Monday, January 14, 2013

2013 Severe Weather Season Outlook

"Tornado Alley Shifts East This Spring"

I expect the spring of 2013 to bring the heart of severe weather into the Midwest and eastern Plains, away from its usual spot in the central and southern Plains. It's time to review the logistics behind this forecast.

First off is the ongoing drought. There are still many states in the central and southern Plains well into severe drought status. This severe drought has actually reached its highest level, 'Exceptional', in Nebraska, Kansas and Oklahoma, just to name a few. With heavy rains only hitting the Gulf Coast in recent days, no relief is in sight to alleviate a very serious drought problem across much of the nation.

This drought plays a significant role in severe weather (and storms in general). When storms go over land, they drop moisture as precipitation and ingest moisture as evaporation, pretty much a give-and-take. However, if the area the storm is going over is in a drought, there is no evaporation to pump more moisture into the system. As a result, precipitation output is reduced, and the storm weakens overall. This does pose a problem as far as getting storms going for the upcoming spring, and this is the basis of something called a baroclinic zone. The term baroclinic zone defines an area of temperature gradient across an area, commonly a zone where storm formation is enhanced. If we apply the baroclinic zone to this situation, we find that the zone would most likely attempt to form in the Midwest, particularly in Wisconsin, Iowa, Illinois, Missouri and Arkansas. This baroclinic zone will form as a result of warmer temperatures in response to a lack of moisture from the drought- the lack of evaporation from the drought-stricken land refuses development of clouds and precipitation, continuing a vicious cycle that enhances the drought and baroclinic zone.

Now, I personally believe this baroclinic zone does not apply to temperatures. While the term 'baroclinic' may only refer to temperatures, there is no doubt that a moisture gradient is another, equally significant piece in the puzzle. This moisture gradient would form in the same states mentioned in the above paragraph, again in response to very dry land versus relatively dry/average precipitation land. This new moisture baroclinic zone is essentially a synoptic-scale dryline. For those unfamiliar with the term, a dryline is the separation of dry air and humid air. It is commonly found in west Texas, along the desert lands and non-desert lands. This is commonly a focal point for intense thunderstorms as well. I have little doubt that, unless several weeks of persistent rains strike the Plains, these two gradient zones will become key players in the formation and development of thunderstorms and severe weather in the Midwest and southeast Plains.

The above image shows sea surface temperature anomalies for the east Pacific. We see here some colder than normal water anomalies off the coast of northwest South America, but notice their wave-like orientation. Do you see that anywhere else on this image? If you don't, then we are most surely looking at the El Nino-Southern Oscillation, or the ENSO phenomenon. When you see these below normal water temperatures, something called a La Nina is effective.

The La Nina influences the weather by producing below normal temperature anomalies over the Pacific Northwest and North Plains during the winter months, as well as dry weather in the Southwest. Further to the east, we find wet to very wet conditions prevailing over the southern Plains, Midwest and Ohio Valley. This clarifies the presence of the storm track going through the aforementioned areas. Dry conditions persist in the Southeast, representing the dreaded Southeast Ridge that works to push storm systems northeast to affect the areas that are listed as 'Wet' in the above image. In the spring, the La Nina produces a drier than normal Plains states and cooler than normal North Plains and Pacific Northwest. Touching on that drier than normal Plains, the La Nina is indeed what kick-started the infamous 2011 drought that continues to this day.

Here is my forecast for the 2013 Severe Weather Season:

Any questions you have can be asked below. No guarantees I will answer the long ones, so try to keep them brief.



Frank-o said...

La Nina blocked us here in North Carolina for 2010/2011 & 2011/2012 winters. Now this winter so far has been a complete bust.So that would make 3 winters of nothing and if the forcasted La Nina occurs then that will mostly likely make winters 4 and 5 warm and dry. I need to move to the Ohio Valley........

Met said...

Eeehhh the baroclinic zone bit is stretching it. While i personally do believe that youre right about the moisture gradient, the baroclinic zone you are referring to would be a warm west/cooler east scenario. While such a zone could possibly exist, there is no baroclinic instability so it would in effect not help storms, simply due to physics. If there was a semi-permanent baro zone to be worried about, it would have to be cold west/warm east. This would strengthen storms due to baroclinic instability. Anyways I think I'm rambling. Essentially what I'm trying to say is that the baroclinic zone you are mentioning is not in fact a true one as it wouldn't actually have an affect on storm systems. Thus, it is simply a thermal gradient. (which adds a whole new piece to the puzzle via the thermal wind equation, but thats too much for this comment). Thanks for the post!

Anonymous said...

Is the risk higher in the center of the "Increased Risk" area?

Anonymous said...

Hi Andrew,
If I read your post correctly you say that severe weather is going to move away from the central and southern planes. I am wondering why they are colored in the red area showing an increase in severe weather. Just wondering. Thanks.

bjenks said...

Here in Kentucky we had more severe storms than any other state. We also were number one when it came to tornadoes compared to size of state. So we are going to be in the bullseye for severe weather again this year. Great No snow for Kentucky, just severe storms.

Anonymous said...

Way to copy what you've read in the forums Andrew.

Andrew said...

Frank-o: Not every La Nina situation is the same.

Met: It is indeed a stretch, more of a semi-permanent gradient if you will. Appreciate the insight.

Anonymous: No.

Anonymous #2: It moved further east away from other portions of the Plains.

bjenks: Pessimism is not what should be coming up for February.

Anonymous at 9:33: How so? If you mean the moisture baroclinic zone, that was on my own terms and discretion.

INNSAEI said...

Hey Andrew,

I live in an area of TX that sits just east of the typical dryline formation indicative to Sv Wx formation.
Would you agree that the propagation of storm tracks has moved further north towards Waco/Dallas with less formation south towards and west of Austin?
I've been a storm spotter for several years and haven't seen the level of sv wx that we were used to say 1997-2001. Agree? Any theories as to why??
I can only assume that you are correct with the barcolinic zone moving NE and leaving the hill country through just east of I35 transitioning into permanent desertification. Thoughts?

Anonymous said...

I read NOAA's predictions talking about neutral conditions again. They are showing a precip. setup like last early spring over Ohio valley. Drought conditions will be over central and southern plains mostly west of I35. Wierd thing is they say we are in a ENSO-neutral winter. I thought it was El Nino winter.

Anyways, NOAA isn't on alert as of now and haven't made predictions yet for mid, late spring and summer.

Forecaster said...

Is Atlanta in danger of getting tornadoes this spring?

Anonymous said...

Southwest Michigan saw almost zero severe weather last year, except for a few marginally severe storms- PLEASE say that will change this year? If anything, we just need some rain this year- i don't want to go through the drought we had last summer again.

Andrew said...

INNSAEI: I have not studied that, so I cannot provide an opinion on it.

Andrew said...

Forecaster: Slightly below normal compared to

Andrew said...

It may change, it may not- you're asking a very specific question for a very specific place. That's not easy to do this far out.

Anonymous said...

From continuous reading, our winter is enso-neutral.

Though the early severe weather season last year was that of La Nina to ASAP neutral conditions, this year may not start as early with the current winter. Only patience and research will tell.