208 FXUS61 KBOX 220845 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 345 AM EST Mon Feb 22 2021 .SYNOPSIS... A frontal system brings a period of accumulating wet snow to the high terrain locations in western and central Massachusetts and northern Connecticut this afternoon into early evening. All rain is expected elsewhere. Dry weather with above normal temperatures arrive midweek. Passage of a cold front Wednesday night ushers in dry, blustery and colder weather for the end of the week. Approaching low pressure may bring some rain or snow sometime during the weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... *** Accumulating Snow Likely Northern CT into Western/Central MA *** 4 AM update... This morning... Cold predawn temps observed across MA/CT/RI in response to a very dry airmass, light winds and just high thin clouds. 3 am observed temps were mainly in the single digits and teens, except around 20 in the urban areas. Temps have leveled off as cloud canopy thickens and lowers early this morning, then temps rise later this morning as southerly flow develops and advects milder air off the ocean. As a result temps will rise thru the 20s and lower to mid 30s by midday. It will become windy toward noon as approaching low level southerly jet combines with cold air aloft and warming low level temps to yield steepening low level lapse rates. Model soundings indicate southerly winds could gusts up to 30-40 mph before precip arrives this afternoon. This afternoon... Fairly robust mid level trough moves across the region this afternoon with 850 mb SSW jet of 50-60 kt, providing strong thermal and moisture advection across the region. Parent low over the Great Lakes gives way to secondary low along the Maine coast. With secondary low developing east of our longitude, southerly flow will persist and warming the boundary layer to support mainly rain across RI and Eastern MA, perhaps beginning as brief period of snow. Rain may be moderate to perhaps heavy for a time this afternoon and and early evening. Farther west across Northern CT into Western-Central MA, cold air will be deeper and slower to erode, especially with surface dew pts in the single digits early this morning. Strong warm air advection aloft will result in a burst of moderate to perhaps brief heavy snow for a time across this region from 18z-00z. Model qpf across this area ranges from 0.25 to 0.40 inches. Expecting SLR to be around 10:1 given snow growth doesn't look ideal. In addition, with snow falling during the afternoon hours, marginal surface temps per hi res guidance and now late Feb sun angle, snow will likely struggle to accumulate on paved surfaces especially at elevations below 1 kft. This combined with poor snow growth, thinking 1-3 inch snow accumulations will be common across Northern CT into Western/Central MA, with highest accumulations likely on non paved surfaces. Low prob of isolated 4 inch amounts if mid level instability is realized, but given marginal qpf, marginal surface temps and poor snow growth, any 4" amounts should be isolated and mainly on non paved surfaces. Thus limiting impacts. For these reasons will hold off on a winter weather advisory and message 1-3 inch amounts via a Special Weather Statement. Windy conditions at midday will diminish as the afternoon progresses, as column wet bulbs and low level lapse rates relax. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... 345 AM update... Tonight... Precip this evening ends from west to east as mid level trough remains progressive. Post frontal/dry weather overspreads the region after midnight in concert with the wind shift from SSW to west. Tuesday... Short wave ridging in the morning behind departing system from tonight. However upper air pattern remains progressive, with next short wave trough moving across MA/CT/RI during the afternoon. This may result in a few afternoon showers, snow showers high terrain. However most of the day will be dry. Seasonable temps with highs in the lower 40s, upper 30s high terrain. Modest SW winds. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Highlights... * Mostly dry with moderating temps through mid week then colder weather arrives to end the week. * Next chance of widespread precipitation comes next weekend Details... Tuesday Night Through Friday... By Tuesday night surface pressure and mid level heights are on the rise as ridging builds in. Dry air invades, bringing clearing skies. A decent 35 kt 925 mb jet overhead but model soundings don't indicate that much will mix down. Gustiest winds will be over the waters, 20-25 kts. Wednesday will sport a good amount of sunshine mixed in with some clouds and very mild temperatures as warm air surges NE ahead of an approaching shortwave. 850 mb temps reach +3 to +4 C which should allow for highs well into the 40s. Not forecasting 50s at this point (neither EPS or GEFS ensemble guidance is too excited about >50 temps), but if we should overachieve, eastern/southeastern MA stands the best chance. The moisture starved cold front swings through Wednesday night bringing temps back down toward normal. Depending on the exact timing, southeast MA may see low 40s twice...once just after midnight then again by afternoon. The cold front will bring clouds and perhaps a widely scattered shower but nothing more. A reinforcing shortwave brings a shot of even colder air late Thursday into Friday, so we won't see any 40s in southern New England on Friday. Saturday and Sunday... Details are uncertain with regards to next weekend but all signs point to our next period of unsettled weather around Saturday. High pressure moves offshore and a shortwave crosses to our northwest. Given the far inland track, would expect this to be a mainly rain event at this point. Milder air on SW flow brings highs back above normal into the mid/upper 40s. && .AVIATION /09Z MONDAY THROUGH FRIDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 06z TAF Update: Thru 17z: high confidence. VFR and dry this morning with SSW increasing as the morning progresses. By noon time or so SSW winds will become quite gusty with sustained winds 15-20 kt but gusting up to 35 kt at times. After 17z: high confidence on trends, some uncertainty on precise timing and details. MVFR but trending down to IFR/LIFR as precip overspreads the region from west to east. Ptype all rain from BOS to PVD to Cape Cod and the Islands. Ptype may briefly be snow at BOS and PVD but will quickly change to all rain. Farther to the northwest across northern CT, western-central MA, ptype will be snow for a few hours before changing over to all rain. A coating to 2 inches possible, but with marginal temps most of this accumulation will be on non paved surfaces. Some of the hilly terrain especially above 1 kft, low risk for a few spots receiving 3-4 inches. Although with marginal temps most of this accumulates on non paved surfaces, except above 1 kft where colder temps will support more snow on runways. Gusty SSW winds will begin to slacken later in the afternoon and early evening. Tonight...high confidence on trends, some uncertainty on exact timing. LIFR/IFR at 00z with rain, except light snow across Northwest MA. Improving to VFR and dry weather after midnight from west to east along with wind shift from SSW to west. Tuesday...high confidence. VFR and dry during the morning, then trending to MVFR in the afternoon with a spot shower, snow shower well inland. Otherwise mainly dry. WSW winds 10-15 kt, but 20-25 kt along the south coast. KBOS TAF...High confidence in TAF thru the morning. Then rain overspreads the region in the afternoon. Rain may briefly begin as snow, but accumulations not expected. SSW winds become gusty around midday, potentially up to 35 kt, then diminishing with onset of rain. KBDL TAF...High confidence in TAF. Outlook /Tuesday Night through Friday/... Tuesday Night: Mainly VFR, with local MVFR possible. Breezy. Wednesday through Friday: VFR. Breezy. && .MARINE... 345 AM update... Today...increasing SSW winds, peaking early this afternoon before rain arrives. SSW winds increasing to 20-30 kt with low risk for a few hours of gale force gusts up to 35 kt at times. Rain overspreads the waters this afternoon, reducing vsby. Tonight...cold front sweeps across the waters, shifting winds from SSW to west. Rain limits vsby in the evening, but improving vsby after midnight with the wind shift. Tuesday...modest SW winds. Mainly dry weather but can/t rule out an isolated shower. Outlook /Tuesday Night through Friday/... Tuesday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Wednesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Wednesday Night: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Thursday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Thursday Night through Friday: Winds less than 25 kt. Local rough seas. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 9 AM this morning to 6 AM EST Tuesday for ANZ232>235-237-254>256. Small Craft Advisory from 1 PM this afternoon to 6 AM EST Tuesday for ANZ231-251. Small Craft Advisory from 9 AM this morning to 3 PM EST this afternoon for ANZ236. Small Craft Advisory from 11 AM this morning to 6 AM EST Tuesday for ANZ250. && $$ SYNOPSIS...Nocera/BW NEAR TERM...Nocera SHORT TERM...Nocera LONG TERM...BW AVIATION...Nocera/BW MARINE...Nocera/BW