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                   Monday, May 11, 2009 - 4:13PM

Unusually persistent western ridge to settle in

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The situation for storm observers out west is worsening with every successive model run. Not only has the huge ridge become all but certain due to much greater model consistency and agreement, it appears that it will be persistent for quite some time. I will likely go ahead and cover the midwestern setup on Wednesday due to the fact that tornado season in the USA will be gone for 2 weeks or more after that.

GFS 500mb pattern for Wednesday

The good news for eastern-US storm observers is that northwest flow will set up on the eastern side of the Plains-Rockies ridge, providing many thunderstorm days in the midwest and east, while the Plains slumber. The best we could hope for now is a repeat of 2005, when a pattern change finally ushered in a nice, productive western trough after the first week of June. This "June or bust" thinking is reflected in the new probability table below. Since the possible Wednesday chase is not going to be a 'true' Great Plains trip, I'm not including it in the probabilities for this week.

Based on the current outlook, this probability table charts the chance of the second Plains storm observing expedition starting on a particular date:

2009 Storm Observing Expedition #2 - Departure Date Probability as of May 11
May 11-150%
May 16-225%
May 23-3125%
June 1-1535%
No trip #235%

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