2017-04-19 EVENT: IA/IL/MO/OK/KS

[Harrison Cater]

The last several runs of guidance is depicting at least a decent risk of some sort of severe weather across parts of the Plains and Upper Midwest Wednesday. A surface low is forecast to develop in the lee of the Rockies as soon as 18z Tuesday. . By 18z Wednesday, guidance places a fairly elongated area of low pressure over Northern Kansas with a warm front draped roughly along I80 in Iowa and Illinois. The environment south of this is characterized by temps in the low 70s and dews in the upper 60s with backed sfc winds over NW IL and E/SE IA. This yields a decent 1500-2500+ CAPE in this area and a fairly impressive 50-60kts of low-mid level shear. There is some weakness to only 30 kts evident between 200-300mb, especially on today's 18z GFS. However this is less evident on the NAM(FWIW), which has 45+kts all the way up. The SPC has outlined this in a 15% D4. Some concerns here could be due to potential capping issues and the all too familiar morning convection.

A dryline is also forecast over C KS/W OK, however severe prospects are looking a bit more conditional here due to some moisture quality concerns especially with westward extent, with dews only in the mid to low 60s. There is also SW sfc winds parallel to the boundary that may make getting organized discrete cells difficult, especially in Kansas. Regardless, at least some decent severe potential exists in this area as well.

 

[Ethan Schisler]

Will be eying this day very closely. The latest guidance is showing a very sharp warm front setting up across Southeast Iowa into Northern Illinois. I've seen these types of events associated with some pretty significant tornado episodes over my area in the past (4/30/2003, 4/19/2011...just to name a couple that come to mind looking at the data). Not saying that it will be a repeat, but shear looks excellent along the warm front along with moisture and instability and we have a developing surface low pushing up into Missouri. Definitely a favorable tornado setup as things stand if you like to play with warm fronts....I know I do . As far as an exact target, I will look at things closer tomorrow and Tuesday.

 

[Devin Pitts]

Currently eyeballing somewhere between I-80 and I-88 for a target, not sure how far west I'll target just yet for obvious reasons. GFS and NAM having a bit of trouble agreeing with the placement of the warm front, with NAM putting it further north(which would be preferable to me personally ) but it's still a few days out so a lot can change. Wind profiles and moisture look good across the board at least.

Edit: and then the 12z NAM3km has a lake breeze wiping out the warm front in N IL, pushing things closer to the Quad Cities.

 

[Billy Faletti]

Although recent runs are not quite as promising as last night's 00z runs, the NAMs still have a rather impressive combination of parameters setting up on the warm front near/just north of the I-80 corridor in eastern Iowa into northwest Illinois. As mentioned, 3km seems to be picking up on a pneumonia front pushing through the northeastern quarter of IL off the lake, which will need to be watched, as it may mitigate the threat east of I-39. This is a setup where I'm actually hoping for some morning convection given it doesn't linger, because a) I don't want the warm front skyrocketing too far north, and b) outflow boundaries in the warm sector could serve as focal points for convective development in an environment lacking much forcing. Impressive wind profiles with great directional shear along the front (given the low deepens sufficiently) combined with favorable moisture and thermodynamics pooling on it may allow for a notable, albeit conditional tornado threat if any storms can take advantage. Sharpness of the boundary may potentially limit the window of tornadic potential, but this isn't my main concern. Regardless of the caveats, you should never let your guard down on a Midwestern warm front in April.

 

[JeremyS]

I like the idea of the warm front as a potential good set up, however so far I'm not seeing any convection breaking out along or just south of the warm front by the hi res NAM or even the 12km NAM. It's keeping all the development pretty much back along the cold front. It'll be interesting to see if the NAM gets more friendlier to the idea of a warm front play. Any thoughts on this?

 

[Harrison Cater]

Setup isn't looking as good overall as it had several days ago, I have a some concerns regarding the lake front crashing down over the east, and the general westward trend of the surface low itself. The greater distance between the surface low has trended to veer the open warm sector instead of backing and now the only backing exists invof the warm frontal zone which is very narrow. Other variables include morning convection. More organized convection would likely thrust out and outflow boundary which would in turn hang up the warm front further south. Then there is the possibility that nothing fires at all, as Jeremy mentioned and advertised consistently on the 3km NAM. Looks like a fairly conditional day at this point, one I will probably decide the day of whether this is one worth going out for.

 

[Devin Pitts]

As of right now I'm looking at targeting the Quad Cities area based on the consistency of good parameters out that way on each model run. It is pretty concerning that not a single one of the CAMs are initiating anything along the front or in the warm sector period though.

 

[Royce Sheibal]

Models are all over the place with the location of the warm front and triple point. Will initiation be in SE Neb or SW IA? STP's near the triple point and warm front are getting pretty high, but there is a pretty heavy CAP issue. Triple Point near Omaha may get dry slotted. All of these things are making tomorrow look really confusing and messy. That being said, across the board, hodographs are huge and nicely curved. Chance of tors anywhere along the line for a short time.

Worst thing about tomorrow: It's my birthday, and I'll be in Grand Island (not chasing). LAME.

 

[Billy Faletti]

I'll post this because I feel my first post was a bit too hypey for the potential:

IF you can get a storm south of the warm front in E IA/NW IL due to mesoscale feature, etc, it would have a favorable environment as it crosses the front. Huge IF. I may head out for a conditional play regardless of whether or not initiation looks likely, as I live close and have nothing else to do tomorrow afternoon. Good chance I get burned, but it would hurt even worse if something did happen and I was sitting at home.

 

[chrisbray]

I am electing not to chase today. Looks like I would have to drive all the way at least to Central Iowa, as no convection allowing models fire anything along the warm front in eastern Iowa/western Illinois. I guess I will keep an eye on it still, but I am not holding out hopes for much. Front is ill defined out this way and lots of convection right now by the Quad Cities.

 

[Ethan Schisler]

Southeast Nebraska into Southwest Iowa along the warm front/triple point is looking rather prime later this afternoon/evening. Latest HRRR shows a 55 knot H5 shortwave entering SE Nebraska by 22z. Ahead of this, CAPE values have risen to 2000-3000 J/KG along with 0-1km SRH values of generally greater than 200m2/s2 along a warm frontal boundary that looks to bisect the Omaha area later and perhaps further east toward Des Moines. Getting a storm to fire, stay discrete, and move in a favorable pattern to this boundary will be the key to today. However I like the prospects that if something DOES indeed do that, we could see a strong tornado or two given the parameter space along the warm front/triple point, given the cold front doesn't muck things up.

 

[Isaac Schluesche]

My take on things:
If some semi-discrete cells get going along the warm front, I do see a definite tornado threat as well as some pretty large hail.
However, I doubt I'm going to be chasing just because of how late stuff might happen. Don't want to be getting back at 2am on a weeknight.
Might head down to Eastern IA and if stuff happens earlier, then wonderful.

 

[cstrunk]

If I were chasing today, I would have to choose from two targets. My first choice would be to start in Seward, NE and play the triple point. My second choice would be central Kansas in the Ellsworth area to watch the tail-end Charlie. The NAM and HRRR seem to highlight these areas as supercell hotspots, and I would choose to start in SE NE with it's proximity to the warm front/triple point.