Wednesday, 29 May 2013

Yet Another Rainstorm

     A major slow-moving Colorado Low is poised to slam parts of southern Manitoba with excessive rainfall Thursday through to early Saturday. This system looks strangely similar to the major 4-day long storm of 2 weekends ago. However, there are a few small differences. The deformation boundary is expected to reach a bit further north and west this time. What this essentially means is that the heavy rains will reach a bit further west and north. Some of the areas that saw little to no rain last time will likely see high amounts this time. The storm is also expected to be a little shorter; lasting 2-3 days instead of 4. But that wont necessarily mean lower rainfall amounts. It will have an ample amount of time to pump in lots of moisture from the deep southern US. The flow of moisture can be seen in the map below.

Precipitable water map from the NAM model for Thursday afternoon showing the flow of moisture straight from the southern US

     Rain, heavy at times, is expected to move into southern Manitoba in the morning tomorrow. It will likely begin to rain in Winnipeg sometime in the morning. However, there is still a little uncertainty in the timing as some models are not bringing it until late afternoon and others early morning. We'll have to wait and see right now.

     Winds will be strong from the east/northeast at 40 km/h with gusts as high as 60 km/h at times. This will create upsloping near the escarpment and Riding Mountains which will give those areas higher rainfall amounts. A general 15-40 mm is expected throughout the day Thursday generally along and south of the Riding Mountains and from the southern Interlake southwards, with as much as 40-50 mm possible along the escarpment and Riding Mountains. 15-30 mm is expected for the Winnipeg region.

     There will be the potential for thunderstorms tomorrow as well. The best risk will remain south of the border, however scattered embedded thunderstorms are still likely close to the US border. Areas to the north of the border will have a smaller chance. I don't think we'll see storms here in Winnipeg, but just remember that the potential is there. Any storm activity will give locally enhanced rainfall amounts.

     On Friday, much of the same. Rain and wind will be the story with an additional 15-30 mm possible, with higher amounts locally along the escarpment. A few embedded storms will be possible in southeastern Manitoba.

     Conditions will improve on Saturday. Scattered showers are still expected in the early morning for southeastern portions of the province before things begin to clear out in the afternoon or evening.

     In total for the entire storm, a general 20-60 mm can be expected in southern Manitoba with locally higher amounts of 75 mm + possible along the escarpment. Here's my personal forecast for some select communities (updated at 11 am May 30):

     Note that amounts in Gimli and Dauphin will be highly dependant on the location of the deformation boundary. Dauphin may get more than forecast if the boundary is further north, but they may get little to nothing if it sets up further south. This is highly visible on the models this morning with a predicted range of 2 mm (NAM) to 94 mm (GFS) for Dauphin. This is a similar situation that Winnipeg experienced during the last storm 2 weekends ago when we were often right on the edge of the heavier rainfall.


  1. JJ,
    can you please put a weather poll up for the rainstorm tomorrow?

    1. Poll added.
      Rainfall amounts will be taken as an average across the city between Charleswood, my place here in South St Vital and from Whyte Ridge.

    2. Is this new way of making polls doing okay with everyone? It seems to be working for me.
      I'm still looking for better ways to create polls, but this will have to do for now.

  2. Consensus is growing that the bulk of the rain will begin in the afternoon tomorrow instead of the morning... We'll have to wait and see though.
    Consensus also becoming that heaviest rain will be Thursday night into Friday. This still doesn't change rainfall accumulations for Winnipeg too much for the entire system, I'm still thinking 30-50 mm right now. But I'll see in the morning tomorrow, I may have to update some forecasted amounts.

  3. Just when predicting the timing of the rain was already difficult, now the Woodlands radar has broken down..

  4. My forecast rainfall amounts in the table on this post have been updated.

  5. I'm already tracking another potential rain event around Tuesday next week. It doesn't look as bad because it's more of a clipper system, so no need to panic right now, but just keep in mind we may get more rain. Right now GEM is furthest north with the system, bringing significant rainfall to Manitoba. ECMWF and GFS are further south, giving us lower amounts. Will keep an eye on it.

    Meanwhile, it has just begun pouring here in south St Vital. Expect moderate to heavy rain to last another couple hours or so.

  6. Rainfall poll will be eliminated if there's no respondents before 6 pm this evening

  7. Rainfall amounts so far today as of 2 pm:

    In Winnipeg:
    South St Vital (me) 7.6 mm
    U of W (downtown) 6.9 mm
    Charleswood 6.3 mm
    Whyte Ridge 6.0 mm

    Southern Manitoba:
    Letellier (just north of Emerson) 17.2 mm
    Winkler 11.8 mm
    Altona 11.5 mm
    Carman 7.6 mm
    Killarney 3.4 mm
    Woodlands 1.8 mm

  8. Just raining in sheets out there in south end right now. Up to 14.5 mm as of 5:10 pm.

    1. I'll update my rain totals on the right side top of the blog right under the weather polls section.

  9. Rainfall totals up to 7 pm:

    Winkler 22.1 mm
    Letellier 20.8 mm
    Reston 18.6 mm
    Altona 18.3 mm
    Carman 15.2 mm
    Morris 13.5 mm
    Woodlands 13.0 mm
    Virden 8.4 mm

    In Winnipeg:
    U of W (Downtown) 20.3 mm
    South St Vital (me) 19.6 mm
    Charleswood 17.3 mm
    Whyte Ridge 14.2 mm

  10. Of the 9 biggest cities in the Prairies, Winnipeg is now the only one that has not had a thunderstorm yet this year!

  11. We're in a bit of a break here in Winnipeg for most of tonight. We may get a stray few showers or maybe a rumble of thunder (however I doubt it), but the bulk will stay to our south, west and north.
    Another wave of rainfall is expected to move in tomorrow early in the morning and that will be giving us a very wet Friday with another 15-30 mm likely.

  12. Based on Grand Forks radar, we could be seeing a lot of heavy rain this morning. That 10-15 mm EC forecasts will be an easy target today. I'm sticking with my 15-30 mm right now.

  13. Sure would be nice to have Woodlands radar right now. Been raining buckets here in the south end for half an hour now.

  14. 3 posts planned for next couple days:
    Rainfall totals summary tomorrow morning
    May summary tomorrow evening
    Spring summary Sunday afternoon

  15. Storm totals so far as of 10 am:

    In Winnipeg:
    South St Vital (me) 37.9 mm
    U of W (downtown) 36.3 mm
    Charleswood 30.0 mm

    Across Manitoba:
    Reston 55.2 mm
    Treherne 53.4 mm
    Portage east 49.4 mm
    Morris 46.6 mm
    Winkler 45.9 mm
    Letellier 40.6 mm
    Carman 35.8 mm
    Altona 35.3 mm
    Deloraine 28.0 mm
    Virden 28.0 mm
    Dugald 27.4 mm
    Steinbach 23.8 mm
    Woodlands 22.0 mm
    Arborg 4.2 mm

    Amounts courtesy of Manitoba Agriculture
    There's also a report of 90 mm near Carberry according to Environment Canada

  16. Well, I doubt we'll see a thunderstorm today and there's no storms in the forecast before June 3. This will likely become the 2nd latest start to the thunderstorm season ever in Winnipeg.

  17. My storm total is 41.3 MM! Definitley a bit more then i expected!

    1. Thanks Willy, got 45.9 mm at my place.
      Will have another storm totals map by late morning/around lunch tomorrow.

      Looks like winning answer to rainfall poll will be 40 to 59 mm. Thank you to the 2 respondents for taking part!

  18. Mistake! My total is 44.4.

  19. Wow I got a total of 88.6 mm for the month of May. How about you Willy?

  20. Good chance for some frost tonight with decreasing winds and dewpoints along with clear skies. Right now it looks like temperatures will drop to between 0 and 2°C... but NAM drops us to -1°C so covering those plants may be a good idea tonight just to be safe. Downtown itself should be fine, but suburbs and outside of city better chance.

  21. There's a report from a cocorahs observer of 108 mm just west of Morden. Also 121.7 mm just southwest of Miami