Currently have a broad upper low off the BC coast with a shortwave trough ejecting out of the southern end of it currently located just off the coast of Vancouver Island and down through WA/OR as indicated on W/V imagery below (first image). This trough is currently firing off the thunderstorms through southern AB/MT at the moment which is forecast to develop a large scale system overnight tonight for western SK, possibly a weak MCS. This trough forecast to push into the Prairie Provinces by tomorrow afternoon which will aid in overall ascent and instability. Second image below (second image) shows the 18Z NAM forecast of where the trough will be which is supported by the GEM/GFS /ECMWF solutions.

At the surface currently have a low located just NW of the elbow of ON with a backdoor boundary pushing through north central SK, northern AB and BC. This boundary is expected to drift south through the overnight which will likely serve as the focus for surface based convection as the trough pushes in.

Tomorrow afternoon this backdoor front along with the trough looks to setup a secondary wave through the Prairies which will help with surface convergence and likely some additional local effects through eastern SK. But the real good energetic air will be just south of the warm front through southeastern SK into southern MB where SBCAPE values are forecast to range from 2000-3000 j/kb, and he GEM is even going as high as 4000+ J/Kg for the Brandon, MB region. There will be some uncertainty with this though as the evolution of any overnight convection from the MCS can bring some lingering cloud which would reduce these numbers.

Second issue is 500 mb flow is forecast to be quite ranging from 15-30 kt, this will lead to any storms being quite slow moving and HP in nature, but at the same time vectors are perpendicular to the forcing so somewhat isolated updrafts look likely (Image below). Low level shear is also quite low but with surface winds out of the ENE and 850 winds from the ESE directional shear is quite good and this just may be enough as the high CAPE values will help with higher vertical velocities and thus able to enhance low level shear present to get some rotation updrafts. That being said tomorrow is case where there is low chance of tornadoes, but the better risk will be associated with the higher CAPE regions. Will have to monitor any ongoing convection through central SK through the day for any additional outflow boundaries, which will easily be able to initiate any storms in the warm sector with such high instability and eroding CAP through the mid-afternoon period. The synoptic situation appears as through storms would initiate in extreme south eastern SK/ND through the 2-4 pm CST and push into southwestern MB through the late afternoon and evening period. Thus there will likely be general thunderstorm risk in the purple region associated with the upper trough and the pink region highest threat for severe; with possible tornado risk in areas of highest CAPE This area includes Yorkton and Estevan, SK. Brandon, MB and south along Hwy 10. Regina region is also in the risk for possibly severe risk but has some uncertainty still as the overngiht convection could prevent suitable airmass recovery for tomorrow. NOTE: This general region could get pushed south and east depending on evolution of system in SK tonight.