November funnels near Bakersfield CA

My friend composer/conductor William Stromberg (who also storm chases with his wife Anna Bonn) sent me the cool photos above taken by his brother Robert Stromberg (production designer and Oscar winner earlier this year for the film Avatar) yesterday morning while driving on Interstate 5 near Bakersfield, California (about 90 miles north-northwest of Los Angeles). These came out of some very low-topped convective showers associated with a potent upper storm system but limited instability, so I thought the setting was worth a look.

The 500mb forecast during the day on 11/8/10 (see 3rd image above) showed a strong upper trough (heavy black dashed line) moving across California and Nevada. Although a surface cool front (not shown) associated with this trough had already moved through the area, there was just enough moisture (surface dew points in the upper 40s F) and cold air aloft for a little sun-driven surface heating to pop some small showers (see satellite image above) in the Bakersfield vicinity, aided by forcing from the upper system.

A RUC model analysis sounding estimate for Bakersfield (BFL, see last image above) at around 16 UTC (8 am PST, near the time of the funnels), indicated a small pocket of CAPE/instability (possibly under-estimated by the RUC model) at around 3000 ft above ground, which is very near the surface. Apparently, enhanced stretching with the CAPE pocket so close to the ground, a steep lapse rate below cloud base, and the strength of the upper system combined to generate these "cold air" funnels within the updraft columns of 1 or 2 of the low-topped showers. As you can see, you don't always need alot of instability to get interesting things to happen with some fall and winter systems moving across southern and central California.

I didn't see any funnel or tornado reports online with the National Weather Service, so it may be that Robert was the only one to photograph these funnels. Many thanks to Robert and William for sharing these photos of an event that would otherwise have probably gone undocumented!

- Jon Davies 11/8/10

Late October EF2 tornado at Rice TX

There's been no shortage of interesting tornado events the past couple months, with a tropical system producing tornadoes in the Dallas TX area and a bow echo type tornado in the Queens/Brooklyn area of New York City in September, and damaging tornadoes in the high country of central Arizona in early October. I've been busy, so no case study posts on those events. Last Sunday saw a photogenic October EF2 tornado at Rice TX, southeast of Dallas and just north of Corsicana TX (see storm chaser Bridget Geaughan's photo above). Video shown on CNN from a range of about 100 yds from the tornado was quite impressive. Although there's nothing terribly unusual about an October tornado in Texas, I thought I'd at least post some brief material about the setting to help make up for lack of posts in recent weeks.

Probably the most interesting aspect of Sunday's afternoon setting is how quickly the low-level shear increased during the afternoon in response to the strong mid-level trough (see 2nd image above at 500 mb) moving west to east across Texas that helped fire up the storms ahead of a pre-frontal surface trough and wind shift (see surface map, 3rd graphic above). The SPC mesoanalysis showed 0-1 km storm-relative helicity (SRH, a measure of low-level wind shear, see 4th graphic above) at 2100 UTC / 4 pm CDT to be in the 100-150 m2/s2 range in the Rice TX area, values somewhat marginal for support of supercell tornadoes. However, by 2300 UTC / 6 pm CDT, about the time of the tornado, SRH values had doubled (> 250 m2/s2, same graphic) in response to the approaching mid-level trough, increasing the combination of SRH and MLCAPE (around 3000 J/kg) that could help generate low-level mesocyclones with stronger supercells (energy-helicity index near 3.0 and above by 2300 UTC, same graphic).

The RUC analysis profile at Corsicana TX, a few miles to the south of Rice at 2300 UTC during the tornado (see last graphic above), suggested strong combinations of parameters for supporting supercell tornadoes, even with a surface wind slightly west of due south. So a strong tornado occurring with a discrete supercell in this environment was not a surprise; SPC had a tornado watch issued well in advance, and a tornado warning was issued by NWS Ft. Worth based on radar roughly 15 minutes prior to the tornado.

- Jon Davies 10/26/10

Wind damage (and mesovortex) near my home 8/20/10

On Friday 8/20/10 while working at home (north of Kansas City), an intense squall line came through and caused an west to east swath of wind damage about two miles south of where I lived. The photos above show sections of corn crops flattened and some tree damage in that swath, damage I wasn't aware of until the next day when my wife Shawna noticed it while driving to Kansas City. There's really nothing unusual about this, except it seems the swath was associated with a forward "notch" in the line on radar, suggestive of a surface circulation with strong winds about 1-2 miles across called a mesovortex. The Kansas City NWS office at Pleasant Hill MO issued a tornado warning (based on this feature) a few minutes after it passed to the south of my house, and wind reports of 70-80 mph winds were verified in Holt MO, about 15 miles to my east. It's not too often a feature like this comes close to your home, so I thought I'd post a little documentation here.

NWS issued severe thunderstorm warnings for Clinton/Platte/Clay counties of MO well before the squall line passed my house. My photos above show views to the south and west as the line approached my home, with a bowing dark cloud shelf to my south and a ragged chaotic cloud base to my west just north of the "notch" on radar (I wasn't aware of the radar feature or damage until later). The forward flank "notch" can be seen on the radar base reflectivity images above (arrows), as well as the low-level base velocity image (circle). It was difficult to pick out a rotational "couplet" with this feature on storm-relative radar velocity images from the Pleasant Hill NWS radar (not shown). However, according to Evan Bookbinder at the NWS office, the closer and more favorably located Terminal Doppler Radar near MCI (KC International Airport, not shown) indicated a pronounced couplet with 80-90 mph winds toward the east on its south side as the feature approached Holt MO, prompting the tornado warning around 1905 UTC. The wind damage south of my home (a swath of 70-80 mph winds) clearly lined up with this radar feature before the tornado warning as it tracked eastward.

A surface map is also shown above, showing the squall line location after 1800 UTC, and surface temps in the 90s F ahead of the line with dew points in the mid-upper 70s F. The early afternoon environment over northwest Missouri (not shown) was quite unstable, with CAPE values near 4000 J/kg, around 30-35 knots of deep layer shear (0-6 km AGL), but little low-level shear (storm-relative helicity less than 80-90 m2/s2). So, the CAPE/shear setting was supportive of strong organized storms (possible supercells) with potential for wind damage, but suggested little support for much in the way of tornadoes. Forward flank squall line circulations in such settings can certainly produce notable wind damage, and even occasional weak/brief tornadoes of non-supercell origin.

- Jon Davies 8/22/10

Rare deadly tornado in Montana - 7/26/10

Killer tornadoes are rare in Montana due to the sparse population. Prior to 2010, only 2 deadly tornadoes had been recorded in the state, with the last tornado deaths occurring way back in July of 1983. But yesterday (Monday 7/26/10), sadly, 2 people were killed and another seriously injured when a large tornado struck a ranch in the northeast corner of Montana west of the town of Reserve (see photo and radar images above). This tornadic supercell moved east-southeast from Canada, deviating rightward under westerly flow aloft.

The surface map at early evening (above) showed a surface low over northeast Montana with easterly upslope winds along and just north of a stationary front where surface temperatures (80s F) did not cool too rapidly across the WNW-ESE boundary, and dew points feeding the storm were in the mid to upper 60s F. RUC model soundings had a little trouble depicting the moisture depth in northeast Montana near this boundary (moisture too dry/too shallow just above the ground, not shown) and wind profiles (hodographs a little "flat" in shape, not shown). However, the SPC mesoanalysis effective-layer sig tor parameter (STP, see graphic above) still suggested a "favorable" environment not too far to the east over extreme northwest North Dakota, likely feeding into northeast Montana on the upslope winds near and north of the stationary front.

A RUC analysis sounding at early evening near Reserve MT (last image above) had to be modified for moisture depth and the easterly wind pattern in order to be reasoanbly represnetative of the environment. This modified profile showed excellent deep layer shear (60 kts), good MLCAPE (2800-3000 J/kg), and workable low-level storm-relative helicity (SRH, > 150 m2/s2). Even though the low-level hodograph/wind profile wasn't large or notably strong, there was a "kink" in the profile and enough low-level shear to support strong tornadoes along and near the boundary. It appears this tornadic storm was able to parallel the boundary, taking advantage of the enhanced low-level wind environment there, along with better moisture just north of the stationary front without too much temperature contrast across it. Tornado warnings from the Glasgow NWS blanketed the area traversed by the supercell well in advance of it.

- Jon Davies 7/27/10

After-dark EF4 tornado in NW Iowa 6/25/10 - a look at the environment

Violent (EF4-EF5) tornadoes are rather rare after dark in the Plains. Last Friday's tornadoes during 03-05 UTC 6/26/10 after dark in northwest Iowa (see video image above) included an EF4 intensity tornado near Sibley, Iowa, which certainly makes the environment worth examining.

The tornadoes occurred just ahead of a cool front moving slowly southeastward (not shown) and an approaching upper trough (not shown), associated with the west end cell of a line sagging southward over northern Iowa (see SPC mosaic radar overlays above). The 03 UTC SPC mesoanalysis of 0-1 km energy-helicity index (EHI; see 2nd image above), which combines MLCAPE and 0-1 km SRH, showed very large values (near 10!) ahead of this west-end supercell over northwest Iowa, suggesting strong potential for low-level mesocyclones and possible tornadoes with discrete or tail-end supercells. The SPC mesoanalysis of low-level CAPE (0-3 km MLCAPE, see 3rd graphic above) at the same time also showed a notably surface-based setting over northwest Iowa, with low-level MLCAPE values near 100 J/kg. From a 2009 NWA electronic journal paper by Davies and Fischer, environments with large CAPE and SRH that are also relatively surface-based offer important support for tornadoes after dark, but aren't that common in the Plains due to nighttime cooling beneath typical warm layers advected eastward from the desert southwest. This latter issue did not appear to be a problem last Friday evening over northwest Iowa.

The 03 UTC RUC analysis sounding at Sheldon, Iowa (just south of the tornadic tail-end supercell; see 4th graphic above) confirmed large MLCAPE and SRH (near 4000 J/kg and 500 m2s2) and sizable deep layer shear (> 40 kts), along with a relatively surface-based setting (0-3 km MLCAPE > 100 J/kg, and MLCIN around -50 J/kg), all excellent supporting ingredients for tornadoes with supercells in that environment. In contrast, 110 miles to the east-southeast with another tornado-warned embedded supercell near Clarion, Iowa, the RUC sounding (see last graphic above) showed _no_ low-level CAPE, and MLCIN was quite large (-250 to -300 J/kg) with not nearly as much total MLCAPE above the CIN layer (only around 1600 J/kg),. This suggested somewhat "elevated" nighttime storms with considerably less tornado potential, and no tornadoes were reported in this area farther east.

NWS Sioux Falls has a page detailing their survey of the EF4 tornado near Sibley, Iowa, north of Sheldon.

- Jon Davies 6/30/10

Matt Hughes

This has been a sad couple weeks with Wichita chaser Matt Hughes (of Discovery Channel's Storm Chasers show) hospitalized in serious condition, and then passing away this past Wednesday. I am so very sorry for his family's loss.

I haven't known Matt for very long, but it is clear he was a bright and enthusiastic person, with much passion, and also very sensitive.

With the deadly Yazoo City MS and Oklahoma City OK tornadoes this year, and now Matt's death, I hope these events will serve as reminders to weather enthusiasts that there are more important things in life besides storm chasing, and to keep all that in its proper perspective.

Matt, we will remember you fondly...

- Jon Davies 5-28-10

Brief "chaser convergence" thoughts, and Missouri cold core tornado setting 5/20/10

Wednesday's massive chaser convergence and careless driving in central Oklahoma has been a huge topic of conversation the past couple days. Shawna and I actually decided not to chase that day because of the expected chaser hordes and narrow severe focus in central Oklahoma, and we both had work to do. Sometimes one asks, "If there's already hundreds of people out there shooting the same storm, what's to learn and what's the point of being out there adding to the dangerous traffic jams?" Wednesday was just such a day. Things don't look to improve in similar future situations, unless someone gets killed in traffic and it is well documented. Shawna and I are getting increasingly picky about going out on "big" days with a small focus drawing hundreds of chasers and weather yahoos to the same spot.

Anyway, stepping away from the situation in Oklahoma, Wednesday 5/19 brought some "cold core" action to the Garden City/Dodge City area of southwest Kansas in the form of "landspouts" along a surface boundary close to the 500 mb low, photographed nicely by Mike Umscheid. And Thursday 5/20 brought a few "cold core" supercell tornado reports to the Sedalia area in Missouri east-southeast of Kansas City (see photo above). I had family visiting in town, so no storm chasing for me or Shawna. But with my interest in such settings, the Thursday setup is worth documenting briefly. Thankfully, as with most "cold core" setups, none of the tornadoes were strong.

The 2nd graphic above shows visible satellite with overlaid surface and 500 mb features at 2145 UTC. Notice the boundary intersection in west-central MO, similar to the "cold core" tornado composite shown in this paper. This can be a favored area of severe focus (enhanced low-level shear and forcing) for tornado development when a midlevel low (strong cold air aloft) is nearby to the west (northeast KS on 5/20) and there is some instability. In this case, the N-S boundary wasn't a dryline, but a subtle wind shift intersecting the warm front southwest of Sedalia at late afternoon, notable on satellite along with some clearing for sun's heating. The 3rd graphic shows selected images from the SPC mesoanalysis at 2200 UTC , including the midlevel low, total CAPE (near 1000 J/kg over west-central MO, but certainly not as impressive as down in Texas), low-level CAPE (a significant maximum near the boundary intersection), and SRH (enhanced northeast of the warm front, but probably under-represented closer to the front in west-central MO). The presence of the 500 mb low in northeast KS and the low-level CAPE maximum over west-central MO near the boundary intersection were probably the biggest "heads-up" flags seen here for tornado potential in what otherwise looked like a fairly benign environment.

The 4th graphic above is a radar image at about 2340 UTC when the tornado in the photo above (likely EF0) was occuring near Sedalia (see arrow for cell location). The RUC analysis at 2300 UTC (last graphic above), as with many "cold core" type settings, showed most of the CAPE below 500 mb, suggesting sizable low-level stretching. The model-derived estimated hodograph (same graphic) suggested good clockwise curvature to the wind profile and more low-level shear than shown on the SPC mesoanalysis during the afternoon. So, while not an easily forecast event, the presence of these ingredients suggested taking rotational signatures on the nearby Pleasant Hill MO radar and spotter reports very seriously. Indeed, the Kansas City area NWS office did a good job jumping on the situation with tornado warnings and statements as the situation developed and evolved prior to the Sedalia tornado, which is what situational awareness is all about.

- Jon Davies 5/21/10