Directwx.com

Summary: Nice supercell near Yankton, SD which produced several funnels and softball sized hail.

Targeted the warm front, dryline, cold front triple point near Yankton, SD. Left Omaha with Christy, Craig, Anton and CJ at 3:45. Had to leave 2 others behind due to lack of vehicles. Environment consisted of temps around 80F with dewpoints of 55-60 in the warm sector. Upper level winds were a little weak for good supercells with speeds of only 40-50 knots from 500-250 mb. In addition there was very little shear from 850-500 mb. However the low levels near the warm front exhibited strong backing with surface winds out of the East at 20 knots and from the South at 30 knots at 850 mb. This resulted in sufficient storm relative helicity of 200-400 m2/s2 in the target area.

Pictures: http://www.directwx.com/index.php?q=node/431

Analysis Data: http://www.directwx.com/index.php?q=node/451

Target: Valentine, NE

Summary:  Chase wih the Weather Explorers Post.  Caught a long-lved supercell with wall cloud and several funnels along with 1 inch hail (and a turtle)

Setup:  Outflow boundary-enhanced weak frontal zone was lying east/west across southern SD.  Strong cap would be broken by combination of afternoon heating and some mid-level cooling from a short-wave trough at 500-700 mb coming out of WY.  This would induce a weak low-pressure area over northwest NE moving east along the NE/SD border bulging the dryline east south of the low.   The goal was to reach the dryline/frontal boundary intersection in order to maximixe convergence and break the cap.  An axis of 15C temperatures at 700 mb was forecast to extend from CO through central NE to just south of the Valentine to Yankton area.  We would work the northern edge of these warm mid-level temperatures.  Dewpoints were in the upper 60's producing forecast CAPE of ~ 4000 j/kg.  Wind shear was favorable in this NW flow type pattern with W-WNW winds of 40 kts at 500 mb and S winds of 20 knots at 850 mb.  SPC had a high end slight risk out with only a 5% tornado threat at 12Z which was upgraded to Moderate Risk at 16Z (mainly for wind event associated with the ongoing MCS in SD).

Pictures:  http://www.directwx.com/index.php?q=node/403

Target: LaCrosse, WI

Summary: Rotating wall cloud/funnel, tornado and 4.5-5 inch hail

May 5, 2007

Target: McCook, NE (secondary target was Hays, KS but deemed too far to be back by 9pm)

Setup:  SPC High Risk day with 30% hatched area for tornadoes.  Early initiation expected around noon along dryline/Warm front intersection.  Target area was ahead of forecasted dryline bulge.  Deep 5500 meter u/l low over AZ with s/w trof rotating NE into CO by 18Z  with associated PVA over target area.  Strong 80 kt mid-level jet at 500 mb punching in from SSW into target area.  Overnight convection had setup diffuse OFB over northern KS/NE border area.  Directional shear above 850 mb not strong but sufficient speed shear for supercells and good low-level shear with flow backed to SE near warm front for tornadogenesis.

April 24, 2007 – Target: Pratt, KS (between DDC and ICT).

Summary: Strong dynamic closed low event that was becoming vertically stacked. Alternative target was the dryline/warm front intersection in NW KS north of surface low. Dryline (DL) was expected to setup near the SW KS/CO border then mix east by 1 pm to between DDC and ICT. Sufficient moisture with Td’s in 60’s, instability with CAPE ~ 1500 j/kg and LI of ~ -6. Low-level shear was expected to be relatively weak near the dryline however as storms fired on the dryline then moved off the line to the NE they would be in a better shear environment. SPC MDT risk that showed possibility of upgrading to HIGH. Tornado potential was 15%. Initiation was expected to occur early, around noon.