Monday will likely be the nicest day of the week with temperatures most likely reaching the mid 20's... assuming we get a decent amount of sunshine. I recommend you enjoy it while it lasts...
The change-maker will be a cold front which will slice through southern Manitoba Monday night into Tuesday morning. Rain is likely with this front, along with the potential for embedded thunderstorms. Winnipeg will likely see this rain in the overnight hours and early morning on Tuesday. General rainfall amounts of 5-15 mm are expected, however any thunderstorms that occur may give some localized higher amounts.
Tuesday looks very Fall-like. There will be a breezy north wind, more cloud than sun and temperatures will only reach the high teens. Tuesday night will be chilly with lows in the mid to high single digits.
A secondary cold front passes through on Wednesday night which will give another potential for showers.
Cool conditions continue through the rest of the work week with highs generally in the high teens and overnight lows in the single digits... More typical of mid September.