The Amazing Power of a Low Level Jet
On Sunday morning June 22, 2003, retired government employee and storm-chaser friend Bill Winkler and I picked SE Nebraska as the area most likely to experience severe weather. SPC had outlooked Ern Nebraska in a as a Moderate Risk area for severe thunderstorms. Late afternoon CAPE values for Ern Nebraska were forecast to be in excess of 5000 joules/kg....plenty unstable! The limiting factor for deep convection was that surface temperatures had to get into the mid to upper 90's along the Ern KS/Nebraska border in order for a cap to break.
What was encouraging to Bill and I was that there was ongoing convection Sunday morning in northeast KS/SE Nebraska. These thundershowers were associated with warm advection just E of a developing low level jet. Before starting out just before noon Sunday, we heard distant thunder to the NW in Lawrence, KS, where Bill lives. Our plan was to work our way W-N of Lawrence...getting past the midday convection into an area getting better solar heating where the cap had the best chance to break later in the afternoon. A cold front would be pushing slowly Ewd into Wrn KS during the day Sunday. The combination of a low level jet pushing 70+ degree dew points Nwd into E central Nebraska...an outflow boundary from the early convection over Ern portions of KS/Nebraska...a favorable vertical shear profile showing winds veering with height...and strong instability made the GRI and LNK areas of Nebraska look particularly promising.
As we passed thru Topeka, KS, we noted that it was rather dark overhead and to the N-E. In fact, it was dark enough that highway lights came on along I-70 as we headed W. According to severe weather reports, storms later that afternoon produced 2-1/2 inch hail as they moved or redeveloped into the Olathe. KS area, SW of metro Kansas City. Turning N on KS 75...we could see strong storms with frequent lightning off to our right. A few straggler elevated storms spit out occasional lightning cloud-to ground and moderate showers with huge rain drops ahead of us along highway 75. But we could see clearing to the distant W. We broke out into partly cloudy skies as we turned W on KS 36 after a quick lunch at 2:30 CDT. However...our mid-level clouds were replaced by a broken to overcast low stratocumulus deck and a muggy haze restricting visibility.
Bill and I knew we had to continue W into an area receiving strong solar heating. As we continued W on KS 36, we noted the cloud bases gradually lifting and becoming broken flat cumuli as the haze slightly thinned out. Things were going great up to this point. The cloud bases by 4PM CDT were becoming higher with scattered small...not quite so flat cumuli in the lingering haze as we proceeded W of Marysville, KS. We obviously were getting into an area of better solar heating.
At this point...our story takes a rather UNEXPECTED TURN. About 10 mile E of Belleville, KS on KS 36, the timing belt on Bill’s Ford snapped and the car died! There we were... in the middle of nowhere in Nrn KS. While we called a towing company and waited for a AAA truck, we listened to NOAA Weather Radio and noted temps/dewpoints of 93/70 at CNK and 96/71 at SLN. Was the cap ready to break? We noted that the cumuli were getting puffier around 4:30 CDT. Brisk SE winds...13V1620 G35 rippled thru the grain fields where our car had stopped.
When the tow truck arrived, we found that the nearest place we could get our car repaired was in Hebron, Nebraska, in Thayer County, some 20 miles NNW of where we were. By default, Hebron was our destination...all other plans we had were on hold until we could get the timing belt fixed. Suddenly, some lower ragged cumuli cleared out of the way to the WNW just as Bill and I got into the tow truck. I noticed some newly formed CB towers that has just begun to glaciate!
The tow truck driver did not think that these towers were storms until we were within 10 miles of Hebron, when he conceded that they were thunder-heads. By the time we reached Hebron, a cluster of smaller cells 10 miles W-SW of Hebron were beginning to consolidate into a more organized storm with a large anvil plume spreading out overhead. At the Riverside Motel SE of Hebron where we were staying...distant thunder and lightning began to increase to our WSW with a few scattered big rain drops. We put out a can to measure rainfall.
Things gradually became more interesting. At about 6:20 CDT (2320Z) we began to see small hail along with the big rain drops as the skies gradually darkened to the W with increasing electrical activity. A strong SE wind howled blowing 45 degrees into the main storm. Over the next hour, precipitation was not very heavy overall... nor did it decrease visibility much. Occasional bursts of hailstones thrown out of the anvil gradually became bigger...some up to 3/4 inch diameter.
At 7:30 PM CDT....a TORNADO warning sounded! See Storm Reports from SPC for more information on the times...location...and occurrences of tornadoes in Nrn KS and Srn Nebraska Sunday evening June 22nd.. PCPN increased by 7:40 to approximately 2SM+TSRA as intermittent bursts of hailstones up to 3/4 inch continued. The surface winds backed around to easterly...08V1225G45...gusts to 45MPH blowing directly into the storm! As I found out the next day, we were definitely in a tornado meso-cyclone circulation as 4 tornadoes were reported during that evening in the Deshler, Nebraska area....8 miles WSW of Hebron. Bill and I took shelter in part of the Riverside Motel that had access to a basement...but we watched the storm from the basement entrance.
PCPN really began increasing after 7:53 CDT. Some quarter size hail began to fall and Bill and I estimated a stone at 1-1/4 by 7/8". By 8PM...we were 1/4SM+TSRA with lots of 1/2-3/4 inch hail pelting down. Thunder and lightning ...all types...was nearly continuous. Spectacular! We were certainly in the HP region of the storm just ENE of the main hail vault and tornadoes! Winds continued fitfully from 03V0825 with gusts to 40. As I ran back to my E-facing hotel room from the basement...a strong ENE wind blew in a bunch of ½ inch hailstones onto the carpet!
This first heavy storm lasted till 8:50 CDT with visibilities frequently 1/4-1/2SM +TSRA and occasional 1/4-1/2 inch hail. After 8PM...very heavy RA rather than hail predominated. Although Bill and I did not actually measure what had fallen up to 8:50 CDT...experience told me that about 1.65 inches had fallen up to that time. Rain slacked off to moderate to heavy the next half hour...with frequent thunder and lightning continuing.
At 9:20 CDT the next wall of water arrived! This rain was even heavier than that of the first main storm....but there was little if any hail. Winds shifted to the N and even NNW...32V0220G40. For the next 80 minutes....we estimated 1/4V1/8SM +TSRA with rainfall rates at times exceeding 5 inches per hour! Frequent thunder and lightning all quads seemed centered to our S from the Motel (but was probably more to the SW as the Satellite Precipitation estimate later showed). The heaviest periods of RA in that 80 minute period showed surges of wind from the NNW that veered around to the ENE with a slight slackening of the very heavy rainfall. We estimate that 3.5 inches of RA fell between 9:20 and 10:40 PM CDT. Perhaps a tenth or two between the 2 main storms! At 11 PM we measured 5.35" for the evening!
We weren’t done yet. Thunder and lightning continued intermittently all night. Near and just before dawn...more close lightning and heavy thunder occurred with downpours contributing to an additional 1.33" RA since 11PM the previous night. Some of the loudest nighttime thunder and brilliant cloud to ground strokes occurred just before dawn on Monday June 23.
The storms were the talk of the town all day Monday June 23 in Hebron. Deshler, Nebraska...8 miles to the WSW...had seen 4 tornadoes Sunday evening with power interruptions from downed power lines along with considerable flooding. There were unofficial reports of 12-15 inches of rain around Hebron. These seemed too high at first but I concede that such amounts were possible SW of town according to satellite estimates.
Another sidelight of the Sunday night storms was that huge hailstones fell from a separate supercell near Aurora, Nebraska, some 40 miles NNW of Hebron. It was at least as large as one of the previous largest hailstones ever recorded: one that fell in 1928 in Potter, Nebraska, that was 7 inches in diameter! The Aurora hailstone also measured 7 inches in diameter. But some of the Aurora hailstone’s mass was lost when the edge of it hit the gutter of a house!
Steve Flood, HPC