I have created this new
section for a couple of reasons. I will use this section to work on several
projects (some nearing completion and some just initiated. Some will have
explanatory text and some will be just maps, radar images and other data.
By having this section linked from other more public areas of the website,
I will permit others to look in on what I am working on.
This topic almost automatically makes one think of the 1997 storm system that spawned the F-5 tornado at Jarrell. That storm formed in an environment characterized by very high CAPE, weak low-level winds, and only moderate mid-level flow. Until the Jarrell event, the "book" on severe storms held that weak low-level winds and moderate mid-level flow were insufficient to generate supercell storms and more specifically, large, devastating tornadoes. Of course, the "book" (if there had been one) would have been full of asterisks leading to mentions of all sorts of exceptions and possibilities.
For example, it had been
known for several decades that supercell storm motion was a combination
of advection by the mean wind (calculated through some layer of the troposphere)
and of propagation (meaning storm regeneration on a flank of the storm
where inflow of moist and unstable air was maximized). [references omitted]
Interestingly, in 1999 and again in 2000, supercell storms in central Texas
occurring in environments of high to extreme CAPE, demonstrated the capacity
to generate significant tornadoes while moving far to the right of the
mean wind. This is one area of research that deserves additional attention.
What follows is but a beginning.
A supercell storm developed
over San Saba and Llano counties, then moved to the south-southwest, producing
two very damaging tornadoes: near Castell and Loyal Valley (on the Llano-Mason
county line), a very large tornado caused at least one fatality and produced
damage rated F4. The same storm system propagated southward into western
Gillespie County and produced another tornado at Harper. F3 damage occurred,
with the town heavily damaged. Some observers believe that the storm system
continued producing tornadoes after it departed Gillespie County, but the
system was over a very sparsely populated area and no other tornadoes were
Day-1 Outlook issued at 6 UTC ... yellow shading is moderate risk.
My hand analyzed maps (in real time) on 5-11-99:
Supercell storms developed over central Texas northwest of Waco as a cold front advanced into the IH-35 corridor. A portion of the NCDC description of the event follows: A tornado formed over the central part of Lake Whitney at approximately 1610 CST. The tornado moved south and dissipated near the dam at 1625 CST. The tornado caused two deaths, both of which occurred in the same home, but no other injuries. The most significant damaged occurred at the Lakewood Harbor Subdivision, three miles northwest of the Dam, around 1615 CST. Thirty-eight homes were destroyed and 27 others were damaged. The most severe damage was rated F3.
The parent storm continued to develop on the south flank, resulting in a long lived wall cloud that moved south through southern Bosque, western McLennan, eastern Coryell, and western Bell counties. While reports of hail and funnels continued through the life of the storm, no additional tornadoes were confirmed.
(click on any individual
base reflectivity image for the corresponding storm-relative velocity image)