State of the Chase Season 2021

Warren Faidley

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May 7, 2006
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It's important to consider there are multiple chase seasons, not just "one size fits all."

I break them down into: "Winter season," generally in the SE states in January February and early March. "Early spring season" starting in late March to Mid-April. "Mid-spring" (the traditional chase season) from late April though early June. "Late-spring and early summer" running through mid-July. There are isolated events for the remaining months and one could argue for a "Canadian season" since things seems to be shifting further north every year.

Each season has it's own climatology and "x-factors," complicating "broad-brush" forecasts. I've seen seemingly "bust" seasons saved by robust Colorado-sets up in June. I've also seen insane set-ups in Western Texas killed repeatedly by strong caps. Trying to forecast, for example, when and if the Hudson Bay Low will form or recovery times for Gulf RH is impossible this far out.

2021 is likely going to be another year where you have to remain flexible if you can, picking out the few early gems (e.g., Midland last year), and rolling the dice for an active week in May or June. Or, move to Canada.
 

Jeff Duda

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I disagree with the notion that there are distinct seasons for severe weather. There is a distinct peak of severe weather/tornado activity in the spring months across the US with a monotonic increase and decrease leading to and going away from that time. The "fall hump" is statistically barely distinguishable from the rest of the year's annual cycle. What actually changes other than the frequency of severe weather is where it occurs. If you want to argue that seasonality is implied by region, then fine. But the transitions are smooth, statistically speaking.
 
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Oct 10, 2004
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Off-topic, but I see AccuWeather's seasonal forecasts as akin to throwing shit against the wall and seeing what sticks.

I don't think there's any reliable way to predict activity level of the spring tornado season beyond aggregate statistics, but we're heading into spring with massive drought in the southwest (although, parts of NW TX, W OK, and W KS have escaped the bad stuff), so that can't be great. Could be looking at strong caps.

Worst part is the synoptic pattern, though. That's what hosed 2018 and 2020. I don't see how that can be predicted at this length.
Perhaps that strong EML, while resulting in a "too strong" cap for the Southern Plains, could result in a more "ideal" EML further north/east (AKA MBY and parts of IA/IL/MN) where a more common failure mode is the lack of a sufficient one to prevent early initiation/MCS mode. But, that still requires we not flip right from "extended winter" in April, to the jet being in Canada.
 
Oct 10, 2004
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Regardless of any positive signs, man the climate models for AMJ are just resoundingly bad. Not even going to bother posting them, but the consensus from the ECMWF/NMME/CANSIPS/etc. is for another very dead season with a poleward retracted jet (even starting in April this time) along with some serious drought problems given torching temperatures and a lack of precip.
Andy, do you think these models were perhaps not taking into account the current winter storm unfolding across the region? After all, it is quite unusual for the Southern Plains to go into spring with any sort of snowpack on the ground. When I think of a bad La Nina chase season my mind immediately leaps to 2012 when it was very mild and dry the preceding winter with very little snowpack anywhere, and the entire Plains and Midwest basically started to bake in March and never stopped until late summer/early fall.

This year so far is behaving more like 2008 or 2011, with a quite active mid-late winter east of the Rockies. Still, it's interesting and somewhat disconcerting that the models would be in such unanimous agreement that flies in the face of the favorable indicators that have been discussed on this and other forums.
 
Oct 10, 2004
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Again, the general thinking going into this year is that things look rather ominous for Dixie Alley, but more uncertain for the Plains/Midwest particularly in "prime" chase season of May into June (as is to be expected with a Nina). The climate models Andy B. posted about kind of throw a wrench into things, but of course they could easily be wrong at this range.

Although, like I said, I'm starting to think they might have been out to lunch since especially with the multiple rounds of widespread winter storms we just had, this year is behaving much more like a "wet" La Nina for the central CONUS than a "dry" one. Spring river flooding is already looming large as an upcoming issue in the Midwest, as it did in active springs like 2008 and 2011.
 

adlyons

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Linking a presentation that some of you may find interesting on the correlation between positive phase of the Trans-Nino index and large us tornado outbreaks. The presentation comes from Dr. Sang-ki Lee of NOAA AOML

Heres the skinny: "The decay phase of la nina (A positive trans-nino value) has been associated with a higher than average number of tornado outbreak and violent tornadoes days."

I updated some of my spreadsheets on ENSO and we have flipped from negative/neutral to a positive TNI. The last time this occurred was spring of 2017. Our values are weaker than past analogs so I still am hesitant to make direct comparisons to 2011 2008 ect. This is a weaker la nina transition, but there is still some evidence that the large scale pattern could favor some enhanced activity early to mid spring. Not sure how the ongoing drought will play into this, but here's some reading material.

1613748622281.png
 

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Oct 10, 2004
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Hmmmm...2017 wasn't a great year for chasing but not the worst of the late 2010s (that distinction goes to the following year). A lot of setups that busted or underperformed including the late April sequence which had some tasty model runs but of which the Canton tornadoes ended up being the only major event; the mid-May high risk and the late May moderate risk (which was primarily issued for a big derecho but with the potential of a tornadic supercell or two on the tail end in northeast OK which never really materialized).
 

Warren Faidley

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May 7, 2006
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Linking a presentation that some of you may find interesting on the correlation between positive phase of the Trans-Nino index and large us tornado outbreaks. The presentation comes from Dr. Sang-ki Lee of NOAA AOML

Heres the skinny: "The decay phase of la nina (A positive trans-nino value) has been associated with a higher than average number of tornado outbreak and violent tornadoes days."

I updated some of my spreadsheets on ENSO and we have flipped from negative/neutral to a positive TNI. The last time this occurred was spring of 2017. Our values are weaker than past analogs so I still am hesitant to make direct comparisons to 2011 2008 ect. This is a weaker la nina transition, but there is still some evidence that the large scale pattern could favor some enhanced activity early to mid spring. Not sure how the ongoing drought will play into this, but here's some reading material.
Do you know if anyone has broken down the data by regions? I seem to remember a similar study where a positive trans-nino was associated with more activity in the eastern / SE US as opposed to the Central Plains, e.g., the 2011 Super Outbreak? Thanks.
 

adlyons

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Do you know if anyone has broken down the data by regions? I seem to remember a similar study where a positive trans-nino was associated with more activity in the eastern / SE US as opposed to the Central Plains, e.g., the 2011 Super Outbreak? Thanks.
Warren, there is a paper by the same author delving into a bit more detail on the topic, but other than that I am not aware of anything else on regionalizing the results. The presentation did hint at more activity across the southeastern US and the Midwest similar to what you said but it is a bit broad/vague.
 

adlyons

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Hmmmm...2017 wasn't a great year for chasing but not the worst of the late 2010s (that distinction goes to the following year). A lot of setups that busted or underperformed including the late April sequence which had some tasty model runs but of which the Canton tornadoes ended up being the only major event; the mid-May high risk and the late May moderate risk (which was primarily issued for a big derecho but with the potential of a tornadic supercell or two on the tail end in northeast OK which never really materialized).
I would definitely caution using 2017 as an analog as it was a substantially weaker La Nina. But, like you said, it was certainly not the worst year ever. I only include that as a reference to the last time we had even remotely similar conditions. Prior to that, 2015 also had positive TNI values but temporally displaced from the method(Single year la nina decay) mentioned in the presentation.
 

James Gustina

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The Euro has been hinting at our first run at a limited severe weather threat on the Southern Plains early next week. Looks to have all the classic problems of an early March setup between cloud cover and uncertain warm front placement but something that may bear watching.

Both the GFS and Euro seem to be pointing to the Southern Plains and Dixie getting some Baja cutoffs mixed in with the overall west coast troughing through hour 240 from the 00Z runs last night/the GFS' 12Z run this morning. Might be interesting to see how our mid-late March shapes up should that type of pattern persist.
 
Apr 10, 2008
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Various model data continues to suggest severe weather potentials for parts of the Plains and Dixie beginning around the middle of the month. Still too much uncertainty to begin hashing out the finer details, however the overall trend does suggest an active second half of March may be in the cards. Really hoping for chasing ops west of I-35 this year, particularly in Kansas. Most spring severe weather outlooks place the bulk of the activity east of I-35 and into the Midwest and Dixie. There are not many positive signs that the ongoing drought in the southwest sees much improvement over the next couple of weeks. The GFS is more bullish on QPF over the southern high plains vs. the Euro. Either way, it appears drought conditions will persist, perhaps worsen in some areas. Right now it's difficult for me to to have a ton of optimism, however I doubt this year will be as bad as 2020.
 
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Jeff House

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Gasoline prices are around $2.25 in Tennessee, and have been somewhat stable for weeks. Our fall low was $1.75. We generally do not stray too far from Kansas and Texas. All are more stable than the Desert Southwest. I'm not sure about Oklahoma. I expect a little spring creep, maybe $2.50 or close to $2.75 some weeks; but, I think <3. Not commodity or futures investment advice.

Mid-Range the weekly models have shown that trough west with SER look mid-month; and, operational models are similar now in the 11-15 day period. Weeks 2-3 are the edge of any forecast value; but, it's nice they agree. Forecast AO/NAO is positive. Bering Sea ridge (not Alaska) could anchor the downstream West or Rockies (then Plains) trough.

Severe Season overall I'm somewhat bullish, but not crazy lit. I see La Nina hanging in there. It's not a pure La Nina resurgence since it's still first year, but it has that bullish lean for severe. Recent MJO activity and Kelvin wave placement in the Tropical Pacific has juiced the La Nina status (esp 3.4 region). +TNI is in question. Right off South America (region 1&2) is still cool. It had been warning up; but, the said activity impacted the whole basin. If 1&2 can warm to near or above normal, while 3.4 stays cooler than normal, then we have +TNI flavor. Either are bullish. Missing one should not be bearish if the other holds.

That said I reject the 2011 mayhem. 2011 was true resurgent La Nina - which has a much more bullish correlation than first year. I don't recall the 2011 TNI but it was probably not the driver if Nina was surging. I like 2012 and 2008 more than recent La Ninas, basically approximate strength and trend (holding rather than fading). Those years had their days, maybe not all season. They were better than 2017 or 2018.

Bottom Line: I'm cautiously optimistic about storm chasing this year. At the same time I pray (and forecast) it's no 2011.
 

Jeff Duda

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For those who ventured out this past weekend... how are gas prices doing in the Central US? We will soon be at $3.00 per gallon here in AZ (was $1.99 in October) and I'm expecting at least $4.00+ in chase regions by May.
GasBuddy is your friend here:

 
Aug 9, 2012
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2.91 is the highest I've seen near my hometown in IL. Went up from the 2.40s a few weeks back to almost 3 dollars a gallon real quick-like. I suspect we will see 2011-12 prices by summer sadly. If that is the case I will likely limit my chasing to one or two trips to the plains tops and mostly local setups, pending they actually happen.
 
May 1, 2011
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From about the 240 hr onward on almost all guidance feature some interesting things we would typically see with deep south and/or midwestern severe weather. Unfortunately GIFS are too powerful for this msg board. but use your imagination a bit here. We see "the look" from mid march all the way out to April 1 on extended runs of the ensembles, weeklies, etc. Almost unanimously.

Initial waves will have to overcome (read: they won't) poor moisture return due to a crashing cold front prior to the period all the way to the Cayman's.

However, save for any additional crashing, subsequent troughs will not have this problem. Now, observation of the EML..we are going to really need those March thermals to reach A+ levels before any significant severe event can take place.

At any rate, Likely BA conditions until about March 15 timeframe, with AA conditions tentatively expected for the back half of March.

P.S. Let's repeat this pattern precisely two months later.

1614633547883.png 1614633643433.png 1614633671662.png 1614634038945.png
 

adlyons

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Feb 16, 2014
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Well, happy spring everyone! It being the start of traditional chase season I feel confident enough to lock in a forecast.

Forecast 20201 Tornado Season (MAMJ) :

Counts: Average (754 tornadoes across the CONUS during spring, 1250 plus or minus 50 for the year)
I feel fairly confident on average numbers for the chase season and year. With a moderate La Nina, but complicating factors such as drought, I think we see pretty normal activity. This activity should pick up fairly quickly here over the next two weeks with the first hints of the spring pattern shaping up. Some killers for this would be an early northward retreat of the jet (Aka Death Ridge) cutting into numbers early. This is a distinct possibility given the ongoing drought. A second, perhaps better for us failure mode would be a weak resurgent la nina. This could throw out some higher tornado numbers, though I think this is less likely. Its about 50/50 which side of the coin we end up on, which means I'm going to hedge to average.

Outbreak Days (10+ Tornadoes within 6 hours): Above Average
Its an emerging trend, fewer tornado days, but more tornadoes per day. Im sticking with that. You can define outbreaks in many ways so I'll have to run some stats to verify, but I think we see a more active outbreak pattern going into April and a few very big count days. The forecast is also calling for an above-normal hurricane year. I think we see another active TC tornado year this summer and fall.

Number of EF2+ tornadoes:
Well Above Average (Greater than 1 STD above the normal mean)
Im taking a bit of a risk on this one but, with the southeast and eastern half (more populated) of tornado Alley looking more favorable, I'm leaning towards a much higher count of sig tors for the simple fact I expect more of them to hit things. The same trend will probably hold for fatalities.

Chasabillity Score: Average 6/10

My completely scientific and no non-sense chasing index, just kidding it's entirely arbitrary. Not a great year, not a bad year, somewhere right in the middle with a bit more chasing potential. We probably won't be chasing west of I-35 as much as we would like putting a dent into the chaseabillity of some systems, but the average counts combined with a few bigger days will get peoples chasing counts up. Midwestern gang and the southeast should have a decent year. Southern and central plains also won't have much to complain about. Perhaps not the best for the front range and Texas Panhandle guys and gals but a few days spark off. A banner year for a few, but sufficient for most.

We will see where we go from here. Good luck to everyone, stay safe and happy hunting!
 
Jan 7, 2006
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On the S2S front, Victor is amped up about the prospects for overall CONUS activity through the month:
And on the seasonal front, I thought it was worth following up on my January post regarding ENSO: thankfully, Nina conditions have not yet begun to fade off. In fact, Nino 3.4 mean SSTAs this week are still -1.2 C, which is near the baseline they've oscillated around ever since November. This nudges the ENSO trajectory a bit more toward the "true Nina" years of 1999, 2000, 2008, or 2011, and slightly further from the very borderline cases of 2006 and 2018 -- in particular because the western equatorial Pacific is still cold, whereas it was already near normal in those years. Really, though, we're sitting firmly between those two clusters of recent ENSO values, with the closest historical comparisons (strictly in terms of Nino 3.4) being 1985 or 1971. Most ENSO guidance still suggests we'll reach the neutral threshold (-0.5 C) by AMJ, which would be quite different from 1999 or 2008, but the spring barrier is obviously at play here. Overall, though, I'll take it as a small win that we haven't yet seen sustained warming and keep drifting from the unmentionables of 2006 and 2018.
 

Jeff House

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Yes Dr. Gensini might have put it into words better than me, at least more succinctly. La Nina (3.4) is still cool not warming yet.

Gasoline was $2.32 yesterday, of course right after my post; so yes, spring creep has begun. It's because Refineries shift blends and/or mix of refining Diesel, gasoline and heating fuel. They're not gouging chasers, haha, but other spring travel demand overlaps the above.

Back to the forecast, yes the next couple low press systems are Deep South and will scour the Gulf Coast a bit. However they are not full latitude phased beasts at all - more detached; so, the moisture is just tempo held.

Mid-month, perhaps convenient with the time change, more southwest flow gets established. Few models have a less warm outcome and MJO interference; however, it's mostly trough West/Rockies and SER. That could get mid-March going Dixie or Hoosier Alleys.
 
Jul 5, 2009
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I feel fairly confident on average numbers for the chase season and year. With a moderate La Nina, but complicating factors such as drought, I think we see pretty normal activity. This activity should pick up fairly quickly here over the next two weeks with the first hints of the spring pattern shaping up. Some killers for this would be an early northward retreat of the jet (Aka Death Ridge) cutting into numbers early. This is a distinct possibility given the ongoing drought. A second, perhaps better for us failure mode would be a weak resurgent la nina. This could throw out some higher tornado numbers, though I think this is less likely. Its about 50/50 which side of the coin we end up on, which means I'm going to hedge to average.
Just a question for my own continuing education - isn‘t the position of the jet independent of drought conditions? I understand the unfavorable impact of drought conditions, but didn’t think it could actually affect the synoptic jet configuration?