2015-04-19 EVENT: AR/IL/IN

Looking at the 12Z NAM and noticed that Arkansas really looks pretty decent for Sunday. Lots of Caveats including terrain and instability orientation of SW to NE but there are some decent looking forecast soundings to the south and east of Little Rock around 00Z.

The closed low looks to be absorbed by the sub tropical jet sunday morning as it drifts east, providing good ascent over Arkansas Sunday evening. Moisture looks to be good with mid 60s dews into Arkansas with moderately good lapse rates in the 7 to 7.5 range.

Right now I'm eying Stuttgart, AR

20150417-SGT-60hr-NAM.png
 
I've had my eye on the northern (surface low) play of this setup. As the wave ejects, a modestly-diffluent left exit region of the midlevel jet streak is juxtaposed over the SE quadrant of the deepening surface low in southern Indiana. The main problems currently shown by the NAM and GFS is tons of precip/storms early in the day, and that the surface low races off to the northeast, outrunning the moisture by mid-afternoon before it can pull any juice into that 0-1km helicity sweet spot east of the low. If the low can slow down in future runs and entrain more of that moisture northward, I believe this will be a classic Midwest surface low "sleeper" day. I'd agree that Arkansas will be a better bet for more robust updrafts/higher instability, however the weak/veered surface winds currently shown down there would have me concerned.

EDIT: added IL/IN to the title
 
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Actually much of the terrain east of LIttle Rock is quite good. Along I-40 east of Little Rock and generally southeast of U.S. 67 north of 40 it is pretty flat and not too many trees. I have not chased very far south of 40, but suspect most of that area is pretty flat, too. North-central and western AR are terrible terrain, but the eastern part is quite good - much better, for example, than most of OK east of I-35.
 
Still seeing some nice soundings depicted in SE of Little Rock and in the MS delta tomorrow afternoon in the 21-00Z time frame... but I don't love the prospects for even getting storms in that area. Feel like the most probable area for convection will be pretty far back west and forced right along the cold front, and wind profiles are entirely unidirectional in this area. Probably a forced line with an appreciable wind threat.

If storms do form further east, they will be in a good environment and I wouldn't doubt some nice supers capable of a few tornadoes.

Not sure on whether or not I'll chase this setup, it's pretty close, so odds are... I will give it a shot.
 
Tomorrow still looks great between Little Rock and Stuttgart in my opinion, with NAM depicting even bigger curved hodos than yesterday along with a bit more CAPE (Almost 3000 J/KG at 00Z at Little Rock)

4km SPC WRF is showing storms in the area between 22 and 00Z. Definitely think it could be a bigger day if we get an isolated supercell around Little Rock.
 
00Z NAM basically just confirmed that I'll be giving tomorrow a shot. Compared to previous model runs, Wind profiles have a much better directional component to them further west just ahead of the front, and some of the 0-3km SRH values are quite impressive. Unfortunately I still don't see this being an eastern AR setup at least not before 00Z, so terrain will suck.

Target for now is Texarkana, AR.

Also, I think a pretty significant after dark tornado threat may materialize 02-04z further east into western MS, as the LLJ really ramps up.
 
I decided not to give this day a go in the Arklatex due to a couple factors. The lapse rates on the 12Z LZK sounding were very poor, and the moisture depth at 12Z SHV sounding was quite shallow. The last factor was terrain if storms do fire.

The HRRR is blowing up nice supercell looking storms from about Alexandria, LA to almost San Antonio, TX this evening
 
I also chose to stay home today. The surface low has been very slow to deepen thanks to weaker than forecast upper support, resulting in a very marginal 0-1km wind profile across southern IL/IN. What's more, the areas of clearing that were evident earlier this morning on visible satellite have filled in. I think there still may be a marginal play in southern Indiana along a Indianapolis/Evansville line. The surface low should deepen along the IL/IN border in response to better upper support arriving as it lifts NE, and some greater instability has been realized upstream of that region. However, terrain in that area is rather poor for chasing once one gets 20 miles northeast of Evansville, and I don't believe it will be worth the 3+ hour drive.
 
I also chose to stay home today. Which is hilarious in hindsight, because I'm currently sitting under the THIRD discrete tornado-warned supercell to track over my town (Alexandria, LA) in as many hours. Does it still count as chasing when the storms come to you?

I've taken a couple of screenshots from my phone's radar app, and got a photo of some mammatus from the anvil of the first storm before it got too dark to do anything but take shelter.

Ah - since I've started typing this I've just found out the third tornado warning has expired. Still a couple more cells behind it, we'll see if they do any organizing.
 
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