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Hey Folks,
For the second time in two weeks, we have a system developing off to the South, which will work North and pass JUST East of the Avalon.
Like last week, this system will have Snow on it's West side and as a result, the exact track of the Low will be critical. And also like last week, I'm watching the forecast models try to nail this thing down, with not much success so far.
On Monday, only 1 of the main 3, go to forecast models for this region (American GFS, European ECMWF & Canadian GEM) had a track close enough to bring Snow for us. On Tuesday they all shifted West, with a track close enough to drop 8-15 cm. This morning, they've shifted back East again, with a track which would drop only 2-5 cm.

**3PM Update: The Canadian and American afternoon forecast models runs have shifted back West again!!! Track close enough for a 15-20 cm Snow event over the Eastern Avalon. 
I received many questions last week and I'm already getting the same questions this week. Why do the forecast models have such a tough time with these Coastal systems? Well, it's not just one reason...
-First, is the fact that these systems develop rapidly. Here we are, 48 hours away and our potential Friday system hasn't even developed yet! The Satellite below shows only the Cold front where the development will take place...

Forecast models will obviously have a harder time forecasting something that hasn't developed, compared something that's been developing for a few days. Storms like a Colorado Lows, which comes at us from the Southwest, or an Alberta Clipper are well in view, days before they reach us.
-Another reason, is the area where these Storms develop. This system will start to come together on Thursday, however the area it which is begins to form will be well off the Coast in the Atlantic Ocean. Well offshore, there is a big time lack of weather data. A few offshore buoys (which are the yellow and red dots below) do provide a bit of surface data, but upper atmosphere data is even more limited. 


Those gaps in data mean forecast models have a better chance of being wrong, even after the Storm develops. Storms that form over the Continent are of course sampled by numerous weather stations and weather balloons in the upper atmosphere.  
-Finally, even as the Storm approaches, a little track change, means a big difference in Snowfall amounts. Here & Now's Senior Producer and former Host, Doug Letto, loves to tell me the story about an old neighbour of his, who was in his 70's at the time. He was a Weather enthusiast and always used to say "Doug boy, with these Northeast Wind Storms, you never know, you could get 5 cm or you could get 40!" 
And there really is quite a bit of truth to that. Quite often the distance between who sees 5 cm and 30 cm is only about a 100 km or so. Proof from yesterday's Canadian model, which has the Western half of the Avalon in the 5-10 cm zone, the Eastern half in the 10-15 cm zone and only about 100 km offshore, amounts of 20-30 cm.  
 -So as this system approaches, we will all once again need patience... especially me! These systems take time, time to develop, time for the forecast models to get a handle on them and time for us forecasters and Meteorologists to figure out whether the forecast models are correct or not.
As always, stay tuned...

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