Christmas Week Snowstorm?

Let me make this clear, we are not guaranteeing a Christmas week Snowstorm, however in the month of December, Christmas week ironically gives us the best opportunity for our area to receive snowfall.

For the past month or so, our region has experienced above average temperatures which will continue for at least the next days 10. Thanks to a positive NAO/Positive AO/Negative PNA combination.

Positive NAO:

Over the past month, our weather pattern has featured a Positive NAO. This is an area of low pressure settled over Greenland, that allows warm air to intrude the eastern part of the United States. Ideally, for snow lovers, you would like to see a high pressure sitting over Greenland, because it creates a block and acts as a cold air supply at the same time. This usually leads to our bigger storms. Without it, storms have nothing stopping it from cutting inland, and floods everybody with rain.

Positive AO:

During Positive Arctic Oscillation weather patterns, the Lower 48, east of the Mississippi is commonly flooded with warm air. A positive AO leads to the cold air being trapped in Canada allowing a disconnect between the Northern Jet Stream and the Southern Jet Stream. All of our storms have been Southern Stream dominant the last month or so, with obviously no cold air source thanks to the storms originating from the south. To produce wintry weather we need the Northern Jet and Southern Jet to interact with each other preferably just south of our region. In the image below, last night’s 00z GFS represents well what a -AO looks like with the two jet streams staying separate. It is actually pretty simple when you think about it, Southern Stream produces the moisture, while the Northern Stream produces the cold air..blend the two together you get snow.
Negative PNA:

I am sure many of you have heard of the dreaded words…”southeast ridge.” The cause of this ridge is thanks to a negative PNA, which is of course what we had over the last several weeks and will continue to have the next 10+ days. A negative PNA signals a trough over the Western Part of the United States, which can often lead to wintry precipitation West of the Mississippi River and lead to numerous Great Lake Cutter Storms. Meanwhile, here in the East we are “torching” under a southeast ridge, with much above normal temperatures here. Once again last night’s 00z shows this well. With the cooler (blue) temperature anomalies representing the trough and the warmer (red) temperature anomalies representing the ridge. So yes, that is the way our current pattern looks like. We have southeast ridging taking place, with no block over Greenland. The good news is, it can only go up from here for snow lovers. This current pattern that we are in, is about as ugly as it gets. But do not be sad Winter lovers..I have excellent news for you.

Expected NAO over the next two weeks:
Taking a look at the future NAO, we remain positive until about the 16th of December when we see a trend Negative. This will allow for blocking over Greenland. This will help storms from cutting inland and also help keep colder air in place. This is one of three key players for a winter storm to develop.

Expected AO:
The Arctic Oscillation also begins to trend Negative after December 16th, not as significantly as the NAO, however well enough to allow the cold air locked up in Canada to funnel down into our neck of the woods. The combination of the active Southern Jet Stream with the colder air, may allow for wintry weather in our region around Christmas Week.

Expected PNA:

Not everything can line up perfect, right? Well in this case, yes. Looking at the project PNA forecast, it is trending negative after the 16th, which will promote a trough over the west. However, as long as we have the -AO/-NAO combo, we will be able to experience some winter storms in our region. It just has to be timed right.

Summary:

The time period to watch for a Winter Storm to impact the region is between December 21st through the 28th. Which ironically places Christmas right in the middle of that period. Now, NO model has this storm around this time, in fact they do not even go out that far. However, teleconnections do favor a storm during this time period with colder temperatures in place. The further inland you live, the better chance it will be to see snow during this time period. Coastal areas may have to wait until January for accumulating snow.

Karma would sure strike big if we see one of the warmest Decembers in the past decade, only to end with a big snowstorm around Christmas time… for now it is a wait and see type of ball game. The players are on the field..now the question is..will they deliver?

The last time the Northeast saw a big snowstorm around Christmas was the Boxing Day Blizzard of 2010. Courtesy of AccuWeather, here is look of how much snow fell between December 25th through December 27th of 2010. For the record, we are not calling for a blizzard to strike the East during the period of December 21st through the 28th, but a storm that has the best potential to produce Snowfall in the month of December to our area nonetheless. -Chris 

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