Late-Season Thunderstorm Risk Kicks off Dreary Weekend

A powerful low-pressure system pushing northwards out of the Dakotas that will bring copious amounts of rainfall to SE Saskatchewan and Western Manitoba will also bring a risk for thunderstorms, perhaps even an isolated severe thunderstorm, this evening in advance of an occluding cold front. This will mark the start of a somewhat dreary weekend for the Red River Valley that will be marked most notably by a wet & windy Saturday and a very cool, albeit sunny, Sunday.

Thunderstorms Possible Today


19°C / 12°C
Mainly cloudy. Chance of showers with the risk of a thunderstorm late in the day.

We’ll see a mainly cloudy day today with relatively nice temperatures as we sit in the warm sector of the low pressure system pushing into the province. Despite the cloudy weather, we should see temperatures climb to around 19–20°C for a high with south-easterly winds to around 30km/h.

We may see a shower early this morning as the warm front pushes through and brings us into the warmer air, although a majority of the activity will be off to our west. If anything manages to push into Winnipeg, it will be relatively short-lived. After that we’ll see no chance of precipitation until later in the afternoon or the evening as a cold front begins pushing into the Red River Valley from the south.[1]

Event outlook for Friday, October 11th.

Event outlook for Friday, October 11, 2013.

While we sit under cloudy skies, this would be a good time to note that the weather to our west will be decidedly different. Rain will push in early this morning and spread NNE through the day, hitting areas west of the Red River Valley and Lake Manitoba the hardest. In total, anywhere from 35–75mm of rain is expected, with the lesser amounts closer to the Red River Valley and the higher amounts running along the Saskatchewan border then towards Lake Winnipegosis with enhanced precipitation near the Riding Mountains as upslope enhancement in the north-easterly winds amplifies the amount of rain. Environment Canada has rainfall warnings out for many regions in Western Manitoba, and you can check here to see if your region is covered by one and find additional details.

As the cold front approaches the Red River Valley this evening we’ll see considerable destabilization of the mid-levels coupled with an extremely strong 60–70kt 500mb jet beginning to poke it’s nose north of the border. The Red River Valley will lie in a fairly diffluent area aloft with strong convergence along the cold front as it pushes northwards. Limited surface moisture will constrain SBCAPE values to only a mere 400–500J/kg, but the extremely strong dynamics, in particular the strong directional and speed shear, may help promote the growth of strong-to-severe thunderstorms along/just ahead of the cold front.

This all is highly dependant on either enough destabilization occurring or enough convergence occurring along the cold front. At this point, I think that the southern Red River Valley will see the strongest storms with a lesser risk of strong storms further north here in Winnipeg. By the time the front reaches us, it seems like it will be a band showers and/or thunderstorms with less organization than when things initiate in the Dakotas. If any of the storms do become severe, the main threats will be large hail and strong winds. There will be a very small risk of a few weak tornadoes with these storms, but I believe that will be most likely in North Dakota with the odds diminishing fairly rapidly as you push northwards through the Red River Valley.

The showers/thunderstorms will push through overnight as we drop to a low of around 11 or 12°C.

Wet & Windy Saturday


↘ 6°C / 2°C
Cloudy with showers. Windy. Temperature dropping through the day.

Saturday in Winnipeg will be marked by wet and windy weather as we move onto the back-side of the Colorado low and see some wrap-around rain and gusty northwesterly winds move in.

The rain will likely be somewhat showery in nature – in that we won’t see solid rain all day long – and there’s some uncertainty on how much we’ll see exactly, but around 5mm seems like a relatively safe bet at this point. If the system is a little faster than forecast we could end up with almost nothing as the rain would fall further north, and if it’s slower than forecast we could see closer to 10mm as we end up under the wrap-around rain for even longer.

The wind will be the main weather story though. Here in Winnipeg we’ll see winds 30–40km/h out of the northwest with gusts up to 60km/h, but it will be a significantly different story for those on the lakes. Winds over the lakes will increase to nearly 50–60km/h on Saturday with gusts as high as 90km/h, which will produce fairly sizeable waves. If you have a home or cottage on the southern or eastern shores of the lakes, you’ll want to make sure you make any preparations you might have to and prepare for some strong wave action and howling winds for Saturday and Saturday night.

With those strong winds will come falling temperatures; here in Winnipeg we’ll likely see temperatures fall to around 5 or 6°C by the end of the day as colder air pushes in on the back-side of the low. Skies will clear and winds will lighten overnight as we drop to around 2°C for our overnight low.

Sunny but Cool Sunday


9°C / -2°C
Sunny. Cool.

Sunday will see the return of the sun, but the price we’ll pay is significantly cooler weather than we’ve been having over the past week. Daytime highs on Sunday will top out at only 9 or 10°C and it will be a slow climb to get there. Temperatures will likely drop well below 0°C on Sunday night with a hard frost likely as temperatures dip to around –2°C.

This will also mark the transition into a cooler pattern. Daytime highs will remain around 10°C through much of the week.

  1. It sounds odd, but this system is essentially sideways with the warm front and cold front both moving from south to north.  ↩

Chilly Start to the Week

We are about to get our first taste of below-normal weather in quite some time. Temperatures on Monday and Tuesday are expected to be several degrees colder than the seasonal average.

GEM model high temperature forecast for Monday

GEM model temperature prediction for 4pm on Monday

High temperatures on Monday are expected to hover around the zero mark in much of Southern Manitoba. Combined with a brisk north-west wind, conditions on Monday will be rather cool. If you consider the wind chill, it will feel closer to -6 on Monday afternoon (calculated using a temperature of 0C and wind speed of 25km/h). Tuesday won’t be much warmer, with highs only expected to creep up in the low single digits. The wind will be lighter on Tuesday, making it feel significantly warmer than Monday…although it will still be chilly. Both Monday and Tuesday are expected to be mainly cloudy, which will also hold our temperature back. If the sun does come out in some areas on a localized basis it will be slightly warmer. In early April the normal high is about 8 degrees in Southern Manitoba, meaning most areas will be between 4 and 8 degrees colder than normal through the first two days of the week. Models show a gradual improvement in temperatures as we move later into the week. By Wednesday we should get up into the high single digits and by Thursday the double digits will become likely.

In the longer range it appears that next weekend could be a bit unsettled. At this time models show a low pressure system moving up into the Northern Plains, spreading rain across a large area, which may include Southern Manitoba. It is too early to say if this system will affect us at all, but it is something to watch.

Looking even further ahead it appears we are in for a period of more normal weather. Longer range guidance is hinting at normal to slightly above normal weather for the next couple weeks. There is also some indication that our weather may remain somewhat unsettled, which is fairly typical for this time of year. Wouldn’t it be something if the first half of April was cooler than the second half of March!

Elsewhere in Weather News

Intense Low Affects Japan

A very powerful low pressure system made landfall in Japan on Tuesday, April 3rd and brought with it incredibly strong winds and much rain. This storm, believed to be the strongest storm to hit Tokyo since 1959, generated 90km/h sustained winds and 150km/h wind gusts at times (highest gust reported in Niigata prefecture, 156.6km/h), in the western part of Japan. Rain rates of over 60mm/h also fell associated with the squall line as it moved across most of Japan’s main island. This caused more than 20,000 homes to lose power, various buildings to collapse and trees to fall – causing 97 injuries and 4 deaths. Flight cancellations and railway closures also had to be taken into mind when traveling, as more than 600 flights were cancelled departing from Japan. The very strong winds resulted in trucks being flipped over on the highways and bridge closures, bringing the traffic to a crawl. Waves of 10m were experienced off the coast, however it was strongly advised to stay inside.

Image of the powerful low centered over the Sea of Japan (East Sea), as and after the squall line passed it produced very high winds. (Source: The Watchers/Japan Meteorological Agency)

Image of the powerful low centered over the Sea of Japan (East Sea), as and after the squall line passed it produced very high winds. (Source: The Watchers/Japan Meteorological Agency)

A high-pressure has since moved into place giving way to sunnier skies with some stronger winds associated with it.

Texas Tornadoes

This past week brought very active weather not only in Japan, but also the US, where violent tornadoes hit populated areas of Texas and caused significant damage. Two supercells dropped tornadoes simultaneously on the afternoon of April 3rd in the Fort Worth and Lancaster areas, causing the most significant damage. Preliminary estimates rate these tornadoes between EF-2 and EF-3, where winds are measured at 177km/h to 266km/h. Tornado warnings had been posted by the National Weather Service well before the storm hit allowing residents to take the necessary precautions; although significant damage was caused to neighbourhoods and industrial parks it could have been much worse. Ten injuries and no deaths were reported, the Dallas mayor called it “miraculous” to see that the numbers weren’t more significant after a big damage path could be seen from aerial view.

Tractor-trailer picked up by the tornado in the Dallas/Fort Worth area. (Source: Reuters/NBC)

Tractor-trailer picked up by the tornado in the Dallas/Fort Worth area. (Source: Reuters/NBC)

Tornadoes had not been the only culprit to cause significant damage that day, as very large hail was also reported with this storm. Hail damage to 100 airplanes at the Dallas airport was reported, with issues ranging from minor inspection needed, to planes being put out of service indefinitely.

Lancaster (just south of Dallas) tornado information, with RADAR captures. (Source: NWS storm reports)

Lancaster (just south of Dallas) tornado information, with RADAR captures. (Source: NWS storm reports)

This week, more storms are expected in Texas and most of the Plains, as the jet stream remains south of the border and systems push through Tornado Alley.

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