Thursday, August 05, 2010

Hot spell forecast for next week.. locally strong thunderstorms possible Saturday into Saturday night

Models are cranking up the heat beginning this weekend, and continuing much of next week. A warm front is forecast to push through southern MB on Saturday, which could trigger some heavier thunderstorms especially by Saturday night. (Note that SPC is indicating a slight risk of severe storms for Saturday over the northern Plains. Models hint at potential for strong elevated thunderstorms Saturday evening/night anywhere from North Dakota into central MB) We start getting into the steambath on Sunday with hot and humid conditions as the warm front pushes north of us, with afternoon highs of 30-33C and humidex values near 40. The hot and humid conditions are expected to persist through Thursday with daily highs in the 30-33C range before a cold front sweeps through late in the week with cooler air by next weekend. Although much of next week should be generally storm free as warm air aloft caps thunderstorm development over southern MB, there is a chance of daily scattered thunderstorm activity as weak impulses ride the upper ridge, especially through the Riding Mtn/Interlake areas. All in all though, looks like a steamy stretch of weather coming up, with potentially 5 straight days of 30C plus weather next week.

28 comments:

  1. Rob!

    Would Environment Canada issue warnings for any area if the actual air temperature got 40 C or higher???

    I know they issue humidex warnings for air that feels like 40 C or higher!!!!

    Like the national weather service has heat advisory and excessive heat warnings but is that for feel like temperatures or actual air temperatures????

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  2. daniel..

    Currently, EC does not issue heat advisories or heat warnings when actual temperatures reach a certain threshold.. they only issue humidex advisories when the humidex is forecast to hit 40C, and dew points are at least 15C. (In Quebec, they call it a "high heat and humidity" warning) For dew points below 15C, the humidity is low enough that the humidex is not significantly different than the actual air temperature, so it becomes a "heat" issue rather than a "humidex" issue as temperatures get to 40C. Temperatures of 40C are rare in Canada, although they occasionally occur in the Okanagan valley (in places like Osoyoos, Lilloet and Lytton) once or twice a summer, but humidity is usually very low in those situations, so "humidex" is not really applicable. Elsewhere in Canada, 40C would likely be accompanied by dew points near or above 15C, so humidex advisories would likely be in effect.

    Note that an actual temperature of 40C with low humidity feels a lot more comfortable than a humidex of 40C with a high dew point (e.g. 30C with a 23C dew point) This is because the body can cool itself more easily when the humidity is low through evaporative cooling from the skin. When the dew point is high, the body's perspiration doesn't evaporate as easily, so you feel "hotter" (more uncomfortable) since your body can't cool down as quickly as in drier air.

    NWS and EC have different heat indeces based on different formulas (they have "heat index" and we have "humidex") I understand that EC and NWS would like to coordinate and come up with a standard heat/humidex index that is consistent between both countries (like windchill) but I don't know the status of that. I see that NWS is issuing a lot more heat advisories and excessive heat warnings this year, and I suspect heat warnings are becoming more of a serious health issue due to the deadly effects of the heat wave in Europe a few years ago.

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  3. Rob Where did that cool air come from?? 8.6C and still dropping?

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  4. Arborg 5.9 at 6am.. What happened to all the moisture and the 'Lake's moderating effect on the Interlake.

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  5. Rob!
    This Russian Heat Wave is now being known as the GREAT Russian heat wave!

    Temperatures are now 14 F above average for the month of July!

    Stunning!
    Read Jeff Master's blog for more information!

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  6. Yeah, that Russian heat wave is something else. All heat records being smashed day after day. It's not only the exceptional heat, but the persistence that's been so amazing. Very unusual. Imagine 4 weeks of 35-40C for us, with a few days above 42C. That would be the equivalent of what Moscow is experiencing.

    I see that Tuesday is now calling for "showers" and a high of 25C. That's based on the GLB model which brings an upper impulse across southern MB and blows up an area of heavy convective precipitation (i.e. thunderstorms) over ND/RRV/SE MB with 75-80 mm of rain indicated. I suspect the model is overdoing things, especially this far out with an upper impulse that may or may not be there, so more realistically the forecast for Tuesday would be "Warm and humid with a few thunderstorms possible. Highs near 30." Note that EC forecasts beyond day 2 (tomorrow) are automated products from the GLB model, and never mention thunderstorms.

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  7. Is the warm front the culprit for the potential storms later tonight?????

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  8. PASPC indicating a moderate risk of severe thunderstorms later today along the MB/SK border with a possibility of isolated tornadoes. SPC carries slight severe risk into ND and western MN. Storms will push eastward into the RRV this evening with an ongoing risk of severe storms (mainly hail or strong winds along with heavy rain) Could be an interesting finish to the Rock at the Range concert at the stadium this evening!

    Further out, I see the GLB model is advertising a quicker end to our upcoming heat spell, with the cold front pushing through on Tuesday rather than Thursday. GFS not as quick on the cooling bringing the cold front in Friday night. ECMWF shows some cooling Tuesday and Wednesday then rebounding a bit for Thursday and Friday before main cooldown for next weekend. I think this may be the best solution. Regardless, looks like a change to cooler weather next weekend into next week. Enjoy the next few days of heat!

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  9. As an upper low tracks eastward through Saskatchewan, an associated surface trough will slowly progress with it towards the SK/MB border. By late this afternoon, the trough line will be positioned from about Nipawin in central SK south towards Estevan, SK. Along with this feature, an upper wave will be moving into the area as well, with a 850mb cold front stacked on top of the surface trough by 21Z.

    With the surface trough/upper cold front triggers in place, any storms that develop will have ample instability (SBCAPES of 1500 J/kg to 2000 J/kg alongside LIs of -6 to -9) as well as favorable wind profiles, with south to southeasterly surface winds veering to westerlies aloft. As well, a 40kt west-southwest jet will be poking into southern SK by late this afternoon.

    The rest of this, including graphic, is up on my weather blog: http://aweathermoment.tumblr.com/post/917938082/thunderstorms-on-tap-for-southwestern-manitoba-and-the

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  10. Well.. a few strong storms near the Mb/SK border last evening and into the interlake.. but not much made its way into the RRV last night. A few cells have popped up this morning over Lake Manitoba and the Interlake ahead of the warm front.. otherwise looks like a couple hot days on tap for us. Should hit 30C today, and 33C possible tomorrow as 850 mb temps climb to 23C.

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  11. The next question is will humidex values reach 40 C today or tomorrow????

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  12. We'll come close to 40 humidex today.. likely hit it tomorrow. Magic number is 53 (temperature + dew point)

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  13. I am really, really surprised that the cap was able to hang on through the day yesterday. It's astonishing that nothing managed to get going other than a little storm near Estevan and a storm southeast of Fargo.

    Today looks like there's a slight chance of TSRA in the RRV if the trof to the west, or an outflow boundary from one of the storms this morning, can maintain its structure through the day. We also need to keep our dewpoints up; with drying aloft we need at least 18-19C dewpoints to be able to have enough juice to make a crack of thunder or two. Storms are much more likely east of the city into the Whiteshell.

    Probably a fairly nice day for Winnipeg today :) Humidex values will probably reach the high 30' (37-39 most likely). Tomorrow looks like a scorcher for the city, with a high likelihood of Humidex values exceeding 40C.

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  14. WOW!

    The dewpoints have gotten quite high already!
    38 C humidex at 1:00 p.m !
    It's like a steam bath out there!

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  15. Ok!
    I have a weather question to whoever can answer!

    On U of M weather central website and under the heading weather events there is a July 26 severe weather recap!

    For the radar maps there is a
    1.5 km CAPPI
    also
    1.5 degree reflectivity!

    What does CAPPI mean???
    It looks the same as the 1.5 degree scan!!!

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  16. Daniel,

    If you could also ask that question at my blog, I would appreciate it (http://aweathermoment.tumblr.com). There's an "Ask me a question..." link on the right side. I do educational posts as well, and I just need to receive the question to manage them properly.

    That being said,

    A 1.5km CAPPI image is a radar composite image. CAPPI stands for Constant Altitude Plan Position Indicator.

    When a radar shoots a beam off in a straight line, it ends up further up in the atmosphere the further away from the RADAR it goes; this is because the earth actually curves away from the radar. When you correct for the curvature of the Earth, you no longer get a straight line for the radar beam path, but rather one that curves upwards.

    A RADAR will shoot many, many beams out; it picks a degree elevation (azumith) from the ground, and then shoots a beam out and changes the bearing of the radar dish and shoots again until it covers 360 degrees. It then increases the azumith (shoots higher up in the air) and repeats to do a full 360 degrees. This results in a whole suite of radar images that represent various lines through the atmosphere.

    A PPI image, i.e. a 1.5 degree PPI image is a straight view of what the radar saw when it did it's suite of scans at 1.5 degrees azumith. With these images, it is important to realize that as you move further away from the center (the radar) of the image, you are viewing reflectivity higher up in the atmosphere.

    A 1.5km CAPPI image is composite from many different azimuthal scans of the radar to create an image that doesn't have a constant radar azumith, but rather lets you look at a constant altitude.

    Does that make sense?

    PPI is most common with Doppler scans and is usually not usually used too much in Canada with conventional scans, which are most commonly either 1.5km CAPPI (Summer) or 1.0km CAPPI (winter).

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  17. WHOA Buffalo seven!!!!

    LOL

    That is quite the science essay!!!

    I'll post the question to your website later on this afternoon!!!

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  18. Lots of cells popping up around the MB Lakes. MLCAPE around 2000J/kg in the RRV and some deep shear hanging on. Could see some interesting activity, main question is whether or not the storms will be able to develop and sustain themselves further from the lake.

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  19. Buffalo Seven!

    Do I need to sign up to TUMBLR to post a question on your blog ????

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  20. No! I forgot to change a setting :) It works now.

    As for weather; lots of bad storms out in the Whiteshell, but with Winnipeg's winds shifted to the NW, I think we're done for today.

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  21. Spoke too soon?

    Gust front approaching the city from the NE. Probably nothing, though. If only the dewpoint was still 23...

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  22. Will be interesting to see how hot it gets tomorrow. GFS pegs the high at 34C, while the NAM puts it at 36C. Any debris cloud from tonight's convection will play a big role in determining temperatures tomorrow. If we get perfectly sunny skies like today, we should be able to add 13C to the 850mb temperature. Winnipeg had an 850mb temp of roughly 18C this afternoon, which led to a high of 31-32C in the city. Using the same formula, YWG should theoretically be able to get to 36C tomorrow, based on the NAM forecast of 23C at 850mb. Will this actually happen?...I suppose it is possible, but I would probably be betting on a slightly lower high temperature.

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  23. Maybe Rob might set up a poll for how hot it will get tomorrow?????

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  24. Out of interest, I thought I'd mention that the 00Z NAM is predicting a small patch of 100F (38C) temperatures centred right over Morris, MB. This is due to three factors:

    1) I believe the models pick up on the slightly lower elevation of the RRV, thereby putting the warmest temps in S MB there.

    2) Dewpoints are forecast to spike down in the afternoon. Td in Morris is forecast to be 13C at the same time the temp is forecast at 38C.

    3) Obviosuly low-level temps need to be warm to support warm surface temperatures - 850mb temperature is 23-24C in the southern RRV. Realize that 24-25C temps at this altitude are what produced the monster heat wave over the south-central US during the past week.

    While I by no means endorse the "100 degree forecast", I thought it was worth mentioning. Tomorrow reminds me of August 12, 2009...the hottest day last summer.

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  25. Good idea daniel! Poll is up, how hot will Winnipeg get Monday (as measured at Winnipeg airport). Current official forecast is 31C, which seems a tad on the low side considering the airport hit 31c today, and Monday should be at least a couple of degrees warmer. We shall see. What's your forecast?

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  26. Now it looks like Tuesday is at 30 C for a forecast high!

    Not the cooler weather and showers that it seemed like it was going to be!

    Now lets see if we can clear out this afternoon and fire up some BIG storms!

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