Tag: Thunderstorms

Stormy Start to the Long Weekend

Brad Leave a comment

The August long weekend will be off to a stormy start today as the threat of severe thunderstorms bears down on the Interlake, Red River Valley and Whiteshell this afternoon.

Tornado near Lake Diefenbaker

One of a couple of tornadoes that the incoming system spawned in Saskatchewan yesterday. Photo by @TheMrsCogs.

A very powerful low pressure, responsible for at least two tornadoes in Saskatchewan yesterday, will move into Southern Manitoba today and push a cold front across the province through the day. Very strong dynamics will accompany this system, a stark contrast from the last few systems which have had comparatively strong thermodynamics instead. Despite the lack of strong thermodynamic parameters that are often looked at when diagnosing severe thunderstorm potential, such as CAPE, EHI or LIs, the strong dynamics will present a significant severe weather threat over south-central and southeast Manitoba.

Dynamics are physical, kinematic properties of the atmosphere, such as jets, shear and lift. Thermodynamics are thermal/energetic properties of the atmosphere such as temperatures, humidity and instability.

A band of showers will push into the western Red River Valley early in the afternoon ahead of the upper low. As the afternoon progresses, the upper low will begin to deepen and enhance the destabilization over the Red River Valley. By mid-to-late afternoon, despite the cool temperatures and cloudy skies, there should be rapid development of storms along the cold front. Tornadoes are unlikely, although not impossible, here in Southern Manitoba; that threat should be relegated to the Dakotas where even greater dynamics and substantially better thermodynamics are present. If any tornadoes do form tomorrow, it’s likely that they will be of the short-lived variety and relatively weak. The greatest threat from today’s storm will be extremely heavy rain giving rapid accumulations of 1-2” (25-50mm) given precipitable water values of 40-50mm and large, damaging hail given the cool temperatures aloft.

Thunderstorm Outlook

Day 1 thunderstorm outlook valid 18Z today through 12Z tomorrow morning.

The storms will exit the province overnight, and we’ll have a brief reprieve from precipitation. On Saturday, some showers will wrap down into the RRV on the back side of this system. Amounts will vary across the region, but in general less than 5mm is expected. Temperatures will struggle to climb to even 20°C; daytime highs of only 18 or 19°C are expected. Winds will be breezy from the NW.

This system will clear out Saturday night before nicer weather builds back in. The second half of the long weekend will see increasingly sunny skies and daytime highs near 25°C.

Warm, Unsettled Weather Continues

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Warm weather will continue to dominate Southern Manitoba as we climb into the high 20’s almost every day this week. We’ll continue to see active weather as multiple systems move through the province over the second half of this week.

500mb Wind Field Valid Friday Night

Forecast 500mb wind field with heights depicting powerful upper low entering Southern Manitoba on Friday evening.

July ended up being a very hot month for Winnipeg, with 14 days of the month with daytime highs over 30°C. The month ended with an average temperature (highs and lows both considered) just over 22°C, which is about 2.5°C above the normal average temperature of 19°C. July marked the 13th consecutive month that Winnipeg has seen above-normal temperatures.

July marked the 13th consecutive month that Winnipeg has seen above-normal temperatures.

We’ll see a chance of afternoon thunderstorms across most areas of Southern Manitoba as a weak disturbance rounds the cold trough left behind yesterday’s system that brought a thunderstorm threat to Southern Manitoba. Chances for thunderstorms will be significantly higher through SW MB northwards through the Parkland region while the Red River Valley will see just a chance of thundershowers in the evening as the upper feature passes by. Daytime highs will be near 28°C through the Red River Valley with an overnight low tonight near a comfortable 15°C.

We’ll see a reprieve on Thursday, with no precipitation expected and a high near 28°C again. A powerful upper low will begin pushing across the Western Prairies bringing rain and cooler temperatures tommorow and will be the main weather-maker on Friday for us. Showers and thunderstorms will push into Western Manitoba on Thursday night and slide eastwards across the province through the day on Friday. It’s likey that we’ll see little precipitation on Friday as most of it pushes through the Interlake, however there’s a good chance of showers overnight on the backside of this system. We’ll see a daytime high of 24°C on Friday and a considerably cooler high near 20°C on Saturday.

Conditions will rapidly rebound through the end of the weekend as sunny skies return and temperatures shoot back up to 30°C.

Pleasant Start to the Weekend

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After a few days that threatened storms for the Red River Valley, we’re heading out the other side with most communities seeing little to no rain. Steinbach is a notable exception, with over 100mm of rain falling1 through a rather unusual rainfall event early Wednesday morning which produced significant overland flooding2.

24hr. Precipitation Totals valid Sunday Evening

24 hour accumulated precipitation from Friday Saturday evening to Sunday evening.

A pleasant start to the weekend is ahead, with no chance of showers until Saturday evening and overnight. Today we’ll see mainly sunny skies as our temperatures rebound from yesterday’s system up to a high near 26°C. The overnight low tonight will be around 15°C. Warmer air pushing in aloft will allow temperatures to climb higher on Saturday and Sunday, with daytime highs close to 30°C expected. Humidity will remain relatively low for Saturday, however things may get a little uncomfortable on Sunday as dewpoints begin to climb closer to the 20°C mark.

On Saturday a disturbance entering the province will generate some showers and thunderstorms over SW Manitoba through the late morning and afternoon hours. The (thunder)showers will spread eastwards through the evening and overnight, however it’s currently looking like the bulk of precipitation will occur through the Interlake. The northern half of the Red River Valley looks to have a decent chance of seeing some sort of precipitation, however the odds look very slim that the southern half will see anything.

We’ll see increasing cloud Sunday afternoon as the back side of this system prepares to swing through Sunday night. As it does, there will again be a chance of showers for Winnipeg and, as it looks now, the eastern RRV. We’ll be sure to provide updates in the comments as this system approaches.

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  1. http://www.steinbachonline.com/index.php?option=com_content&task=view&id=30218&Itemid=100413 ↩
  2. http://www.steinbachonline.com/index.php?option=com_content&task=view&id=30192&Itemid=100413 ↩

Thunderstorm Risk Returns

Brad Leave a comment

The risk for thunderstorms returns to the Red River Valley today as a cold front with a history of producing severe weather pushes into the region.

850mb Analysis from the GFS

850mb Analysis from the GFS model for mid-morning today.

We’ll see some clouds/light showers clearing out early this morning across the Red River Valley, leaving us in sunshine for the latter half of the morning and early afternoon. By early afternoon, a cold front will be draped N-S over the western RRV. With temperatures climbing into mid-to-high 20’s by mid-afternoon, there should be enough heat and moisture to get storms going along the cold front. It’s likely, but not certain, that some thunderstorms will deveop on a north south line from near Winnipeg south towards the International Border. These storms will track eastwards across the RRV through the mid-to-late afternoon.

They will certainly have the potential to be severe. This cold front has a history of producing storms capable of damaging winds, large hail, and isolated tornadoes. For us, conditions don’t look quite as favorable as they did yesterday in SK or the day before in AB. We’ll be looking at:

  • 1000-2000 J/kg of CAPE
  • LI values near -7
  • Bulk shear values of only 20-35kt
  • 0-3km EHI values only 1-1.5

Wind shear will be the biggest limiter to storm development today. Storms may struggle to develop a distinguished structure, which could result in a relatively tame outcome. There’s just enough support to not be able to rule a severe storm out, however, and I expect we’ll likely see some watches issued for the RRV midday. The main threats for these storms will be heavy downpours with rapid rainfall accumulation and large hail. There’s a secondary threat of strong winds and, while tornadoes cannot be ruled out, the threat for the RRV is nowhere near the threat yesterday in Saskatchewan. Ultimately, though, the chance for seeing storms depends highly on the speed of the cold front; we’ll have to wait and see how quickly it moves into the RRV today to refine the thunderstorm forecast.

Things should clear out in the evening before a chance for showers returns late overnight and Thursday morning as the main upper low tracks over the RRV. We’ll see a mix of sun and cloud on Thursday with a high near 25°C. Friday heading into the weekend looks fairly nice. Sunshine should dominate and temperatures will climb back into the high 20’s or low 30’s. We’re certainly shaping up for another above-average month for temperatures. If July’s mean temperature is above normal, it will be the 13th consecutive month with above-normal temperatures in Winnipeg.