Wednesday, 18 July 2012

Extreme Heat Returns

     It will be a mostly cloudy day today in Winnipeg, before things begin to clear mid/late afternoon. There may be a few showers, with perhaps a rumble of thunder, this afternoon and evening. Highs will be generally ''only'' around 27 or 28°C.

     The oven really turns on tomorrow. We will be under a thermal ridge, which will bring us some very hot and humid weather. 850 mb temperatures are expected to rise into the low to mid twenties throughout southern Manitoba. *The reason why we use 850 mb temperatures is that it can be used to estimate the temperature at the surface. In the RRV, you can add about 10 to 13°C to the 850 mb temperature to get the surface temperature on a sunny, light wind summer day.* Therefore, with 850 mb temps in the low to mid twenties, you can estimate highs in the mid to high thirties for southern Manitoba tomorrow.
     A westerly wind in the afternoon will also give a favourable downslope effect to the RRV, which will help maximise the daytime high.
     However, there is a limiting factor to the heat tomorrow; and that will be humidity. Dewpoints are only expected to drop into the high teens in the afternoon. The problem with too much humidity is that humid air does not heat up as well as drier air. Thus, if we stay humid during the afternoon, we will likely only see highs between 33 and 36°C across southern Manitoba. If we manage to get dewpoints lower, into the low to mid teens, then highs between 36 and 39°C would be possible.

     Currently, my best guess is for a high of 34°C in Winnipeg tomorrow, with 35 to 36°C highs in the western and southern RRV (Carman, Portage, Morden, Emerson). What are your guesses? You can write your guesses in the comment section of this post.


  1. Of note, there will also be a chance for thunderstorms in the morning and evening tomorrow. The Interlake will have the best chance for these storms, however an isolated storm to the south of the Interlake is not out of the question.

  2. There is a good risk of some severe storms in eastern Saskatchewan and western Manitoba this afternoon and evening. This risk should be taken seriously since there will be an elevated risk of tornadoes. The best risk for tornadoes will be north of Riding Mountain up to Swan River, then west.

    Large hail and damaging will also be likely. Some of these storms may move into the Interlake overnight tonight, bringing some damaging winds and large hail to those areas. Some storms will be possible with this in the RRV and southeastern Manitoba, however the risk is quite small.

  3. Watch out if you are near the Swan River area. Strong storms are moving in from Saskatchewan and will arrive within the next hour or two. Large hail and damaging winds will be the main threats.

    Some more isolated, non-severe storms are further south, north of Brandon and south of Dauphin as well.

  4. 3 confirmed tornadoes touched down in Saskatchewan today, around the Wadena and Tisdale regions. Even more tornadoes may have touched down, however they have not been confirmed. This brings the number of tornadoes in Saskatchewan this year to about 20 to 25 tornadoes!