Severe Risk For Tuesday ... My Thoughts Inside!
The Storm Prediction Center has a slight risk for part of our area on Tuesday and I wanted to discuss this. We will talk about the area they have in their risk and my thoughts on the risk in this blog. Let's dive in.
SPC Severe Weather Risk For Tuesday
The Storm Prediction Center placed the northeast sliver of our area in a slight risk for Tuesday. Here is the location they are watching.
SPC Categorical Risk Of Severe Weather On Tuesday
Notice only a small fraction of our northeast counties are included in this slight risk.
SPC Probabilistic Severe Weather Risk Tuesday
Notice SPC has a 15% chance of severe weather over their slight risk area with a 5% chance to around Louisville.
Severe Weather Discussion
As we dive into the severe weather discussion for Tuesday, let me start by reminding you of the severe weather ingredients I look for when analyzing a severe weather threat.
This is kind of a unique discussion today because the forcing is not strong, not good, and actually fairly weak. The lift will have to come from the "left exit" of a jetstream in the mid levels moving up from the south. While jet lift can be significant at times, this is no 130 knot jetstream so forcing doesn't look good at all.
Wind Energy / Shear
This is the area that Tuesday is very rich. Not only is the wind energy supportive of severe weather, but it contains some "directional" wind shear over northern KY and OH. Remember that directional wind shear is the type that support rotating storms and sometimes tornadoes. There is a value called "helicity" that can help us to identify the areas where rotating storms are possible.
Helicity Values at 5 PM Tuesday
Notice the wind energy is most supportive of rotating storms over Ohio and extreme northern KY.
Rather than going through each level, we will accept that there is no question that the wind is supportive of severe weather on Tuesday. This is directional shear and it does support rotating storms.
The instability tomorrow simply put is not strong at all. There is a very, very narrow window where there could be some small instability in our area. Notice tiny surface based instability values near 750 units in the northeast part of our area around 2 pm on Tuesday.
My Thoughts On Tuesday's Severe Weather Threat
First off, Tuesday is a very difficult forecast. The complexities come from the narrow window of instability, the marginal forcing from a mid level jet, and highly supportive wind energy. In these situations where forcing is very weak, there is no guarantee you will get storms and if they do form they can be very weak. The profile of the atmosphere seems to suggest the storms won't be able to penetrate deep into the atmosphere. Looking at AdvanceTrak and the HIRES NAM at 2 PM show very shallow showers that may not even classify as t-storms.
NAM Precip at 2 PM
Notice the small area of rain/t-storms mainly over northern KY.
NAM Precip at 5 PM
Notice the small area of rain/t-storms has now moved over Ohio by this time.
The location SPC is identifying clearly near an exact copy of the "helicity" values on Tuesday. They are placing the slight risk right over the area where the rotational wind energy is located. With that said, it is clear that Ohio has the best threat of isolated tornadoes and our northeast counties are truly on the extreme fringe of this area. I cannot fault the SPC location and to be honest, I would probably place the slight over the exact same area. Our counties don't have quite the same instability as Ohio and the rotation energy is lower, so to me damaging winds would be the main threat for the extreme northeast part of our area. I think it is something we need to watch, but I don't see a tornado outbreak from this setup in our area.
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