5/31/05 FCST: S. High Plains

Dec 18, 2003
Norman, OK
The 12z ETA is forecasting an interesting weather situation for Tuesday.

At the upper levels, a relatively strong (35-45 kts at 500 mb) shortwave trough is forecast to enter the southern High Plains by Tuesday evening. As a result, a lee trough is developed by the ETA in E. NM which induces southerly low-level flow across the Plains. This in turn is forecast to draw very rich moisture (Tds >65 F) northward and northwestward toward the western Texas panhandle.

As a result of the moisture transport (Tds in Lubbock may be >65 F, which would be incredible considering the elevation) and good lapse rates, strong instability is forecast to develop over west Texas (on the order of 3000 j/kg of CAPE).

Surface winds are forecast to be very backed (SE), winds at 850 are forecast to be reasonably strong (30 kts) and southerly, and the upper-level winds from the west and west-southwest at almost 50 kts. As a result, ETA forecasts a broad swath of helicity > 300 m2/s2 over west Texas.

It should be noted that the 12z GFS develops a significantly weaker shortwave trough for Tuesday evening. However, the upper-level height pattern is fairly similar, and both models forecast precipitation over the region of concern by 00z.

It looked great for a while there on the Eta, but pretty much each successive run has been consistent in weakening the shortwave trough, and the flow associated with it, as it moves into TX. Also, the 500 mb winds are now progged to be out of the WNW, not the WSW, as before. The problem here is that the trough is running into another one to its southeast by this time, weakening the trough, and keeping the flow from backing to the WSW at mid-levels. In other words, this is one of those "setups" that has looked increasingly worse with time on the models, rather than better (I hate those!). I also see no signs of a significant low-level jet developing, which might help to increase the shear towards dark. I still think we will see supercells, but given the marginal (how many times have we said that this year) flow, I'm not impressed with our tornado prospects. We'll continue to monitor, of course :).
I will likely be heading toward Jayton, TX on Tuesday.

They are definetly some positives
Surface based CAPE should approach 3000 J/kg
500mb winds around 35 kts providing around 40 kts of 0-6km shear
Helicity values around 250 m2/s2 by evening
Looks to be some upward vertical motion(500mb) to help get things started

This is based off 00z eta , haven't seen the other models yet
Will probably wait till around 2pm to head out.
The key today will be the supercell's interaction with the outflow boundaries left over from the overnight/early morning convection. Once can clearly be seen a little northeast of Midland, oriented northwest/southeast. Radar picks it up nicely and it's noticable on visible statellite. There are others that can be seen on radar, but are not as well defined. I do believe these boundaries are the key to finding a tornadic storm today. Otherwise, looks like a great day for supercells nonetheless.