A severe thunderstorm threat returns to Southern Manitoba today as very warm and humid conditions persist in the region for one final day before a cold front pushes cooler and drier air into the region. The passage of the cold front will not be an end to the unsettled weather, though, as a couple more days of showers or thunderstorms will occur with a large upper-level low passing over the region.
Today brings a notable severe weather threat to southern Manitoba with a slight risk of severe thunderstorms developing over southwestern Manitoba and a moderate risk in the Red River Valley eastwards through the SE corner of the province.1 The thunderstorms will develop mid-day and push eastwards with the cold front through the remainder of the afternoon. It is most likely that the thunderstorms develop over southwest Manitoba first, and then push towards into the Red River Valley this evening. Stay aware of any watches or warnings issued by Environment Canada.
The HRRR develops a line of thunderstorms along the cold front and pushes it into the Red River Valley this evening.
Otherwise, this mornings cloud cover will break up a bit to produce mixed skies and the relatively small amount of sunshine will push the daytime highs to around 26°C. With very humid air in place, it will be a fairly uncomfortable day, feeling more like the low- to mid-thirties. After the thunderstorms move through this evening, we’ll head to a low near 16°C with breezy southerly winds.
Tomorrow will likely bring some sun first thing in the morning, but more clouds will move in with a good chance of more shower or thunderstorm activity in the afternoon. At this point severe thunderstorms aren’t expected, but we’ll keep an eye on things to see if anything changes. Winds will be pick up to be gusty out of the north near 40km/h. Expect a high near 23°C and a low near 14°C with a continued chance for showers overnight.
Wednesday will be a cool and cloudy day with a good chance of more rain. The daytime high will only be around 20°C and winds will continue gusty out of the northwest, although not quite as strong as Tuesday. The shower activity will taper off in the evening as temperatures head to a low near 14°C.
The latter half of the week is looking like a return to seasonal temperatures and a chance of actually drying out a little bit.
Winnipeg’s seasonal daytime high is currently 26°C while the seasonal overnight low is 13°C.
Apologies for the lack of an outlook image; time constraints have prevented me from making one. ↩
Unsettled weather is on its way back to the province as a trough of low pressure develops over the western Prairies and draws humid air northwards out of the United States. For people heading out to Bird's Hill for the Folk Fest, this means increasingly muggy weather through the weekend with the potential for thunderstorms both Saturday & Sunday.
Today will be a fairly pleasant day. The system that brought up to 20 mm of rain to the Red River Valley yesterday1 will be moving off the east and any remaining cloud from it should clear out through the morning leaving just a few clouds around for the afternoon. Temperatures will climb to a high near 25°C. Expect just a few clouds overnight and a low near 14°C.
Saturday
Saturday will see more humid air beginning to work into the region. Morning sun will be replaced by clouds as the day goes on while the temperature climbs to a high near 26°C. There will be a slight chance of thunderstorms in the evening, but the main threat will occur through the overnight period. There will be a very small chance of severe thunderstorms.
Update: Severe Thunderstorms Hit SW Manitoba on Saturday July 9, 2016
Severe thunderstorms developed over SW Manitoba on Saturday and focused into one primary strong supercell thunderstorm that organized near Virden, MB and then moved southeastwards through Minto & Ninette before continuing on across the US border. It produced a variety of severe weather, with numerous reports of heavy rain, large hail and severe winds:
A summary of the severe weather over southwestern Saskatchewan on July 9, 2016
Sunday
Sunday will see the humidity move into the region full force with dewpoint values climbing up into the low 20's. This will make the high near 27°C feel very warm, however conditions will be a bit more bearable due to the fair amount of cloud cover expected through the day. Any times the sun does poke out, though, will likely see things begin feeling very warm very quickly.
A organized line of thunderstorms sweeping across Southern Manitoba is possible Sunday night.
Rain-wise, we may see some remnant showers or thunderstorms in the morning from any activity on Saturday night, and then things should diminish for much of the day. By Sunday evening & overnight, the thunderstorm threat once again returns. Sunday night will see a slight to moderate threat of severe thunderstorms across the Red River Valley. Large MUCAPE values overnight coupled with 30-50 kt of bulk shear ahead of an incoming shortwave will support the development of organized thunderstorm activity across a wide area of Southern Manitoba. The primary threats will be large hail and strong winds, with rapid rainfall accumulations also a concern.2
It will be a very mild night with a low near 21°C.
Long Range
The start of next week continues warm and humid with a thunderstorm threat late in the day into the overnight period. Heading through Tuesday into mid-week, the main upper low associated with the weekend's weather pattern moves into the region, bringing relief from the humidity and cooler temperatures alongside more cloud and chances for showers.
While Winnipeg saw nothing but a few light showers late in the evening, the rain managed to push as far north as St. Adolphe, which saw 2mm. ↩
Although the thunderstorms will likely have very intense rainfall, they will be moving relatively quickly, making accumulations not as prominent a threat as the hail or wind potential. ↩
Anyone looking for a good long stretch of hot, dry weather really should consider broadening their horizons because generally unsettled weather continues throughout Southern Manitoba right through the coming weekend.
Today will be the most pleasant and "summer-like" day of the coming few as the sun makes a prominent showing with temperatures climbing into the mid-20's for a daytime high. While some showers or thunderstorms are possible over southwestern Manitoba today, Winnipeg & the Red River Valley should see just a few clouds with no precipitation expected.
Tonight will continue to be fairly pleasant with a low near 13°C.
Thursday will bring unsettled weather back to Winnipeg as an upper low moves into southern Manitoba. Increasing cloudiness and showers will spread from the southwestern Red River Valley to the northeast through the morning, and then the unsettled conditions will persist through the afternoon. At this point no thunderstorm activity is expected. Temperatures will reach a high near 23°C and then head to a low near 14°C on Thursday night with a continuing chance of showers.
Several models are showing an area of rain or showers moving through the Red River Valley on Thursday afternoon.
Friday will continue with fairly cloudy skies and a slight chance of more light shower activity. Some sunny breaks are possible in the afternoon as the temperature climbs to a high near 23 or 24°C. Temperatures will drop to around 14°C with clearing skies.
Hot, Unsettled & Increasingly Humid This Weekend
The weekend weather will be dominated by a developing trough of low pressure through the western and central Prairies that will draw humid air northwards from the Central Plains of the United States and bring with it the potential for multiple days of thunderstorm potential. Early indications are that severe thunderstorms will certainly be possible on both Saturday and Sunday. Highs will be in the upper 20's with Sunday in particular beginning to feel very muggy.
The GFS is forecsting potent SBCAPE values in excess of 4,000 J/kg by Sunday evening.
With the Winnipeg Folk Festival starting off this weekend, we'll be sure to keep a close eye on this system as it develops. Early indications are that the days will be fairly pleasant with more of a chance for thunderstorms through the overnight periods both Saturday night and Sunday night. By Sunday, there may be a significant severe threat with any thunderstorms due to the sheer amount of instability that is forecast to be in place over the region. We'll have a closer look at the weekend forecast on Friday morning.
Winnipeg’s seasonal daytime high is currently 26°C while the seasonal overnight low is 13°C.
This week will start off on a stormy note in southern Manitoba, with a risk of thunderstorms in most areas from today until at least Wednesday. Severe storms will be possible on most days with this risk.
Severe storms will be possible along a dryline (brown) and cold front (blue) in southern Manitoba today.
Today
Today will feature a risk of severe thunderstorms in many parts of southern Manitoba due to the warm and humid air mass over the region. It will be a fairly unconventional severe weather setup with a complicated frontal regime in place. It appears that a dryline-type feature will be present through the Red River Valley on Monday afternoon, with a cold front cutting through the southern Interlake. The most unstable air is expected to reside near the cold front and east of the dryline, putting the Red River Valley and south-eastern Manitoba at the highest risk for severe weather. However, a secondary severe risk may develop along the cold front, especially through the interlake. It appears storms could also form further west along the cold front in parts of western Manitoba. The instability regime further west is less certain, therefore the thunderstorm risk in that region is also less clear. Prior to the initiation of thunderstorms, most of southern Manitoba will be quite warm, with temperatures near 30C in many areas. Winds will range from southerly/easterly ahead of the cold front/dryline to westerly/northerly behind these features. A technical discussion using the “MIST” technique is provided below for those wanting more specific details.
Technical Discussion
Moisture: Copious low-level moisture is expected ahead of the triggers today. Surface dewpoints of 20-22C are expected (ET enhancement should be in full swing), with 100-mb mean mixing ratio values of 14-16 g/kg.
Instability: Steep low- to mid-level lapse rates are expected today due to the presence of an elevated mixed-layer (EML) between 925 and 700 mb. These large lapse rates combined with the aforementioned mean mixing-ratio values should result in MLCAPE of 2500-4000 J/kg by late afternoon. MLCIN should be mostly eliminated with surface temperatures near 30C, assuming the 14-16 g/kg mean mixing ratios are realized.
Shear: Deep layer wind shear values will be variable and uncertain today. The 500-mb flow is expected to be 30-40 kt from the west, which would normally offer respectable wind shear on such a convective day. However, surface winds are also forecast to have a strong westerly component, even ahead of the triggers. Since southwesterly winds are expected ahead of the dryline, the effective bulk wind difference (EBWD) is expected to be less than the 500-mb flow. Conversely, some models have suggested easterly winds could be present ahead of the triggers, which would enhance the EBWD. A conservative approach would give an EBWD of 20-35 kt ahead of the triggers tomorrow, with the caveat that an easterly low-level flow could push said values to 40-45 kt. Given the expected westerly-component surface flow, it follows that low-level veering is also expected to be poor. Helicity values in the 0-3 km layer are only expected to be between 100-200 m2/s2, again with the caveat that an easterly surface flow would enhance these values.
Trigger: As mentioned previously, a cold front slicing in from the north is expected to provide a focus for storm develop along and north of the Trans-Canada highway through most of southern Manitoba. A north-south oriented dryline is expected to be in place in the Red River Valley during the day, providing a secondary trigger. Height falls during the afternoon-evening are unimpressive, and indeed could actually end up being height rises. The absence of any strong mid- and upper-level forcing for ascent should help keep storm coverage on the more isolated side, especially given that there will be a respectable, but breakable, cap to surface-based convection.
Discussion: A severe weather setup with impressive thermodynamics, but unimpressive kinematics/dynamics, is expected in southern Manitoba today. A respectable cap will be in place to surface-based convection until late afternoon, at which time strong low-level convergence along the dryline/cold front should be sufficient to trigger isolated severe storms. However, temperatures must reach near 30C for this to happen, therefore if strong surface heating does not occur, storms may fail to develop.
AWM Convective Outlook for July 4, 2016
The CAPE-shear space today is sufficient for marginal supercells structures, but stronger supercells are possible should the stronger shear develop (previously discussed). The main threats today appear to be large hail and damaging wind gusts. A few very large hail reports are possible given the extreme instability and steep lapse rates, especially if the stronger wind shear is realized. The tornado threat is marginal given the weak helicity values. However, low-level CAPE and LCL heights are in the tornadic range, suggesting that a right-deviating supercell could produce a brief tornado. The overall risk of severe weather is slight.
Tuesday
Tuesday could see another risk of severe storms develop across southern Manitoba. Models suggest a front may be stalled just north of the international border in the afternoon, providing a focus for storms to develop. Any storms that develop could become severe, with damaging winds and large hail being the main threats. Areas away from the storms should see temperatures in the mid to upper twenties with skies being a mixture of sun and cloud.
Wednesday
A third risk of storms may evolve on Wednesday, though forecasting thunderstorms three days into the future is far from an exact science. Current models show a general non-severe storm risk across southern Manitoba. This means gusty winds, small hail, and heavy rains are the main threats from any storms that develop. Like Tuesday, conditions outside of storms will be nice, with temperatures in the upper twenties and breezy easterly winds.
Long Range
The long range forecast is looking unsettled for the remainder of the week in southern Manitoba. At this time there don’t appear to be any additional threats of severe weather late in the week, but more thunderstorms can’t be ruled out. Looking out further in the long range, models hint at a more sustained period of hot weather as we move into mid-July, although that would certainly not be unusual for this time of year!
