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.

Western Prairies get Hammered by Severe Thunderstorms

Severe storms fired across much of Alberta on Tuesday evening and Wednesday morning as well as Saskatchewan on Wednesday, and brought with them some large hail that inflicted major damage in some cities.

[map autofit=”1″ disable_scrollwheel=”1″] [pin]Lacombe[/pin] [pin]Kerrobert[/pin] [pin]Priddis[/pin] [/map]

A deep trough on the west coast of Canada was present on Tuesday and provided plenty of shear in the region to support organized storms. That, combined with some relatively high amounts of instability off the foothills of Alberta made for an environment not only supportive of organized storms, but created conditions that were prime for producing hail. In addition to these factors, the freezing level was low (just above 700mb) which meant that the hail had less time to melt before it reached the ground.

In total, there were two notable severe storms that caused major damage. The first was on Tuesday evening as it initiated off the foothills and headed west and at times had supercell characteristics as it drifted east and rooted down into the boundary layer. Lacombe, Alberta took a direct hit from this storm – hen’s egg-size hail or even slightly larger was reported across town. Damage was widespread in town, with car and house windows blown out, siding shredded, and crops badly damaged. The second storm, which occurred on Wednesday in the late morning and initiated off the foothills, also dropped large hail in the Calgary area. This time however, the supercell produced a rare Albertan tornado near Priddis, AB. The tornado didn’t do any significant damage to any structures (passed through a forest) but it did provide the opportunity for stunning photos.

The tornado near Priddis, AB as seen from air by cloud seeders. (Source: Twitter - @Ringosmyuncle)
The tornado near Priddis, AB as seen from air by cloud seeders. (Source: Twitter – @Ringosmyuncle)
The same storm later consolidated with another storm nearby and reached central Saskatchewan by mid-evening. The town of Kerrobert, SK was especially hard hit with hail larger than the size of golf balls. It even prompted the town to issue a state of emergency because the damage was so severe to buildings and property – according to residents, over two thirds of the town’s houses had broken windows. Damage costs from these storms has yet to be determined but is estimated to be in the tens of millions at the very least.

Golf green in Kerrobert, SK badly damaged by the hail. (Source: Twitter - @EarlsSalesMarc)
Golf green in Kerrobert, SK badly damaged by the hail. (Source: Twitter – @EarlsSalesMarc)

A Sunny, Hot & Muggy Weekend Ahead

After a very busy day across Southern Manitoba yesterday that brought strong winds but, more significantly, absolutely drenching rainfall to many areas, much quieter weather is in store for the weekend.

The weather over the coming few days will, fortunately, take little space to explain. For all the coming days, we’ll see daytime highs in upper 20’s or just cracking the 30°C mark. It will feel a bit warmer than that, though, as a moderate amount of humidity remains in the region. Dew point values will fall to around 16 or 17°C this afternoon, but then rebound back into the upper teens or low 20’s for Saturday & Sunday. This will make for quite a hot and humid weekend.

RDPS Forecast Dew Point valid 00Z Saturday July 25, 2015
The orange colours in the Red River Valley show dew point values remaining near 20°C.

Winds will remain fairly light over the coming days. Overnight lows will sit in the upper teens.

Little precipitation is expected; and little is expected in the way pop-up showers or thunderstorms are expected. There’s a chance of some shower activity moving through tonight, but it’s not expected to be particularly significant.

Unsettled Start to Next Week?

The beginning of next week may potentially have a stormy and unsettled start as a low pressure system moving through the region brings another round of thunderstorms to Southern Manitoba. At this stage, it doesn’t look like nearly as widespread an event as the extensive system that affected Southern Manitoba on Thursday. With the heat and humidity in place, though, severe thunderstorms may be a possibility. As we move further into the weekend, we’ll be keeping an eye on things and issue a convective outlook for Monday or Tuesday if it looks significant enough.

Until then, enjoy the hot and humid weather!

Humid Weather Brings Thunderstorm Threat to Southern Manitoba

The remainder of this week will be marked by a notable increase in the humidity as a deep southerly allows the moisture to build into Southern Manitoba. Alongside the sweltering conditions, a low pressure system pushing across the Prairies over the coming days will bring a threat for strong to severe thunderstorms across Southern Saskatchewan & Southern Manitoba.

Today will be a hot day with the humidity gradually building in through the day. Winds will strengthen through the day out of the south to southeast to around 30km/h or so as temperatures climb into the upper 20’s. Skies will remain mainly sunny with just a few clouds expected. While the humidity will be comfortable to start the day with dew point values around 14°C or so, the weather will get considerably stickier as the day progresses with dew point values climbing into the upper teens or perhaps even hitting the 20°C mark in the evening. This will make for very humid conditions with humidex values in the mid–30’s.

RDPS Surface Dewpoint valid 21Z July 23, 2015
The RDPS shows dew point values climbing over the 20°C mark Thursday afternoon resulting in very humid conditions.

Thursday will be the significant weather day for the second half of the week as a trough of low pressure passes across Southern Manitoba. Temperatures will soar towards the 30°C mark with significant humidity as dew point values once again push towards the 20°C mark, making the afternoon feel more like the upper 30’s. Winds will be lighter on Thursday than they will be on Wednesday, but there may be some brief breeziness late in the morning or early in the afternoon.

AWM Day 2 Convective Outlook for Thursday July 23, 2015
A slight risk of severe thunderstorms exists today across much of southwestern Manitoba extending into the Interlake and Red River Valley.

The heat and humidity will combine to pose a risk for some potent thunderstorm activity tomorrow afternoon. A trough of low pressure moving across the Red River Valley will serve as a trigger for convective activity sometime mid-to-late afternoon.[1] Winnipeg & the Red River Valley will see the risk for strong to severe thunderstorms – given a few conditions work out, more on that later – with large hail, strong winds and torrential downpours the primary threats. If an organized supercell manages to develop, the tornado threat with it (or them) will be slightly elevated. Looking through the guiding MIST principle for assessing convection:

  • Moisture: Abundant. Moisture transport coupled with vigorous evapotranspiration will combine to produce elevated surface dew point values near or exceeding 20°C by the end of the day.
  • Instability: Moderate instability with marked height falls ahead of an approaching shortwave coupled with the elevated moisture available through the boundary layer will produce MLCAPE values in the 2500 – 3000 J/kg range. The instability will carry into the evening hours with MUCAPE values remaining in the 2000+ J/kg range.
  • Shear: Pretty good. Bulk shear values of 20–30kt will increase towards 30–40kt in the evening hours. Additionally, low-level profiles show moderate veering. The wind profiles support supercell or multi-cell storm development with upscale growth likely in the evening hours.
  • Trigger: As mentioned, the trough pushing through the region associated with a low pressure system moving through the Dakotas will provide sufficient convergence to trigger thunderstorm activity.

The end result of all this is that thunderstorms are likely through Southwest Manitoba in the afternoon, with the threat pushing eastwards into the Red River Valley late afternoon into the evening. Storms will likely originate as supercells or multi-cell storms. Primary threats will be large hail and torrential rain, shifting towards hail/rain/wind as the storms organize & expand in coverage heading eastwards. Any supercell storms that manage to develop will likely pose a slight tornado risk.

Showers or thunderstorms are very likely Thursday evening/night as the system moves through. Stay alert of any watches or warnings issued by Environment Canada through the day into the evening on Thursday.

Friday will be a fairly quiet day. Things will stabilize behind the departing trough of low pressure, bringing clearing skies and a high in the upper 20’s with decreasing humidity. Expect a low in the upper teens on Friday night.

Summer Heat Returns for Weekend

The reprieve from the heat and humidity will be short-lived, however, as temperatures will climb back up to the 30°C mark with humid conditions returning as dew point values of 20°C or greater building back into the region. No precipitation is expected through the weekend.


  1. Although a wildcard remains of how long nocturnal convection from Wednesday night will persist into the daytime hours on Thursday.  ↩