Quincy

There are failure modes for sure. If there’s too much convection too early, that would also throw things off. To get a major outbreak, the needle really has to be threaded just right. Low-level instability is one limiting factor. I’m mostly concerned because global and mesoscale models alike show CI in the unstable/highly sheared warm sector, which is what you’d expect to see during an outbreak. How high will the ceiling be? We’ll see. I’ve been burned for being too bullish on occasion. All it takes is one... Let’s hope that for the sake of the local residents, this does perform below expectation.

6.8 C/km is the average 0-3km lapse rate for significant tornadoes: https://www.spc.noaa.gov/publications/mosier/2018-JOM1.pdf Taken verbatim, the NAM shows 6-6.5 C/km lapse rates with around 100 J/kg 3CAPE through much of the risk area. Given the wind profiles, that’s definitely supportive of strong, long-track tornadoes. Maybe if the low-level lapse rates were steeper we’d be talking about a historic event. I would not go there yet, but I think to argue against a tornado outbreak at this stage is a stretch.

Uh, that’s a sounding from hour 59 in NW Mississippi. I see plenty of warm sector CI by 19-20z. (Including cells directly over the 33.82, -88.65 data point at 23z if you look closely. I would normally advise against detailed sounding analysis of the 59hr 3km NAM, but FWIW:

It’s a convectively contaminated sounding at 23z that’s near a squall line associated with a cold front. The NAM shows multiple rounds and areas of warm sector storms, to the east and several hours earlier. I don’t think low-level lapse rates are a big issue here. The models show a relatively uncontaminated warm sector around 18-21z. You can get QLCS tornadoes even with the surging cold front, but I’d be more focused on the warm sector and any pre-frontal trough.

CIPS analogs show a relatively high correlation with tornadic events based on the 00z GFS. 4/27/11 is #2 and yes, some other analogs are much more tame. Percent of analogs with at least one long-track tornado:

I think it’s more about placement. To be clear, I’m not seeing any significant trends with respect to speed and orientation of trough amplification. It’s more about a gradual westward tick. Hopefully that makes sense. I’m trying to make sure I don’t get too hung up on specifics either.

Want to try to not get too specific on details this far out, but the synoptic signal is there for a potentially higher-end event. There are some key differences, but 4/27/11 is ranking as a relatively close analog at this stage. Speaking of details/trends, the GFS/Euro have been trending a bit slower and to the west. That’ll be something to keep an eye on, which may put AR/LA more into the action, as opposed to AL and areas farther east. If the system slows a bit and remains more neutrally tilted as opposed to negatively tilted, that’s setting off more alarm bells. The shortwave is looking somewhat more progressive and compact than some historical major events. 4/27/11 and 4/28/14, for example, were more amplified with upper level lows cutting off. If the progs are correct, a northwesterly 100kt 500mb jet will spell trouble. Remember your MS vicinity climo. Mean MLCAPE for tornadoes is only ~500 to 1000 J/kg and 1000 to 2000 for significant tornadoes. Global models and longer range NAM get you into the latter camp. Wind profiles speak for themselves, very impressive at face value. Global models showing a string-of-pearls QPF signal ahead of the cold front is alarming, especially if there is a pre-frontal trough. I try to not look at forecast soundings too much, but a warm nose/cap around 850-750mb during the first half of the day would suppress precipitation and with cooler temperatures aloft penetrating, that’s why you’re seeing seasonably large instability profiles. Summary: Don’t get hung up on details. The synoptic signal is alarming. Watch for a slower/westward trend.

Is central Iowa going to explode soon?

The LSX / STL area vertical wind profile has improved quite a bit as the low-level jet has started backing.

Which is what we’re just about seeing now:

Better lapse rates aloft will help to some degree, but time will tell soon. High res guidance shows surface temps spiking up over the next 1-2 hours, so we’ll find out soon if that verifies.

Ugly veer-back signature in the wind profiles right now across central Illinois. Think the early convection played a role. High res guidance does show improvement with time and that jives with mesoanalysis (better wind profiles advecting in from MO). It’s going to be a few hours before kinematics support sustained, organized severe storms in IL.

It’s an ever-evolving setup, but I see two main areas to watch based on morning trends: 1. Eastern Iowa closer to the surface low. While low-level moisture and surface heating may be less impressive than areas further south, steeper mid-level lapse rates and stronger low-level shear should compensate. 2. West-central/central Illinois on the southern flank of lingering convection. Here, dew-points are likely to be in the mid to upper 60s. Despite less impressive lapse rates than points NW, stronger surface heating and quality low-level moisture should yield moderate to seasonably large instability. Low-level shear is a bit of a grey area, as models show less here, but one wonders if a reinforced warm frontal boundary in the wake of ongoing convection may help with locally enhanced SRH.

Beware early day convection... I was a bit bullish last night. Not going high risk was the right call. Convection over the Ozarks is on a trajectory to move into central/northern IL by late morning and midday. The area most consistently progged to have the best environment may actually be southeastern to east-central Iowa. The area is aided by limited convective overturning and some dry slotting as the surface low winds up in the Missouri Valley. I could still see multiple scenarios yielding some tornado potential in northern Illinois: 1. Mixed/messy storm mode, but still a threat for embedded supercells. The tornado threat here would probably be more short-lived as the instability field is fragmented and/or storms interact with each other. 2. “Last minute” storms fire near sunset in a broken, arcing line. Models have gone back and forth with this, but it’s still a possibility. With respect to Chicago... I wouldn’t completely call off a tornado threat, but the combination of convective overturning and their easterly displacement from the greater risk zone leads me to believe they’ll probably dodge a bullet here.

Oof. Granted it’s mainly 12z/00z data, but SPC climo doesn’t show any >63F RAOB dews at ILX until early April. For DVN, there are none until May. https://www.spc.noaa.gov/exper/soundingclimo/

FWIW, NSSL WRF has some of that early day, elevated junk, then initiates across south-central/southeastern IA by 21z. To the east, it barely convects at all in NW IL until around sunset. A key difference with the HRRR is that it shows a trough-like feature ahead of the cold front, that initiates convection earlier and slightly farther NE.

Local obs:

I didn’t realize there are already fairly widespread 66-68F dews across southern IL. Sure, the warm front may have trouble making much northward progress prior to midday, but dews in the mid to upper 60s in the warm sector look quite likely, barring some unforeseen massive junkvection in the morning.

Verbatim, it keeps the warm front down around US-136 through about 19-20z. A lot of that early convection quickly advances over the warm front. Elevated convection/hail threat. Dew points are about 3F lower than the HRRR, but the parameter space around the NE MO/SE IA/NW IL area is still highly supportive for tornadoes.

The synoptic signal is strong. Mesoscale and global models more or less in agreement that there’s at least modest destabilization ahead of the cold front. Even with the HRRR being a bit overdone with dewpoints, it still yields an eerily volatile setup. With low LCLs, fast storm motions and large low-level instability, expect multiple long track tornadic supercells. It’s hard to imagine this not going high risk, in my opinion.

There may be a slight SW nudge, but if I’m looking at the data correctly, it looks like the occlusion process is slower/delayed. Testing this image embed:

There has been a subtle trend from a model consensus of slightly slower/southwest. I think northern (possibly central) Missouri may be in play here more so than areas north of DVN. The HRRR is not backing down. In terms of warm sector moisture quality, the latest HRRR brings 67F dews to I-70 in Missouri by 15z. Assuming that warm sector is largely undisrupted, the result is impressive low-level moisture and instability for such a kinematic environment.

That ABR sounding looks insane with the severe weather parameters, but what stands out to me is relatively weak/sub-marginal winds in the mid to upper levels. Particularly 700-500mb, where winds are <30 knots. The 00z BIS sounding is arguably more impressive, but it's in close proximity to the cold front. It showed a large capping inversion, but even stronger deep layer year. Another thing to note is that >30 knot deep layer shear is not uncommon at all in the Northern Plains in late June. In fact, sounding climatology suggests that mean 0-6km shear for 00z 6/30 at ABR is 35 knots and 38 knots at BIS. One of my favorite times of year and places to storm chase would be the Dakotas in early to mid-summer. The ABR low-level lapse rates are not bad, but near-term point forecast soundings for the enhanced risk zone in central/eastern North Dakota show relatively weak 0-3km lapse rates of near or <6 C/km. It looks like there was no sustained convection in the area until just the past hour when a storm initiated near Jamestown, ND. Even that storm is struggling at this point. One of the issues with the Northern Plains this time of the year is that cap busts are fairly common. All you need is extreme instability to juxtapose with marginal/modest shear to see severe weather parameters go off the charts.

The 5% tornado threat area did not produce anything tornadic, but I was able to witness this supercell in north-central Kansas, in Courtland, last night:

There may be some elevated severe potential toward the middle/end of next week as a more robust jet is progged to eject into the central/northern Plains, but until then the pattern appears relatively quiet for mid-June standards. Given the orientation of a trough across the eastern half of the country, it is noteworthy that the southern Plains, south of I-40, will see some severe threats today and tomorrow. Areas near the Red River are well past their peak season and usually don’t have much severe activity this late in the year.