Monday, September 28, 2009

Thursday's Severe Weather Possibilties Update

A quick update to share what the 12Z model runs are showing. The GFS continues to move the cold front rapidly through the Southern Plains. The 12Z run speeds up the frontal passage and puts it near the I-20 corridor by 7PM Thursday evening.(See image below) I feel this may be a little too fast. The instability forecast is also much lower on the 12Z run decreasing the severe threat.

The 12Z NAM is now in the forecast time frame and is showing a much slower and better severe weather set up than the GFS. The NAM is forecasting a dryline to set up Thursday afternoon across central Oklahoma and hangs the actual cold front across northwest Oklahoma Thursday evening. This will allow for plenty of Gulf moisture to move in across the Southern Plains(See image below).

Below is the forecast for CAPE (convective available potential energy) for the NAM Thursday evening. Notice the energy is pooling along the dryline in central Oklahoma.

With the much faster GFS solution CAPE is confined to East Texas and is no where near as much as advertised by the 0Z GFS.(See image below) This solution would still produce storms and with the shear available, we could see a line of storms with gusty winds across the Southern Plains.

Overall I feel the GFS is too fast and the NAM is a bit too slow. Both models do not point to a significant tornado threat as wind shear will be mainly unidirectional. However, if a secondary low develops as the 0Z GFS advertised, we could see an enhanced tornado threat along and just north of the low. This system still bears watching and may be a worthwhile chase for me later this week.

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