Monday, February 23, 2009

Wintery weather to return to southern MB

It’s been fairly quiet weatherwise across southern MB over the past couple of weeks.. but Old Man winter is by no means done with us yet.  On Tuesday, a system tracking across the northern Plains will bring an area of snow across southern MB, moving into the Winnipeg area around the lunch hour. Snow will steadily increase through the afternoon into the early evening before tapering off Tuesday night. 5 to 10 cm of snow is possible over the Red River valley and SE MB including Winnipeg, with up to 15 cm possible over southeastern MB. Behind the system, an arctic ridge of high pressure will bring a fresh Arctic outbreak over southern MB for Wednesday through Friday with well below normal temperatures.  


  1. how cold are the overnight lows going to get in southern Manitoba??

    I hope it does not get as cold as northern Manitoba and with there - 50 C windchills

  2. My prediction...

    I am expecting 4 to 8cm in Winnipeg, Brandon, Portage, and Gimli. I expect the southern RRV (including Morden), and south-eastern Manitoba will receive 5 to 10cm of snow. Local amounts may exceed 10cm in extreme southern Manitoba, especially in the extreme south-east corner.

    In ND some places could see substantial freezing rain and/or ice pellets.

  3. The 00Z NAM run gives Winnipe 8.5mm of accumulation tomorrow, and Steinbach 9.5mm of liquid. Should this solution be true, it would equal about 10 to 15cm of snow in Winnipeg, and 10 to 20cm of snow in Steinbach. However I have very little confidence in this run. It does give a very realistic 6-9 hours time frame for this system. I think the model is picking up on convective properties, along the lines of what daniel had mentioned earlier.

  4. NAM shows bulk of the snow falling between 6 pm and midnight in Winnipeg.. with about 10 cm of snow within those 6 hrs. That's a fairly heavy rate of 1-2 cm/hr.. but if NAM timing is right, the worst of it should occur after the drive home.

  5. Snow has just started to push into the Brandon area.. look for snow to develop in Winnipeg by 2-3 pm, and become moderate to heavy at times for the drive home with snowfall rates of 1-2 cm/hr. Snow tapers off tonight with total accumulations of 5-10 cm likely for Winnipeg area. Looks like bulk of the snow will fall along and north of the TransCanada.. less to the south.

  6. Rob what time do you figure the snow will be past Winnipeg?

  7. I have a question. Does anyone think its time to re-evaluate the normal temperatures for any given time period? My argument is as such:

    It is nothing for the temperatures to drop 10-15 degrees(sometimes more) below the normal in winter months. Thursday's daily high is a prime example.

    On the other hand, in July and August our daily high is 26 degrees. I can't honestly tell you I remember a day where Winnipeg has hit 40 degrees celsius (14 degrees above normal)in quite a few years, and it certainly doesn't happen as often as we see much below normal temps in the winter.

    What do you guys think? This is 1 man who is thoroughly tired of the 08-09 winter.

  8. To my understanding do they not re- adjust the average daytime highs and lows every year!!!!

    Every year they would add the previous year and drop the the "oldest year".... but I'm just speculating how it is done!

    Anyone else????

  9. Daryl.. Main area of snow lasts for about 4-6 hours. If snow starts by 3 pm, it should be over by 9 pm or so.

  10. My understanding of averages is that Environment Canada updates them every 10 years and they use a 30 year average. The last update was in 2001 when they used 1971-2000 temperatures to arrive at the averages (this updated the old 1961-1990 averages). I assume the next one is coming in 2011, using 1991-2010 temperatures.

  11. Oops, I meant 1981-2010.

  12. I have a question maybe someone will be able to answer!!!

    I noticed on the Environment Canada radar that the "legend" to the right of the radar shows returns that could go up to 20 CM OF SNOW PER HOUR!!

    Is that even possible???
    Could you imagine a 20 cm per hour snowfall.....LOL

  13. Chris..

    My understanding of the averages is as follows:

    e.g. If you have one day in January that is +4, and another that is -22, the average temperature for the month (assuming it was two days long, for example purposes) would be -13. Just scale this idea up, and you will realize that you will have days that are way above normal, and way below normal. The result is a "middle-of-the-road" average temperature. The average isn't the mode, meaning that most days in January aren't necessarily -13, it is just the average or mean of all the days combined.

    Looks like the main area of snow shifted farther north than expected. The actual track of the system is completely contrary to what the models were showing last night.

  14. Snow coming down pretty good with visibility down to 1/2 mile at the airport.. snow rates of 1-2 cm/hr being reported upstream. Back edge moving in quickly from the west.. main snow area should be through the city by 6-7 pm. Look for snowfall totals of 5-10 cm by then..

  15. Total snowfall 7 cm here in Charleswood.

  16. 5-6cm here in Steinbach. Preliminary liquid equivalent is 2.2mm. That gives a snow ratio of 20-30:1.

  17. Attention now turns to the cold. A quick check of forecast lows for Saskatoon and Edmonton show very optimistic values from EC. 1040 mb high and 850 mb temps of -24 to -26 C by dawn Thursday in that region. Lows under the high this morning in NWT from -40 to -45 C.

    Fly in the ointment is cloud associated with the fast zonal jet stream off the pacific. Interestingly, GFS hints at this moisture streaming over top of the shallow high pressure. 700 mb RH fields show the clearing right from Edmonton to Saskatoon by Thu morning.

    The high is progged to erode those clouds by Thurday afternoon over S Manitoba setting the stage for a cold morning on Friday. GFS having a little trouble resolving exact pressure pattern over Winnipeg by 6 am Friday.. but general high seems to be east of us by that time giving a light southerly flow.

    If that pans out then EC's forecast low of -31 C at YWG may verify. However rural areas outside of Winnipeg and likely Rob's site may flirt with -34 C.

    A fast zonal flow characterized by a strong temperature gradient across the northern plains is the hallmark of a la nina pattern. This may not bode well for us as we enter the spring/flood season.

  18. Rob I have a question for you. It seems that this Winter has been a seemingly never ending pattern of air masses from the northwest and overall, below normal temps. Given "normal" highs are now around -6 we seem stuck in a pattern I worry about extending into a cool and disappointing Spring. I know long term forecasts are tough to predict. Do you see any break in this pattern? Thanks

  19. Mark..

    Unfortunately I don't see any signs of a rapid warmup into spring. A persistent La Nina pattern will likely maintain a storm track through the central and northern Plains through early spring.. putting southern Manitoba on the cold side of systems. What this means is that we will generally be colder than normal over the next month or two.. (not everday, but overall) with a gradual melt as we get into April. Similar patterns to this winter have resulted in colder than normal March and Aprils. The big question is how much preciptation we will get over the next couple of months.. it all depends on how closely that storm track sets up to us, and the frequency and intensity of storms along that track. That's a much more difficult thing to predict with any accuracy.. as a shift of 100 miles or so in overall storm track can mean a significant difference in preciptation distribution over an area. However the potential is there for above average precipitation over the northern Plains or into southern MB as we head into flood season.

    That's the way it's looking right now.. but as usual, it's up to Mother Nature to show us what really happens. Hopefully, she'll surprise us with a warm and dry spring..

  20. Daniel..

    Latest temperatures guidance showing lows of -30 to -35C across southern MB Friday morning with a low of -33C for Winnipeg. A light NW wind could get the airport site down to -35C. Not nice for the end of February, but note that Winnipeg has recorded -35C temps as late as March 20th (oh, joy!)

  21. A couple of comments about "normals"

    As mentioned in previous posts, "normals" are based on 30 year averages which are re-calculated at the start of every decade. This is the standard set by the World Meteorological Organization (WMO), and is used by weather services all over the world. Currently, normals are using averages over the 1971-2000 period. In 2011, normals will be based on the 1981-2010 averages.

    Normals are thus derived by looking at 30 years of weather data for a common day, and coming up with an average high, average low, etc. over that 30 year period. But using just a single average value and calling it "normal" does not give the whole story about what the weather should be like on a particular day. In reality, "normal" should be defined as A +/- B, where B is the standard deviation based on the variability of the weather over those 30 years. So if the average high for today is -6C, and the standard deviation over 30 years of data is 4C, then "normal" is really anything between -2 and -10C. (-6C +/- 4C) The average of -6C is just the midway point within a range of equally probable values for that day. Thus, a below normal temperature for this day should be defined as anything below -10C, and above normal would be anything above -2C. "Normal" is anything in between.

    In the winter, the standard deviation is large because temperatures can vary so widely, much more than summer. So in the winter, the "normal range" is much wider than in the summer. That's why you can't compare 14 degrees above normal in the winter to 14 degrees above normal in the summer. They are completely different distributions. (If none of this makes sense, look up normal distributions and standard deviation on the web or statistics book..)