March 26 1975 Lefors, TX Tornado
Brief Overview
A strong
tornado hit Lefors, TX around 1140 pm CST on March 26, 1975. About half
of the town of Lefors was
destroyed and 2 people were killed.
Two-inch hail occurred in Groom, TX(24 mi. SW of Lefors) around 1110
pm from
apparently the same storm.
Sequence of
events
The 12 UTC
March 26 500mb chart showed a deep trough over the southwest US with
strong flow across the plains states.
At 15
UTC, a 991 mb surface low was located over western Colorado with another
low over northern, NM. A warm front
stretched from south Texas northwestward
to south of Amarillo to southern Colorado.
At
21
UTC a strong "pacific" cold front was moving east into central NM. A
986mb surface low was located over central
Colorado. Two drylines were
apparent. The westernmost dryline stretched from near east of Amarillo to east
of Lubbock to
near Midland. But the really rich low level moisture
was quite a bit further east and confined to the east of a line from east
of
Del Rio to near Abilene. A front that was mainly
stationary or moving very slowly northward stretched from south of
Houston
to north of Abilene to east of Amarillo, then north into
western Kansas. However, persistent rain into a dry, cool airmass
had
resulted in a cooler airmass over far northern Texas into
much of Oklahoma and Kansas. The leading edge of this airmass
was
charging westward through western Kansas. I chose not
to label this boundary as a front but as a dashed pink line.
By 00
UTC the warm/stationary front stretched from near Houston to just south
of Waco to southwest of Childress. The
cold front was still charging east into
eastern NM. A surface low was over central CO with another low along the
front
in New
Mexico.
The
00 UTC
500mb showed a longwave trough over the western US. Shortwave
troughs were rotating around the main
trough and one of these was approaching
the southern plains. 500mb temps
were very cool--around -18C in the Texas
panhandle.
The 02
UTC surface chart showed a the pacific cold front charging east
into the western Texas panhandle. Two drylines
were still evident with
the western most one located west of midland and barely east of Lubbock. A warm
front stretched
from south of Childress to south of Waco. A rain cooled
airmass still persisted further north and the boundary
associated
with this airmass was located over far north Texas. An
arctic front was barreling down the front range of
Colorado.
Note the lower 60sF dewpoints north of the warm front
advecting back to the NW through Childress.
At 03
UTC the pacific cold front was just west of Amarillo and about to
overtake the dryline. The cold front actually
overtook the dryline
between Amarillo and Lubbock around 4 UTC--perhaps in western Swisher county. The offending
storm
apparently developed in this location around 4 UTC and moved
rapidly NE. The movement of the front(to the east at
30 mph) allowed
the storm(moving northeast at ~ 50 mph) to stay very near or just ahead of the
front. The 05 UTC
surface map can be found here.
Note that the warm front had progressed through Childress. By 0540 UTC, the cold
front
was located very close to Lefors, which also corresponds to
the time of a strong tornado. Also note that the warm front
was
located just southwest of Lefors at 5 GMT. Thus, it appears
that the storm developed near the location where the cold front
was overtaking the dryline between Tulia and
Happy, then moved rapidly NE and encountered the intersection of the
cold front
and warm front near Groom around 5 GMT. The
winds immediately north of this front were very backed and dewpoint
depressions
were near zero. T/TD values were
probably around 61F/60F at 887mb based on the obs at Childress and adjusted for
elevation.
I adjusted for elevation since in a upslope regime,
temps on the higher terrain will usually be a little cooler at night
with no insolation.
The elevation of Childress is only 1800ft while
Lefors is about 3000ft. Using 700/500/400/300/250/200mb temps. of
3/-18/-30/-44/
-52/-60C yields a surface based CAPE of 3000
j/kg and lifted index of -13!!! This storm did not produce
any more significant
tornadoes after the Lefors tornado.
Apparently the storm crossed the northern boundary and encountered very
stable cold air over
the eastern Texas Panhandle. The
positions of the boundaries at varying times and location of the
tornado and large hail are shown
here. I suspect that the Lefors tornado did not touch down in Lefors and left immediately after leaving Lefors. But there were
probably no structures to hit ne and sw of
Lefors.
The 12 UTC
500mb chart can be found here.
