May 10 1991 West Texas Tornadoes
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Brief Overview
At least 2
significant tornadoes occurred northwest of Lubbock on May 10, 1991. The first tornado touched down
1 mile north
of Pep on the border between far northwest Lamb county and far
southwest Hockley county and moved
northwest into
southeast Bailey county. This tornado evolved into a large
multi-vortex 1/2 mile wide tornado. The tornado
passed across
Bula and lifted northwest of town. Around 20 homes suffered damage(some
of the damage was "heavy").
Another
tornado moved very slowly and very erratically about 3 miles northwest
and 4 miles north of Lazbuddie.
One home was
demolished and another damaged. This tornado occurred in a very rural
area. Hail up to baseball size
was reported
with this storm.
Severe storms
also occurred south of Wink, TX with 6" hail reported in Ward county.
Hail up to 5" in diameter was
reported in
the northwest Nebraska panhandle. A tornado was reported in Dallam
county TX with no damage report.
Golfball sized
hail also occurred in Dallam and Oldham counties.
Synoptic Sequence of
events
At 12 UTC May 8 , an upper level low pressure system was located over Western Oklahoma. Fairly cool
500mb
temperatures were noted even along the Gulf Coast(-10 to -13C). This
kind of pattern is conducive to
widespread
thunderstorms across the southern plains and Gulf Coast. Indeed, the
effective frontal boundary
was located
along the immediate Gulf Coast by 21 UTC May 8. By 12 UTC May 9, the upper low had
moved into
southeast Texas and was closing off from the westerlies. Thunderstorms
were widespread across the
Gulf Coast
region and northern Gulf. By 21 UTC May 9th, the effective
frontal boundary was located across the
northern Gulf
into south and southwest Texas. However, cool dry air was nowhere to be
found across the southern
plains. With
lowering heights in the west, some lee troughing was resulting in
return flow up the high plains. The
real warm
sector with tropical moisture was trapped in the southern plains
though. The upper trough persisted
even on 12 UTC May 10. At 15 UTC May 10, the effective frontal boundary was still draped across deep
south Texas.
This kind of surface pattern leads to more backed winds on the southern
high plains. Upslope flow
generally
results across West Texas in this pattern. Interestingly, the very
sharp elevation gradient in west central
Texas lead to
the development of an upslope driven thermal gradient between Midland
and Amarillo or in this
case just
north of Lubbock. North of this boundary, temperatures were cooler but
dewpoints still high. Storms
Temperatures
and especially surface potential temperatures became very warm across
eastern New Mexico around
Clovis and
Tucumcari. Storms apparently developed near the synoptic warm front and
the cool upslope flow.
The shear
profile was also enhanced just on the cool side of the upslope driven
boundary. I am convinced this
boundary is
often occurs in west Texas as a result of that very sharp terrain
gradient east of Lubbock. When
the low level
flow is southeasterly or easterly, a thermal gradient often sets up
around the Lubbock area.
By 19 UTC May
10, The T/TD at Lubbock were 84F/68F while it was cooler but still
moist 70F/63F at Amarillo.
As in the
April 21, 1957 case, southerly mid level flow existed across the high
plains on the leading edge of the
westerlies.
Deep upper level lows were present in both cases in the southwest with
light southerly mid level flow.
despite this
fairly innocuous mid to high level pattern, terrain features and
resultant low level thermal gradients
created a
favorable mesoscale storm environment. The 500mb pattern on May
11, 1991 at 00z(near the time of
tornadoes) can
be found here.
Surface charts:
21 UTC May 8
21 UTC May 9
15 UTC May 10
17 UTC May 10
19 UTC May 10
21 UTC May 10
23 UTC May 10
500mb charts:
12 UTC May 8
12 UTC May 9
12 UTC May 10
11 UTC May 11
250mb charts:
12 UTC May 10
00 UTC May 11
700mb charts:
12 UTC May 10
00 UTC May 11