What the Hail is Going On this Year?

Lightning Amid Storm Clouds Over Southern Lamar

The 2018 severe weather season over southeast Colorado started slow this year. With dry southwest mid-level flow over the region, the area experienced below normal precipitation and above normal temperatures through most of the spring (April, May and into June). With the warm and dry weather over the region, thunderstorm coverage was less than normal, and little severe weather occurred over the region.

Gathering Storm Off South 14th Street

One notable exception did occur, however. During the early morning hours of June 13th, a thunderstorm developed over the Colorado Springs region. The atmosphere during this time was quite unstable for this time of the day, and the wind flow aloft allowed for the storm to become severe. In addition, the steering winds allowed the storm to move slowly south-southeast. The combination of the unstable atmosphere, the slow storm motion and the strong wind shear permitted the storm to produce destructive hail over the Ft Carson and Security areas. Several reports of hailstones of 2 to 3 inches in diameter were received. The storm lasted for over 2 hours, and only traveled about 15 miles during this time period.

During July and into August, the severe weather activity increased over the region. Typically during this time of the year, severe weather activity decreases as the jet stream retreats northward into the northern Plains and Canada, and monsoon moisture moves into the Southwest United States. However, this year has been different as a modest northwesterly jet stream has remained over the region at times. The combination of this modest northwesterly flow aloft and monsoon moisture has allowed for strong storms to develop over the region, with some of these storms being quite severe.

On the afternoon of July 23rd, a long tracked supercell thunderstorm affected the region. This storm initially formed in Park County and then moved southeast into Teller County, affecting the US Highway 24 corridor from Woodland Park down into Manitou Springs. Significant flash flooding was noted along Fountain Creek from Woodland Park into Manitou Springs, along with damaging hail. This same thunderstorm continued south-southeast across south and western Colorado Springs, the Fort Carson region, Security/Widefield area and then into Pueblo County, finally weakening in east central Pueblo County. Significant hail was reported along most of the storm’s track. Flash flooding destroyed a culvert north of Pueblo in which a vehicle crashed into. A fire rescue team responded to this crash, but did not see the destroyed culvert as they approached the scene and also crashed into the culvert. Two fire personnel were injured. Twenty power poles were also destroyed in Pueblo County on Old Pueblo Road by the storm along with a 78 mph wind gust measured at the Pueblo Airport. Overall, this long lived storm traveled over 120 miles and lasted over 5 hours.

Another devastating hailstorm affected the Pikes Peak region during the afternoon of August 6th. This storm originated in eastern Park County and moved east-southeast across Teller County and then into El Paso County. This storm then took a similar track as the June storm as it tracked from the Broadmoor region of Colorado Springs and then south-southeast across Ft Carson and Security. Hail up to 4.5 inches in diameter was reported. Severe hail damage occurred at the Cheyenne Mountain Zoo where multiple people were injured and several animals were killed. Hundreds of cars in the zoo’s parking lot were pulverized by the large hail. Hail damage across Ft Carson was also widespread.

So why has there been so many destructive hail storms in the Colorado Springs region this year?

The answer is related to the combination of the northwesterly jet stream flow AND monsoon moisture. Typically during July and August, the monsoon flow is over our region, but the winds aloft at jet stream level are weak. This year we have had both the jet stream over us and plenty of moisture. The combination of these two events working together allows storms to become severe. In addition, the northwest jet stream flow allows the storms to move on a more southerly track and affect the metro areas along the I-25 corridor. Typically during our spring severe weather season storms move due east and become severe over the eastern plains well east of the I-25 corridor.

By Stephen Hodanish
(excerpted from NWS Pueblo Newsletter)