Author: Brad

Brad lives in Winnipeg with his wife and two children and is the founder of A Weather Moment. He has loved weather from a very young age and has followed that passion through his life so far. He received a B.Sc. in Earth Sciences with Specialization in Atmospheric Sciences and is currently employed in the field of meteorology. You can find the author as WeatherInThePeg on Mastodon.

Humid Weather Brings Thunderstorm Threat to Southern Manitoba

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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.  ↩
RDPS Surface Temperature Forecast – 00Z Tuesday July 21, 2015

Pleasant, Sunny Conditions to Start the Week

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Tired of the phrase “chance of a thunderstorm” and want to just have a couple days without rain? Good news! It looks like Winnipeg & the Red River Valley will finally shake the unsettled weather pattern and see a couple days of calm, pleasant summer weather with very little chance of precipitation thanks to an upper-level ridge that will build into the Eastern Prairies.

The coming few days will see gradually warming as we transition from the cool air mass left behind from the systems that tracked across the region on Saturday & Sunday into a warmer air mass pushing in from the west. Today will be the coolest day with a daytime high of just 22 or 23°C under partly cloudy skies. There may be some isolated shower or thundershower activity, but at this point it looks like it would be very spotty in the Red River Valley. Temperatures will dip to around 12°C tonight.

Tomorrow and Wednesday will both be beautiful summer days with highs climbing into the mid-to-upper 20’s under mostly sunny skies. Winds look fairly calm, although by Wednesday afternoon we could see southerly winds begin to strengthen. At this point it doesn’t look too bad – perhaps 30km/h with some gustiness on top of that – but if the pattern speeds up a bit, we could end up seeing quite windy conditions out of the south by then. Conversely, if the entire pattern is a bit slower we’ll see calm conditions throughout the day. Overnight lows both nights will be in the low-to-mid teens.

Hot, Humid & Stormy Weather Returns for End of Week

Looking ahead into the second half of the week, the trend seems to be for the hot and humid weather to return. As the upper ridge transitions across the region, deep layer southerly winds developing will tap into more humid air to our south and begin increasing the dew point. By Thursday evening, the dew point could be as high as 20–22°C, making it feel very sticky out there. Depending on the exact daytime highs, Thursday and Friday could both end up feeling more like the mid-to-upper 30’s instead of the upper 20’s thanks to the humidity.

GDPS Surface Dew Point Forecast – 00Z Friday July 24, 2015
The GDPS is forecast dew point values climbing into the 20-22°C range by Thursady evening.

In addition to all that heat and humidity, a low pressure system tracking through at the end of the week looks to bring the potential for strong to severe thunderstorms, likely on Thursday. More on that later this week!

Thunderstorm Chances Continue into Weekend

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The generally unsettled weather that has been in place over Southern Manitoba over the past week will continue for at least a couple more days as a large upper-level low pushes across the Prairies. For those tired of sweating the heat, though, a reprieve is on the way as drier air finally works its way into the Red River Valley.

Today will be a fairly pleasant day with a fairly sunny start and temperatures poised to climb up to around 26 or 27°C. As the temperatures warm up this afternoon, shower and thunderstorm activity will likely develop as a cold front pushes eastwards into the Red River Valley. Most areas through the valley will have a chance at seeing some shower or thunderstorm activity, however the chance will increase the closer you find yourself to the U.S. border. Any convection that does develop will push out the eastern RRV early in the evening, ushering in some cooler, notably drier air into the region behind the cold front. Friday night will mark the end of a very humid streak that has seen dew points in the upper teens or low 20’s for over a week. Expect a refreshingly cool overnight low of around 12°C.

GDPS Forecasted 500mb Heights & Vorticity for Mid-day Saturday
Saturday will bring a risk of thunderstorms and funnel clouds to the Red River Valley as a vorticity-rich upper-level low moves over the region.

Saturday will bring yet another chance for showers and thunderstorms as the main upper-level low moves over Southern Manitoba. Temperatures will climb to around 22°C, which may be enough to pose a marginal risk for some severe thunderstorms in the afternoon; the biggest impact to be aware of, however, is the potential for cold core funnel clouds. These funnel clouds are developed through entirely different mechanisms than their stronger, supercell thunderstorm counterparts, and are substantially weaker and rarely result in a touchdown. If a cold core funnel cloud does reach the ground, it’s considered a landspout tornado. These tornadoes are short lived and usually very weak. While they do not pose the level of threat that a supercell thunderstorm tornado would pose, strong winds of any type can be dangerous. The shower and thunderstorm activity will push out of the region in the evening and we’ll see clearing skies as the low heads back down to around 12°C.

Sunday’s forecast will be short. Beautiful weather is on tap with highs in the mid–20’s, comfortable humidity, light westerly winds and mostly sunny skies. No complaints! Expect a low on Sunday night in the mid-teens. Finally some good weather news for a change!

Unsettled Weather Continues To Week’s End

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The unsettled weather that’s been in place for the last few days will continue through the end of the week as the general instability remains in place as more weather systems push through the region.

Today will be a fairly pleasant day that’s quite similar to yesterday other than a couple degrees warmer. Temperatures should climb to around 28°C this afternoon with more clouds popping up and developing into an afternoon/evening chance of some scattered thunderstorms. Thunderstorm activity should be fairly limited as the main story will be the low pressure system that will move into Southern Manitoba overnight and will set the stage for Thursday’s weather. Expect temperatures to dip to just 19°C as increasing cloud and the humidity continue to keep temperatures warm.

Thursday Brings Heavy Rain Potential

Tomorrow may actually end up being quite a wet day as multiple models are showing a low pressure system moving through tapping into the ample moisture in the region to produce a fairly large, and intense, area of rain.

NAM Precipitable Water Forecast for 15Z Thursday July 16, 2015
NAM Precipitable Water Forecast for 15Z Thursday July 16, 2015

The NAM (shown above) is forecasting precipitable water values as high as 1.8 to 1.9” (in the 45–50mm range) which is very high for our region. Precipitable water correlates strongly to potential rainfall amounts of storm systems[1], so it’s not unrealistic to say that rainfall totals of 1.5” to 2” (~ 35 – 50mm) are not out of the question albeit on the high end. If heavy convection were to set up, then even higher amounts would be possible. We’ll keep an eye on things and see how the storm progresses this evening; if the outlook changes much, we’ll provide an update at the bottom of this post.

So, the general forecast for Thursday would see the rain moving in overnight on Wednesday night and see the rain persisting at least until mid-day, but possibly into the late afternoon or early evening. Rainfall totals may end up being variable, but in general will likely be 20–40mm with the potential of seeing double that if system becomes vigorous enough. The high temperature will be in the 21 to 23°C range with an overnight low around 16°C. Winds will be fairly light much of the day.

Friday

The thunderstorm risk returns Friday, although it will be a fairly mild risk with just some isolated to scattered non-severe storms possible. The daytime high will sit near 26 or 27°C with light winds out of the southwest. The humidity continues to remain fairly high with dew points in the high teens. Skies will clear out Friday night as we head to a low near 15°C.

  1. Thunderstorm rainfall totals can greatly exceed PWAT values due to the convergence of the inflow wind that can “accumulate” PWAT from areas around the storm.  ↩