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.

Slight Cool Down Before Mild Temperatures Return

26 temperature records were broken across the Southern Prairies yesterday as warm Pacific air flooded the region tied to a low pressure system tracking through central SK/MB. The RRV will see a cooler weekend as colder air is creeping southwards on the backside of this system, however the deep freeze is still a little ways off.

Overnight Snow along a weak trough in NW flow

3hr. QPF from the 12Z Jan 06 GEM-REG valid at 09Z Saturday Jan. 7

An area of snow will slowly push southwards through the RRV today, brining only minor accumulations to the region. The system should clear out by this evening, with the chance of a few light flurries through the night in a weak northwest flow. A ridge of high pressure will then work across Southern Manitoba Saturday & Sunday, brining cooler temperatures to the area with daytime highs in the -10 to -5°C range and overnight lows in the -10 to -15°C range through the region.

By Monday, another low pressure system tracking through the northern Prairies will drag more Pacific air over the Prairies once again pushing temperatures above 0°C. Many areas in Southern Manitoba should see daytime highs Monday near 5°C. Currently, it doesn’t look like temperatures will reach nearly as high as some places did yesterday, but things will become a little clearer closer to the day (naturally). It’s quite likely we’ll more daytime high record temperatures broken on Monday.

850MB temperatures from the GEM-GLB

850mb temperature from the 00Z Jan 6 GEM-GLB valid at 00Z Thurs. Jan 12

After that, it looks like we’ll be seeing a bit of a cold snap. On the back side of the system, a fairly strong push of Arctic air will flood through the Prairies, bringing us our coldest temperatures in a while. It looks reasonable, as temperatures in Oymyakon, RU have dropped below -50°C (-55°C when I checked last night), with daytime highs only around -35°C, which is a good indicator for colder weather pushing over the poles towards the Prairies. We won’t get nearly as cold as they are, but by the middle of next week, daytime highs around -15°C with overnight lows around -25°C are certainly possible, as 850mb temperatures are forecast to dip down to -25 to -30°C over Souther Manitoba . This system looks relatively dry, however we may shift into a pattern that will favour clippers tracking along the international border which may bring long-awaited snow to southern portions of the Prairies and the Northern Plains.

Chance of Freezing Rain Over The Red River Valley

A large upper trough swinging across the Prairies is supporting two low pressure systems, one in central Saskatchewan and one in the Northern Plains of the United States, that will move across Manitoba overnight and tomorrow morning, bringing with them snow and the risk of freezing rain.

Dec. 31 Prog

For southern Manitoba, the main concern will be the precipitation generated along the apex of the frontal wave as it occludes southeastwards from the northern low in Central Manitoba to Minnesota. The warm front will align somewhere near a line from Winnipeg to Sprague, and slowly shift south/southeast through the day. Areas near the International Border have the greatest risk of freezing rain, due to the higher intensity of the precipitation expected there. The risk diminishes as you head north towards Winnipeg. I agree with the latest Environment Canada forecast that calls for ice pellets in Winnipeg; the warmest air should stay south of the city and we will likely have enough cold air entrenched to freeze any rain that comes out of an above-freezing layer. I can’t exclude the chance of a brief period or two of freezing rain, especially late overnight and early tomorrow morning. As this system develops, snow will become the predominant weather type, and much of the RRV can expect between 2-4 cm of the white stuff, while a few localities may get up to a couple inches.

I think it’s likely areas south of Morris will see some duration of freezing rain before sitching over to snow. The good news is that this doesn’t have the makings for a large-scale freezing-rain event, so there shouldn’t be any concern of widespread highway closures. Given that some roads are already very slippery, however, drivers should take caution when travelling overnight or tomorrow as fresh snow may be hiding a layer of ice underneath. Always drive with care when freezing rain and snow occur.

This system should clear out tomorrow afternoon, bringing in strong northwesterly winds behind it gusting up to 70 km/h. Fortunately, the arctic cold front is well to our north, so while chilly, we likely won’t even seen our temperature drop to even -15 to -20°C for overnight lows before the next swell of warm air pushes across the Prairies, bringing us continued pleasant winter weather with daytime highs in the -5 to 0°C range! The strong winds will move in tomorrow evening and last through much of the day on Sunday before tapering off, bringing us wind chill values as low as -25 in Winnipeg.

So hang in there, a couple chilly days and we’ll be back to pleasant temperatures with a fresh coat of snow! Happy New Year!

Rainy Day on Tap for Winnipeg

Winnipeg will see a few showers this morning develop into a rainy afternoon before it all turns to wet snow this evening as the first “summer-y” system of the year pushes through Southern Manitoba.

Hand-analysis of the 925mb Height/Thermal Field for 12Z March 20

A very summer-y low is passing through North Dakota this morning, with a warm front draped west-to-east across much of the state, just south of the international border, before it dives south through Iowa. This system has brought with it copious amounts of warm air and is the first real summer-like system of the year.

East of the warm front, in Iowa, a complex of thunderstorms are moving across the state, supported by a 60 kt 850mb jet riding over the surface warm front, bringing with it moist air with Θw values near 20°C. This 60 kt LLJ then arcs north and pushes into Northwestern Ontario. As can be seen by the red shading in the analysis I have done this morning, warmer air is being pushed up through much of Southern Manitoba, including the RRV, Interlake and Parkland regions of west-central Manitoba. With the surface warm front just south of the border and plenty of warm air overrunning it, this has brought a mix of precipitation for areas in Southwestern Manitoba across the Trans-Canada highway into the Whiteshell and north.

1.5km CAPPI Radar Reflectivities

Pilot Mound, Morden, Steinbach and Sprague should escape most of the precipitation until later today. Being so close to the warm front, the precipitation is actually developing north of them where the air aloft that is being lifted is saturating. For those areas, expect a cloudy day with drizzle likely and if the wind manages to calm a bit (say to 15 km/h or less) fog patches are certainly possible. By later this afternoon, rain should move into the area, though with accumulations of about 5mm. For Portage la Prairie, Winnipeg, Dugald, Selkirk/Gimli and the Whiteshell, showers seen this morning will continue to develop and intensify to an area of rain by this afternoon. Expect to see about 5-10mm of rain before switching over to wet snow this evening. Do not be surprised to see a few snowflakes today, though; as it is quite likely for there to be embedded convection in the rain bands, areas of heavier precipitation may be able to produce rain mixed with snow as the shallow warm pool is unable to completely melt all the precipitation.

12Z 20 March 2011 GEM-REG 12h QPF Accumulation valid 00Z March 21 2011

Further west, over the higher terrain, the precipitation will predominantly be snow. Dauphin/St. Rose/Minnedosa are under a heavy snowfall warning as 10-15cm of snow are expected by this evening. Fortunately, as this weather system is driven primarily by warm air, the precipitation should end quite quickly as the low pulls out of our area this evening.

All in all, it’s quite a good day to stay inside with a hot drink and read a book. A little bit of everything will be seen through the afternoon, and unless you’re a big fan of having a new “Rally Inspired” paint job on your car, it’s best to stay off the messy, messy roads.

The next significant weather system will pass through on Tuesday, and this system will receive plenty of attention as it develops as it has the potential to produce significant amounts of snow/rain, and could add uncomfortable amounts of water into the Assiniboine/Red River drainage basins. I’ll post some more information about that system on Monday when things are a little clearer.