Overall, the basic setup for this winter storm has not changed, but we now have some finer details to narrow down the impacts of this storm and what to expect with this storm. The areas that remain highly volatile in this forecast remain the I-95 corridor and I expect that to be the case to the very end of this storm.
As seen on the impact map, the gradient from snowfall over 12″ to 2″ is very tight over the Philadelphia metropolitan area and eastern suburbs, central New Jersey, New York City, through Long Island. In these locations, snow, sleet, and rain can be expected. The more rain and sleet that linger on early Thursday morning, the less time for snow accumulation. Locations to the north of this area will have steady moderate to heavy snow and south of these locations, heavy rain.
The complex nature of this forecast comes down to the evolution of the 925 MB to 700 MB upper-low pressure systems. The NAM is the warmest and the EPS is the coldest. I adjusted the forecast to illustrate the fact that there will be warm air nosing into the coastal plain a bit further inland, however, I stayed away from the extreme totals either way. I have a concern here that the 00Z guidance could shift colder as well as the “northern trend” was pretty much the GFS recorrecting itself. The rest of the models on the overall storm structure have not changed, but what has changed is that the 850 MB upper-level low-pressure system cuts through southern New Jersey rather than just south of New Jersey. I should note that 850 MB temperatures over Philadelphia’s eastern suburbs warm at most to 1°C at 4 AM on the NAM and below freezing elsewhere. The warm nose is found at 925 MB and with strong lifting could be overwhelmed pretty quickly. This is a factor we need to watch very carefully as the storm develops.
So given these factors, I have introduced more sleet and rain from Philadelphia to New York City with accumulation based on the rate at which the change over will occur back over to snow on Thursday morning as the storm departs.
We will discuss this more in the Live Chat tonight at 7 PM!