Hail of a Night: Lower RGV Pelted by Ice the Size of Golfballs to Baseballs and Larger, April 2nd 2017

After a hazy, lazy, summer–like Sunday across the Rio Grande Valley, where afternoon temperatures once again surged into the 90s but high humidity made it feel closer to 100°F, a very unstable atmosphere was triggered just after sunset by the combination of weak surface convergence, aided by a light easterly flow near the coast, and the approach of the tail of an upper level disturbance which provided the "nudge" the atmosphere needed. Within a half hour (between 730 and 8 PM), scattered severe thunderstorms exploded high into the atmosphere from the Yturria Ranch in southeast Kenedy County into extreme northern Willacy County. As the initial storms waned, southward moving boundaries from them converging with very unstable air in central Willacy County fired off another severe storm, whose updraft supported and sustained hail the size of quarters to golfballs along State Highway 186 from near La Sara through Raymondville, San Perlita, and Port Mansfield. The final explosive development of the evening, shortly before 9 PM, began between La Feria and Harlingen and would soon bring quarter to golfball sized hail to the north half of Harlingen, from near Bass Boulevard north of Interstate 2 eastward to Loop 499 and Valley International Airport; a second round would form on the rear flank of the initial storm and drop another round of smaller hail 15 to 30 minutes later over some of the same areas. The first Harlingen cell peaked in Rio Hondo, 7 miles east of Harlingen, between 905 and 920 PM where hailstones up to 3.5 inches in diameter fell.

In all, dozens of vehicles in each storm sustained damage from cracked windshields and dinged or dented exteriors; as of this writing, an unknown number of roofs were likely impacted mainly in Rio Hondo from the impressively large stones. Damage totals in all areas will be calculated over the next several months after local assessments are conducted.

What the Hail? Some Reasons for the Wild Evening
Though the setup was notably different that that for April 20th, 2012, the outcome was eerily similar for the Lower Valley between Harlingen and Port Mansfield, particularly in Rio Hondo. On April 20, 2012, a vigorous upper level disturbance dove south into the Southern Plains, and was assisted by an upper level jet streak crossing through South Texas that provided additional lift. On the evening of April 2nd, just before the action started, the atmosphere was similarly "stoked"; Just enough low level moisture (heat and humidity from the surface to a few thousand feet above) to be lifted by the tail of an approaching disturbance (top image at right); a streak of higher level winds from the southwest arrived overtop of the mid level disturbance, adding to the lift potential. Convergence of near surface boundaries from the west (decaying dry line) and east (remnant sea breeze) were all that was needed to nudge the low level moisture into the unstable zone, where it was able to rise very rapidly and set the stage for rapid updrafts into a colder atmosphere that ultimately produced the large to very large hail.

The Rio Hondo hailstorm is shown in three dimensions, below (center). Note the "overhang" of precipitation above lower reflectivity near the surface, a sign of the suspended updraft. Also not the concentration of a likely combination of hail and supercooled water well above the freezing layer; reflectivity above 65 dbZ was noted at nearly 25,000 feet, with 50 dbZ above 40,000 feet. Fortunately, these cells did not dwell and were pushed along by healthy winds (see the wind barbs in the sounding at left) that kept hail accumulation low, a far cry from the slow moving supercell that wracked McAllen earlier in 2012 (March 29th) with more than $600 million in insured damage as of 2016. A few hail storms even formed right along the 500 mb trough axis itself, with penny sized hail reported near midnight in Mission (see report listing and map below). Soon after midnight, the trough axis whipped by and dry air arrived, leading to a gorgeous Monday to begin the first full work week in April 2017. Thanks to our numerous social media followers who provided dozens of photos and stories of this hail event. For others not on social media, you can track the photos on our Facebook Page here.