689 FXUS61 KBOX 102122 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 422 PM EST Sun Feb 10 2019 .SYNOPSIS... Dry and seasonably cold conditions will continue through Monday as high pressure ridge builds across. Snow and sleet overspread most of the region Tuesday afternoon with a significant impact to the evening rush hour likely, especially across the interior. The snow and sleet change to rain later Tuesday night across eastern MA/RI, but a period of freezing rain is likely across parts of interior southern New England. Steady precipitation should wind down by early to mid morning Wednesday with temperatures rising above freezing in all locations. Mainly dry later Wednesday into Thursday, but a period of unseasonably mild temperatures and rain is on tap sometime later Friday into Saturday. Dry and colder weather arrives on Sunday. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... Veil of thin cirrus clouds continues across the region into S NH/S VT at 21Z. Scattered lower clouds also remain across the Berkshires into the mid Hudson valley. Short range forecast models suggesting that mid level clouds will shift eastward this evening with the weak mid level short wave that will approach. Two batches of moisture approach as well, but drier air right across southern New England seems to be splitting them apart. The stronger short wave, with its good moisture feed, will pass across the mid Atlc states and offshore. Can not completely rule out a few brief snow showers or snow flurries that could sneak into the E slopes of the Berkshires from about 03Z through the remainder of the night, but most will weaken in the drier airmass. Otherwise, will see lower clouds crossing the region, with the lowest across S RI/S coastal Mass. H85 and H925 temps remain cold, on the order of -8C to -11C through the night, even as H5 heights begin to rise. So, expect temps to bottom out from the mid-upper teens across the higher inland terrain to the lower-mid 20s across the coastal plain and lower CT valley. && .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... Monday... Strengthening high pressure will push across Quebec, with ridging pushing S across New England during this timeframe. This will keep a N-NE wind flow in place with good subsidence. Clouds will push S to the S coast and into central CT by around midday Monday into early afternoon, the clearer conditions across N central and NE Mass where the best ridging will occur. So, expect partly to mostly sunny conditions. Temps will range from the upper 20s to lower 30s across NE, N central and W Mass ranging to the lower-mid 30s across the coastal plain into N CT. Monday night... With the ridge across the region, low level cold air will spill across the region out of the Maritimes by way of Maine. As the ridge axis shifts slowly E overnight, will start to see clouds push back N as leading edge of moisture from frontal boundary off the mid Atlc coast. Will see clouds slowly return from SW to NE mainly around or after midnight. Dewpoints will continue to drop overnight, down to the single digits to just below zero across most areas except along the immediate E coast with winds shifting to N-NE. So, will be tough for any precip to reach into the region as the front slowly lifts N. However, can not rule out some ocean effect clouds developing across the outer Cape after midnight Monday night as seen on BUFKIT soundings. Expect temps to drop to the upper single digits to mid teens well inland, ranging to the upper teens to mid 20s along the coast. && .LONG TERM /TUESDAY THROUGH SUNDAY/... Highlights... * Snow/sleet develop Tue and while accumulations remain uncertain significant impact likely for the Tue PM rush hour esp interior SNE * Most areas change to rain late Tue night, but pockets of icing may persist across parts of the interior overnight * Rapid improvement early to mid morning Wed with temps rising above freezing in all locations and steady precipitation ending * Rain and turning unseasonably mild late Friday into Saturday with a low risk of some minor river/stream flooding Details... Tuesday and Tuesday night... A winter storm will impact the region Tuesday into Tuesday night with a variety of precipitation types. When ever we are dealing with transitioning ptypes, confidence in specific snow/ice amounts is going to have uncertainty. This is particularly true with an event that is 60+ hours out in the model guidance world. With that said...a significant impact is likely for the Tuesday PM commute especially across the interior. We will break things down a bit more below. 1) Timing A modest 1040 mb high pressure system over Quebec will provide plenty of low level cold on the front end of the approaching storm. An initial low pressure system lifting northeast across the Great Lakes will increase the forcing for ascent. While it appears dry weather prevails through late morning in most locations, snow/sleet should overspread the region from southwest to northeast mainly Tuesday afternoon and likely have a significant impact on the evening commute. The ECMWF is the slowest model, which if correct could delay the arrival of snow until after 4 or 5 pm across eastern MA. 2) Potential Snow Amounts/Uncertainty Tuesday afternoon/evening: The biggest uncertainty with this forecast is just how fast the mid level warmth in the 750 mb to 850 mb layer advances northward. The NAM model is the most aggressive with the mid level warmth. This would mean just a few inches of snow, followed by a lot sleet. The reason is the Canadian high pressure system, which still has 925 temps between -6C and -8C through 00z Wednesday. On the opposite end of the spectrum...the GFS is slowest with this advancing warm layer and would result in a hard hitting front end thump of 5 to 9 inches of snow across a good portion of the region. The Euro and Canadian are more in between those solutions. Given the uncertainty and the fact that we are still 60+ hours out from the event, have opted to blend the solutions. Therefore...will go with 4 to 7 inches of snow/sleet near and north of the MA turnpike with 2 to 5 inches south of that region. Keep in mind these numbers are likely to change depending on latest model forecasts. We have opted to issue a Winter Storm Watch for western/central and northeast MA, where there is 50/50 chance of reaching marginal warning criteria. 3)Later Tuesday Evening into early Wednesday morning: The primary low will track northeast across the eastern Great Lakes, while a secondary low pressure system develops across eastern MA. Regardless, mid level warmth will overspread the entire region. The result will be snow/sleet changing to rain across eastern MA and RI. The amount of low level cold air that maintains itself across interior southern New England will depend on secondary low pressure development/location. However, it does appear that there will be enough for at least a period of freezing rain across portions of interior MA and into CT. Ice accretion in most locations should be under quarter of an inch, so odds of tree/power outages are rather low at this point. 4)Main Concern: Tuesday PM Commute The main concern is a likely significant impact to the Tuesday PM commute, especially across interior southern New England where heavier snow/sleet arrives earlier. While most of the guidance has snow overspreading the region Tue afternoon, the ECMWF is slower and may hold things off until after 4 or 5 pm across eastern MA. Even if this slower solution verifies, there still would be some impact at the tail end of the rush hour in eastern MA. An earlier arrival would result in a significant impact across all of southern New England during the Tuesday pm commute. The other issue will ptype be mainly heavy snow or sleet. If things are snow, the commute could get quite ugly with 1 to 2 inch per hour rates for a time with a classic front end thump. Sleet would still make for difficult travel given surface temperatures in the 20s, but would be more manageable than heavy snow and poor visibility. Wednesday through next weekend... Most of the time was devoted to our upcoming winter storm. Other than a few left over rain/snow showers Wed, temps rising above freezing even in the distant interior will result in improvement Wed am and afternoon. Dry weather continues Thu, but a potentially strong low pressure system will bring mainly rain to the region later Fri into Sat with period of unseasonably mild temperatures. There will be a low risk for some minor river and stream flooding given the potential dynamics of this system and abnormally wet weather of late. Colder/drier weather likely returns Sunday. && .AVIATION /21Z SUNDAY THROUGH FRIDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday Night/...High confidence. Through 00Z... VFR. West winds around 10 kt. May see a few gusts to 20 kt mainly across central and western terminals. Tonight... VFR. CIGS lower to 5-8kft after midnight. May see a few snow flurries across the interior after midnight. Monday and Monday night... VFR. CIGS may lower to MVFR late Monday night over Cape Cod and SE coastal MA. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Tuesday through Friday/... Tuesday: MVFR/IFR conditions possible. Windy with areas of gusts up to 30 kt. SN, PL, FZRA likely. Tuesday Night: Mainly IFR, with areas MVFR possible. Windy with gusts up to 35 kt. RA, PL, FZRA. Wednesday: Mainly VFR, with local IFR possible. Strong winds with areas of gusts up to 40 kt. FZRA likely, slight chance SHRA. Wednesday Night: Mainly VFR, with local MVFR possible. Strong winds with areas of gusts up to 40 kt. Thursday: VFR. Windy with gusts up to 35 kt. Thursday Night: VFR. Friday: VFR. Chance SHRA. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday Night/...High confidence. Through 00Z... W wind gusts up to 20 kt across the eastern waters through around 00Z. Have ended the Small Crafts there. Good visibility. Tonight through Monday night... Winds and seas below SCA. NW winds shifting to N on Monday, then NE Mon night. Good visibility. Outlook /Tuesday through Friday/... Tuesday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of seas approaching 5 ft. Snow and sleet likely. Local visibility 1 nm or less. Tuesday Night: Moderate risk for gale force winds with gusts up to 40 kt. Rough seas up to 14 ft. Rain, sleet. Local visibility 1 nm or less. Wednesday: Moderate risk for gale force winds with gusts up to 45 kt. Rough seas up to 17 ft. Chance of rain showers. Wednesday Night: Moderate risk for gale force winds with local gusts up to 45 kt. Rough seas up to 17 ft. Thursday: Low risk for gale force winds with gusts up to 35 kt. Rough seas up to 13 ft. Thursday Night: Winds less than 25 kt. Local rough seas. Friday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Chance of rain, slight chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...Winter Storm Watch from Tuesday afternoon through late Tuesday night for MAZ005>007-013>016. Winter Storm Watch from Tuesday afternoon through Wednesday morning for MAZ002>004-008>012-026. RI...None. MARINE...None. && $$ SYNOPSIS...Frank/EVT NEAR TERM...EVT SHORT TERM...EVT LONG TERM...Frank AVIATION...Frank/EVT MARINE...Frank/EVT