From DT @11pm last night: FIRST GUESS MAP FOR JAN 19
To begin with… for anybody in the state of VA this is a non-event. Almost the entire state will miss out on the snow and I expect that is going to be the case for Washington DC as well. There might be a 1 inch snow accumulation in the far NW corner of VA. BUT this will be a pretty good snowfall for most of WV. The 6-inch band of snow in the Greenbrier Valley may end up being more like 9 or 10 inches because of the high snow ratio.
The HIGH SNOW RATIO due to the arrival of the Arctic air is going to be a factor in the storm which was going to make the snow forecast particularly tricky. Remember that most of the snow amounts on the models are based upon a 10 to 1 snow ratio. That is to say 1 inch of rain equals 10 inches of snow. But in Arctic air… the snow ratio goes up and it can easily approach values of 13 to 1 or 15 to 1.
On the other, as I have stated earlier, this is a VERY FAST MOVING ystem. So we are not looking at a long duration event here. The upper level energy and the surface LOW not get together in time to produce a big Coastal storm.
Looking at the latest data I do see some interesting Trends which are occurring in the short range models. The system continues to look quite innocuous and not significant on the 18z WED and 0z THU op- GFS. And the 12z and 18z op-European models aren't showing much of anything either.
However the high resolution short range models are showing something interesting. The 0Z THUR 3km NAM shows an explosion of moderate to heavy snow developing in central PA pushing into northern NJ by midday on Friday. As the upper level energy and the surface LOW finally begin to coalesce the snow becomes extremely heavy Friday afternoon for several hours in southeast PA including the Philly metro area all of NJ NYC LI across southern Rhode Island and the extreme Southern portions of Mass.
This is also supported by the high-resolution mesoscale HRRR model which shows more the same. It also develops a burst of extremely heavy snow from northeast MD into northern DEL (including Wilmington) into the Philly metro area and then up into northern NJ and NYC which expands later on Friday afternoon across all of Long Island coastal CT and again the far southern tip of Mass. .
If these snow rates actually materialize the next updated snow map will probably have 6 inches into a good portion of Central and southern NJ Again I am worried about the snow ratios producing amounts closer to 8 inches portions of eastern PA including Lehigh Valley and the Philly Metro area.
