An upper-level trough is set to eject into the North American Continent this weekend, thereby ending the stretch of nice weather experienced over the Prairies this week. Pictured above is said "trough" and associated upper-level Low seen in British Columbia. While exact timing and location of said trough will vary, this depicts a fairly classic Prairie severe weather setup. We break down each day below:
Sunday will be an Alberta/Saskatchewan story as southerly flow returns to the Prairies and moisture will once again be transported to the Prairies.
Threat level: LOW to MODERATE
Confidence: HIGH (based on model trends)
Most likely hazard: LARGE HAIL // DAMAGING WINDS
Regions impacted: most of southern Saskatchewan
A surface Low pressure (denoted by the "L") will form as a result of the ejecting trough somewhere in Alberta on Sunday morning/afternoon. This will provide the surface convergence, aided by the upper-level support, to initiate robust thunderstorms on Sunday afternoon.
With plenty of instability (seen above), severe thunderstorms and supercells can be expected. Above depicts Saskatchewan as the most favoured area for supercell thunderstorms.
Monday will be the day to watch as the setup moves eastwards into Manitoba. A significant severe weather event may unfold if everything goes "as expected".
Threat level: HIGH
Confidence: MODERATE (based on model trends)
Most likely hazard: LARGE HAIL // DAMAGING WINDS // POSSIBLE TORNADOES
Regions impacted: most of southern Manitoba
Timing: early to mid-afternoon southwestern Manitoba // evening to overnight southeastern Manitoba
A fairly complex combination of surface features should ultimately bring some pretty robust thunderstorms to southern Manitoba Monday afternoon. A warm front (depicted in red above) will first lift into central // possibly northern Manitoba early Monday. This will drag warm/moist air from the south. Then, a cold front (depicted in blue above) will slice to this very unstable airmass in the afternoon. You can see this cold front in southeastern Saskatchewan. A preliminary area of concern has been outlined for Monday.
All of this will result in a very unstable airmass in southern Manitoba. The atmosphere should be primed and ready to go in the morning and with little to no "cap", otherwise preventing thunderstorm development, storms should fire fairly early in the afternoon. An issue remains in place to put a damper on an otherwise "perfect" setup:
To notice this, we need to pull a sounding, which is shown above. This is basically a vertical profile of the atmosphere at a specific point, in this case, in southwestern Manitoba at 1pm CDT. An 91F convective temperature needs to be reached for convection to occur in this area and the sounding surface temperature indicates only 81F. This may ultimately favour elevated convection over surface-based convection. This will need to be monitored.
Further east, soundings reveal a "cap" will be present. The sounding above reveals this, it was pulled from southeastern Manitoba near the Minnesota border. This will need to be overcome for thunderstorms to initiate there. The most likely scenario will be a line of storms move into this region in the evening from the west.
NOAA's Storm Prediction Center has issued a SLIGHT risk on their Day 5 thunderstorm outlook for Monday: