Update: Major Wind Storm Likely Thanksgiving Monday

An incredibly abrupt change is in store for Southern Manitoba as a powerful low pressure system is set to blast the near-record warmth out of the region and replace it with unquestionably fall-like weather. As it often is in the shoulder seasons, though, it’s going to be quite the spectacle.

Temperatures have soared into the mid–20’s quickly this morning, rapidly approaching the record high for Winnipeg of 26.1°C set in 1941. A powerful low pressure system to our northwest is approaching, though, and it is going to pack a mean cold front.

Surface analysis valid 12:45PM October 11, 2015
Surface analysis valid 12:45PM October 11, 2015

The midday surface analysis shows us three primary features. The first is the frontal wave with warm front across the northern Interlake and cold front draped southwards along the Manitoba/Saskatchewan border. To the southeast of these fronts is the unseasonably warm air mass that is bringing very warm temperatures to the region. The second feature is a low pressure center over central Saskatchewan. The last is a broad cold front that stretches from Central Alberta into Northern Manitoba.

Important to note is that the low pressure centre has occluded[1] and that there is a trowal developing (visible on the satellite image). This lonely low will trundle along for a little bit, until it can re-attach to the cold front slumping down behind it. The temperature gradient along the northern front is actually quite significant, and as the low re-attaches to that frontal wave, it will rapidly intensify. This low will move east-southeast as the steering flow amplifies and digs the upper-level trough.

While we may warm another degree or two, it’s more or less all downhill from here. Wind will continue to pick up out of the west-northwest late this afternoon to around 30km/h as an area of showers blossoms over Southern Manitoba. Widespread shower activity is likely much of the night as strong cooling aloft results in persistent destabilization of the atmosphere. Winds will remain around 30km/h with gustiness on top of that.

The real story will be when the cold front slams through early tomorrow. More rain is likely with the passage of the front, but winds will be the primary issue. As the cold front passes, winds will shift to be out of the northwest and pick up in speed significantly. Sustained winds will likely reach around 55–65km/h, but very strong gusts are possible; it’s highly likely that Winnipeg & the Red River Valley will see wind gusts to 90km/h, however with very strong winds within the conditionally unstable layer and precipitation very likely, it’s possible that wind gusts exceed 100–110km/h. Winds at these speeds can be hazardous when driving and cause damage to buildings (especially roofs) and trees.

NAM forecast sounding for Winnipeg, valid 12Z October 12, 2015
NAM forecast sounding for Winnipeg, valid 12Z October 12, 2015

This forecast sounding for Winnipeg from the NAM shows very strong winds near the surface, with up to 60kt present at the top of the low-level instability.

The strongest winds will begin to subside mid-to-late morning, but strong northwesterly winds of 50km/h gusting to 70km/h will likely be in place for the remainder of Monday. The day will start of with a temperature around 9 or 10°C and see it drop to around 4°C by the end of the day. The bulk of the precipitation should taper off with the winds mid-morning, and when all is said and done, this system will likely produce around 5–10mm of rain over the Red River Valley, although for the northern half, there’s a slight chance of seeing more along the lines of 10–15mm.

Environment Canada has issued a wind warning for the Red River Valley regarding this system with the following discussion:

An intense low pressure system will track across central Manitoba tonight and Monday morning. A strong cold front extending southward from this low will sweep across southern Manitoba tonight. Very strong northwest winds will develop in the wake of this cold front with the strongest winds in the Red River Valley as winds will funnel down the valley. Sustained winds of 60 to 70 km/h with gusts over 90 km/h are likely beginning late tonight and lasting until early afternoon on Monday. Winds will gradually subside Monday afternoon from west to east as this system heads off into Ontario.

Damage to buildings, such as to roof shingles and windows, may occur. Loose objects may be tossed by the wind and cause injury or damage. Be prepared to adjust your driving with changing road conditions due to high winds. Avoid wooded areas to prevent injury from falling trees or branches. Campers should move to sturdy shelters.

Be sure to tie up any loose objects and remove fabric canopies from gazeboes. Bring in any objects that could catch the wind, and maybe flip your trampolines over so the wind doesn’t do it for you. It’s going to be a bit of a busy night and a wild Monday morning, so batten down the hatches!


  1. Occlusion is a part of the natural life-cycle of low pressure systems. In simple terms, it means the low has “detached” from the fronts.  ↩

Severe Thunderstorm Threat Marks Transition to Summer Heat Wave

A threat of severe thunderstorms will come to Southern Manitoba today as a trough of low pressure pushes across the region, tapping into very muggy air near the surface. The passage of this system will mark the beginning of a transition towards a summer heat wave as a potent upper ridge begins building over North America.

Friday: Severe Thunderstorm Threat

This morning’s cloud and drizzle will break up through the morning as our winds finally begin swinging around to the west/southwest, finally allowing some sun to begin poking through and allowing us to start climbing towards our daytime high near 25 or 26°C. As we move towards the afternoon, however, a trough of low pressure will begin pushing into the Red River Valley from the west, bringing with it the threat for severe thunderstorms.

Taking a look at the basic MIST principle for today’s convective potential:

  • Moisture: Moderate moisture will be in place today with surface dewpoints near 18°C and mixed layer dewpoints around 16°C.
  • Instability: As the trough swings into the region, mid-level lapse rates will steepen significantly alongside the erosion of the capping inversion thanks to daytime heating. By mid-afternoon, MLCAPE values near 2000 J/kg will develop with little to no capping inversion along the trough line.
  • Shear: Slightly backed surface winds ahead of the trough line coupled with approximately 25kt of 0–6km bulk shear will be sufficient to provide organization to any thunderstorms that develop.
  • Trigger: This is the most questionable aspect. Models differ on the strength of the trough line as it swings through; while some show little strength to it resulting in a lack of convergence and no convection, others show a stronger trough which would be sufficient to focus the energy and produce more substantial thunderstorm activity.
AWM Convective Outlook valid 12PM Friday August 7, 2015 to 7AM Saturday August 8, 2015
AWM Convective Outlook valid 12PM Friday August 7, 2015 to 7AM Saturday August 8, 2015

As a result, a slight risk of severe thunderstorms is warranted for much of Southern Manitoba. Any storms that develop will likely initiate as single-cell or supercell thunderstorms before growing upscale fairly quickly into linear convective elements. The primary threat with any storms that develop today will be strong winds and large hail, however rainfall rates may pose significant impact in storms despite accumulations likely not hitting any severe criteria.

Thunderstorms will move off towards the east through the evening, leaving behind clearing skies and a pleasant overnight low near 15°C.

Beautiful Weekend Ahead

There isn’t much to say about the coming weekend other than it will be quite nice. Daytime highs on both Saturday & Sunday will be near the mid–20’s with overnight lows in the mid-teens. Winds will be relatively light out of the northwest on Saturday and fairly calm on Sunday. There will be a bit of cloud cover left over on Saturday while Sunday will be mainly sunny.

Heat Wave Builds In Next Week

Next week will see very warm weather return to Southern Manitoba as a potent upper-level ridge builds across much of North America.

GFS 500mb Height & Wind Forecast valid 00Z Thursday August 13, 2015
The GFS 500mb Height & Wind Forecast valid 00Z Thursday August 13, 2015 shows a significant upper-level ridge over much of North America.

As the upper ridge builds, a deep southerly flow will develop over the eastern Prairies, bringing significantly warmer air into the region. With 850mb temperatures forecast to reach 20°C or warmer, it seems likely we would see daytime highs in the low 30’s several days next week. One of the big questions is exactly how humid it will get, but we’ll have to wait until we’re closer to better assess that question. At this point, though, it seems quite likely that we’ll see a stretch of dry and hot weather next week.

Early Week Risk of Storms

This week will start out with a risk of thunderstorms. Monday will likely feature severe storms from eastern Saskatchewan into western Manitoba, while Tuesday may see storms through the Red River Valley and south-eastern Manitoba.

A low pressure system over North Dakota will be the focus for severe storms today. The red line is the warm front, brown line is a dryline, and blue lines is a cold front.
A low pressure system over North Dakota will be the focus for severe storms today. The red line is the warm front, brown line is a dryline, and blue lines is a cold front.

This Week

Monday

Today’s weather will have two key features; the risk of thunderstorms, and hot, humid conditions (these two attributes are linked incidentally). Temperatures are expected to climb into the low thirties across southern Manitoba, with the humidity pushing humidex values to around 40 in many areas, making it essentially a repeat of Sunday. However, there will also be a risk of severe storms in western Manitoba. This risk of storms will result from the combination of a hot, humid air mass over the region and a strong jet stream aloft. Any storms that do develop, particularly during the evening hours from south-eastern Saskatchewan into south-western Manitoba, could be very severe. There will be a risk of large to very large hail, damaging winds, heavy rain, and tornadoes. There is a risk that storms may fail to develop due to warm air aloft, although it seems more likely than not that there will be storms. A technical discussion on the thunderstorm risk over the next two days is available at the end of this post.

Tuesday

Tuesday will see a strong cold front push through southern Manitoba. The atmosphere ahead of this front will be unstable, potentially allowing some storms to develop ahead of it. The front is expected to pass through southern Manitoba relatively early in the day, limiting the potential for severe storms. However, if storms do develop early in the morning, we may see some strong cells push through the Red River Valley and south-eastern Manitoba before they exit into Ontario. Once the cold front passes, the humidity will drop noticeably, but temperatures will remain in the mid twenties with a gusty south-west wind.

Wednesday

Wednesday should be a fairly benign day in southern Manitoba, with breezy west winds and temperatures in the mid twenties. Skies should be mainly sunny and no significant precipitation is expected. For many thunderstorm-weary residents of Manitoba, this will come as a welcome break.

Technical Discussion

Monday

Dynamics:
An unseasonably strong upper trough will move across the southern prairies early this week. A lee cyclone will push onto the great plains early Monday, with the surface low centre being located near Dickinson, ND by Monday evening. A warm front will arc northwestward from the surface low to near Melita, MB and up toward the southern basin of Lake Winnipeg. A dryline will extend southward from the low, and a cold front will extend off to the south-west. This low will be associated with a strong upper trough, with 500 mb jet streaks of 50 kts over Wyoming and southern Saskatchewan on Monday evening. The exit region of a strong 80 kts 250 mb jet streak will be edging into the Dakota by Monday evening. In the low-levels a 30-40 kts LLJ will extend from the central plains into southern MB/SK. The result of the synoptic regime will be effective shear of 40-60 kts in the vicinity of the warm front.

Thermodynamics:
A moisture-rich air mass will be in place within the warm sector of the surface cyclone. 100 mb mean mixing ratios of 17-19 g/kg seem likely in the vicinity of the warm front, generating MLCAPE in the 3000-4000 J/kg range. A strongly veering low to mid-level wind profile will result in strong WAA in the 850-700 mb layer, generating sizeable capping inversions in most of the warm sector.

Overall Discussion:
Today will feature a moderate risk of severe thunderstorms from SE SK into SW MB. A moderately to extremely unstable air mass will be coincident with strong effective shear and strong ERSH. Main concern is the capping inversion that will result from low/mid-level WAA. It appears probably that some surface-based supercells may occur along the warm front, through the triple point region, and down the cold front today. Strong moisture convergence near the warm front, aided by the expected ejection of numerous weak vort maxes from the upper trough should trigger storms. Any storms that develop will produce large to very large hail, damaging winds, and potentially a few tornadoes. Tornado chances will likely be maximized through mid-evening at the LLJ increases and LCL heights decrease. The location of the warm front remains a question, as isentropic ascent of the LLJ on the warm front may generate extensive elevated convection in parts of southern SK. The primary surface-based risk may be pushed into ND under that scenario. Later in the period cold-pool mergers may allow for upscale growth into one or more forward-propagating MCSs. The cloud layer shear and LLJ orientations suggest a westward-moving system in ND that may impact parts of southern Manitoba, with the potential for severe weather primarily being along and south of the intl border. A second MCS may track NE-ward into the Interlake region. This second MCS would be non-severe owing to an unfavourable LLJ orientation – preventing strong dynamic lift for slabular convection – and decreasing deep layer shear.

Tuesday
A strong cold front will move through southern Manitoba on Tuesday, potentially triggering thunderstorms. Strong effective shear will be present in association with the frontal passage, however thermodynamic profiles suggest some capping to surface-based/near surface-based convection. Thus, it remains unclear if any storms will be possible before the front exits the province. Should storms develop, they may be severe with large hail and damaging winds being the main threats.

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
LocationRainfall Total (mm)
Melita90
Bede*83
Gretna63
Carman60
Deloraine*57
Deerwood55
Morden51
Kleefeld48
Reston*48
Dugald*45
Pilot Mound44
Emerson43
Pierson*43
Letellier*41
Winnipeg (Forks)41
Portage East*40
Portage Southport40
Woodlands*38
Oak Point37
McCreary36
Winnipeg Airport36
Pinawa36
Great Falls34
Carberry33
Sprague32
Virden*30
Brandon29
Fisher Branch29
Cypress River28
Glenboro*27
St. Pierre*25
Wasagaming24
Dauphin22
Teulon*21
Killarney*20
Wawanesa*20
Minnedosa*17
Eriksdale*16
Roblin16
Souris*15
Berens River14

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
LocationPeak Wind (km/h)Time (CDT)
Winnipeg936:44PM
Gimli Harbour899:38PM
Carberry874:57PM
Brandon8310:00AM
Kleefeld814:14PM
Cypress River815:01PM
Pilot Mound812:45PM
Gretna812:28PM
Melita806:11PM
Emerson804:21PM
Gimli804:21PM
Porgae la Prairie804:51PM

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
LocationSnowfall Total (cm)
MacGregor15
Teulon15
Arnes10
Boissevain10
Treherne10
Hollow Water FN5
Albert Beach5
Dauphin5
Deloraine5
Wasagaming5
Winnipeg3

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.