After an all-too-brief respite from the wet conditions of the past week, more chances for rain are on the way as a series of disturbances move through southern Manitoba.
The rain train is heading back to Winnipeg Station today as an occluding frontal wave moves across the southern portion of the province ahead of a deepening low pressure system. As the wave approaches this morning, mostly cloudy skies will be in place and there is a chance that some morning showers will materialize.1 The main action — a mix of showers and thunderstorms — will begin developing near midday over southwestern Manitoba and then quickly expand and move eastwards into the Red River Valley for the afternoon. These will move out of the region by the early evening.
Severe thunderstorms are not expected over a widespread area, however there are just enough energetics and dynamics that an isolated storm or two may become marginally severe.2
Showers and thunderstorms are expected across much of the Red River Valley, Interlake and points eastwards today.
Temperatures will climb to a high near 21 or 22°C today with southerly winds of 30-40 km/h gusting up to 60 km/h shifting to westerly after the frontal passage in the afternoon. Expect some clearing in the evening, then variable cloudiness developing towards morning. Temperatures will dip down to a low near 13°C.
Thursday will bring mixed to mostly cloudy skies to Winnipeg and much of the Red River Valley as strong westerly winds of 40-50 km/h build into the region. There will be a chance of showers as rain wraps around on the back side of the passing low pressure system, but much of the guidance suggests that the rain will remain mainly north of the Red River Valley. Temperatures will climb to a high near 19°C and head towards a low near 12°C under mostly cloudy skies with light rain likely on Thursday night.
An area of light rain/showers will slump southwards through the Interlake into the northern Red River Valley on Thursday night.
Friday will bring cloudy skies with a chance of showers as the overnight activity on Thursday tapers off through the region as an upper-level trough exits. Winds will be out of the northwest at 30-40 km/h with gusts up into the 50-60 km/h range. Skies continue cloudy overnight with a chance of showers as temperatures drop to a low near 10°C.
Long Range
Saturday will remain unsettled with a chance of showers as a weak disturbance ripples through the region from the north and cooler air spills southwards. Conditions finally improve on Sunday, which looks likely to be a fairly sunny day. Temperatures will remain below normal, however, through the weekend and into early next week as Manitoba remains under the influence of a large upper low over Hudson Bay.
Winnipeg’s seasonal daytime high is currently 24°C while the seasonal overnight low is 12°C.
These showers would be elevated, meaning they are formed at higher altitudes and would occur ahead of the incoming front. ↩
In this case, we would expect either wind gusts just over 90 km/h or severe hail in the 20-25mm range. ↩
A complex low pressure system will bring several chances for thunderstorms to Winnipeg & the Red River Valley today and tonight into Saturday morning, some of which may be severe. All the unsettled weather will clear out on Saturday afternoon, leaving us with a seasonably mild and dry weekend.
The risk of thunderstorms returns to Winnipeg today as an approaching warm front moves into the region. As it advances eastwards, leftover cloud cover from overnight thunderstorms in Saskatchewan will spread into the Red River Valley. Before we get into the thunderstorm details, today’s high in Winnipeg will be a balmy 27°C with dew points climbing up to the 16-17°C range, making it feel a bit humid in the afternoon. Winds will be out of the south-southeast at about 20-30 km/h. Expect a low tonight near 18°C. Now, onto the thunderstorm details!
The first potential thunderstorm threat is for this afternoon, and will be focused primarily over southwestern Manitoba.
Moisture: Surface dewpoints will climb into the 15-17°C range ahead of the surface trough moving into the region. This moisture will be relatively deep, dropping only to around 13°C at 850mb.
Instability: MLCAPE values will climb to 1000-1500 J/kg of CAPE through the afternoon, although capping may be an issue depending on the timing of the 700mb thermal ridge passage.
Shear: Shear is fairly good with veering profiles and 45-50 kt of bulk shear. Low-level shear is relatively unidirectional with moderate speed shear.
Trigger: Low centre with trough line extending northwards will provide focus for low-level convergence. Additional, the triple point of a frontal wave tracking along the U.S./Canada border will also provide more focus and convergence.
The main uncertainties are tied to how quickly warmer air at 700mb1 can exit area. While it’s in place, it will likely prevent the development of thunderstorms until the evening. Should thunderstorms develop, the primary threats would be large hail and strong winds. The storms should be moving quickly enough that the threat for localized flooding due to rain is minimized, and higher cloud bases coupled with relatively small amounts of low-level wind shear will also reduce the tornado threat. If these thunderstorms develop, they will track eastwards into the Red River Valley in the early evening and make their way through.
The second thunderstorm threat will develop this evening and will impact much of southern Manitoba. Another disturbance will push into the region and initiate thunderstorms.
Moisture: The low-level jet will be supplying air with dew points near 16-17°C, providing ample moisture for thunderstorm development.
Instability: MUCAPE values will hover near 1000-1500 J/kg, enough energy to strong to severe thunderstorms.
Shear: Will be excellent; a very potent low-level jet will develop, strengthening to 50kt by 03Z. 500mb winds will be out of the west to southwest at 45-50 kt. This shear will be very supportive of thunderstorm development.
Trigger: Shortwave and associated frontal wave will be trigger for thunderstorm development.
Even now, there’s significant uncertainty with this afternoon’s convection. That said, it seems likely that thunderstorms will likely develop over portions of southwest Manitoba near 6-7PM and then undergo rapid upscale growth and develop into a line that tears eastwards across the Red River Valley; the primary threats associated with these storms will be large hail and damaging winds. Significantly elevated precipitable water values also suggest very intense downpours are likely as well.
AWM Thunderstorm Outlook valid 12PM Friday June 9 – 12PM Saturday June 10, 2017
Saturday will bring some more morning showers or thunderstorms, then breezy westerly winds of 30 gusting 50 km/h will usher in drier air in the afternoon as the clouds break up and clear out. Temperatures will climb up to a high near 23°C. Expect a low near 13°C under mainly clear skies on Saturday night.
Sunday will bring mainly sunny skies to Winnipeg with winds strengthening out of the southwest to around 30-40 km/h. Temperatures will climb to a high near 25°C. Winds will taper off Sunday evening as temperatures dip to a low near 15°C.
Long Range
Next week becomes quite uncertain as a major low pressure system develops in the Northern Plains of the United States and then slowly meanders northwards. As we move into summer, these systems will increasingly be driven by thunderstorms, which carry an inherent level of uncertainty, especially in the long range as how the various rounds of thunderstorm activity develop can impact the overall development of the low pressure system. That said, conditions will turn unsettled next week with near-seasonal to slightly above-seasonal temperatures.
Winnipeg’s seasonal daytime high is currently 23°C while the seasonal overnight low is 10°C.
An Additional Note
This will be the last forecast we issue here at A Weather Moment for the next while. We’ll be taking a bit of a vacation and won’t have our regular forecast posts on Monday June 12th or Wednesday June 14th. We suggest you check Environment Canada’s forecasts while we’re away!
