A strong cold front will act as a trigger for isolated severe thunderstorms across the Eastern Townships and Southeastern Quebec Wednesday. Damaging winds, torrential rainfall giving 25-50mm of rain in a short duration, frequent lightning and isolated supercell(s) are risk factors with these storms.
Thunderstorms may track into Northern New Brunswick bringing heavy rainfall and lightning as they begin to weaken and become elevated.
A developing area of low-pressure will track out of Northeastern Ontario into Quebec Wednesday, deepening rapidly. An area of height-falls & falling atmospheric pressure will overspread the warm sector, ahead of a seasonably sharp cold front. Temperatures will rise into the mid-20s with dew-points nearing 20c. Pockets of 1500J/kg of CAPE should develop across the warm sector. Largely unfavourable lapse rates will be compensated by a strong tendency for ascent. 65 knot, 500mb flow will overspread the Eastern Townships & Southeastern Quebec – ahead of an amplified, positively tilted trough. A modest low-level jet should be sufficient for moisture transport across the warm sector, and a damaging wind threat. Speed-shear and wind shear will be sufficient enough to sustain long-lived updrafts – well-tilted updrafts capable of rotating. A threat for stronger bowing-linear segments or super-cells exists between 1-5pm. Additional risks, include torrential downpours, frequent lightning and hail in the stronger updrafts.
Timing of the cold front and pre-frontal clearing will be important determining factors considering how severe thunderstorms will be.
Showers and a risk of severe thunderstorms for Southern Ontario. Heavy rainfall from East of Lake Superior to the Quebec border Wednesday (June 13th, 2018).
A strengthening low pressure system will track East of Lake Superior through the Nickel Belt Wednesday, bringing a risk for heavy rainfall for Northern Ontario and a risk of severe thunderstorms in Southern Ontario.
A swath near the low track, from East of Lake Superior to the Quebec border will likely see rainfall amounts of 25-50mm between Wednesday morning to evening.
Further south, across Southern Ontario – there will be 2 rounds of precipitation. The first, along a warm front as it edges north into Southwestern Ontario, bringing scattered showers Tuesday evening through Wednesday morning. Once the warm front moves north, there will be a clearing allowing for sunny breaks and energy to build ahead of a cold front acting as a trigger for thunderstorms Wednesday afternoon. Some of these thunderstorms may be severe with damaging winds as the primary threat.
A window for a low tornado threat is possible from mid to late afternoon in our red highlighted area. The greatest threat will be along a “triple-point” – between 1pm and 6pm. This region may expand to include municipalities near the Lake Ontario shoreline.
Environment Canada (OSPC) is calling for a “moderate” risk of severe thunderstorms. The primary threats according to their risk map is damaging winds up to 100km/h. Please note: these maps are still in the experimental stage.
After the passage of the cold front the low will continue to deepen as it moves into Quebec. Strong wrap around winds will develop Wednesday evening and overnight. Gusts between 60-80km/h are expected across much of Southwestern, and South-central Ontario. Localized gusts to 90km/h are possible in higher elevation South of Georgian Bay, as well as, near the lakeshore.