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First severe weather threat tomorrow for Manitoba

Possible radar depiction of storms for Wednesday May 15th 2019

General Setup

A low pressure will eject east across the Northern Plains on Wednesday. This will drag along a cold front and a large warm sector. Southern Manitoba will be in the warm sector on Wednesday afternoon, which will allow warm temperatures and moisture to invade parts of the province.

Temperatures could reach the 30C mark on Wednesday late afternoon for parts of extreme southeastern Saskatchewan and extreme southwestern Manitoba.

Surface temperatures (in C) depicted by the NAM 12km resolution model for 4pm CDT Wednesday

With the warm summer-like temperatures expected and the moisture advecting northward, severe thunderstorms are likely. With moisture in the mid-50s (F) will provide ample fuel for storm development. As seen below, moisture will be well into central Manitoba. It will be a warm and muggy day tomorrow for Manitoba/North Dakota.

Moisture advection in (F) for Wednesday

While moisture provides the fuel needed for storms, fairly modest instability values are also expected across North Dakota and Manitoba. Mixed-layer CAPE values should be in the 1000J/kg value, which is pretty high for this time of year. This will provide ample instability for storms to become severe with large hail/damaging winds.

Mixed-layer CAPE (instability) and overlayed risk area and cold front

For Manitoba

While severe storms are likely in North Dakota, severe storms are more conditional for Manitoba. Morning rain showers will swing through and redevelopment of strong/severe storms will depend on how much airmass recovery can occur in Manitoba. If strong heating can occur, areas such as Killarney to Morris could see severe storms tomorrow. Regardless whether storms reach severe levels or not, gusty winds and heavy downpours are likely for areas from and east of Killarney-Carman-Morris line.

...Northern Plains...
   As a shortwave trough crests a midlevel ridge, a surface low will
   develop and move across the Canadian Prairies. A trailing surface
   trough will move across the Northern Plains during the
   afternoon/evening. Strong heating/mixing near and west of the
   surface trough and at least modest large-scale ascent attendant to
   the midlevel shortwave will support isolated thunderstorm
   development across central/eastern ND by late afternoon. While
   boundary-layer moisture will remain relatively limited, dewpoints in
   the 50s F, temperatures warming to near 80F, and steep midlevel
   lapse rates will support moderate instability along and ahead of the
   surface trough. Effective shear/helicity will be sufficient to
   support organized structures, with potential for isolated supercells
   capable of large hail and locally severe wind gusts. 

   Some upscale growth is possible into Wednesday evening into portions
   of western/central MN. However, increasing MLCINH and decreasing
   buoyancy with eastern extent should result in a gradually
   diminishing severe risk through the night. 

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