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. ↩
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!
A pleasant and dry Canada Day is on tap for Southern Manitoba thanks to a ridge of high pressure over the region that will bring sunshine to most regions. Heading into the weekend, slightly warmer weather will bring with it more unsettled weather.
Southern Manitoba is set for a beautiful Canada Day as temperatures climb into the low 20's with mainly sunny skies and light winds. Some cloud cover will begin pushing into the region late this afternoon, likely bringing partly cloudy to mixed skies by midnight. The overnight low will dip down to near 12°C.
Saturday will bring mainly cloudy skies–although a sunny break here or there is possible—and just a very slight chance for some showers here in Winnipeg. A disturbance moving through the southwestern portion of the province will spread more organized shower activity that will pass through the southwestern Red River Valley, but likely remain south of Winnipeg. Temperatures will once again climb to around 23°C, but the wind will be a bit breezier at 20-30 km/h out of the southeast.
Cloudy skies will continue on Saturday night with a chance of showers in Winnipeg & the Red River Valley. Temperatures will drop to around 15°C for the overnight low with a continued chance of showers through the region.
The NAM simulated RADAR imagery shows a band of showers or thunderstorms moving through Winnipeg on Sunday evening.
Sunday will be the warmest and most unsettled day of the weekend. Temperatures will climb to a high near 25°C under mostly cloudy skies. There will be a chance of showers for much of the day, but as a trough passes through in the afternoon the risk for thunderstorms will be added into the mix. At this point, there doesn't appear to be a severe threat with the storms, but we'll keep an eye on the situation through the weekend. Winds will once again be southeasterly at 20-30 km/h. Expect a mild low on Sunday night near 17°C.
Long Range
Looking into next week, conditions look fairly warm with daytime highs in the upper 20's and increasing humidity as dew points climb into the upper teens. Early indications are that there will be chances for rain or thunderstorms every day through the first half of the week, with a slightly drier and cooler pattern returning for the second half of the week.
Winnipeg’s seasonal daytime high is currently 25°C while the seasonal overnight low is 13°C.
Southern Manitoba will see one more day of showers and thunderstorms before a calmer, drier pattern moves in for the remainder of the work week.
Today will bring another round of showers and thunderstorms to southern Manitoba as a cold front sweeps through the region. Under mixed skies, showers will develop through the morning, spreading southwards from the Parkland & Interlake regions into the Trans-Canada corridor and areas south through the afternoon. With MLCAPE values of 750-1250 J/kg and only around 25kt of bulk shear, the threat for severe thunderstorms will be minimal, although a quick pulse thunderstorm that quickly produces large hail and then falls apart isn't out of the question.
Temperatures will climb to near 25°C before cooling off as the cold front swings through in the afternoon. Winds will be relatively light, but we may get some slightly breezier conditions with winds out of the north to 20-30km/h behind the cold front. Skies will clear this evening and temperatures will dip down to a low near 11°C overnight.
This simulated RADAR image from the NAM shows the showers expected over Southern Manitoba this afternoon.
Thursday will see a ridge of high pressure moving into the province, which will bring mainly sunny skies, breezy winds near 30km/h out of the north and a high near just 19°C. Expect an overnight low near 8°C on Thursday night with light winds.
As the ridge of high pressure moves east of the Red River Valley on Friday, winds will gradually shift out of the south and slightly warmer air will move into the region, pushing daytime highs in Winnipeg to near 22°C with a few afternoon clouds.
Long Range
The dry weather won't be long to stay as things turn more unsettled on the weekend. A pattern shift back towards a more active storm track that brings the chance for rain or thunderstorms. Saturday will likely be dry, but the chance for rain and thunderstorms appears to return on Sunday and then persist through much of next week as a very unsettled pattern takes hold.
