Saturday, April 9, 2011

Supercell buffet

It appears that parts of Iowa, near Mapleton and points east and southeast were hit hard by 3/4 mile wide tornado (according to the storm reports).  The storms took a while to develop and mature but sure enough once that cell crossed into Iowa it was going nuts. Here's why:

1. The instability was high, up around 3600 J/kg and moisture was 13.6 g/kg through a deep layer.
2. The low level shear was 27 knots and the bulk deep layer shear was 62 knots.
3. The hodograph is a classic quarter circle up to 6 km.

Of course the other storms in Nebraska were prolific splitting supercells, with the left mover racing north.  A very impressive supercell buffet. This area was highlighted well by SPC, despite the NSSL WRF having nothing in this area today. This was also despite a relatively good forecast by the same model for events last night in the Ohio River Valley. The cloud simulation looked good too, but perhaps the resolution was just too coarse to really capture the boundary layer processes responsible for convective initiation of relatively small thunderstorms.

UPDATE: Sounding image obtained from SPC, and radar image from College of DuPage (