CheeselandSkies Posted May 19 Share Posted May 19 ***Edit: Added tomorrow (Monday) to the thread title as there is broad agreement among the CAMS in an MCV-driven setup along the IL/WI border region tomorrow (SPC added a small slight risk to the updated SWODY2 to account for this). These events are subtle with generally modest parameters depicted beyond Day 1, but if everything comes together just right they are capable of producing some prolific localized outbreaks in this area, such as 8/9/21 and 7/12/23.*** Guidance has been in good agreement for several days now that a compact, negatively tilted shortwave will impinge upon the IA/MN/WI/NW IL region on Tuesday with strong southwesterly flow at 500mb. At the surface, a low will deepen throughout the day with warm sector dewpoints well into the 60s, if not upper 60s by 00Z Wednesday. Basic pattern recognition suggests a very high ceiling and I'm frankly baffled why SPC's day 3 outlook does not at least include an all-hazards hatched area for wind potential if nothing else. That said, strictly in terms ofchase potential, there are several potential flies in the ointment as it seems there always are. One of them is, exactly how many rounds of storms initiate, where and when? For example, models have EXTREME levels of SRH along the warm front in southern Wisconsin, but suggest late-morning/early afternoon convection preventing that area from destabilizing. Other models suggest supercells might initiate in western Iowa, but might not be colocated with the best tornado parameters until they have begun to congeal into a QLCS (of course, this was also a concern with 3/31/23). Regardless, I think this day will end up a noteworthy regional severe weather event and worthy of its own thread. 3 Link to comment Share on other sites More sharing options...
vpbob21 Posted May 20 Share Posted May 20 Might have to extend this thread into 5/22. Could be an interesting day in IN/OH if we get close to full sunshine early on. SPC has us in a 15% day 4 2 Link to comment Share on other sites More sharing options...
Chinook Posted May 20 Share Posted May 20 Given the day-3 information, I would guess that there is a significant chance of tornadoes with discrete cells in the Midwest on Tuesday. Link to comment Share on other sites More sharing options...
MidwestChaser Posted May 20 Share Posted May 20 Small Moderate risk added. Link to comment Share on other sites More sharing options...
KokomoWX Posted May 20 Share Posted May 20 ACUS02 KWNS 201759 SWODY2 SPC AC 201758 Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1258 PM CDT Mon May 20 2024 Valid 211200Z - 221200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHERN IOWA...NORTHWEST ILLINOIS AND FAR NORTHEAST MISSOURI... ...SUMMARY... Severe storms are expected Tuesday across the Midwest, especially including portions of Iowa and Missouri into Wisconsin and western/northern Illinois. Tornadoes (a few strong), damaging wind gusts, and large hail are expected. ...Lower/Middle Missouri Valley to the Upper Great Lakes... A notably strong belt of cyclonically curved westerlies (70+ kt 500 mb) will extend from the south-central Great Plains to the Upper Midwest and Upper Great Lakes on Tuesday, with a lead/convectively augmented shortwave trough likely to spread from the central High Plains toward the Lake Superior vicinity late Tuesday night. An elongated surface low over eastern Nebraska Tuesday morning will deepen and lift northeast to northern Wisconsin/Upper Michigan by evening, with a surface warm front lifting northward ahead of the surface low, although its effective position will likely be influenced by the early day precipitation. Meanwhile, a trailing cold front will surge east across Iowa/eastern Kansas/northern Missouri from mid-afternoon into the evening. Remnant clusters of storms will likely be ongoing Tuesday morning across central/eastern Nebraska, with the possibility of additional storms farther east across southern Iowa/northern Missouri in association with a warm-advection regime. Some key uncertainties persist about the influences of this early day convection, but trends will be for quick air mass recovery given a progressive/highly dynamic pattern. Very steep mid-level lapse rates will overspread the increasingly moist warm sector, supporting aggressive diurnal destabilization especially on the southern fringe of lingering convection/cloud cover. Significantly strengthening mid-level winds and a diurnally persistent strong low-level jet will support initial supercells capable of large hail and a few tornadoes, including strong (EF2+) tornado potential. But a mixed/transitional mode is expected overall, as upscale growth occurs given the degree of forcing for ascent, with likely evolution into a well-organized/fast-moving QLCS capable of increasingly widespread/intense damaging winds and a continued QLCS-related tornado risk. This scenario currently appears to be most probable across southern/eastern Iowa into northwest Illinois and nearby far northern Missouri. The severe risk will persist into the Upper Great Lakes region and middle Mississippi Valley overnight. ...Southern Plains... Convective coverage will likely decrease with southward extent as large-scale ascent focuses northward toward the Great Lakes. Nevertheless isolated storms are possible into northeast Oklahoma/northwest Arkansas by late afternoon/evening, and more conditionally with southwest extent near a dryline from central Oklahoma into central Texas. Large hail and severe gusts will be possible with this activity. ...Northeast States... A weak upper shortwave trough will move across southern Quebec and northern New England. This will result in a band of enhanced westerly deep-layer flow from northern New York into Maine. A seasonally moist airmass will be in place with surface dewpoints into the low 60s F, with strong heating and steepening low-level lapse rates. MLCAPE to around 1000 J/kg and effective shear magnitudes around 35 kt will support organized cells. Elongated hodographs and favorable vertical shear suggest marginally severe hail will be possible along with locally damaging wind gusts. ..Guyer.. 05/20/2024 1 Link to comment Share on other sites More sharing options...
frostfern Posted May 20 Share Posted May 20 Too far west for me to reach in an afternoon. Link to comment Share on other sites More sharing options...
Chinook Posted May 21 Share Posted May 21 This morning's WRF-NSSL predicts a storm complex going into Illinois well before a main line of storms. Link to comment Share on other sites More sharing options...
CheeselandSkies Posted May 21 Author Share Posted May 21 CAM solutions have varied wildly from model to model and run to run since this event came into range. Still clear as mud how tomorrow might evolve. Link to comment Share on other sites More sharing options...
cyclone77 Posted May 21 Share Posted May 21 I've seen a few cams fire off some convection well ahead of the main show near the MS river. That would be concerning if that were to happen. Either way it's looking like a serious wind threat with the main show tomorrow evening. Link to comment Share on other sites More sharing options...
miamarsden8 Posted May 21 Share Posted May 21 Yeah, based on all the solutions I've seen so far, southeastern Iowa is going to only get wave three, whereas northeastern and southwestern Iowa are scheduled to get hit by waves 1 and 2. If that happens and it's a linear threat, that's all well and good, but what happens if a cell develops ahead of that line? That's going to be interesting to watch. We'll need to see more info on this, but I think if there's going to be a strong tornado, based on the models I've seen, areas south of the QCA out to Galesburg and back into the Mt. Pleasant are going to be under the gun. If a cell develops there ahead of that line, I'd be concerned. Link to comment Share on other sites More sharing options...
Chinook Posted May 21 Share Posted May 21 The 00z models pretty much get things going in mid-Iowa Link to comment Share on other sites More sharing options...
A-L-E-K Posted May 21 Share Posted May 21 not expecting much beyond garden variety plus imby but happy to watch it play out online with friends 1 Link to comment Share on other sites More sharing options...
King James Posted May 21 Share Posted May 21 LOT sounds pretty high on the severe event 1 Link to comment Share on other sites More sharing options...
CheeselandSkies Posted May 21 Author Share Posted May 21 Thinking about targeting the Waterloo-Webster City area. Multiple HRRR runs and the 06Z 3K NAM suggest slightly better backing of the surface winds in north-central to northeast Iowa, with a relative maximum of 3CAPE/EHI and some discrete-ish cells making their way through there in the afternoon. Besides, along and north of the US-20 corridor is the best chase terrain in Iowa. Almost as flat and open as western Kansas. I got lucky that Keota was in a fairly open spot along Highway 92 but encountered issues with hills and trees while trying to chase it toward Wellman/Kalona. 4 Link to comment Share on other sites More sharing options...
A-L-E-K Posted May 21 Share Posted May 21 hrrr keeps shitting out a dry fropa here and i would prefer not 1 1 Link to comment Share on other sites More sharing options...
sbnwx85 Posted May 21 Share Posted May 21 Storms yesterday did some impressive damage in Laporte County. https://x.com/nwsiwx/status/1792727617529135390?s=46 5 1 Link to comment Share on other sites More sharing options...
hawkeye_wx Posted May 21 Share Posted May 21 Models have not handled the morning convection well at all. The CAMs had (and still have) all this stuff quickly weakening and lifting into northern Iowa, but that is not happening. Instead, one line has moved through my area and a bigger line is moving into central to south-central IA. 1 Link to comment Share on other sites More sharing options...
Radtechwxman Posted May 21 Share Posted May 21 Really unsure where to target today. Part of me wants to get on the storms near low before they line out but afraid they may get undercut. Part of me is afraid something will go east along a remnant boundary and shear vector orientation and hodograph curvature is better east. Tricky forecast today Link to comment Share on other sites More sharing options...
Chicago916 Posted May 21 Share Posted May 21 1 hour ago, A-L-E-K said: hrrr keeps shitting out a dry fropa here and i would prefer not A lot more CAMs than HRRR doing that now. I feel like anecdotally that always happens and the squall will actually survive past the Lake. 1 Link to comment Share on other sites More sharing options...
SluggerWx Posted May 21 Share Posted May 21 PDS Watch issued for almost the entire state of Iowa and part of Southern MN. 90/80 probs. Link to comment Share on other sites More sharing options...
nwohweather Posted May 21 Share Posted May 21 32 minutes ago, SluggerWx said: PDS Watch issued for almost the entire state of Iowa and part of Southern MN. 90/80 probs. I almost wonder if threads need to be merged since it's on the edge of C/W as well. Regardless, some extremely strong wording coming from the SPC today. Looks like a lot of CIN still in the region, definitely need that to erode and instability. Link to comment Share on other sites More sharing options...
Chicago Storm Posted May 21 Share Posted May 21 Really not expecting too much of intertest around here with this. Environment really tails off with east/southeast extent. So much of the guidance that is showing activity quickly weakening as it moves through is probably is correct. SPC is way too overzealous with the enhanced risk. 1 Link to comment Share on other sites More sharing options...
jwalsh1 Posted May 21 Share Posted May 21 Forgive me, but are you saying you anticipate weakening as it enters LOT area? Link to comment Share on other sites More sharing options...
Chicago Storm Posted May 21 Share Posted May 21 13 minutes ago, jwalsh1 said: Forgive me, but are you saying you anticipate weakening as it enters LOT area? Expectation should be that it'll be in a weakening phase as it passes through the CWA. 1 Link to comment Share on other sites More sharing options...
andyhb Posted May 21 Share Posted May 21 1 Link to comment Share on other sites More sharing options...
Chinook Posted May 21 Share Posted May 21 There might be a tornado getting going around Villisca. Link to comment Share on other sites More sharing options...
andyhb Posted May 21 Share Posted May 21 1 minute ago, Chinook said: There might be a tornado getting going around Villisca. Large tornado confirmed on this storm. Link to comment Share on other sites More sharing options...
Powerball Posted May 21 Share Posted May 21 The atmospheric recovery in Des Moines has been nothing short of incredible. Link to comment Share on other sites More sharing options...
Chicago Storm Posted May 21 Share Posted May 21 Twins in SW. Iowa right now. 1 Link to comment Share on other sites More sharing options...
MidwestChaser Posted May 21 Share Posted May 21 Amazing tornado on Vince Waelti's stream. Link to comment Share on other sites More sharing options...
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