TornadoVideos.Net | Very strong cap in MN -- Supercells still possible today

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Very strong cap in MN -- Supercells still possible today

News - General

Written by Reed Patrick Timmer

Monday, 13 August 2007 10:59

After analyzing the 4km WRF precip forecast last night, we decided that the chase event today in Minnesota had far too many negative factors to make the 15 hour drive to our target area. Specifically, here are the limiting factors for tornadoes we considered:

1. WRF and GFS did not forecast precip until after 00z, and the 4 km WRF indicated a large MCS would form at around 8:00 pm. This indicates that the convection would be forced by the strengthening LLJ and would likely be elevated.

2. Convective temperatures on most soundings were >100F, and to attain this convective temperature the T/dewpoint spreads would be very high, and conducive to quick transitions to outflow dominance.

3. 700 mb trough moves east and north of the instability axis by peak heating.

4. In recent forecasts, the warm front has become oriented more north-south, and thus it would be more difficult for a storm to root on the boundary.

Here are some selected RUC forecast panels confirming the above:

Despite the negative factors listed above, if a storm can become surface-based in the warm sector along or the west and south of the warm front, then the shear and instability are more than sufficient for tornadoes. There are also storms approaching MN from eastern ND, and these will have a chance to become surface-based and supercellular as they move southeast towards the better instability and weaker cap. Stay tuned for updates!