Damaging downburst winds and more heavy rainfall possible for SW Manitoba

Today July 2, 2020

Threat level: LOW

Confidence: MODERATE (based on model agreements)

Expected hazards: DAMAGING DOWNBURST WINDS // HAIL // FLASH FLOODING

Locations impacted: Southwestern Manitoba: Melita, Souris, Virden, Killarney and surroundings.

Timing: 7pm CDT to 10pm CDT

Expected watch(s): Severe thunderstorm watches

PASPC Day 1 Thunderstorm Outlook

Manitoba

• Area(s): Southwestern, wes-central and Interlake

• Timing: Thursday late afternoon into the evening

• Threats: 3-5 cm hail, up to 110 km/h gusts, 50-75 mm of rain, slight risk of a tornado

There is a conditional severe threat for thunderstorms over southwestern Manitoba on Thursday and a minor threat extending northwards through the Parklands area of western Manitoba. A shortwave trough over central Saskatchewan extending into western Manitoba may initiate thunderstorms Thursday late afternoon into the evening hours. Modest moisture and instability will aid in thunderstorms to become severe over western portions and be capable of 2 to 4 cm hail, 90 km/h wind gusts and 50 to 75 mm of rain. A tornado or two cannot be ruled out. Over southwestern Manitoba, there is a higher overlap of ingredients such that 3 to 5 cm hail, 50-75 mm rainfall and 110 km/h wind gusts will be possible. A tornado or two cannot be ruled out here as well. These thunderstorms will move northeast in the late evening hours and weaken to below severe thresholds.

HRRR Simulated Reflectivity for 7pm CDT

Discussion: ENHANCED risk issued by the Canadian Prairie and Arctic Storm Prediction Centre (PASPC) and MARGINAL risk issued by the U.S. Storm Prediction Center (SPC) with mention of tornadoes for Manitoba by the PASPC. Thinking PASPC too reliant on HRRR, which shows more discrete cells across the forecast area. Thinking tornado threat is low to non-existent (<2%) since multicells will be primary storm modes and storm initiation conditional. A cold front will move through the moderately to highly unstable airmass and likely trigger storms near the SK/MB/ND border, which will move northeast across southwestern Manitoba. Thinking storms will trigger around the Souris-Melita-Killarney area along the cold front and likely aided by subtle terrain effects from the Manitoba Escarpment. Convective temperatures will need to be reached for surface-based storms, but any storms that can develop in southwestern Manitoba will be severe with localized large hail, downbursts and heavy rain. Storms will die quickly or became elevated with the lost of daytime heating after or near sunset.