Saturday, September 18, 2010

Frost likely tonight across Red River valley

Winnipeg and the Red River valley were spared from frost last night due to a steady westerly wind that kept temperatures above zero. Tonight however, winds are expected to be light as a ridge of high pressure builds into southern MB. That ridge brought a hard freeze to much of southern SK and Alberta last night with overnight lows of -2 to -7C. Clear skies and light winds in the ridge allowed for maximum radiational heat loss from the surface, resulting in the frosty temperatures. Overnight lows aren't expected to be quite as cold tonight over southern MB as temperatures moderate somewhat today and some high level cloud moves in tonight, however widespread readings of 0 to -2C are likely by early Sunday morning across the Red River valley including Winnipeg (except downtown which should remain above zero due to the urban heat island effect). The southern Red River valley may also be spared from frost with some thicker cloud cover spreading in from Montana. Overall though it looks like the growing season will officially come to an end Sunday morning in Winnipeg, a good 10 days earlier than last year (first frost last year at Winnipeg airport was on September 29th with a minimum of -2.4C during the city's warmest September on record)


  1. Can someone tell me where the weather station is at the FORKS????

    Is it in the parkade?? LOL
    The winds readings are usually half of what the airport is and the temperatures are a few degrees warmer than the airport (urban heat efferct)!

  2. No, the Forks weather station is not in the parkade.. but it's close! The station is on a small plot of grass right behind the Inn at the Forks hotel. The station was set up in 1998 when there was considerably less development at the Forks and the site was better exposed, so winds and temperature were more accurate. With the addition of the hotel just south of the site a few years ago, winds are now more sheltered, especially from the south. It should be noted however that even if the Forks site was better sited, the winds would still be lower than at the airport due to wind dampening effects from trees and buildings downtown. Temperatures from the Forks are still not bad though and generally reflect the urban core of the city.

    Speaking of which, the Forks had a minimum of +3.5C this morning while the airport got down to -1.5C (a full 5 degrees colder). So the growing season is officially over for Winnipeg, but not downtown. Most areas around Winnipeg were at or below freezing last night, while areas south of Hwy 2 escaped frost due to cloud cover that spread in along the US border.

  3. Same situation in Steinbach as Winnipeg. Low temperature at the airport was around -1.5C, and the temperature in 'downtown' (my house) was +0.9C.