2018 severe wx/chase season discussion

[Royce Sheibal]

Warren mentioned the drought and fires. Interestingly they are both have been shown to impact tornado chances.

Droughts, obviously, are bad for outbreaks as low soil moisture prevents evapotranspiration, which is becoming a bigger and bigger buzzword for low-level moisture every year. High E-T situations can rapidly boost CAPE and lower LCL's, making tornadoes much more likely than they would appear (See June 2014 in Nebraska). The NAM seems to have the best grip on E-T from my experience.

Fires, on the other hand, can be great for tornadogenesis. There was a study a couple years back that correlated fire events in the Southern Rockies and Northern Mexico to increased incidence of tornadoes in OK. The conclusion of the study was that the aerosolized particles from the fire create a short-term greenhouse effect when they are at lower heights and can boost CAPE from daytime heating (See May 2013 in OK). I'm not familiar with any model that factors aerosolized smoke into their system, but maybe DUDA knows.

So if Warren is right and we have a drought in the S Plains, that will hurt TOR chances, but upstream fires could potentially add a boost to a system or two if timing is right.

 

[Alex Elmore]

It would be interesting to note how many chasers from outside the Alley have altered their chasing schedules to accommodate for the drought conditions? It seems the last week in May and the first two weeks in June have become more popular?

As someone who lives in the Midwest, the conditions in the Plains have very little impact on when I plan my chasecation. I'm currently a student, so I wait until the semester finishes up in early May. My current work allows for some of the greatest flexibility I've ever had and probably ever will in allowing me to decide when I'm going to chase, so I can make the decision to be out for a week a day prior to leaving if I wanted. There are many others who are obviously not as fortunate. Many chasers that I talk to on a regular basis have to make a decision on their vacation time for this year early in the year or even near the end of the previous year. There's a lot that can change regarding drought conditions and the atmospheric pattern in just a months time, let alone a couple months. What I've done in the past when I've needed to choose a week well ahead of time is just pick a week in May and hope for the best. I know others who also pick a week in April for chasing just to mix things up.

I feel it's great conversation to talk about chasing impacts due to droughts, fires, teleconnections, and (insert your favorite variable here), but when it comes down to picking a week or so to set aside for chasing, I have and will always choose mid- to late-May due to climatology. If I'm lucky and something happens during my time off, then that's obviously great. If not, the Midwest usually has a couple decent events throughout the year that I can chase with only taking a day off, and there's always the following year.

 

[Andy Wehrle]

Well, regardless of what individual systems do, models are at least hinting that by the end of next week and beyond we should be turning the corner into a less frigid and more convectively active pattern.

 

[Royce Sheibal]

Recent EURO for 4/13/18 - I'll just leave this here...

 

[Quincy Vagell]

The models are changing quite a bit with this event. One could argue that the trend is slower/farther west, but synoptically this thing is changing too and it's not just about surface low placement. I try not to get too caught up in details a week out. For example, the 12z Euro on Wednesday showed a 970mb low over eastern Iowa at 18z Friday, while today's 12z run has a 985mb low over the Colorado/Nebraska border at the same time. It's easy to see how much models can continue to change, considering that the shift over the past two days has been so significant.

I would also keep in mind about residual troughing over the northeastern U.S. While it may not have a big impact, were a low to intensify over the Midwest, you'd have to be at least somewhat concerned about the size of the warm sector and moisture transport with northward extent. Sure, an intense surface cyclone can offset that concern a bit, but we're certainly not seeing a pattern like April 2011 or 4/4/12, where there's a big ridge over the eastern U.S.

 

[JeremyS]

The last few runs of the Euro have really exemplified what Quincy said above. At one point the Euro had a nice warm sector and a decent warm front play where storms that crossed the warm front might have a chance to survive a while. Now the last few runs of the Euro have had a very narrow warm sector near the surface low and once any storm crosses the warm front, it's going to be going into air temps that won't support tornadoes or really much of any kind of storm.

 

[JamesCaruso]

It would be interesting to note how many chasers from outside the Alley have altered their chasing schedules to accommodate for the drought conditions? It seems the last week in May and the first two weeks in June have become more popular?

I posted my strategy in the “...worthy tornado day” thread so don’t want to bore anybody again here but to answer Warren’s question....

Short answer is I am NOT changing my schedule. I am sticking with my usual strategy. I have a little flexibility but not much. I can take a 2-week chase vacation but I keep a roughly 3-week window open. If week 1 of my “window” looks good then I start my trip. If week 1 does not look good, I delay my departure until it looks active. This way I start on a good pattern and don’t waste any of my available days by starting the trip at a bad time. No matter what the weather, I still head out by the time week 2 of my “window” begins, so that I still get a full 2 weeks on the Plains before the end of my 3-week “window”, which is usually pretty much a drop dead return date for me.

This year my window is 5/14-6/2. So if things look great that first week I’ll be out from 5/14-5/28. Or if the week of 5/14 doesn’t look good, it may be 5/19-6/2. Or something in between, for example 5/17-5/31.

I am already thinking I will probably end up on the later end of this, and I like that better anyway. I always feel like I am leaving something on the table if I come back before May is over. I like having at least a couple days on June. But I would also hate the feeling of missing the end of May. An all-June trip (e.g., first two weeks of June) just seems too late to me and leaves way too much on the table. I have never had a ton of luck in June. Admittedly there are some years where late May and early June are both uneventful and suddenly there is some significant event in mid June, i.e. Pilger or Aurora. But I wouldn’t want to build a trip around that expectation.

Let’s face it, us chase vacationers are always going to miss stuff and be subject to the luck of the draw no matter what we do.

 

[Paul Knightley]

It's interesting that @Jeff Duda mentioned 2013 above - the last comparable major SSW event was in 2013, although it occurred earlier - early Jan as opposed to Feb. However, the effects are similar, of course: southwards displaced jet, lots of high-lat blocking at times, and a prolonged end to winter across the landmasses of the N Hem (we've been having a cold time of it here in the UK). The effects of this will continue to wane from now on.

 

[Todd Lemery]

On my earlier post I said that the decision to head South is based primarily if there will be moisture in place. I should have pointed out that it takes the moisture being in place a minimum of three days to plan on heading down. It’s a really long drive for only one or two days of chasing...

 

[John Homenuk]

High latitude blocking remains very stout on most forecast model guidance through the end of the month of April. The proverbial paint from the stratospheric warming event back in February is certainly still dripping, as the stratospheric/tropospheric coupling has led to dramatic effects. This is almost a 30+ day period of higher than normal heights in the Atlantic higher latitude on rolling averages, obviously with the climax in March when the NAO bottomed out near -5 SD.

Nevertheless, we can use the pattern evolution now and roll forward some analogs over the next few weeks to at least get an idea as to how these things have progressed in the past. I am most interested in 1962 and 1958 as a whole, as they were both analogs heading into DJF and remain relatively strong analogs now - with the ENSO state, Pacific evolution, and higher latitude pattern. Both of these months featured an expansion of ridge heights in the Four Corners during the month of May, both both also featured "opportunities" for severe weather opening up from the tail end of May into early June. 1962 I believe had an event of significance near Memorial Day.



As we all know, analogs are only a small piece of the puzzle. We can use them to get an idea how the patterns with a similar atmospheric base state have progressed in the past, but they don't offer much in terms of definitive long term forecasting ideas. We have to piece together the forecast based on observations from the past week or two and move them forward using the analogs as a tool. When we consider this, I will be keeping an eye out for a pattern "shift" that allows for more ridging to develop in the Intermountain West during May. While such a development would be a thorn in storm chasers sides, it is the transition period that will be of interest to me.

I wanted to take a moment also to talk about the upcoming severe weather event anticipated around Day 3 -- the MJO is smack in the middle of Phase 2. Matches up quite nicely with the Roundy research that has been floating around. If you haven't read that paper, I strongly recommend it. There is some astounding research available that connects larger outbreaks and tornado activity to the MJO Phase 2 RMM.



Anyway, I digress. Over the next few weeks, it will be critical to monitor the state of the Tropical Pacific and higher latitudes. I think the overall potential for widespread severe weather activity will remain low. Warm sectors should be modulated by deeper troughs which will be persistent across the Eastern and Northeastern United States, often even progressing into the Ohio Valley. The NPO Ensemble forecasts suggest a brief jet retraction centered around Days 7-10. This will be juxtaposed with MJO weakening and stalling in Phases 2/3 so there is some support for Western USA troughing anomalies during this time.

Still, as evidenced by the above graphic, even the jet retraction itself should be short lived - and the troughing to the Northeast should limit moisture return and warm sector breadth. In the longer term, it will be important to watch how the overall AAM progresses. I suspect we will see some pull back in high latitude blocking by 5/5, which should open the door for more plentiful severe weather opportunities by the second and third week of May.

 

[Jamie G Cox]

How would I find that paper John?

 

[Jeff Duda]

How would I find that paper John?

I suspect he's referring to this paper, which I referenced in a post last year: https://journals.ametsoc.org/doi/full/10.1175/MWR-D-12-00173.1

 

[John Homenuk]

I suspect he's referring to this paper, which I referenced in a post last year: https://journals.ametsoc.org/doi/full/10.1175/MWR-D-12-00173.1

Correct - Thank you Jeff!

 

[Warren Faidley]

I guess the "light at the end of the tunnel" is that the GFS has begun a favorable trend of bringing RH back to a quasi-stationary, seasonal position in the Southern Plains region by about April 20 onward. This is the first time the GFS has done this so far this season. This is one thing I like to see by late April.

 

[Jeff Duda]

I posted this on Twitter last night. Thought it spelled out the odds of a successful southern plains chase season fairly well.

Consider it a neighborhood forecast akin to an SPC convective outlook - apply a 40 km radius around the contours. That means Childress, Amarillo, Hollis, Enid, Wichita...yeah...stay home.