A Snowy Start to the Weekend

Brad Leave a comment

A compact shortwave moving across southwestern Manitoba will bring snowfall to the Red River Valley and areas west today and tonight.

500mb vertical velocities for 18Z today

500mb vertical velocities for 18Z today. This image shows an area of lift (air moving upwards) over the Red River Valley by noon today. This will contribute to the generation of snowfall over the area.

A broad area of moderate lift ahead of a shortwave is producing an area of snow that will push eastwards into the Red River Valley by late morning, although the exact eastward extent of the snowfall will be quite tricky to nail down as the lift creating the snow will [somewhere near the Red River Valley] slow down and pivot to the south as the shortwave dives into the Dakotas.

Before we get to snowfall accumulations, we’ll quickly cover our temperatures for the weekend. Because no surface fronts are associated with the weather we’ll get (all of the forcing is aloft), temperatures through the Red River Valley will not vary too much from yesterday. Daytime highs through the weekend will vary from about 0°C to 2°C. Overnight lows through the weekend will generally sit around -4°C, plus or minus just a couple degrees.

Onto the snowfall! Snow has spread into SW Manitoba overnight, bringing light to moderate snow that will last another 12-18 hours. Snow will begin to push into the RRV by late morning, however the eastern extent is difficult to pin down with amounts likely diminishing somewhere over the eastern Red River Valley into the Whiteshell. One of the biggest challenges to this system will be the SLR: snow-to-liquid ratio. This is a measure of how much snow a certain amount of water will generate. Typically on the Prairies, SLRs tend to be in the 10:1 to 15:1 range; if you had a 10:1 SLR, that would mean that 1mm of liquid water would produce 1cm of snow. If it were 15:1, then 1mm of liquid water would produce 1.5cm of snow.

Over southwestern Manitoba models are predicting generally 10mm of precipitation, over the Parkland regions of Manitoba about 5-10mm is expected to fall and over the Red River Valley, 2-5mm is forecast. Best guidance is showing SLR values of around 11:1, which would result in the following snowfalls:

  • Southwestern Manitoba: 11cm
  • Parkland Manitoba: 6-11cm
  • The Red River Valley: 2-6cm

The greatest uncertainty with this system is how far eastwards the snow will push, but in general, this will be the first accumulating snowfall in quite a while over Southern Manitoba. Winds will be light throughout this event, which will prevent blowing snow from being a problem, but drivers should be prepared for the potential of poor driving conditions through the Red River Valley and areas across the west and southwest portions of the province tonight through tomorrow morning.

Some lingering light snow will be out and about through the rest of the weekend, but no significant snowfall is expected.

Small Warm-Up

Brad Leave a comment

We’ll see warmer conditions for the beginning of this week. Temperatures may even climb above normal!

Shower activity on Monday

Light rain over parts of Manitoba on Monday

While Sandy hits the eastern coast of the United States hard during the early part of this week, the weather in Southern Manitoba will be very quiet. Temperatures on Monday will be in the mid to upper single digits in Southern Manitoba, which is near to slightly above the average daytime high of 5C. In terms of precipitation, a passing upper-level disturbance on Monday will generate cloud and some light showers in Southern and Central Manitoba. The most favoured area for shower activity is Western Manitoba, though other parts of Southern Manitoba stand a small chance of seeing a light rain shower. On Tuesday a passing trough of low pressure may once again generate a few showers, though they will be very light and scattered in nature. Tuesday’s high temperatures will be very similar to Monday’s, once again being in the mid to upper single digits.

Halloween Wednesday will be a chilly day, as cool north-westerly winds flow out of a surface ridge over Saskatchewan. Temperatures during the daytime will only be slightly above zero, but will drop near to or slightly below zero by the trick or treating hours. No precipitation is expected on Wednesday.

Conditions through late week will remain fairly seasonable, with daytime highs hovering near to or slightly below 5C. No major shifts in our weather are expected in the foreseeable future. In general, seasonable to slightly below seasonal values are expected over the next while.

Elsewhere in Weather News: October 27th, 2012

Matthieu Leave a comment

Hurricane Sandy – A Unique Storm

Even though hurricane season might be nearing the “official” end (November 30th), the largest and most threatening storm of the year is yet to come. This past week, what could be a historical hurricane for the United States, spun up in the south-east Caribbean and has already caused major damage to surrounding countries such as Cuba, the Bahamas and Haiti.

After initially making landfall near Kingston, Jamaica as a category one (winds of 130km/h), Sandy quickly skipped across the island to make a second landfall on the north-east side of Cuba, leaving significant damage in its wake. In Jamaica about 70% of the island lost power, curfews were issued and all public services closed until the coming week. Three lives were lost in Jamaica and the damage was significant; roads washed out and banana farmers reporting losses to over 50% of their crop. Haiti and the Dominican Republic were not left untouched either, with severe flooding in the deforested regions – it was predicted that widespread rainfall accumulation ranged between 200-255mm. Unfortunately, 10 deaths were related to Sandy in Haiti and three in the Dominican Republic, mainly due to extensive flooding.

Jamaica storm surge

House in Kingston, Jamaica gets inundated by water associated with Sandy’s storm surge. (Source: AP)

Sandy, fuelled by very warm waters, quickly strengthened to a category 2 hurricane between Jamaica and Cuba. With a second landfall in north-eastern Cuba, Sandy brought more grief as it ripped roofs off homes and damaged local coffee and tomato crops. It was also reported from Cuban state media that the hurricane was blamed for 11 deaths in the country.

Continuing its track, though now weakened to a category one hurricane, Sandy moved in a north north-easterly fashion into the Bahamas where similar damage to what was observed in Jamaica occurred as well as an additional three deaths.

Earlier in the week some weather models showed Sandy curving out to sea after moving out of the Bahamas, thanks to a large trough swinging through the Eastern US. Unfortunately, this will not be the case and all of the models now show a landfall somewhere on the East Coast – more precisely somewhere between Maryland and Southern New England. With Sandy being an unusually large storm, tropical winds spanning 450km from its centre, this storm will have to be taken very seriously by residents in the concerned area on the East Coast. The biggest problem with Sandy is that as it nears landfall, its south-easterly flow in the top-right quadrant of the storm will bring significant storm surge to the areas north and north-east of the storm. Models also predict up to 250mm of rain in some areas along the coast and sustained winds that will be at or near tropical storm force extending a significant distance out from the centre of the storm. The storm will also bring large amounts of snow into higher elevations of West Virginia. A state of emergency has been issued.

Sandy

GFS 850mb analysis of Sandy at 7am Tuesday morning, shortly after it makes landfall. Circled area is area most likely to have high snow accumulation, red square is New York City and black shoreline is the area at risk for severe storm surge. (Source: Twisterdata)

Most models predict a landfall on the East Coast just south of New York Tuesday next week, with lasting effects for many days. Updates will be forthcoming as the event unfolds this coming week.

Cool Weekend Ahead

Brad Leave a comment

Arctic air will keep temperatures cool through the weekend with daytime highs some 5-7°C below normal. Scattered flurries will be common through the weekend, while a significant lake-effect snowfall event will impact portions of the Whiteshell and Eastern Manitoba.

850mb Temperatures Valid Saturday Morning

850mb temperatures valid Saturday morning. A deep pool of Arctic air will flood across the Prairies this weekend.

As the low that brought rain to Southern Manitoba the past few days pushes northwards into Hudson Bay, it will intensify quite considerably1 and induce a strong northwesterly flow over the Canadian Prairies. This cold air will likely produce isolated scattered flurries, however the largest effect will be strong lake-effect snow bands, primarily from the basins of Lake Winnipeg. These lake-effect bands will mainly effect the Bisset region and slowly push northwards towards Berens River as the winds back slightly to westerly through the weekend. Substantial amounts of snow are possible with these bands, with the potential for anywhere from 15-30cm of snow possible in areas that see a band have a particularly long residence time over them.

Daytime highs over the next few days will sit within a degree or two of 0°C, with overnight lows near -6 or -7°C. No significant improvement in temperatures is expected until potentially early next week as a low pressure system moves through the Central Prairies and brings ever so slightly warmer air back to the region.

  1. It’s currently forecast to deepen from a 982mb low this morning to a 967mb low tomorrow morning. ↩