Friday, May 17, 2013

Unsettled weekend.. locally heavy rain possible at times.. but rain-free periods as well

3 day precipitation outlook (Fri - Mon)
from HPC, amounts in inches
showing heaveist rain of 75+ mm
south of the US border
A complex weather pattern will be setting up over the Northern US plains this weekend,  which will be impacting the weather over southern MB for the May long weekend.  A series of disturbances will be triggering showers and scattered thunderstorms over North Dakota and northern Minnesota over the the next few days, some of which may bring areas of heavy rain to southern MB.  Models however are having a tough time coming to a consensus as to when and where most of the precipitation will be falling over southern MB. It appears there will be an initial band of showers and thunderstorms developing tonight over North Dakota and spreading into southern MB overnight into Saturday, with the potential for locally heavy rain in showers or scattered thunderstorms.  On Sunday, a stronger system developing over South Dakota will move into northwest Minnesota, triggering more widespread showers and thunderstorms south of the border. This area of precipitation is expected to push over southeast MB Sunday night into Monday, although models having varying opinions on how far northwest this second wave of showers will spread. Some models are indicating that most of the heaviest precipitation will stay over extreme southeast MB and miss Winnipeg and the RRV. Other models are indicating that showers will push into Winnipeg and the southern Interlake by holiday Monday. Thus, the forecast for the latter half of the holiday weekend is still in doubt. Bottom line: not the best holiday weekend, but not a total washout either. Note however, that the potential for locally heavy rain (50 mm or more) is possible this weekend for parts of southern MB including the Red River valley.  (Consult  HPC precipitation forecasts for updated trends on expected precipitation patterns this weekend) 

30 comments:

  1. I hope we get some storms. Normally by May 1st we have seen our first thunderstorm of the year and our last recorded one was in the 3rd week in august last year so almost 9 months or 3 quarters of a year since we've had a tstorm! :(

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  2. Wow NAM giving over 100 mm for Winnipeg by Tuesday. Thankfully it looks like it's an outlier right now... at least let's hope it stays that way, that's a little too much.

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  3. "Capt. John" at CBC is guesstimating 40mm total accumulations by Sunday night on his model runs. The rain event will sure make for a quieter weekend here in the burbs since pool/patio/BBQ events will be rained out. And speaking for myself, - that's just fine with me. The rain will help to keep the dust down and the peanut gallery quiet.

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  4. Mike (St.James, Winnipeg)7:09 PM, May 17, 2013

    Wunderground is now predicting thunderstorms for the Winnipeg region tomorrow, it was very accurate last year in our summer season. Remember the storm on july 19th, no one was predicting them to occur except old faithful wunderground & sure enough we got it. So I think we'll get our storms tomorrow...

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  5. About 5-10 mm of rain over far SW Manitoba so far today, with small area of 25-30 mm in the bossevain area with some locally heavier showers there. Looks like area is moving slowly northward with little eastward motion evident towards Winnipeg/RRV. Models still struggling with precip amounts and timing with this complex and evolving pattern. GEM most aggressive with rainfall amounts for this afternoon for Winnipeg while other models are lighter and later with precip, which appears will be the case based on current trends.

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  6. Area of showers getting better organized to our southwest.. now showing better progression towards Winnipeg and RRV. Based on current trends, rain should be spreading into Winnipeg this afternoon.. perhaps 5-10 mm by evening with locally heavier amounts to our south.

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  7. Been raining steady here in Windsor Park for the last couple of hours.

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  8. rob,
    what is the difference between "Rain" and "Showers"?

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  9. >> wilber said...rob,
    what is the difference between "Rain" and "Showers"?

    "Rain" generally refers to an area of steady "stratiform" precipitation that is usually associated with a synoptic scale system. It often falls at a fairly steady rate and can last for hours.

    "Showers" generally refers to precipation that is convective in nature and can fall intermittently (off and on) with varying intensities. Generally, showers don't last as long and are more mesoscle in nature, but can be quite heavy at times depedning on instability.

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  10. Well, models have shifted large area of rain back up towards Winnipeg for tonight into Monday, with amounts of 45-90 mm depending on which model you believe (or don't believe) That area of rain is pushing into SE MB this morning and will likely push up towards a deformation boundary just SE of Winnipeg. Eventually this boundary shifts northwest of the city, allowing that area of rain to advance into the city from the south and east. Model precip amounts look overdone based on embdedded convection, however it's quite possible Winnipeg would be seeing 20-40 mm over the next couple of days.

    Note also a brisk E-NE wind off Lake Winnipeg over the next 2 or 3 days which will likely pile some lake ice up along the western shores of Lake Winnipeg (Matlock to Gimli and north) Winds won't be as strong as they were for the Ochre Beach situation, and I'm not sure what ice conditions are like on the south basin now, but a sustained E-NE flow off the lake for a few days may make for some interesting ice piles depending on how much ice is still on the lake.

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  11. EC has a rainfall warning for south-east. How much can we expect over the next few days?

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  12. Aaron..

    50 to 80 mm possible in the warning area by Tuesday (including the 20-30 mm they got today).. with about 20-40 mm possible for Winnipeg. Looking at latest radar south of the border.. area of convection has fired up over central Minnesota into northern ND spreading to the N-NW. Looks like bulk of it will be pushing into southwestern RRV.. unless more develops over northern Minnesota. Very challenging trying to figure out where elevated convection will fire up and where it will migrate to.

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  13. Windows are getting a nice cleaning with the easterly winds.

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  14. Rob, How much ran have we gotten so far and how much more do you think we will have once this system finally moves on?

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  15. Anonymous..

    Winnipeg airport has picked up almost 20 mm since Saturday.. with only about 5 mm today so far. Should see another 5-10 mm before its done overnight. A lot more to our south with 50 - 80 mm since Saturday over southern RRV, and along US border. Click on my name for a summary of rainfall amounts over the holiday weekend..

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  16. As of 9 pm today, 17 mm at my place in south St Vital for today. Total of 32 mm since Friday. South end got hardest hit this weekend.

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  17. As of 11 pm, 15 mm at my place today in Windsor Park, mostly this evening however as a steadier rain fell through the south and east side of the city. Total of 29 mm since Friday. Enough of this rain and wind already.

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  18. Hi Rob,
    I wondered if you knew where I could find the archived severe thunderstorm warnings and tornado warnings? I have heard that EC transitioned them from wwcn messages to wucn and wfcn messages? I can't find those anywhere however.

    Thank you for answering

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  19. Humidex of 38C in Windsor and Sarnia yesterday, the highest reading this year in the country.

    Also sad news about that massive tornado hitting OKC.

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  20. Beb..

    You can access archived WU and WF bulletins at

    http://dd.weatheroffice.ec.gc.ca/bulletins/alphanumeric/

    You will need to drill down through dates, bulletin headers, issuing office and time, but eventually you'll be able to get them from there, although the archive is only a few months.

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  21. 27 mm total at my place since Saturday, with amounts in Winnipeg ranging from 40 mm in the south end to about 20 mm in the north.

    Heaviest rain was over western RRV along Pembina escarpment where 3 day totals were in the 75-100 mm range (3-4"), probably enhanced by NE upslope flow. Even higher amounts along that escarpment into North Dakota where they had 5-6" near and south of Walhalla.

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  22. Rob, does the long range offer any hope of warmer more summer like weather over the next couple of weeks or so?

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  23. Rob, you really think that it is by chance that Moore Ok, has been hit by 3 F4 or F5 tornadoes in the past 15 years, or something in the geography that is causing the tornadoes to go in that general direction??

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  24. IMO the intensity and frequency of storms here and world wide will increase. It's all part of Global Warming (call it Climate Change if you must) and there is nothing we humans can do to reverse it. We're way past the tipping point (400PPM CO2 and climbing). It's time to take action and protect ourselves. Move away from coastal cities, build a storm shelter in hurricane & tornado impacted areas of the country.

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  25. >> Anonymous said... Rob, you really think that it is by chance that Moore Ok, has been hit by 3 F4 or F5 tornadoes in the past 15 years, or something in the geography that is causing the tornadoes to go in that general direction??

    I was wondering the same thing myself, but I think it's just by chance they got hit so hard by tornadoes in the past 14 years. That part of central Oklahoma does lie in a prime area for tornadic storms, between drier air over western parts of the state and more tropical humid air over the eastern half.. setting up a prime supercell zone right through central OK. But when and where a supercell drops an EF4-5 tornado is still very storm specific and by chance.. and I don't know if local topography plays a part in that area. Perhaps.. but again, I don't know. But when you live in tornado alley, the odds increase of getting a violent tornado at some point. I do wonder though if an overall warmer and more moist climate is providing additional fuel to generate more frequent F4-5 tornadoes compared to before. If so, it becomes statistically easier for a violent tornado to hit a populated center given the increase in urban sprawl..

    Still, it's unbelievable how similar this track was to the 1999 Moore event. The 1999 storm however developed well before it hit Moore, while this one developed more rapidly and closer to Moore. So the tornado in yesterday's case was a more rapid event (similar to Joplin where the storm spawned a tornado that very rapidly went to F5 strength) while 1999 was a longer lived event that happened to peak right over Moore.

    Note that the town of Codell Kansas was hit by tornadoes 3 years in a row, each on May 20th! So fluky things can happen!

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  26. >> Anonymous said... Rob, does the long range offer any hope of warmer more summer like weather over the next couple of weeks or so?

    I don't see much evidence yet of a big pattern change to sustained warm weather over southern MB. Looks like we'll be in a more variable pattern for the next couple of weeks with building heat to out south, and a storm track across the northern Plains/southern Prairies according to the 6-14 day outlooks.

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  27. Rob, does this mean we could see more heavy rain and thunderstorms, possibly severe over the next couple weeks with the storm track over our region?

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  28. It's possible we may start getting into a more active pattern for thunderstorms next week, depending on how far north that storm track sets up. If it stays along the border, we won't get as warm and may just get bouts of showers.. but if pushes further north, that will allow warmer and more humid air into southern MB, with an increasing liklihood of thunderstorms. We're heading into that time of year, so we should be starting to see our first thunderstorms soon.. (although we'll need to some more humidity building to our south)

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