Quincy

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.

The overall pattern looks unseasonably quiet across the Plains through at least the next 5-7 days. This is reflected well by the CFS severe weather guidance dashboard, which has blue boxes in the coming days, something that is very unusual for early to mid-June. The Northern Plains area into the Upper Midwest may see some severe thunderstorm activity this weekend, as a trough ejects eastward. What happens with that trough next week is the glaring issue. Medium-range guidance and ensembles are fairly consistent with broad troughing across the Missouri Valley/Midwest/Great Lakes vicinity through much of next week. In uncharacteristic form for mid-June, instability appears limited through at least the middle of next week and possibly the end of the week as well. Northwest flow events tend to become more common into July and sometimes even mid to late June, but with modest instability, at best, that does not bode well for severe thunderstorm prospects via NW flow next week. As we approach next weekend, there have been signs that the pattern shuffles and there could be a return to at least near average severe thunderstorm activity for the third week of June. European ensemble data and the weeklies, to a lesser degree, show a more zonal flow-type pattern across the northern tier of states by next weekend or early in week 3. (roughly the June 15-18 window) The potential may exist for one or perhaps a few shortwaves to impinge on the northern High Plains/Northern Plains vicinity with an uptick in severe potential there. This is also highlighted by the CFS dashboard, although it does not take much in the way of wind shear to throw blanket regions of elevated SCP values in June when there is seasonably-typical instability in place. (The CFS dashboard is based on supercell composite parameter / SCP values, either over a broad area or elevated in any area) On the other hand, the latest Euro weekly data seems to imply that any pattern shift is short-lived and that more Upper Midwest/Great Lakes troughing could set up by the middle or end of June week 3. As we go deeper into June, the Great Lakes/Midwest vicinity could experience northwest flow severe threats, but that type of pattern needs instability in place. The trends suggest that moisture is going to be scoured south and east (quite a feat for June), even when there is appreciable upper level flow in the northern states. Who knows, maybe that could result in an unusual late season threat across the Mid-South, but that's speculation on an already conditional scenario. Any way you slice it, the prospects for severe thunderstorm activity in the Plains in the near future are very slim. Sure, you can get some High Plains magic here or there, but that's to be expected, even in the quietest months of June. I'd be cautiously optimistic about prospects for June week 3. On the bright side, that period (June 16-22) has featured some significant events over the past decade. Almost each year seems to have at least one noteworthy event in that window, but we'll see.

In all honesty, the moderate seemed a bit overdone. It's a very complex setup and it doesn't take much to throw a wrench in higher-end potential, especially with a seasonally anomalous setup so far south. On the bright side, drought areas have and should continue to get drenched with much needed rainfall.

You do realize tomorrow was upgraded to a moderate risk? Granted it's not looking like an outbreak of discrete storms, but significant severe seems likely given the degree of shear and instability expected.

The low-level jet signal is pretty intense given the latitude this late in the season. Yes, there's some convective feedback, but LLJ is progged to reach 50 knots by 03z (near the solstice, that's only an hour after sunset around here) all the way down into Oklahoma with 50-60+ kts in Kansas. Have to imagine a big wind producing convective system evolves late, but earlier day is more of a question mark. It may be a convective mess with the degree of instability with storms just firing all over the place. Who knows. I can't say I've chased long enough to see a similar setup south of I-70 in late June. It will be interesting, but this year especially has taught me to not get too excited about a forecast two or more days out. The fact alone that we're seeing noteworthy upper level flow this far south for 2-3 days is intriguing. Beyond this weekend, such flow (probably even stronger) looks to return for much of next week from the northern Plains to Upper Midwest/Great Lakes. The severe season is not entirely over... yet...

The season is cooked for anywhere near/south of I-70. Mega death ridge reigns for the next 7-10 days, but the pattern could favor some AOA severe activity from Idaho/Montana/Wyoming into the Dakotas. The week two period favors more Great Lakes troughing, so that would tend to suggest an MCS/derecho pattern from the Upper Midwest into the Lakes vicinity.

There's pretty solid reliability in the end of May. Even in a bad year, odds favor that more than half (sometimes all) of the days should feature at least something worth chasing. This year has been abysmal for tornadoes, but there was the Wyoming event yesterday and several other days have featured supercells and "interesting" storm structure. The window during which one chooses to go on a chasecation does seem a bit risky. If you go before the final week of May, odds increase that there will be several down days and possibly a busted period. Go before May 15th and you're doomed, unless you get really lucky. Wait until June and while the ceiling may be higher for at least one or two higher-end days, there's also increased odds that there will be down time. I guess if tornadoes are all that you're after, it's a bit risky. At least it has been this year and last year as well. Unless we're really moving into a new pattern (I doubt it), late May is king and produces well in the vast majority of years.