Here is the WED evening an update about the event on Saturday for the Mid-Atlantic, the Ohio Valley, and New England. For many locations, this is likely to be the last winter hurrah until next season.
WHATS GOING TO HAPPEN AND WHY?
Lets take a look at the BIG picture first to see how events develop. This image shows 500mb map across North America valid for the afternoon of March 11. There is a massive TROUGH extending from Minnesota to New Mexico and Texas. This monster Trough is going to pull down a significantly colder than normal air mass into the Plains and the Midwest which will generate a strong cold front starting on Friday in the Midwest and in the lower Plains.
By Saturday the Trough has become neutrally tilted — that is to say in a north to South orientation. I have drawn in the TROU axis in order for you to see exactly what it is I am talking about.
This map shows the surface conditions expected for 1 am on Saturday. This cold font represents a very sharp and distinct line between mild air on the east side of front vs. semi Arctic air and gusty North winds on the north side of the front. By 7 am there front is located on the line from northern Vermont — Albany — Scranton — Altoona- Martinsburg -along the Virginia West Virginia border — Blacksburg — Asheville — Atlanta Georgia.
Notice that by 7 am on Saturday morning it will be snowing in Atlanta, especially on the north suburbs and the snow could be quite moderate or even heavy. Heavy snow seems to be falling in Asheville, Nashville, Knoxville, eastern Kentucky and far southwest portions of Virginia. Moderate snow will be falling in most of central and eastern Ohio, all of West Virginia, western Maryland, central and northeast Pennsylvania and most of New York except for the Southeast third.
Meanwhile on the EAST side of the front temperatures are surging into the 50s across most of North Carolina and Southeast Virginia, 45–50 in the rest of Virginia and the Delaware, 40s central Maryland, New Jersey, New York City, eastern Pennsylvania and 30s in northeast Pennsylvania, most of New York and New England.
The key issue has to do with the transition from west to east as a cold front moves out of the Appalachians into central and eastern North Carolina, Virginia, Maryland, eastern Pennsylvania, New Jersey, and New England during the midday hours on Saturday.
This image shows a comparison between the GFS model in the European models both valid 1PM on Saturday. Notice that the European has a lot more snow on it which extends further into central and western Pennsylvania, all of central, northern, and western portions of Virginia, western Maryland, West Virginia and southwest Virginia. These two maps are VERY different and it is important because it has to do with how much if any snow is going to fall
In looking at the snowfall Maps you have to keep several things in mind.
First all areas ahead of the front on Saturday morning will see mild temps and rain. Some of the rain will be heavy perhaps even thunderstorms. This means not only will the grounds be very warm from the recent mild temps, but they will also be quite wet. Also,the transition is quite rapid so there is little chance of the snow ratio being the standard 10 to 1. ( 1 inch of rain equals 10 inches of snow).In these kinds of situations the snow ratio is going to be more like 5 :1 or 6:1; — Perhaps as much as 8 to 1 in the mountains of Pennsylvania and New York State as well as portions of West Virginia
This image is from the operational GFS model valid 18z WED with total snowfall by Sunday morning. Notice there is no accumulating snow in any portion of Virginia except for perhaps Winchester and most of central and eastern Maryland and Delaware and Philadelphia do not see any snowfall at all. The model does produce heavy snow in much of New York State and the 5 fingers area across Binghamton into the Catskills and Adirondacks. Notice the snow is much less impressive in New England because of the Heavy Rain ahead of the front. But as I discussed above this kind of snow map is not going to verify because
It is not the middle of winter
there will be rain on the ground
Ground temperature so quite mild.
Indeed, when we take an 18z GFS snow depth map which is the actual amount of snow with forecast to be on the ground, we need to see much less heavy snow in the Adirondacks and the Catskills of New York State, central and northeast Pennsylvania, western Pennsylvania, West Virginia and eastern Kentucky. These are can still see some accumulating snow, especially at elevations above 800 feet but it is not nearly as impressive.
Here is the European snow map using the superior KUCHERA snow algorithm. The map here is shows a heavy snowstorm in the western interior portions of New England, much of New York State, (except for NYC), all of northern, central and southwest in Pennsylvania, western Maryland a much of West Virginia. But again I need to emphasize that this is using a 10 :1 snow ratio which we are not going to see on Saturday morning and midday.
This is supported by the dramatic change we see when we look at the European snow depth map. Notice that all the 6…. 10… and 15 inch snow amounts that were showing up in Pennsylvania New York State and western New England are much more reasonable. Instead, we looking at anywhere from 2 to 4 inch snows in West Virginia, far eastern Kentucky, western Maryland, central and northeastern Pennsylvania, much of New York State, and interior portions of New England.
East of the mountains there may be several hours of decent snow in places such as New York City Philadelphia Baltimore Washington Charlottesville perhaps Richmond in Roanoke. But it’s not going to accumulate on any of the roads and present any kind of travel problems.
Finally let me emphasize that all of this is based upon the European model which is not done a great job this winter. The GFS model has a lot less rain changing to snow south of the Pennsylvania Maryland border. In other words the GFS models indicating that the rain could shut off during the morning hours on Saturday before the cold air gets into Maryland Delaware and Virginia so that any change over to snow in these areas will be extremely minor.