The second major snowstorm in just over 2 weeks is now on final approach to New England. The beast is being born off the Mid Atlantic Coast now, and a very rapidly-deepening low pressure center will result, tracking northeastward, passing just southeast of Cape Cod Wednesday morning. This continues to look like a progressive system, that is, one that is not going to slow down or stall. Nevertheless, the rate of strengthening, track, and available moisture will be enough to crank out major snow for just about all of Massachusetts and southern New Hampshire.

Again, the wildcard remains the issue of how much mixing and rain will occur over Cape Cod. It still looks like most of the mix/rain will be confined to the Outer Cape, including Chatham. Snow amounts could range from as little as an inch or 2 near Chatham building up rapidly to around 10 inches near the Cape Cod Canal. For the remainder of Massachusetts and southern New Hampshire, it is now a pretty safe bet that all areas will see 10 or more inches of snow. The upper limit of accumulation expected has been hard for me to determine, as I have been concerned about the speed of the storm being too fast to allow the amounts you may have seen in some places to verify. That said, there is enough potential with this system that I will set my widespread upper accumulation limit at 16 inches.

Some specifics…

Once snow gets underway, look for a fairly rapid drop in visibility from south to north across the region, southern MA first, southern NH last, between 1am & just before dawn.

There should be up to a few inches of snow on the ground in many areas, especially in MA, by dawn.

Thundersnow remains possible during the heaviest snow in the morning hours. Snowfall rates of 1 to 2 inches per hour can be expected for much of the morning, but can reach 2 to 3 or even 4 inches per hour during thundersnow. These extreme rates do not usually last too long, however.

Blizzard conditions? 3 or more hours of sustained 1/4 mile or less visibility is possible, especially near the MA East Coast, as winds there will be steadiest and strongest (northeast to north 25-40 mph with higher gusts). Winds will be gusty inland, but not as strong as near the coast. Winds closer to Cape Cod may gust over 50 mph to even near 60 mph at times.

Tides… Astronomically low tides should limit flooding problems this time, in contrast to the storm of December 26-27. There will be some splashover and mostly minor flooding. But it also appears that the high tide and the strongest part of the storm will not coincide, which will further limit flooding.

What can go wrong with snow amounts? 2 things: If convective snowbands (thundersnow) are more prominent, snow amounts can be higher than forecast in some locations (isolated amounts over 16 inches). Also, this low pressure area will be deepening so rapidly, it may act almost like a tropical cyclone for a while. When this occurs, you sometimes see drying in the mid levels of the troposphere. That is, the air around where the snow forms can dry out, and you see lighter areas or even holes in the snow areas on the radar. Something similar to this happened in the last major storm, cutting down on snow amounts in central MA. This is something to watch for as the low pressure area makes its closest pass.

Any way you look at it, most of us are in for a good belting of snow and wind. Travel is not recommended, at least Wednesday morning through mid afternoon. Anyone that has to be out should allow alot of extra time and use extreme caution.

930pm Tuesday 1-11-2011