The little warm spell we’ve been in over the past several days has come to an end. Cooler temperatures are in store for this week, but conditions will remain above-normal.
Cooler weather is expected in southern Manitoba on Monday
Monday
Monday
-8°C / -13°C
Mainly cloudy with a chance of flurries
Today will see temperatures fall from the very mild conditions experienced on the week. High temperatures will be in the upper minus single digits, with a gusty north wind. There is a chance of flurries during the day, particularly in the morning. Unfortunately, even this change in the weather isn’t expected to reveal the sun, as we continue to languish under mainly cloudy skies.
Tuesday
Tuesday
-11°C / -15°C
Mainly sunny
Tuesday will be slightly colder than Monday, but not by much. High temperatures will be around the -10°C mark, with a light north-west wind. The sun should finally come out, making for a mainly sunny day.
Wednesday
Wednesday
-10°C / -18°C
Mix of sun and cloud
Wednesday will see temperatures that are very similar to Tuesday. Highs will once again be near the -10°C mark. Winds will be light, making for a fairly pleasant day. Cloud cover will be variable, with generally a mix of sun and cloud through the day.
Long Range
The long range forecast suggests we’ll see a gradual warming trend as we move towards the weekend. Temperatures will likely move towards the mid minus single digits, which is still above-normal for this time of year. No major arctic blasts are currently in the forecast, allowing our mild December to continue!
The West Coast of North America has been subject to several systems after coming onshore in the past couple weeks, bringing with them heavy rains and strong winds which has led to flooding. Once again, the culprit for the moisture-laden systems in this region has been the atmospheric river. This atmospheric river is a term used for streams of moisture typically originating in the tropics, which head Poleward. Eventually the water precipitates out – it is often enhanced along the west coast due to orographic precipitation, leading to flooding.
Higher PW values streaming from the tropics to the Californian coast are associated with the atmospheric river. (Source: CIMMS)
Earlier this week, the BC coast was hardest hit where over 400mm fell on parts of Vancouver Island in 6 days. Flood watches were issued as towns on the Island watched waters rise. The towns of Courtenay and Port Alberni were soaked with over 150mm by Wednesday – some residents were forced to evacuate their homes due to the rising waters. Strong winds were also a problem; gusts over 100km/h were recorded across the coast, even in large cities such as Portland, OR. These winds knocked out power to roughly 75,000 residents in BC alone. In addition to the wind and rain, landslides also became of concern in Southern California. Saturated grounds led to a large slide in Camarillo Springs, CA, which affected over a dozen houses.
Estimated rainfall along the BC coast from December 4 to 10. (Source: Environment Canada)
The system even brought a weak EF-0 tornado which was spun-up in one of the stronger rain bands that came onshore. The tornado passed through a small area in southern Los Angeles yesterday morning and stripped roofs of their tiles – no one was injured thankfully. Reports of 60-100mm were common along the Californian coast, but localized amounts of 200mm or higher did occur. The highest precipitation report as of Friday came from an area in the northern Sierra Nevada Mountains where 450mm of precipitation fell; the amounts here were enhanced by orography.
Unfortunately models are showing another system impacting most of the West Coast early next week, not leaving much time for things to dry out.
The weather pattern that has brought temperatures well above seasonal to Winnipeg[1] – despite the persistence of low cloud supplied by the outflow winds of a high pressure system to our southeast – will continue to pump warm Pacific air eastwards into the region for another couple days. By the end of the weekend, however, a cold front is set to push through bringing more seasonal temperatures back to the Prairies.
Friday
1°C / -2°C
Mainly cloudy
Saturay
3°C / -3°C
Mixed skies
Sunday
-1°C / -13°C
Mainly cloudy; slight chance of flurries
Winnipeg will see cloudy weather today as low cloud entrenched in the Red River Valley refuses to exit as southerly outflow winds continue to reinforce the low-level moisture trapped underneath the substantially warmer air just off the surface[2] that has spread over southern Manitoba.
The cloud will be accompanied by breezy southerly winds to 30-40km/h. The temperature will only climb to around 0 or +1°C today. Some clearing is possible later in the day as drier air begins pushing eastwards into the Dakotas and may work its way northwards in the flow. It’s far from certain, but we could see some breaks in the cloudy skies later today into the evening. Temperatures will drop to around -2°C tonight.
This Winnipeg forecast sounding – valid at 10AM CST Friday, December 12, 2014 – shows a thin layer of saturated air right at the surface which will continue to produce low-level cloud.
Saturday looks to bring mixed skies with a lot of uncertainty on exactly what we’ll see. Weather models want to clear things out fairly well and give us sunny skies with a high near 6°C. Unfortunately, I’m not entirely convinced that’s what will happen. The Red River Valley will sit on the cusp of where the return flow from the high pressure system meets drier air pushing in from the southwest. However, a low pressure system approaching from the west will likely back the winds slightly, tapping into the low-level moisture in the outflow winds from the high. Additionally, large-scale lift ahead of the low could also work to develop more low cloud ahead of the approaching cloud. So while the day may end up sunny, it seems a bit more likely we’ll see mixed skies or increasing cloud through the day. Due to that, I think the high will be closer to 3 or 4°C with temperatures dropping to around -3°C overnight under mainly cloudy skies.
Sunday will be a mainly cloudy day as a low pressure system passes to our south. Northwesterly winds will bring more seasonal Arctic air into the region through the day, limiting our daytime highs to -1°C with just a slight chance for some light flurries.
Through much of next week seasonal to slightly above seasonal temperatures are expect with no significant precipitation events in the forecast.
Our daytime highs near -1°C are about 8°C above seasonal for this time of year. ↩
As shown in the figure mid-way through this post, while surface temperatures will struggle to climb just above 0°C, temperatures just 1.5km off the ground are nearly 17°C. ↩
Mild temperatures, above seasonal for this time of year, will be in place over Southern Manitoba, but the potential warmth will be limited over much of the Red River Valley and areas east thanks to an extensive area of low cloud that has moved into Manitoba and North Dakota within the outflow from a ridge of high pressure situated over Michigan.
Wednesday
-2°C / -3°C
Mainly cloudy & windy.
Thursday
0°C / -2°C
Mostly cloudy and mild
Friday
+1°C / 0°C
Mixed skies and mild
Today will be 7-8°C above seasonal for this time of year[1] with temperatures climbing to the -2 to -1°C mark by late this afternoon under cloudy skies. It will be moderately windy too with sustained wind speeds in the 30-40km/h range with gusts up to around 50km/h, making it feel like a much cooler day than it actually will be.
As the jet stream lifts northwards, warmer air lifts northwards as well.
The warming temperatures are thanks to a large upper-level ridge moving into the region which will develop an increasingly southwesterly flow across the Prairies and shift the jet stream further north. These two things together are helping push mild Pacific air into the southern Prairies. Unfortunately for Winnipeg, a ridge of high pressure anchored over Michigan will result in a persistent flow of colder air near the surface which, coupled with the cloud cover, will result in temperatures much lower than will be seen further west where a combination of more sun, terrain and some slightly more favourable wind directions will push temperatures towards record high territory.
Temperatures will barely drop tonight, perhaps just a degree or two, with winds tapering off to around 20km/h. The cloud cover will possible break up a little bit, but will likely remain cloudier than not.
Thursday will likely be another mostly cloudy day as the stratus continues to limit our daytime highs. We should see the temperature climb up to around 0°C with the southerly winds near 20km/h diminishing to light through the day. Thursday night will bring some scattering of the clouds, although mixed skies persisting until morning is the most likely situation at this point. Indications right now show that there may be a slight risk for freezing drizzle on Thursday night. Expect a low near -2°C.
Friday will be the nicest day of the three with a little sunshine looking a bit more likely than today or tomorrow. Temperatures will likely climb up to around 0 or +1°C, however if we end up with substantial amounts of sunshine, +2 or +3°C may even be possible.
Much Warmer over Western Manitoba
For areas in Western Manitoba, especially those on the northern side of the Turtle Mountains or those in the Dauphin area near the Riding Mountains, temperatures will be quite a bit warmer over the coming days. A combination of several factors, including:
Further proximity from the ridge over Michigan will minimize the amount of cold air being reinforced near the surface in a return flow.
Winds have a more southerly to slightly southwesterly component which will help tap the warmer air.
Terrain is not a valley that likes to keep cold air caught in it.
Downslope mixing on the northern side of larger terrain features will help couple the surface and warm air aloft.
This all means that for several days, beginning today, daytime highs will generally climb into the +2 to 5°C range for areas in the more generally open area to warmer values of +5 to +8 in regions downwind (north of) major terrain features such as the Riding Mountains or Turtle Mountains.
Warmth Spreads into the Red River Valley on the Weekend
The even warmer weather will spread into the Red River Valley for the weekend, however, as winds shift into a more southwesterly flow, helping push out the cold air and get some of that more substantial warmth into the region. Saturday looks to bring highs in the low-to-mid single digits with cooler air filtering in on Sunday, dropping highs back to the cooler side of 0°C alongside a chance for some light snow.
The seasonal daytime high for Winnipeg this time of year is around -9°C. ↩
