Elevated Supercells in Eastern Colorado on May 8th, 2017

On Monday, May 8th, there was the potential for isolated thunderstorms across eastern Colorado with possible supercells (a rotating thunderstorm) along the Interstate 70 corridor in vicinity of the Palmer Divide. Although the tornado threat was very low, there was certainly a good chance of observing photogenic storms in the High Plains of Colorado. 

Forecast soundings and other realtime observations the night before indicated the potential for scattered thunderstorms across eastern Colorado, including a few isolated severe storms. Evening soundings across the region from Albuquerque, New Mexico, northwestward into Dodge City, Kansas, sampled a modest elevated mixed layer (a layer of cool, dry air above a temperature inversion; air can rise freely within this layer pending erosion of the cap) advecting northward into the region. The combination of the thermodynamics in addition to other wind shear factors served as a very good indicator that there would be the potential for supercells on Monday.

A developing high-precipitation (HP) supercell near Simla, Colorado, on May 8th, 2017. Image credit: Harrison Sincavage

The morning of the chase, water vapor satellite imagery revealed a plume residual convection and outflow from the storms that had occurred Sunday night across eastern Colorado. These outflow boundaries were in the vicinity of the warm front that was draped near the I-70 corridor in western Kansas and eastern Colorado, and would later serve as a boundary for storms to anchor themselves on to after their genesis Monday afternoon.

Morning water vapor imagery with realtime mesoscale analyses overlaid (theta-E and mean sea level pressure). The purple oval delineates our initial target area near the Palmer Divide in eastern Colorado. Image credit: College of DuPage Department of Meteorology; edits to the graphic made by Harrison Sincavage

In addition to the satellite imagery and realtime surface observations, short-term operational model guidance indicative that the atmospheric instability, or CAPE, would increase to about 1,000-1,500 J/kg. As previously mentioned, this region of instability was already moving into the region the night before; the atmosphere recovered efficiently for the evolution of afternoon thunderstorms across eastern Colorado.

The main storm mode on Monday was multi-cellular given weak dynamics, with supercells forming along the tail end of the complex of evolving thunderstorms along the west-to-east oriented outflow boundary. As storms formed, we repositioned from the town of Limon, Colorado, west towards Simla. Moving north out of Simla, the first supercell of the day began to organize with photogenic structure. 

Upslope surface winds from the east aided in enhancing low-level storm-relative helicity, which eventually enhanced the evolution of mesocyclogenesis within the initial high-precipitation (HP) supercell. A mesocyclone is a region of rotating air within a severe convective storm. They are one of the necessary contributors that can sometimes result in the formation of tornadoes. However, on Monday, the cloud base height (lifted condensation level; LCL) was quite elevated and deep moisture was lacking. As a result, the tornado potential was limited. 

An organizing mesocyclone north of Simla, Colorado, on May 8th, 2017. Image credit: Harrison Sincavage

While positioned north of Simla, we observed the supercell for several minutes and eventually observed the first funnel cloud of the day. High based, the vortex appeared as a mid-size lobe descending out of the base of the mesocyclone with a brilliant, high contrast look with laminar rotation (note that while the condensing vortex descends, the air within the funnel is rising). 

The funnel cloud as it descended from the base of the mesocyclone north of Simla, Colorado. Image credit: Harrison Sincavage
The mesocyclone continues to strengthen as the funnel cloud descends north of Simla, Colorado. Image credit: Harrison Sincavage

With time, the vortex contracted into a needle-like form and began to intensify in rotation. The funnel cloud persisted for just over 10 minutes, and the condensation funnel continued to descend roughly one quarter of the way to the ground. The vortex may have extended further towards the ground, but there is no way to tell as the dry air surrounding the funnel was not condensing around the parent vortex. 

The vortex as it contracted and began to rotate rapidly north of Simla, Colorado. Image credit: Harrison Sincavage

Eventually, the funnel cloud dissipated and we continued to travel north back towards Interstate 70. Continuing northward along I-70, we repositioned south of the town of Agate, Colorado, and observed the rear-flank downdraft (RFD) undercutting the mesocyclone that produced the funnel cloud. A hail core was within clear sight of our position, as it moved over parts of Agate and I-70. 

Hail core as it moved over parts of Agate, Colorado. Image credit: Harrison Sincavage

As the rear-flank downdraft undercut the old mesocyclone, a new one developed to its east along the aforementioned outflow boundary. Storms continually formed along this outflow boundary in a west-to-east orientation. Repositioning to the south and east, we headed back towards Limon and traveled northward on Highway 71. A new mesocyclone was observed north of Limon, and albeit elevated, it did have modest rotation at one point in time. 

However, given the cold thunderstorm outflow from the complex of the thunderstorms to the north of the mesocyclone (to the right in the photo), the outflow air was more dense than the surrounding air and thus undercut the inflow region that aided in the genesis of the mesocyclone. Eventually, its inflow was undercut and thus dissipated. 

Elevated mesocyclone north of Limon, Colorado, on May 8th, 2017. Image credit: Harrison Sincavage

The last mesocyclone of the evening that we observed formed to our east, and we continued on within close proximity to it. There was a well defined wall cloud for a few minutes; however, it would then succumb to the same fate as the earlier storm scale processes and be overtaken by the outflow produced by the merging cluster of thunderstorms. It did, however, leave a picturesque view as the hours of sunset started to near. 

Occluding mesocyclone north of Limon, Colorado, on May 8th, 2017. Image credit: Harrison Sincavage

In all, it was a successful storm chase and the first one of the year for myself. The convective pattern appears to be active over the next two days across the central Plains as well. While tornadoes are not a guarantee, there is nothing like being able to witness the formation of supercells with your own eyes. Below is a short video clip of the funnel cloud that formed north of Simla, Colorado.

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