A lot of rain has affected our Memorial Day holiday and it looks like you will be greeted with more storms as you head back to work tomorrow. The story for Tuesday will be the severe risk issued by the Storm Prediction Center and in tonight's blog, I will give you a timeline for the storms and analyze the risk
Storm Prediction Center Severe Weather Risk For Tuesday
The Storm Prediction Center (SPC) for two days has had our area in the slight risk for severe weather. They have made some brief adjustments to the risk, but it still does include the Louisville metro area. Here is the latest.
SPC Categorical Risk Of Severe Weather Tuesday
Notice all but our extreme western counties are in the severe risk for Tuesday.
SPC Probabilistic Risk Of Severe Weather Tuesday
Notice SPC has a 15% of severe weather for slight risk area with a 5% chance for our far western counties.
My Thoughts On Our Severe Weather Risk On Tuesday
To get organized severe weather, we traditionally need specific ingredients present. Since we haven't discussed severe weather in little while, I want to refresh you quickly on the ingredients I look for when assessing whether a severe weather event could occur.
The forcing Tuesday will come from a low bringing severe weather over Texas right now. That storm will arrive here early to mid afternoon on Tuesday. It is not terribly strong, so it won't have the ability to overpower other weaknesses in the severe weather fields.
The atmosphere has general rules it must meet to be able to support organized severe weather and wind energy is a distinct part of that equation. For the atmosphere to support organized severe weather, we traditionally need 35 knots / 40 mph winds somewhere from the surface to 6 miles above the surface. Without that wind, the storms will be pulse type and never develop a long lived core necessary to produce organized severe weather. On Tuesday, they barely (and I mean barely) meet severe thresholds. As we look at the sounding, notice the wind energy (in knots) on the right side of the graph
Atmosphere Sounding Tuesday
Notice the wind energy is not strong, but one could argue it barely meets criteria to support organized severe weather.
The wind energy is not strong in any way, shape, or form, but it still does barely meet our minimum to support organized severe weather.
The instability is going to be complicated. While I know some are telling you that moderate instability is a lock on Tuesday, the computer model data would argue that is not the case. The NAM, which is the more reliable convective (t-storm) computer model, shows only about 750 units of instability on Tuesday. 750 units of instability is weak at best.
The GFS is showing more instability, but it also doesn't generate the storms until later in the day.
So which model do we believe? The NAM will deal with the speed of the severe storms in Texas better and results in rain breaking out much earlier in the day. The GFS computer model simply doesn't have the skill with small scale meteorology to deal with those storms and therefore it's instability is highly unreliable in my opinion.
My Thoughts On Severe Weather Chances Tuesday
I feel like Tuesday is being sold a bit as something it is not. The data shows wind energy that barely meets criteria for organized severe weather, but I do want to be clear it is enough. The forcing is decent and should arrive early afternoon bringing a lot of clouds and storms. Since these storms arrive early, it means the atmosphere will never have the chance to heat up limiting instability to the weak category in my opinion. A lot of "marginal ingredients" normally does not equate to large organized severe weather threats. I think there is a lot of evidence to say this won't be anything close to a severe weather event.
AdvanceTrak shows the storms generating early in the day limiting the heating and never generates a second line for our area. It shows a limited severe weather threat.
The bottom line is I cannot rule out a couple of severe storms on Tuesday. The storms should pop early afternoon and continue through early evening. Hail and damaging winds would be the primary threat. At the same time, I do not see any evidence of a larger scale severe weather event.
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