Vortex2 Blog - CU Boulder Disdrometer Team
While the storms we intercepted yesterday in western Nebraska weren’t tornadic, they were notable for a different reason: hail fog. The supercell core that moved over our location coated the ground with marble-size hail in a matter of minutes, transforming the Plains into a winter wonderland. The ice cooled the humid air to its saturation point, forming a sea of white clouds at the ground that wafted across the landscape in the breeze. With the sunset in the background, it was both eerie and beautiful.
Our newly aggressive strategy to pursue storms anytime and anywhere during the last two weeks of our mission is yielding results. We got into position early yesterday in Kimball, NE, with some uncertainty as to how intense the thunderstorm activity would be that afternoon. There was a strong cap (warm layer) in place about a kilometer above the ground that would have prevented surface-based thunderstorms from forming, barring the cap’s dissipation. Since we are in the home stretch of our project, however, we are not in the business of being particular about the events we select for research. We need all the data we can get.
Through the early afternoon, the environment did not look particularly favorable for storm development. We had clear skies through 3 pm at our location in Kimball. The few convective towers that struggled to form near the horizon quickly crashed and burned due to the strong cap that suppressed upward motion.
Back toward the higher terrain of the Rocky Mountain front range, however, the ingredients were coming together. There, the cap was weaker, and the terrain was forcing the air to rise more vigorously than it could over the flatter Plains. Thunderstorms began to blow skyward as they traveled east towards us. A brief relocation to Mitchell put us in position to intercept.
The first storm was the “weaker” of the two, but still powerful. We deployed north of Mitchell and moved back to the south as a gust front (line of moist, rain-cooled air) pushed out of the storm and crossed the road in front of us. From our location, the storm wasn’t visually impressive, but to the northeast, there was enough inflow being sucked into the storm that its updraft began to rotate. A mobile radar unit, DOW6, recorded this rotation. Due to the magnitude of the winds observed in the rotational couplet, it is likely the radar signature was a tornado. We will analyze this data more thoroughly when our field work is complete.
Most importantly, the tornadic portion of this storm avoided Mitchell.
The second storm developed in an unusual position for a tornadic supercell. It was directly to the west of the first storm. Cool, stable air left behind by the leading supercell generally inhibits additional development within a few tens of miles to the west and north. That was not the case in this event. As we pulled away from our deployment site, we began taking hail the size of tennis balls as the downdraft wrapped around the storm, curling up into a hook. When we reached Scottsbluff, 50 mph winds and blinding rain made driving impossible. We sought shelter behind a building next to the road and anxiously glanced from the downburst outside to the radar screen. A new mesocyclone had formed almost directly over us, and the wind and rain were whipping furiously into the circulation. A minute later and a tornado was confirmed on the ground in Scottsbluff by our radar and probe teams. We couldn’t have been more than a few miles away, but we could barely see across the road. A close call.
While we were fine, not everyone was so fortunate. At least 6 trailer homes were flipped in Scottsbluff, and injuries were reported. There is no question: these storms are scary and life-threatening. At times, they are sorely unpredictable. And that is why we are here.
Yesterday was an action-packed day for VORTEX2 in eastern Nebraska. We departed early from Valentine, NE at 9 am. Our travels took us father south and east from that location to intercept severe thunderstorms forecast to develop in Nebraska and Iowa later that afternoon and evening. The scenery along the way was stunningly beautiful, with a series of green, rolling hills giving way to the cobalt blue waters of the Missouri River. The river itself was a quarter-mile wide, with the current swift and the surface whipped into frothy waves. We took lunch along a small inlet along its banks, and watched as fishing boats ferried out and in. Judging from the smell, some of the expeditions were quite successful. We watched and waited.
At about 3 pm, the first cumulus clouds began to bubble skyward to our southwest. Their updrafts were narrow and doughy. A minor repositioning placed us in front of a small cell struggling to establish itself in the distance. It looked prone to fizzling, with little upward motion into its skinny base and a weak precipitation core. Sure enough, the storm began to shrivel and die just 15 minutes later, and our eyes turned to new convection initiating farther to the west.
This set of thunderstorms proved more stout. Within minutes, a large base developed as the storm approached. Ragged, low clouds rose quickly, evidence of the rising motion fueling the updraft. We were well positioned and able to deploy our instruments nearly 20 minutes prior to the arrival of the core. As the storm continued to develop, however, rain-cooled air began to encroach on the main updraft, which had the effect of choking it off from the feed of warm, unstable air that had been rising into the storm. In response, a new updraft began to form farther to the south, quickly placing our instruments out of position. We scrambled to return to our instrument sites for collection, but were beat by a lowering that briefly rotated near the location of the old updraft. Several of our team members saw funnel clouds attempt to form. Although nothing touched down, we had to wait until it dissipated. By that time, it was too late to get back in front of the storm to reposition
ourselves. Nevertheless, Carlos and George collected very useful rain and wind data at their deployment site.
We stayed the night in Sioux City, Iowa at the Stoney Creek Inn. It did not lack personality, as the Inn was an interesting cross between a log cabin and a hotel. The beds were to die for, and after 18 hours on the road, we needed that more than ever.
We are now traveling back to the south and west. Who knows what today will bring us in our adventures.
Howdy from Kearny, Nebraska! Today is a chase day; we are planning to intercept developing supercells in eastern Nebraska and western Iowa. Surface-based CAPE is expected to exceed 3000 J/kg this afternoon, and wind shear is expected to be sufficient for a few strong tornadoes. Very large hail is also forecast to accompany these thunderstorms.
Today's activity is a marked change from the last few days. Sunday and Monday were mostly down days, with the exception of a short period of travel to Kearny from North Platte on Monday. Although we didn't actually chase, one of our team members was fortunate enough to snap an extremely rare picture of twin tornadoes racing across our hotel lobby on Sunday. Okay, not really. But the trees were definitely rotating. I swear. ;-)
“Got some cow juice for ya. Yep, when I was a kid, we had
six cows, and we milked ‘em all by hand. And they always gave more milk on
Sundays and holidays, because God is great!”
--Told to me at breakfast this week by a Nebraskan
Yesterday was (mostly) a travel day. We left Fort Collins,
Colorado and headed north to Spearfish, South Dakota, which is the coolest
sounding town we’ve stayed in yet (sorry, Colby). Along the way, we couldn’t
help but notice how close we were to a certain national monument. A few “wrong”
turns conveniently led us to Mount Rushmore. Abe was
worried when he saw us; tornadoes just don’t do much for his looks. Not to
worry, buddy: today’s a down day for our team. =)