“The moon on the breast of the new-fallen snow, gave a luster of midday to objects below…”twas-the-night-before-christmas

We are another week closer to Christmas, and another week closer to finding out if things will be white, or green.  Unfortunately, a white one may be getting a little tougher.

Here is my probability outlook (White Christmas is defined as 2 cm or more on the ground at 7:00 am on Dec.25th, as per Environment Canada):

white-christmas-two

How can it not be white – we already have snow?

If Christmas was next weekend, then yes, it would almost be 100% chance for everyone in Ontario to have snow.  However we have a couple upcoming storms that want to track west across the Great Lakes.  One is on Dec.18-19th, the other around Dec.22-23, as well as a possibility of something around Christmas day.  If all these storms did work out most locations would have a foot or more of snow (not including the Lake Effect regions which already have 2 feet of snow in spots).

The upper level patterns wants to return to the pattern back in late November early December with upper level atmosphere block trough out west,  and the Southeast Ridge in the east.  These upper atmosphere conditions are common in a La Nina type winter like ours, and force storms from the west to our area.  The jet stream (upper level steering winds) typically takes the path of least resistance, and goes around these areas. The below is an example of what occurs:

trough-ridge-map

Unfortunately too big and strong of a Southeast Ridge can cause storms to really cut west and bring rain and warmth to our region, like the below:too-big-ridge

On the other hand cooperation with the Southeast Ridge staying small and in place helps our area obtain more storms and snow as it forces them to our area and away from the US East coast.

The Outlook

The long range models (weeklies) had been maintaining cold conditions right up to Christmas Day, but slowly starting to trend warmer.  We still need another week to see their continued trend.  If things can stay muted and not extreme in either direction, we could have a better chance.  Unfortunately when you have this type of pattern set up, you have to wait until a day or two before the event or storm to truly know what will happen.  A lot will depend on what happens with the upcoming December 18-19th storm and the conditions behind it.

However at this point it’s safe to say a warm up is coming from December 22 to December 30th.  How much, how extreme and how many rain storms come with it is still to be determined.  We should have a better idea come my part 3 update next Sunday.  For now, enjoy the snow we have coming.

 

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