#cbcmar Good evening and thank you for your patience. I jsut wanted to write a brief discussion on Mondays system. On Sunday a centre of low pressure moving out of southern Ontario is expected to trigger the development of another low pressure system around the northeastern US. The two systems merge and track towards northern New Brunswick on Monday, with the system tracking into the Gulf of St. Lawrence by early Tuesday morning. Being to the east of the system the bulk of the Maritimes will be on the warm side of this low. In fact the system will serve to strengthen the southerly flow bringing warmer air into the Maritimes that starts on Sunday. Most of the region is likely to experience a moderate rainfall and high wind type of day on Monday. Exceptions may be the extreme north of New Brunswick which may see accumulating wet snow. Additionally as the system moves out Monday night into Tuesday morning the back edge of the rain may turn over to snow (see the maps attached). Province-by-province heres what I currently expect: Periods of rain with Campbellton to Edmundston starting as snow, mixing to rain during the day, then turning back to snow Monday night. Rainfall amounts may be as much as 20 to 40 mm for parts of the province. From Campbellton to Edmundston as much as 10 cm of snow may accumulate before the turn to rain, then an additional 5 cm when the change back to snow happens. As the back edge of the rain turns to snow across New Brunswick Monday night into Tuesday morning other areas may see 5 cm of snow. Winds will be southerly and high on Monday. Some gusts of 60-80 km/h are possible around the coast, 50-70 km/h inland. Periods of rain with totals in the range of 15 to 25 mm on Monday. The rain will be accompanied by some southerly winds that may gust as high as 60 to 80 km/h. If the system slows down enough so that the back edge of the rain is still around late Monday night it may turn over to some wet snow with accumulations of near 5 cm possible. Periods of rain with totals in the range of 20 to 40 mm on Monday. The rain will be accompanied by south southerly winds that may gust as high as 60 to 80 km/h. While not looking to likely, there remains the possibility that the back edge of the rain turns over to wet snow Monday night into Tuesday morning. Should this happen snow accumulations of 5 cm would be possible before it clears. There has been, and continues to be, a high degree of uncertainty in the specific details of rain and snow with this system. Ive posted an image along with this write up illustrating 3 different runs of the same forecast model (GFS in this case and the runs in order are from 8 AM Thursday, 8 PM Thursday, and 8 AM Friday) and you can see the snow amounts are bouncing run-by-run. There are similar discrepancies with other long range forecast models. Some of the issue is that if the low tracks even slightly farther west the warmer air will be pulled completely across the Maritimes so that even northern New Brunswick essentially just sees rain. The other concern I have is with the speed of the low as it moves into the Gulf of St. Lawrence. Some forecast models move it out fairly quickly, others have it linger as it enters the Gulf. Should it linger this will increase the odds of enough cold air wrapping in behind the low to turn the back edge of the rain over to snow Monday night. That may lead to some accumulations of 5 cm of snow Maritime wide by Tuesday morning. Certainly a tricky system to deal. Ill update as I can. Enjoy the weekend.
Posted on: Sat, 17 Jan 2015 00:22:52 +0000
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