2003 Tour 1 happened to occur during one of the most active severe weather patterns in recent memory. In multiple corridor outbreaks associated with strong mobile upper-tropospheric storm systems interacting with tropical lower-tropospheric moisture, a record-setting barrage of tornadoes ravaged the plains and adjacent portions of the mid-Mississippi River Valley during the second half of this trip. Despite the onslaught of tornadoes, intercept was not easy! Very fast storm motions (attributable to ludicrously strong mid-tropospheric wind speeds), Mexican smoke/tropical haze (resulting in atrocious visibility - the worst since 1998) and hilly, tree-dotted terrain all made for very difficult intercepts on most of these days. These issues were further compounded by the fact that so many of the tornadoes scored direct hits on towns and farmsteads, leading to road blocks and jittery/erratically driving locals and storm chasers. Nonetheless, our group experienced rousing intercept success, especially on May 4. The joy experienced by the participants was tempered by the sobering reality that so many lost their lives and homes to these storms.

Chase Days: April 30 - May 9
Group leaders: David Gold and Roger Hill
Days on which storms and/or tornadoes were observed: April 30, May 3, May 4, May 5, May 6, May 8, May 9

Day 1 - April 30: Three supercells observed: (1) Classic to HP supercell evolution observed from north of Oregon, Missouri (MO) to Bethany, MO. (2) LP sodacan storm observed at Lathrop, MO and (3) HP supercell to convective line evolution observed near Cameron, MO at and just after sunset. Complete meteorological synopsis, chase summary and pictures are posted here.

Day 4 - May 3: Severe multicell to classic supercell evolution witnessed over Hall County, Texas (TX); left-mover split associated with right-moving classic supercell over Haskell County, TX raced northward, killing our storm just as it was about to enter a tornadic phase! Complete synopsis, summary and pictures to be posted here.

Day 5 - May 4: Three classic tornadic supercells observed: (1) Classic supercell that moved from north of Parsons, KS to Camdenton, MO, producing several strong to occassionally violent tornadoes; we witnessed the early stages of the Girard, KS tornado from the distant west. (2) Classic supercell that produced a significant tornado near Baxter Springs, KS; we witnessed one stovepipe tornado to our distant west over extreme southern Labette County, KS. (3) Classic supercell that produced two weak tornadoes near Miami, OK and then one strong to occasionally very strong tornado that moved from 3 miles WSW of Pierce City, MO to Springfield, MO. We witnessed nearly the entire evolution over a span of 35 minutes. Complete synopsis, summary and pictures to be posted. Digital images of the Pierce City devastation will also be posted.

Day 6 - May 5: One short-lived thunderstorm exhibiting classic supercell structure for about 25 minutes near Walnut Ridge, Arkansas (AR). Summary will be posted here.

Day 7 - May 6: Several outflow-dominant supercell thunderstorms near Nevada, MO, Fort Scott, KS and Lockwood-Greenwood, MO.

Day 9 - May 8: Tough day! Two supercell storms in eastern Kansas; one storm struggled against the shear and ultimately died despite being in an area initially diagnosed as being favorable for tornadic storms; another storm was the tail-end of the storm that produced a large tornado near Osage City, KS. After our original target storm got shredded by the environmental shear we dropped down to intercept this storm, eventually intercepting near Lawrence. I've never seen a storm die a more rapid death. Summary and synopsis to be posted here.

Day 10 - May 9: Crazy day! It culminated with our intercept of a beautiful classic, striated barberpole supercell over northwestern Logan County, OK and then we had a very interesting encounter with the nocturnal Oklahoma City tornado.

The first tour chase day of the year was treated to a fairly intense, almost tornadic supercell. In fact, this storm may possibly have produced a tornado just before we caught sight of the low-level mesocyclone to our north near Maitland, MO. Fast storm motion and crazy roads prevented a more timely and proximate intercept.

Note: In this day's synopsis and the ones to follow, all terminology numbered (1), (2), etc... is given further elaboration below the images at the corresponding footnote number. Refer back to these explanations in synopses given for future events.

Meteorology:

The meteorological set-up for this event was a warm-up to what was to become one of the most prolific tornado-producing weather patterns in history during the latter half of the expedition. As always, we used the model forecasts the day before (and the specific observation that the low-level moisture was returning northward in the wake of a springtime cold front) to get a general idea of where to be the next day (April 30). This info suggested that the region from southern Kansas to northern Missouri would be one to scrutinize. On April 30, the observations provided more clues about where conditions favorable for supercell storms might materialize. In the wake of a cold front, low-level moisture was surging northward into the central plains ahead of the residual polar frontal boundary - hereafter referred to as the pre-dryline boundary (see Fig. 1 below).  Using the morning's soundings (1)  launched at Dodge City (Fig 2., red solid line=temperature profile, red dashed line=dewpoint profile) and Topeka, KS (Fig. 2, blue lines) and forecasting a surface-based lifted parcel possessing a surface temperature and dewpoint of 78/63 respectively, I created a composite sounding that I hoped would represent atmospheric conditions over the target area later that day. The modified "guesscast" sounding reveals CAPE eyeballed at about 2800 J/KG and CINH of 150 J/KG. Of course by mid-afternoon surface temperatures in the warm sector ranged from the mid 70's to the lower 80's (refer back to Fig. 1), suggesting that I had been a bit conservative in my surface temperature forecast used to generate a lifted parcel. Nonetheless, the composite sounding analysis (one of my favorite forecasting devices for gathering all of the relevant information onto one diagram to reveal the likely state of the atmosphere at peak heating) suggested that there would be plenty of instability throughout the warm sector wherever the capping inversion present over the area (i.e., the remaining CINH eyeballed from the forecast sounding) could be removed locally by lifting. Thunderstorm development looked to be possible along the pre-dryline boundary trailing southwestard across central/southern Kansas (black dashed line in Fig. 1) and perhaps along and just north of the warm front (the leading edge of the warm, moist air) extending eastward into northern Missouri. The final task was to forecast where vertical shear would be strongest (2) and most well-matched (4) to the CAPE because this factor is what determines convective mode (supercell or otherwise). Aloft, a current of moderately strong west-southwesterly flow was superposed over the moistening low-level airmass (Fig. 3), with stronger 500 mb winds noted to be edging into KS from the southwest. A glance at the 850 mb analysis (Fig. 4; valid 19Z) generated by the SPC mesoanalysis page (3) showed a fairly uniform 25-30 kt SSW flow at this pressure level over the plains. Hence, the one place where the vertical wind profile would be sheared more than any other (in the absence of significant low-level pressure falls farther south along pre-dryline boundary) was along and north of the warm front and downstream of the triple point (warm-front/predryline boundary intersection) where surface winds would maintain the most pronounced easterly component. Moreover, it appeared that the most convergent low-level flow (and thus the region where lifting was most likely to be sustained) was going to be located near the triple point. Thus, we targeted the area from northeastern Kansas to extreme southeastern Nebraska/northwestern Missouri. Radar downloads (Fig. 5) and visual observations revealed the show beginning east of Falls City, NE and we moved north and east to intercept.

Chase Summary:

Leaving OKC at 7:30, we made our way to Topeka, KS. My optimism regarding the potential for visible tornadoes had evaporated the evening before due to the upper-tropospheric wave responsible for surface cyclogenesis being progged to fill/weaken rapidly due to stretching deformation (a tendency apparently underestimated rather badly by most models 2-3 days prior to the event). Nonetheless, we were optimistic about the likelihood of HP supercell thunderstorms initiating along the frontal boundary from NE KS to S IA/N MO. The focus of our afternoon data analysis was on finding the likely initiation point and best environment for daytime supercells; NE KS to S IA is an unacceptably large target area when storm motion vectors are going to be 35-40 kt. We became convinced that initiation would be near Falls City, NE with rapid intensification and maturation of supercells across extreme NW MO. Our mistake was that we didn't have enough confidence in this to set up shop downstream of the expected initiation point - there have been many times when I overshoot the area of initiation and have to backtrack westward. We moved north from TOP on Hwy 75 at about 4pm CDT, observing congested (albeit mushy) CU and TCU to our NW through E. At the Hwy 36 junction we observed glaciated convective towers to our not too distant N and NNE; additionally, the developing congestus N through NW was being visibly undercut by scud apparently associated with the leading edge of the cold front, so we continued on eventually crossing into MO east of Falls City. When we turned north on Hwy 59 in east-centralHolt county we could make out much cloud base structure associated with our target supercell. We observed a well-defined dryslot with developing RFD gust front; to the NE of that was a very ominous block-shaped lowering/wall cloud that definitely had a tornadic appearance. We were too far to discern any detail. We continued stair-stepping N and E and when we were just east of Maitland on CR A we observed a fully occluded wall cloud with truncated cone shaped funnel cloud about 4-5 miles NNW of our location; the wall cloud and accessory scud tags were wildly rotating and I estimate its location to have been close to the town of Skidmore; I don't remember the exact time (too busy navigating to keep a log) but it was probably around 6-6:15pm and we were too distant to confirm/deny that the funnel cloud was actually a tornado. I would not be surprised if a large tornado occurred somewhere N or W of Skidmore. Unfortunately, we had been effectively outflanked by the storm so could not achieve the desired position due E or ENE of the meso. New mesocyclogenesis was rapidly underway to our immediate ENE and the RFD gust front was loaded with vorticity and wild, fluid vertical motion. Soon thereafter, the storm tended more to HP characteristics and developed a menacing rear-flank core with encircling shelf cloud. However, it refused to give up on trying to develop a forward flank updraft/meso as inflow stratus continued to fly into the storm from the E and SE and scud rose and attached to cloud base at the E edge of the core. East of Conception Junction in eastern Nodaway County we were briefly overtaken by the southern edge of a tightly circular precip curtain, the apparent center of low-level circulation passing just to our north. Our winds turned from SSE to W, gusting to near 50 kt. We finally got to the junction of US Hwy 169 and CR O at Gentry. The storm was now decidedly HP in character with a substantial surging RFD core/gust front bearing down on us from the SW and a less menacing FF core to the NW; we were sitting in the notch at this crucial intersection with no more east option. To our immediate SW and almost overhead a patch of cloud base was swirling wildly as the RFD core pivoted around from the W and SW to overtake us. The rotating cloud base moved quickly to our east across open pastures near Gentry, MO and we were forced north into the SW edge of the FF core,letting the more dangerous RFD core pass to our SE. After the maelstrom passed we once again attempted to outflank the storm but decided to blow it off at I-35 in favor of targeting a more isolated storm SE of STJ. Downloading radar as we drove (my goodness gracious, I never failed to get a wonderful cell phone connection yesterday), we headed directly to I-35 exit 40 at Lathrop. Too late (we heard the warming for the spotter-indicated tornado near Edgerton); it was an interesting looking sodacan LP storm (we got 1" diameter in the vault and cars were briefly blocking the interstate at an underpass) with an amusing array of sheriff deputies and other gawkers staring up at the sky. On the way south, we were mightily distracted by a ridiculously explosive convective bomb forming over STJ. As we drove south on the interstate we watched as the fat convective tower expanded, grew, overturned and went crazy. We turned around at Lathrop and stopped west of Cameron on Hwy 36 for a very entertaining lightning show (great anvil crawlers in the vault/overhead anvil). Stayed around until the storm lost supercellular characteristics and lined out.

FOOTNOTES:

(1) Soundings are balloon-borne measurements of atmospheric temperature, dew point temperature, pressure and wind; this provides a graph of the vertical structure of the atmosphere at a given point at a specific time and represents arguably the single most important dataset collected daily to probe the atmosphere and initialize the numerical weather prediction models. An analysis of individual soundings is a very important part of each day's severe storm forecast; unfortunately the paucity of this dataset makes it a challenge to forecast how the vertical atmospheric structure will change. Determining how warm and moist the input lifted parcel will become, how much CAPE/CIN will result and how much lifting is necessary to remove remaining CIN can nonetheless be a very enlightening process that forces the analyst/forecaster to focus on the data and make a best guess of how the atmosphere will evolve over the region of interest. Then, as conditions change during the day (particularly at the surface where hourly observations are collected over a much finer network than aloft) one has at least some clue as to how unstable and capped (or uncapped) a specific area is likely becoming just due to changes in surface thermodynamic properties alone.

(2) It is well established from theoretical, modeling and observational results that the interaction of nascent thunderstorm updrafts with a vertically sheared wind (i.e., a wind that changes speed and/or direction with respect to altitude) can result in a multitude of outcomes, with thunderstorm updraft rotation about a vertical axis being increasingly likely with increasing shear magnitude and the total shredding of storm updrafts occurring if the shear is too great for a given amount of CAPE and/or forcing. The way in which the shear within each layer varies with height and the strength of the mean horizontal flow in the storm-bearing atmospheric layer are the primary determinants of whether right-moving supercells are favored.

(3) The products generated on this page are analyses that blend 1-hour forecasts generated from the NCEP RUC model with the most recently available observations. The chief advantage of using model analyses rather than true observations is that the native model grid possesses much finer temporal and spatial resolution than do the observations.

(4) Some of the same studies revealing the importance shear flow-updraft interaction for the rotation and maintenance of the latter also reveal the necessity of having "well-matched" CAPE and shear; too much shear relative to the realized CAPE will destroy a storm before it gets going and too little shear will result in disorganized storms that fail to attain a rotating updraft. As a complicating factor, a storm interacting with an extant boundary (e.g., an outflow boundary left by overnight storms) oriented to the right of the flow in an environment possessing lots of low-level moisture and large CAPE may become a significant tornadic supercell in the absence of significant environmental shear.

A classic "corridor" tornado outbreak occurred this day. We sampled three separate tornadic storms, ultimately witnessing a long-track strong to occasionally violent tornado that moved from 2 miles SW of Pierce City, MO to Springfield, MO. We captured the most dramatic close-range video footage of a strong multiple vortex tornado I've seen.

Meteorology:

This event was a classic "Fawbush-Miller" (1) tornado outbreak. As with most such events, a significant upper-tropospheric mobile trough was involved in generating the very strong vertical wind shear and instability over a large portion of the outbreak region. The 500 mb chart valid 12Z May 04 (Fig. 1) illustrates the strength of this trough, evinced in part by the strength of the wind maximum noted in the base of the trough at this time (80kt at Tucson, AZ and El Paso, TX). Fig. 1 is also a very simple example of "compositing" - presenting information from various levels on a single chart. On this particular map, I've only drawn two items: (a) the orientation and likely location at t+3 hours of the 500 mb jet streak and (b) the morning location and orientation of the moisture axis (closely corresponding to the position of the low-level jet stream), including maximum wind speed and highest dewpoint temperature (TD), noted at 850 mb. Full-blown composite charts are much more complete, attempting to consolidate salient information from many pressure levels. However, Fig. 1 is sufficient to show that there is tremendous "cross-over" between mid and lower level wind maxima over the plains, implying the presence of enormous vertical shear (especially given the magnitude of the winds at 850 and 500 mb) and potentially large CAPE (implied by the superposition of -11C to -13C 500 mb temperatures over TD=16C at 850 mb). Moreoever, it is clear that the 500 mb trough is not going to sit over the southwestern U.S. but rather is clearly mobile and will move northeastward into the plains during the day. A short-term forecast of the 500 mb (Fig. 2) and 850 mb (Fig. 3) pressure level conditions suggests that indeed the mid-level trough and associated intense mid-level winds will superpose strong southwesterly lower tropospheric flow, resulting in large vertical shear over a large region. Sounding analysis (not shown) clearly demonstrated that the thermodynamic stratification was classically favorable for tornadic supercells; the morning sounding composite analysis (described in the April 30 synopsis) revealed that the "free atmosphere" (i.e., that portion above the boundary layer) was nearly homogenous (i.e., characterized by a well-defined EML - elevated mixed layer) and that the soundings taken in the "warm sector" possessed a breakable cap atop deep, rich low-level moisture. Daytime heating with little further moistening yielded CAPEs of 3000-4000 J/KG, more than sufficient for severe thunderstorms. The presence of a moderately strong cap (i.e., non-negligible CIN) and deep-layer mean wind vectors oriented across the dryline suggested that discrete supercell storms would rule the day. Recent efforts to develop parameters consolidating the CAPE, shear and other data into single measures of tornado potential have produced some success. The so-called "significant tornado parameter" (STOR; Thompson et al. 2002) can be a useful tool for measuring the likelihood of strong tornadoes given the initiation of discrete thunderstorms. The STOR parameter is designed so that a value of 1 or greater denotes "threshold" strong tornado potential based on the findings of earlier studies establishing empirically-derived approximate threshold values of the component parameters that contribute to STOR (of course, conditions may occasionally be favorable for the production of strong tornadoes even if the STOR parameter fails to highlight the threat); by mid-afternoon May 4, the STOR parameter was "off the charts" (Fig. 4), further underscoring the potential gleaned from analysis of the individual components (CAPE, shear, etc..). One aspect of the day's setup that caught my attention was the restricted width of the unstable warm sector (Fig. 5, note the relatively narrow width of real estate between analyzed warm front and dryline), attributable in part to the cold air mass sitting over the Midwest. This factor, plus the obvious presence of "outbreak conditions" over all of the prospective target area, influenced our decision to play storms that we felt would surely form down the dryline over southeastern Kansas/southwestern Missouri where the warm sector was wider as opposed to storms forming near the warm front/dryline intersection (the triple point; the region that produced the devastating Kansas City tornadoes earlier in the afternoon) near the northern end of the instability axis. The idea is that storms would first develop near the triple point and then "back build" down the dryline as the cap broke progressively further south; moreover, the prevalence of conditions supremely favorable for significant tornadoes (see preceding discussion) suggested that every single isolated supercell would have an excellent chance of producing tornadoes. Under this working notion, any storm that you targeted east of the dryline within the larger target area would produce a tornado so that even if you screwed up intercept on one storm, you'd get a second chance. Such a "luxury" is very rare, indeed, and on this day our idea worked.

Chase Summary:

Unbelievable day in the southeastern plains today! We began the day in OKC, determined to consider playing the tail end of this system. My concern (in addition to storm motion) was that the best show might occur in a narrow and early window over SC-E Nebraska (16-19Z) and then it would be over. Upon waking and looking at the data, it became apparent that the setup was indeed outbreak-like and that therefore one could likely pick about any storm and expect to see large tornadoes. Analysis soon suggested that the cap would break explosively in the HCRs (horizontal convective rolls - bands of congested cumulus from which the most important storms of the day often develop; these bands are generally oriented along the low-level shear vector) embedded within the highly unstable, strongly sheared warm sector. Stopping in El Dorado for fuel we watched as our surface winds slowly veered and our dewpoint spiked lower. Surface analysis revealed an intense low-level dry punch surging inexorably eastward towards SE KS and NE OK. I couldn’t believe it when I downloaded the SPC STOR and saw the 8-11 values blanketing the entire risk area from SE NE to N TX.

We decided on the spot to target SE KS, first intercepting storms on the northern portion of the E KS theta-e tongue and then dropping southward on different storms. We drove east on Hwy 54 to Iola and then north on 169 to Welda, KS where we sat for close to an hour watching convective towers get shredded to bits. Radar downloads revealed an intensifying cell moving NE towards the area south of CNU; rather than jumping on that as soon as we saw the first reflectivity core in NE Osage County, Oklahoma we sat watching convective towers closer to us. However, as the cell slowly matured and moved into Chautauqa Co. (see the radar downloaded via cell phone at the time, shown in Fig. 6 below), we could no longer sit still as we became convinced that this storm would become a prolific tornado producer. Driving south and then navigating around the NE side of CNU, we dropped SE in a desperate attempt to get ahead of this incredible storm (radar shot at the time, Fig. 7). As we passed the junction of Hwy 57/59 driving south on Hwy 59, we drooled at the spectacle of the rock hard convective bomb to our ESE. Following the western edge of the updraft down to cloud base, we immediately spotted a classic stovepipe tornado spewing debris about 7-8 miles to our E, somewhere near or just east of the Neosho wildlife area. Cursing at our failure to jump right on this storm as quickly as we noticed it on radar, we drove east on 160 out of Parsons, quickly taking up the rear of a very long and very sloooow moving caravan of storm chasers. We busted north and east on Hwy 126 intending to eventually intercept the classic tornadic supercell east of Girard, KS at or near the MO border. I gasped at the radar depiction of the storm’s hook overtaking Girard and wondered what kind of devastation was in store for towns east of this storm. We were making great time and might have actually outflanked the storm as planned. However, fresh radar downloads revealed a very good looking tail end storm in Nowata Co. OK and we became convinced that this storm would eventually go on to produce significant tornadoes provided the dreaded 80-mph left mover to its SSE didn’t interfere too badly (this bit of bad luck killed what might have been a strong tornadic storm the day before near Childress, TX). On the way south to intercept the OK storm, we quickly detoured to check out the updraft base of another supercell moving NE through Labette Co., KS and quickly spotted a truncated cone tornado emanating from cloud base to our distant west. The storm started to look a bit more organized shortly afterwards and we pressed south, worrying that the Labette Co. storm would be interfered with by the tail end charlie and would too seriously detract us from intercepting the southern storm. Driving through scattered golfball-sized hail in the FF core, we observed the updraft (completely separated from FF core) and immediately noticed a fat, nubby funnel cloud just NE of Fairland, OK (we later learned that this was a weak tornado but couldn't see the ground-based circulation for all of the trees and hills). Soon thereafter, the storm became rather disorganized as it merged with the left mover. Nonetheless, we persisted chasing this storm noting that inflow was still quite strong and moist southeast of the RF gustfront. The storm began to intensify and take on scary HP/classic hybrid characteristics east of Neosho (which was devastated by a tornado on 4/24/75). Racing east on Hwy 86, we attempted to get to Hwy 60 north of Newtonia but the storm’s horrendous looking rear-flank core soon overtook the road before we got there and, fearing very large hail and powerful winds, we turned around and continued E and SE on Hwy 86, eventually turning north on Hwy 37 at the town of Purdy. All this time, we were experiencing the storm’s ambient inflow which was 76/66 on 1725 winds. A new radar download revealed that this storm had retained classic supercell character with a vengeance and we wasted no time at all getting north to Monett, MO. The clefted-out barrel-shaped meso of an incredible beefy tornadic storm revealed itself to us soon after turning north out of Purdy and, 1 mile south of Monett, we observed a very large strong/violent tornado just northeast of town. We turned east on 60 and for the next 35-40 minutes experienced one of the most thrilling and fascinating tornadic experiences I’ve had. We watched in amazement as this fat, inky black-blue tornado rampaged across the countryside between Monett and Verona, spewing huge plumes of dirt/debris skyward. The tornado morphed into a fabulously fluid and dynamic multiple vortex tornado with evolutions that are best viewed on video rather than described. We got closer and closer to this high-contrast, long-lived tornado, watching as it lofted debris into cloud base and fearing for all in its path. I relayed reports to people with access to NWS numbers the best I could. I fear the tornado hit the north side of Aurora, MO. At times we got as close as 2/3 of a mile from the tornado as we drove northeast on Hwy 60 and then east on farm road 2200 south of Marionville and then Hwy 173 east of town. We got farther south of the tornado than we would have liked by this time (after being so close for so very long) but we got view of it again beneath the center of the incredible ground-dragging, clefted mesocyclone SW of Springfield: now it was an intense looking high-contrast stovepipe tornado with a fan-shaped debris cloud near Battlefield, MO. We watched as the tornado endured a classic rope-out on the west side of SGF, sparing the fortunate citizens of that city a bad tornado disaster.

FOOTNOTES:

(1) Fawbush and Miller were two USAF officers who got extremely lucky with a tornado forecast that ushered in the modern era of severe thunderstorm forecasting. Read an interesting article about that fateful first experiment at tornado forecasting here.