Issues with surface temperatures until you get north of the Mason-Dixon, and there are some mixing issues along the southern and eastern parts of the snowfall. First snow map of the year!
I ended up going more bullish with the southern fringe of the different snow contours east of the mountains and across south-central Pennsylvania, otherwise my thoughts are pretty similar to yesterday.
Still looking at a fair amount of uncertainty regarding snow accumulation east of the mountains due to the very warm temperatures leading into this event. A good pasting of snow is expected once temperatures cool down early Thursday morning, but a 1-2 hour shift in either direction with the introduction of colder air could add or remove some 1-4″ of snow. That being said, once the changeover to snow is made, it will be snowing quite hard, and heavy snow can overcome marginal surface temperatures.
This time it’s the 40N crew that will cash in with this upcoming snow storm. After a very mild Wednesday along the East Coast, temperatures will come crashing down overnight as a disturbance develops over Virginia and tracks just south of Long Island.
Ultimately, the strengthening and position of the surface low will have a large impact on how far north/south the 1″+ snow amounts end up. The snow will also be battling against a very warm antecedent air mass that will keep most spots as rain for at least the onset of precipitation. This means places like D.C. and Baltimore will struggle to change over to snow overnight. Heck, D.C. stands a risk of never changing over to snow at all Thursday morning if the more northern model solutions are correct.
As the initial storm system moves out Thursday morning and early afternoon, a second upper-level vort. max will slide through the Mid-Atlantic. This could trigger snow showers across more of the Mid-Atlantic Thursday afternoon and evening. Most places around/south of D.C. will still be too warm to see this light snow stick, but a little “snow TV” is better than nothing… I think?
This storm has a complicated setup. You have multiple surface lows within a broader upper-level trough, marginal surface temperatures, and large discrepancies in QPF placement between the models.
Temperatures along and east of I-95 are the most uncertain, which are expected to be in the low-to-mid 30s through most of the event. Areas north and west of I-95 will start above freezing, and will cool to at or below freezing depending on how strong the snowfall rates are tonight.
Snowfall rates will be one of the most important factors in determining which areas see 4-8 inches, and which areas get 1-4 inches. The best rates are likely to be along the Maryland/Pennsylvania border into southern New Jersey.
The intensity of the initial coastal low, the secondary coastal low development, the strength of the low over the Great Lakes, and the timing of the strengthening and weakening of these lows are wreaking havoc on the QPF output on the various models.
I tried my best to offer a realistic compromise between the differences in QPF, while also accounting for the surface temperature and snowfall rate issues. I could definitely see a tighter gradient between accumulation amounts than what I have on the map.
Not much difference from yesterday’s forecast, with the 1-2″ contour extending further south around DC/MD and a bit further north in central PA. Cut back totals in the westernmost areas in WV and OH. Areas west of I-95 remain at risk for a likely amount of 0.1″+ of freezing rain after the snow falls, with some areas (mostly around I-81) getting into the 0.25-0.5″+ range.
So I’m going to just ignore tonight’s snow in the northern areas in order to focus on the Sunday event, which is quite challenging with a strong CAD signal from a 1036+ mb High over PA as the precipitation starts to move in from the south and west. I expect most areas to start off as snow or a snow/sleet mix before changing over to sleet/freezing rain and eventually just rain. There is some potential for significant impacts west of I-95 on Sunday if the sleet and freezing rain persist for awhile, but most/all of the region is expected to be just rain by Monday morning rush hour. The highest freezing rain totals are expected to be around I-81, but even areas just west of I-95 could end up with at least a tenth of an inch of freezing rain. There is still some question as to how much cold air gets locked in east of the mountains and how much QPF overruns the cold air before above freezing mid-levels bring in the sleet and freezing rain.
There’s still plenty of uncertainty and room for change, so stay tuned for updates here and on Twitter! My second (final) forecast will be up tomorrow morning.
One of the more promising events I’ve forecast this winter…
Plenty of cold air aloft, but surface temperatures look to hurt the initial snowfall accumulations before either the rates get high enough of the surface temperature cools to the freezing mark. Higher elevations stand a better chance of snow (both for surface temperatures and for snow ratios).