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Since my last forecast update, both the GFS and Euro models have done a significant about-face in terms of the overall pattern. Instead of a major central US ridge, a shortwave trough is moving into the Plains today, which could start the tornado production back up in the Texas Panhandle region. Tomorrow (Wednesday) the system could bring a significant tornado event in western Oklahoma - a solidly chaseable event. Then, a major western trough could begin impacting the Plains on Sunday, followed by a potentially multi-day period of good tornado setups into next week. The GFS shows a better situation for observing, pushing the front side of the trough and its strong southwest flow aloft into the Plains, and parking it there. The Euro model shows a less chaseable situation, still showing the big trough, but keeping it far to the west so its strongest southwest winds aloft never make it over the Plains.
Now - as I get farther into storm season, particularly after I've seen tornadoes - my standards for observing Plains setups tend to increase dramatically. Mainly because if the early season has been active, as it has been this year (I've already had two Plains trips this season), my observing funds have been heavily used. As a result, I get more picky about which setups I decide to go after late in the season. I look for not only good storm observation days, but multiple-day setups that offer more than once chance to observe tornadoes. That factor will begin pulling more weight in chase probabilities from here through the rest of the season. So, the probability table from here on out primarily reflects that decision criteria more than tornado potential for a given period.
Case in point: Wednesday (tomorrow) looks like a solid tornado day in western Oklahoma - however, due to it being only a single-day opportunity and a long distance drive, I'm not planning to observe storms. This weekend could be a different story, however. A high-probability, multi-day event like the GFS shows would be very worthy of a storm observing expedition. However, if the Euro ends up being right, it would likely not meet my late-season expedition criteria. So, at this point, I can only go as high as 50% on a storm observing expedition happening during the period starting on May 22.
|2010 Storm Expeditions - Probabilities as of May 18|