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Small chance of QLCS tornados today across the region as the mainly linear line moves through late this afternoon into this evening. 0-3km CAPE is low/non existent but low level SRH exists such that it might cause quick, small spinups.

There remains considerable differences amongst guidance this morning regarding timing/placement/intensity of the thunderstorm event this afternoon. Despite the variability amongst models, it seems likely one or more rounds of thunderstorms will move into S ON from Lake Huron / MI. MLCAPE values will likely surpass 2000 j/kg, especially along and south of the Hwy. 402 corridor. Modest deep layer shear of 30-35KT and strong flow in the 850-700mb layer (especially north of Grand Bend) will help support organization, possibly into one expansive MCS with bowing segments. Effective SRH values of 100-150m2/s2 will aid in the chance for a weak QLCS line-embedded tornado or two where the best CAPE/shear/LLJ overlap takes place this evening, which seems like the south Lake Huron basin and surrounding areas inland.

Hi-res guidance is in loose agreement on a SVR risk for the SW during the afternoon - evening with the main difference amongst models being timing. The HRRR is the earliest, bringing storms off Lake Huron and also into Lambton/Essex Counties by 3-4PM. The 3KM NAM is generally later and also shows a more disorganized mode, firing several clusters of small storms over several hours instead of a more focused area. Regardless, an environment characterized by 1250-1750j/kg MLCAPE, 150-200m2/s2 effective SRH, 40KT 0-6km shear (up to 50KT LCL-EL shear) will overspread the SW by mid afternoon allowing for sustained convection with a wind / isolated tornado threat. Notable curvature exists in forecast hodographs with plenty of low level shear in place to support rotating updrafts. A mix of multi-cell clusters and supercell storm modes appear favoured. The degree of upscale growth would likely be greater if the incoming front was still anchored to the SFC. Instead, model projections show an occluded front with SFC dewpoints remaining in the low 70s well after passage. The 850/700mb charts show the overriding shortwave trough well, however, and it may be a case where several storms develop over a broad area as the height falls translate across the region. This precludes greater confidence in timing/intensity/coverage.

Although the risk appears to be low, morning convection seems to have cleared quicker than modeled leading to an environment that can build more energy as the day goes on. Hence the tornado risk will be present. Biggest risk today remains the high winds with these storms.

Unidirectional shear should make for a dampened tornado risk this afternoon across southern Ontario, although there will still be a non-zero tornado risk stretching from portions of Essex County and the Windsor area into Barrie and the Greater Toronto Area. Late in the evening/overnight, a few models have lingering but capable instability along the western flank of the Saint Lawrence river, with increasing turning in the lowest levels shown by model fcst hodographs. Due to this, have decided to issue a CHANCE tornado risk from the Windsor region along the coast of Lake Ontario to the Saint Lawrence River border of ON/QC.

Tornadoes should be expected along that Huron shoreline with isolated cells that come onshore.

Model agreement has improved with the 00z suite in regards to an environment capable of all hazards including tornadoes. A couple strong tornadoes seem likely should a discrete storm mode persist for 1-2 hours after landfall from Lake Huron. Most forecast soundings from hi-res models exhibit moderate to strong instability coupled with deep layer shear of 40-55KT. 0-3km shear values are expected to be in the 30-40KT range. Large looping hodographs suggesting strong storm-relative inflow and effective SRH values near 300 m2/s2 put an emphasis on the tornado threat that will exist with any supercell storm.

Increased 500mb flow will be present across Ontario tomorrow, attendant to a shortwave trough extending from portions of northern Quebec into northern Ontario. Enlarged hodographs are evident on some forecast model soundings across extreme Southern Ontario, where some models pinpoint a stationary/warm front stalling over by early afternoon.

Initiation is questionable, however if instability is in the range of 1,500-2,500 J/KG MLCAPE, and initiation occurs along the frontal boundary, an isolated tornado or two could occur where low level shear is most favourable. Differing model trends are evident, and convective allowing models seem to avoid initiation. Despite this, have decided to contour a 1/3 risk (CHANCE) across portions of the aforementioned region.