Composite maps of significant Indiana tornado outbreaks

[Hoosier]

I was curious to see what type of large scale pattern was in place during some of the state's more significant tornado outbreaks, so I made some surface, 850 mb and 500 mb composites. I chose an arbitrary number of at least 10 tornadoes. In the last 50 years, Indiana has experienced 12 outbreaks with at least 10 tornadoes. They are:

3/6/61

4/11/65

6/26/73

4/3/74

3/12/76

6/2/90

11/22/92

4/19-4/20/96

6/11/98

4/20/04

5/30/04

10/26/10

Most of the times that make up these composites are from 18z but a few are different to better reflect the start time of those particular outbreaks.

Surface:

500 mb:

850 mb:

No real surprises here. There is a surface low located west or northwest of the area. The 500 mb map has Indiana on the eastern side of the trough with the lowest heights in the northern Plains. The 850 mb map reveals a strong low level jet pointed up the Ohio Valley which is a key component in creating sufficient shear.

Now, would it be wise to dismiss a setup that doesn't resemble this? Not necessarily. But large scale setups that do resemble this should warrant extra scrutiny.

[Hoosier]

Of the dates above, 3 of them had at least 20 tornadoes. They are:

4/3/74

6/2/90

5/30/04

Let's take a look at just these 3:

Surface:

500 mb:

850 mb:

As you can see, they look pretty similar to the larger composite.

[Reed Stough]

Thanks for posting that. I use to live in Indiana and I remember the 1974 Super Outbreak.

[KokomoWX]

Really good stuff.

[Thundersnow12]

I'd be curious as to what was the cause for each day, cold front, warm front, OFB, etc.

very nice job, Hoosier.

[Hoosier]

I'd be curious as to what was the cause for each day, cold front, warm front, OFB, etc.

very nice job, Hoosier.

Well, I'm gonna guess that you know enough about the really high profile events like Palm Sunday and the Super Outbreak. There are a few that I'm not really familiar with but I can try to help with some of them.

The warm front was way north on 3/12/76 so I'm guessing that was more of a cold frontal event. Same thing with 6/2/90. 11/22/92 is sort of an oddball on this list as that occurred with with a cutoff low ejecting northeastward from the southern Plains (sfc/500 mb features were displaced farther east than the composite map). You probably know about 96 and 4/20/04. 5/30/04 had a huge warm sector and was part of a massive severe weather outbreak...a lot of cells went up in the free warm sector with another round on the cold front that evening. 10/26/10 was the Octobomb of course.

[Indystorm]

Thanks for the research. Useful reference to keep in mind. Classic outbreaks seem to have a predictable pattern at the levels you highlight. The difficulty comes when serious events occur when some parameter initially seems to be missing or not adequately modeled and the event surprises us.

[Fred Gossage]

Hoosier, divide them by upper-level trough tilt and see what you come up with. I'd like to see a direct comparison of your area's events to mine in that respect....

[NIU Jeff]

I'd be curious as to what was the cause for each day, cold front, warm front, OFB, etc.

very nice job, Hoosier.

10/26/10 was more of a cold front initiation, with a linear storm cell formation. Likely with either some embedded/discrete supercells, or with spin-ups (gustnados on a gust front). Although, because occlusion had occurred, these storms were also very close to the leftover warm front. And in that case, that probably correlated with the best available wind shear.

The others will take some more research.

Great information, Hoosier.

[beavis1729]

10/26/10 was more of a cold front initiation, with a linear storm cell formation. Likely with either some embedded/discrete supercells, or with spin-ups (gustnados on a gust front). Although, because occlusion had occurred, these storms were also very close to the leftover warm front. And in that case, that probably correlated with the best available wind shear.

The others will take some more research.

Great information, Hoosier.

NIU Jeff - welcome to the board.

I graduated there with a met degree in 1995...great school!

[Hoosier]

Fred, I'm not ignoring you just so you know. I'll post more tomorrow.

[Thundersnow12]

10/26/10 was more of a cold front initiation, with a linear storm cell formation. Likely with either some embedded/discrete supercells, or with spin-ups (gustnados on a gust front). Although, because occlusion had occurred, these storms were also very close to the leftover warm front. And in that case, that probably correlated with the best available wind shear.

The others will take some more research.

Great information, Hoosier.

I know about this one..it was the older ones I was curious about.

[Hoosier]

By request, here are the tornado outbreaks by upper level trough tilt.

3/6/61: negative

4/11/65: positive

6/26/73: neutral

4/3/74: ??? (more on this below)

3/12/76: neutral

6/2/90: negative

11/22/92: negative

4/19-20/96: positive

6/11/98: positive

4/20/04: negative

5/30/04: negative

10/26/10: negative

That makes 6 negatives, 3 positives and 2 neutrals. The reason I didn't list anything for 4/3/74 is because I wasn't sure how to classify it. There was a rogue early morning tornado but the vast majority of the activity held off until later in the day. Also, as Fred noted in this thread, the upper level trough evolved throughout the day.

This shows that any type of trough tilt can produce a substantial tornado outbreak, but for the larger outbreaks, negatively tilted troughs are favored from a historical perspective, at least in Indiana.

[IWXwx]

By request, here are the tornado outbreaks by upper level trough tilt.

3/6/61: negative

4/11/65: positive

6/26/73: neutral

4/3/74: ??? (more on this below)

3/12/76: neutral

6/2/90: negative

11/22/92: negative

4/19-20/96: positive

6/11/98: positive

4/20/04: negative

5/30/04: negative

10/26/10: negative

That makes 6 negatives, 3 positives and 2 neutrals. The reason I didn't list anything for 4/3/74 is because I wasn't sure how to classify it. There was a rogue early morning tornado but the vast majority of the activity held off until later in the day. Also, as Fred noted in this thread, the upper level trough evolved throughout the day.

This shows that any type of trough tilt can produce a substantial tornado outbreak, but for the larger outbreaks, negatively tilted troughs are favored from a historical perspective, at least in Indiana.

Do you think that neg tilt troughs have a propensity to develop severe systems in this area due to creating more shear? I don't have data to back it up, but it seems that high shear/low instability scenarios tend to perform well here. Hope this isn't a silly question. Just trying to learn. Any help in directing me to environmental conditions creating tornado outbreaks for the Midwest would be appreciated.

[janetjanet998]

By request, here are the tornado outbreaks by upper level trough tilt.

3/6/61: negative

4/11/65: positive

6/26/73: neutral

4/3/74: ??? (more on this below)

3/12/76: neutral

6/2/90: negative

11/22/92: negative

4/19-20/96: positive

6/11/98: positive

4/20/04: negative

5/30/04: negative

10/26/10: negative

That makes 6 negatives, 3 positives and 2 neutrals. The reason I didn't list anything for 4/3/74 is because I wasn't sure how to classify it. There was a rogue early morning tornado but the vast majority of the activity held off until later in the day. Also, as Fred noted in this thread, the upper level trough evolved throughout the day.

This shows that any type of trough tilt can produce a substantial tornado outbreak, but for the larger outbreaks, negatively tilted troughs are favored from a historical perspective, at least in Indiana.

if all three types occured equally then this might work as a better stat but what percentages of totals systems are pos, net, or neg?(no way to tell really) if 2 major outbreaks occured when the systerm was neutral at the time in Indiana but a neutral system was only 20% of the the total systems then it would be the same as 4 major outbreaks occuring with a negative trough if a negative trough was present 40% of the time....or something

[Hoosier]

if all three types occured equally then this might work as a better stat but what percentages of totals systems are pos, net, or neg?(no way to tell really) if 2 major outbreaks occured when the systerm was neutral at the time in Indiana but a neutral system was only 20% of the the total systems then it would be the same as 4 major outbreaks occuring with a negative trough if a negative trough was present 40% of the time....or something

I had to read that a couple times but I see what you're saying. I don't know what percentage of all systems are positive/negative/neutral and it would be difficult if not impossible to figure that out.

[Hoosier]

Do you think that neg tilt troughs have a propensity to develop severe systems in this area due to creating more shear? I don't have data to back it up, but it seems that high shear/low instability scenarios tend to perform well here. Hope this isn't a silly question. Just trying to learn. Any help in directing me to environmental conditions creating tornado outbreaks for the Midwest would be appreciated.

You can get good vertical shear with any type of trough setup, but negative tilt troughs tend to have more forcing and greater storm coverage. Too much forcing and things will tend to go linear, but if you have a highly sheared environment, you can still get tornadoes. Several years ago there was a study that suggested that nearly 50% of Indiana's tornado days come from QLCS's...in other words, they might not be pretty but they still count.

I might do more with this when I have time, like examining the violent tornado days.

[Thundersnow12]

You can get good vertical shear with any type of trough setup, but negative tilt troughs tend to have more forcing and greater storm coverage. Too much forcing and things will tend to go linear, but if you have a highly sheared environment, you can still get tornadoes. Several years ago there was a study that suggested that nearly 50% of Indiana's tornado days come from QLCS's...in other words, they might not be pretty but they still count.

I might do more with this when I have time, like examining the violent tornado days.

first thing that comes to mind when I think of that is the Evansville night tornado which was a QLCS.

[Hoosier]

Since 1950, Indiana has had 12 days with at least 1 violent tornado (F4/F5). Only 3 out of 12 occurred with a negatively tilted trough with most others occurring with a positively tilted trough.

Now, if I use the criteria that Fred used in his thread...

1.) At least one instance of F5/EF5 damage occuring during a tornado event.

2.) At least two instances of F4/EF4 damage occuring during a tornado event.

3.) At least one occurence of F4/EF4 damage, accompanied by at least three F3/EF3 tornadoes.

...there are only 4 days since 1950 (3/12/76 is arguable but omitted) and they are:

4/11/65: positive

4/3/74: evolved from negative to positive

6/2/90: negative

11/22/92: negative

April is a hot month with 5 out of the 12 violent tornado days occurring during that month. The median occurrence for a violent tornado is day #115 or April 25. Indeed, 2 violent tornadoes happened on or near this date, those being 4/25/61 and 4/26/94. Also, over half of the dates (7 out of 12) fall within the 60 day window of April 3 to June 2.

[radionicist]

I really enjoyed reading this thread, Hoosier - I learned a great deal. Thanks for posting it!

Tony

[OceanStWx]

Good stuff Hoosier, I love doing this kind of analysis.

Another thing that might shed some light onto Indiana outbreaks might be anomalies along with the means. For instance, mean 500 heights change with the time of year, but they may all be lower than normal by the same amount.

[KokomoWX]

Some is presenting this at the advanced spotter training.

[Hoosier]

Some is presenting this at the advanced spotter training.

No kiddin? I've hit the big time.

[KokomoWX]

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[KokomoWX]

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[Hoosier]

Looks like they have some different dates on there. It doesn't really change the overall look though.

[KokomoWX]

Looks like they have some different dates on there. It doesn't really change the overall look though.

The presentations will be online in a few days. I'll link to it when available.

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[Chinook]

It looks like those big pictures are depicting something from April 11 1965. Back then, my mom and dad were 15 and they didn't know each other. They lived in cities maybe 60 miles away from each other. A tornado tracked over 100 miles and almost hit both of them!