Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 170939 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 439 AM EST Thu Jan 17 2019 .SYNOPSIS... Quiet weather today under high pressure. One weather system slips past Southern New England Friday, bringing a period of snow changing to rain Thursday night and Friday. All eyes are on a second storm that brings a mix of wintry weather for Saturday night and Sunday. Arctic air returns for early next week. Another weather system may bring rain and snow next Wednesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... The cold front has passed offshore this morning ushering in a very dry airmass...dewpoints across the region range from low teens to near zero! Still seeing a few gusty spots but as high pressure rapidly builds in we`ll see these winds comes down across the board by early morning. High pressure currently over southern QC will cross into New York and then cross northern New England today. Temperatures start very cold this morning, especially in those locations with light winds that still have a chance to radiate well before sunrise. This combined with CAA under high pressure will bring high temperatures down 10-15 degrees from the mild day we saw yesterday; highs top out in the upper 20s. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... Thursday evening winds shift out of the east ahead of an incoming warm front. As the high pressure moves offshore, a shallow midlevel shortwave ushers a quick moving low pressure south of the area which will bring light snow to the region overnight. As the warm front approaches winds will turn out of the south and snow starts over western CT and MA around 06Z, spreading east over the early morning hours. With low temperatures in the teens and low 20s, we`ll see light accumulations of snow. Though light, it will have bad timing, coming ahead of and during the Friday morning commute. Under a split flow pattern, this shortwave does not have a good tap of moisture with it, and models have been consistently backing off on the QPF amounts with this system. Thus, snow amounts have been lowered a bit this morning. Eventually this transitions to rain for much of the coastal plain of MA and RI before precip tapers off by late morning/early afternoon. Currently looking at snow totals of a half inch to an inch for most, with 1 to 2 inches possible in the high terrain of the interior. Take it slow on the roads Friday morning as untreated surfaces will become slick and hazardous. Temperatures warm into the upper 30s and even the low 40s in coastal MA and RI, though there is still some uncertainty on just how far north this warm air can make it. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... 17/00Z guidance suite remains consistent with previous runs of phasing mid level flow late this weekend. This phasing of the northern and southern jet streams is expected to deepen a low pressure as it passes by our region. Have high confidence in an impactful storm for our region. However, the thermal profiles will be absolutely critical, and continue to exhibit a rather large spread. This is leading to low to moderate confidence in the precipitation type details. Fully expect these forecast details to evolve over the next couple of days. 17/00Z GFS remains the warmest of the operational guidance, with the Canadian and ECMWF are quite a bit colder in the low levels. 00Z NAM was closer to the ECMWF, but it was the very end of the model cycle. Favored a slightly colder solution than the operational GFS, as the operational run was towards the northern end of its ensemble spread, but cannot dismiss it entirely just yet. Based on this, the forecast starts with snow everywhere Saturday night, then brings rain into the South Coast by morning. Rain spreads up to Boston and the North Shore Sunday, also across RI and much of northern CT. North of that zone will be a band of sleet/freezing rain across the interior, snow continuing across parts of northwest MA. Shifts in the forecast storm track will of course impact the location of these precipitation bands, and also affect total accumulations of each. Strong east winds will reach 35-50 mph speeds along the coast, especially over Cape Cod and Islands. Inland speeds will be more like 25-35 mph. Issued a Winter Storm Watch for much of southern New England due to the threat of significant snow and ice accumulation. Sunday night-Monday The storm should wind down during this time. Winds will quickly shift out of the north and northwest. Strong pressure gradient at the surface will generate strong sustained winds, and cold advection will draw strong winds aloft down to the surface with gusts of 25-40 mph possible. The combination of wind and cold air will bring wind chills to single digits and below zero Sunday night and Monday. It will also raise the possibility of a flash freeze of any remaining wet surfaces. Wednesday... Another weather system moves up the Ohio Valley, spreading rain and snow into Southern New England sometime Tuesday night into Wednesday night. Details of this evening will come into better focus with later forecasts. && .AVIATION /09Z THURSDAY THROUGH MONDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday/...High confidence. This morning... VFR. Winds have switched to NW and will continue through the morning, diminishing into Thursday. Today and tonight... Mainly VFR. Lowering CIGS through the overnight hours. Light winds shift from NW to E-SE through the evening. Snow approaches from the southwest after 06Z. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Friday Night through Monday/... Friday Night: VFR. Breezy. Saturday: VFR. Chance SN. Saturday Night: Mainly IFR, with areas MVFR possible. Windy with gusts to 35 kt. Wintry mix of SN and FZRA. Sunday: Mainly IFR, with local MVFR possible. Strong winds with local gusts to 40 kt. Wintry mix of SN, RA, FZRA and PL. Sunday Night: VFR. Windy with gusts to 35 kt. Chance SN, slight chance FZRA. Martin Luther King Jr Day: VFR. Windy with gusts to 30 kt. Slight chance SHSN. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday/... High pressure builds over New England today, bringing lighter winds to the waters. The high then moves off to the east tonight. This will bring quieter boating weather to the waters. An approaching weather system will spread snow and rain over the waters after midnight Thursday night, with reduced vsbys by morning. Outlook /Friday Night through Monday/... Friday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Saturday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of snow. Saturday Night: Low risk for gale force winds with gusts up to 40 kt. Areas of rough seas. Snow changing to rain. Areas of visibility 1 nm or less. Sunday: Moderate risk for gale force winds with gusts up to 45 kt. Rough seas up to 13 ft. Rain. Visibility 1 to 3 nm. Sunday Night: Strong winds with gusts up to 35 kt. Rough seas up to 13 ft. Chance of snow and rain. Martin Luther King Jr Day: Strong winds with gusts up to 30 kt. Rough seas up to 12 ft. Chance of snow showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Winter Storm Watch from Saturday afternoon through Sunday evening for CTZ002>004. MA...Winter Storm Watch from Saturday afternoon through Sunday evening for MAZ002>019-026. RI...Winter Storm Watch from Saturday afternoon through Sunday evening for RIZ001>004. MARINE...Small Craft Advisory until 9 AM EST this morning for ANZ250. Small Craft Advisory until 5 AM EST early this morning for ANZ251. Small Craft Advisory until 11 AM EST this morning for ANZ254. Small Craft Advisory until 7 AM EST this morning for ANZ255- 256. && $$ SYNOPSIS...Belk/BW NEAR TERM...BW SHORT TERM...BW LONG TERM...Belk AVIATION...Belk/BW MARINE...Belk/BW

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