Another Severe Threat Posted For Wednesday! My Analysis Of The Threat Including When & Main Threats...
We had our first severe weather threat today with virtually all of the severe weather occurring to our west. The Storm Prediction Center has another slight risk of severe weather for Wednesday, so I want to share my analysis of that threat in tonight's blog...
Storm Prediction Center Severe Weather Risk For Wednesday
In their early afternoon update, SPC upgraded a chunk of our area into a slight risk of severe weather for Wednesday. This takes us from the general t-storm risk to a low end severe threat for Wednesday. Let me show you the location of the risk and severe weather probabilities.
SPC Categorical Risk Of Severe Weather Wednesday
Notice SPC has almost all of our area in a slight risk of severe weather for Wednesday. A few of our eastern and northeastern counties are not included, but most are included.
SPC Probabilistic Risk Of Severe Weather Wednesday
Notice SPC has a 15% chance of severe weather for the slight risk area and a 5% chance for the rest of our area.
A Discussion Of The Severe Weather Risk On Wednesday
I always like to start severe weather discussions with a refresher on the ingredients I look for when trying to determine if severe weather is possible. We need all three of these ingredients in abundance for severe weather events.
Wind Energy / Instability
Like today, the instability on Wednesday will be absolutely through the roof. This assures us of fuel for t-storms, but that is almost always the case in the summer. The problem in summer tends to be wind energy coinciding with actual storms. To simplify this blog a bit, I will show you wind and instability on the same graphic. To assess wind energy, we are going to look at a value called bulk shear, which is a measure of the wind energy from the surface to about 6 miles above the ground. Traditionally, we need a minimum bulk shear value of 35 knots / 40 mph to support organized severe weather and you can see we just make it barely again on Wednesday. Conversely, the instability is nearly 4,000 units for part of the area which is borderline extreme instability.
With favorable instability and somewhat favorable wind energy, this again comes down to whether there is forcing to fire storms in the heat of the afternoon on Wednesday. Like today, the data shows a disturbance, but it is very weak and likely comes through after peak heating on Wednesday. The problem is that the very warm mid level air acts as a cap / lid on the atmosphere and can limit storm development in the absense of a strong disturbance, so this weak disturbance becomes the key.
My Thoughts On Severe Weather Chances Wednesday
Once again, the data for Wednesday shows strong to borderline extreme instability in our area. This is easily supportive of severe weather. While the wind energy is not what I would call strong, it is still sufficient to support organized severe weather. The weak forcing becomes the big question mark yet again on Wednesday. With such weak rising motion from this disturbance combined with the fact that it won't likely come through until late means the severe threat is not high. The high resolution data and AdvanceTrak show the storms don't arrive for our area until late Wednesday night and they quite frankly struggle. As you look, notice the timestamp is on the top right part of each image.
With the mid level temperatures warming like crazy right now, we have a barrier to storms referred to as a cap/lid. It does appear that the cap will hold during the afternoon on Wednesday keeping storms from forming in the most unstable air. The disturbance arrives Wednesday night and that appears to be the best chance for storms. Since the storms seem unlikely in peak heating, this does limit the severe potential. SPC has gone with a low end slight risk at 15% and I cannot argue that low end threat. Damaging winds and hail would be the primary threats, but again it doesn't look like a widespread threat.
As always, I will be watching...
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