Fall Stormchasing: A Little Season

[Darrin Rasberry]

To me, 2008 isn't over yet - once the second-worst chasing month of August fades out, fall will come. Of course, the memory of visiting Ames mere days after the football stadium-clearing storms of Nov. 12, 2005 are in my head, and I also recall Tim Vasquez mentioning that October 4, 1998 was the biggest chase event of that year.

Some questions about Fall:

1. What are the typical setups for the Fall season, and how do they differ (statistically or by their natures) from Spring setups?

2. What dangers or other considerations are important to look out for in the Fall?

3. Where do Fall setups typically occur, and how often do they occur?

4. What is the storm mode and (when applicable) supercell type that is generally prevalent for Fall, how fast do they move, and how likely are they to become tornadic in comparison with an in-general knowledge of spring and early summer storms?

5. In my mind (even knowing well that there are differences between the two) Fall is kind of Spring run backwards. I'm assuming that the jet drifts back down over the States at this time, but given my extremely limited knowledge of upper-level patterns, this is likely not exactly right. Even if it is, though, why isn't Fall just as dangerous and widespread severe-weather wise as Spring?

Thanks for considering the questions. I'm gonna prepare for some local chases once Fall rolls in ... 2008 isn't over for me until that big ball drops.

"... and after that he must be loosed a little season."

D.

 

[MatthewCarman]

5. In my mind (even knowing well that there are differences between the two) Fall is kind of Spring run backwards. I'm assuming that the jet drifts back down over the States at this time, but given my extremely limited knowledge of upper-level patterns, this is likely not exactly right. Even if it is, though, why isn't Fall just as dangerous and widespread severe-weather wise as Spring?

D.

November 12, 2005. A tornado outbreak occured in Iowa including the F3 Woodward Iowa tornado and the Stratford tornado. I believe a ederly woman was killed. To me fall can be just as dangerous and widespread as spring. I know there are reasons why fall is usually not as active and the two that come to my mind is less daytime heating and daylight because the sun sets sooner and less warmth. Fall is usually cooler than Spring is. This could be because of stronger cold fronts and less daytime heating.

I am no expert so if anyone want's to correct me please do so.

The November 12, 2005 outbreak and the February outbreak of 2007 in KS/MO and the outbreaks in 2008 in January and February show us the season never realy ends and severe weather can occur at any time of the year if the conditions are right. Every year is different from the next year. August can be very active. I remember one August when there was nice tornadic storms with wall clouds over central Iowa several times. This July has been pretty active. Severe storms has occured almost everyday this month somewhere in the heatland. Tornades has not been plentifull (atleast in reports) but there have been days with tornadoes. To me the season never ends. Some years it just quites down or takes a break for awhile.

21 days of July had tornadoes reported and every single day so far has had severe storms somewhere in the central plains or eastern Rocky Mountain area. 08/07/27 for Example had 5" hail,70-75 MPH winds and 5 tornado reports (a few confirmed and atleast 1 photogenic tornado) with storms in the heartland. The Derecho event of 08/07/20 had estimated winds of 100+ mph with a confirmed windgust at 94 mph in Moline IL and there was also large hail reported with this derecho of 1-2". The event mostly affected IA and IL. 08/07/28 had a few good supercells with nice hooks and 1 confirmed tornado atleast half a mile wide. Those are just examples of a few of the very active days we have had so far in July. July has been a good month for "storm" chasers in my oppiniun. Mabey not for you're area but for the central plains. August could be just as active if not worse. Sorry for going offtopic.

 

[Chris Lott]

Back on October 11, 2001 a very nice supercell produced a high end F-2 about 7 miles west of my house, and actually touched down again about 1 mile south of me. It was a very strong storm that actually produced two tornadic circulations. The thing I remember about that day was that it was very warm and humid, and a cold front was plowing into the area. I really don't recall hardly any surface winds early that day but as the evening went on they began to pick up out of the south. To me the fall season is very similar to spring, where you have the general "clash of the air masses" with warm air at the surface and cold air aloft. Throw a little wind shear in there and it's the perfect mix. I used to never pay attention to severe weather in the fall, but after past years, I start to gear up for the "second season." December 29, 2006 brings back some memories of another unusual setup that produced between 9 to 11 tornadoes around the Waco,Tx area. Here's an article I found on google that has to do with some record severe weather events that have occured in Kentucky in the fall.

http://www.crh.noaa.gov/jkl/?n=fall_severe

 

[Dean Baron]

Correct me if i'm wrong, but from what i've noticed since i started watching storms/setups is that fall setups occur in Iowa/Nebraska/Kansas in the early to mid fall, and Oklahoma/Texas in the mid to late fall, to me it just seems like the opposite of spring, instead of the setups heading northward with time, they head south.

 

[Steve Miller]

One of my favorite very photogenic tornadoes occurred west of Stillwater, OK on 10/4/98. I am a believer in the fall season although generally here in OK we get about a two week season with two to three good shots at severe weather.
I would imagine if you're willing to travel a lot you could manage four to six weeks worth of chasing starting in the last week of September.
I agree with Dean. It seems the potential inches down from the north - opposite of the spring season.

 

[Shane Adams]

There is a climatological chase "window" each Fall, but it's far less reliable than Spring. The reason is, as has been said, the season is the opposite of Spring, so you're gradually cooling instead of warming, which means you're losing instability via thermodynamics as the season evolves. Fall systems are typically shear-driven events. Once in a while you'll get true, awesome thermodynamic setups, and those are the days you remember. Like 10-4-98 and 10-9-01. Instability = there is no substitute.

Fall chasing has a feel and flavor all its own; all tornadoes are absolutely delicious, but the ones in Fall are more akin to a perfectly-seasoned burger cooked on a grill at home, where the typical Spring tornadoes are more like sirloin. Both are fabulous, but different.

However, experience has taught me that you can't count on Autumn. Some years there's bounty, others there's nothing. I've had two great tornado days in the Fall in 12 years. This doesn't mean there hasn't been more, but most people aren't set up to chase unrestricted in October and November, as opposed to Spring, so it's more difficult to travel further that time of year. Even if you could chase unlimited, I still don't believe Fall produces on the same level as Spring.

 

[Angie Norris]

You also get a secondary maximum in the TN/OH Valley region and the deep south in the late fall. A quick peek at some data bases from the Memphis and Birmingham WFOs showed several significant episodes, especially 11-27-1994, 11-24-2001, and 11-10-2002. I remember the models for 11-10-2002 looked incredibly similar to the Superoutbreak.

 

[Bobby Prentice]

Some questions about Fall:

1. What are the typical setups for the Fall season, and how do they differ (statistically or by their natures) from Spring setups?

Animations of the Severe Storm Annual Cycle by Dr. Harold Brooks (National Severe Storms Lab) indicate that the "secondary fall severe storm season" really only exists over the southern Mississippi River Valley (between central OK/TX eastward to Alabama), but even there it is not very impressive. This secondary max shows up best for "high end" severe weather which is almost always produced by supercells. That's why chasers think so highly of it. For significant (F2+) tornado, the best week of the fall season (centered on Nov 25 over MS/AR/LA near Vicksburg, MS) is only 30% of the best week of the spring season (centered on May 6 over OK). For giant (2-inch+) hail, the best week of the fall season (centered on Oct 14 north Texas near Mineral Wells) is only 20% of the best week of the spring season (centered on May 20 over north/west TX and western OK near Childress, TX).

These Fall severe weather events are usually "synoptically evident" which means they are associated with strong weather systems which can be predicted many days in advance.

2. What dangers or other considerations are important to look out for in the Fall?

These Fall severe storms usually occur during October/November when the length of daylight is relatively short. This is the equivalent of chasing during late January to mid March. These storms are typically fast-moving and located in marginal or poor chase territory (trees/hills, etc.).

3. Where do Fall setups typically occur, and how often do they occur?

See above.

4. What is the storm mode and (when applicable) supercell type that is generally prevalent for Fall, how fast do they move, and how likely are they to become tornadic in comparison with an in-general knowledge of spring and early summer storms?

These Fall severe storms are often associated with strong weather systems which favor upscale growth into squall lines. I have seen no research that discriminates annual cycles of supercell type, but my personal experience is there's no big difference. See above for the other answers.

5. In my mind (even knowing well that there are differences between the two) Fall is kind of Spring run backwards. I'm assuming that the jet drifts back down over the States at this time, but given my extremely limited knowledge of upper-level patterns, this is likely not exactly right. Even if it is, though, why isn't Fall just as dangerous and widespread severe-weather wise as Spring?

The biggest reason why the Fall severe storm season is a "faint echo" compared to Spring goes back to atmospheric (tropospheric) temperature variations. The surface of the earth receives peak solar insolation (heating) on the first day of summer (around June 21 in the Northern Hemisphere) and minimum on the first day of winter (around December 21 in the Northern Hemisphere). However, The processes which control temperature in the troposphere lag the calendar by about 1-2 months. Thus, jet streams and weather systems are usually weaker and the atmosphere is less unstable during Fall than Spring.

 

[Jason Young]

I am also a believer in fall chase's , but not the insane speed of the storm's like we saw last fall in N.C. and C . Oklahoma .

 

[Darrin Rasberry]

November 12, 2005. A tornado outbreak occured in Iowa including the F3 Woodward Iowa tornado and the Stratford tornado. I believe a ederly woman was killed. To me fall can be just as dangerous and widespread as spring. I know there are reasons why fall is usually not as active and the two that come to my mind is less daytime heating and daylight because the sun sets sooner and less warmth. Fall is usually cooler than Spring is. This could be because of stronger cold fronts and less daytime heating.

I am no expert so if anyone want's to correct me please do so.

The November 12, 2005 outbreak and the February outbreak of 2007 in KS/MO and the outbreaks in 2008 in January and February show us the season never realy ends and severe weather can occur at any time of the year if the conditions are right. Every year is different from the next year. August can be very active. I remember one August when there was nice tornadic storms with wall clouds over central Iowa several times. This July has been pretty active. Severe storms has occured almost everyday this month somewhere in the heatland. Tornades has not been plentifull (atleast in reports) but there have been days with tornadoes. To me the season never ends. Some years it just quites down or takes a break for awhile.

21 days of July had tornadoes reported and every single day so far has had severe storms somewhere in the central plains or eastern Rocky Mountain area. 08/07/27 for Example had 5" hail,70-75 MPH winds and 5 tornado reports (a few confirmed and atleast 1 photogenic tornado) with storms in the heartland. The Derecho event of 08/07/20 had estimated winds of 100+ mph with a confirmed windgust at 94 mph in Moline IL and there was also large hail reported with this derecho of 1-2". The event mostly affected IA and IL. 08/07/28 had a few good supercells with nice hooks and 1 confirmed tornado atleast half a mile wide. Those are just examples of a few of the very active days we have had so far in July. July has been a good month for "storm" chasers in my oppiniun. Mabey not for you're area but for the central plains. August could be just as active if not worse. Sorry for going offtopic.

"Somewhere in the HEATland"? What an appropriate typo given the oven Iowa's been the last few days.

Problem is the winds are all up in Canada. Yeah, yeah, I know: winds can dip all the way down to, heck, Missouri (remember the supercell chorus line in N MO the other week?). But the ingredients just don't come together unless you live in the far north of the States or in Canada.

I read that August was traditionally the worst "tornado" month (some other sources state December). Of course it doesn't mean it can't happen. I think an F5 happened in August, in fact. However, unless the wind support starts shifting down before the month is over, we'll have to rely on die rolls to get anything but messy severe setups.

I have chased the numerous days here in central Iowa. While chasing is always fun to me, I've grown a bit tired of the whale's mouths and outflow-dominant mess on every storm that fires because the winds are pretty much 0 knots throughout the troposphere. But when winter's here I'll be wanting even that, so I'm enjoying what I get regardless. I did chase the derecho event that you mentioned from here in Ames until just before sunrise in Grinnell while relaying reports on the way, but that's the only time I've felt a local chase has been worthwhile lately. Perhaps it's just more of my bad luck, lol.

Certainly January and February have tornadoes, and this year had plenty (Super Tuesday outbreak Feb 5 is still the top 24-hour regional outbreak this year, isn't it?) but they are almost all setups that fire fast storms over the jungles and hills of the Southeastern States. It's like hard mode for chasers, and I probably wouldn't consider chasing even a high risk event over that time frame in that area for a few more years.

To rerail: someone a long while back, maybe my stepfather's dad who spotted for decades for Wichita County, Texas, told me the Fall was kind of like from early April backward through March severe weather wise. Some kind of rule of thumb like that. I don't know how valid it is, though.

 

[Darrin Rasberry]

Correct me if i'm wrong, but from what i've noticed since i started watching storms/setups is that fall setups occur in Iowa/Nebraska/Kansas in the early to mid fall, and Oklahoma/Texas in the mid to late fall, to me it just seems like the opposite of spring, instead of the setups heading northward with time, they head south.

It's the general flow of the jet streak, isn't it? I guess it ends up in Mexico or somewhere close to the tropic while it's blistering cold here in the States, then rises into the Southeast (and sometimes S TX) in January.

 

[Darrin Rasberry]

There is a climatological chase "window" each Fall, but it's far less reliable than Spring. The reason is, as has been said, the season is the opposite of Spring, so you're gradually cooling instead of warming, which means you're losing instability via thermodynamics as the season evolves. Fall systems are typically shear-driven events. Once in a while you'll get true, awesome thermodynamic setups, and those are the days you remember. Like 10-4-98 and 10-9-01. Instability = there is no substitute.

Given my jet streak "hypothesis" I guess it's fair to say, then, that things run like this little bored-while-waiting-for-class musing:

Maximum Daytime: Late June. Maximum distance the supportive wind patterns travel north before generally shifting south again: occurs in August.

Thus there's an eventual lapse in Fall between the prime heating quality and the jet streak passage over a given tornado-prone area, compared to the Spring standard. In the Fall the supportive winds don't arrive over the mirroring change in temperature as it does in Spring. In short, any supportive wind patterns in Fall happen over cooler, and thus less unstable, areas than in the Spring analogy. Thus Fall is in general the weaker season.

Suppose we can do some SimEarth here. Should we repattern the Earth to where the jet flows southward in the Fall Season in a way analagous to how it flows north in the Spring Season (probably at least by realigning the hottest part of Summer over the longest day of the year and the coldest part of Winter over the shortest day, which probably would necessitate breaking many thermodynamic laws) then we'd have an exact mirror image in reverse of Spring setups for our Fall setups except for a minor conjecture I offer below. However, I'd wager a kind of "averaging out" in general severe potential for this case, since the day-length/warming vs. jet motion lapse for Spring Season setups in actuality probably would enhance potential in general as opposed to the above theoretical setting.

The only complaint here for the Fall is the "upper low dig" problem. A southerly drifting streak, in my mind, implies a predominance of southerly drifting or "digging" upper lows on the synoptic scale (can't find in my weather texts whether this is true or not however); digging upper level lows IIRC cause winds along attendant surface development areas to be more linear than those attendant to their northerly-moving cousins. Thus directional shear is more random to occur in the Fall, and storms probably have to end up depending on boundaries to become tornadic. Additionally, Mr. Prentice pointed out that the supportive wind patterns attendant to Fall will be not as strong as Spring due to the aforementioned lapse between peak warming and peak daytime, presenting a weaker speed shear than Spring as well. This problem coupled with the unfavorable latter-year longest/hottest day vs. southerly jet progression lapsing the supportive winds over unsupportive instability is the working theory in my tired brain to why Fall can be such a sore.

This is just speculation. I don't mind, and in fact desire, criticism of this little theory of mine.

D.

 

[MatthewCarman]

Just a guess but one reason why August is not as productive or active could be because it is so warm capping things off and making it harder for storms to become severe. That and the cold fronts not being that strong. The last cold front to move through Iowa had no cold air with it and just a shift in the winds according to the met on CH13.

We had several years back, a day in August where a magor tornado outbreak was expected across Iowa. I remember SPC having my area in a high risk from a triple point and I could see that conditions were good for storms because of the clouds outside. Only one big storm formed by the Iowa State Fair in Des Moines (never severe) but I remember KS/MO having alot of tornado warnings. Not sure how severe the outbreak was but it is very interesting to see a high risk in August. I think the event was capped over here in Iowa. WI had a big outbreak around this date or on this date. It occured in central WI and traveled east if I remember right. Some years can be asome but I see your point and agree that August is one of the least active months of the year because of what I said above.

 

[MatthewCarman]

According to Wikipedia only 1 high risk day has ever been issued in August. Mabey I am thinking about a mod risk day but I am sure it was a high risk day. Anyway here is the info on the one high risk outbreak for August taken from another site:

August 27, 1994: A rare summer high risk day in the upper Midwest. According to the storm reports archive, 9 tornadoes occurred in Wisconsin, with 2 of them of F3 strength. There were 4 fatalities and 51 injuries.

 

[Brandon Goforth]

I am a believer in the fall season although generally here in OK we get about a two week season with two to three good shots at severe weather.

Yep, usually that's the way it seems to work out, and in mid-October.