Friday 22 August 2014

More Rain to Come

     A very slow-moving cold front last night in the RRV helped trigger one of the biggest rain events of the year in Winnipeg. A heavy thunderstorm remained stationary over central and southwestern parts of the city for over an hour. Generally 40-80 mm of rain fell from Charleswood to Whyte Ridge to dowtown. Much lower amounts fell in southeastern, eastern and northern parts of the city where amounts ranged anywhere from a trace mm to 30 mm. I received 16 mm here in River Park South. Here are some amounts from yesterday via Cocorahs, Weatherfarm, Environment Canada and other backyard stations (Robsobs, Kyle, Matt and myself) (including the rains from the morning):


Community
Rainfall total August 21, 2014
Whyte Ridge
60-84 mm
Bridgwater Forest
70 + mm
Lindenwoods
57-66 mm
Downtown (UofW)
64.8 mm
St James
50.6 mm
Charleswood
41.9 mm
Old St Vital
29-31 mm
South St Vital
17.9 mm to 31 mm
Wpg Int’l Airport
20.6 mm
Transcona
5-7 mm

    Considering the normal August rainfall in Winnipeg is 79.2 mm, some parts of the city saw a month's worth of rain in just 2 hours. It's no mystery that there was major road-flooding last night. The rain is also on top of another heavy rain event in the Lindenwoods area  (30-40 mm) back on Monday.

     It was also extremely moist/humid yesterday. With a maximum dewpoint observation of 21.5°C at the airport at 6:00 pm, we were just shy of a dewpoint record (old is 21.7°C in 1969). However, the minimum dewpoint observation yesterday was just 17.2°C, a record high minimum for the day. Old record high minimum dewpoint was 15.1°C in 1981.

     Unfortunately, the gloomy weather continues. Cloudy skies are expected today and tomorrow with minimal breaks in the cloud. A bit of drizzle or light rain may fall at times before the big rain event tomorrow night.

More rain is on the way
     A strong low pressure system moving up from the United States will bring a widespread rain event to southern Manitoba late tomorrow into Sunday. At this time, it appears the bulk of the rain will begin tomorrow evening for Winnipeg and last until Sunday morning. The rain may be quite heavy at times and there may be a few embedded thunderstorms. 15-30 mm or more could fall throughout the RRV and southeastern Manitoba, including Winnipeg. Localized amounts up to 40 mm are possible under the heaviest bands and if any thunderstorms do occur, but most areas will see less than that. Stay tuned in the comments below for updates.

     Scattered showers with embedded thunderstorms remain possible through the afternoon and evening on Sunday. There could even be some sun, allowing temperatures to reach low 20's. Generally cloudy skies look to continue Monday with a few showers possible at times. Chilly, fall-like conditions look to continue through to mid-week before things begin to warmup by the end of the week.
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12 comments:

  1. AnonymousAugust 22, 2014 12:20 pm

    Looking at your extremely easy to understand helpful record books, JJ, it looks like we may have a chance at breaking a daily rainfall record with this up coming Colorado Low this weekend. On sunday the rainfall record sits at 35.6 mm; if the GEM is right we would break that record easily.

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  2. AnonymousAugust 22, 2014 12:40 pm

    Is it the GEM that overestimates rainfall x yesterday most often.

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    1. jjcwpgAugust 22, 2014 12:51 pm

      Tough to say really. I suspect there may be some overestimation given the likelihood of convective activity. Just to what degree are they overestimating is hard to say. I'd say 40+ mm is possible under any trailing bands of heavy rain and in areas that get some thunderstorm activity, but most areas probably would see less.

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  3. jjcwpgAugust 22, 2014 1:13 pm

    By the way, the city of Winnipeg has posted a map of rainfall totals in the city from last night. Link here: http://www.winnipeg.ca/waterandwaste/pdfs/drainageFlooding/rainfallReports/140821Map.pdf

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  4. jjcwpgAugust 22, 2014 10:31 pm

    Not much has changed yet for this weekend system. Still anticipating rain to begin sometime between late afternoon and evening tomorrow in Winnipeg and continuing until Sunday morning. 20-40 mm looks likely at this time. NAM weather model has trended westward in recent runs which may help increase our chances of some embedded thunderstorm activity. Also due to the westward trend, we may actually end up in the warm sector of the system on Sunday, making it quite humid; dewpoints may push into the high teens to near 20°C in this scenario. Thunderstorms would also be more likely in the afternoon and early evening for us. Severe activity would even be possible IF we can get some sunny breaks, especially closer to the Ontario border. Of course, all this is assuming the more westward trend holds true.

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  5. jjcwpgAugust 23, 2014 9:14 am

    Rain, heavy at times, is set to begin this evening as scheduled and last until early or mid morning tomorrow. There is the potential for thunderstorms in the overnight and tomorrow morning as well, which could give higher rainfall totals. 20-40 mm still looks like a good range for Winnipeg at this time.

    Further west track still holding strong at this time. This would put us into the warm sector of the system for the afternoon tomorrow. This could mean some sunshine and also the risk for additional thunderstorms. Very tough forecast with this because Winnipeg may end up quite close to the edge of the warm sector. In addition, there is no guarantee that the sunshine actually will appear in the afternoon - there is the chance we may stay under low cloud. This makes temperature forecast a nightmare for tomorrow - a high anywhere from 19 to 27°C could occur depending on sunshine AND how far west the system pushes. Pop up showers and storms will be possible in the afternoon and evening. Best risk for storms and severe activity will most likely be to our east.

    Cloudy on Monday with a few light showers and drizzle possible at times. No major accumulations. MUCH colder behind the low with a high only in the low teens, maybe mid teens if we're lucky.

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  6. jjcwpgAugust 23, 2014 12:18 pm

    Clearly there's some uncertainty about rainfall amounts tonight. New GEM model this morning is keeping the bulk of the activity to our south and east with only around 5-15 mm in Winnipeg. Other models not so keen on this idea yet.

    A note that I will have a post about my forecast evaluation sometime in the next few days.

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    1. AnonymousAugust 23, 2014 1:00 pm

      thats really weird because according to ec the bulk of rain is supposed to go to our west (brandon and further west)!? They've got rainfall warnings out there!?

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    2. jjcwpgAugust 23, 2014 1:12 pm

      Yes, you are correct. Being on the backside of the system, rain is expected to fall in southwestern Manitoba through the night and throughout the day tomorrow... continuing into early Monday. Grand totals of 50+ mm are possible, especially closer to the Saskatchewan border and in the Parklands region. For us here in southeastern Manitoba, a bit of a different story. Rain will be shorter-lived, only through the night tonight, but could be heavier, especially due to thunderstorm activity. New GEM run this morning was hinting that the bulk of this heavier rain and thunderstorm activity may skirt Winnipeg to the southeast... which is why I was saying the bulk may be to our south and east.

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    3. AnonymousAugust 23, 2014 1:27 pm

      Thanks, JJ. Now i get it.

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  7. jjcwpgAugust 23, 2014 4:55 pm

    EC has dropped amounts to 10-20 mm for tonight. However, I still think we could get more if we get under any heavier bands and thunderstorms. 20-40 mm is still possible if this does occur. Tough forecast...

    As for tomorrow, certainly starting to look more interesting for thunderstorm potential. Severe risk looks to have pushed further west into the RRV. Definitely will have to keep a close eye on this risk. Dewpoints are expected to push the low 20's in the afternoon as we enter the warm sector. Big question mark is sunshine. We're definitely going to need a least some sunshine to get a bigger severe risk going. Can't rule out some funnel clouds.

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  8. jjcwpgAugust 23, 2014 9:20 pm

    The heavier rains should begin to move in later this evening. Don't be surprised to be woken up by thunder tonight as well. Heavy thunderstorms cannot be ruled out in the late overnight and early morning. Just a wait and see how things evolve type of situation.

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