Severe Weather Events and Timeline
 

                A deadly tornado outbreak occurred on April 17, 1970 across west Texas and the Texas panhandle, with 23 people killed.
                Most of these tornadoes occurred at night and in the fog.

                As I studied this event I was very surprised at the lack of severe weather reports in New Mexico just prior to the Texas
                tornadoes. As one can see from the severe reports page, there were a few large hail reports and tornado reports, but I
                would have expected many reports given the synoptic situation. Keep in mind that much of eastern New Mexico is
                extremely rural, with only a few widely spaced little towns. So it is possible that other tornadoes occurred that did not do
                damage, and hence not documented.

                Three quarter inch hail occurred northeast of Las Vegas at 2330 UTC. Golfball sized hail was reported at 00 UTC
                about 25 miles northwest of Roswell, New Mexico, which is just northeast of the Capitan mountains. Apparently this
                storm developed on the lee slopes of the Capitan mountains. This storm eventually became tornadic with mainly minor
                F1 or F2 damage in Curry county NM. Prior to becoming tornadic, the storm apparently produced 1.5 inch hail
                in DeBaca county.

                Other storms developed further south and a tornado occurred in northern Lea county at 0030 UTC. Before this report,
                there were no prior reports of severe weather with this storm. But note that the area between Artesia and northern Lea
                county is mostly open country. Baseball sized hail and 1 inch hail were reported near the time of the tornado. The only
                other severe weather report of the day occurred near Clovis at 0445 UTC.

                The first severe weather report in the Texas panhandle was a violent tornado at Whiteface at 0249 UTC, along with
                4 inch hail. This storm moved northeast at 35 mph, producing several violent tornadoes through 0710 UTC and killing
                17 people.

                At 0330 UTC, a tornado was reported 5 miles SW of Lazbuddie. This tornado killed 1 person as it moved northeast to
                3 miles northwest of Dimmit. There was a long break with no tornado reports from this storm. At 1230 am a tornado
                did damage at the southern edge of Pampa.

                At 0700 UTC a tornado was reported in Swisher county or about 15 miles northeast of Tulia. This violent tornado or
                family of tornadoes continued through about 09 UTC. This storm move over very rural areas around the Paloduro Canyon,
                between 07 and 08 UTC. Then after 08 UTC the tornado hit Clarendon and killed 17 people. A piece of wood was
                driven through iron pipe near Clarendon.
 
 

Weather Situation

                The 12 UTC 500mb chart showed very high 500mb heights(594 dm) in the Gulf of Mexico. One shortwave trough was
                located over the Great Lakes area. There was also a shortwave trough over the deep south with a strong associated
                500mb jet. A deep trough was noted over the desert southwest with a center over California. There was strong
                southwest flow across the southern Rockies. 500mb temps across west Texas and the panhandle ranged from -12C
                to -14C.
 

                At 18 UTC, a surface front extended from eastward from Albuquerque to near Midland and east across north Texas and
                into Mississippi. Upslope flow north of the front across west Texas resulted in dense fog from Amarillo to Clovis to Lubbock.
                Rich gulf moisture was present south of the front as far west as Midland and Wink. But there was no lack of moisture north of
                the front, with 59F dewpoint well north of the front at Lubbock.
 

                At 21 UTC the surface front was slowly lifting north and extended from north of Abq. to north of Roswell to south of
                Lubbock. Dewpoints were very high for April with lower 60sF dewpoints into southeast New Mexico. North of the
                front at Lubbock the T/Td were 61F/61F with fog.  Another front stretched from the northern TX panhandle across
                northern Oklahoma. Between the 2 fronts, gulf moisture was adundant with low-level upslope flow. The surface dryline
                was located west of Roswell and Carlsbad. A pacific cold front was  located across western NM.

                At 00 UTC  the southernmost front extended from southwest of Clovis to south of Lubbock to south of Mineral Wells.
                The surface dryline was located on the immediate front range, or west of Roswell and Carsbad. The pacific cold front
                was oriented north-south had passed El Paso and Alamogordo, NM. The T/TD at Reese AFB(Lubbock) was up to 62F/62F
                but the visibility had increased to 4 miles. Lubbock was still north of the warm front.

                The 00 UTC 500mb chart showed a shortwave trough beginning to eject northeast from southern NM. 500mb temps
                across the Texas panhandle still ranged from -12 to 14C, with 65-75 kt 50mb winds.The 500mb temp. at El Paso had
                dropped to -15C from -13C.

                At 03 UTC, the surface warm front stretched from near Clovis to just south of Lubbock to near Fort Worth. The T/Td at
                Reese AFB(the closest observation to the initial tornadic storm) was up to 65F/64F(station pressure 885mb). Using a
                500mb temperature of -13C gives a -9 lifted index at Reese at 03 UTC. So surface based instability was high even north
                of the warm front with a "cool" temperature of 65F. But keep in mind that the actual surface temperature is meaningless
                without considering elevation. It is the potential temperature that is important. For example, a surface temerature of 65F
                at Reese has the same potential temperature as a temperature of 84F at 1000mb. And a 64F dewpoint at Reese a mixing
               ratio of 14.6 g/kg, which has the same moisture as a 67F dewpoint at 1000mb. So 65F/64F at Reese has the same
                T/Td as 84F/67F along the Texas coast. So be very careful when assessing the "coolness" of an airmass. As mentioned
                previously, the first tornado occurred about 35 miles west-northwest of Lubbock or about 25 miles west northwest
                of Reese at 0249 UTC. So I feel that the conditions at Reese at 0255 UTC were representative of the inflow into the storm.
                I also feel that the storm produced a violent tornado upon intersecting the warm front. The warm front slowly progressed
                north throughout the night, so the tornadic storms remained along or north of the warm front all evening. The is some question
                as to whether the last violent tornado at 07 UTC was north or south of the front. This will be addressed as soon as I can
                finish the 05 UTC and 07 UTC surface maps.

                At 12 UTC the 500mb chart showed that the aforementioned shortwave trough had ejected rapidly NNE into the central
                plains.