Total Miles: 350
Tornadoes: 13 (just kidding! 0)
Garden Showers: Heavy
Both Wednesday April 17th and yesterday the 18th I went out to the IN/IL border to chase some “storms” and both times I came back with little to show for it! This is the reality of storm chasing! Sometimes you drive a long way and/or sit in the car for hours to watch it rain, or sometimes even stare at blue skies. Wednesday’s bust didn’t come as much of a surprise, but Thursday was more of a let down. I’ll cover each day individually:
This setup was very similar to a week ago, in that it was a warm front play, with halfway decent wind shear and instability. One issue, however, was that there was no surface low near the target area, so forcing for ascent was reduced. Indeed, my biggest concern was that there was nothing to initiate storm development. While I had originally planned on leaving the house around 12 or 1, I ended up staying and looking over each model run (which got progressively worse), and didn’t leave until 4:30. I was actually considering going fishing instead, but then came an MCD, and later a Tornado Watch, so I decided to just go to Covington, IN and sit and wait. There were some elevated storms north of the boundary, and from the sounds of the discussion they expected the warm front to continue to push north, eventually putting these storms in the warm sector, allowing them to intensify.
I don’t consider myself to be an “SPC chaser,” however I realize that they have MUCH more education and experience forecasting than I do. At the same time, I realize that their forecasts are for the general public, and not for storm chasers. We each require a little different forecast. In my mind, the tornado threat was certainly not zero, but it wasn’t a whole lot more than that. Hindsight is always 20/20, so it’s easy for me to say now that I shouldn’t have chased. However, I’ve missed tornadoes close to home in the past in marginal setups, so I made a promise to myself not to do that anymore! Even with marginal threats, if it’s with a couple hours of home, I’ll be there!
So long story short, a few storms did develop, and produced some decent hail, though I was not in position to intercept the hail. The storms were mainly elevated, and I suspect that they were initiated by an outflow boundary from the cold sector convection. Updrafts were not very strong, likely as a result of weak forcing, as well as weak instability. A decent amount of shear allowed the hail to form, but the tornado chances were clearly limited as the storms developed. I watched some lightning as the storms moved off and dissipated after dark, then went home.
After getting back from Wednesday’s bust, I immediately went to the models to check out Thursday’s potential. I had pegged it a couple days earlier as perhaps the better of the two days. Indiana was under a Moderate Risk at this time. I woke up Thursday morning to see a 10% hatched swath covering most of the state, and extending further south into AR/MS. The tornado threat, I felt, was still conditional, however. In order for tornadoes, there really needed to be discrete supercells, or at least semi-discrete cells embedded in the line.
A squall line had developed overnight from storms further west, and had already made its way to central IL early in the morning. The cold front was trailing behind it at this time in MO. I arranged to get off work by 9 am, and when I got home to look at the models, there was already an MCD out, and shortly thereafter a PDS Tornado Watch! Woah! I had not expected that! From my analysis, it looked like the greatest threat wouldn’t be until the late afternoon/evening hours when the cold front actually came through. Based on the SPC discussions, they expected the squall line to intensify, and perhaps discrete cells to develop ahead of the line. It didn’t happen. The whole day we saw nothing but rain!
I read a few comments from people talking about how over-hyped the storms were, and I agree. I didn’t think there was a need for a PDS watch. These are typically reserved for events where the forecaster has high confidence in multiple strong or violent tornadoes in the watch area. The last time we had a PDS watch in Indiana was March 2, 2012; the Henryville EF-4 tornado. Conditions were MUCH different for that event, and the PDS watch was certainly warranted.
So what happened? I had my ideas, but posed this question on the Storm Track forum to get answers from more knowledgeable chasers/meteorologists. Pretty much everyone was confused as to why they issued a PDS watch, and as someone pointed out, the PDS portion was quickly taken down (I hadn’t noticed this, as I never went back to the watch page).
One of the reasons why storms never intensified is that there was not a great deal of instability in the atmosphere ahead of the squall line. It went through early enough in the morning that daytime heating had not really taken effect yet, even though it was quite muggy in the morning hours. I think that they expected the cloud cover to break up more, and surface heating to increase. It actually was sunny in Indy at 9 am, but the clouds were still around, and they never let up. In fact, I think the cloud cover got thicker. As a result, instead of the line intensifying, it actually weakened.
I looked at the mesoanalysis after the watch had been issued, wondering if there was something in northern IN I had missed, as my plan was to go toward Evansville, since this area was showing the best veering winds later in the day. I didn’t see anything on the analysis to change my mind, so even with a PDS watch extending all the way to the MI border, I eliminated everything north of Indy at that time. I was still in hopes of some clearing in the cloud cover to the south, where the line was further west. So I went out to Terre Haute, where my plan was to wait, and then adjust south if need be, or just catch the line from there and continue to drop south to catch the next area of interest as the line proceeded.
Back to the conditions, even without a lot of instability, a highly sheared environment can still produce strong tornadoes. However, data was not showing the strongest shear over Indiana, and adequate shear was not set to enter the area until at least late-afternoon. The area of the strongest shear was actually behind the cold front. Another issue is that the 500 mb jet was running parallel to the cold front. In contrast, on March 2nd last year, the 500 mb jet was bisecting the cold front (thanks to Skip Talbot for pointing this out). Storms were also along the cold front on that day, instead of well in front of it.
To put it in terms most of you will understand, the environment was just too stable for strong storms to develop yesterday. Even for high winds, which is essentially a strong downdraft, there needs to be a strong updraft. In a stable environment, with no forcing mechanism to get air to rise, it just wasn’t possible for severe storms to develop.
So why did the SPC hype this event up so much? Why had they not seen these parameters not meeting the criteria needed for severe weather? That I can’t really answer, but perhaps there were some pieces to the puzzle that were nearly in place for a significant severe event to happen. Had there not been that squall line in the morning, perhaps it would have been clear and sunny all day, and storms would have formed along the cold front where they would have had a much better chance of reaching severe thresholds. That still doesn’t really explain the PDS watch, but I honestly have no idea what they were thinking. I guess all I can say is they will always play better safe than sorry, as in recent years there have been a number of deadly tornado outbreaks in the US.
Looking ahead, there is really nothing of interest in the next week or so as of now. The colder than normal pattern has played a role in limiting the amount of severe weather events so far this spring. I’m okay with next week being quiet, as it’s my last week of work. The week after, however, I have off as a planned week (or at least a couple days) of storm chasing. I sure hope I get the opportunity!