2018-05-03 EVENT: IA/NE/KS/MO/IL/OK/TX

[Dean Baron]

This is understandably overshadowed by today's setup, but the SPC has upgraded Thursday 5/3 to an enhanced risk for parts of IA/NE/KS/MO/IL.

Looking at the models, the low finally starts to move east tomorrow, with the center of the low roughly over Omaha by 21z, with a warm front stretching off to the northeast and the dryline to the south. Surface winds near the triple point don't look nearly as nice as they did on Tuesday, with more of a southwesterly component to it.

The biggest complicating factor appears to be ongoing clouds/precip throughout the day in the warm sector. The NAM and 3km NAM still want to recover temps to the mid 70's to near 80. Obviously, it is impossible to forecast how this will actually play out, and it could be one of the biggest ingredients for tomorrow's forecast. The more sun we get the better. If clouds and crapvection stick around too long, there won't be a ton of instability.

For now, the NAM and 3km NAM want to break out storms in southeast NE, southwest IA, and northwest MO around 21z. Unlike Tuesday where the best shear came in later in the evening, Thursday's storms should have the best opportunity for a tornado right after they fire. However, models want to go linear pretty quickly, with a broken line by 00z.

LCL's shouldn't be a problem, with mid 60 dews pretty common, possibly approaching 70 where moisture pools along the fronts.

Not sure if I will be out tomorrow or not, but right now I would be thinking about targeting southwest IA, perhaps starting off in Nebraska City, NE which gives me access across the river. Fwiw, DMX is more impressed with tomorrow's setup based off of their forecast discussion.

Also, I have attached a forecast sounding for southwest IA tomorrow around 21z. Don't let the PDS tornado hazard type fool you. A lot of times when the atmosphere is primed for a strong squall line, forecast soundings show a PDS tornado hazard.

 

[Royce Sheibal]

The NAM doesn't seem to be handling the ejection of the low very well Thursday. The 12Z NAM today has the surface low located in NW KS at 12Z....and suddenly passes it all the way to SW IA by 21Z, 300 miles in 9 hours, after having not moved more than 300 miles in 3 full days. The EURO/HRRR/NAM3KM/GFS are all holding the low much further back into NE, but then the GFS diverges. It predicts precip will ruin the warm sector and a very low-key day. The others including CAMS show a clearing, with nice heating and moisture return just ahead of the TP.

One thing all of the models today do have in common is long and fairly straight hodos. So if we do get some action on the TP storms will be splitting like mad and moving pretty fast. Tornado action will be most likely within a short time after initiation, as the SPC mentions. Further east along the warm front hodos get a bit more exciting, so N MO/ S IA could have some potentially higher TOR threat, but it seems fairly conditional upon recovery after the morning round of storms, of which all of the models are fairly certain.

One mandatory mention: The massive vort max over the rockies will finally release tomorrow. This is a huge complicating factor, as a solid vort max can potentially turn a pea-size hail worthy storm into a baseball machine, and a bird fart into a drill bit. If storms do go tomorrow in relation to that vort max, I would expect a short burst of significant severe weather for a couple of hours.

We could see an upgrade to a moderate for tomorrow, or we could see a hold on ENH, mainly for wind / hail. I doubt I'll be going out, as anything in my area E NE/ W IA will be quite hard to predict / chase / spot. S IA would be a better trip for those of you on a chase-cation.

 

[Quincy Vagell]

One key wildcard that I'm interested in is any favorable outflow leftover from overnight/morning convection. There is reasonable support from multiple models/ensembles that outflow may be evident from southern Iowa/northern Missouri into central Illinois by midday Thursday. While there is some potential for semi-discrete (perhaps discrete for a time) storms along a cold front in eastern Kansas, an intriguing scenario would be for isolated storms farther east in the warm sector.

Iowa gets a cringe from many chasers, but it does perform on occasion. Too bad it seems like it tends to perform when least expected... Additionally, a boundary in Illinois can also get overlooked by non-local chasers as well.

It's still early and convective trends tonight will play a key role in resolving details for tomorrow's threat.

 

[Royce Sheibal]

Latest HREF run: Looking pretty solid. E Neb lights up first with some moderate UH but low STP cells, might be low-topped fast moving mini-supercells. Further east into IA things light up a bit later. Note the strong absence of storms in S KS and OK.

 

[Dean Baron]

You guys make some good points about the TP. The 12z NAM is quite bullish along the warm front in southern IA. Temps only rebound to the mid to upper 70's by late afternoon but the NAM still throws out MLCAPE values in excess of 2500. The biggest thing that caught my eye is how much more backed the surface winds are in south central Iowa compared to farther west along the TP. Both the 12z NAM and 3km NAM max out supercell composite and STP along the IA/MO border by 21z. It's unfortunate that this is all dependent on how things evolve overnight, and we won't know much until tomorrow morning (or even early afternoon).

 

[Quincy Vagell]

Not too much clarity for tomorrow yet... It may be one of those events where you just play with the target that's closest to you. While I was originally intrigued by the potential outflow boundary play from southern Iowa into northern Missouri/central Illinois, the setup over eastern Kansas seems to have the greatest model consensus for potential. Also, after a lot of driving the past few days, the last thing I want to do is to commit to driving all the way to Iowa, only to miss storms in Kansas. Not to mention there has been a very subtle westward trend with the setup and the 850/500mb crossovers (eastern Kansas) indicate better shear than some model progs from earlier today.

I still think that northern Missouri (possibly southern Iowa) is a good play, albeit somewhat conditional. If one goes with northern Missouri, be ready to adjust (probably south or southwest) if early day convection is too overwhelming to the environment. Some remnant boundaries are likely, but I would tend to think that this area will have more sporadic/localized severe, rather than something more widespread. There's also the plus that models show near-surface winds backing around to southeasterly.

Unless there is stronger surface heating (limited morning convection) than progged, I don't see a strong case for Illinois at this point. With that said, if you live in that area, it would be silly to drive somewhere else. Even if boundary layer heating is minimal, I'd expect at least one or two boundaries to come into play, offering at least a conditional or localized severe threat.

Eastern Kansas is probably the safest play --- accompanied by better chasing terrain and a decent road network. Convection allowing models seem to like at discrete/semi-discrete storm modes and show several cells firing. This may be due to the dryline potentially remaining ahead of an approaching cold front, keeping multiple initiating boundaries in play. Buoyancy also looks primed here with at least 2000-3000 J/kg CAPEs. Even if the wind fields aren't perfect, strong instability can overcome that, to some degree. Deep layer shear vectors are actually close to perpendicular to the dryline, based on the latest HRRR guidance. Shear with the cold front is decent too. The only issue might be storm interactions, given the amount of cells that may fire, coupled with some slight flaws in the wind fields. (hodographs are long or at least a bit jagged across much of the area)

The eastern half of Oklahoma is game as well. Maybe you're from the area and don't want to stray far for another chase. The terrain isn't ideal, especially with eastward extent, but storm initiation should be more sparse here and strong boundary layer heating is likely. Any cells that do initiate could mature very quickly. LCL heights look favorable too. I guess you could lump northeastern Texas into this region too, but the terrain down there is just as bad, if not worse in spots.

 

[Quincy Vagell]

Update:
Morning convective trends are not very favorable. Ongoing rain/storms from Oklahoma into southeastern Kansas and Missouri are going to substantially limit boundary layer heating later today, particularly from far eastern Kansas and points eastward. The convection also seems to play a role in disrupting mid-level wind fields. The result is messy hodographs across much of the 06z day 1 enhanced risk area.

There still is at least some severe potential over the lower Missouri Valley later this afternoon as the boundary layer attempts to recover. It's just a glaring red flag that southerly near-surface inflow will be disrupted by ongoing convection. Nonetheless, deep layer shear should remain quite favorable and a narrow zone of enhanced low-level vorticity near/just ahead of a surface low in the southeastern Nebraska vicinity could result in sporadic hail and a few brief tornadoes.

There could be some action farther north/northeast in Iowa along a warm front, especially if low-level wind fields are not disrupted much by earlier convection.

Any potential along the cold front/dryline seems conditional at best. While latest guidance suggests a narrow plume of moderate instability may be realized from eastern Oklahoma into southeastern Kansas, the signal for convective initiation is trending downward.

 

[Royce Sheibal]

Ladies and gentlemen, welcome to your annual Mini-Supercell Appreciation Day in Nebraska.

Low Cape, Shallow Shear, Insane Vorticity, what else do you need? Expect a good chance of numerous short lived bird farts and maybe a few photogenic twisters from these low-topped non-mesocyclone storms. And because they lack an easily identifiable meso, they are very difficult to spot on the velocity radar. Here's a nice HREF that shows the type of potential today could have. Good luck and good hunting. You might even catch a real supercell or two way out near Ottumwa if you are lucky!

 

[Dean Baron]

This is looking like a pretty marginal day even in Iowa, at least from a chasing perspective. Models are in pretty good agreement that there will be a lot of precip breaking out this afternoon across southern IA. Not saying there won't be tornadoes, but it will likely be a low contrast grungefest. Certainly not ideal for chasing. On top of that, I am not seeing a ton of strong updraft helicity swaths for this afternoon/evening. I am opting out of today's setup. There will be better setups soon.

 

[Jeff House]

VIS and surface show an outflow boundary OFB approximately through St. Joseph, MO as of about 19Z. Personally I'd favor the OFB over the synoptic WF in Iowa; but, the somewhat veered LLJ may require the more backed surface winds on the WF.

Chasing is not all about highest prob. of tornado. Also need it visible; so, I'm forecasting for the OFB in Missouri. Said OFB extends back into extreme northeast Kansas. Appears to intersect the slow moving synoptic cold front in far northern Kansas. Dry line DL is trying to poke into central Kansas. However I do not forecast an OFB/DL intersection today. Might have to just settle for the OFB just east of the synoptic front and low press.

Well, we all know today had challenges right out of the box with the MCS/MCC wash-out. I'm surprised dews recovered this much. If the LLJ is not totally disrupted by storms well south (OK on TOP 12Z) there is a small chance. 5% strong!