My Analysis Of Our Severe Weather Threat On Sunday!
The Storm Prediction Center has upgraded our area into a slight risk of severe weather for Sunday. In this blog, I am going to analyze this threat and give you a timeline on when to expect potentially strong storms. Let me start by refreshing you on the severe weather threat.
Storm Prediction Center Severe Weather Threat Sunday
I was kind of surprised SPC did not have our area in a slight risk during their outlooks they posted yesterday. I felt our area needed to be in the slight risk and today they made the adjustment.
SPC Categorical Severe Weather Risk On Sunday
Notice SPC has placed our entire area in the slight risk of severe weather on Sunday.
SPC Probabilistic Severe Weather Risk On Sunday
Notice SPC has our entire area in the 15% chance of severe weather.
Sunday Severe Weather Discussion
As we get ready to start our discussion about the severe weather threat on Sunday, let me remind you of the severe weather ingredients necessary for organized severe weather threats.
The forcing for Sunday's storms will be a front moving across our area with a distinct upper level low moving almost direction overhead. Notice the mid level low as of 5 pm Sunday.
Wind Energy / Shear
Yesterday I told you this system had "speed shear" and quite a bit of that kind of wind shear. Speed shear is much more supportive of damaging winds, but can occasionally produce an isolated tornado. Speed shear is defined as winds that increase in speed as you go higher in the atmosphere, but those winds do not change direction. Let's look at the data again today and see if that speed shear is still present in the data. We will start at the ground and move up.
NAM Surface Winds at 5 PM Sunday
Notice the winds are out of the southwest at about 10 - 20 mph. It will be a breezy day.
NAM Winds 1 Mile Above The Ground at 5 PM Sunday
Notice the winds once again are out of the southwestat this height. These winds are near 40 - 45 knots or 45 - 52 mph. These are actually very strong winds at this height.
NAM Winds 6 Miles Above The Ground at 5 PM Sunday
Notice the winds once again are out of the southwest at this height. The NAM also shows an impressive mid level jet of around 60 - 65 knots or 68 - 73 mph.
The instability on Sunday will be the most difficult part to diagnose. The NAM is showing more instability than the GFS as is always the case. In this situation I am more inclined to believe the NAM forecast. It shows instability values peaking near 1000 units by 5 pm Sunday. Notice the slightly higher instability values south of the river.
My Thoughts On Our Severe Weather Potential On Sunday
We talked extensively over the last few days how the storm would likely be slower than what the computer models said. Wednesday the data suggested storms near 7 AM Sunday, then yesterday they showed the storms in our area by 2 PM, and now they move the storms in during the warmest part of the day. Finally, I think they are correct since the US network of upper level data has been able to sample this storm. At this point, it looks like the storms would be in the western part of our area mid afternoon, I-65 during the late afternoon, and finally in the eastern part of our area during the evening. Notice the NAM shows the line near Louisville by 5 PM on Sunday.
The wind energy these storms will interact with is very supportive of severe weather. The forcing is unquestionable with a front and disturbance moving across our area late Sunday. The instability is weak, but I think enough to support severe storms considering how strong the winds are just 1 mile above the ground. Right now it appears damaging winds are the primary threat, but I cannot rule out a rogue / isolated quick tornado.
At this point, thesetup doesn't look like a major severe weather event because of the lower instability. Low instability with a lot of wind energy many times creates a setup where the storms cannot penetrate deep into the atmosphere because the strong winds just blow over the storms. If we do get a lot of sunshine on Sunday (seems unlikely right now, then the threat would be a bit larger and that is something I will be watching over the next couple of day.
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