Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 080819 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 319 AM EST Thu Dec 8 2016 .SYNOPSIS... A strong front crosses the region late today. Mainly dry, but unseasonably cold temperatures are on tap for our region Friday into Saturday. Low pressure will likely bring at least some rain, snow, and/or even some ice, sometime Sunday into Monday. A shot of arctic air is then expected by mid to late next week. && .NEAR TERM /THROUGH TODAY/... Some risk for patchy black ice this morning on untreated surfaces. Travelers should be cautious, and allow some extra time to reach their destinations this morning. Lower clouds have moved out from most of southern New England, except for those areas where denser fog has developed. Light west winds to start out the day, which will steadily increase through the day as an arctic front approaches from the northwest. Low level moisture is lacking. While there is some moisture in the dendritic snow growth region, there is not much lift to maximize it. Cannot completely rule out a stray flurry or two. Little to no snow accumulation. Seasonable temperatures today, as the arctic front should arrive fairly late in the day. && .SHORT TERM /TONIGHT THROUGH 6 PM FRIDAY/... Tonight...Arctic cold front moves offshore during the night. Lowering humidity, meaning even less risk for precipitation. West winds will increase slightly, in response to the increased pressure gradient. There should be enough of a surface inversion to prevent the maximum momentum transfer. Below normal temperatures. Friday...Colder air will continue to overspread southern New England. More sunshine early in the day will lead to deeper mixing, and stronger west to northwest winds. Diurnal clouds expected to develop through the day. Temperatures should only rise at most 10 degrees from morning lows. Mainly dry weather should continue. There is the possibility for a stray snow shower across the interior, but not a large one. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Highlights... * Unseasonably cold but mainly dry into Sat * Period of light snow possible Sun into Sun Eve * Uncertain late Sun night/Mon whether a secondary low brings more significant rain/ice/snow or misses us to the south * Shot of arctic air likely mid to late next week Details... Friday night and Saturday... Still can not rule out a spot flurry/snow shower or two Friday evening. Otherwise, expect low temps to bottom out in the teens to around 20 in many locations. Winds will not decouple which will allow wind chill values to drop into the single digits. Despite partial sunshine, high temps will only recover into the upper 20s and lower 30s. Saturday night... Large high pressure settles across southern New England. This will result in mainly clear skies/light winds and an ideal night of radiational cooling. Low temps should drop well down into the teens for most locations, with some single digits likely in the normally coldest outlying locations. Sunday into Sunday evening... High pressure moves off the coast as a weak wave of low pressure moves up towards the Great Lakes. Enough of a pressure gradient may allow the development of a southwest low level jet of 30 to 40 knots. This will over ride the cold dome at the surface and may allow light snow to break out from west to east Sunday into Sunday evening. If this occurs, antecedent airmass is quite cold so mainly light snow would be expected near and northwest of the Boston to Providence corridor. Southeast of that line, ptype probably should start as light snow but warming boundary layer should allow for a change to light rain. One interesting thing to note, 850T are still below -10C at along the south coast at 18z Sunday with southerly winds developing. Ocean SST between 50 and 55 may even allow scattered ocean effect snow showers to develop along the south coast, before any change over to light rain. Overall, there really is not any organized system Sunday into Sunday evening. We are mainly just looking at southwest low level jet, over riding the cold dome at the surface. So while snow accumulations are certainly possible, amounts look to be on the light side at this time. Late Sunday night and Monday... Forecast confidence is quite low at this time. A stronger wave or two of low pressure may develop and threaten the area with more significant precipitation. Model guidance and ensembles are all over the place on the location/track and potential strength of any low pressure system. There are 3 main scenarios on the table right now. The first solution would be a stronger inside runner which would bring mainly rain to the coastal plain and a mixture of rain/ice/snow to the interior. The second would be a weaker wave passing to our southeast, bringing mainly accumulating snow from the I-95 corridor points northwest. The third scenario would have the wave sliding so far southeast that we end up mainly dry late Sunday night and Monday. All options remain on the table at this point, but certainly is the potential for some wintry weather Sunday into Monday. Tuesday and Wednesday...Specific timing remains uncertain, but cross polar flow will result in a shot of very cold air by the middle of next week. In fact, a period of arctic air appears likely some time in the mid to late next week time frame. Specific timing though is uncertain and some models hint at a wave of low pressure, slowing its delivery until late next week. && .AVIATION /07Z THURSDAY THROUGH MONDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short term...through Thursday night. Today and Tonight...High confidence. Mainly VFR. Some MVFR possible in higher terrain due to lower CIGS, and even a low risk for light snowfall late in the day. W winds increase, with gusts 15-20 kt at times by late afternoon, continuing into the overnight. Some gusts up to 25 kt along the immediate coast. Friday...High confidence. Mainly VFR. Low risk for brief MVFR cigs toward the Berkshires. Winds becoming northwest, and increasing. Gusts up to 35 mph possible during the afternoon. This will mean wind chills in the single digits and teens. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Friday Night through Monday/... Friday night and Saturday...High confidence in VFR conditions. Sunday and Monday...Low to moderate confidence. A period or extended period of MVFR-IFR conditions are likely later Sunday and possibly into Monday in some rain/snow and/or ice. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday/... Today and Tonight...High confidence. With cold frontal passage late today, expect an increase in W-NW winds late in the day and continuing into tonight. Gusts up to 25-30 kt is likely at times. Conditions may briefly diminish below Small Craft Advisory levels across the outer RI coastal waters today. That said, will continue the Advisory through today, with the expectation of increasing winds and seas later this afternoon. Small Craft Advisories will start across most of the other coastal waters this afternoon. Friday...High confidence. Strong cold advection will result in widespread northwest wind gusts of 25 to 35 knots. Not enough confidence 35 kt will be widespread enough, long enough, to convert the Gale Watches over the eastern outer MA coastal waters to Gale Warnings. Will let the next shift take another look. Outlook /Friday Night through Monday/... Friday night...High confidence. Strong cold advection will result in widespread northwest wind gusts of 25 to 35 knots. Opted to issue a Gale Watch across our eastern outer-waters, where the winds look to be the strongest. At the very least strong small craft winds are expected elsewhere, with even the risk of brief marginal gale force gusts. Saturday...High confidence. Despite weakening pressure gradient enough cold advection over the relatively mild ocean will allow northwest 20 to 30 knot wind gusts to continue. Small craft headlines will be needed. Sunday...High confidence. High pressure builds overhead and finally allows winds and seas to drop below small craft advisory thresholds. Sunday night and Monday...Low confidence. Winds and seas are quite uncertain and will depend on location/track and strength of a potential wave of low pressure. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 7 PM this evening to 1 AM EST Saturday for ANZ231>234. Small Craft Advisory from 7 PM this evening to midnight EST Friday night for ANZ230-236. Small Craft Advisory from 3 PM this afternoon to 1 AM EST Saturday for ANZ235-237. Gale Watch from Friday morning through late Friday night for ANZ250-251-254. Small Craft Advisory from 1 PM this afternoon to 9 AM EST Friday for ANZ250-254. Small Craft Advisory from 7 PM this evening to 9 AM EST Friday for ANZ251. Small Craft Advisory from 1 PM this afternoon to 1 AM EST Saturday for ANZ255. Small Craft Advisory until 1 AM EST Saturday for ANZ256. && $$ SYNOPSIS...Belk/Frank NEAR TERM...Belk SHORT TERM...Belk LONG TERM...Frank AVIATION...Belk/Frank MARINE...Belk/Frank

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