March 23, 2009

Statistics:

Initial Target: Wichita, KS
Departure: Bolingbrook, IL 9:00 pm, March 22
Arrival: Naperville, IL 9:00 am, March 24
Intercepts: Burrton, KS 3:00 pm
Tornadoes: 0
Hail: Non-Severe (Pea Sized)
Wind: Non-Severe (not measured)
Features: RFB,  Wall Cloud
Miles: 1471

Summary:

Strongly sheared, marginal instability dryline chase.  Targeted Wichita, KS where an afternoon initiation would best utilize cape/shear combo.  Intercepted isolated cell near Burrton, KS and storm northeast noting rain free base cycling, lowering, and possible wall cloud.  Lost storm due to accelerating storm speeds and lack of road options.

Crew and Equipment:

Solo Chase.  Equipment: TH-F6A Tribander, and GPS/mobile data card equipped laptop.  Pictures by Skip Talbot

Details:

Despite lacking dewpoints, Monday's setup looked to be the first real chase opportunity.  A deep trough and strong cyclone was forecast to move through the plains firing storms along a dryline before a cold front would sweep through that evening.  Cape values were only forecasted to reach 1000 along the dryline, but a very strong low level jet and backed surface winds were to provide great directional shear.  Another concern, however, was the backed mid level winds which would create northerly storm motions and created uncertainty about storm mode.
I initially considered playing the northern half of this setup.  In Nebraska, a cut off 500 mb low created almost cold core like conditions, which are favorable for low topped supercells and tornadoes.  The cold mid level air here would create the steepest lapse rates and a vorticity max was forecast to move through the area for enhanced directional shear.  Storm motions were forecast to be about 50 mph, however, and I didn't want to chance the marginal moisture, in favor of a more classic warm sector, dryline setup to the south.  I targeted Wichita, KS where storms were expected to fire later in the afternoon than compared to the northern areas, where they better utilize the meager Cape.  I left Bolingbrook at 9 pm Sunday night and drove to almost Des Moines, before camping out in the van for a few hours of sleep.

I stopped at the Best Buy in Overland Park, KS the next morning and picked up my new camcorder, the Sony XR500.  SPC went with a 15% tornado risk with strong tornadoes mentioned.  I was surprised by the high probabilities, but I also wasn't complaining.  As expected, Nebraska got the first tornado watch, followed by Kansas and Oklahoma.  As I approached Wichita from the east, storms fired much earlier than I expected. at about 1:30 pm.  One cell emerged from the group and I setup to intercept it as it crossed highway 50 between the towns of Hutchinson and Newton. 

Although the cell was not warned, for a couple of scans it took on a nice hook echo on the radar.  I went south through Burrton to get a look at the base.  Through the precip I couldn't see much organization, however.  There was definitely a rain free base, and possibly an RFD cut, but no lowerings.  I let the storm pass overhead before starting my long zig zagging race to keep up with it.
As the storm passed north of Newton it picked up a severe thunderstorm warning and the base started to cycle.  Scud was feeding in with the inflow and I was hoping for a developing wall cloud.
A pointy lowering stuck out from the base.  I don't think I'd call this a full fledged wall cloud as it was probably more of just an inflow band.  It didn't last more than a few minutes.
The base gusted out.  The roads in this part of Kansas are great.  I had nice north/south, east/west highways that I could race down to keep up with this storm that was moving northeast at 45 mph.
Driving under the occluded base:
The base cycled and started to organize again, but the storm was also accelerating.  Now moving more than 50 mph, I was having trouble keeping up with it despite the nice road network.   Through the rain I could see to my north what was most likely a wall cloud.  I was too far to discern rotation, but it did look quite low to the ground.  Note the big billows of dust streaming into the storm on the right side of the shot.  The surface winds were insane, gusting often to 40 mph, making driving in a straight line difficult.
The storm started to pull away from me, but this gave me a great view of the tower.  I couldn't frame the whole storm with my camera, but you could tell how dramatically the storm was sheared over.  Note the blue ski that was directly over the storm's base, both on the left side of the picture, while the tower and anvil stretched off the right side of the photo.  It was tilted almost 45 degrees.
Bob's road.  My nice highway gave way to to a twisted stretch of unpaved gravel and dirt.  I had to greatly reduce speed to handle the road, and knew then that the chase was over as the storm continued to speed away from me.  Luckily it hadn't rained here so I didn't have to worry about getting stuck.
The storm I was on never gained a tornado warning, despite producing a couple of hook echoes on the radar.  As the storm screamed off to the north, a squall line filled in behind it, and the next warned storm was more than a hundred miles away to the south.  I called it a chase and started back for home at just after 4 pm.  I camped out in the van again near Iowa City, and made it into work on time Tuesday morning.
Conclusion:

Despite the decent tornado probabilities in Kansas, only a few tornado reports came in from a storm by the OK/KS border.  There was a little more tornado activity on the northern end in Nebraska, but these tornadoes were also brief, low visibility, and produced by extremely fast moving storms.  There was some marginally good structure on the storm I intercepted, but given the distance and slightly higher expectations, this chase was a bust. 

 

Lessons Learned:

  • High shear/low instability setups may not justify a plains run.