Clipper Discussion...A New England Special...

Hello this is Junior Meteorologist Kyle Elliott...and a clipper will affect the region from the Ohio Valley through the central Appalachians to the Mid-Atlantic and Northeastern parts of the U.S. between tonight and Tuesday evening. Currently, the upper air disturbance that is providing incredible dynamics for the rather moisture starved storm is situated around St. Louis, Missouri. Over the next 24-36 hours, this disturbance will track through the Ohio Valley to a position over West Virginia by tomorrow afternoon. Along its path, a swath of 3-6" of snow will occur over Kentucky, northern Tennessee, southern Illinois and Indiana, and right into west Virginia and the mountains of western Virginia. From there, though, models are still all over the place concerning eventual track of the surface low that will develop off the coast of the Delmarva and New Jersey tomorrow evening into tomorrow night. Also, models differ greatly on the amount of Quantitative Precipitation that will occur from Pennsylvania into New York and the remaining northeastern states. The GFS wants to deepen the surface low quickly and hold an area of precipitation back into Pennsylvania and New York for about 4-6 hours longer than models such as the NAM, Sref, and CMC. The Euro is along the same boat as the GFS, along with the WRF model that is run at Millersville University. Others models, such as the high-resolution NMM and ARW, are more in the camp of the NAM and CMC in that they bring an area of warm air advection snowfall through PA and New York but wait until later to explode an area of precipitation into CT, MA, NH, and Maine. Basically, the models are pretty clear-cut on what will fall west of the Appalachians, and also that Massachusetts, southern and central New Hampshire, southeastern Vermont, northern Connecticut, and Maine will see a fairly decent 6-12" snowfall from this storm. The major differences between the modes occur in the area from northern Virginia into Maryland, Pennsylvania, New Jersey, and New York State, along with the NYC metro area. Also, precipitation type is a concern in the I-95 cities as timing of the precipitation might cause rain and sleet to cut down on any snow accumulation that might occur. If snow commences around 2-5 PM from D.C. to NYC, then rain and sleet will likely mix in as we will be at the height of afternoon warming. If the precipitation holds off until, say, 5-8 PM from Baltimore to NYC, then precipitation would have a better chance to fall as snow as surface temperatures would have a chance to cool to around freezing before snow commences. Finally, the other major differences between the models is that some try to bring a surge of warmer air aloft into the cities, too, which would cause freezing rain and sleet. Some suggest a mere .1-.3" of liquid equivalent precipitation between Baltimore and NYC, while others like the GFS suggest a bolder solution with .35-.6" of liquid precipitation falling in that corridor. So, what do I as a forecaster make out of this? Well, considering the model guidance and what I have witnessed in the past in situations like these, I have come to a conclusion which takes a blend of the guidance and adds some of my own input as well. Granted, this is a very fine, delicate situation which, if the low pressure takes a slightly different track and is of a different intensity than forecast, snowfall amounts could be drastically different in areas as the heaviest band would be shifted 50 miles either side of what is forecast currently. In all honesty, I can only guess as to the eventual solution and due my best to apply what I know to make what I believe is the best forecast I know how to come up with at this point. Things may change, and they will if I am off in my thinking by only 50 miles or so. I have come, though, to conclude the following points about this system as I make my final forecast:

1) I believe the best snows will occur from the Poconos through New England. I am leaning toward the NAM as far as PA and NJ are concerned, along with Maryland and the I-95 cities, in that I believe precipitation will occur in merely a 4-7 hour burst from NYC to Washington, D.C. The low pressure along the coast, in my opinion, will develop somewhere off of central and northern New Jersey instead of the Delmarva, and the upper level low will track south of the Mason/Dixon line through approximately Baltimore, Maryland. South of that track, an all-snow event can pretty much be ruled out as rain and sleet will ultimately mix in. North and west of a line from Frederick, to Parkton, to Coatesville, PA, to Trenton, NJ, to Poughkeepsie, NY, to Hartford, CT, to Worcester, MA, and Portland, Maine...an all-snow event is almost a given at this point. Along and south of that line, though, sleet and rain may have to be dealth with along with the snow as I believe a track such as is occurring with this storm will bring a treacherous mix to cities such as Baltimore, Philadelphia, NYC, and possibly Boston...though Boston is a tricky forecast. Anyway, I believe a general 2-5" accumulation will be found across northern Maryland, southern, central, and eastern PA, into northwestern New Jersey. In the Poconos, 5-9" should fall...and those accumulations can be increased to 7-12" across southeastern New York, northwestern CT, VT, western MA, NH, and Maine.

2) In my opinion, this is NOT an I-95 special. As I stated above, surface temperatures, along with warming aloft, should cause mixing in the cities. Therefore, I believe D.C. will not see more than a trace-1" of snow accumulation, Baltimore sees 1-2", at best, and Philadelphia sees the same as Baltimore. In NYC, snow will commence but should mix with rain and sleet at times during the height of the storm. As the low pressure moves northeast from NYC, though, precipitation could once again change back to sleet on the backside of the storm. If enough moisture can wrap back into the city, then additional snowfall accumulation could be had. At this time, though, I am going to go extremely conservative in NYC and say that a dusting-2" is the most likely call at this point. One would have to travel but 80 miles to the north of the city, though, to find much higher accumulations on the order of 6-10"...

So there you have it...my thoughts on the storm. I may be wrong, and the cold air may hold its ground as the cities could walk with more snow. At this point, though, I believe the conservative call is the best call with this storm as moisture is severely limited and all that places south, southeast, and southwest of the Poconos have to work off of is upper level dynamics. Not until the surface storm taps Atlantic moisture does precipitation really blossom as the storm goes to town. As a result, a minor event should occur, as I stated above...with places in central and southern PA seeing a general 2-4, 3-6" accumulation with the higher amounts in the central and west-central part of the state...along with 5-10" in the Poconos. So overall, this is nothing compared to the last few blizzards...but this time, New England should be the place to be for the big snows. Frankly, I doubt that disappoints many in the Mid-Atlantic as snow covered roadways and miserable traveling conditions are still plaguing many, some of who are still without power, in PA, MD, and Delaware, and NJ. Well, that's about all I have for now...so New Englanders, enjoy this storm as this will be the first significant storm in awhile for you folks as the Mid-Atlantic has been getting hit this year with the snow. So enjoy your 6-12" up there, be safe, and I'll update again tomorrow with any latest changes or information on the clipper storm. My final storm snowfall map will be posted within the next hour...so look for that soon. This is Junior Meteorologist Kyle Elliott reporting for the AKStormtracker Forecasting Center.