Before beginning: No, not everything here will be about weather! Just maybe most of it for the next few weeks…
The final countdown is on to the departure for two weeks of storm chasing. The plan is to leave Maryland
around the crack of dawn on Sunday and head west (our South ?) [Midday update: Leaving tonight it seems. Going to be a race to Arkansas area for storms tomorrow].
In the wake of one of the greatest and saddest tornado outbreaks in recent history that has become the deadliest since the Great Depression, it sort of makes me wonder exactly why I want to go storm chasing. Being that it was the second major tornado outbreak in a month full of tornadoes, it also makes me wonder if 2011 has already shown its best hand and will bluff from here out.
The pattern is changing up a bit, at least on certain levels. The past few weeks have seen a very positive North Atlantic Oscillation (NAO) which has been shown to correlate with increased activity over the Southeast U.S. When you add in remnant effects of a La Nina (also shown to produce tornado outbreaks in the Southeast), the tale of this month and the multiple cities hit is hopefully one not to be repeated anytime soon.
That said, tornadoes hit where they hit regardless of who is watching, and I still want some storms to follow around the empty spaces of the central U.S.! Let me start the “analysis” by saying I’ve done more model watching in the day 8-16 range for this trip than I would ever do normally, as guidance in that range is a bit of a fantasy.
It’s been a roller coaster ride. Even at this late date I find myself vacillating in thought from “wow, we’re going to be busy” to “hey, it could be a cool story to tell about the quiet period of the record 2011 tornado season.”
There are some unknowns with this pattern changeup. If we go into a negative NAO, there should be a tendency for East Coast toughing, which could be somewhat problematic in that it keeps wavelengths short across the country and promotes at least temporary upstream or even West Coast ridging. So, at the very minimum, it seems the first week out there is not screaming “major” storm.
At the same time, the active jet stream partially behind all the severe weather this season appears to continue mostly unabated, with waves of storminess at varying strength and in varying positions every few days. There could easily be at least one break of 2-3 days with little to no activity, but there is other stuff to do out there… I think.
There is potentially something of interest on the way out, especially if we went the southern route. The problem is that cooler air has invaded a good portion of the country following the last big storm — at least one shot of even cooler air is ahead as the negative NAO induced Greenland Block flexes its muscle. It appears any severe weather would be fairly deep into the South and perhaps not that energetic, though it’s still evolving and models are keying in more heavily on this system now.
It’s likely that there would be at least some break after that initial system (perhaps a several day one?), though energy continually wants to spill into the northern Plains, and the models have had trouble with the strength of this energy for months now until the short range. However, it’s pretty early for activity up there, especially with the trough orientation fairly fast from northwest to southeast. Hopefully the dryline will activate on quieter days, but the drought over Texas and growing north might complicate that.
The northwest flow, as modeled, could ultimately transition into a situation where convective systems form along it as warm air begins to advect back north heading toward or into next weekend. That could provide a more generalized storm risk each day, though the storms could be fast moving, and perhaps mainly non-tornadic in nature.
There are indications that by next weekend things could be more interesting in an “outbreak” sense. The question is if it’s still a fantasy or something real. The idea of more troughiness through the Rockies and into the Plains has been pushed back a little already, from near the 5-6th to the 7th-8th, but it’s been there on many runs.
On varying runs, this trough is modeled by the GFS to dig deep through the Rockies and spawn a surface low pressure somewhere near the Texas Panhandle into Kansas before strengthening and traversing east. In a scenario like that, a significant tornado event would be possible.
Another potential scenario spit out is weaker, but consistent troughiness over the southwest and into the Rockies. This may allow for a regular feature of a weaker low pressure somewhere just east of the Rockies, which would at least promote the risk of storms through the period by drawing moisture in from the Gulf and creating instability plus some turn to the atmosphere.
The “no storm of consequence” scenario is a bridge we can cross if we get there. I’m cautiously optimistic, but perhaps slightly less so than a week ago. It could just be nerves…