High waves due to the strong winds in Gimli.

Colorado Low Slams Southern Manitoba Over May Long Weekend

Southern Manitoba was slammed by a powerful Colorado Low this past weekend that brought a wide array of severe weather to the province. Between heavy rain, ice pellets, snow and very strong winds, the storm wreaked havoc on the regions infrastructure with widespread damage to trees, power outages, closed highways, structural damage and overland flooding.

The system was, fortunately, well forecast by Environment Canada with fairly accurate forecasts issued in the days leading up to it alongside special weather statements addressing the numerous impacts the system may have on the region.

Significant Rainfall Began Saturday Afternoon

Fortunately, the weather was able to hold for much of Saturday. Temperatures climbed into the low 20’s across Southern Manitoba with increasing cloudiness. Rain & thunderstorms developed through North Dakota & Montana and lifted northwards through the day, first spreading into SW Manitoba in the afternoon and then eastwards and northwards through the evening and overnight period.

Some of the hardest hit regions were in SW Manitoba where hours of training thunderstorms & convective showers produced moderate to heavy rain. The Melita region was hit the hardest with 72mm of the grand total 90mm of rain falling by midnight on Saturday night. For areas further east, through, much of the rain fell through Saturday night & Sunday. Total rainfall amounts for Saturday and Sunday combined were:

Rainfall Totals for May 16–17, 2015 – Environment Canada & Manitoba Agriculture (*) Stations
Location Rainfall Total (mm)
Melita 90
Bede* 83
Gretna 63
Carman 60
Deloraine* 57
Deerwood 55
Morden 51
Kleefeld 48
Reston* 48
Dugald* 45
Pilot Mound 44
Emerson 43
Pierson* 43
Letellier* 41
Winnipeg (Forks) 41
Portage East* 40
Portage Southport 40
Woodlands* 38
Oak Point 37
McCreary 36
Winnipeg Airport 36
Pinawa 36
Great Falls 34
Carberry 33
Sprague 32
Virden* 30
Brandon 29
Fisher Branch 29
Cypress River 28
Glenboro* 27
St. Pierre* 25
Wasagaming 24
Dauphin 22
Teulon* 21
Killarney* 20
Wawanesa* 20
Minnedosa* 17
Eriksdale* 16
Roblin 16
Souris* 15
Berens River 14

This rainfall is in addition to the 25–50mm of rain many areas in the region saw just a couple days prior to this storm. There were several areas that saw significant overland flooding due to the sheer quantity of water that fell over the short time frame.

Additionally, there were reports of sewage back-up and spotty basement flooding across Winnipeg.

Then Came the Wind

Sunday is where the brunt of the storm impact was felt. As the main low pressure centre lifted northwards into the Dakotas, a strong 1037mb high pressure centre was building into the central Prairies.

Surface analysis for early Sunday morning.
This surface analysis for early Sunday morning shows the strong low in the Dakotas and the strong high building into the central Prairies.

These systems produced a strong pressure gradient over southern Manitoba and produced some of the strongest, longest-duration winds for a major storm in recent memory. Winds were in excess of 50km/h for 20 hours in Winnipeg with a 6-hour stretch beginning late Sunday with winds of 60km/h or greater. Very strong gusts also accompanied the winds with Winnipeg recording the highest wind gust at 93km/h:

Peak Wind Gusts for May 17, 2015
Location Peak Wind (km/h) Time (CDT)
Winnipeg 93 6:44PM
Gimli Harbour 89 9:38PM
Carberry 87 4:57PM
Brandon 83 10:00AM
Kleefeld 81 4:14PM
Cypress River 81 5:01PM
Pilot Mound 81 2:45PM
Gretna 81 2:28PM
Melita 80 6:11PM
Emerson 80 4:21PM
Gimli 80 4:21PM
Porgae la Prairie 80 4:51PM

The winds may have been the most significant impact from this storm. The strong winds resulted in havoc on the highways, property damage, hundreds of downed trees, and widespread power outages. The strong winds also produced significant wave action on Lake Winnipeg and some overland flooding as rising lake levels resulted in the lake overspilling its banks and pushing inland in some locations.

Winds tapered off to 40 gusting 60km/h on Sunday night, but remained fairly strong until tapering off Monday afternoon.

Oh, Snow Too

If the rain and the wind wasn’t enough, cold air moving in with the high pressure system resulted in precipitation switching over to ice pellets then snow beginning over Parkland Manitoba and then spreading southeastwards through the Interlake, Red River Valley & Whiteshell through the afternoon and evening. Areas through the Interlake southwestwards towards the Melita region saw the heaviest snow, with MacGregor reporting the highest amount of snow at 15cm. Amounts of 10–15cm were seen from Arnes, on the western shores of Lake Winnipeg, through Teulon, MacGregor, Treherne and down towards Boissevain:

Snowfall Totals for May 17–18, 2015 – EC Spotters & Social Media
Location Snowfall Total (cm)
MacGregor 15
Teulon 15
Arnes 10
Boissevain 10
Treherne 10
Hollow Water FN 5
Albert Beach 5
Dauphin 5
Deloraine 5
Wasagaming 5
Winnipeg 3

In Winnipeg, we saw just a few cm of snow on Friday evening and overnight. Flurries persisted through Monday but temperatures were warm enough to prevent any more accumulation.

All in all, this was certainly one of the most powerful storms Southern Manitoba has seen in a good long while. Perhaps the best thing that can be said is that at least it happened now and not a month earlier, where almost certainly it would have been a historic blizzard.

Brad

Brad

Brad lives in Winnipeg with his wife and two children and is the founder of A Weather Moment. He has loved weather from a very young age and has followed that passion through his life so far. He received a B.Sc. in Earth Sciences with Specialization in Atmospheric Sciences and is currently employed in the field of meteorology. You can find the author as @WeatherInThePeg on Twitter.