Mild weather continues Monday.. then turning colder this week with coldest airmass of the season moving in by Christmas

The relatively mild weather over the first half of December across southern MB will continue for one more day Monday, before significantly colder weather moves in this week. Even colder weather is expected by next weekend as the coldest airmass of the season so far pushes in across the Prairies for the Christmas holidays.

Temperature forecast for Winnipeg over next 10 days shows cold trend
setting in this week, with temperatures near -30C possible by Christmas
(graphic from weather.us)

In the short term, a westerly push of mild air will sweep across southern Manitoba Monday pushing temperatures up to the 0 to +1C mark over southern Manitoba, including Winnipeg. There may be some wet snow pushing across areas south of the TransCanada highway to the US border Monday morning through midday as a weak disturbance pushes through. In the wake of this system colder air will move into southern MB for Tuesday with temperatures dropping to the -10C mark by late afternoon. This will be the start of a period of much colder weather with temperatures near -20c expected by Wednesday morning. Highs Wednesday through Friday will only be in the minus teens with lows near -20C which is actually about average for this time of year (Normal hi -10C, low -20c)

Frigid weather expected for Christmas holidays

850 mb temperature forecast by European model for Christmas morning
shows massive Arctic vortex pushing across Manitoba with temps near -30C
(graphic from weather.us)

Unfortunately, things look to get even colder by next weekend just in time for Christmas as a massive push of Arctic air plunges south ushering in the coldest airmass of the season so far into southern Manitoba. This will bring daytime temperatures only in the minus 20s, with overnight lows  around -30C or lower.  Windchills may push into the warning criteria of -40 or lower at times over the Christmas holidays. Weatherwise, it looks mainly dry with no major storms or snowfall expected over the holidays with Arctic high pressure in place, so travel conditions should be okay across southern Manitoba. Otherwise, be prepared for frigid weather as you make your holiday plans!

Forecast temperatures Christmas morning shows widespread temps
of -30 to -35C across much of Manitoba with local -40C possible
(graphic from weather.us)

Surface map for Christmas morning shows massive Arctic high (1062 mb!)
over southern Saskatchewan driving frigid Arctic air across Manitoba
(graphic from tropicaltidbits.com)

Snow on the way Monday as pattern changing storm system impacts southern MB and NW Ontario. Colder weather to follow..

Forecast map valid midnight Tuesday shows strong winter storm system near
Thunder Bay with strong winds and snow on backside of system. Low will
track from South Dakota and increase in intensity as it heads northeast   

A storm system tracking across South Dakota tonight will move into Minnesota Monday and intensify as it heads into NW Ontario Monday night into Tuesday. This system is expected to bring snow to southern MB Monday, with the highest amounts expected near the Ontario border where 10-15 cm is expected by Tuesday morning. For Winnipeg and the RRV, 5 cm is expected with up to 10 cm for eastern and southern areas (Steinbach, Emerson, etc)  However, northerly winds are expected to increase Monday afternoon into Monday night which will lead to deteriorating conditions due to blowing and drifting snow with poor visibilities. Temperatures will also be falling into the minus teens Monday night with little recovery Tuesday. Cold weather is expected for the rest of the week before some moderation by week's end. So be prepared for a return to winterlike conditions for the new work week after a pleasant weekend and mild end to November.  

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.