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The Data Shows Concerning Severe Weather Signals For Part Of The Weekend... A Full Analysis Inside!

The data rolling in regarding Sunday is somewhat concerning. With that said, some of the data shows a low end scenario, while some of the other data is rather concerning. This creates distinct complexity regarding how this setup unfolds on Sunday. In tonight's blog, I have a timeline for the severe storms and the primary threats for our area. Let's start with a refresh of the SPC severe weather risk.


Storm Prediction Center Severe Weather Forecast Sunday


The Storm Prediction Center did not make really any changes to the severe weather risk for our area. We remain in the slight risk, but you can now see they have a large 30% chance of severe weather for our area.


SPC Categorical Severe Weather Risk Sunday

SPC is keeping us in the severe risk on Sunday.


Spc 3 cat


Severe Risk 1

SPC Probabilistic Severe Weather Risk Sunday

Notice the huge 30% chance of severe weather from the Canadian border southward through Tennessee.


Spc 3 prob



Severe Weather Discussion For Sunday


Many of my regulars to the blog know the severe weather ingredients I look for when assessing whether organized severe weather is possible for our area. Here is a quick reminder of the ingredients I look for when evaluating the potential for organized severe weather.


Severe Weather Ingredients



The forcing Sunday is a done deal. It is there and we have no questions. One note, the low continues to look like a negatively tilted low. The negatively tilted low allows the air aloft to spread apart which effectively creates a vacuum aloft that sucks the air upward. Notice the arrows east of the low are spreading apart showing diffluence aloft which effectively creates very intense rising motion.


Nam_500_vort 1



Wind Shear / Energy

The wind energy late Sunday continues to look very strong. Once again tonight, the data suggests the more dangerous directional wind shear will be present on Sunday, but the data also shows slightly weaker winds on the setup. The slightly weaker winds are not notable enough to preclude any severe weather in our area... simply put they are very supportive of severe weather. Remember, directional wind shear occurs when the winds shift direction as you go upward in the atmosphere. Directional wind shear is supportive of rotating storms and must be monitored more closely.


NAM Surface Winds Sunday

Notice the winds at the surface are from the south-southwest at about 15 - 25 mph and those winds will likely gust to 40 mph.

NAM Winds 1 Mile Above The Ground Sunday

Notice the NAM shows winds that are about 10 mph weaker than what was shown at this level yesterday. They are still quite strong though at nearly 60 - 70 mph and they still shift to the southwest. While this is not huge directional wind shear, it still qualifies as directional wind shear.


 GFS Winds 6 Miles Above The Ground Sunday

Notice the winds continue to increase to nearly 90 knot or 100 mph in the mid levels and shift to the west-southwest. This is a very strong mid level jet.


The wind energy is slightly weaker than indicated yesterday, but still incredibly supportive of severe weather. We do see a direction change in the wind as we climb upward in this atmosphere and that is important to note. This is indeed directional wind shear and needs to be watched more closely.




Instability is always the most important part of the equation in transition or cold seasons. More often than not, we have wind energy but no instability. Since instability is the fuel for t-storms, without instability there are no storms. This is an important point to note. Looking at the data, we see very different information from the GFS and NAM tonight. The NAM is much more bullish with the instability while the GFS is a bit flat.


GFS Instability Late Sunday

Notice the GFS shows about 300 - 500 units of instability area-wide on Sunday. The GFS bases this on a temperature of about 64 per the raw gridded data.


Gfs CAPE 1


NAM Instability Late Sunday

Notice the NAM is showing quite a bit more instability with peak values of about 1,200 - 1,500 units in our area. This instability is very concerning. The NAM is basing it's instability on a temperature of 73 per the raw gridded data.





My Thoughts On Severe Weather Sunday


The forcing is intense on Sunday with a powerful low moving moving through. We will also see enhanced lift as the low tilts negatively which causes strong rising motion in the atmosphere. The wind shear is extremely supportive of severe weather. The wind does change direction with height indicating we do have directional wind shear. Remember, directional wind shear supports rotating storms and the potential for tornadoes. From here, we move into instability. If you believe the GFS, then we rain all morning and have very little instability for Sunday. If you believe the NAM, then we have little rain in the morning and warm to about 73. The NAM solution is concerning and would create a considerably larger severe weather threat. At this point, the storm is still entering the US, so the data is not locked yet. I can tell you I believe that we will warm into the lower 70s and I think instability higher than what the GFS states is entirely possible. With that said, 48 hours out still leaves uncertainty and I need another 24 hours to lock. I will say that I am concerned. The primary threat on a setup like this is damaging winds and I do think there is a threat for tornadoes. If we do get the instabiliy values over 1,000 on Sunday then we are going to have problems.


Looking at the data, we see the HIRES data continues to show a broken line of severe storms on Sunday and some even suggests supercells ahead of the line. If those supercells go ahead of the line, then they would have an enhanced tornado potential. The GFS (which is colder) creates a flatter line of storms and a lower severe threat.


GFS Precipitation Late Sunday

Notice the GFS shows a line of less intense storms moving across the area. With that said, the instability it shows is easily enough for this type of line to produce severe weather.




NAM Precipitation Late Sunday

Notice the NAM continues to show a line of severe storms moving across the area. This is definitely more concerning.




HIRES NAM Precipitation Late Sunday

Notice the HIRES NAM shows a very concerning situation. I have placed a dot over Louisville so you can get your bearings on where you are looking. Notice the HIRES NAM shows a line of storms with damaging winds and individual cells ahead of the line with a tornado threat.


NAM Hires 1



The NAM has the ability to tell you if the atmosphere is supportive of rotating storms with a value called "Supercell Index".  Notice it has very high values for our area on Sunday indicating rotating storms are likely. Remember this is hinged on the higher instability values the NAM shows.


Nam supercell index


AdvanceTrak Precipitation Late Sunday

AdvanceTrak seems to indicate a broken line of storms moving across our area on Sunday. That would highlight a damaging wind threat, but the broken parts of the line would have a tornado threat.


AdvanceTrak 1


AdvanceTrak 2


AdvanceTrak 3


AdvanceTrak 4


AdvanceTrak 5


AdvanceTrak 6


I know many are wondering when to expect the storms. Right now all the data suggests late afternoon or early evening on Sunday for our area. Almost all the data shows storms entering our area early evening on Sunday, then in Louisville around 7 pm - 9 pm, then exiting our area by 11 pm.



This is a setup that we must watch very closely. I am not willing to say it will or will not be an outbreak at this point because there are considerably uncertainies with how the rain will develop Saturday night and Sunday morning. I can tell you if we warm to near or over 70 on Sunday, then we have real problems. Damaging winds will be a real problem and tornadoes are possible. I think this has the POTENTIAL to be a problem, so we must watch closely. Please keep checking back with the blog and on TV as we lock in how this will unfold.




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Heading toward Texas Sunday, I'll be in memphis, tn by 12:00 pm. Where wil the storm be then.

I haven't noticed discussions about potental severe weather this early and with this much concern since the storms of March 2012. Any similarities? Thanks.

Kevin, looks close to 10 pm in Memphis.

Doug, none whatsoever. I think that is simply the most recent memory in our area, so many go to that. There is no data that shows anything similar. I mention concern as "potential" right now. I want to be clear, this is not a done deal at all.

What volume of rain can we expect?

Chris, it depends on whether that first wave of morning storms develops. It seems an inch or so is a good bet now.

Marc, still a low CAPE set up like you told me last night? That 70 degree temp seems like the magic # to cross which I would assume would mean sunshine. Folks Mar, 2 was a historical and at best once a decade scenerio(so we hope). I still remember the blog Marc wrote 2 days before than, it was jaw dropping how concerned he was with the data and he nailed it. I mean bullseye. Marc is hands down the Severe Weather expert in this market

This looks like something we all shoud keep a close watch on.

John, first off I appreciate the comments. :)

CAPEs above 700 j/kg would be the critical number I would look for. I think that can be achieved near 70-72 on Sunday. That is entirely reachable without sunshine if the rain ends early enough. 850s are very warm so mixing can make that happen on such a windy day. The key for that scenario to occur is widespread rain ending in the morning.

Marc, noticed the NOAA page has us in the 45% range now. What i find wild for this time of year, it extends way North to areas of the country that are a lot of times dealing with Lake Effect Snow this time of year, Cleveland, Detroit and South Bend. Amazing. Wonder if the 1PM Browns at Bengals game could have issues.

I enjoy your blogs by the way Marc. Thanks for your work. Between you, Rick and Eric WDRB scored big.

Doug, we appreciate!

Appreciate it. :)

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