Tuesday, February 06, 2007

Currently in Winnipeg, it's -27C... or is it?

Well turn on the radio or look on the web, and you'll find that the current temperature in Winnipeg is -27C as of 1 pm. However, a look at weather stations in and around the city tell a different story. Most stations in the city are around -22C with even some -19C readings around St Vital. (see Google map of Winnipeg area temperatures) So why the big difference from the "official" temperature? That's because the official temperature is taken from the Winnipeg airport weather station, which is located in a remote field in the northwest part of the city. Most times of the year, or if it's windy, there's not a big difference between the airport temperature and the rest of the city. However under clear and cold conditions with a light northwest flow, the airport site is usually several degrees colder than the city itself since it's getting cold air drainage from surrounding snow covered fields. In the city itself however, that light northwest flow is modified by buildings, trees, pavement, etc. so that temperatures can be several degrees warmer than at the airport.. sometimes as much as 5 to 10 degrees warmer. This is known as the "urban heat island effect". This effect will become even more noticeable over the next few weeks as the sun gets stronger and warms up the city core even more. So cheer up.. it's not really -27C, it's a balmy -22C instead! (unless you're standing in a field on the northwest side of the airport!)

4 comments:

  1. I read this post last and had already added to your earlier post from Feb 3 with my 2 cents about the effects of the 'urban heat island'. Although not as strong in Regina I find myself explaining it to people all the time. I find it quite interesting ever since we did a study on it good ol' Stoon back in University. We drove around the city one evening taking temp readings and then plotting them. When we are 'bragging; about how cold it is we tend use the airport temp and when we are bragging how warm it we will use a value from a PWS if it higher. Makes for a better story. :-)

    Dean in Regina - http://nwrweather.com

    ReplyDelete
  2. Sounds like a fun project to do!

    Okay...one last comment about the airport ;-) Because of the heat island...the city should be warmer than the surrounding countryside with light winds, etc.

    However..as previously mentioned, there appears to be dramatic cold air drainage at the airport. Temperatures drop off faster than at stations in small towns like Gimli, Fisher Branch, etc. Maybe there are a few more trees or buildings next to those locations.

    Even the airport made it above -20 today...heatwave! The "warmer" air seems to have backed in all the way off the North Atlantic and around Hudson Bay. The coldest temperatures are now in Saskatchewan.

    Btw...the google map is quite cool!

    Dan

    ReplyDelete
  3. You want to see cold air drainage, check out some of the temperature readings at my place:

    http://www.bezte.ca/weather

    I live just northeast of Birds Hill Park and I am almost consistently colder than the airport in Winnipeg. I hit -44°C on Feb. 5th. Kind of an interesting local affect if you are a weather geek like me, but not so great in the spring when you are trying to start your garden!

    Keep up the great work Rob.

    Daniel

    ReplyDelete
  4. Thanks for the link Daniel. I've added it to my favorites.

    ReplyDelete