Tag: Humid

Heat Wave Continues Until A Stormy Transition to a Cooler Sunday

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The heat wave across Southern Manitoba will continue through today and tomorrow as even more warmth and humidity build into the region. Significantly cooler air will move into the area on Sunday, behind a cold front passage on Saturday that will bring another round of potentially severe weather to the province.

Friday: Hot With Increasing Humidity

Today will be a hot day with increasing humidity as a deep southerly flow develops ahead of a deepening low pressure system ejecting northeastwards out of Montana. Temperatures will climb into the low 30’s with high temperatures reaching around 32 or 33°C this afternoon. Winds will also pick up out of the south to around 40km/h with gustiness on top of that. The humidity will be less than some days of late, but still fairly moderate with dew point values in the 18–20°C range. This will make it feel more like more like 37–40.

Some afternoon clouds will be about associated with the low pressure system lifting NE out of Montana. No precipitation is expected, though.[1] We’ll have a very mild low temperature tonight of 21 or 22°C.

Cold Front Brings Severe Weather Threat for Saturday

Saturday’s weather story will be dominated by a cold front pushing eastwards across the Red River Valley. The southerly winds combined with pooling ahead of the cold front will make for very humid conditions with dew point values climbing to 23–24°C. With a high temperature near 33°C, it will feel more like the low 40’s and make for very uncomfortable conditions. As the cold front pushes eastwards, showers and/or thunderstorms are quite likely.

AWM Day 2 Convective Outlook – Saturday August 15, 2015 to Sunday August 16, 2015
A moderate risk of severe thunderstorms exists through much of the Interlake, Red River Valley, and Whiteshell regions of Southern Manitoba on Saturday.

There are two possible outcomes for Saturday’s setup:

  1. Nocturnal advection develops in the Northern Plains of the United States and pushes northeastwards. Scattered showers and thunderstorms persist over the Red River Valley through much of the day before clearing out with the cold front.
  2. No or very little precipitation develops Friday night, leaving things dry and sunnier for Saturday. Severe thunderstorms would then be possible in the afternoon along the cold front.

At this point, it appears as if option 2 is the more plausible one. As always, looking at the MIST principles of thunderstorm development:

  • Moisture: Abundant. A deep layer of dew points ≥ 20°C will be in place over the Red River Valley, resulting in tremendous amounts of fuel for thunderstorms.
  • Instability: High. While the environment will be capped much of the day, significant instability will be in place through the mid- and upper-levels of the atmosphere. Steep mid-level lapse rates coupled with the high surface moisture will produce SBCAPE values in excess of 4000 J/kg and MLCAPE values of 3000–4000 J/kg.
  • Shear: More than enough. In general, a 40kt jet at 500mb over the region will combine with surface winds out of the south at 10–15kt to create around 25–35kt of 0–6km bulk shear. Hodographs show strong curvature, indicating likely supercell storm mode.
  • Trigger: The strong cold front pushing eastwards will provide focus for convection. While the capping inversion will hold surface-based convection back, the forcing from the frontal feature should be sufficient to initiate convection. 35–40kt southwesterly low-level jet may combine with steep mid-level lapse rates to produce elevated convection.

Given the extreme instability in place over the region (even elevated convection would have 1500+ J/kg of energy to work with), severe thunderstorms would be possible with either mode of convection. With the extremely high dew points in place, any thunderstorms that develop will be capable of torrential rainfall. Strong winds and large hail will be significant threats with any thunderstorms that develop. The threat of tornadoes cannot be ignored either; with strongly curved hodographs and such enormous amounts of energy, any supercell thunderstorms that develop would be capable of producing a tornado. The highest probability would be relatively close to the low pressure centre where the surface winds will be backed slightly more.

Saturday Severe Weather Update

Everything appears to be on track regarding today’s severe weather potential. There is a moderate risk of severe thunderstorms through much of the Red River Valley, Interlake and areas eastwards to the Ontario border. This includes large swaths of popular beaches & cottage country.

AWM Day 1 Convective Outlook for August 12, 2015
AWM Day 1 Convective Outlook for August 15, 2015

For the most part, all the expected conditions continue to pan out. Some elevated convection has developed overnight, however it doesn’t look like it will inhibit surface heating through the Red River Valley very much today. Very warm daytime highs in the low 30’s combined with dewpoint values in the 22-24°C range will combine to produce MLCAPE values of 2000-2500 J/kg and SBCAPE values exceeding 3000 J/kg. Combined with over 30 kt of 0-6km bulk shear and looping hodographs, there is sufficient energetics, dynamics and shear vectors to support strong supercell thunderstorms. Throughout the entire slight risk region, there will be a risk for large hail, strong winds and torrential downpours. Further north, in the moderate risk area, surface winds will be backed slightly more as the surface low pressure system continues moving northeastwards. Additionally, areas slightly further north will be closer to the upper-level jet and see enhanced 0-6km shear values. As such, any thunderstorms that develop in this region will pose a tornado threat, with the possibility of the production of a significant tornado today.

A strong cap in place will keep surface-based convection from triggering until late in the day as a trough pushes eastwards into the Red River Valley. Discrete supercell thunderstorms will likely develop between 4 and 6PM and then push east-northeastwards. As the line of thunderstorms pushes eastwards, upscale growth is likely as the system evolves into an MCS capable of all modes of severe weather.

Today could end up one of the most significant thunderstorm days of the year in Southern Manitoba. Stay aware of any watches and warnings issued by Environment Canada through the day today.

Sunday: A Cool Clean-Up

Sunday will bring partly cloudy skies on the back-side of the low as it departs Manitoba. Significantly cooler weather will be in place with daytime highs of just 23°C expected. There may be a slight chance of some light, isolated showers, but the threat looks minimal at this point. Temperatures will dip to around 12°C on Sunday night.

Next Week? Quick Rebound

Taking a quick peek at next week, it appears that the cool down will be short-lived as significantly warmer air begins pushing back into the region mid-week. Alongside the warmer temperatures will come the potential for more unsettled, stormy weather.

  1. A few showers may drift towards the Red River Valley from the NW this morning, however they should dissipate before it reaches our region.  ↩

Unsettled Wednesday Marks Return to Warmer, Humid Weather

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The pleasant spell of cooler, drier weather is coming to an end today as a warm front pushing eastwards across the Prairies brings unsettled weather today and then a deeper southerly flow which will help the heat and humidity slowly build up through the region into the end of the week.

Wednesday

Today will be the first active day of the week as a warm front approaches from the west and pushes through the Red River Valley later this afternoon & into the evening hours. This system will spread showers and thunderstorms across southwestern Manitoba this morning and gradually push them towards the valley through the day. The rain will likely hold off until late in the afternoon or early this evening here in Winnipeg. Temperatures will climb into the low 20’s across the valley with winds picking up out of the south-southeast to 20–30km/h with some gustiness on top of that by mid-to-late afternoon.

NAM Simulated Reflectivity valid at 00Z Thursday August 6, 2015
The NAM simulated RADAR refliectivities show a large swath of showers moving through Southern Manitoba this evening as a warm front pushes eastwards.

With the showers there will be a slight chance of an embedded thunderstorm…if we can manage some heating through the day with a bit of sunshine. If it ends up being overcast for a large area ahead of the front, the thunderstorm activity will likely be fairly mild with little-to-no chance of severe weather. On the other hand, if some sunshine manages to heat things up a bit, there will be a very borderline risk of some marginally severe wind or hail with some of the storms. That said, it doesn’t look particularly likely that we’ll see too much thunderstorm activity and, rather, we’ll see more moderate shower activity. The exception to this rule will be over southwestern Manitoba where there will be a slight risk of severe thunderstorms with main threats of large hail and damaging winds.

By the time things clear out late in the evening, most places will likely have seen around 5–10mm, but localized amounts of 10–20mm are possible. Temperatures will drop to lows in the mid-teens tonight.

Thursday

Thursday will be a muggier day with temperatures climbing into the mid–20’s. There will be some sunny breaks, but skies look to be trending towards the cloudier side of things. Another disturbance begins pushing into our region later in the day, which will bring another chance for showers or thunderstorms mid-afternoon into the evening hours. Temperatures will dip to the mid-teens again on Thursday night with a continued chance of shower activity.

Friday

Friday will see a more organized thunderstorm threat return to Winnipeg & the Red River Valley as the main upper-level disturbance swings through the province. Temperatures will climb to around 26°C or so with any leftover humidity getting flushed out by drier westerlies at around 30km/h. We may see some pop-up thunderstorms through the day, but at this point they don’t look like they’ll bring any severe weather. Friday night will see temperatures dip back to the mid-teens with a chance of some wrap-around shower activity pushing into the Red River Valley form the north on the back-side of the departing upper low.

Weekend Looks Pleasant

Looking ahead, the weekend looks great with high temperatures in the upper 20’s, relatively comfortable humidity, and little in the way of precipitation expected thanks to a ridge of high pressure working its way across the Prairies. Finally, rainy weather during the work week turning beautiful for the weekend!

A Sunny, Hot & Muggy Weekend Ahead

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After a very busy day across Southern Manitoba yesterday that brought strong winds but, more significantly, absolutely drenching rainfall to many areas, much quieter weather is in store for the weekend.

The weather over the coming few days will, fortunately, take little space to explain. For all the coming days, we’ll see daytime highs in upper 20’s or just cracking the 30°C mark. It will feel a bit warmer than that, though, as a moderate amount of humidity remains in the region. Dew point values will fall to around 16 or 17°C this afternoon, but then rebound back into the upper teens or low 20’s for Saturday & Sunday. This will make for quite a hot and humid weekend.

RDPS Forecast Dew Point valid 00Z Saturday July 25, 2015
The orange colours in the Red River Valley show dew point values remaining near 20°C.

Winds will remain fairly light over the coming days. Overnight lows will sit in the upper teens.

Little precipitation is expected; and little is expected in the way pop-up showers or thunderstorms are expected. There’s a chance of some shower activity moving through tonight, but it’s not expected to be particularly significant.

Unsettled Start to Next Week?

The beginning of next week may potentially have a stormy and unsettled start as a low pressure system moving through the region brings another round of thunderstorms to Southern Manitoba. At this stage, it doesn’t look like nearly as widespread an event as the extensive system that affected Southern Manitoba on Thursday. With the heat and humidity in place, though, severe thunderstorms may be a possibility. As we move further into the weekend, we’ll be keeping an eye on things and issue a convective outlook for Monday or Tuesday if it looks significant enough.

Until then, enjoy the hot and humid weather!

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.  ↩