3-21-11 and 3-22-11 storm forecasts - the "cap" made so much difference!

With a big trough in the west ejecting waves of energy into the Plains early this week, at first glance, both Monday 3-21-11 and Tuesday 3-22-11 all looked to be possible severe weather days over the KS/NE/MO/IA area. But the "cap" (warm temperatures advecting/moving northeastward from the desert southwestern U.S. in southwesterly flow aloft, called the "elevated mixed layer" or EML) made all the difference between the 2 days. Monday was a bust, with the EML completely inhibiting surface-based thunderstorm developing. But a strong wave in upper flow on Tuesday quickly eroded the EML and allowed storms to fire, some becoming tornadic over Iowa (see pics above from my storm chase with Shawna on Tuesday in the Bridgewater-Greenfield, Iowa area)

When looking at model forecasts for upcoming days, 700mb temperature forecasts can be useful in gaging when the "cap" may be too strong for storms to form. I like to use the chart above as a very rough guideline east of the high plains. In March, 700mb temperatures around 5 deg C (see the chart) are usually warm enough to completely inhibit storm development, unless one is in the high plains with a moist easterly upslope wind to provide mechanical lift (for example, last Saturday evening 3-19 around Lubbock TX - not shown -, where a couple supercells formed), or daytime temperatures become unseasonably warm (for example, 90's F).

The first 700mb forecast graphic above shows NAM and RUC forecasts for Monday evening (00 UTC 3-22-11) from the UCAR online site. Notice how temperatures 5 deg C and warmer on both models were forecast to extend all the way to the NE/SD border, blanketing the central plains in warm air aloft. As a result, Shawna and I did not chase on Monday, with MLCAPE all "tucked" in under this warm air aloft. No daytime storms formed across the KS/NE area due to this strong cap, even though appreciable MLCAPE was present south of a warm front (see the first panel of Earl Barker's RUC CAPE forecast graphic above at the same time). The 2nd 700 mb forecast graphic above shows NAM and RUC forecasts for Tuesday evening (00 UTC 3-23-11) that were dramatically different from the day before, with a strong upper wave moving through the plains, removing the "cap" over KS/NE/IA as much cooler temperatures aloft poured in (notice how the 5 deg C line was forecast to move well southeastward from the day before). This energy and cooling aloft easily triggered thunderstorms in northern KS and eastern NE during the afternoon that moved eastward into Iowa where combinations of MLCAPE (see the 2nd panel of Earl's RUC CAPE forecast above) and low-level shear (not shown) were favorable to support a few tornadoes.

Use the 700 mb temperature chart above as only a rough guide, and not a hard and fast rule. The most helpful thing is to watch _trends_ (for example, how the temperatures around 5 deg C and above moved out into the plains and increased aloft on Sunday 3-20 and Monday 3-21 on model forecasts, then retreated again with the approach of the strong wave on Tuesday 3-22). And don't think that temperatures cooler than the guidelines in the chart mean that storms will defintely occur! On Sunday 3-20 (not shown), 700 mb temperatures cooler than 4-5 deg C were over northern MO and IA, but storms did not develop along a weak frontal boundary. This was probably due to subsidence (sinking motion) behind a short wave that had moved across the Midwest earlier in the day, and boundary layer moisture that was not that deep or rich.

Hopefully the above helps some chasers be more aware of the trending of temperatures aloft and the "cap"/EML over the plains... that can really impact storm potential.

- Jon Davies 3/23/11

ChaserCon Forecasting Class, an Oscar-winning Storm Chaser, & New Book on the 1966 Topeka Tornado

Wow... tonight it has already been 2 weeks since I taught a tornado forecasting class for the first time at the National Storm Chaser Convention (ChaserCon) in Denver (see pic of me above). It was fun to do, well-received and well-attended (110 people), and I've had several attendees ask about access to some of my Powerpoint slides. I've managed to whittle down the presentation and put a subset of the slides online. If you were one of the people who paid to take my class, send me an e-mail at davieswx@gmail.com, and I'll direct you to the URL address where you can find these.

On another subject, Bill and Anna Stromberg are good friends who work in the film music business in the LA area, and they love to storm chase. Amazingly, Bill's brother, production/art designer Robert Stromberg, won his 2nd Oscar in a row last Sunday night for his work on last year's Alice in Wonderland ! Bill and Anna's storm chasing bug has caught Robert a bit, who was kind enough to share his photos through Bill on this blog last November when he was the only one to document what looked to be a rare morning tornado near Bakersfield CA. Go back and check those pics out here. Congratulations on your Oscar win, Robert!

Last but not least, on Wednesday night 3/2/11, our Kansas City AMS chapter had author Bonar Menninger as a guest speaker on his new book about the deadly 1966 Topeka tornado, And Hell Followed With It (see image above). This is an awesome account of a seminal tornado event that was the first $100 million tornado, grabbing a nation's attention. It was also one of the first events to take full advantage of a relatively new tornado warning system in our nation. Menninger's book relates some searing experiences of people whose lives were literally turned upside down by this tornado. It's important for storm chasers and weather enthusiasts to be reminded how terribly serious and gut-wrenching some weather events can be... weather is not all "fun". This book does that very effectively. Topeka storm chaser and friend Rick Schmidt helped provide some photos for the book taken in 1966 by his father, Topeka Daily Capital photographer Delmar Schmidt. It is a gripping read and an important book documenting a key weather event! I strongly recommend it. Check out the web site at www.topekatornado.com.

- Jon Davies 3/4/11

The U.S. megastorm of 1 Feb 2011 - Why no tornado outbreak?

The big storm on Feb. 1st that affected much of the central U.S. and Midwest with blizzard conditions and massive snow (see photo above of snow shoveling pile at my house N of Kansas City) was quite a news maker, with several deaths blamed on the dangerous conditions. Often, such strong winter systems (in this case, an intense negative tilt wave moving northeastward out of a large trough, see 500 mb chart above) plow up enough moisture, wind shear and lift to generate an outbreak of tornadoes somewhere in the southern U.S. near the Gulf coast. I heard meteorologists on TV mention the "T" word as a possiblilty in the Deep South several times as this storm intensified. But so far, only 3 weak/brief tornadoes have been reported where several tornado watches were issued. Why the lack of tornadoes on the south end of this intense system?

Using Mobile AL as a spot check location with scattered storms approaching at mid afternoon on Feb. 1st (see 3rd graphic above showing radar and tornado watch in the Mobile area), I saved some RUC analysis soundings at 2000 UTC (2 p.m. CST), using several different parcel lifts (see skewT plots on 4th graphic above). Even though low-level wind shear and storm-relative helicity (SRH) was quite large and seemingly favorable for tornadoes, notice that low-level lifted air parcels from both surface and 1 km above ground showed little if any instability/CAPE (red hatching), and lots of convective inhibition (CIN, green hatching). The most unstable lifted parcel was found well above ground at 2 km (CAPE > 700 J/kg), so that was where the true instability fueling the storms was coming from. In other words, the environment along the Gulf coast appeared mostly _elevated_ in nature, with little instability to be found from air lifted near the ground. This was confirmed by the SPC mesoanalysis at 20 UTC (last graphic above), showing SBCAPE and lowest 1 km MLCAPE to be confined offshore out in the Gulf.

Its been a cold January 2011 with repeated intrusions of Arctic air penetrating southward to the Gulf and cooling the boundary-layer and surface waters. So maybe it's not a surprise that this strong system was unable to pull adequate instability northward at the _surface_ to support tornadoes. Another problem on Feb. 1st was the convective mode, which was largely linear or clumped into complex structures, rather than discrete cells (see radar in 3rd graphic above). Both these factors probably combined to limit the tornado potential. However, with the very strong low-level and deep layer wind shear present (see the Mobile AL hodograph above), it would be remiss for SPC to not alert the public to the possibility of tornadoes via watches, as small increases in CAPE near the coast not forecast by computer models might help support brief tornadoes. Small CAPE/large shear situations near the Gulf coast are often very difficult for forecasters to assess regarding tornado potential, as subtle changes in the low-level moisture profile can make significant differences in the environment.

Jon Davies - 2/2/11

Reed Timmer to speak in Kansas City January 18

My wife Shawna is currently vice president of the Kansas City AMS/NWA Chapter. She asked me to announce that Reed Timmer from "Storm Chasers" will be our guest presenter at the January 18th chapter meeting! It will be held at Ameristar Casino, 3200 North Ameristar Drive in Kansas City MO. See the flier above.

Reed's talk is "TVN Storm Chasing and Extreme Tornado Research -- the Measurement of Vertical Tornado Winds from Inside the Funnel." He will also have his book "Into the Storm" available for purchase.

This is open to the public. The price is $24.00 per person for both dinner and talk. Make sure to RSVP by January 14 (Friday) 11:00 a.m. by e-mail to my wife Shawna at shawnadavies@gmail.com or to Jim Keeney at Jim.Keeney@noaa.gov.

Storm chasers and weather enthusiasts in the Missouri/Kansas/Nebraska/Iowa area, please pass the word!

Thanks!

- Jon Davies 1/12/11

Long-lived tornadic supercell complex kills 7 in AR/MO 12/31/10

Killer tornadoes in Missouri are somewhat rare during the month of December, but do happen (5 such events since 1950 prior to 2010). Last Friday's tornado outbreak that left 4 dead in central MO (in addition to 3 dead in northwest AR) was also rare in that the Missouri tornadoes occurred at mid morning (see photos above at Ft. Leonard Wood and Rolla). Another interesting aspect of the outbreak was its evolution from a complex beginning with 2 supercells close to each other in eastern OK into a bow echo structure over eastern MO, persisting for over 6 hours through parts of OK/AR/MO/IL.

The 2nd and 3rd graphics above are regional radar reflectivity composites showing the broad evolution of this complex from 2 distinct long track supercells (circled in white) around 1200 UTC/6 a.m. through 1600 UTC/10 a.m., toward merging into a bow echo type structure after that, with several embedded tornadoes in the St. Louis area around noon. Locations of some stronger tornadoes (EF2+) and deaths are indicated on these graphics. Some of the tornadoes in the latter stages of this complex may have been bow echo/QLCS tornadoes associated with mesovortices instead of deeper mesocyclones. At any rate, this is an interesting example of an event metamorphasis from quasi-discrete supercell mode to a more linear or bow echo mode with embedded tornadoes continuing during both modes.

The environment ahead of the large upper trough (not shown) generating the storms was a classic "small CAPE/large shear" setting so common with winter tornado events. The RUC sounding analysis for 1500 UTC (9 a.m.) at West Plains MO (UNO, see 4nd graphic above) during the hour before the Ft. Leonard Wood and Rolla tornadoes (both from northern supercell, 2 deaths) and Lecoma MO tornado (southern supercell, 2 deaths) showed this, with massive low-level shear and a very large clockwise-turning hodograph/wind profile in the lowest 1 km. Total CAPE of only 400-600 J/kg (620 J/kg sfc-based CAPE) in a close-to-saturated low level environment with little or no convective inhibition (CIN) was more than enough buoyancy to support strong supercell updrafts and deadly tornadoes in such a highly sheared environment.

Composite supercell tornado parameters sometimes have problems working well as indicators in such small CAPE environments. The last graphic above shows the significant tornado parameter (STP, effective shear version) along with radar and surface features around the time tornadoes were occurring in the St. Louis area; notice that not much "sig tor threat" was explicitly indicated over Missouri. Conditional sig tor probabilities (same graphic, same time, developed by Bill Togstad using one of my RUC sounding databases) suggested more tornado potential in the St. Louis area, probably because Bill's equation seems somewhat more "tuned" toward detecting smaller CAPE settings with potential for tornadoes, a nice characteristic, but also one that can sometimes increase false alarms in marginal situations.

At any rate, such a prolific, persistent, and mode-evolving complex (6 hrs+ life span, 7 total deaths) is a rather rare event in the Missouri area, particularly on New Years Eve Day! More survey information can be found at NWS Tulsa, NWS Springfield, and NWS St. Louis sites.

- Jon Davies 1/5/11

Rare EF2 tornado in Oregon 12/14/10

Yesterday (Tuesday 12/14/10) saw an EF2 intensity tornado strike just southeast of Salem, Oregon shortly before noon PST (2000 UTC) at Aumsville (see photo above), with 2 injuries reported. It's been 17 years (1993) since a tornado that strong occurred in Oregon, and it was only the 4th tornado of F2/EF2 or stronger intensity to occur in the state since the early 1970's. Such events are so rare that they are typically unforecastable, as they usually occur in settings with small CAPE (<> 40 deg F) from western Washington into west central Oregon, and some spotty sun's heating on satellite. Although SPC mesoanalysis graphics showed total CAPE amounts not really registering (less than 250 J/kg, not shown), some low-level CAPE (SBCAPE below 3 km AGL) was indicated over the same area where dew points were maximized (see red areas in 4th graphic above at 1900 UTC). The small tornadic cell formed rapidly around 1910 UTC and began producing a five-mile track tornado around 1945 UTC (see radar inset on 4th graphic).

As is often the case in small CAPE settings, RUC soundings tended to under-estimate the environmental CAPE in this setting, showing surface temperatures around 45 deg F and surface dew points around 40 deg F. However, actual surface observations at Salem at 1900 UTC (not shown) before the tornadic cell formed were 47 F (temperature) and 42 F (dew point). When plugged into the RUC analysis sounding for Salem at 1900 UTC (last graphic above), these updated surface obs combined with cold air not far aloft (-10 deg C at 700 mb !) boosted total CAPE from around 100 J/kg to over 300 J/kg, with the "fattest" CAPE located in the 950-850 mb layer, very close to the ground. Even though total CAPE was unimpressive, this "packing" of CAPE down low in the sounding environment would likely help promote rapid vertical stretching in a local updraft, and given the accompanying sizable low-level and deep-layer wind shear, was able to support a tornadic storm as reported above. But picking out these subtle ingredients in a rapidly evolving environment is more than difficult, and everything apparently had to come together just right to generate a tornado in this case. Another similar setting might generate only storms with small hail. Adding to these problems, rotation in small cells (like this case) more than 25-35 miles from radar is usually not detectable for advance warning purposes.

Although it's not hard to go back and see contributing factors after a climatologically rare small CAPE event like this, detecting in real time these subtle ingredients that might make for a mesoscale "accident" in a location where tornadoes don't often occur is next to impossible.

- Jon Davies 12/15/10

Data collecting inside tornadoes - Will it improve warning lead times?

The Discovery television show "Storm Chasers" concluded another exciting season this past week. A repeating theme on the show is getting armored vehicles or probes into tornadoes (which makes for exciting storm chase footage) on the premise that this will help improve tornado warning lead times and save lives. But, in reality, that's really doubtful. Chuck Doswell's blog here discusses this issue very well. Measurements inside tornadoes may be useful toward understanding dynamics inside ongoing tornadoes (a valid goal), but will tell us next to nothing about which environments and storms will produce potentially deadly tornadoes. Chuck also points out that warnings for tornadoes most likely to cause deaths are already pretty good. Looking at four tornado days featured this season on "Storm Chasers" that each generated at least one violent EF4 tornado helps drive this point home rather well.

4/24/10 Yazoo City MS EF4 tornado (see photo by Dick McGowan above) - This tornado caused several deaths and was on the ground for 100+ miles in a setting that was well-recognized by NWS meteorologists as having high potential for tornadoes well in advance (for example, see experimental conditional sig tor probabiliities on 1st map graphic above). The specific warning for Yazoo City was issued approximately 30 minutes before the tornado hit town, and warnings for the same tornadic storm farther west had been ongoing for an hour. Can we really improve on those good lead times?

5/10/10 Tornadoes in central OK, including EF4 tornadoes just southeast of Oklahoma City - Again, the potential for this day was outlooked well in advance, with the coming together of environment ingredients quite evident (see 2nd graphic above). Tornado warnings in central Oklahoma were generally issued 30 minutes in advance of damage and deaths.

5/22/10 EF4 tornado near Bowdle in north-central ND - This setting was also quite evident in advance (see 3rd map graphic above), where a large tornado hit mainly in open country. A tornado warning for Bowdle was issued nearly 30 minutes in advance of the tornadic storm passing just northwest of town, and tornado warnings farther west had been ongoing for about an hour.

6/17/10 Tornadoes in MN, including the EF4 Wadena MN tornado - Another setting where tornado environment ingredients were very evident (see last graphic above) in advance, and most warnings were issued 30 minutes before sizable towns were struck.

Here are some representative values of individual bulk environmental ingredients associated with the above cases:

4//24/10 MLCAPE 1950 J/kg 0-1k SRH 670 m2/s2 0-6km shear 70 kts
5/10/10 MLCAPE 3340 J/kg 0-1k SRH 610 m2/s2 0-6km shear 62 kts
5/22/10 MLCAPE 3930 J/kg 0-1k SRH 345 m2/s2 0-6km shear 52 kts
6/17/10 MLCAPE 2525 J/kg 0-1k SRH 270 m2/s2 0-6km shear 54 kts

Any competent NWS meteorologist on days with environment ingredients like those above would be primed and ready to issue warnings immediately at the first indication on radar or credible information from spotters. The next level of improvement regarding saving lives will likely involve sociology to find ways to get people to hear and pay attention to those warnings already being issued.

The Discovery show is about 95% thrills and entertainment, and maybe 5% real science. But it makes interesting watching for legions of viewers, and I do commend the show producers this season for balancing the adrenaline quotient with some sober reality by showing the aftermath of tornadoes, including damage and injuries.

- Jon Davies 12/5/10