Category: Forecasts

Severe Weather Threat Returns to Southern Manitoba

Brad Leave a comment

Southwestern Manitoba will be under the gun again for the potential of strong to severe thunderstorms.

In what has suddenly become a somewhat busy start to the season, more thunderstorms are expected through the remainder of the week, with a threat for severe thunderstorms tomorrow in the southwest corner of the province.

Today & Tomorrow

Wednesday
25°C / 13°C
Cloudy periods

Thursday
28°C
Chance of morning showers or thundershowers. Risk of a thunderstorm late in the day.

Thursday Night
15°C
Showers or thunderstorms likely.

In Winnipeg today we’ll see some cloudy periods but overall a very nice day with light winds and a high near 25°C. The main focus for weather will begin in Southern Saskatchewan where conditions are very favourable for severe thunderstorms. Storms will likely initiate mid-afternoon in south-central Saskatchewan and begin tracking eastwards.

The storms will quickly grow into supercells thanks to ample available energy and strong veering wind profiles. The storms across Southern Saskatchewan will carry with them the risk of all severe modes of weather: damaging winds, flash flooding due to torrential downpours, large hail and tornadoes. It will be a potentially dangerous afternoon in south-central Saskatchewan.

The RDPS 3hr. precipitation panel depicts the strong thunderstorms in south-central Saskatchewan
The RDPS 3hr. precipitation panel depicts the strong thunderstorms in south-central Saskatchewan this afternoon.

The storms will continue northeastwards through the overnight period, sustained by a strong low-level jet. The storms will enter Manitoba later in the overnight period, with the main focus through the Parkland region, but with the potential for storms extending southwards into SW Manitoba to the US border. At this point, it doesn’t appear that the storms would carry a significant severe threat, but there does seem to be a slight chance that they would be able to produce marginally severe hail if they do develop.

We’ll see the remainders of that convection move through the Red River Valley Thursday morning. It may still be thunderstorms at that time, it may just be some scattered showers and cloud; it will depend highly on exactly what develops in the overnight period.

Moving into Thursday afternoon, the thunderstorm risk returns to Southern Manitoba with a slight risk of severe thunderstorms in southwest Manitoba and possibly creeping into the southwestern Red River Valley. A low pressure system lifting northeastwards through the province will drag a cold front slowly eastwards through the afternoon. While a few unknowns still hinder the forecast – primarily what effect morning convection may have on the environment and how much cloud will linger, preventing things from warming up too much – the setup looks favourable for the development of strong to severe thunderstorms.

Primary issue of our thunderstorm outlook for Thursday afternoon through to Friday morning.
Updated issue of our thunderstorm outlook for Thursday afternoon through to Friday morning. View initial outlook.

A favourable storm environment will be in place by the afternoon hours in southwest Manitoba, with CAPE values exceeding 1500J/kg, decent convergence along the cold front, very unstable mid-levels and a fairly favourable vertical wind profile. It seems quite plausible that supercell thunderstorms could develop along the cold front in the mid-to-late afternoon and then slowly track eastwards. Should severe storms develop, all modes of severe weather would be possible, including localized flash flooding, large hail, and strong winds. Tornadoes cannot be ruled out, however the low-level wind structure may not be quite conducive enough to generate the required environment.

The forecast sounding from Brandon clearly depicts the capping inversion in place on Thursday afternoon.
The forecast sounding from Brandon clearly depicts the capping inversion in place on Thursday afternoon.

Some uncertainty plagues the forecast, however, and it’s mainly focused on the “cap” in place. A “cap”, or capping inversion, is a layer of warm air usually somewhere in the first 2-5km of the atmosphere that inhibits air being lifted from the surface from continuing to higher altitudes. This feature can be overcome with enough forcing, which then allows the air parcel to rise since it’s warmer than the air around it – depicted with red shading in the image.

If the cap stays strong, there will be little hope for storms until late evening into the overnight period, and those storms would only be marginally severe.

It seems likely, though, that the cold front will erode the cap and provide enough forcing to generate thunderstorms, so our current outlook calls for a slight risk of severe thunderstorms over southwestern Manitoba into the Red River Valley. There is a chance that we may push the slight risk area further north and northwest, including more regions along the Trans-Canada Highway as well as some areas in Parkland Manitoba, but we’ll wait for further evidence that supports that move before we jump on that.

The storms will slowly track eastwards and showers and thunderstorms are likely over much of the Red River Valley overnight Thursday into Friday morning.

Friday & Beyond

23°C / 15°C
Showers likely, then clearing in the afternoon.

Friday will bring the remnants of any precipitation along the cold front through the Red River Valley in the first half of the day, then we’ll see clearing skies as this system pushes off to the east. The high will be near 23°C and the temperature dip into the mid-teens on Friday night.

The weekend is looking drier for the most part. A system tracking through North Dakota may spread some rain into the southern Red River Valley, but at this point its looking like things should remain south of the border. Sunday looks like quite a pleasant day with sunny skies and temperatures in the mid-20’s.

AWM Chase Day

Much of the AWM team will be out chasing storms in SW Manitoba today. You can follow along with them through their tweets here:


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Warm Weather to Continue

Brad Leave a comment

Seasonal to above seasonal weather will continue this week, a nice change from the miserable first part of May.

There will likely be a chance of thunderstorms in southern Manitoba on Tuesday
There will likely be a chance of thunderstorms in southern Manitoba on Tuesday

Monday

Monday
24°C / 13°C
Mix of sun and cloud

Today will feature much calmer weather than what was experienced on the weekend. High temperatures will be in the low to mid twenties in southern Manitoba under a mix of sun and cloud. The wind will generally be light and from the north or east.

Tuesday

Tuesday
27°C / 15°C
Mix of sun and cloud with risk of a thunderstorm

The threat for thunderstorms will resume in southern Manitoba on Tuesday. At this point there is still a lot of uncertainty as to how the thunderstorm risk will evolve. At the high end, there could be numerous severe storms, and even a slight tornado risk. At the low end, storms would likely just produce small hail and gusty winds. It’s too early to say what the storm mode will be on Tuesday, but bear in mind that severe storms are a possibility. The chance of thunderstorms on Tuesday will make the temperature forecast a bit uncertain as well. If there are no storms, and therefore no additional cloud cover, then we’re looking at temperatures in the upper twenties. However, if there is additional cloud from thunderstorm activity, then highs will probably be in the mid twenties. More details on Tuesday’s potential for storms will no doubt be found in the comments below over the next couple days.

Wednesday

Wednesday
25°C / 16°C
Mix of sun and cloud with risk of a thunderstorm

Wednesday is another tricky forecast, as rain may or may not affect the forecast again. Some weather models bring an area of rain and thunderstorms through southern Manitoba in the morning, which would greatly impact the temperature forecast. Like Tuesday, it’s too early to say if this will happen, but it’s certainly a possibility. High temperatures in the mid twenties look most probable, but that outlook could change depending on what happens with the chance of rain.

Long Range

The long range forecast continues to look stormy through the end of the week. Most weather models suggest that there will be a risk of severe thunderstorms in southern Manitoba on Thursday and/or Friday. I feel like I’m saying this a lot, but there is still a lot of uncertainty in this part of the forecast. Models are still not correctly resolving the speed of this system, and until that happens it will be tough to say much about the thunderstorm potential with any certainty. Beyond this week, the weather will likely stay near, to slightly above seasonal values, a nice way to transition into June!

Summer Arrives!

Brad Leave a comment

Southern Manitoba is set to bathe in summer-time warmth as temperatures soar well above normal.

A broad upper-level trough developing over the Rocky Mountains will combine with a strengthened sub-tropical ridge over the southeastern United States to produce a southerly flow that will bring substantially warmer air to our region. As well as the warmer temperatures, humidity will become more noticeable heading into the weekend as higher dew point temperatures are advected northwards into the region. With the warmer weather will also come the potential for some shower or thunderstorm activity across much of Southern Manitoba.

Friday
25°C / 16°C
Mainly sunny. A little breezy.

Saturday
30°C / 17°C
Cloudy periods with a slight chance of showers or thundershowers. Windy and warm.

Sunday
24°C / 14°C
Chance of a morning shower or thunderstorm.

Friday

Today will be a very pleasant day. Under a mainly sunny sky, the temperature will climb to near 25°C as a southerly wind at 20-30km/h provides just enough of a breeze to keep things comfortable. The humidity will be more prominent than it’s been so far this year, but it will still be quite comfortable with dew point values climbing to around 15°C.

Heading into the night, temperatures will drop to about 16°C with variable cloudiness through the overnight hours with a slight chance of some shower .

Saturday

Tomorrow will start with a fair amount of mid-level instability riding ahead a warm front pushing eastwards. This will present itself with a slight risk for showers or thunderstorms through the early morning. Afterwards, we’ll see cloudy periods with fairly windy conditions with a southerly wind at around 30-40km/h. Very warm air will work in aloft, driving our daytime high up to 29 or 30°C. In addition to the warmer air, the southerly winds will also advect more humid air northward with the dew point climbing towards 17 or 18°C which will start to make it feel a little sticky outside.

Temperatures of 30°C or greater (dark green) are expected across much of Manitoba on Saturday.
Temperatures of 30°C or greater (dark green) are expected across much of Manitoba on Saturday.

As everything heats up, there will be a potential for thunderstorms, but there will be little in the way of a threat for severe storms. If we quickly look at the ingredients required for thunderstorms:

  • Moisture: Dew points will climb into the mid-to-upper teens, through a suitably deep layer, and be supportive of storm generation. The dew points are on the low side for the atmospheric thermal profile which will result in relatively high-based storms.
  • Instability: Deep instability will be present. Mid-levels are fairly unstable, and low-levels will destabilize fairly dramatically by mid-afternoon thanks to intense surface heating driving temperatures towards 30°C.
  • Shear: This is where things fall apart. While the low-level winds will provide favourable inflow into the storm bases, winds will be very slack through the mid-levels. This will dramatically impact the ability for storms to organize and will limit their potential growth.
  • Trigger: Triggers for storm generation look fairly weak. The synoptic triggers look to remain outside our region; the warm front will be in Central Manitoba, the cold front will be hanging back through Central Saskatchewan and the main warm sector trough also will trail back into southeastern Saskatchewan. The intense surface heating will likely produce many mesoscale triggers, especially along significant terrain such as the western escarpment of the Red River Valley and the Riding Mountains.

As a result, we’ll see the potential through much of Southern Manitoba for thunderstorms, however they’ll likely be short-lived, high based storms whose main threat will be strong winds or large hail.

It’s likely that rain with embedded thunderstorms will develop in North Dakota on Saturday night and lift northeastwards into Southern Manitoba, bringing the risk of rain and thunderstorms to somewhere in Southern Manitoba through the overnight period into Sunday morning. The areas that will see the risk will depend highly on exactly where the precipitation develops in North Dakota.

Temperatures will remain quite mild Saturday night with the overnight low bottoming out at only around 17°C.

Sunday

Sunday will be the most organized day for precipitation of the weekend. The system bringing the warmer air to the province will push off to the East through the day, dragging a cold front across the province. Widespread showers and thundershowers will be associated with the cold front as it pushes eastwards, and as a result showery weather is likely. It’s a little early for too much detail, but it seems like the chance for precipitation will start around mid-to-late morning and taper off by late afternoon.

The temperature will climb to around 23 or 24°C before the cold front swings through. Things will clear up by Sunday evening and we’ll see a beautiful night with a low near 14°C.

UPDATE: An updated look at Sunday’s weather is available in the comments section below.

Next Week

Next week looks to continue the warmth with highs in the mid-20’s, but by mid-week it looks like unsettled weather will return to Southern Manitoba and bring multiple days with chances for showers or thunderstorms. It seems like we’ll lock into seasonal to above seasonal temperatures, so get out and enjoy the summer weather that we’ve all waited so long to see!

Summer Weather on the Way

Brad Leave a comment

After another stretch of below-normal temperatures, some truly summer-like weather is finally on the way.

Winnipeg will be under the influence of a ridge of high pressure that will keep us dry through the remainder of the week. A developing flow from the Gulf of Mexico looks poised to set up Southern Mantioba for a quick shift into summer-like weather for the end of the week.

Wednesday
15°C / 6°C
Mixed skies with a clearing trend.

Thursday
23°C / 12°C
Mainly sunny.

Friday
26°C / 14°C
Mainly sunny.

Today will bring mixed skies to Winnipeg and the Red River Valley as the system cloud associated with the low that moved through on Monday and Tuesday begins exiting the province. Cloud will likely persist through the afternoon as some fair weather cumulus develop as we warm up to our high near 15°C. Skies will clear tonight as the temperature drops. The temperature will drop to around 6°C tonight.

Tomorrow will bring mainly sunny skies, relatively light winds and a high temperature returning to a seasonal to slightly above seasonal 22 or 23°C. Things will be calm and mainly clear Thursday night with temperatures dropping to near 12°C.

Friday will mark the shift towards decidedly more summer-like weather. Under mainly sunny skies, warmer air pushing into the region will push our daytime high towards around 26°C. In addition to the warmer weather, we should also see the first days of the year that could potentially be considered “humid.” For a quick summary of the relationship between dew point and how humid it feels, and why relative humidity is a poor choice, check out the brief primer at the bottom of this post.

There’s uncertainty in exactly how humid it will get here in Southern Manitoba. Some weather models, such as the Canadian GDPS[1] are pushing dew point values as high as 20°C in the Red River Valley, but values that high are likely overdone thanks to the delayed start to the growing season due to the abnormally cold spring. It’s likely we see dew points climb into the mid-teens at least, though, so it’s fairly safe to expect that we’ll be seeing our first real shot of summer heading into the weekend.

Unsettled Weekend

There’s still a lot of uncertainty associated with the large amplitude upper-level pattern that’s expected to develop this weekend, so in general vagueries…

As the NAM shows, a broad flow from the Gulf of Mexico all the way to Southern Manitoba will be established by Saturday morning.
As the NAM shows, a broad flow from the Gulf of Mexico all the way to Southern Manitoba will be established by Saturday morning.

It’s going to be quite warm on Saturday. Daytime highs in the upper 20’s seem quite likely as well as dew points climbing into the mid-to-upper teens, although as mentioned above, there’s some uncertainty to exactly how high the dew points will get. Sunday will also be warm with highs in the mid-20’s.

Thunderstorms, potentially severe, will be possible both days, although exactly when and where is far too uncertain at the moment. It seems entirely possible that the thunderstorm activity will be constrained to the evening/overnight periods when elevated thunderstorms can develop, although late afternoon severe storms cannot be ruled out at this point. For both days the best chance for thunderstorms appears to be over Parkland Manitoba, SW Manitoba and into SE Saskatchewan and Montana/North Dakota. Here in the Red River Valley, nocturnal elevated activity looks like the most plausible scenario.

We’ll be taking a closer look at the thunderstorm and severe weather potential in Friday’s post. Until then, enjoy the imminent summer weather!

A Quick Lesson on Dew Points

Perhaps the most convenient way to quantify how humid it is outside is to look at the dew point temperature. The dew point is the temperature where water evaporates into the air at the same rate that it condenses out of the air; to put that in simpler terms, if the air comes in contact with something cooler than the dew point, water will condense out of it. Think of it as the temperature your cold glass of your favorite hot weather beverage needs to be to “sweat”.

The higher the dew point temperature is, the more water is in the air. This is an important distinction from relative humidity. Air has a quirky trait that allows it to hold more water the warmer it is. This means that air at -5°C cannot hold as much water as air at 25°C. This makes relative humidity ambiguous since it is a measure of how much water is in the air versus how much water the air can hold, or “how full the glass is.”

So a relative humdity of 100% at -5°C has less water in the air than a day where the temperature is 10°C with a relative humidity of 35% because the dew point in the first case is -5°C, while in the second case, despite the relative humidity of only 35%, the dew point is around -4.8°C.

As the dew point climbs, your perception of it being humid increases as well. In general, once the dew point rises to around 15 or 16°C, you’ll begin to notice that it feels humid. By 18 or 19°C it can begin to be uncomfortable. By the time the dew point climbs into the low-to-mid 20’s, as long as there’s sunshine, it can be extremely sticky feeling outside. Dew points in excess of 25°C are dangerous and can pose extreme health risks.

  1. Global Deterministic Prediction System  ↩