The End of The Arctic Deep Freeze

After a couple days of bitterly cold temperatures, the end is already in sight for Southern Manitoba. Perhaps we shouldn’t complain, though, as Southern Manitoba got off pretty easy compared to the rest of Prairies, where temperatures plummeted to nearly -40°C through most areas, let alone considering the wind chill on top of that.

Pacific Analysis of Incoming System

Analysis of the Eastern Pacific, Jan. 12, 2012 02:45Z. A powerful low pressure system situated approximately 1000km off the British Columbia coast will bring a significant change to our weather pattern.

A powerful system pushing towards B.C. will bring a significant change to our weather pattern this weekend. As this system pushes into the western portions of the continent, the Arctic Vortex, currently situated near Baker Lake, NU, that has been pushing extremely cold air over the Prairies will begin to collapse and retrograde back towards the Gulf of Alaska.

As this happens, the large-scale flow over the Prairies will shift from northwest to southwest, and what a difference 60 degrees can make.

Temperatures will begin to rise on Saturday, as the arctic air begins to be pushed back northwards, and most areas in Southern Manitoba should see temperatures rise to around -12°C. Temperatures will continue to rise overnight and through Sunday up to around -5°C over the RRV as the actual low approaches.

We’ll likely see a couple of cm of light snow Friday night through Saturday as the warm front slowly lifts from North Dakota into the Interlake region. Past that, it gets a little tricky, as some models are forecasting substantial snowfall through Sunday while others keep all snowfall well north of the Trans-Canada Highway. Best case scenarios bring only light snow to the RRV on Sunday night in the wrap around for this system, while more pessimistic approaches bring close to 10cm of snow to our area through light-to-moderate snow through Sunday and Sunday night. It should start to become a little clearer over the next day or two, as the low approaches the coast. Currently, ensemble models predict that we’ll see little snow, and that accumulations should occur through the Interlake, and not as far south as Winnipeg.

After Sunday, we’ll cool back down to seasonal to slightly-above seasonal temperatures through much of next week, with daytime highs generally between -15°C and -10°C. All in all, next week looks quite pleasant. We’ll be sure to provide updates in the comments on how much snow we can expect for Sunday through the coming days!

Continued Cold This Week

Cold air will remain entrenched over Southern Manitoba for the remainder of this week, until a large scale pattern shift once again brings warmer than normal temperatures to our area.

January 18, 1800Z (Noon) MSLP & Snow Accumulation Prog

January 18, 1800Z (Noon) MSLP & Snow Accumulation Prognosis

Snow will taper off by early afternoon today as an arctic high pressure system builds into Southern Manitoba as it pushes across Southern Alberta and Saskatchewan. Much of Southern Manitoba will see a total of around 2cm of snow when all is said and done, with a few localities along the international border seeing 2-4cm.

The big story over the next couple days will be the ridge building across the Prairies. Southern Manitoba will see the coldest temperatures of the winter with daytime highs continuing to be well below normal.

The average daytime high for the 18th of January is -13°C. The average overnight low for the same day is -23°C. Winnipeg will experience temperatures close to 10°C colder than average over the next few days.

This high pressure system has brought bitterly cold temperatures to Alberta & Saskatchewan, with daytime highs of only -29°C in Calgary, -28°C in Edmonton and Saskatoon, and -27°C in Regina yesterday. This air mass will push into our region today, which will limit our daytime high to about -23°C and bring us our first overnight low below -30°C tonight.

January 19, 1500Z (9AM) Wind Chill Prognosis

January 19, 1500Z (9AM) Wind Chill Prognosis

Attached to this cold arctic air mass will be increasing northwest winds to 20km/h, which will produce bitter wind chill values below -40 overnight Wednesday and through much of Thursday morning. At those values, exposed skin can freeze in 5 to 10 minutes, so be sure to dress warm!

Why don’t wind chill values have a °C attached?

Wind Chill is a value calculated from a complex equation that takes the air temperature, the wind speed, and some empirically calculated values for heat transfer through skin into account. When the calculations are done, the units cancel out, and you’re left with a unit-less number. So while the equation was tweaked to produce numbers that resemble temperatures, they aren’t!

If the current forecast works out, it’s likely that we’ll see a large portion of the Prairies covered with wind chill warnings Thursday morning. Little changes for Friday, so there’s a good chance we’ll see another repeat of exceptionally cold daytime highs and bitter wind chills at night.

Current forecasts show a pretty substantial area of warm air pushing into the Southern Prairies on the weekend, bringing daytime highs up by 10 to 15°C. Combined with the CPC’s new forecast of above normal temperatures returning to Southern Manitoba, it doesn’t seem like this winter spell is long to stay.

Another Day of Record Highs, Then…Winter.

Winnipeg has enjoyed 32 consecutive days with above average temperatures, making this one of the more pleasant winters in recent memory. This is about to abruptly change as winter is making an ungraceful return tonight. Before that, however, is another beautiful day with a good chance that more daytime temperature high records will be broken.

2012-01-10 21Z Surface Prog.

Jan. 10, 2012: 21Z (3PM) surface prognosis from the GEM-REG. Blue line represents cold front, red line represents the warm front.

This afternoon will bring more record-setting temperatures to southern Manitoba as the area is drenched in one last shot of Pacific air. By mid-afternoon, Winnipeg will be firmly in the warm sector, and with 850mb temperatures of 2 or 3°C, temperatures should reach as high as 6 or 7°C through a majority of the RRV, Winnipeg included. There is a slight chance that some areas close to the western escarpment of the RRV could see another day of 9 or 10°C with the extra push from downslope winds and their continued lack of snow cover. That being said, I fully expect daytime high records to be broken in many communities in the RRV today.

Tonight, however, is a whole different story.

Winter Returns

After being held well to our north for over 4 weeks, Arctic air will surge across the Prairies today and tonight, bringing a drastic change to the weather. The cold front will sweep through Winnipeg between 00Z and 03Z (6PM & 9PM, respectively), ushering strong northwest winds and much colder air. Much of the southern Prairies will see snowfall with this system, with areas closer to the international border receiving 2-4cm. Winnipeg will be near the northern fringe of the snowfall, but I think that we’ll see at least 2cm of snow here. I think that 5cm is very unlikely, but there is still some uncertainty in how intense the band of snow will be. The most significant snowfalls will occur through the Northern Interlake, where they’ll be under the influence of a hang-back trough from the main low pressure system, bringing them snow for a longer period of time than us in the southern portions of the province.

2012-01-11 15Z 850 Wind Prog

Jan. 11, 2012: 15Z (9AM) 850 wind prognosis from the NAM

With winds at 850mb forecast to be 30-40kt, surface winds have the potential to gust as high as 70km/h overnight. Likely, we’ll see a period of sustained winds near 50km/h before things settle out with sustained winds near 40km/h with gusts to 60km/h. Combined with temperatures that should fall to near -15°C tomorrow morning, wind chill values will be as low as -25 overnight.

2012-01-12 06Z 850 Temp Prog

Jan. 12, 2012: 06Z (Midnight) 850mb temperature prognosis from the NAM

A second cold front will pass through the RRV between 15Z and 18Z tomorrow morning (9AM and Noon), reinforcing the strong winds and causing temperatures to either remain steady or drop through the afternoon. The gusty northwest winds should continue through the whole day, with some light flurries and temperatures that will start near -15°C and drop to close to -20°C by evening. These temperatures combined with the wind should result in wind chill values near -30 for most of the day.

Normal daytime highs for this time of year are around -13°C and normal overnight lows are around -24°C. For the first time in over a month, Winnipeg will experience below-normal temperatures.

Extremely cold air at 850mb will move over the southern portion of the province Wednesday night; with 850mb temperatures in the -25 to -30°C range, we can expect overnight lows close to -25°C for Wednesday and Thursday night, with a daytime high on Thursday barely above -20°C. The GEM-REG is a little warmer than the NAM on the cold air moving over the RRV, so there is a chance of temperatures being a couple degrees warmer than this, but I’ll always bet on the cold air.

Fortunately, it looks like the cold weather will be relatively short lived. Current indications are that another low tracking across the Prairies should push warmer air into Winnipeg for the weekend, with daytime highs near -5°C. More on that later in the week.

UPDATE: 6 records fell again today across Manitoba as most places enjoyed yet another mild day.
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Location New
Old Record
Fisher Branch 4.9 2.4 2002
Gimli 4.7 3.0 1990
Gretna 7.5 2.6 2006
Melita 4.3 2.5 2002
Pinawa 6.5 3.5 1990
Winnipeg (Tie) 5.1 5.1 1990

Changes Coming To Our Weather Pattern

Our remarkably warm January weather will continue for at least a couple more days before some large-scale changes begin to reshape our weather for the rest of January. The weather for the second half of January will certainly be colder than the first half, but just how much colder?

WRF Model Model Temperature Output for Monday, Jan. 9 at 12pm

WRF Model Temperature Forecast for Monday, Jan. 9 at 12pm

Temperatures will remain very warm to start the week. High temperatures on Monday will likely be in the mid single digits in much of Southern Manitoba. As a result, more temperature records will be threatened. Tuesday will also be unusually warm, but temperatures will be slightly lower, with highs closer to zero. The remainder of the week will be colder, with high temperatures for Wednesday through Friday being near to or slightly above normal (normal high being -13C). There is potential for some snow on Tuesday night into Wednesday with the passage of a low pressure system. Current indications suggest that we’ll see a few centimetres of snow from this system, but that could still change. We will continue to monitor this system and provide updates as we get more information.

Beyond this week the forecast becomes somewhat unclear. Most forecasts suggest that we’ll cool off significantly for the second half of January (see CPC outlook above). However, the extent of the cold weather is quite uncertain. We may have to deal with a so-called “roller-coaster pattern”, where big warm-ups are followed by big cool-downs. These roller-coaster patterns tend to bring a fair bit of snow, along with many days with gusty winds. As we move further into January the details will become clearer.

CPC Outlook for late January 2012

Climate Prediction Center’s Forecast for mid January 2012

Many people are wondering what is causing this spell of remarkably warm weather in Southern Manitoba. The main reason for the really warm weather this past December (and early January) is the Arctic Oscillation. The AO, for short, is a cycle which helps forecasters determine whether cold air will be bottled up in the north, or be allowed to spill down into Central North America. For most of December the AO was strongly positive, meaning that arctic air was kept well to our north. Current modelling suggests that a switch to a negative phase of the AO is likely by mid to late January. Once the AO switches to negative, Southern Manitoba will finally be able to get some real winter weather.

UPDATE: 6 records fell across Manitoba today as most places enjoyed yet another mild day.
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Location New
Old Record
Brandon 4.5 4.4 1986
Gretna 8.0 7.2 1958
Island Lake -0.2 -0.6 2002
Melita 8.6 3.9 2006
Sprague 5.9 5.0 1958
Thompson -3.3 -3.8 1983

All in all, 29 records were broken across the Prairies, with a majority of them happening in Alberta and Saskatchewan. Tomorrow will see another day of above-average temperatures in Southern Manitoba before cooler weather arrives on Wednesday.