Tuesday, October 9, 2012

Tornado Outbreak Threat Looms For Midwest and Plains on Saturday

Preword: What follows is STRICTLY my personal opinion and SHOULD NOT be used to make personal decisions regarding your safety. This is ADVICE, NOT TRUTH. **Use the following information at your own discretion.**

I am becoming increasingly concerned with the potential Saturday has to cause a widespread severe damaging wind and tornado threat throughout the Midwest and portions of the Plains. I have been manually tracking certain parameters of the past several GFS model runs, and have found that the model is trending stronger with shearing and moisture in the region, enhancing severe and possibly dangerous weather. Let's get right into it. All charts below are valid for Saturday evening.

At the 500mb level, a strong disturbance is progged to dig into the Plains and Midwest with a negative tilt and winds upwards of 80 knots accompanying the system. A negative tilt means the system has its winds pointed towards the southeast, like is shown above. Systems with a negative tilt possess more severe weather potential than regular systems, and some of the worst weather has come from negatively tilted storm systems.

This model chart is valid for Saturday evening, and is extremely worrisome to me. The presence of such strong upper level winds means that the atmosphere will be charged up and rearing to go. Such mid level winds enhance storm strength, already setting the stage for a dicey evening. But things only go downhill from here.

This is a map of 850mb winds, commonly known to enhance tornado potential and severe thunderstorm strength if they are high. On Saturday evening, the lower level winds look to be absolutely screaming, with winds maxing out at 70 knots, with some spots going into the 80 knot threshold.

It is uncommon to see such strong wind values, and such values are only associated with the stronger types of storm systems, including negatively tilted systems like this one. I worry that the presence of such high winds will only encourage severe thunderstorms to form and drastically increase tornado potential.

The Storm Prediction Center has already set up a 'Day 5' risk area for much of the Midwest and eastern Plains, indicating that confidence is relatively high that some form of severe weather will occur. An examination of the discussion issued by the SPC on this matter shows that the concerns are severe winds and tornadoes. The threat does indeed exist, as we saw in the 850mb chart above.

This is a map of surface-850mb wind shear. Wind shear is, in simple terms, wind going in different directions at different strengths. The more wind shear there is, the higher the chance of some tornadic activity. One glance at the shearing chart above, and we can already define that the Midwest may be in for a rough night, with high shearing combined with strong lower level winds to give a potentially blockbuster show for the region.

I believe that the Midwest will get the worst of this event, but a fairly large area, including part of the Plains, is at risk for a tornado outbreak. THE RISK GETS HIGHER CLOSER TO THE CENTER OF THE CIRCLE. Places like northwest Illinois, Iowa and northern Missouri may face some serious trouble on Saturday night.

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Aran Jacobs said...

Valpo is on the orange/yellow line.What does that mean?

Aran Jacobs said...
This comment has been removed by the author.
Eric said...

Do you think that prior thunderstorm convection could limit some of the instability in the region?

Anonymous said...

ICT is taking this alittle more seriously. Still uncertainty though hinting the worst to be E of I35. I will be in Arkansas City, KS in the noon hours when this begins. I'll see later what's around my neighborhood.

Seems the worst will be in the MO river valley. OK had a fall tornado outbreak last year which had an EF4. Can't say about this one even though populated areas are highlighted.

I'm excited but concerned since populated areas are highlighted.