Wednesday, 6 February 2013

Snowstorm On Its Way For Eastern Canada

Winter Storm Discussion: Feb 7-8

Meteorological Synopsis
An alberta clipper system is currently located across the dakotas with a minimum central pressure of 1009mb. Snows are breaking out already in advance of this system across the american midwest. This system is expected to move towards the eastern great lakes region on thursday, bringing heavy snowfall along with it. This is not your typical alberta clipper because it will be phasing with a disturbance currently over the western gulf of mexico. This system will move up towards the eastern great lakes and bring with it plenty of moisture from the gulf. These two storms will phase across the interior northeast leading to intense lifting along the northwest side of the system. This zone will be located along the shores of lake ontario as well as most of southern ontario from london/kitchener northeast towards toronto and ottawa. As this phasing occurs the upper trough will go negatively tilted leading to the heaviest snowfall friday morning into the noon hour. All of the major models are showing heavy snowfall across ontario and southern quebec with the european/NAM the most bullish on amounts(30-50cm from toronto to ottawa). The GFS is also showing widespread 25-40cm amounts.

Light snowfall will begin to take place thursday morning and afternoon with heavier snowfall beginning thursday night from 8-10pm as the deformation band gets well established across southern ontario. Eastern ontario will get in on the heavier snow around midnight thursday. Moderate to heavy snowfall will continue through friday morning with gusty winds and blowing snow probable. On friday morning, convective bands of snow will intensify on the south side of the storm leading to the heaviest snowfall rates from 8am-1pm, where several cm's can pile up per hour. Location of the convective and deformation bands will be key as this area will bear the brunt of the storm. 

Risks and Uncertainties
1. Thunder Snow- I think the potential is there for isolated thunder snow friday morning but it should stay isolated across the area. This process will come down to nowcasting to see if some convective bands can become established and move into the cold air. If this comes to fruition snowfall totals will be enhanced in effected areas. We will need to follow guidance from the RUC and RAP to see if this setup is possible.

2. Lake Effect Enhancement- As the system tracks to the south of the great lakes a SE, E and then NE wind will rotate around the storm centre which may lead to some higher snowfall totals along the west end of lake ontario. According to the latest skew-t charts, it does look like quite a bit of wind shear will develop between 900mb and 700mb which should limit intense LES in my opinion but nonetheless some lighter bands may organize along the lake shore with delta-t values and surface winds very favourable. Again we will have to use the short range models for guidance.

3. Snowfall Ratios- I do believe snowfall ratios will be more favourable then 10:1 across most of the province. On friday morning surface temperatures will remain below the -10C mark from toronto northwards. 900-600mb temperatures are very cold with the highest vertical velocity values at this level. I think 12:1-16:1 ratios are likely from toronto to ottawa in this setup which can increase snowfall amounts.

With all these factors in front of us here are my forecasted amounts across eastern canada
Toronto: 17-27cm
Ottawa: 17-27cm
Kingston/Belleville: 17-27cm
London: 14-20cm
Windsor: 8-15cm
Montreal: 15-25cm
Barrie: 14-20cm
Hamilton: 15-25cm
Newmarket: 17-27cm
Mount Forest: 14-20cm
Guelph: 15-25cm
Niagara/St Catherines: 15-25cm
Cobourg: 20-30cm

If you have any questions, comments, criticism or would like a forecast your area please ask and I will be happy to answer.

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