There are times when looking at models and studying them all day can create a lot of confusion, especially when almost every one has a different concept of how this storm will evolve from a miss to 2 feet of snow, now that's what I call volatility.
When this happens I do two things, research and more research. I've been studying past storms and set ups that are very similar to this situation. Note though I am NOT going to copy the previous storms snowfall results because each storm is of course different.
In this case, as you can see above we have one heck of a dynamic upper level disturbance with the Sub Tropical disturbance. This disturbance is already producing strong to severe thunderstorms along the Gulf Coast, which is adding latent heat release into the equation, you know, cause this forecast isn't hard enough. So we clearly are dealing with a very dynamic storm here in the Sub Tropical jet stream.
Meanwhile, a very strong Polar disturbance is diving into the Northern Plains. This disturbance is digging south and is setting up to interact with our Sub Tropical disturbance over the Mississippi River Valley.
Now let me be clear, the key to this winter storm in terms of results will come down to when the phase of these disturbances starts to kick off. The Polar disturbance will reenforce the cold air over the Northern Mid Atlantic and New England while the Sub Tropical disturbance provide the moisture transport and mid level instability. We can clearly see that when the two disturbances phase, the cold air floods to the coast, the precipitation shield explodes, and locations to the northwest and north of the storm track end up with a very heavy snowfall. So an earlier phase of these two disturbances will lead to snowfall totals being increased along the coast, especially for southern New Jersey.
I think by tonight we'll see stronger agreement in the models on the overall 500 MB pattern and when this storm will phase. Of course, there will be high volatility still in this forecast, but I expect the ECMWF and GFS to be able to lock into an agreement with a storm less than 66 hours out. Of course, that's not always the case.
Another factor to consider with this storm that I just can't forecast this far out is mesoscale interactions. I have several factors here that are showing up that has me concerned. There is the fact that strong frontogenesis is showing up at the mid levels from Philadelphia to Boston that could significantly enhance snowfall totals above current forecasted values and lead to a faster change over for the Philadelphia metro due to dynamic cooling. There is also the threat for significant instability leading to thundersnow in this storm that could produce snowfall rates at 1 to 3 inches per hour. I can go out but then I'd pull out some calculus equations, you don't want that.
So here is the overall forecast considering when the phasing will occur and the overall evolution of the storm.
For eastern Pennsylvania, I think most of these locations will see just plain snow, mixing with sleet at times. However the best dynamics will be to your east, thus the 3 to 6 inch snowfall. If this storm is able to back build further west as the ECMWF Ensembles suggest, you can pile on a lot more snow, but I am not ready to go that route yet.
For locations along the northern Delaware River, much of northern and central New Jersey, New York City, and Long Island; I am looking at 6 to 12 inches with potential for locally higher amounts to account for mesoscale banding issues. There will be mixing issue here, especially with sleet and rain on Friday afternoon before the precipitation goes over to all snow on Friday night and piles on.
For the Philadelphia metro to the central New Jersey coast, roughly Ocean County, New Jersey; I like the idea of 3 to 6 inches of snow with an icy mix. The precipitation will start as light snow and sleet, mix with and briefly change over to rain and then go back over to snow on Friday night towards Saturday morning. The faster the change over, the higher the snowfall potential.
For much of southern New Jersey, I think the warm air wins out for much of this storm but loses in the end with a change over to snow on Friday night into Saturday morning. Again, the faster the change over, the higher the snowfall totals.
Finally, for the eastern Hudson River Valley through Connecticut, get ready for a big snow storm with all snow expected and the best lifting areas expected. The forecast for 12 to 24 inches with locally higher amounts is a good bet here. These locations are going to have the highest snowfall totals in the region unless something drastic happens over the New York City metro with a mesoscale lifting phenomena.
This forecast is going to be touch and likely another NOW-casting event. Get me the coffee! One thing is for sure, be prepared for coastal flooding with this storm and wind sustained at 15 to 30 minutes with gusts over 40 mph. Yes, blizzard like conditions will be possible with this storm as visibility falls below a mile at times. I expect the storm to start to move in on Friday morning with scattered snow showers, however the brunt of the storm will be Friday evening on through early Saturday morning.
Looked at my notes and on the night of Feb 9, 2010 moderate to heavy snow accumulated 9 inches but around 5 AM on Feb 10 the precip changed to rain with temps around freezing.
This was not expected to occur this far from the shore. However the rain changed to snow around 10 AM here in Delaware County, Pa and temps fell into the mid 20's and by afternoon wind and heavy snow was incredible. The final totals were around 20 inches as backend snow did not end until around 9 0r 10 PM.
Of course just four days earlier we had over 25 inches on Feb 6 2010.