Winter Storm Forecast Discussion:
A 996mb storm is currently located across SE new mexico and is expected to move northeastwards towards the lower great lakes region. Snows are already breaking out across the eastern rockies as the storm taps into cold air from the north. A swath of snow will develop along the rim of the cold air which will effect southern and eastern ontario starting early wednesday morning and continuing into thursday for southern quebec. The storm is expected to occlude as it does so which will cause a prolonged period of wintry precipitation (12-24 hours). Heavy wet snow will begin to develop across southern ontario by 3am wednesday as boundary level temperatures stay well below zero. Moderate to heavy snow will work into the ottawa/montreal regions by the afternoon hours. This type of snow will be quite moisture laden sticking to any exposed surfaces including trees and power lines. Power outages will become a concern from kitchener through the GTA and up towards kingston as winds gust up to 60kph at times. By wednesday evening precipitation will begin to taper off across southern ontario but light to moderate snowfall may add an additional accumulations wednesday evening/night.
Forecast Risks and Uncertainties:
TROWAL- A trough off warm air aloft will form south of lake erie allowing for intense lifting to occur along the west end of lake ontario. The location of this deformation band will determine who picks up 30cm+ from this event. The 0z european run showed this band pivoting over the GTA but the current run has shifted this 25-50 miles further NE. If the next run of the euro returns to its original ideas accumulations will have to be taken up along the west end of lake ontario.
Dry Slot- Some models are pointing towards a dry slot potential across the area. Dry air intrusion will occur because of the strength of the storm. The strength and location of the secondary low will determine the strength and duration of this. If the secondary tracks further west we will see longer duration precipitation moving into S, E On and quebec. I think most areas from kitchener to kingston see a primary thump of 14-20cm from the main band with additional wrap around precipitation afterwords. Ottawa, montreal and SW ontario will see slightly weaker returns on the primary band.
Temperatures- I think boundary layer temperatures are supportive of predominantly snow from london to montreal and ottawa. I think southern niagara, windsor and areas directly along lake ontario will see some mixing but most of the province should stay as all snow. The heavy precipitation caused by the storm will help cool the column especially in the heavier bands. Ratios should stay between 8-10:1, being highest at night or when the sun angle is lower.
With all these factors in front of us here are my forecasted amounts across the effected area:
Toronto downtown: 15-25cm, winds gusting to 60kph
Toronto (St Clair to Steeles): 17-27cm
York Region: 20-30cm
Bruce/Walkerton/Mount Forest: 5-15cm
Montreal North: 15-25cm
Montreal South Shore: 10-20cm
St Catherines: 13-23cm
If you have any questions, comments or would like a forecast for your area just ask away! I will update snowfall amounts if needed tuesday evening.