Monday, February 20, 2017

Thaw coming to an end.. colder weather on the way

After another mid winter mild spell that featured thawing temperatures and rain, things will be cooling off this week as a colder airmass spreads over western Canada. Preceding the cooldown will be a fast moving clipper system that may bring a coating of snow (Tr - 3 cm) Tuesday night into early Wednesday across Winnipeg/srn MB.  Temperatures will be dropping behind the system for Thursday into the weekend, with temperatures more seasonable for late February (normal high -7, low -17C)  That will be good news for outdoor enthusiasts and winter events such as the Festival du Voyageur which has had to cancel several outdoor events due to the mild springlike weather. In addition, no major storm systems are expected through early next week over southern MB, so the colder weather should also be accompanied by dry and mainly sunny conditions. Good opportunity to finally wash that car again!  

18 comments:

  1. Hey rob. Any ideas on the upcoming spring? There's a lot of bare fields here in Winnipeg now too. What snowdepth are you picking up?

    Are there indications it will be yet another early spring like last year or should the colder weather persist into March?

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    1. In terms of snowcover, you need to look at depths over the open country which surrounds the city. In those areas, there is barely 5 cm with many bare patches as you noted. Once the generalized snowpack is gone, it allows temperatures into the double digits and rapidly melts the large piles in protected areas like backyards etc.

      That will not happen in the near future (next week), but the degraded/ sparse snowpack is allowing for modification of the cooler airmass overhead (above guidance) and will result in seasonable temperatures.

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    2. Matthew.. No idea what type of spring we'll have.. but based on what we've seen so far this winter, I would expect to see an average to milder than normal spring. As mentioned, snow cover is getting sparse across the Prairies and northern Plains, and that will help to bring milder air into southern MB. Latest CPC outlooks indicate cooler than normal temps for us for the beginning of March then a trend towards milder than normal temperatures over the southern Prairies by mid March.

      The big question of course is precipitation. If we stay drier than normal, that would help us get into a milder weather pattern sooner. But if we get into a snowy pattern, the increased snowcover would delay progress into warmer weather. Unfortunately, predicting precip patterns and future snowfall is a lot more difficult.

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    3. As of today (Feb 25th), Winnipeg airport is reporting 18 cm snowdepth while I have 25 cm in my yard (usually I have more due to less exposure than the airport).

      Looking at past years with similar snowdepths at this time of year, we generally lost our snowcover by the 3rd-4th week of March. That varied of course from year to year (anywhere from March 10th - Apr 14th), but that was the general average. Given that we'll likely be cooler than normal for the beginning of March this year, I'd say our snowcover will likely stick around through at least the third week of March, barring any major snowstorms in the next 2-3 weeks.

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    4. As discussed before, snow sensor data can be quite unrepresentative. There is always spatial variability of snow depth due to the effects of wind, sun etc in open regions. Currently, there are extensive bare patches showing up, and in terms of a spatial average there is likely considerably less than 18 cm (at least around S. Winnipeg). The generalized snowcover should melt fairly rapidly when we start getting above zero temperatures again (barring further significant snow accumulations).

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    5. Anonymous.. that's quite true that snowcover is quite variable in a given area depending on wind and solar exposure. Generally, snowcover in residential areas will be higher than more exposed areas where snow can easily blow away. That's why it's important to maintain snowcover measurements at consistent locations to monitor trends from year to year, with the understanding that snowcover will vary locally depending on exposure.

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    6. Yes, and your records representing residential conditions are appreciated. Ideally a range would be very informative of snow-depths at sites with different exposures etc for a specific area.

      The current snow cover analysis from NOHRSC shows anywhere between 5-25 cm around Winnipeg, with higher pockets in the southern RRV (>= 50 cm). Last aerial survey however was before the big melt, so should be taken with a grain of salt.

      As it stands now, the remaining snowpack is very dense in terms of moisture, with water likely frozen at its base (which had just started running off before temperatures cooled). Those regions will quickly contribute to high runoff locally vs areas with deeper snow cover and slower response. Therefore an accurate estimation of depth is critical to flood forecasts. The province seems to conduct its own snow surveys to estimate snow water equivalent, but also relies considerably on NOHRSC data.

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  2. Snow storm next weekend?

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    1. Looks more like a clipper system tracking through the MB lakes.. bulk of the snow would be over Interlake and central Manitoba rather than the south. We'll see how models trend over next few days..

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  3. Hey Rob,

    Does next week look like a week of snow? Weather network has lots of snow in the forecast.

    Thanks

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    1. Models hinting at two systems next week.. one in the Sunday-Monday timerange (Mar 5-6) and the other later in the week possibly around Thursday (Mar 9)

      The track of both systems looks like they'll be spreading in some mild air over the RRV that could be accompanied by a messy mix of rain, freezing rain and snow. That would tend to limit snowfall amounts for us.

      Right now, there is not very good model agreement on these systems, so all in all, I would say I don't have a lot of confidence that we'll be seeing a lot of snow next week due to uncertainty in storm track and precip type issues.. but there will be a couple systems to watch.

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  4. I'm very surprised how much snow we've lost already considering we had a 54cm depth in early January. I hate these awful mid winter thaws. After the latest start to winter on record, yet another early spring. It just sucks. I'm hoping next week's systems will fall as snow so that will keep us in winter for a bit longer. The last 2 years snow was gone on march 15th and I expect it'll be around the same this year.

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  5. Things are getting a little more interesting on that system for Monday.. depending on what model you believe. The Canadian GDPS is the most aggressive in terms of snow over southern Manitoba.. taking a Colorado low track through western Minnesota into NW Ontario, pasting the RRV and SE MB with 20-30 cm of snow Monday into Tuesday. The GFS takes the storm across southern MB, putting the heaviest snow over the Interlake. Euro is similar, putting bulk of snow over nrn Interlake/central MB with minor amounts over southern MB after some rain initially. So still a big discrepancy with storm track which will have significant impact of where the heaviest snow sets up, and how much. Right now, the GDPS looks like the outlier.. but we can't discount it yet, and will just have to wait and see how all models trend over the next few days to get a better idea of how this storm may impact southern MB.

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    1. 18Z GFS more in line with GDPS now.. taking storm track a little further east over NW Ontario which puts heavier snow through RRV instead of further north and west. GFS now showing 15-20 cm for Winnipeg Monday into Monday night. We'll see if they maintain this solution or shift it again. Getting interesting though.

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  6. Thanks for the update

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  7. Note.. even if track is further west and we don't get a lot of snow out of this, all models agree that it will be getting windy and colder Monday afternoon into Monday night behind this storm system.. so any melted precip/slush Monday morning will be freezing hard by Monday evening which would lead to some slippery and hazardous driving conditions Monday afternoon/night, especially if accompanied by some snow. Something to keep in mind..

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  8. I will look at model runs tonight and will put up a new blog post on the Monday system tomorrow.

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