Friday, August 22, 2014

Torrential rains swamp Winnipeg

6 pm radar shows nearly stationary
thunderstorm complex over SW
Winnipeg into downtown core
After an extended period of warm and humid weather, Mother Nature unleashed over Winnipeg late Thursday afternoon with a nearly stationary thunderstorm complex that swamped much of the central and southern parts of the city. Thunderstorm cells started developing near the city around 5 pm.. and by 530 pm, a nearly stationary band of heavy thunderstorms had set up from the southwest part of the city into the downtown core.  Over the next 90 minutes, some 50 to 80 mm of rain /a month's worth of rain/ would fall across this swath, resulting in extensive flooded roads and underpasses, as well as flooded buildings (including Polo Park mall).  The rush hour deluge led to traffic chaos with several main streets in and out of downtown restricted or blocked due to floodwaters. City officials are describing the event as a 1 in a 100 year storm based on rainfall intensity. ( More photos and stories on the flooding from Winnipeg Free Press and Winnipeg Sun. )

In one of the more popular images from Thursday's deluge,
a resident snorkels in floodwaters in Whyte Ridge
(SW Winnipeg) where 80 mm of rain fell in 90 minutes.
Flooded underpass at Higgins Ave.. one of several
underpasses that were flooded in Thursday's deluge
For some, a canoe offered a better mode of
transportation on flooded city streets

Select rainfall amounts from Thursday's deluge..  (unofficial)
Rainfall amounts over south Winnipeg from
WeatherFarm mesonet

Whyte Ridge ............ 81 mm
U of Winnipeg .......... 65-75 mm
Tuxedo .................... 70 mm
Waverly South ......... 70 mm
Grant Park ............... 65 mm
Linden Woods ......... 56 mm
Forks (EC) .............. 53 mm
Charleswood ............ 41 mm
St Vital ....................  25 mm
Winnipeg airport ....... 19 mm
Transcona ..............    5 mm

This was the second time this week that the Tuxedo to Linden Woods area has been hit with heavy rainfall. On Monday afternoon, a narrow band of heavy showers and thunderstorms dumped 35 to 50 mm along this swath. Tuxedo Park school recorded 49 mm Monday with another 70 mm Thursday, for a total of 119 mm within 4 days. Linden Woods has recorded 109 mm since Monday. Normal August rainfall is 77 mm in Winnipeg.

City of Winnipeg rainfall - Aug 21 2014 (between 4 and 10 pm)

The following is a map from the city of Winnipeg showing the distribution of rainfall in the city from Thursday's rainstorm. One can see the heaviest rain axis stretching from the southwest Perimeter into the downtown core up towards North Kildonan. The maximum was in the Whyte Ridge area which saw over 80 mm of rain between 530 and 730 pm. (NOTE: The Fort Whyte station recorded an erroneously low number on this map due to a plugged gauge) The city has a network of over two dozen rain gauges scattered throughout Winnipeg to monitor rainfall within the city, which can vary widely in short distances during convective storms (which is the primary mechanism for precipitation in the summer months here)  This network of stations helps give the city a much more detailed picture of rainfall distribution within Winnipeg, compared to only 2 official Env Canada sites in the city (Winnipeg airport and The Forks)  Link to City of Winnipeg rainfall map.


  1. This city/province is doomed, move out, this will be the trend from now on!

  2. Rob Great Post particularly showing how every home in Lindenwoods is now LakeFront
    WBg mobile at 410 pm gave me NWS warnings of another 1 to 3 inches 25-75mm of rain by Sunday along the US border for all my locations Portal, Antler, Bottineau, Maida Sk border to Winkler between now and Sunday.
    Will we see that much in Wpg.?

    1. Don.. Almost all guidance is indicating 30 to 40 mm for Winnipeg and possibly more Saturday night into Sunday. They are also indicating Winnipeg/RRV may briefly warm sector Sunday afternoon with temperatures rising into the mid 20s along with increased humidity again which could result in locally heavy showers and thunderstorms once again. Tough call though as onset of precipitation Saturday evening will likely be convectively driven, which can result in highly variable amounts. Heaviest rain axis may shift into western MB Sunday (and along SK border) as precip shield wraps around on backside of system. But definitely a system to keep an eye on this weekend, particularly for those who were soaked this week.

  3. Also heard a marine warning on CBC radio for all of southern Lake Winnipeg of 3 to 5 foot waves and swell on saturday afternoon as North winds of up to 65 K were expected . This brings the lake precariously close to the top of the berm dike built in 2005 or whats left of it.
    Do you see anything positive in the forecast after this weekend as in heat wave?

    1. Warming back up to normal or even above normal by the end of next week, but no change to prolonged heat indicated at this point.

  4. Yeesh. I think that EnivroCan should just separate the heavy rainfall part of severe tstorm warnings into flash flood warnings, just like the NWS does down south. That'd more accurately depict the situation, as I didn't hear anything about hail, nor strong winds.

  5. Connor I heard the marine fcast about 20 minutes after the NWS flazh flood warning.

  6. Morning run of RGEM has cut down rainfall amounts substantially for Winnipeg for tonight with only about 10 mm shown now.. while other guidance continues to indicate some 30-40 mm for the city tonight into Sunday morning. Looks like it will be a solid band of showers and embedded thunderstorms moving in this evening heavy at times and then pushing north and west into Interlake and western MB by Sunday morning where rain will persist much of the day on the NW flank of the low pressure system. This is where there's a better chance of more substantial amounts of rain (and where current rainfall warnings are in place) For Winnipeg, area of rain will be more transitory which may cut down on the amounts, but it will likely be heavy at times tonight so local urban flooding possible once again tonight into Sunday morning..

    For tomorrow, we briefly warm sector in Winnipeg, and we may even get into the mid 20s if we get get some sunny breaks (Euro giving us a high of 28c!) But then notably cooler for Monday as colder air sweeps in on backside of system with highs only in the low to mid teens (feeling more like fall)

    1. Rainfall forecasts for Winnipeg from various 12Z model output..

      RGEM ...... 10 mm
      GGEM ....... 60 mm
      NAM .......... 40 mm
      GFS ........... 23 mm
      ECMWF .... 28 mm

      Average them all out and you get around 32 mm as a multi-model ensemble.. but the estimates vary widely between 10 and 60 mm. Not surprising given that precipitation will be convectively driven this evening before morphing into a stratiform area of precipitation, especially to our north. Also, some models are hinting at a split in the main precip axis, with a maxima over Lake Winnipeg/NW Ontario and another maxima over southern SK into Montana, while other models show less of a split occurring with a wide swath of heavy rain across northern RRV/Interlake into western MB. As always.. we'll see what happens. Pay close attention to radar trends over the next few hours especially over North Dakota and southern MB to see how these showers develop and move. Models indicate bulk of rain in Winnipeg will fall between 9 pm this evening and 9 am Sunday morning.

    2. By the way, NAM and HRRR models are hinting at some elevated convection overnight over RRV and Winnipeg, with precipitable water values soaring to 2" (50 mm) overnight. That could mean some thunderstorms with very heavy downpours overnight into early Sunday morning, with rainfall rates of 25-50 mm/hour possible. These storms should be faster moving than Thursday's slow moving complex, but even 30 minutes of torrential downpours can cause problems especially in a city like Winnipeg. Bottom line.. be prepared for possible heavy downpours again overnight into early Sunday.

      In addition, things get unstable Sunday afternoon as we warm sector briefly with surface based thunderstorms developing in the RRV and SE MB, possibly severe depending on how much sunshine can break through (increasing instability). An interesting 24 hours coming up!

    3. So much for 10 mm.. 18Z RGEM now giving 67 mm tonight for Winnipeg and another 10 mm Sunday afternoon. Just goes to show you how fickle and unreliable models can be in convective situations. Better bet is to go with an ensemble average as a first guess. .

  7. Glad to see your comments again Rob. There may be others but you're the best in my view. Mark.

  8. Re Thursday's event..

    I second the opinion that intensive type extreme events driven chiefly by meteorological processes such as training of thunderstorms (and not hydrological factors like run-off coefficients, snow-melt over a large basin) should fall under the responsibility of the weather service and not provincial water stewardship.

    I would question based on what analysis was the event declared a 1 in 100 year rainfall by the city. There are specific methodologies for determining values of 100 year return interval meteorological events. I would be hesitant to use data from the airport which seems to underestimate precipitation 10-20% and is often unrepresentative of other parts of the city which are more prone to heavy convection.

    Thirdly, the event also raises some questions as to the cities road infrastructure and drainage system.. if 50-75 mm can place such a strain, what would 100-150 mm that other cities have recently experienced do?

  9. Re Rainfall Sat night/Sunday:

    As Rob suggested, two main windows for heavy rain to affect the Winnipeg region within the next 24 hrs. 50 kt LLJ noses into the area accompanied by deep moisture and elevated instability overnight. Best potential for heavy convection and torrential rain appears to be from about 1-4 AM based on convergence from the LLJ. Precipitation should push north of the city by tomorrow morning and evolve into a stratiform, deformation zone type rainfall for areas well to the NW of Winnipeg. Dry slot pushes in with best potential for clearing and destabilization over SE Manitoba. Based on past experiences..with SE Manitoba in a capped warm sector, elevated convection (capable of producing heavy rain and hail) often forms on the cool side of the front (particularly if warm advection continues just off the surface as the models hint for tomorrow). If the cap is not strong, formation of surface based storms would be favored in the warm sector, ahead of the front over Falcon Lake, Sprague, etc. We'll have to see the exact position of the front and cloud trends tomorrow afternoon..