Tornado threat returns to SK/MB today

Today August 12th, 2020

Threat level: HIGH

Confidence: HIGH (based on model agreements)

Expected hazards: DAMAGING DOWNBURST WINDS // BASEBALL-SIZE HAIL // FLASH FLOODING // TORNADOES

Locations impacted: in Saskatchewan: Regina, Estevan, Yorkton, Moosomin, Yellowhead Highway and surroundings. In Manitoba: Swan River, Dauphin, Virden, Roblin, Shoal Lake, Winnipegosis and surrounding areas.

Timing: 2pm CDT to 12am CDT

Expected watch(s): Severe thunderstorm watches // Tornado watches

Possible scenario at 21z (4pm CDT)

DISCUSSION: morning analysis (see below) depicts low pressure over Leader, SK near the AB/SK border with ongoing complex of storms near Fargo, ND along a stationary front. This stationary front (warm front) will move northward following the low pressure throughout the day. Cold front situated over western Montana. Low should occlude north-northwest throughout the morning/afternoon hours towards N AB with occluded front across west-central SK, cold front just west of Regina and warm front (WF) along the Yellowhead Highway. Intersection of WF and occluded front will bring the highest chance of rotating supercells in the afternoon hours. Instability will be modest along the WF, but veering of the winds, elongated hodographs with very good lapse-rates will bring the threat of classic WF supercells with tornadoes from a line from Humboldt-Yorkton-Swan River. Along the cold front (CF), high instability in the 3000 J/kg MLCAPE, more southerly flow (rather than southeasterly along WF) and very steep lapse-rates (~9C/km), will bring a main threat of very large hail, some the size of baseballs and damaging downburst winds.

GEOS-16 satellite at 14UTC (9am CDT) with station plots, 500mb RAP analysis and streamlines



Environment Canada Day 1 Outlook


Saskatchewan

  • Area(s): Most areas with risk of severe weather over eastern Saskatchewan

  • Timing: Through Wednesday evening

  • Threats: 3-5 cm hail, 110 km/h wind gusts, local 50 mm rainfall, isolated tornado over eastern areas

A trough of low pressure tracking across Saskatchewan will trigger scattered thunderstorms through this evening. Thunderstorms over eastern regions will have the potential to produce 3-5 cm hail, 110 km/h wind gusts and locally 50 mm/hour rainfall. An isolated tornado or two also cannot be ruled out. The thunderstorms will track northeastwards into Manitoba in the evening. Thunderstorms may develop over Montana and move into southwestern Saskatchewan tonight.


Manitoba

  • Area(s): Western regions and into the RRV and Interlake through the overnight

  • Timing: Wednesday late afternoon, evening and overnight

  • Threats: 3-5 cm hail, 110 km/h wind gusts, local 50 mm rainfal, isolated tornado over western areas; locally heavy downpours, pea sized hail, gusty winds elsewhere

A trough of low pressure tracking across western Manitoba will trigger scattered thunderstorms this afternoon and evening. These thunderstorms will have the potential to produce 3-5 cm hail, 110 km/h wind gusts and locally 50 mm/hour rainfall. An isolated tornado or two also cannot be ruled out. The thunderstorms will track eastwards into central Manitoba and the RRV this evening into the overnight hours.