Monday, May 10, 2010

May 10 the forecast for tornadoes?

It isn't rare to have a day 2 moderate risk for the central plains including OK and KS. It is rare to see a moderate risk during VORTEX2 operations ;) . The prevailing wisdom is that if you put 100 vehicles and 400 scientists and 8 radar trucks in the Plains ...ain't nuthin' going to happen.

So I thought I would get in on the forecast action.

Broad scale specifics from the NAM model: a sfc low races out of CO tonight across southern KS and moves into northeast KS by tomorrow night. This feature is due to a pretty sharp shortwave trough at 500 hPa (about half way up in the atmosphere in terms of mass) which gives the appearance of a negative tilt into tomorrow. Note that the flow around this trough (the jet streak too) is cyclonically curved. The jet streak itself is actually located across OK and TX panhandle. The jet streak at 300 hPa is located further north and there is a hint that the flow aloft will be anticyclonic in nature across southern Oklahoma.

Players in Convective initiation: The warm from will be a breeding ground for all kinds of convection tonight into tomorrow evening. The dryline will be a major player as it punches into Oklahoma City. BUT the shear appears to be oriented perpendicular to the boundaries ... a sign that storms should start and possibly remain discreet.

The odd things I see:
The motion is fast for the shortwave aloft, and thus the moisture return may be in question ... moisture takes time to be transported in great quantities. 0500 UTC data in Texas show 60's creeping into the TX panhandle but dew points only 50 at OKC and DFW. Hi-res NSSL model is consistent through 6 hours with observed data. Models are indicating this to be the case ... that only low to mid 60's with high temperatures near 83 will be possible, though behind the dryline it may hit 90.

NSSL model also indicating the low may stall. Operational models may be aggressive in bringing this system out. Complicating factor is the system to the NW that drops in behind, and system to the east which seems to not move too much. Hard to know since the jet aloft to the rear of the shortwave is not fully ashore.

Day 1 outlook updated to reflect a high risk. Can't argue against that. Models are all producing favorable parameters for Oklahoma tornados. This is easy to forecast maximum risk where all parameters come together nicely. However, as a chaser, where would you want to be knowing:
1. fast storm motions
2. seemingly moisture limited to the east (from the limited model runs I have seen)
3. complicated cloud forecast
4. complicated surface low and dryline evolution and thus placement.

It appears SPC is playing up the moisture (to 70 F) with temps in the mid 80's, and heavily favoring the track of the midlevel jet (rightfully so).

The BIG question is what kind of supercells will be the norm? low precip, high precip, or classic? If low precip come off the dryline how will they evolve in the face of ridiculous shear (40 meters per second) and a somewhat strong cap which is sure to come out given the steady fetch from ABQ?

I have to wonder if there will be early storms in KS that get into OK and further complicate this situation with outflow boundaries. There doesn't appear to be a whole lot of limiting factors the models are picking up on, so the devil is in the details ... morning models will be key as well as the radar and moisture progress on the soundings.

High risk is warranted but there is more going on here. May 3rd 1999 comes to mind in terms of an OKC to Tulsa outbreak. Needless to say I will have the radar looping tomorrow.