A potent Mackenzie Low dropped southeastwards through Saskatchewan yesterday riding along with a frontal wave that increased temperatures here in Winnipeg overnight. Behind this system is—for one of the first times this year—a potent Arctic air mass ready to surge southwards.
Today’s major weather features.
As a result, very strong winds developed in the rear of the cold front, supported through a deep layer as evident by a 120 km/h+ jet just off the surface that was visible on Doppler RADAR earlier this morning. Surface winds reached as high as 80-90 km/h behind the cold front which, combined with plenty of loose snow from our extra fluffy snowfall event the other day and some light falling snow, produced white-out conditions across many parts of Southern Manitoba.
The strong winds will move off to the east-southeast with the low pressure system through the morning and visibilities will improve. However, that bitterly cold Arctic air mass will move in through the day, sending temperatures south to around -26 or -27°C by the end of the afternoon here in Winnipeg. Temperatures will continue to drop to a low near -33°C on Friday morning with wind chill values of -42 to -45.
The cold weather will be short-lived as a mild Pacific air mass will begin building into the region this weekend.
It will be a very windy Thanksgiving as a strong low pressure system ushers in potentially damaging winds. By the time you’re reading this your loose objects will probably already be in your neighbour’s yard!
Monday
Today will not be the most pleasant Thanksgiving, as rain and strong winds wreck havoc outdoors. A strong low pressure system and corresponding pressure gradient will generate high to extremely high winds over southern Manitoba on Monday. The highest winds are expected Monday morning, when sustained speeds of 60-80km/h, and gusts to 100km/h or more, are expected. The period of extreme gusts likely won’t last more than a few hours, but during that time it will certainly do some damage, not to mention the fact that you’ll have a lot more leaves to rake!
A strong pressure gradient (shown above as tightly packed black lines called isobars) will bring very windy conditions to southern Manitoba on Monday
Today will also be rather soggy, as moderate rainfall occurs in association with this low pressure system. Today’s rainfall amounts will likely be around 5-15mm in the Red River Valley. You’ll have to wait until at least Tuesday for all those wet leaves to dry out!
Tuesday
Tuesday will be much calmer than Monday. Temperatures will climb into the mid teens under mainly sunny skies. Winds will remain breezy from the west, but they will feel light compared to Monday!
Wednesday
Wednesday will feature much the same weather as Tuesday. Temperatures will be in the low to mid teens under mainly sunny skies. Winds will be breezy from the north-west, but once again it will feel like nothing compared to Monday.
Long Range
Long range models continue to show a strong signal for warmer than normal weather through the end of October. Hopefully this will continue to be the trend as we move into winter due to the effects of El Nino.
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
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
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!
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. ↩
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
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.
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.
