Wednesday, 4 September 2013

Heat Returns Tomorrow

     A cold front that sliced through southern Manitoba yesterday has tamed the summer temperatures for today. We'll reach a more seasonal high of about 21°C today in Winnipeg. It will be fairly cloudy this morning, with a bit more sun by afternoon.

     We return into a southerly flow tomorrow, bringing back summer. It looks like another 30°C day in southern Manitoba. Highs of about 30 to 31°C are expected around Winnipeg with the warmest temperatures in southwestern Manitoba. There will be a breezy south wind. Humidity will increase throughout the day ahead of a weak cold front tomorrow night. A thunderstorm will be possible with this front overnight into early morning Friday.

     One more 30°C day is expected on Friday with a high of 30°C expected.

     A slightly cooler day is expected Saturday, but still well above normal with highs in the mid to high 20's expected. At this point, the next better chance for showers and storms looks like in the Sunday-Monday timeframe.

     Thankfully, no prolonged cool down is in sight in the near future. Long range models continue a generally above normal temperature trend well into September.

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
     Just an official note that the thunderstorm records are now on the record books page which you can access whenever you need. Note that whenever I could, I used metar data which allows you to see observations in between hourly observations... ensuring that no thunderstorm was missed. However, this was only possible for part of the 70's, and for the 80's and beyond.

     I just wanted to share the following graph. This graph shows how many years since 1953 have had a thunderstorm on any given day of the year.

July 18 = Day with the highest frequency of thunderstorms (20 years, or 33% of the record period, had a thunderstorm on this day)
July 14 = Median day (meaning approximately 50% of thunderstorm days occured before this date and the other 50% occured on and after this date)
June 18 to July 18 = 30-day period with the highest frequency of thunderstorm activity; or in other words, the peak of the thunderstorm season

Top 5 earliest thunderstorms:
1. March 19 .... 2012
2. March 27 .... 2004 and 2012
4. March 28 .... 1960
5. March 29 .... 1999

Top 5 latest thunderstorms
1. December 5 .... 1966
2. December 2 .... 1982
3. November 8 .... 2007
4. November 7 .... 1975
5. November 1 .... 2000


  1. JJ,
    What is a model and what is a jet stream and a troph. I have heard all of those scientific turms on a number of weather blogs. thank you.

    1. A weather model is a computer generated weather forecast. Meteorologists or whoever is making a forecast, will use these weather models to help them make forecasts. Personally, I use the NAM and HRRR most often for my short-term forecasts, but will also use the GEM (canadian), GFS and ECMWF (european) sometimes, especially for long-term forecasts. is a good website to view model data for anyone who isn't too much into meteorology. Otherwise, there is a list of weather models in the form of maps under the ''weather models'' section on the right side of my blog.

      The jet stream is a very rapid moving channel of air at the high levels of the atmosphere (around the 10 km above sea level mark, plus or minus a few km). Generally this separates the colder air to the north with the warmer air to the south. This jet stream sometimes moves on a meandering path, or in other words moves similarly like a river, twists and turns instead of straight eastward. This is where ridging and troughing comes into play. The area where the jet stream dips southward is a trough ('' trough in the jet stream''), whereas the area where the jet stream climbs northward is a ridge (''ridge in the jet stream''). Here's a visual:

      Sometimes I will mention ''low-level jet'' or ''llj'' in short. This is a rapid (but not nearly as rapid as the high-level jet stream) flow of air just above the surface. This jet is a good moisture-transport in the summer as it brings moisture in from the south, good for thunderstorms.

  2. One particularly interesting late season thunderstorm case was November 8, 2007. At 11:47pm local time -TSSN (Thundersnow) was reported by the observer at the airport. I'm not sure if you consider thundersnow a thunderstorm occurrence, but I would be curious to know how often Winnipeg experiences that phenomenon.

    1. For this case, I considered anything with lightning/thunder a thunderstorm occurence.. so anything with ''TS'' in the metar data. That Nov 8, 2007 is the only case of thundersnow (TSSN) I could find. However, there have been cases where thunderstorms with freezing rain occurred, such as Dec 5, 1966 when the thunderstorm had occurred with a temperature of -1°C.

  3. Actually Saturday does not look as warm as I originally stated in this post. Looks more like low 20's at the moment as we get another push of cooler air from the north. A smaller rebound comes Sunday/Monday, but also an increased chance of precipitation.

    Revised temperature outlook:

    Today 29-30°C
    Tomorrow 31-32°C
    Saturday 22-23°C

  4. Do you have any expectations for winter or is it still much too early to say? What about the rest of fall?

  5. I personally don't bother too much with seasonal forecasts. Some things we just cannot know more than a few weeks ahead of time.
    I wish I could give you a better answer about October and beyond, but I just can't give you an answer that I would feel confident about.

    1. Fair enough! To be honest I prefer that answer to some sort of gobbledegook I read on the Internet, full of "analog years" and lots of technical mumbo-jumbo about the Arctic Oscillation. I like reading seasonal forecasts (even if I take them with a hefty grain of salt), but I hate the jargon a lot of amateur forecasters use when writing them.

  6. Small chance of a thunderstorm overnight tonight and early tomorrow morning remains. Nothing to get too excited about though right now.

    1. Thunderstorms actually did occur overnight, east of Lake Winnipeg and around Lake Manitoba. Another miss for Winnipeg, but not a big surprise.

  7. Not sure what the low at the airport was this morning; wont know until tomorrow. It was somewhere around 17 or 18°C. But either way that's very close to a record high minimum for today... unless we drop below that mark before midnight tonight which is possible. Old record high minimum today is 17.2°C in 1967.

  8. Today's certainly the hottest day I've experienced in September.
    Humidex advisory in place for humidex values near 40 today, not sure when the last time that has occurred, but it's sure been many years.
    Isolated thunderstorms today forming along some boundaries in the Interlake north of Winnipeg. Chance of Winnipeg getting something today is small, but there. Isolated severe storms possible.

    1. Than why the hell does ec have severe storm warnig

    2. They didn't. They had a watch.

    3. My mistake, Billy! I've since heard that EC did send a warning out in error yesterday. Good grief.