Friday Morning Storm Update: Details Becoming More Clear, Updated Forecast

Good morning. Below is my updated forecast for Sunday night into Monday's Storm. Overall, this is an interior winter storm off the coasts. For some areas its mostly rain for others its mostly snow and ice. The cutoff will be fairly sharp and will depend on how quickly the storm draws in warm air. Those details still are unclear and I made my estimate on how this will play out. There will be two more forecast map released tomorrow and Sunday morning with adjustments if necessary. I will say regardless of who gets what, the storm will be strong and winds will be gusting for most areas.

Lets take a a look. My updated map is below. Unlike yesterday, I tried to start putting more details and narrowing in the zones of snowfall potential....

You can see above how the accumulating snowfall and ice is for interior areas. For any zone in green shades I expect more wet conditions than frozen conditions outside potentially parts of CT and RI.

This storm will be quite strong and precipitation very heavy at times. For the areas that see accumulating snowfall on this map, I expect that snowfall will pile up fast on the front end of this storm before changing over to ice. The peak of this storm will be Monday morning. By the afternoon things will start tapering off for many.

Looking at our evolution of the storm, I will use the GFS model below to illustrate. It not exactly what I think happens but close enough at this point in time...

On early Sunday morning we will have very cold air over our region due to high pressure in control ahead of our developing storm south of us...

This storm will then try to rapidly develop up into this cold air and high pressure. The result will be the high pressure will slide off to the east and the cold air will start to errode. A big variable to this forecast is how fast that happens. Models often times overestimate how quickly cold air gets broken down. Given the air will be quite cold Sunday morning vs averages we need to see if models adjust. 

At the surface our storm then starts to move into the area Sunday evening. Notice below how the warm air surge on the eastern flank of the storm...

By just after Midnight the storm is underway for many...

This is a critical forecast period. Notice the rain along the I-95 and the snow just to the NW of the fall line in NW NJ etc. This makes sense to me and follows historical examples of similar storms. This is where I expect the snow to accumulate in the broadline zones on my map. A few hours late just before daybreak notice the rain advancing more north....

This should happen as the warm air surge will be pretty strong. However the question is how much precipitation falls as snow before this. For NW NJ NE PA I think several inches will. I will also include part of CT in this mix as well. For the far interior this is a full out snowstorm at this time.

Below, you can see the warm air surge on the models as indicated by the non grey colors. This will happen the question in how far does it advance and how quickly...

The reason why this will happen is our upper level low is to our west. In simple terms this means warm air is supported to move in...

The biggest forecast detail I am looking at next 48 hours is how far east the upper low gets and if there is any resistance from the cold air to the north. If there is just a little shift in that green circle you see above it could be big changes at the surface in terms of snowfall placement. I tried to anticipate some shifts in my forecast.

Thats all for now. May cut a video later tonight to break this down. The next 24 hours of data coming in will be key.