Rob's Blog: Dec 4 2015 - Morden soars to record 14.2C. Warmest December day since 1969

Morden resident cuts his lawn on Dec 4 2015
as temperatures soar to 14.2C (from CBC)

One of the more remarkable milestones of this current December warm spell was registered in Morden, MB on Friday Dec 4th when the mercury soared to an astonishing 14.2C, making it not only the warmest spot in Manitoba that day, but in all of Canada. Having a place in Manitoba get national hot spot honours in December is exceedingly rare, as the balmy west coast, Maritimes or southern Ontario are typically the warmest areas of Canada in winter. The 14.2C reading was a record high for Morden for Dec 4th, beating the previous record high of 12.2C in 1916. It was also Morden's 3rd warmest temperature ever recorded in December, surpassed only by a 14.4C reading on Dec 1 1969, and their all time December high of 17.8C on Dec 6 1939 (yes, 17.8C!). The 1939 record was established during a historic warm spell that brought the warmest temperatures ever recorded in southern Manitoba in December, including Winnipeg's all time December high of 11.7C on Dec 6th (the only time Winnipeg has observed a temperature of 10C or more in December). That year went on to see a green Christmas across much of southern Manitoba, including Winnipeg.

Max temperatures across southern MB - Dec 4 2015
Warmest readings in snowfree and downslope areas

So how did Morden get so warm on Friday? Two main reasons: no snow on the ground and warming downslope winds off the Pembina escarpment. A look at the max temperature map on Dec 4th shows the warmest readings that day were observed over southwest Manitoba (where there was no snow cover), especially in areas with warming south-southwest downslope winds off higher terrain.This included areas east of Riding Mountain (Dauphin, McCreary), north of the Turtle Mountains (Boissevain, Deloraine) and east of the Pembina escarpment (Morden, Miami) Downslope winds off higher terrain can add 2-7C (and sometimes more) to downwind localities compared to areas outside the downslope zone.

Relief map of Pembina valley (left) shows Pembina escarpment running just west of Morden, dividing higher terrain to the west and the lower flat plains of the Red River valley to the east. South to southwest downslope winds blowing off the higher terrain can result in warmer temperatures immediately to the east of the escarpment (like a mini-chinook) Image on the right is a visible satellite image taken Dec 4th at 2:45 pm showing snowcover over southern MB. There was a distinct line from Portage La Prairie through Carman to Emerson, separating snow-covered areas to the east and bare ground to the south and west. Temperatures were some 5-10C cooler over the snow-covered areas, with highs of +2-4C, including a windy +2.3C in Winnipeg (surface plots on image are in degrees F. Morden is shown as 57F (14C) at this time) The high resolution image below shows the snowcover in greater detail. Note the distinct snow line running through Carman to northeast of Emerson. Note also deeper snowpack (brighter white area) still evident west and northwest of Winnipeg.

High resolution MODIS satellite image showing snowcover
over Red River valley on Dec 4 2015

Synoptic set up - Dec 4 2015

Sfc map - 6 am Dec 4 2015

925 mb - 6 am Dec 4 2015

On the morning of Dec 4th, southern Manitoba was is a southerly flow of very mild air between a surface ridge south of Lake Michigan, and a trough over western Saskatchewan.

Of note is how warm the air was just above the surface that day. Air temperatures up to +14C were observed over the Morden area at 925 mb, or about 700 metres above ground. This is exceptionally warm air for December, and was helped northward by a strong south-southwest wind of 50+ knots (90+ km/h) at this 925 mb level. These warm values would eventually cool off to +8C by mid afternoon, but it showed the potential for temperatures over 10C in snowfree areas that day. Morden got the greatest benefit of this warm air aloft, helped by sunshine, snowfree ground, and downslope winds. It should be noted that on this day, the downslope winds did not reach much further east of Morden, and in fact, nearby Winkler, just east of Morden, only got up to 9.5C that day as their winds were more southeast through the day tapping cooler air off the snowcovered Red River valley.

A look at Morden's hourly temperature chart for Dec 4th shows that temperatures rose from +5C at 9 am to +10C by 11am, and 12.7C by noon. It would climb to a maximum of 14.2C shortly after 2 pm, before downslope winds from a 200 degree direction shifted to the southeast (160 degrees) tapping cooler air over the snow-cooled Red River valley. Temperatures dropped quickly to 8C by 3 pm and +5C by 4 pm.

Road trip to Morden

Snowcover becomes meager
east of Carman

It's not very often that a place in Manitoba experiences 14C in December, so I decided to take a drive to Morden that day to witness such a rare event. Considering it was just an hour away from Winnipeg made it that much more amazing to experience. I left Winnipeg shortly before 1 pm heading off on Highway 3 through Sanford to Carman. There was a brisk southerly wind gusting to 60 km/h, keeping temperatures in the +2 to +3C range almost all the way to Carman. As I got closer to Carman, the meager snowpack started to diminish and the temperature rose to +6C in Carman.

Snowcover disappears south
of Carman

Green fields north of Morden
Dec 4 2015

As I turned south on Hwy 3 heading to Morden, the snowpack disappeared completely just south of Carman and from there on, there wasn't a hint of snow anywhere, with the landscape resembling something from October or April. The temperature rose to 10C by the Hwy 23 intersection and 11C by the turnoff to Morden.

Hwy 3 to Morden - Dec 4 2015

Once I headed west to Morden, the outdoor temperature on my car thermometer climbed 1C per kilometre as I headed into the downslope region, reaching 14C by the time I got into Morden. My car thermometer would peak at 15C at 2:15 pm. Getting out in Morden, it felt like April.. no snow on the ground, a balmy breeze under clear blue skies, and temperatures in the teens. It was quite the difference from chilly snowcovered Winnipeg just an hour away! By 3 pm, the temperature had dipped to 11C as winds shifted into the southeast and by 3:30, it was down to 7C as I headed back to Winnipeg. It was a quick visit, but certainly a novelty to experience springlike warmth just an hour outside of Winnipeg! If you're looking for a balmy getaway near Winnipeg, keep an eye on those downslope winds!