Tag: Showers

Slow-Moving Pacific Low Brings Stormy Weather to Manitoba

Brad Leave a comment

A slow-moving low pressure system that has meandered into the Prairies from the west coast will very gradually make its way through the province over the coming few days, bringing with it numerous chances for showers and thunderstorms.

The coming few days will be rather unsettled over the Red River Valley, however there’s no guarantee any one location will end up seeing all that much rainfall as multiple rounds of showers and thunderstorms swing across the region. Given that the next three days will all be under the influence of the same system, I’m going to break down the forecast in a slightly different way than usual and cover the weather elements individually instead of talking about each day.

Temperatures

Temperatures are expected to climb into the mid-20's on Thursday in the Red River Valley.
Temperatures are expected to climb into the mid-20’s on Thursday in the Red River Valley.

First off, the temperatures. Today and Thursday will both be days with near-seasonal high temperatures of about 25°C. Overnight lows for today & tomorrow will be slightly warmer than normal with a lows of 16-17°C.

A cold front will sweep through on Thursday night, ushering in cooler temperatures for Friday with a daytime high near 22°C and an overnight low near 13°C.

Cloud Cover & Wind

Skies will become incrementally more cloudy over the next three days with a mix of sun and cloud expected today in Winnipeg, fairly cloudy skies with a few sunny breaks on Thursday, and mainly cloudy skies on Friday.

Winds will also be fairly light over the coming few days; expect easterly winds between 10-20 km/h today & tomorrow, then a shift to northwesterlies for Friday with slightly breezier conditions as winds climb to around 30 km/h.

Precipitation

This is the much harder thing to nail down in today’s forecast. The Red River Valley will be dealing with several waves of precipitation over several days, much of it convectively driven which automatically injects some uncertainty into the forecast. Here goes as best an overview as we can!

Variable amounts of rainfall are expected over the next 3 days in the Red River Valley with more confident rainfall amounts in Central Manitoba and North Dakota.
Variable amounts of rainfall are expected over the next 3 days in the Red River Valley with more confident rainfall amounts in Central Manitoba and North Dakota.

Wednesday: There will be a chance of showers or thunderstorms today as two areas of convection pass by to the south and north of the Red River Valley. Conditions will likely remain fairly dry, however there is the off chance of some areas being clipped by either of these systems. A more organized system will develop tonight as the frontal wave associated with the Pacific low moves through the region and the low itself moves in.

Wednesday Night/Thursday: A risk of elevated convection will be in place tonight into Thursday morning. There’s still uncertainty with exactly where the storms will develop, but it’s safe to say that the entire Red River Valley is at risk of seeing thunderstorms and rain. Some of these storms may be severe. We’ll produce a convective outlook image once the situation is a little more clear.

Then the threat for thunderstorms returns on Thursday afternoon as a cold front sweeps across the Red River Valley and the low slumps from Western Manitoba into the Red River Valley. It looks, at this point, that any storms that develop on Thursday afternoon could be strong to severe.

Friday: The main low will move through on Friday, bringing widespread shower activity. An isolated thunderstorm or two is possible, but they are not expected to be severe should they develop.

Long Range

Briefly looking ahead to the weekend, it appears that Saturday could bring some more scattered showers with a chance of an isolated thunderstorm. Sunday is looking like the day where things return to slightly more pleasant conditions with the sun returning and temperatures climbing back into the mid-20’s.

Winnipeg’s seasonal daytime high is currently 26°C while the seasonal overnight low is 12°C.

Risk of Storms to Start the Week

Scott Leave a comment

This week will start out with another risk of severe thunderstorms across southern Manitoba. On the bright side, conditions prior to the storms will be warm.

A low pressure system moving into southern Manitoba will bring a risk of severe storms to the region
A low pressure system moving into southern Manitoba will bring a risk of severe storms to the region

This Week

Today will be a warm and increasingly humid day across southern Manitoba. High temperatures will generally be in the upper twenties, although some locations may reach the 30C mark. The increased humidity will push humidex values into the mid-upper thirties. The approach of a strong low pressure system will result in a stiff southerly wind developing across southern Manitoba. Wind speeds in the Red River Valley will be 40 km/h gusting to 60 km/h by late afternoon. Other portions of southern Manitoba will also be windy, but with speeds perhaps a bit lower than those in the RRV. This same low pressure system will bring a risk of severe storms to most of southern Manitoba as a cold front slices into this warm, humid air mass. All hazards will be possible with storms that develop, with the primary risks being large hail and damaging wind gusts. Tornadoes will be possible with any storms that remain isolated, although the tornadic risk is somewhat lower than last Wednesday.

AWM Day 1 Convective Outlook for August 8, 2016
AWM Day 1 Convective Outlook for August 8, 2016

Models hint at an organized convective system perhaps developing out of the afternoon/evening storms. Should such a scenario play out, the Red River Valley and southeastern Manitoba may be at risk for more widespread damaging winds from the evening into the overnight period.

Moisture: Surface dewpoints of 17-21 C are expected across southern Manitoba, with 850 mb dewpoints of 12-15 C by early evening. Moisture is expected to be well mixed within the boundary layer, giving a 100-mb mean mixing ratio of approximately 12-13 g/kg.

Instability: The aforementioned well-mixed boundary layer will sit beneath mid-level lapse rates of approximately 7 C/km. Steep low-level lapse rates will be present owing to the well-mixed, and relatively deep boundary layer. Resulting MLCAPE values will be near 2000-2500 J/kg across south-central Manitoba by early evening. Early evening instability will generally be poor in the Red River Valley and points east, with MLCAPE of 1000 J/kg or less. However, by the late evening period (03Z onward), MLCAPE/MUCAPE will increase to near 2000 J/kg in the region.

Wind Shear: A 50 kt 500-mb jet streak pushing into SW Manitoba will be preceded by approximately 40 kt of westerly flow over southern Manitoba. Except near the surface warm front, surface winds will generally be southerly, and as a result will not enhance the effective bulk wind difference (EBWD) in a notable way. The result will be EBWD values of 30-40 kt across southern Manitoba, with locally higher values near the surface warm front. More interestingly, a strong southerly low-level jet of 30-40 kt is expected over south-central Manitoba by late afternoon. This will result in 0-1 km wind shear of 15-25 kt. Effective storm relative helicity values will also be strong, at 250-400 m2/s2 during the evening. Low-level shear and helicity are also expected to benefit from the decoupling of the boundary layer by mid-late evening, as the LLJ increases to 45 kt by 0300 UTC.

Trigger: The primary trigger for deep convection Monday evening will be a cold front moving in from eastern Saskatchewan and a warm front extending eastward from a low pressure system near the MB/SK border. Forcing for ascent will be quite strong, especially over western Manitoba, where a potent shortwave trough will help knock down heights by the afternoon. The combination of the low-level mesoscale ascent with the surface fronts and mid-level ascent from the incoming shortwave should easily be able to trigger storms by late afternoon across western Manitoba.

Discussion: Severe thunderstorms are likely to develop across western Manitoba/central Interlake beginning Monday afternoon. Initial storms will likely be a mix of supercells and multicell clusters, owing to the strong forcing. Any initial cells that are able to maintain relatively unpolluted surface-based inflow will present a tornado risk, owing to the strong low-level shear/helicity and steep low-level lapse rates. All initial severe cells will be capable of large hail and damaging wind gusts. As the evening progresses, some models hint at upscale growth/cold pool mergers leading to the development of a bowing system over the southern interlake, or adjacent regions. Should such a system develop and have a significant line-trailing cold pool, it would tend to move ESE/SE, potentially impacting Winnipeg, the Red River Valley, and southeastern Manitoba. A system will a less pronounced cold pool may take a most easterly track, primarily avoiding the Red River Valley. Latest models suggest a well-organized, cold-pool driven MCS is the less likely outcome. The overall risk is slight for all of southern Manitoba. A future moderate risk is possible should a forward-propagating system become more likely.

The cold front which triggered today’s storms will pass through the Red River Valley early Tuesday, likely bringing with it some showers and/or weak thunderstorms. After the front clears the region, skies will begin to clear, allowing temperatures to climb into the low twenties by afternoon. Winds will be northerly at 20-30 km/h behind the front.

Wednesday’s forecast remains fairly uncertain at this point. Models hint at the potential for rain across much of southern Manitoba, though the amount and duration of this rain is quite uncertain. Some models bring significant rain to the region, while others bring only light showers. It appears regions along the international border may be at the highest risk for significant accumulations, though that could change as new data becomes available. Outside the rain, skies will be mainly cloudy with temperatures near 20C. Winds will be easterly at 20-30 km/h.

Long Range

The long range forecast shows little change in our pattern over the next couple weeks. Expect to see 1 or 2 weather systems rolling through our region every week, with stormy conditions associated with the passage of each system. Between systems we can expect generally pleasant conditions, with temperatures near to above-seasonal values.

Potent Severe Thunderstorm Threat For Manitoba

Brad 1 Comment

A low pressure system tracking eastwards through Saskatchewan will bring a potent severe thunderstorm threat to Southern Manitoba today. The development of severe thunderstorms capable of producing damaging hail and winds, torrential downpours, and tornadoes is expected this afternoon over portions of southwestern Manitoba. These thunderstorms will then track eastwards across the Red River Valley & the southeastern corner of the province through the evening hours.

Hot and humid weather will return to Winnipeg today as temperatures soar to the 30°C mark while dewpoint temperatures climb towards the 20°C mark in the Red River Valley courtesy a gusty southeasterly wind of 30-40 km/h that will develop midday. This hot and humid weather will serve as the pressure cooker for severe thunderstorm development as a low pressure system tracks into the province this afternoon.

Through the morning hours, a few isolated thunderstorms are possible across the southwestern and south-central portions of the province, but they aren’t expected to be particularly notable. By early to mid-afternoon, the “main event” will start with thunderstorms developing along a north-south line west of the Red River Valley. Through the late afternoon into the evening, these thunderstorms will move eastwards across the Red River Valley and southeastern Manitoba.

These thunderstorms will be capable of producing large and damaging hail, dangerous straight-line winds exceeding 100 km/h, and torrential downpours capable of flash flooding. In the early hours of the system, over portions of southwestern Manitoba and possibly extending into the western Red River Valley, these thunderstorms will also be capable of producing a tornado.

Going over the MIST ingredients for convection:

  • Moisture: Dewpoints climbing into the 20-23°C range will combine with moderate vertical extent as an organized moisture feed advects into the province from the Dakotas.
  • Instability: Significant moisture coupled with moderate mid-level lapse rates to produce MLCAPE values 2000-3000 J/kg. MUCAPE values of 1500-2000 J/kg will continue overnight into northwestern Ontario.
  • Shear: Significant speed and directional shear will be in place over the province with textbook-quality looping hodographs present under 50-60 kt of 0-6km bulk shear will practically guarantee supercell development upon storm initiation and will be completely supportive of upscale growth into the overnight period.
  • Trigger: A frontal wave passing by the province and associated low pressure system and trough will provide ample lift and convergence to trigger thunderstorm development.

As storms develop, they will very quickly begin rotating and mature into supercell thunderstorms. These storms will very quickly develop hail and severe wind threats. Low lifting condensation levels coupled with the strongly veering hodographs and notable low-level CAPE also suggests a tornado threat for the first few hours of the storm life-cycle. This will most likely be constrained in an area from Brandon to Winnipeg along the Trans-Canada Highway and then south to the American border.

The severe thunderstorm threat will continue eastwards with the line through the evening into Ontario.

AWM Day 1 Convective Outlook for August 3, 2016
AWM Day 1 Convective Outlook for August 3, 2016

The thunderstorms will track eastwards through the evening hours, with Winnipeg most likely seeing the activity between 8PM and 1AM.

Winds will diminish tonight behind the thunderstorm activity as temperature dip to around 17°C.

Update: EC Event Summary

Environment Canada has issued a summary of the severe weather that occurred across ‪#‎MBstorm‬ yesterday. The highlights are two confirmed tornadoes, loonie to quarter sized hail, wind gusts up to 111 km/h, and 4″ of rain!

Weather summary for Manitoba
issued by Environment Canada
at 5:04 a.m. CDT Thursday 4 August 2016.

Discussion.

An intense low pressure system tracking across the Prairies brought
widespread severe weather to much of southern Manitoba on Wednesday.
Two tornadoes have been confirmed, and numerous reports of heavy
rain, damaging winds, and large hail were also received.

The following reports have been received by ECCC meteorologists
(event times are approximate):

A funnel cloud was reported 8 km north of Hartney at 5:00 pm CDT.

A brief tornado was reported near Margaret at 5:10 pm CDT. No damage
was reported with this tornado.

A larger, longer lived tornado was reported 10 km west of Baldur at
5:20 pm CDT. It tracked northwards towards Stockton where a large
shed was destroyed shortly after 5:30 pm CDT.

ECCC meteorologists continue to investigate these and other
unconfirmed tornadoes.

Hail reports:

Loonie sized hail at Brandon at 6:05 pm CDT.
Quarter sized hail at Shoal Lake at 9:20 pm CDT.
Loonie sized hail at Wasagaming at 10:10 pm CDT.

Peak wind gust reports:

111 km/h at Morden at 7:26 pm CDT.
93 km/h at Portage la Prairie at 7:10 pm CDT.
92 km/h at St. Adolphe at 9:05 pm CDT.
85 km/h at Gretna at 7:46 pm CDT.
74 km/h at Winnipeg Airport at 9:45 pm CDT.

Rainfall totals in millimetres:

Erickson 104
Neepawa 75
Glenboro 66
St. Adolphe 64
Holland 56
Ethelbert 53
Fisherton 53
Morden 53
Killarney 50
Souris 49
Cypress River 45
Elm Creek 43
Snowflake 43
Winnipeg The Forks 2.7
Winnipeg Airport 1.4

Environment and Climate Change Canada meteorologists are actively
seeking pictures or videos from Wednesday's severe weather events
and further damage they may have caused. Should you have any
information regarding these events or to report severe weather at
any time, please call 1-800-239-0484, email storm@ec.gc.ca, or tweet
#MBStorm.

Please note that this summary may contain preliminary or unofficial
information and does not constitute a complete or final report.

End/PASPC

The Rest of the Week

Thursday will be a cooler day with a high near just 21°C with gusty northwesterly winds at 30-40 km/h. There will be a slight chance of some showers as the wrap-around from this low moves across the province. The humidity will be flushed out of the province making for more comfortable conditions. Temperatures will dip to 13°C Thursday night with clearing skies and diminishing winds.

Friday will be a pleasant day with winds out of the northwest at 20-30 km/h, highs in the mid-20’s and mainly sunny skies.

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

Near-Seasonal Temperatures This Weekend

Brad Leave a comment

Near-seasonal temperatures will be in place this weekend with just a chance of a shower or two across the Red River Valley as a few weak upper disturbances ripple through.

Winnipeg & the Red River Valley will see a beautiful day today with plenty of sunshine, light winds and a high near 24°C. There will be a very slight chance of a shower or two in the Red River Valley, but these will likely be confined to the extreme western portions of the valley, particularly close to the escarpment.

Skies will continue fairly clear tonight with a low near 13°C.

Saturday will bring more pleasant conditions to Winnipeg & the Red River Valley, although there will be slightly more cloud and an incrementally higher chance of some scattered showers throughout the valley, particularly through the afternoon hours. Temperatures will climb to a high near 25°C with light winds once again.

Expect a low near 14°C on Saturday night with partly cloudy skies.

A cold front located over central Manitoba on Sunday morning will sweep southwards through the day.
A cold front located over central Manitoba on Sunday morning will sweep southwards through the day.

A weak cold front will sweep into the Red River Valley on Sunday, almost certainly bringing some precipitation with it. Temperatures will still be mild with a high near 25°C, however skies will become mixed to mainly cloudy in the morning, with scattered showers developing by midday. There will be enough instability to produce a thunderstorm threat, but at this time no organized severe thunderstorm threat is expected.1 Winds will shift from 15-25km/h out of the southwest ahead of the cold front in the morning to about the same speed out of the northwest behind the cold front.

Temperatures will dip to a low near 13°C on Sunday night with clearing skies and diminishing winds.

Next Week Brings the Heat

Heading into next week it's beginning to look like a bit of a mixed bag: we'll definitely be seeing a prolonged stretch of summer-like heat as daytime highs climb into the upper 20's after one cool day on Monday, but with Southern Manitoba left on the edge of an upper-level ridge building through central North America, we likely won't see nothing but sunshine all week.

The CPC is forecasting a near-certain probability of above-normal temperatures extending into southern Manitoba next week.
The CPC is forecasting a near-certain probability of above-normal temperatures extending into southern Manitoba next week.

It will be impressive heat that Southern Manitoba will be on the fringes of, with daytime highs soaring into the upper 30's or low 40's through the Great Plains of the United States. Some of that heat may surge further north in the second half of the week and produce daytime highs in the 30-35°C range across the southern Prairies. These high temperatures combined with dewpoint values in the 18-20°C range could result in humidex values approaching the 40 mark across southern Manitoba in the second half of the week.

This warm weather will be hampered, however, by the potential for several rounds of thunderstorm activity.2 With the upper-level ridge not quite fully building into our region, we'll be under the threat for multiple "ridge riders," upper-level disturbances that move up and over the top of an upper ridge. These features are common producers of thunderstorms and can often result in severe weather as well, so although we'll be warm, it doesn't appear that we'll get a completely dry stretch either. Precipitation should primarily be convective, so you may be able to sneak through the week without getting anything, but the potential will be there for wet weather.

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

  1. As usual, we'll keep an eye on things and update if the thunderstorm potential looks worse as we get closer to the date. ↩
  2. I've installed chicken wire for protection from the farmers. ↩