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.

More Unsettled Weather

Although nothing as notable as this past weekend’s rain event is in store, unsettled weather returns for the second half of the week.

Another sizeable low pressure system is making it’s wet presence felt, but this time the hardest hit area will be Southern Alberta where some portions in the foothills may receive as much as 200mm of rain this week. This system will slowly lumber eastwards through the next few days, slowly weakening as it does so but still producing thunderstorms and showers as it goes.

Wednesday: Severe Thunderstorm Risk for Extreme SW Manitoba

Wednesday
25°C / 13°C
More cloud than sun. Warm & breezy.

Winnipeg will see fairly pleasant weather today with mixed skies, likely leaning towards more cloud than sun, and a high near 25°C with a fairly stiff easterly wind at 30-40km/h thanks to a surface trough building southeastwards through North Dakota.

The main upper low, the heart of this large disturbance, will gradually edge eastwards through the day and will trigger thunderstorms, with some severe storms possible, through portions of southern Saskatchewan and southwestern Manitoba. Shower activity will start off the day in much of Southern Saskatchewan, but the southeast portion of the province will likely see things destabilize enough through the day that thunderstorms are likely by mid-to-late afternoon. The storm activity is most likely to initiate through western North Dakota and then build north/northwestward along the surface trough into SE Saskatchewan and into extreme SW Manitoba through the early evening.

There is an organized threat of severe weather with these storms; we’ve gone with a slight risk due to almost every severe weather parameter looking fairly good except lacking in some subtle way. The main threats will be strong winds and large hail, especially out of any storms that develop early and are sustained as discrete supercells. If the storms develop into a cohesive line, the severe threat will be diminished, although non-zero. There will be a very slight chance for tornadoes thanks to excellent low-level shear, low cloud bases, and a vorticity rich environment being advected eastwards by the upper-level low.

Today will bring a slight risk of severe thunderstorms into SE Saskatchewan and SW Manitoba.
Today will bring a slight risk of severe thunderstorms into SE Saskatchewan and SW Manitoba.

The severe storm threat will push eastwards into the Virden & Melita regions of Manitoba in the early evening with the main threats being strong winds and large hail. It does look like the tornado threat should be restricted to the Saskatchewan side of the border. Southwest Manitoba is in for quite a soaking overnight as the storms expand into an area of convectively driven rain; around 15-20mm is likely for most areas south of the Trans-Canada Highway and west of the Red River Valley (RRV), with as much as 40-50mm possible in areas that see thunderstorm activity as well.

As the area of showers pushes eastwards, it will gradually weaken into an area of showers with possible embedded thundershowers. It looks to reach Winnipeg by Thursday morning.

Thursday: Back to Wet Weather

Thursday
23°C / 14°C
Periods of rain. Around 10mm.

Thursday will be a cloudy day with a high near 23°C. Shower activity will be in the region in the morning and lift off to the northwest, however while that happens a new batch of rain will be develop to our south and lift northwards through the RRV. Around 10mm seems most likely through the day across most of the region, although if heavier shower activity ends up developing we may see closer to 15mm here in Winnipeg.

The shower activity will taper off on Thursday evening as it all lifts northwestwards into the Interlake and Parkland regions of the province. Winnipeg will see some clear breaks and a low near 14°C.

Friday: Cold Low Showers

Friday
23°C / 14°C
Mixed skies; showers or thundershowers developing midday.

Friday will see us underneath the upper-level low which essentially means that there will be a bunch of cold air high up in the atmosphere. With mixed skies, we’ll see temperatures increase towards our high of 23°C fairly quickly through the morning. By mid-day, we’ll likely have hit our high temperature and the atmosphere will become quite unstable. Expect widespread shower and thundershower activity through the Red River Vally. Rainfall amounts will be highly variable and dependant on how many showers any one spot sees and how fast things move along.

Overnight, the shower activity will consolidate to right around the upper low on Friday night as it drifts through our region and into Minnesota. The temperature in Winnipeg will drop to around 14°C.

Elsewhere in Weather News: June 7th, 2014

Large Hailstorm causes Millions in Damages

This past week featured severe thunderstorms that tore through the Nebraska countryside producing extremely large hail in the region. Conditions were primed for a severe weather outbreak this past Tuesday; moisture streamed up from the Gulf of Mexico, a strong jet streak was in place overhead and the environment was relatively uncapped. Convective Available Potential Energy (CAPE) was quite high that day which was a significant contributor to the large hail sizes observed. Generally the higher the CAPE, the faster the updraft velocity which means that the updraft can support larger hailstones. Supercell thunderstorms were triggered Tuesday afternoon and persisted through the evening, trailing along the warm front that bisected the region.

In total over 200 hail reports were submitted on Tuesday and of these 38 were considered large hail reports (hail of 5cm in diameter or larger). The most damage caused that day appeared to come out of the town of Blair, Nebraska where hail caused major damage. Windows were blown out and car windshields smashed by the baseball size hail that fell – damage totaled in the hundreds of millions. Other storms along the warm front, the weather feature that triggered the severe weather, moved into the Omaha area not only bringing hail, but also torrential downpours. 13.5mm of rain was recorded in 3 minutes at the Omaha airport!

Hail damage in Hoover, NE shows the strength of baseball size hail, completely shredding the siding and breaking the windows. (Source: Kevin Krohn)
Hail damage in Hoover, NE shows the strength of baseball size hail, completely shredding the siding and breaking the windows. (Source: Kevin Krohn)

There is a possibility for more severe storms this weekend in Texas and New Mexico, but the parameters are not as as favourable for severe weather as seen this past Tuesday in Nebraska. Models show the active pattern continuing in the US Plains into next week, and rightfully so as severe weather season nears its peak.