One More Chance for Thunderstorms, Then Cooler Weather Arrives

The heat will stick around for just one more day before a cold front ushers in cooler temperatures that will persist through the remainder of the week. That cold front will also bring the threat of severe thunderstorms to the Red River Valley this afternoon as it slides southeastwards through the region.

Today’s weather focus for Winnipeg & the Red River Valley will be the continued heat and humidity in place and the cold front that will be shunting it out today. Temperatures will rise quickly this morning towards a daytime high near 30-31°C. With dew points still in the 18-20°C range, humidex values will climb into the upper 30’s once again. By early afternoon, a cold front will start slumping southwards into the Red River Valley, bringing with it a risk for thunderstorms.

EC³ Day 1 Thunderstorm Outlook for July 31, 2017

As shown in ECCC’s thunderstorm outlook, there is a chance for severe thunderstorms over the Red River Valley and southeastern Manitoba.

Going over the MIST ingredients:

  • Moisture: Surface dew points near 20°C will provide large amounts of energy for thunderstorms to work with.
  • Instability: The high dew points will combine with moderately steep mid-level lapse rates to produce MLCAPE values near 2500 J/kg.
  • Shear: Shear is lacking somewhat; 500 mb winds of 30-35 kt layered on top of south to southwesterly surface winds of 10 knots will produce bulk shear values near 25 kt.
  • Trigger: A cold front slumping southwards through the region.

The high instability coupled with middling shear but sharp trigger will combine to produce the threat of severe thunderstorms that quickly develop into a multicellular line and move to the southeast.

The primary threat with today’s thunderstorm will be large hail. As shown in ECCC’s outlook, hail up to 5 cm diameter — a bit larger than a golf ball — is possible in the worst storms that form today. Heavy rain will be the second threat as it’s quite likely the rainfall coming out of the line of storms is torrential. Whether or not there’s overland flooding will depend on how quickly the line is moving; at this point, it seems like things will be progressive enough that while the rain will be heavy, it won’t reach severe criteria (50 mm in under 1 hour). There may be strong winds in some of the storms, but it won’t be as common as large hail and heavy rain. There is not a significant tornado threat today.

The biggest uncertainty will be when exactly the thunderstorms start. If they form early, around 1PM or so, then they’ll initiate to the northwest of Winnipeg and move through the city early to mid-afternoon. Should the capping inversion hold longer and storms don’t form until 3-4PM, then it will be likely that the cold front has passed through Winnipeg and the storms fire to the south and southeast of the city. The southern Red River Valley and southeastern Manitoba have a high probability of seeing thunderstorms this afternoon.

Behind the cold front, winds shift out of the northwest to around 20 km/h as skies clear. Temperatures will drop to a low near 17°C tonight.

The 3km NAM model shows a line of thunderstorms moving through the Red River Valley late this afternoon.

Tuesday will start off sunny with skies becoming mixed in the afternoon as a weak disturbance moves towards the region. Temperatures will climb to a high near 26°C, but the humidity will be much more comfortable as dew points fall to the 11-13°C range in the continued light northwesterly winds. There may be a slight chance of some isolated showers in the afternoon. Tuesday night will bring some clearing in the evening, but then more organized cloud will begin moving in ahead of a low that will impact the region on Wednesday. Temperatures will drop to around 11°C.

Wednesday will bring cloudy skies and a good chance of showers to Winnipeg and the Red River Valley. It will be a relatively cool day with highs around the 20°C mark and continued light northerly winds. The chance for showers will taper off in the evening with temperatures dropping to a low near 11°C.

Long Range

The remainder of the work week looks quiet with temperatures near-seasonal, if not a bit below. There may be some chances for showers on Friday or Saturday, but it’s still looking a bit unclear at this point.

Winnipeg’s seasonal daytime high is currently 26°C while the seasonal overnight low is 13°C.

The Heat Is On; Thunderstorms Possible Saturday

While July has been relatively pleasant, temperatures have [somewhat surprisingly] been largely below seasonal for much of the month. That’s all about to change as significant heat builds across the region to round out the month.

A developing southerly wind of 20-30 km/h this morning will draw warmer air northwards out of the United States and help push daytime highs up to around the 30°C mark. Skies will remain mainly sunny and humidity in the mid-teens should keep things feeling relatively comfortable. Expect lows to fall to around the 19°C mark tonight with winds continuing out of the south and partly cloudy skies.

An upper ridge in place over Southern Manitoba today will bring warm temperatures to the region.

Saturday will see a cold front slowly sweeping across the province, bringing with it a severe thunderstorm risk. Before that, though, there will be a hot summer day on tap with highs once again near the 30°C mark under mixed skies. With the southerly winds slowly diminishing and dew points rising to around 19 or 20°C, it will end up feeling quite humid in the afternoon. The cold front will progress eastwards through the day, reaching the Red River Valley mid- to late-afternoon. As it pushes into the valley, it will bring with it the risk of severe thunderstorms.

Going over the MIST ingredients:

  • Moisture: Low-level moisture will be plentiful with surface dew points climbing towards the 20°C mark and with deep moisture extending towards 850 mb.
  • Instability: Slight to moderate instability will be in place. Mid-level lapse rates leave a bit to be desired with expected values only around 6-7°C/km, but this is somewhat offset by the substantial latent heat available through surface moisture. Depending on the exact orientation of this system, the heights may be rising as the front stalls, which would work against thunderstorm development.
  • Shear: Bulk shear values around 25-30 kt will be in place which is on the lower end of values. Low-level shear will likely be weak and mid-level shear largely unidirectional.
  • Trigger: The cold front will slowly slump southeastwards, gradually slowing into the evening hours.

The primary threats with any storms that develop will be large hail and damaging winds, although with dew points so high, torrential rain is likely as well. They would move southeastwards through the Red River Valley. The biggest question will be whether or not storms actually develop. The threat will exist generally around the Trans-Canada Highway corridor and south, but we’ll provide an update on Saturday with a new look at the day’s potential.

A cold front will be in place across Southern Manitoba on Saturday afternoon.

The thunderstorm threat will diminish before midnight and temperatures will then drop to a low near 17°C under clearing skies.

Sunday will be another hot day with a high near 31°C but more comfortable humidity as the dew point drops back towards the mid-teens. Skies will be partly cloudy and winds will be light out of the east. Winds will shift out of the south on Sunday night and increase to 15-25 km/h, keeping temperatures fairly warm; the overnight low will be just around 19 or 20°C.

Long Range

Temperatures will continue to be warm through the start of next week with partly cloudy skies and highs generally around the 30°C mark. Monday will likely be moderately humid again, but things will dry out on Tuesday as a cold front moves through. The rest of the week looks fairly quiet with near-seasonal temperatures and low humidity.

Get The Sunscreen Out; Plenty of Summer Sun & Heat On The Way

A beautiful second half to the week is ahead for Winnipeg as an upper-level ridge building into the Prairies brings plenty of sun and warmth to the area!

It’s been a while, but the forecast today is finally short once again. The next few days will be great across Winnipeg and the Red River Valley as upper-level ridging clears skies and ushers warmer weather back into the region. Today will bring highs near 26°C to Winnipeg and area with mainly sunny skies until late in the afternoon. A very weak upper-trough moving through late in the day will bring a few clouds to the region and perhaps trigger an isolated evening shower, but the main chance will be north of the city and it’s not expected that Winnipeg or areas south have much of a chance of seeing any rain.

The RDPS shows some isolated showers, mainly through the Interlake, late today in to the evening.

Temperatures will head to a low near 16°C tonight. Thursday and Friday will both be mild with high temperatures climbing towards 30°C on Friday. Both days will have plenty of sun; Thursday should bring nothing but sunshine while Friday brings partly cloudy skies. Winds will be out of the northwest today at 15-25 km/h, light on Thursday, and then increase out of the south on Friday to 20-30 km/h. Temperatures will dip down to around 17°C on Thursday night, but Friday will see a warmer overnight low near 20°C.

Long Range

Warm weather will continue throughout the weekend. A low pressure system moving through the Prairies on Saturday will bring increasing humidity and a risk of thunderstorms to much of Manitoba. For Winnipeg and the Red River Valley, the risk for storms will likely be in the late-afternoon and evening. Sunday will see northerly winds usher in drier air while temperatures return to near-seasonal values.

Next week looks to bring near-seasonal temperatures with a slight chance of some thunderstorms on Tuesday and Wednesday.

Winnipeg’s seasonal daytime high is currently 26°C while the seasonal overnight low is 13°C.

Warm With A Chance of Thunderstorms, Then Turning Drier

The weather returns to slightly warmer than normal summer fare for Winnipeg to start the week with highs in the upper 20’s and mild lows. It will also be relatively dry, with the only significant chance for rain coming on Monday night as a cold front slowly moves through the Red River Valley.

Today will be a warm and windy day in Winnipeg as breezy southerlies bring summer heat and slightly muggy conditions to the Red River Valley. Skies will become mixed fairly early in the morning as the south-to-southeasterly winds ramp up to 30-40 km/h. These gusty southerly winds will bring mild temperatures into the region, pushing daytime highs just short of 30°C. In addition to the warmth, these winds will maintain the slightly humid conditions in place with dew points remaining in the 16-18°C range. Closer to the cold front — primarily over the southwestern corner of the province but also possibly into the western Red River Valley — moisture will pool and dew points will likely rise into the low 20’s, making for quite a muggy day in those areas.

A potent low pressure system over western Saskatchewan will spread gusty southerly winds across the Red River Valley on Monday afternoon.

By evening, a cold front will be pushing eastwards into the Red River Valley, bringing with it a chance of showers or thunderstorms to much of southern Manitoba.

Going over the MIST ingredients:

  • Moisture: Dew points will climb generally into the mid-teens, but elevated moisture is expected near the cold front as moderate southerly winds enhance moisture pooling ahead of the front. Moisture is also expected to be moderately deep, extending to roughly 850 mb.
  • Instability: Moderate mid-level lapse rates on the order of 7-8°C/km will combine with the low-level moisture to produce MLCAPE values of 1500-2000 J/kg.
  • Shear: Shear will be somewhat lacking with only 25-30 kt of 0-6 km bulk shear; this is fairly low and may be the real limiting factor in any thunderstorm activity that may develop.
  • Trigger: A pronounced cold frontal trough moving eastwards will provide the focus for any convective development.

Overall it seems that there will be enough energy available for severe thunderstorms, but the lack of shear will throw a wrench into the certainty of a large-scale severe weather outbreak.

The highest risk for severe weather in southern Manitoba will be over the southwestern corner where scattered thunderstorms first fire up along the cold front. These storms will have the potential to produce significant hail and strong winds. While an isolated tornado is possible, it won’t be an elevated threat with today’s thunderstorms. As the cold front moves eastwards through the evening and spreads the thunderstorm threat into the Red River Valley, the threat shifts towards favouring strong winds. Temperatures will bottom out overnight around 18-19°C with the winds tapering off.

This simulated RADAR image from the 3km NAM model shows a forecast of thunderstorms for the Red River Valley on Monday evening.

The weather then settles for Tuesday and Wednesday as a broad ridge of high pressure builds into the Prairies. Skies will clear and remain mainly sunny for much of Tuesday and Wednesday as temperatures climb to highs near 27°C both days. It will remain slightly humid with dew points remaining in the mid-teens through the middle of the week. With that humidity remaining in the region, it will keep overnight lows in the mid-teens as well.

Long Range

Gradual upper-level ridging will build into the Prairies late this week and into early next week, bringing continued mild weather and low probabilities of rain. The odd system may slide across southern Manitoba from the northwest, returning temperatures back to seasonal alongside a chance of showers. Overall, though, it appears Winnipeg and the Red River Valley will be entering into a fairly dry pattern.

Winnipeg’s seasonal daytime high is currently 26°C while the seasonal overnight low is 13°C.