Tuesday: Winter Storm Chances Increasing for Sunday-Monday

Good morning. To continue from where we left off yesterday, data continues to support a winter storm system Sunday-Monday along the east coast. As always, many details need to be worked out but there is enough on the table to start to take this seriously. I have updated the winter storm outlook banner to moderate confidence. 

Summary:

• Chances for a winter storm increasing Sunday into Monday
• Target region is northern Mid-Atlantic (Philly northward) into New England
• Threat type is mixed precipitation changing to snow for northern Mid-Atlantic and all Snow for New England
• this type of storm setup is New England biased
• Finer details need a few days to be worked out

So where we left off yesterday I showed the image below...

It is important to sniff out the overall pattern before you look at what is happening at the surface. What really drew my attention to this period was the presence of signifigant atmospheric blocking (50/50 low) which causes jet stream to buckle and high pressure to lock in over southern Canada (due to confluence or air coming together at high altitudes).

I have seen many times where the models struggle to handle the interaction between an approaching low pressure system and the locked in high pressure to the north in situations like this. In many cases the models are too aggressive driving the low too far into the high pressure. What normally ends up happening is the low/storm slides under the pressure area and redevelops off the coast sooner than the models initially indicate. I believe this is what we are now seeing the models start to pick up on.

Lets take a look at the European ensemble model...

Looking above, the image on the left is new model the one on the right is from 24 hours ago. Notice in the circled region the high pressure or orange color is stronger on the new run. The result is the storm undercuts sooner and maintains a little more cold air over the region...

As you can see the storm is forced to redevelop. This whole threat will come down to how soon this occurs. If it happens later its a warmer storm and just New England focused. If it happens sooner then its more winter weather to the south. This is what we need to work out over the next few days.

It really is too early to discuss snow amounts etc as this whole thing still can shift north or south. If we look at historical setups right now the highest probability for accumulating snowfall is in this region...

I do think we can see accumulating snow more south of this but at this time this is the best conservative forecast of where to expect the most impacts.

Stay tuned, daily updates and videos (if necessary) on tap.