2 hour period with one tornado rated EF2 on the south and east side of Fayetteville, North Carolina (see photos above).

Unexpected events are always useful to look at to see if there are clues from which we can learn as forecasters. Looking back at Friday's case, there was a strong short wave and wind max aloft forecast to eject northeastward across the Carolinas (see 700 mb forecast map above), out ahead of the large blizzard-producing trough over the central plains. At the surface, there was a significant axis of dew points pointing northward into the Carolinas ahead of the shortwave (see circled area on the SPC dew point analysis, 3rd image above, at early to mid afternoon). On the same map, I've drawn in the estimated position of the freezing line at 700 mb. Notice how this colder air aloft was overlying the dew point axis over North Carolina. This would likely contribute to more significant instability in that area than one might detect on available total CAPE analyses (only around 250 J/kg, not shown).

In the 4th image above, I've drawn in the surface front on the 20 UTC SPC surface wind and pressure analysis, and also included the 20 UTC 850 mb map and 20 UTC analysis of estimated low-level CAPE below 3 km AGL. Notice how there was a low-level jet of 30-40 kts at 850 mb overrunning the surface front over northern South Carolina and southeast Nouth Carolina, ahead of the short wave aloft. This would provide lift and focus for storms near the warm front/stationary front, and probably increase the wind shear. The low-level CAPE map also indicates that there was a maximum of CAPE close to the ground in this same area, suggesting significant CAPE that might be missed when looking at relatively small values on corresponding total CAPE analyses.

The last image above shows a small supercell storm (see arrow) approaching Fayetteville (FAY) on radar at 2024 UTC and 2057 UTC, and a NAM/WRF model forecast profile for Fayetteville near the same time. Notice how the CAPE on the profile was bunched down low, with the fattest CAPE located near 700 mb (3 km above ground). A more typical tornado sounding in the Plains associated with supercells would have the CAPE distributed through a much deeper layer, with the fattest CAPE area located up around 400 mb (near 6-7 km above ground), more than twice as high as the 3/27/09 Fayetteville profile. Even though the low-level shear and storm-relative helicity (SRH) on this profile were not impressive (< 100 m2/s2, a value reinforced by RUC model profiles and SPC estimates, not shown), the rapid upward acceleration of updraft parcels due to CAPE residing so close to the ground may have facilitated tilting and stretching of the available low-level SRH near and north of the front. This could be a key issue regarding tornado potential in this case that involved tornadoes from very low-topped supercells.

Events and settings like this appear to reinforce the importance of detecting areas where CAPE is located atypically low in the atmosphere. This is particularly true when total CAPE looks marginal (say, < 500 J/kg), yet there are other favorable features present such as a short wave aloft, surface boundary, and surface dew point axis in place. Thankfully, tornadoes in most such events are not that strong (usually EF2 or less in intensity).

- Jon Davies 3/29/09

9th Annual Severe Symposium in Lawrence KS, and Storm Chasing Series Shelved

Shawna and I will both be speaking at the 9th Annual Severe Weather Symposium in Lawrence, Kansas this Saturday 3/21/09. The Symposium will be held from 7:30a - 1:00p at the Lawrence Arts Center, 940 New Hampshire St. in Lawrence. Here's the web site.

Shawna's talk will be about how storm chasers can help with first response, and also educate those in their local communities about severe weather awareness. I'll be doing a talk about the tornadoes in Kansas and Iowa on June 11, 2008.

Some other news... The storm chasing series that was to be broadcast this spring has apparently been shelved or cancelled by network executives. Shawna and I were to be in a couple episodes, but it now looks like it won't be aired. Such is the uncertainty of TV :-(.

Hope to see some people at the Symposium on Saturday.

- Jon Davies 3/19/09

Storm chasers featured on The Weather Channel's web site

FWIW, I'm being featured currently on The Weather Channel's web site along with several other prominent storm chasers. See:

http://www.weather.com/tv/programs/Storm-Chasers.html

There's some photos, video, and miscellaneous information about me there. Thanks to Tony Grohovsky at TWC for setting this up.

Shawna and I just got back from the Denver Chaser Convention. It was great talking with so many chasers there, including Reed Timmer, Tim Samaras, Roger Hill, Mike Umscheid, Matt Crowther and Betsy Abrams, Jim Leonard, Tony Laubach, Brandon Ivey, Kory Hartman and Kenny Allen, and I could on and on. The presentations by experts such as Rich Thompson, Dr. Greg Forbes, Tim Marshall and others were excellent. And Shawna's talk about chaser preparedness and first response was very well received.

Here's a good recap of the convention at examiner.com:

http://www.examiner.com/x-219-Denver-Weather-Examiner~topic86015-weather-events

- Jon Davies 2/17/09

Deadly tornado after dark in south-central Oklahoma on 2/11/09

Sadly, 2009's first "tornado disaster" has come with a tornado after dark at Lone Grove (near Ardmore) in south central Oklahoma. With news reports of at least 8 dead, one has to wonder if darkness contributed to the death toll. In 2007, 2008, and now 2009, we continue to see damaging and deadly nighttime tornadoes in the Plains, something more commonly associated with the southeastern United States.

Above, two radar reflectivity images (see white arrows) show the deadly supercell at 0000 UTC, and again at 0135 UTC, just after the time the tornado was hitting Lone Grove. With a large line of storms to the west and north, this reaffirms that discrete supercells tend to produce the strongest tornadoes, removed from immediate interference by adjacent storms. As the line to the west overtook and engulfed the supercell after 0200 UTC, tornadoes ceased.

The environment was very primed for tornadoes after dark. Strong forcing was occuring with the upper system, seen in the 500 mb NAM/WRF forecast graphic above. The RUC model was forecasting strong combinations of CAPE and low-level shear (storm-relative helicity or SRH) well in advance of this event, seen in the first part of the forecast graphic above. The second half of the same graphic suggested a very moist, surface-based environment forecast in the same area, with large low-level CAPE.

A modified RUC analysis sounding at Ardmore (also seen above) as the tornadic cell was passing to the north and west, also suggests that an excellent setting for strong or violent tornadoes was present. Instability was large for after dark at this early time of year, with MLCAPE > 2500 J/kg, while 0-1 km SRH was also very large (> 500 m2/s2) for support of low-level rotation in storms. Deep layer shear was quite strong, approaching 60 kts to intensify updrafts, and low-level MLCAPE below 3 km (> 250 J/kg!) indicated a strongly surface-based setting with essentially no inhibition (MLCIN).

Excellent tornado warnings were issued for this storm by the National Weather Service. Better awareness and action by the public in response to such warnings and settings is what will save more lives with nighttime tornadoes.

My wife Shawna will be giving a talk at the Denver Chaser Convention this weekend (Feb 14-15) about how chasers can help with severe weather education, and be better prepared to assist in first response situations. This deadly early season Oklahoma event reminds me that it's an important talk.

- Jon Davies 2/11/09

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: http://chaserconvention.com.

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

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

Damaging thunderstorm winds in south Kansas City on 12/27/08

It's unusual to get severe thunderstorms in the Kansas City (KC) area around Christmas, but it sure did happen yesterday morning (Saturday 12/27). The setting involved a very strong upper trough that brought unseasonably warm air northward ahead of it (record temps in the 60s F in KC on Friday), and an early morning bow echo type thunderstorm feature that interacted with a quasi-stationary outflow boundary in the south KC area.

The first graphic above shows the deep mid-level trough around midnight going into early morning on 12/27, along with SPC storm reports, and a WRF forecast of low-level CAPE suggesting an unstable surface-based environment extending northward into the KC area overnight. The 2nd graphic is a radar reflectivity image showing an ENE-WSW outflow boundary in place across the south KC metro area at 4:00 am, the result of thunderstorms that had moved across to the north of KC in the 2-3 hours prior. The bow echo thunderstorm feature is also visible approaching KC from the SW. Surface temperatures south of the ENE-WSW boundary were in the low-mid 60s F, while north of this same boundary, temperatures were at least 10-15 F colder as a result of storm outflow.

The 3rd graphic is a RUC analysis profile estimating the environment just south of the ENE-WSW boundary at Olathe KS (OJC) about 40 minutes before the damaging winds hit Johnson County (the SW side of the KC metro area). Although there was not a lot of CAPE (maybe about 200 J/kg), the profile was fairly surface-based with a deep low-level moist layer and around 50 J/kg of CAPE below 3 km. Also notice how strong the southerly low-level winds were at only 2000 ft above the surface (roughly 900 mb), with sustained speeds to 50 kts (nearly 60 mph)! It wouldn't take much storm downdraft to move these winds downward to the surface, particularly in a surface-based setting like that just south of the ENE-WSW boundary. In contrast, the 4th graphic above is a RUC profile at KC International Airport (MCI), roughly 20-25 miles north of the same boundary. Notice that with colder temps north of the boundary, this profile is "elevated", with no CAPE at all from lifted parcels in the lowest 100 mb. Even though the strongest part of the radar bow echo went across northward near the airport, the damaging winds were limited to the area along and just south of the ENE-WSW boundary. That's probably because that's where the warm surface-based environment was, where it was relatively easy to move strong winds downward from not far aloft, whereas farther north the cold near-surface setting probably kept damaging downdrafts from reaching the ground.

The last graphic above is both reflectivity and velocity showing the strongest winds coming into the south KC area around 4:40 am, reaching measured speeds around 80 mph. This was south of the strongest radar echo, but along the advancing outflow southeast of the bow echo feature. Again, that's where the warm surface-based setting was (south of the ENE-WSW boundary), better for allowing damaging winds to reach the surface.

What a weird week in the KC area... sub-zero (F) temperatures early on (Sun-Mon), then temps recovering to record high levels on Friday with thunderstorms, and back to ice and snow during the day on Saturday. On Friday evening, Shawna and I found ourselves driving in a heavy thunderstorm in north KC with sharp CG lighting, then getting up to ice covered trees on Saturday morning while more storms raged to our southeast. If you live in the Plains, just wait a few minutes... the weather will probably change :-).

- Jon Davies 12/28/08