Storm Highway by Dan Robinson
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Thursday, May 20, 2010 - 2:15AM CDT

May 20 Plains update

By DAN ROBINSON
Editor/Photographer
25 Years of Storm Observing
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The 00z ECMWF (Euro) model won't be out for a couple of hours, but looking at the 12z Euro and the 00z GFS, I think I have enough information to speculate about what the upcoming week may hold chase-wise in the Great Plains. Currently, Monday in western Nebraska looks like the only solid storm observation day per the GFS - strong southwest flow at the mid and upper levels, a surface low to help back the low level winds, great moisture and instability, and precip shown breaking out across western Nebraska and possibly far northwest Kansas. After that, the GFS agrees with the Euro in retrograding the trough back west - and building a strong ridge over the central US for the extended range. Regardless of the ridge, a vast expanse of deep moisture in place across the majority of the Plains and Midwest will provide almost daily chances of thunderstorms across those regions, indicated by the GFS breaking precip out most every day and night. The downside of thunderstorms in the middle of a strong ridge is that flow aloft is very weak, meaning no deep-layer shear will be present to allow for widespread severe storms. However, the chances for evening/nighttime lightning across the Midwest and Plains could be very good during this period.

Despite the looks of Monday in Nebraska, I'm just not that excited about embarking on an expedition for it. The target as shown will be a considerable distance from St. Louis for a single-day tornado prospect, which in my opinion is just not worth the effort and expense. Again, I'm just not a tornadoes-at-all-costs observer. I'm leaning heavily toward just ending my Plains observing plans for the season, and going into full-time Midwest chase standby mode. June through August is the period when the upper/lower Midwest region (including the states of Missouri, Iowa, Illinois, Indiana and immediate surrounding states) sees a higher probability of supercells and tornadoes. I simply have better feelings about focusing on this region from this point on, with its lower costs, no observer crowds and decent chances of success. Of course, I reserve the right to change my mind should the models be wrong about the upper trough holding back next week!

2010 Storm Expeditions - Probabilities as of May 20
May 20-210%
May 22-2630%
May 27-3130%

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