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Freezing Rain, Mixing Possible on Thursday

We've moving through a very unsettled weather week in New England. Rain will be falling all day today with another round coming in tomorrow evening. It will be colder today than initially expected, but temps will still be above average. The same goes for tomorrow. A widespread quarter to a half an inch of rain is possible through the next two days.

Attention is shifting toward unsettled weather expected for Thursday. Colder air will drain into the region Wednesday night, setting up mixed winter precipitation and snow for the region during the day on Thursday. This event can bring moderate to major impacts across northern New England, where freezing rain and some icing is possible. The NWS states:

"Cold high pressure is expected to be positioned over southern Quebec Wednesday night into Thursday while low pressure to our southwest moves in our direction. At the low levels, the cold air will likely win out, with colder Surface temperatures oozing southward through the forecast area Wednesday night and Thursday. At the same time, a short wave trough and aforementioned low pressure system approaches from the southwest and aids in overspreading precipitation across the forecast area, starting in the southwest by late Wednesday afternoon and early evening, eventually progressing northeastward across the forecast area as Wednesday night progresses."

This setup is highly conductive for mixed winter precipitation including freezing rain. On Wednesday night, the precipitation will likely be plain rain across the region. As the cold air spills into New England from Canada, a change to freezing rain is possible across northern New England during the day on Thursday. The NWS goes on to state:

"The tricky part here is where will be the surface freezing line be through most of the night. Based on previous southward sagging low level cold air events, we have trended the forecast a bit colder...Therefore, the forecasts calls for a change from rain to freezing rain and sleet for most of the area by 7am Thursday, albeit fairly light. With temperatures warming aloft, it is uncertain as to where the all-snow line will end up 7am Thursday, but it could still be in the mountains while the rest of the county warning area trends toward sleet/light fzra and at times a mixture with snow. While not an overly heavy event, it will be a nuisance for the Thursday morning commute. The exception may be southeastern NH and the Merrimack Valley where temperatures may not hit the freezing mark by the Thursday morning commute."

The good news about this particular forecast is that the precipitation from this event is expected to be heavy, and freezing rain, sleet and snow will likely be very light, causing more of a nuisance than anything else.

Light precipitation is expected across southern New England during the day on Thursday as well. Freezing rain is most likely across the higher elevations of central and Western Massachusetts. Subfreezing temperatures are possible as far east as Essex county, so icing and mixing is possible there as well. Moving southward toward Boston and the south shore, plain light rain is expected. The NWS states:

"...This will likely be the most impactful weather period of the extended forecast. The areal extent of the impactful (i.e. frozen) precip vs the non impactful (i.e. liquid) precipitation will hinge on the magnitude of cold air damming associated with an area of surface high pressure over southeast Quebec. Cold air draining down from NH/VT will be enhanced Wed night/Thu as a low pressure crosses the region increasing cold N/NE surface flow into southern New England. For this forecast, have continued to lean toward the colder NAM guidance, but we`re just beginning to get into the hi-res data which should help better hone in on the extent of the sub-freezing surface air. At the moment BUFKIT soundings indicate a textbook freezing rain temperature profile for locations in the northern Worcester Hills and northern Berkshires, with subfreezing air in the lowest 3,000 ft and a warm nose around 850 mb. Fortunately QPF isn`t impressive during this time period, so thinking that ice accumulations will stay south of 0.1". The colder NAM guidance does indicate the subfreezing air makes it into northeast MA/Essex county so the eastward extent will have to be monitored, since we know even light icing can cause deteriorated travel conditions."

The potential for frozen precipitation on Thursday will be the most impactful weather of this very active week. Unsettled weather will continue into Friday, with snow showers falling across much of the region, with rain showers possible closer to the coast. Accumulations across the region is expected to extremely light at this time, with no more than an inch expected anywhere in New England.



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