Thursday, 10 May 2012

Thunderstorm risk over the next 12 hours

      It is not looking likely we'll see much in the way of storms late this afternoon and early evening with the cold front. Moisture is just too low, with surface dewpoints only from 5 to 10°C so far this afternoon, and are not expected to rise much higher. Generally, when it comes to predicting more severe and widespread storm activity, we look for dewpoints in the mid teens or higher. A few storms are not out of the question, although they will likely be isolated and non-severe. The main risk with the storms in this setup is gusty winds due to evaporative cooling

  • Evaporative cooling: « When precipitation in a downdraft evaporates while falling into the drier air below the cloud. The evaporation causes this parcel of air to be colder than the surrounding air. This makes the air more dense which subsequently strengthens the downdraft. This can cause sudden, stronger gusts of wind at the surface. » (Source)
Graphic representation of a dry downburst caused by evaporative cooling

     The best chance of rain and storms for Winnipeg is mid/late evening behind the cold front. A line of rain and/or embedded thunderstorms is expected to form behind the cold front, thanks to forcing from the jetstream. A good 5 to 15 mm will be possible in and around the RRV. The risk of storms significantly decreases past midnight though, due to reduced instability. Personally, I wouldn't expect any thunderstorms in the city in my opinion. I will provide updates in the comment section of this post when they become available. As well, as always, please check the thunder forecast tab at the top of the page when it has been updated for the latest forecasts.


  1. Temperatures will really plummet behind the cold front tonight, with a low overnight of around 5 or 6°C expected. Only expecting a high of about 16°C in the city tomorrow, which is closer to normal, with plenty of sunshine.

  2. Cold front is currently positioned from just west of Gimli, down to Elie, to between Morden and Killarney (as of 6:50 PM).

    Portage's temperatures plummeted with the passage of the front, dropping from 28 to 22°C in 1 hour. That is a sign of what is coming for us in a couple hours.

    Widely scattered showers with a few lightning strikes near the US Border near Killarney right now, although nothing significant. Most of these pop up showers are brief, and appear to just vanish after an hour or so, likely because it is so dry. Therefore, I still don't expect much storm activity with the cold front. By the way, the cold front is easily seen on radar this evening, with what appears to be a light blue line. That is the convergence line, or cold front. It's a good way right now to see the progression of the front.

  3. Cold front just approaching west Perimeter at the moment, so the cold front will be passing through the city within the next hour. You will notice its passage by a marked shift in the wind direction from the NW. Temperatures will begin to plummet as well.

    Line of rain and storms stretching from the northern Interlake all the way down to Gladstone, Cypress River and Killarney. Lightning is being detected by lightning detection, which you can view here:
    or here

  4. Cold front just went through my place about 8 minutes ago (south end). I was sitting outside, and felt the sudden shift in the wind direction. Temperature has fallen 1°C in past 10 minutes at my place, currently 24.3°C. It is now 19°C in Charleswood, so say bye bye to the twenties!

  5. Very strong winds are moving through the RRV at the moment, behind the cold front, with a sustained wind of 63 km/h, and gusts well over 70 km/h as of 10 pm here in Winnipeg. Quite stormy already! Straight from the NW as well, which has caused our temperatures to plummet to the low teens. Only 13°C in the city at the moment. That 26°C just 2 hours ago is just a distant memory now!

  6. Seeing some lightning in the distance now, and heard the first small rumble of thunder about a minute ago.

    Rain pushing into the city any minute now. There could be some embedded thunderstorms as well, with distant lightning if you don't get a direct hit, though nothing significant. Risk of lightning continues to diminish with the loss of daytime heating/instability.

  7. Carman and Portage hit 30.1°C yesterday, the first 30°C readings of the year in Manitoba :) Winnipeg hit 28.4°C, not too shabby!

    As for last night, got a few lightning strikes and a brief torrential downpour in the city, with south and east areas of the city hit directly. There were some close ones, I was sitting in bed when all of a sudden there was a big flash of lightning, followed by a huge crash of thunder. Love it :) It poured rain for a while as well, after the storm; love sleeping with the sound of rain!

    I measured about 7 mm in total, which seems like the normal for most of the city.

    Will have today's forecast soon, I'm working on my forecasts now.

  8. Just some lingering cumulus this morning behind that system, which should begin to clear soon. Some more cumulus looks to move in mid/late afternoon, otherwise it looks quite pleasant today if you don't like the heat. Expect highs around 15 or 16°C in the city today, with west/northwesterly winds of 30 gusting to 40 km/h.

    Tomorrow looks spectacular, with highs around 20 or 21°C, under crystal clear skies. It will be breezy again though, with westerly winds of 30 km/h.

    As the ridge over western Canada continues to dominant over the next several days, we're expecting highs in the twenties until at least Wednesday next week. A few days in the high twenties and close to 30°C will be possible Monday to Wednesday. More details will come before then.

  9. Keep in mind some of these cumulus are becoming a little more vertically developped than others. As a result, looks like an isolated shower will be possible today for us. One is approaching north Perimeter now. This is just as a result of some lingering instability behind the system. Nothing big.