Tag: Thundershowers

Ontario

[UPDATED] – Historic Weekend Ice-Storm and Strong Wind Gusts…


A strengthening, and ultimately a strong low pressure system from the Central Plains of the USA will approach Ontario and Quebec this weekend and stall as strong High Pressure in Northern Canada will force the low to become incredibly stagnant over the regions. There will be breaks in the precipitation at times [and a couple pulses of significant moisture, especially Sunday], but overall, the ‘quantitative precipitation forecast (QPF)’, or measurable total precipitation will be high from Saturday through Monday.

It is important to note that this storm will have EXTREMELY tight gradients between precipitation types and amounts (and hence, temperature). One region to the next in as little as 20 or 30 kilometers could receive drastically different amounts of snow, ice-pellets, and/or freezing rain. The difference between -1 and +1 could pose significant changes in traveling conditions for residents across ON/QC.

Importantly, regions who receive ice-pellets should note that the water content for snow and ice-pellets are drastically different. While snow is, on average, 10:1, ice-pellets are typically 2 or 3:1. This means, that 20-30mm worth of ice-pellets will “look” drastically different than 20-30cm of snow. On our forecast map, ice precipitation totals are displayed in mm. Please note that this is the equivalent amount of moisture that will fall as ice pellets. If 25mm falls – 75mm worth of ice pellets would accumulate; 3:1 ratio.

What to Expect

1) Heaviest Snow Region: Colder air will invade much of this region leading to mostly exclusively heavy snow. Some snow will occur Saturday/Monday; significant snow through Sunday.

2) Mostly Heavy Snow Region: Colder air will also invade much of this region. Most impacts through Sunday and residual on Monday.

3) DRY-SLOT. Some of: Snow/Ice/Rain Region: There appears to be somewhat of a dry-slot that will force itself within the large pulses of moisture – one across Northern Ontario – one across Southern Ontario. This dry-slot appears to encompass a large swath. However, while impacts will be reduced, they will still exist. This region can expect between 5-10cm of snow (locally up to 15cm), and a mixture of 5-10mm of ice precipitation in the form of ice and/or ice-pellets. Regions around Parry Sound and east will likely receive more freezing rain (than snow), while regions around Ottawa will receive more snow (than ice). It is possible, that regions just south of Ottawa could receive ~15cm. Ottawa itself is likely to receive closer to ~10cm and brief ice or ice pellets.

4) Wintry Mix Zone Region: Much of this region will receive snow, ice-pellets and light freezing rain. The colder air appears to be digging in more and more, and as such, freezing rain will likely no longer be a large threat (but will still lightly mix within at times). Regions such as Wiarton, Owen Sound, Barrie, Orillia, Midland, Collingwood, Meaford, Bracebridge, Gravenhurst, Peterborough, Bancroft and Muskoka are more likely to receive snow (>15cm); ice pellets (>15mm) for regions a little south of a line from Owen Sound east to Barrie and due east to Brockville.

5) Ice-Pellets [possibly Snow] and Ice Region #1: The Northern Lake Ontario shoreline is expected to receive a mixture of heavy ice-pellets and some ice. There is some potential that snow alongside ice-pellets could fall thereby reducing ice-pellet amount and increasing snowfall amounts in the 10-20cm range (lesser snow and more ice-pellets closer to the Western and Central Lake Ontario shoreline, such as: Ajax, Oshawa and Pickering; more ice for Eastern Lake Ontario sections such as Kingston and Brockville).

6) Ice Pellets [possibly Snow] and Ice Region #2: This region in Southern Ontario is expected to receive a mixture of ice-pellets and ice. There is some potential that snow alongside ice-pellets could fall thereby reducing ice-pellet amount and increasing snowfall amounts in the 5-15cm range (the lesser snow and more ice-pellets will be towards the Lake Huron shore-line, such as Goderich – higher amounts of snow for regions closer to Owen Sound and Barrie, than regions further away).

7) Highest ICE STORM Threat Region: This region continues to represent the highest potential for significant ice. Widespread 25mm is likely with some evidence suggesting 30mm or more by late Sunday.

8) High ICE STORM Threat Region: This region continues to represent a reasonably high potential for significant ice. Widespread 20mm is likely with some evidence suggesting closer to 25mm.

9) Moderate ICE STORM Threat Region: This region now shows some risk of an ice-storm. Early rainfall on Saturday may keep the ground warm enough where impacts for much of Saturday will be somewhat limited until early to mid evening. Impacts however by the end of Sunday could still pose a significant impact/risk. Depending on the cold air, it is possible this region may extend due west along the 402 through Komoka, Strathroy, Watford, Petrolia and Sarnia.

10) Risk of Non-Severe Thundershowers Region: Extreme SW Ontario is expected to receive mostly rain. Non-severe thundershowers are indeed also possible early Saturday. Expect a heavy and soaking rain. Very brief or slight ice is possible (1-3mm).

11) Critical Zone – Heavy Rain and Ice vs. Location Region: The Toronto region represents one of the hardest forecasts in this entire ‘storm’. Toronto will be extremely location dependent. People who live near the lake-shore will likely experience mostly rain with negligible amounts of ice. However, within the city there could be roughly 5-10mm of ice, and regions outside the city, 10mm+ of ice is possible.

This is due to a strong easterly and stiff (but shallow) wind off Lake Ontario which will create a small plume of far less freezing rain than surrounding counterparts.

[UPDATED] Which Regions are most likely to be Hit the Hardest from Ice? How Much?

25mm or more of accretion is expected.

St. Thomas
London,
Woodstock
St. Mary’s
Ingersoll
Brantford
Port Dover
Tilsonburg
Stratford
Mitchell

[UPDATED] In Southern Ontario which Regions are most likely to Receive the most Snow? How much?

Snowfall of 20-30cm, locally higher.

Owen Sound
Wiarton
Barrie
Orillia
Collingwood
Meaford
Gravenhurst
Minden
Haliburton
Angus
Bancroft
Whitney

City of Toronto – A ‘Tough Call’

For right in the City of Toronto, it is expected that a strong easterly wind will result in a slightly milder air-mass at the surface. As such, we at TCW believe the city itself should escape some of the ice, in comparison to regions further (although slightly outside) the city.

Therefore, we expect Toronto to receive mostly rain [especially the lake-shore] – perhaps still some freezing rain at times, late Saturday into early Sunday — however, rain will likely infiltrate before and after any freezing rain, thereby melting most of the ice that happens to fall and/or stick to the surrounding environment.

Nearby cities such as Mississauga, Brampton, Oakville, Ajax, Bowmanville, etc, are expected to see some ice. The closer one is directly to Toronto itself, the greater chance of more rain, and less ice. Once you reach roughly 10-15km outside of Toronto however, it is expected ice will be of concern.

Notice: QEW Region (Niagara, St. Catharines. Welland, etc)

This region is also an important place of interest due to again, slight warming from Lake Erie and Lake Ontario. This means regions very close to Lake Ontario and Lake Erie (within 10km of the shorelines or less) will receive 15-20% less ice than regions further away. However, irrespective of proximity towards the lake-shores, it is expected still, significant icing will occur.

How Bad Will This “Ice-Storm” Be?

This ice-storm has the potential to be significant. While it may be slightly less significant than if this event occurred in the typical winter months (due to stronger April diurnal heating in addition to a wet ground from late Fri to early Sat), it will still pose a significant threat to travel, trees and could lead to widespread and significant power-outages.

When Will Most of the Icing Occur?

Regardless of location, even regions who receive lesser ice accretions, the most widepsread, and heaviest icing will occur between the late morning or early to mid afternoon hours on Saturday, through Sunday. Even more specifically, most of the heaviest freezing rain will occur early to mid Sunday morning.

Monday Temperatures

Many regions are expected to transition to rain of some magnitude during Monday (slowly beginning later on Sunday).

Northern Ontario is expected to continue with further snow however, therefore temperatures although may climb above 0C, relatively humidity will be quite low and moisture will be quite high, therefore, regions will continue with snow.

On Monday Night, snow (3-7cm) may usher in towards the highlands and regions such as Shelburne and north of Toronto as cooler air returns.

Watch for widespread gusty winds for many regions up to 80km/h.

Please stay tuned, as we at TCW are monitoring this situation attentively.

Drive safe and always be alert during hazardous conditions.

For hourly and live storm updates around the clock, follow us on Twitter.
https://twitter.com/TransCANWeather

Ontario

[UPDATED 04/03/2018] Intense April Storm: Snow, Thunderstorms and Powerful…


An incoming system will bring a mixed-bag of wet snow, heavy accumulating snow, rain and thunderstorms across Southern, Central, Eastern and Northern Ontario, as well as, Quebec.

Tuesday
Through the overnight Monday, an arctic front will descend south coalescing with a strengthening area of low-pressure tracking through the Midwest United States. Temperatures will be falling across Northeastern Ontario, the Nickel Belt, Manitoulin Island, and, the Bruce Peninsula with the passage of the cold front. Light snowfall will begin in the aforementioned regions overnight Monday into Tuesday. Continuing through the day Tuesday – lasting into Wednesday. Total accumulation will range from 15-25cm by Wednesday evening.

Tuesday Thunderstorm and Rainfall Risk: Southwestern Ontario
An associated warm front looks to be staying south of Lake Erie Tuesday afternoon, lessening the arrival of a warmer airmass into extreme Southwestern Ontario. Nevertheless, the track of the low will bring rainfall and embedded thunderstorms ahead of a cold front Tuesday evening. Primary threats include embedded heavy downpours, and gusty winds to 60-80km/h.

A cloudy and wet day is expected cross Southern Ontario. Generally, 15-25mm of rainfall is expected across a large swath of Southern and Eastern Ontario. Locally higher amounts of 20-40mm is expected in extreme Southwest Ontario (with local thunderstorms) and a parts of Eastern Ontario.

Wednesday
The strengthening area of low-pressure will continue on a north-east trajectory towards Quebec Wednesday. The passage of the low will be accompanied by colder air and powerful wind gusts across Southern Ontario. Gusts between 70-90km are expected Wednesday.

Residual snowfall will continue in parts of Northeast Ontario. Some Lake effect flurries may impact the snow-belts.

What’s to come?
Cold temperatures will continue through the first week of April, with continuing below seasonal temperatures through the 2nd and 3rd week of April. There is some confidence continued snow-systems will embed themselves across the region, with the potential for snow reaching as far south as the 401 corridor.

When will the cold relinquish?
As recently predicted and outlined in our Spring/Summer forecast, it is [and we expect] Spring to be relatively cool across much of Eastern Canada with above normal precipitation. However, we do believe more moderating temperatures will begin to enter the Eastern half of the country beginning very late April, and more prominently into early May.

Please stay tuned, as we at TCW are monitoring this situation attentively.

Drive safe and always be alert during winter conditions.

For hourly and live storm updates around the clock, follow us on Twitter.
https://twitter.com/TransCANWeather

Ontario

Snow, Freezing Rain and Thundershowers for Ontario and Quebec

A Low Pressure System from Missouri Targets Ontario and Quebec This Weekend.

A quick moving Low Pressure System from Missouri will track and swing through Ontario and Quebec giving bountiful types of precipitation.

As a result of its fairly quick speed, precipitation amounts will not be overly significant, but, still pose a reasonable inconvenience depending on the region.

The heaviest snowfall will be due East of Lake Superior with moderate accumulations elsewhere across Northern/Northwestern Ontario and much of Quebec.

Parts of Ontario will be inundated with patchy freezing rain, however, significant accretions are not expected at this time.

Southern Ontario, along the 401 corridor and East to the Niagara region, can expect 10-20mm of rain with embedded non-severe thundershowers and gusty winds up to 60-75km/h.

Please adjust your driving accordingly based on the current driving conditions.

For hourly and live storm updates around the clock, follow us on Twitter.
https://twitter.com/TransCANWeather