Friday, December 01, 2017

Mild weekend will give way to colder weather next week as upper pattern shifts

The mild weather of the past week or two will continue for the upcoming weekend.. but changes are brewing by early next week as the upper weather pattern changes. The mild weather this past week has been the result of an upper "zonal" flow which brings milder Pacific air across the Prairies while preventing cold Arctic airmasses from advancing south. This pattern will persist over the upcoming weekend but will begin to change to a more amplified "wavy" upper pattern next week which will allow colder air from the Arctic to advance south into southern MB.  The transition to this colder pattern will be marked by some snow Sunday night into Monday with a few cm possible* (see UPDATE below), before northerly winds bring in colder air Monday afternoon into Tuesday.  Temperatures will drop into the minus teens through mid week before some moderation by the end of the week as temperatures rebound back to normal (or even above normal) by mid December.

After that.. there is some uncertainty in how the upper pattern will evolve over Manitoba. The current thinking is that the upper pattern leading up to Christmas will be dominated by an upper ridge over the west coast and  troughing over the Great Lakes/eastern NA.  This would place Manitoba in a northwest upper flow which generally means below normal temperatures here with occasional very cold outbreaks. However, the intensity and duration of these cold snaps will depend on the strength and location of these upper features. At this point, the core of the coldest air is expected over eastern North America which would imply occasional but transitory cold snaps over southern Manitoba modified at times by periodic clipper systems. Until then, get ready for a return to colder weather this upcoming week.

UPDATE (Sun Dec 3):  Storm system will be intensifying overnight through Monday as it tracks across northern Minnesota into NW Ontario. Current guidance indicates the bulk of snow with this system will fall over SE MB into NW Ontario, with Winnipeg and RRV on the western flank of the snow shield. Snowfall from this system will range from 5 cm in the RRV to 10-15 cm closer to the Ontario border overnight through Monday. Increasing winds Monday afternoon into Monday night along with falling temperatures will produce worsening traveling conditions especially south and east of Winnipeg with blowing and drifting snow likely.