Significant thunderstorms are expected to develop east of the Rockies in Alberta on Thursday afternoon. These thunderstorms will become supercells fairly quickly as they move east into a very unstable airmass. These will have all severe weather hazards with them.
Threat level: HIGH
Confidence level: HIGH (based on model trends)
Area: Medicine Hat, AB and adjacent // southwestern Saskatchewan
Timing: 1-4pm local time (MDT) Alberta // 4pm and evening Saskatchewan
Main Hazards: Tornadoes, very large hail for Alberta // large hail, damaging winds Saskatchewan
Why? The risk has classic upslope severe weather event written all over it. A Low pressure (marked by "L" in these maps) will "pool" warm moist air from the Gulf of Mexico into Alberta. This warm airmass will hit the Rockies, thereby preventing their westerly progression and "pool" in southeastern Alberta. A graphical depiction of this is shown below:
As can be observed in the picture above, the warm-moist air will be dragged and influenced by the counterclockwise rotation of the Low pressure system. This is denoted as red arrows above. This will create a very unstable airmass in southeastern Alberta by early Thursday afternoon.
As depicted above, Mixed-Layer CAPE (a measure of instability in the atmosphere) will be well into the mid-2000J/kg, which is pretty high for Alberta. This unstable airmass, combined with upslope and favorable low-level veering winds will create the right conditions for tornadoes and very large hail in southeastern Alberta Thursday afternoon and adjacent Saskatchewan.
Above is a bit complex, but shows a very favorable environment for rotating supercells and favorable low-level winds for tornadogenesis. Please make sure to keep up to date with watches/warnings on this day.
What's the threat for Manitoba? Check out our discussion here: https://www.nzpchasers.com/post/severe-to-return-to-manitoba-this-weekend