Wednesday, May 19, 2010

The devil is in the dynamics

A nice little potential outbreak today for OK and North TX. Complicated situation as the night time MCS moves away from OKC, with no outflow boundary clearly visible. The low level cloud field is eerily similar to previous days. The complications are that the elevated mixed layer is well into the area, and the 500 hPa frontal zone is already through AMA. Surface convergence will be there to the north but it may be the dynamics that sets this thing off.

The cap is the big player and the models favor this opinion. NCAR ARW run from last night says multiple periods of initiation to the north, remniscent of May 10, again occurring earlier in the 18-19 UTC time frame. Then later on initiation occurs along a dryline boundary (around 22 UTC) before growing upscale. NSSL ARW run is a lot different probably because of the poor precipitation forecast it produced to the west of the MCS. So too much precipitation to the west virtually ensures that a subsequent trigger for new convection occurs earlier.

Both models agree that initial development will be scattered but not isolated. Thus storm interactions and outflow development may hinder chances at discreet, cyclic tornadic supercells. Today may be a tail-end Charlie kind of day.

The models are not very different with the dryline, but it appears the 500 hPa front is much stronger in NCARs run...though i have no proof since the NSSL run does not make available fields aloft...however the CI that occurs in NCARs run appears associated with the 500 hPa frontal circulation. This is inconclusive however because the 850 RH field is near saturated as well. Breaking the cap is easier when the PBL top becomes saturated.

If I were chasing today, I would try to be south of OKC, probably in Norman. Wait to see how the cap holds to the north and if early storms stay isolated and discreet go for them. Then haul ass south later in the day as the next wave of CI occurs along the 500 hPa front. Otherwise south and east of Norman. The show should start by 19-20 UTC either way...3 hours from now.

Not sure of the tornado potential. Yesterday appeared to be ripe for tornados, yet the pictures and reports indicate short lived but strong tornados. Nice supercells on radar, though. wonder if the shear profiles were not ideal enough. The shear profiles from NCARs model at OUN at 21-23 UTC appear good enough, so this may be a right time right place scenario...brief window is implied. To the north it is less certain since storms may be on the warm front. I am still hedging my bets southward of OKC ...