About Illinois' Tornado Risk (Chicago, Peoria: houses, neighborhood, calculated)

[SJaye]

Recently, in some other threads in the Illinois forum, the subject of tornadoes and Illinois' tornado risk has come up. As someone who has studied weather and severe weather, I am starting this thread as an offer to answer anyone's questions about tornadoes in Illinois, including where and why they happen, and what the risk is. As many of you know, although when most people think of tornadoes, they think of Texas, Oklahoma, Kansas, and Nebraska first, tornadoes are not all that uncommon in Illinois.

[rockfordsucksbigtime]

Originally Posted by SJaye

Recently, in some other threads in the Illinois forum, the subject of tornadoes and Illinois' tornado risk has come up. As someone who has studied weather and severe weather, I am starting this thread as an offer to answer anyone's questions about tornadoes in Illinois, including where and why they happen, and what the risk is. As many of you know, although when most people think of tornadoes, they think of Texas, Oklahoma, Kansas, and Nebraska first, tornadoes are not all that uncommon in Illinois.

yes we know they pick houses up and shoots them into magical kingdoms to where girls have to click their heels 3 times to get home lol...

all joking aside i know what a tornado can mildly do i was in one on the big 4th of july storm a few years back tore through my neighborhood

[linicx]

A lot of Illinois land is in crops and the land land is generally flat and open for miles. There are isolated ares with groves of trees, but few forested areas in the fields. There are creeks, streams, rivers and small lakes scattered throughout, plus three large deep channel rivers, that support the barges that carry our goods, form two IL borders and divide the state.

The largest communities are Peoria. Springfield and Bloomington-Normal, of which Peoria has the largest MSA. According to NOAA records in a roughly 60 year span, Peoria County had 21 tornadoes, Sangamon County had 68 tornadoes, and McLean County had 97 tornadoes during the same time.

Springfield and B-N are surrounded by open corn fields. The common denominator is i-55 that runs NNW for approximately 60 miles between the two counties. The City of Peoria faces the widest part of the Illinois River, at Peoria Lake where it is one mile wide. Additionally, Peoria is cursed with an abundance of steep hills(9), high tree covered bluffs and forested area on both sides of the river. plus nine more steep hills across the river. .

The areas most affected by tornadic activity in Peoria County seems to be NW of Peoria between Brimfield and Galesburg in Knox County . The common denominator appears to be US 150 which passes through a large area of corn fields, scattered villages and small towns located near the route of US 150.

Will topography or the overall size of a community deter the path of a tornado?

Why do tornaodoes tend to spawn in open fields?

Does the time of day a tornado strikes have significant meaning? .

How does weather cause a tornado to spawn?

How fast do tornadoes move?. The F-5 that hit OKC was 2100 feet wide and had a 40 mile path. Obviously it did a tremendous amount of damage. How long did it last and why was it so unusual?

How is tornado speed calculated?

Why are straight-line winds just as, or more dangerous than a tornado?

[Steve-o]

Im no tornado expert, but Ill try and answer these.

Originally Posted by linicx

Will topography or the overall size of a community deter the path of a tornado?

No. Tornadoes strike wherever and whenever conditions are right. They tear through fields, trailer parks, small towns, etc. They even struck in downtown Salt Lake City, UT, many years ago. Remember that one?

Originally Posted by linicx

Why do tornaodoes tend to spawn in open fields?

Well, the parts of the country where they mostly occur (called "Tornado Alley") are sparsely populated and are consisted of mostly farmland/ranches/etc. States like TX, OK, KS, IA, SD, etc, are mostly fields and lie squarely in Tornado Alley. But, as shown above, tornadoes strike wherever conditions are right. Atlanta, Amarillo, Salt Lake City, Chicagoland, and even Phoenix have had tornadoes, but on far less occasions as Tornado Alley.

Originally Posted by linicx

Does the time of day a tornado strikes have significant meaning?

.

Id say yes. Nighttime when most are home and sleeping is the most dangerous time. Not only are most sleeping and miss hearing the tornado sirens (if applicable), but spotters on the ground have the darndest time spotting them in the pitch black skies. Its scary.

Originally Posted by linicx

How does weather cause a tornado to spawn?

Long story short... warm air front meets cold air front, they collide, spin horizontally until the speeds are high enough to cause the air to move vertically and VOILA! Tornado is spawned and it begins its descent towards the ground and the ensuing destruction.

Originally Posted by linicx

How fast do tornadoes move?. The F-5 that hit OKC was 2100 feet wide and had a 40 mile path. Obviously it did a tremendous amount of damage. How long did it last and why was it so unusual?

Some are slow and short lived, others are fast (upwards of 60 mph) and long lived. Depends on the weather conditions.

Originally Posted by linicx

How is tornado speed calculated?

Not exactly sure, but should be easily measured via satellite, Dopplar, GPS, etc.

Originally Posted by linicx

Why are straight-line winds just as, or more dangerous than a tornado?

No idea. lol

[linicx]

It appears that straight-line winds and tornadoes are similar in damage and wind force. The difference is straight-line winds travel in a more or less straight path while tornadoes rotate.

Straight-Line Winds - Madison Weather News Story - WISC Madison

[mdand3boys]

If you remember the Ft. Worth tornado that struck the downtown area; it actually twisted the Bank One building (before Bank One was sold out to JP Morgan). No straight line wind has done that to a skyscraper. I was there the next day as part of the bank's disaster recovery efforts; and stayed for several weeks.

[doll lady]

Living in a rural area we get lots and lots of straightline winds. Usually at least 3 to 4 times in the season, straightline winds knock over a string of power line poles.....usually at least 10 to 15 at a time. These major poles have always been on a north/south highway so that means the highway is closed too since the downed poles are across the highway. This also means our village is without power until the power company can reset poles.

I'm scared to death of tornadoes....been through some....and it's horrifying.

[SJaye]

I'll take a stab at this since I started the thread.

Originally Posted by linicx

Will topography or the overall size of a community deter the path of a tornado?

Topography. yes, in a fairly complicated manner. The Rocky Mountains actually provide a source of dry air aloft which is crucial to development of tornadic storms. This is part of the reason that tornado alley is so tornadic. It is also the reason that although it has been pointed out that tornadoes have his Utah, Arizona, etc. they are quite rare there. Topography on the scale of Peoria's Illinois River Valley will not affect the development or path of a tornado.

Size of a community will not affect the path or development of a tornado, but may show up in tornado statistics. This is because prior to the invention of doppler radar, many tornadoes occured that simply did not get observed, by anyone, and therefore are not in the record. This causes the official tornado data set to have a bias toward populated areas, but Scientifically they do not prefer any level of population density.

Originally Posted by linicx

Why do tornaodoes tend to spawn in open fields?

Steve-O's answer to this one pretty much covers it, there are a lot of open fields in the Great Plains. Tornadoes do occur in woodland areas in the Southeast, and are quite dangerous there.

Originally Posted by linicx

Does the time of day a tornado strikes have significant meaning? .

For the number of casualties, yes, if it is dark out, they are more likely to kill people than tornadoes that occur when it is light out. States like Tennessee, Alabama and Georgia are more likely to have tornaodes at night because their peak tornado season is actually March-April, when there is less daylight than the May-June peaks further north and west.

As far as mythological/ metaphysical meaning behind time of day, you would have to consult someone else.

Originally Posted by linicx

How does weather cause a tornado to spawn?

First, there is a large scale, or synoptic (same root word as synopsis) storm system. These are the fronts that you see on a weather forecast on the evening news with the Ls and Hs on the map. This storm system, if the conditions are right will produce thunderstorms on a smaller, meso-scale (meso being the same root word as mesonene, meaning middle sized). These storms, if the condiditions are right, will produce a tornado, which is a microscale event. I can explain the condiditions in more detail if you want, this is the shortest summary I can possibly type.

Originally Posted by linicx

How fast do tornadoes move?.

Anywhere from nearly stationary (those storms do not last too long) to 60 miles per hour

Originally Posted by linicx

The F-5 that hit OKC was 2100 feet wide and had a 40 mile path. Obviously it did a tremendous amount of damage. How long did it last and why was it so unusual?

This tornado lasted several hours. The vast majority of tornadoes actually last a mere couple of minutes. The longest lasting tornado ever was March 18,1925's Tri-State tornado, which was the only tornado ever to track across three staes, forming in Missouri and dissipating in Indiana.

Originally Posted by linicx

How is tornado speed calculated?

Usually wind speeds are estimated based on surveys of damage after the event. In the event that there is a specific experiment going on, like VORTEX2 which is occuring right now, there will be insturments taking mesaurements.

Originally Posted by linicx

Why are straight-line winds just as, or more dangerous than a tornado?

On an indvidual basis, I'd say a tornado is more dangerous than striaght line winds, but straight line wind storms occur more frequently and often cover a much larger area than a tornado.

[cubssoxfan]

I found this in the Austin TX forum where they were debating if Austin is somehow immune to Tornadoes due to its location or topography. The answer was NO.
This map will show central IL has a higher incidence of tornadoes and that we are the eastern border of tornado alley. http://upload.wikimedia.org/wikipedi...nado_Alley.gif

[SJaye]

Everyone who thinks their city is immune to tornadoes for any reason should see this map showing all tornado tracks since 1950!

USTORNADOES 1950-2005

and these maps showing the average number of tornado days per year.

nssltornadoprobmaps

The only topographic features that significantly reduce the likelihood of a tornado in your area are major ones like the Rockies or the Appalachians, not Charles Mound near Galena, not Texas hill country, and not the Illinois River Valley.