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Conditional severe weather threat for Manitoba today

Similarly to yesterday, warm/dry air contributing to a stable environment will prevent thunderstorm development throughout the day across Southern Manitoba. A cold front (blue line in our forecast map) and occluding front (purple line in our forecast map) may ultimately break that cap and initiate supercells, however it will unlikely be similar to what we saw yesterday in NW Ontario (see below).

A more technical discussion on today's threat follows below.

Saturday June 5, 2020

Threat level: LOW

Confidence: HIGH (based on model agreements)

Expected hazards: DOWNBURST WINDS // HAIL

Locations impacted: Manitoba Interlakes and Portage La Prairie in Manitoba

Timing: 5pm CDT to 8pm CDT

Expected watch(s): none

Forecast map issued at 9:30am CDT and valid for 7pm CDT. Blue line = cold front, red line = warm front, purple line = occluding front.

Discussion: a low pressure will slowly occlude throughout the day along the MB/SK border, dragging with it a slow-moving cold front across Southwestern Manitoba and a warm front moving northerly across the MB Interlakes. Similar to yesterday, a strong capping inversion will be present (see sounding below), which could persist throughout the day. However, two areas of possible initiation remains: (1) at the convergence between the occluded front and the warm front and (2) along the cold front. Soundings at 21z for Winnipeg (in the warm sector ahead of the cold front) shows a fairly stable environment near the surface and convective temperatures unfavourable for storm initiation. Frontal forcing will likely not be enough for initiation, similar to yesterday.

4pm CDT sounding from NAM 3km for Winnipeg, MB

However, soundings closer to Lake Manitoba show a slightly different story. A fairly stable/dry layer at the surface will contribute to LCL heights near 2.8km. This means that the cloud base will be roughly 2.8km above the ground. With a fairly moist layer in the mid-levels, storms that are able to initiate will be elevated in nature, with difficulty to become surface-based, especially near the lake-modified air. Therefore, tornadoes are unlikely, but would be high-based & photogenic if one occurs. Elevated storms may try to initiate, similar to yesterday, but surface-based storms will be very difficult today.

5pm CDT sounding near Portage La Prairie, MB

Bottom line: drier air (stable) at the surface along the cold front will contribute to an unfavourable environment for storm development in Southern Manitoba today. The better chance of storm development will be along the occluding front in the Manitoba Interlakes, however lake-modified air may ultimately contribute to a stable environment unfavourable for storm development. All this led to a LOW risk for today, with no watches expected to be issues by Environment Canada.

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