Tuesday, September 29, 2009

2009 growing season ends for most of southern Manitoba

Clear skies and a light wind allowed temperatures to drop to below freezing this morning across much of southern MB, officially ending the 2009 growing season. The exception was near Lake Winnipeg and western MB where clouds kept temperatures above freezing overnight (see map) At Winnipeg airport, the temperature dropped to a low of -2.4C, ending a 114 day growing season that began late due to a record freeze on June 6th.

At Winnipeg airport, the average date of the first fall frost is Sept 22nd so today's frost was a week later than "normal", although the first fall frost date varies quite a bit from year to year. Average date for the last frost in spring is May 23rd which gives an average growing season of about 121 days using airport data. Last year, the airport had a 116 day growing season (Jun 3rd - Sept 26th), virtually the same as this year.

Within the city of Winnipeg however, frost was not widespread this morning. The Forks downtown had a low of +1.4C, and in Charleswood, my station registered a low of +0.5C with just some some light frost noted. Downtown Winnipeg has a much longer growing season than the airport, due to the urban heat island effect that keeps night time temperatures warmer than rural areas. The average first fall frost downtown is Oct 5th, while the last spring frost is May 4th giving an average growing season of 159 days downtown, or 38 days longer than the airport. For most areas of the city, the length of the growing season lies somewhere between downtown and airport values.


  1. Here in Silver Heights, I dropped to +0.9C this morning, but there was a hint of frost on the grass. My Stevenson screen sits about 5 feet above ground level.

  2. Very nice graphic Rob.. what is the source? Too bad the lake effect clouds off the south basin dissipated by 1 am in our region. When I went to sleep it was still 8 C and cloudy!

    Also the did not shift to SE until 9 am.. had that happened just 2 hours earlier that large spike below zero would not have happened at YWG.

    It would be interesting to compare the length of growing season before and after the recording station was moved to its current location in the early/ mid 90s. It used to be much closer to the terminal building and away from the current drainage effects.

  3. Daniel.. that map comes from the Manitoba agriculture guys.. (http://tgs.gov.mb.ca/climate/)

    Shows the frost distribution quite nicely..

  4. Daniel I was interested in that as well until I cmae across an EC map of growing seasons . Link on name

    Apparently a few days doesn't change things much in Canadas Ag world


  5. Thanks for the links Rob and Jim.

  6. Any guess on how much rain Winnipeg will be getting tomorrow????

  7. How much rain will we get? Good question.. it depends where you live. Models coming in line that rain will overspread southwest MB overnight into Thursday morning and then into the western Red River valley mainly west of a Portage to Emerson line. The rain shield then magically stops as it pivots to our west and south with the main upper low cutting off and drifting over the Dakotas. Winnipeg and areas north and east get little or no rain while areas west of a Portage-Emerson line get a good soaking of 20-30 mm into Friday. It will be interesting to see how well the models do on the eastward extent of the rain shield.. right now, Winnipeg looks to be on the edge of any significant rainfall but it will be a sharp boundary between rain/no rain. It's looking likely though that areas west of Winnipeg will be getting a good soaking with this system.

  8. Has anyone noticed that the forecast from Environment Canada's WEBSITE has NO mention of any wind in their forecast while the forecast on the TV does!!!

  9. Just when you think you can interpret some of the data it takes on a hidden meaning of its own.

    The CYWG Airport History page shows yesterday and todays avg Hi Temp as 11C and Low as 0C. (Would roughly be MEAN 5.5.)

    Averaging CYWG records back to 1996 substantially differ from this.as do the EC 1971 - 2000 averages.

    My name or

  10. The models are in relatively good agreement for rainfall amounts tomorrow. Here are my predictions:

    Steinbach: 2 to 4mm
    Winnipeg: 5 to 10mm
    Brandon: 20 to 25mm
    Portage: 10 to 20mm
    Morden: 20 to 30mm

  11. Re: Weatheroffice forecasts with no wind. This started last night for some reason. Very odd. It's occurring right across the country, not just southern MB. Looks like some sort of data feed problem.

  12. Note that Woodlands radar is down.. and will be down until sometime tomorrow for repairs. You'll have to use Foxwarren, Minot and Grand Forks radars to see progress of rain into southern MB.