Sunday, May 26, 2013

Multi-Day Severe Weather Outbreak Possible

I believe a multi-day severe weather outbreak is possible (if not likely) across the Plains and Midwest over the next 7 days.

The pattern really is primed for such a multi-day event. It begins with an unusually active upper air flow. The image above shows the projected upper air field for five days out. We see an unusually strong Pacific jet screaming into the West Coat above 130 knots at some points. This active Pacific jet will lead to a more active pattern in general for the United States, and will enhance potentials for severe weather.

As the Pacific jet stream amplifies, we will see a more meridional flow set up. If you don't recall, meridional flow is when the jet stream is very wavy and not in a straight line. We are expecting that type of upper air flow in the coming week. As this happens, a general low pressure trend in the West Coast should set up, leading to massive high pressure formation in the Central and East US. This type of synoptic set-up would not be all that different from the pattern that was present for the Moore, OK tornado event. Now, we can't predict if we will see EF-5 tornadoes, because it is practically impossible to predict tornadoes at any given time, unless you're predicting them as they happen.

For this particular multi-day event this week (the days themselves remain uncertain), multiple low pressure systems will be making their way onshore from the active Pacific storm train. A major difference we expect to see between the Oklahoma tornadoes and this upcoming week's potential is that the storms should be further north. I anticipate the Central and Northern Plains to get in on the action more-so than the Southern Plains.

One thing that is very concerning is what the CIPS analog system is putting out. This map combines storm reports from 15 of the best analog dates (dates that have similar atmospheric features as a forecast period (in this case, 5 days away)) into one image. Looking at this image, it is apparent that this potential outbreak would most likely affect states from Minnesota into Oklahoma, but with eastern Nebraska into western Iowa and western Missouri into much of Kansas receiving the highest threat. Note that many of the tornado reports you see in red on the image above included F5 and F4 tornadoes, as this post from AmericanWx shows.

I don't really want to make a map for this week's potential, because I find it to be entering this post with a little too much uncertainty. However,


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