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November 2003
Storm of the Month
(The Tale of Two F1s) November yielded several
rounds of low-topped thunderstorms on the 18th and 23rd as the High Shear/Low Cape
environments began to make their return to the Deep South. However,
on the morning of Thanksgiving, the 27th, a more classic Supercell
developed in the predawn hours which became the most impressive radar
image for the month. We decided to label this month's images as
"The Tale of Two F1s"
due to the different convective modes which produced similar damage
patterns.
The first set of images below were taken at
539 am cst as a line of storms moved from Northeast Louisiana into Western
Mississippi, about 60 statute miles northwest of the
radar. A persistent break in the convective line was the principle
indicator that this storm was unusual and in fact was producing F1
Tornadoes. The core of
50-55dBz returns reached only 15,000 feet and had storm tops of only 28,000
feet. The storm rotation was noteworthy and several power poles were knocked down in
Issaquena and Sharkey counties. The storm track algorithms have a
difficult time with these cases due to their shallow nature and in fact,
one of the two F1s virtually went unidentified except that high
velocity(63kts) winds were seen at nearly 5500 feet in the vicinity of the
storm as seen in the zoomed Fig.3 image below.
The second set of images came from 440am cst on
Thanksgiving morning over southeast Mississippi between the Laurel and
Collins areas. This more classic Supercell had already produced an F1
Tornado in northern Marion and southern Jefferson-Davis counties.
The storm reached a peak intensity in Figs. 4 and 5 images below when
the 50-55dBz core reached 29,000 feet(upper right of Fig.4) producing VILs of 40-45kg/m*m and
well-defined Mesocylcone of about 10,000 feet in depth. The
broken track of F0 to F1 damage extended from Covington County into Jones County with
this storm destroying a chicken house and knocking down numerous trees and
powerlines along Highway 588 as seen in Fig. 6. Clearly,
these two different style of storms make the warning process very
challenging to say the least.
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A 4 Panel of Storm Relative Velocity cuts(0.5, 1.5, 2.4,
3.5 slices) at 539 am cst FIG. 1
A 4 Panel of 3 Reflectivity Elevation cuts(0.5, 1.5, 2.4) and
VIL at 539 am cst | FIG.2
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Corresponding image of Lowest elevation cut of high
resolution Storm Relative Velocity at 539 am cst FIG.3
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A 4 Panel of Reflectivity cuts(0.5, 5.3 slices) and Velocity cuts(0.5,1.5 slices) at 440 am cst FIG.4
A 4 Panel of VIL, Composite Reflectivity, TVS, and Mid Layer Reflectivity(24-33k ft) at 440 am cst | FIG.5
A map of surveyed tracks | FIG.6
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