Predicting the 2007 Tornado Season

  • Thread starter Thread starter Michael O'Keeffe
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I know moisture is important but how about considering it on a synoptic scale? I think that a prerequisite for a very good chase season is a progressive pattern and lower-than-normal SLP's across the CONUS. Strong lows can really transport moisture at a very rapid rate...something that the models are actually underdoing this year. Also I think the SPC published a good paper on how the WRF has so far underdone CAPE in the long ranges (which for it is from 48-84 hr).
 
Well I'll go ahead and throw out my crystal ball prognosis.

Seems in all years in recent history (last 20 or so) have been good chase seasons for the central and southern plains when coming out of a good El Nino episode. On of the greatest chase seasons on record, 1995, was during during an El Nino that was fading by late spring.

I am sure many of you can recall some famous tornado events during that year...Pampa, Lazbuddy, Ardmore...

Just a general observation as well. Mother nature has a way of balancing things out, and with the overall lack of tornadoes in TX and Ok the last couple years, combined with the recovering from the drought, I have a feeling that is going to play well for chasing in these parts this year.

I fully expect a healthy year south of the Nebraska border!
 
Though I am unsure if it has been posted and I may have over looked it. Does anyone have any predictions for the Great Lakes and the Northern Planes. Generally I am hoping for a better year than last year, not getting my hopes up for another 2004 and 2005. Seems patterns don't flow particularly well, and most past predictions have gone slightly(or entirely) misdirected. Anyone have any ideas?
 
David Drummond said:
Well I'll go ahead and throw out my crystal ball prognosis.

Seems in all years in recent history (last 20 or so) have been good chase seasons for the central and southern plains when coming out of a good El Nino episode. On of the greatest chase seasons on record, 1995, was during during an El Nino that was fading by late spring.

I am sure many of you can recall some famous tornado events during that year...Pampa, Lazbuddy, Ardmore...

Just a general observation as well. Mother nature has a way of balancing things out, and with the overall lack of tornadoes in TX and Ok the last couple years, combined with the recovering from the drought, I have a feeling that is going to play well for chasing in these parts this year.

I fully expect a healthy year south of the Nebraska border!
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I have heard a lot of comparisons to 1995 and this year in terms of the trends we are following and such as far as upper air trends and el-nino, etc. go. IMHO, I think that with the drought stricken areas of NW and W Oklahoma diminishing as time goes on, I think we won't have to worry about quick dryline surges and/or not enough evapotranspiration. If you guys remember the Wheat Crops were HORRIBLE in W and SW
Oklahoma last year and there are a lot of places out there where crop fields are all you see for miles. The crop should be much better if the precip can keep being consistent which will help things green up. That'll at least get us 1/2 the way there with things going alright near the surface. I think we can count on warm days with decent gulf moisture every year, there are those x-factors that can really separate a year though.

The other 1/2, getting upper air support in is at best a crapshoot this far out. I will note that seeing big upper air system after upper air system plow over Oklahoma and Texas this winter was a welcome sight as it seemed we never really could get them this far south the past couple of years. I hope that's a sign we can get the systems much farther south rather than up in Nebraska/South Dakota, at least for a little while. You guys can share with us for awhile can't you? We've been mighty gracious the past several years making the long treks up that way. :D

Either way, I hope the 1995 comparisions prove true as that year featured a ton of famous events that I can only vaguely remember as a much younger one back then! It should be a fun year as always regardless of the actual number of storms!
 
Dan Robinson said:
How much of a factor is evapotranspiration in the whole of the boundary layer? I knew it could create significantly higher DPs in a very shallow layer close to the ground, but I understood when it came to actual convection, it was fairly inconsequential when compared to the ambient moisture depth and was usually mixed out easily and quickly during the day.
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My understanding is that it does play a major factor. I also know that several papers have been done on this, I dont know of the exact name/journal, but one was in regards to an increase in severe weather in the Texas Panhandle and parts of Oklahoma once irrigation became very widespread in the Great Plains. I think a little research has been done regarding the corn/soybean crop in Iowa/Illinois area as well, since corn has a larger moisture flux than grassland does.

This semester I am attempting to get acquainted with a regional climate model in an effort to simulate changes in the land surface and how it relates to precipitation, moisture, and temperature.
 
This winter bares a striking resemblence to 1963/64 in terms of Nino3.4 SST. El Nino died rapidly late winter into early spring that year. By March/April/May La Nina had developed. There is a discussion about the possible developing La Nina here http://www.stormtrack.org/forum/showthread.php?goto=newpost&t=10841 .

The 500mb pattern from March - May of 1964 was a trough over the West/Rockies and a ridge over the Southeast. That's a great pattern for severe weather outbreaks, or great storm chasing.

My money's on La Nina by April/May, which means an active severe weather pattern mid/late March - April, possibly May as well.
 
Well here is something that I want to throw out there for areas of the central/northern plains and their severe threat later on in the season. We know the effect evapotranspiration has had in increasing the dew points dramatically in the late summer months and in some cases being the factor of allowing thunderstorms to develop...
Well this years agriculture reports are showing that instead of the near 50/50 ratio of soybeans to corn we are leaning towards a 30/70 ratio of beans to corn. This would likely dramatically increase the evapotranspiration across the plains with corn being a much better producer of moisture for the atmosphere. Maybe another helpful thing to get near-record dewpoint over the area and create some explosive setups...
 
It's pretty well accepted lore for the AZ monsoon that a good storm the previous day tends to inhibit storms the following day (except in the mountains). The soil and boundary actually becomes too moist; and evaporation and enhanced low-level cloud cover diminish daytime heating.

I really think some substantial quantitative calculations are in order about how much marginally enhanced evapo-transpiration really can add to the strongly mixed and dynamic environment feeding severe storms. I think this should be done before one tries to test statistically or assert a large-scale relation between pre-season rainfall and extent of severe weather.

I'd even suggest a counter-hypothesis. Ample pre-season rainfall enhances wide-area early greening of the natural vegetation in semi-arid areas, characteristic of much of the high Plains dryline area. The albeido (solar reflectance) of green vegetation and moist soil is much less than barren, dry soil -- on the order of 20% or more, I believe. This would have the effect of adding both latent (humidity) and sensient (temperature) specific heat to the boundary layer, but has no causal relation to evapo-transpiration. FWIW.
 
Paul Knightley said:
Surely violent storms and tornadoes have been taking place across the Plains long before man started growing crops there?
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Yes a good deal of the plains was a tall-grass prairie before civilized settlement (the "prairie plains") and the western expanse was a short-grass prairie (the "high plains.")

I think it is fairly well understood that evapotranspiration is a significant component of the hydrological cycle, especially in inner continental regions. From the studies I've read, it seems - on balance - that evapotranspiration contributes to convection, and certainly adequate soil moisture is a necessary ingredient for evapotranspiration. Over the decades, it does seem like some processes of desertification wax and wane over the southern and western margins of the great plains. While I wouldn't go so far as to assert a pure cause-and-effect, it did seem like the dry line setups in 2006 were occurring about 1/2 state-length east of the more traditional locales. On the mesoscale, it seems like factors such as evapotranspiration and differential land use boundaries are very interesting, but - similar to factors such as anvil shadows - far from being very well understood.
 
Paul Knightley said:
Surely violent storms and tornadoes have been taking place across the Plains long before man started growing crops there?
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Yes it is a guarentee that they were occurring before we had such of an abundance of corn and beans. What I was simply implying by my post above is that there could maybe be an area of enhanced thunderstorms or at least the potential for them this year along the plains states due to the abundance of evapotranspiration. This all caused by the fact that corn is going to be grown much more than beans this year and corn is by far a better evapotranspirator than soybeans.

Sure, there may not be a direct relationship between the volume of moisture in the air thanks to evapotranspiration and thunderstorm development. But hey, it certainly won't hurt it, right?
 
As the season becomes more into view it looks as though we could possibly be in for a fun season. Though I'm not guarenteeing anything, once we get out of the East trough the mid-late April period should become active once again. After that my prediction is a slow first week maybe into the second week of May, but the last few weeks should be exciting such as mid-late March and what could happen in mid-late April this trend will continue into early June and settle down again in mid June before maybe 1 or two more events in late June. Of course this is a wishcast :rolleyes: , but I'm pretty confident in a few good events in May and June.
 
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