Saturday Update: Nusiance Snow Event Tomorrow, Major Storm Later Next Week

Good morning. Many areas off the coasts will see their first snowfall tomorrow. For most it is more of a nuisance event , but some areas will see several inches. This will be very elevation dependent. Our eyes then turn to a major storm that will impact the region and the end of next week. Winter weather will be in the cards for some. 

Summary:

• A light to moderate snow event impacts the interior Sunday
• mostly a nuisance with some moderate accumulations over the mountains

• All eyes then point for a potential major storm later next week
• Focus looks to be off the coasts NW of I-95 for winter weather
• Big potential with this system

• Our pattern change has arrived. There will be colder than normal temps and multiple shots at snow through Christmas this year. 

Starting off here is my updated forecast for tomorrow...

Outside the darkest zone, this is a nuisance event. If you do not live in an elevated location, there is not much to worry about with this system. Rain will fall in areas not shaded to the south. Timing is tomorrow mid morning into the evening. 

Moving on, we have a potential major storm to track for the end of next week. The atmosphere is setting up something known as a blocking pattern. This mean energy gets clogged up under high pressure along the eastern seaboard. With cold air to work with this time, there is a good chance for snow off the coasts.

Lets take a look...

A big storm forms over the west early to middle of next week...

Normally this would cut into Canada, surge in warm air and eventually rain into our area. However, there is a massive block or high pressure sitting to its north. This will force the storm to stop and reorganize itself over the eastern seaboard. Below shows this blocking pattern...

This is a very uniquie pattern we do see often in December. When there is this much high pressure to our north, and the the mild air is also blocked off from the pacific, storms can slow down and blow up near eastern seaboard.

The european model is the most agressive with this system and does exactly this on Friday and Saturday..

Think of it as the storm energy that gets blocked to our west "slides" under the high pressure system then restrengthens off the coast. That was what you are seeing above. The key is going to be the exact placement of this. As of now I like the idea of a potential major snowfall for areas NW of I-95 especially into PA, NY State and interior New England. There will be mixing issues the closer you get to the coast.

If this system misses us it wont be missing north it will be missing to the south if the block ends up being too strong. That is what the GFS shows...

This seems wrong to me. I do not trust the GFS lately in the long range. It gets much better in the short range (model was just upgraded and showring some issues). 

Now heres the key. What fits the pattern? A few days ago models where cutting this storm into the lakes. Now all of a sudden they are turning it into a coastal storm. This is simply the model adjusting to the pattern, not the other way around. As the function of time decreases, the model figures out what should happen given a patern like this. Below shows the adjustment in the GFS model over last several days. Pretty extreme, notice how it adjusts the storm track as it figures out there is a block to the north. This is a good lesson in long range forecasting. The models usually adjust to the pattern not the other way around.

So bottom line is this, Major potential is on the table for end of next week and the period to follow through Christmas, which can feature more storm threats. The pattern change discussed has arrived and it really can deliver a December we haven't seen in a decade. Stay tuned.