Category: Forecasts

Rainy Day on Tap for Winnipeg

Brad Leave a comment

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.

Miserable Weather on Tap

Brad Leave a comment

Don’t let the bits of sun and relatively warm temperatures fool you; tonight is going to be downright awful.

A complex double-barreled low pressure system (a term used when two separate lows are moving together as one entity) is moving out of Saskatchewan and Montana into Southern Manitoba this morning.  This system has brought a mix of precipitation into Southern Manitoba this morning, including freezing rain over western areas and heavy snow in the Interlake.  Numerous warnings have been issued across the region for weather happening now or expected to happen this evening.

The risk of freezing rain will persist through much of Southern Manitoba for an hour or two longer before temperatures will be warm enough that any precipitation will simply fall as rain.  Even though little precipitation has fallen over the Red River Valley this morning, Manitoba Highways is reporting that many sections of Highway 75 and Highway 1 heading west of Winnipeg are partly iced cover due to the slight melt and re-freeze yesterday afternoon.  As temperatures will just barely get over 0°C today, there may be portions of highways that are still quite slippery throughout the day.

Tonight
Perhaps the biggest impact from this storm will occur tonight over the Red River Valley.  As the low passes to the east, cold air will plummet down the backside of the system through the RRV.

 
24hr Accumulated QPF valid 12Z Saturday March 12, from the 00Z run of the GEM-LAM REG Model 

As the system passes, an intense band of wrap-around precipitation will move into the RRV, bringing heavy snow to Winnipeg by 6 or 7PM tonight.  Along with this heavy snow, this system will bring significant winds as well.


Surface Winds valid 06Z Saturday March 12, from the 06Z run of the GEM-LAM REG Model 

Sustained winds of 50-60 km/h with gusts potentially as high as 90 km/h will blast cold air into the RRV, which will plummet the temperature from 0°C or +1°C down to approximately -14°C or -15°C over the span of a few hours.  This will rapidly freeze any standing water which will very likely create extremely slick roads tonight.  And last but not least, these winds, combined with the heavy snow, will very likely produce blizzard conditions through a good portion of the night.

The weather conditions will deteriorate extremely quickly this evening to become a significant winter storm.  Anyone who has plans to travel in the Red River Valley tonight should keep updated on warnings, forecasts (or for a smartphone), the RADAR, and highway conditions to be able to make safe, educated travel plans.  Good satellite imagery to track this system can be found here at the U of M.

Snow on the Way

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A significant storm system is currently developing in Montana this morning that will push it’s way eastwards across the Northern Plains of the United States and into Northwestern Ontario by Thursday morning.

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Snow will push into Saskatchewan today and a snow band will develop aligned somewhere between Shaunovan and Kamsack, as shown in the above model image. There is a slight chance that some of these sites will see warning-level amounts of snow, however it currently looks like the possibility of that is borderline. This band of snow will then consolidate and push into Central Manitoba, while a second impulse brings an area of lift into Southeastern Saskatchewan and Southern Manitoba.

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This second band of snow will move eastwards through Southern Manitoba, giving most areas somewhere between 5-10cm of snow. Brisk northerly winds will push into the Red River Valley on the backside of the low as it moves into Northwestern Ontario, and with fresh snow, significant blowing snow will exist in any open areas inside the valley. Based on this projection, the snow would begin in Winnipeg late Thursday morning and last until sometime Friday morning, with the heaviest snow and worst conditions coming by late Thursday afternoon. Significant blowing snow would most likely occur during the evening and overnight period, which will be important to take into account for anybody planning to travel on Thursday evening/night, especially through the southern Red River Valley.

At least, that is how this system should evolve. The jury is still out on what will actually happen. The last 5 runs of the GEM-REG model have all produced drastically different results. The GFS and NAM offer little consensus on where the heaviest snow will be, the UKMET shows similarities to the 00Z GEM-REG run (from which I’ve gotten these images), and ensemble models show little confidence in the track and evolution of this system. Why is this? One look at the Water Vapour imagery shows the problem:

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The two +’s in this image are the two main vorticity centers for this incoming system, and the yellow arrows depict their rough paths given the streams they are each in, respectively. This system is a somewhat unique scenario, wherein the two “streams” of air are close together, and are moving in sync. Typically, the reason this is a problem is because the models can have a hard time dealing with the energy distribution between the two streams. We have seen many times in the past where model solutions flip flop back and forth and back and forth, even when the event is close (less than 36 hours away) where the model error could be attributed to the complex dynamics that occur when this situation occurs.

So if we don’t actually know what’s going to happen, what’s going to happen?  Odds are that the RRV will get snow on Thursday.  I’ll go on record saying we’ll get at least 3-4 cm.  In a worst case scenario, a line from Pilot Mound to Winnipeg could get as much as 10-15 cm, however I think that’s quite unlikely.  If we get fresh snow in the RRV, there will be blowing snow Thursday night as the winds pick up to 50G70 km/h out of the north.  And sadly, our wonderful warm spell is going to come to an end this week, with temperatures plummeting to -20°C by Friday morning.

I’ll keep the comments of this post updated as the system develops and try to narrow down the impact it will have on Southern Manitoba.  Stay tuned!

Snow For Much of Southern Manitoba Today Into Tomorrow

Brad Leave a comment

A system moving through the Northern Plains of the United States will push snow northward across the international border into much of Southern Manitoba, with warning-level amounts in some areas close to the International Border.

Heavy snowfall occurring in Montana is pushing east-northeastward into southeastern Saskatchewan and Southern Manitoba. Heavy snow giving near zero visibilities at times is expected to develop in southern regions near the international border, including the Melita, Pilot Mound, Morden/Winkler, and Emerson regions. Environment Canada has issued Snowfall warnings for the Melita and Pilot Mound/Kilarney regions, with 10cm of snow expected in areas close to the border, and the potential for amounts in excess of 15cm in upslope snowfall areas of Pilot Mound. All sorts of warnings exist for most of North Dakota, so anybody who has to travel south today should take extra precautions and prepare for extremely poor driving conditions.

For Winnipeg, the snow will push into the city mid-to-late afternoon and stick around for 18-24 hours. Thoughts based of previous model runs would have been for just some light non-accumulating snow, even taking into account that all models were keeping this system too far south. The new GEM-REG run has, however, pushed the system (in my opinion, correctly) further North and is bringing more substantial snow into the Winnipeg area.


GEM-REG 24H Cumulative Precipitation valid 12Z Tuesday 21 Dec. The heavier snow expected along the International Border and through North Dakota is the dark-ish green shading, indicating 7-10mm of liquid equivalent precipitation. This covers Monday morning to Tuesday Morning.

While we won’t deal with the extremely poor traveling conditions of our neighbours to the south, we will see accumulations of 2-4cm when all is said and done. South of the city, amounts of 5-10cm should pile up. The bulk of the precipitation will pull out of the province overnight, however there will be a weak trough that hangs back through the RRV and southeastern Manitoba that will continue to produce light snow through much of the day tomorrow.


GEM-REG 24H Cumulative Precipitation valid 00Z Wednesday 22 Dec. This shows the precipitation expected to occur Monday evening through Tuesday evening. Light snow, without significant accumulation, is expected to occur through much of southern Manitoba through the day on Tuesday.

After this system, we should have a fairly pleasant rest of the week, with highs just above or near -10C and lows in the low minus teens.

Another small point of significance to this event is that it may be one of Winnipeg’s last chance to break the record for wettest year ever. The current record is 723.6mm from 1962. We currently sit in 3rd wettest year ever at 716.0mm, with second place only a hair ahead of us at 718.4mm (which was from 1953). We need only another 7.7mm to break the record, and this system, in a worst case scenario could give us something in the 4-6mm range.

Worth noting, is that in many of the wettest years ever, a major flood did not occur in the following spring; just shows how the melt rate and spring precipitation are the most crucial aspects in our annual floods.