Friday, April 8, 2011

Chasing supercells

Pretty good chase day today. Any chase day is a great day, but this was good because it ended my absence on the Plains after roughly 4 years. It culminated in a splitting supercell with near tennis ball size hail in a marginal low level shear environment, but favorable bulk shear environment.

Hard to say what the issue with convection initiation was, but most of the updrafts that initiated at least marginal vertical cumulus growth seemed to tilt and then result in small turrets on the top. The clusters of clouds that did manage to grow finally did so after 2200 UTC, and by 2300 UTC we had a nice storm to chase at least from its radar presentation. The base was elevated a bit but a clear updraft bell had formed, and when we drove north on I35 to stay ahead of it, noticed pretty good size hail on the ground. Maybe 2-3 inches in diameter, low-density. I even found some that had split in half so you could see the rings. Most of the hail in the grass was unbroken, but the stuff that had hit the pavement was easily smashed.

The model scenario played out fairly well. A moisture pool was left over from the late afternoon mixing of the dryline further south. Last nights NSSL WRF simulation had 1 storm form west of Tulsa and I took this to be a positive sign that CI was probable. Of course the model had some pretty high moisture values so that was a concern. However, afternoon observations indicated that dew points would hold near 64 F. Of course the low level shear was weak as was the SRH, but the bulk shear was up around 20 m/s. Plenty good for supercells, but not so good for tornados.

The focus for initiation was along a convergence zone in Northern Oklahoma that would eventually redevelop rapidly north, at least in model land. I will have to investigate if this actually occurred.  I think its worth investigating from the modeling standpoint, especially the structure of the boundary layer that led to the mixing out event further south but kept enough moisture further north.

The storm we were on is to the east-northeast  of WDG on the image below at the time tennis ball hail was falling while we were on I-35.

Glad to be back chasing storms...