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Severe Weather Events and Timeline
 

                                A deadly tornado outbreak occurred on April 17, 1970 across west Texas and the Texas panhandle between 845 pm
                                and 2 am CST, with 23 people killed. These tornadoes occurred at night and perhaps in the fog. Storms developed on the
                                dryline in the foothills between 4 pm and 5 pm MST from northwest of Roswell, NM to to w/nw of Carlsbad, NM. Violent
                                tornadoes occurred as these storms crossed a warm front in west Texas.
       
                                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 no
                                damage and hence were not documented.    

                                The storms that wreaked havoc across west Texas and the Texas panhandle during the evening and overnight developed
                                along the dryline which was situated out ahead of a pacific cold front. The low level winds were so backed on this day that
                                the moisture was wedged up against the higher terrain west of Carlsbad and Roswell. Storms developed around Carlsbad
                                and northwest of Roswell in the afternoon.

                                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.  A man living in
                                McDonald, NM(south of Tatum) observed 2 tornadoes(one of which was large). 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. If the time of the tornado south and southwest of Tatum, NM is correct(530 pm MST), then this was clearly not
                                the same storm that went on to destroy Whiteface, TX. I believe that this was the same storm and I believe that the time
                                given in storm data is off by 1 hour.  Is it pure coincidence that the Lea county, NM tornado lines up perfectly with the
                                path of the tornadic storms to the NE if one extends this path back to the southwest? Probably not. Also, a time of 
                                630 pm MST for the Lea county storm would yield a storm motion of 35 mph which is the same speed at which the
                                tornado moved across west Texas. Thus, it appears that the storm that eventually trashed Whiteface and Whitarral, TX
                                developed west-northwest of Carlsbad or southwest of Artesia in the foothills in far western Eddy county around 430 pm
                                MST. Indeed, the remarks in the surface observations from Carlsbad at 5 pm indicate CBs to the north and west. Also,
                                the area southwest of Whiteface is wide open country. I suspect there was a family of several tornadoes from southwest
                                of Tatum, NM to Whiteface to Plainview, TX and on to Silverton, TX as well as Brice and Hedley.  The tornadoes
                                apparently became violent upon crossing the warm front around Whiteface.

                                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.  It is unclear when this storm initiated and where. This storm may have not
                                developed along the dryline. Perhaps this storm developed later in the evening when the cold front was overtaking the
                                dryline.

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. I suspect that the latter tornadoes all occurred in the warm sector south of
                                the warm front. It looks as though the warm front underwent rapid frontolysis during the late evening. But I am fairly
                                confident that the first violent tornadoes in near Whiteface and Whittaral occurred immediately north of the warm front.

                                At 12 UTC the 500mb chart showed that the aforementioned shortwave trough had ejected rapidly NNE into the central
                                plains.
   
                                It is widely accepted that the tornadoes occurred in dense fog. While dense fog may have occurred out ahead of the storms
                                or well ahead of the warm front, the observations at Reese AFB indicate that the  visibility increased to 4 miles as the tornado
                                was passing to the west-northwest of the station.