Monday, May 10, 2010

Post storm wrap up

Wild day. 37 reported tornados. maximum hail size of 4.25". Max reported wind gust to 100 mph.
Looks like a number of fatalities have occurred as well.

Well forecast event by SPC. The uncertainty was well forecast at 1200 and 1300 Day 1 outlooks:
1. Initial storms would take time to organize thus Initiation area would be removed from maximum tornado risk.
2. moisture return would not be an issue.

BUT, the 1630 UTC update suggested that 21 UTC would be the new initiation time. Doubt crept in. Even to go as far as to say that central and southern OK would be capped and that models were over-aggressive. The 2000 UTC update re-instated the aggressive coverage southward based on the satellite data: cumulus cloud field developed in advance of and in proximity to the dryline.

What was not well forecast was the timing of CI. SPC was calling for a 18-19 UTC CI in SW KS, with another bout further south into OK by 21-22 UTC then further south into central and southern OK. The focus was on the cap and favorable moisture return.

Indeed the actual event sequence began like SPC said: SW KS near DDC for 2nd and 3rd storms in a bunch at 18 UTC. The storms appeared further SE into OK to the northwest of WWR by 1850 UTC and another east southeast of Gage and a few weak storms further south. These storms never really got going though they were players later when they merged with the northern storm ... that storm became tornadic after those mergers though it isnt clear they were the cause.

Now heres where the forecast goes awry. The dryline has not been dogged by storms. It was still going strong. At 2000 UTC a weak storm complex was near JWG. It almost dies, then out of nowhere re-intensifies into a nasty linear looking supercell. Much like the Nov 2005 Ames tornadic supercell or really much like high shear supercells.

By 2100 UTC a new batch of weak storms in advance of the dryline form and these quickly become supercellular in a cluster. The dryline is far removed from these storms. Much further south more storms get going, more likely previously involved storms with the dryline down there. Between these 2 areas another loan supercell formed and merged with the OUN cluster. This rogue supercell seemingly merged into the southern side of the northern supercells and that was in Norman or close by. differential storm motion for some reason on that storm.

New storms form off the dryline by JWG and move northeast to form a more linear looking cluster. By 2142 more storms form on the dryline to the west of OUN. This cluster appeared to form a line before devolving or maybe evolving into nasty hook echo supercells. Quite spectacular.

The supercells came in waves, seperated by time and/or space in clusters. They were at times poorly spaced but productive, and well spaced and spectacular. We saw the whole range of high shear supercells. More importantly we saw that the model forecast paradigm broke down. The soundings launched by vortex2 will be invaluable to assessing the environment on this day. This will be one of the most studied days in VORTEX2.