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Long-term Plains shutdown ahead
The next dominant upper feature advertised by models to develop in the coming week is a deep and unseasonably cold cutoff low over the central US. This is shown stalling over the Plains and Midwest for an extended period of time as part of a 'blocking' pattern that could shut down storm observing prospects for the first half of May.
This cutoff low will evolve from an incoming western upper trough that may bring a marginal severe weather day or two to the Great Plains region as it moves in. However, currently these setups are in question due to 1.) the upper support coming in too far north away from the deep low-level moisture, and 2.) yet another cold frontal surge that will favor linear, undercut storms.
A "cold core" tornado setup or two may present itself in the Midwest region as the cutoff low becomes established, but this is highly conditional on cloud cover issues. Such "stacked" cutoff lows are notorious for being rainy, cool and cloudy messes for days on end. For this reason, once the cutoff low settles in and becomes fully stacked (the surface and upper low pressure being in the same position), the prospects for severe weather will be very minimal as cool, stable conditions become firmly entrenched and deep moisture is shunted well south and east of the Plains and Midwest.
I am not at all excited about the upcoming system, and any Plains storm observing expeditions look solidly out of the question for at least the next 2 weeks. Although we can't really speculate much beyond 10-14 days, the pattern shown by models in the long term is not one that looks to break down any time soon. It is possible that the Plains/Midwest severe weather season may not return until well into the second half of May.
This, of course, is nothing to worry too much about in terms of the overall season. This pattern should be completely gone by the second half of May, and what will replace it has an equal chance of being good or bad for severe storms and tornadoes. All we can do is wait and see.
The following table charts the probability of a Great Plains storm observing expedition for the indicated date ranges:
|2013 Plains Storm Expeditions - Probabilities as of April 28|
|April 28-May 4||1%|