DAYS 1-5 (DECEMBER 22-26)
There have been no drastic changes in the forecast since the last blog post, so I will try to summarize that with any tweaks built in. Today, it’s basically about snow, steadiest this afternoon in NH and northern MA, though some will occur before that and already has, but little in the way of any steady precipitation to the south with just spotty light snow and even mixed with rain near the South Coast. The advertised warm front will struggle moving through as expected. You have to remember to think of something like a warm front not as a solid object, but a boundary between air masses, which are made of fluid. This warm air will move into areas with less resistance much more easily than others, and one of those areas it has great difficulty doing this is interior valley locations where dense cold air stays near the ground. This will be a classic case of that as it warms aloft and sets up a freezing rain situation. The good news is that some icing may be prevented due to a lull in the precipitation this evening just as it warms aloft to turn snow to rain. A second batch of steadier precipitation is expected to arrive in the pre-dawn hours of Saturday and continue through the morning to the middle of the day. This is when most of the icing will take place as by then it will be too warm aloft for any more snow anywhere. So during this it will become essential to watch the surface temperatures and the amount of rain. There may be some sleet involved closer to the time the first batch of snow moves out this evening and near the beginning of the steadier precipitation from batch number two, but the main issue will be the freezing rain, which will last longest over interior MA and southern NH. However enough cold air may drain southward through eastern MA and into northern RI, areas away from the immediate shore, for a period of freezing rain in many of these locations too. A piece of more positive news lies in the fact there is a good shot at another precipitation lull for a portion of Saturday afternoon, which would limit additional icing and reduce the risk of power outages from downed wires and trees/branches on wires. Of course throughout this watch for hazardous untreated surfaces as always! By Saturday night, it should have warmed up in all but deepest valleys enough for the final batch of precipitation to be in the form of plain rain and not last all that long. By the early hours of Sunday the entire mess is gone and Sunday itself will be a dry day. Temperatures should rise above freezing in most areas to be able to get rid of some of the ice build up, but it may not be enough to melt it all, so keep that in mind going forward as there is more cold and some snow in the forecast. Christmas Eve itself, from day to evening, will be dry. The next precipitation threat will come from a new area of low pressure passing to the southeast of New England late Sunday night and early Monday, but with a trough of low pressure extending from it back to a weaker storm coming out of the Great Lakes, enough cold air will be in place for a period of snow in most of the region with the exception of Cape Cod. We may have to watch a rain/snow line to see if it moves northwestward for a period of time, but I do think at this point that rain will be confined mainly to the Cape and that a couple to several inches of snow will occur elsewhere. I’ll put some numbers to this part of the forecast on the next blog post, leaving the numbers for today’s event (in the detailed forecast section below). Beyond the Christmas snow threat comes a shot of colder air Tuesday. Forecast details…
TODAY: Overcast. Periodic snow southern NH and northern MA becoming steadier midday-afternoon with a coating to 2 inches from near the Mass Pike northward for about 20 miles and 2-4 inches northern MA and southern NH. Spotty light snow to the south except snow or rain South Coast with no snow accumulation. Highs 22-38, coldest north central MA and southwestern NH, mildest southeastern MA and RI. Wind light NE.
TONIGHT: Overcast. Snow / sleet / freezing rain southern NH and northern MA with rain nearer the coast tapering off early with little additional accumulation, spotty light sleet / freezing rain / rain elsewhere. Temperatures nearly steady 22-29 north central MA and interior southern NH, 30-38 elsewhere. Wind light N to NW.
SATURDAY: Overcast. Freezing rain except rain immediate coast through southeastern MA and southern RI, steadiest morning and midday when some significant ice accretion is likely especially north central MA to southwestern and south central NH, then precipitation tapering off for a while in the afternoon. Temperatures rise very slowly to 27-34 interior, 34-40 coast. Coldest air remaining in deepest valleys. Wind light NW.
SATURDAY NIGHT: Overcast evening with one more period of rain which may still freeze in deepest valleys. Breaking clouds overnight. Temperatures rise slightly to 32-37 interior, 38-43 coast. Wind variable to SW 5-15 MPH, shifting to NW overnight.
SUNDAY: Partly sunny. Highs 35-43. Wind NW 5-15 MPH.
SUNDAY NIGHT – CHRISTMAS EVE: Clouding over. Snow likely around or after midnight except mix/rain Cape Cod. Lows 25-33. Wind light N.
MONDAY – CHRISTMAS DAY: Overcast morning with snow likely except mix/rain Cape Cod. Partial clearing afternoon. Temperatures steady 25-33. Wind N to NW 5-15 MPH.
TUESDAY: Partly cloudy and windy. Lows in the 10s. Highs from the middle 20s to lower 30s.
DAYS 6-10 (DECEMBER 27-31)
The final 5 days of 2017 will be colder than normal and there is the threat of a storm around December 29-30 that will be watched.
DAYS 11-15 (JANUARY 1-5)
The first 5 days of 2018 will likely be similar to the end of 2017 with another storm threat potentially looming.