Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 231946 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 346 PM EDT Mon Apr 23 2018 .SYNOPSIS... High pressure remains in control through Tuesday bringing dry weather with mild daytime temperatures. Low pressure approaches and then passes through New England Tuesday night into Wednesday night, bringing rain to the area. Another weak low pressure center may bring another round of showers to the area Friday night. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... 250 PM Update... The high pressure that was centered overhead today begins to shift to the southeast of our area tonight. Clear skies continue. With winds expected to be light, expect good radiational cooling. Forecasting lows in the 30s for much of the area, except for low 40s in some urban centers and portions of the Cape and Islands. Patchy/areas of frost are expected to develop. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... Tuesday... As the surface high moves further offshore, Tuesday will bring developing S to SW wind. A sea breeze is possible along east coastal MA for part of the day, however as the SW flow increases some during the afternoon, the east coastal sea breeze should come to an end. Mostly sunny skies expected for much of the day, with increasing clouds during the afternoon. A slightly warmer day with highs in the 60s across much of the area, some locales may reach 70 degrees. The cooler area will be the immediate south coast of MA/RI, where the persistent S wind will keep highs in the upper 50s to near 60. Tuesday night... Models show mid level ridging moving east of our area while deep trough currently over the lower Ohio/Mississippi Valleys works its way eastward. This pattern shift prompts a moisture-rich low pressure system to track eastward towards the Delmarva coastline. Moisture well ahead of this system will result in skies becoming cloudy during the evening, but it will take some time to moisten the column with respect to any precipitation. Expecting rain to become likely after midnight. PWATs during the overnight increase to 1 to 1.3 inches, so some moderate rainfall possible but generally thinking rainfall of a tenth to half inch prior to 12Z Wed. Cloud cover and increasing dew points will keep overnight lows somewhat milder, lows in the low to mid 40s for much of the area. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... Highlights... * Wet weather Wednesday, diminishing Wednesday night * Another round of showers possible Friday night and late Saturday Discussion... The 23/12Z operational guidance has come into better agreement with the details into Thursday. Fairly good overall agreement thereafter, although the Canadian model really goes off on its own later this weekend. Preferred a solution more like the GFS and ECMWF camp. Further prefer an ensemble mean approach, especially after Thursday. Wednesday and Wednesday night... Essentially the same story from the past few days. Multiple waves phase in the vicinity of the central Appalachians, or perhaps into the Mid Atlantic. Coastal low develops and tracks north through southern New England Tuesday night into Wednesday night. This will mean a period of wet weather for our region. Modest elevated instability still present, so cannot dismiss the possibility of isolated thunderstorms. Still looking like a general one half to one inch of rainfall when all is done. Locally heavier amounts possible in any persistent/slow-moving thunderstorms. Thursday through Friday... Except for possibly widely scattered late Thursday afternoon or early evening instability showers over the NW higher terrain, it looks dry Thursday afternoon through at least most of Friday. Confidence has increased of at least most of daytime Friday remaining dry. Friday night... A weak coastal low pressure may pass by just close enough for a risk of showers late Friday into Friday night, mainly across southeast MA and RI. Also will have to monitor the progress of a cold front associated with a low pressure in the St. Lawrence valley, which could also bring a chance for showers across the western half of southern New England late Friday night. Confidence remains rather low on these details, so later forecasts may change. Rest of this weekend... A cold front associated with a northern stream trough may result in scattered showers Saturday, but confidence in details remains low. Monday...High pressure expected to build in with drier weather. && .AVIATION /20Z MONDAY THROUGH SATURDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday Night/...High confidence. Remainder of this afternoon...VFR with clear skies and excellent visibility. Local sea breezes persist. Tonight...VFR with clear skies and excellent visibility. Tuesday...VFR. Prevailing wind out of the SSW, initially light enough where a sea breeze may develop along east coastal MA for a time. Then as winds aloft strengthen somewhat during the afternoon, the winds along east coastal MA should shift back to the SSW. Tuesday night...VFR to start. Becoming mainly MVFR after midnight, with local IFR possible towards daybreak. SHRA spreading into the area mainly after midnight. KBOS Terminal...High confidence in TAF. Sea breeze this afternoon, with a sea breeze probable for late morning into early afternoon Tue. KBDL Terminal...High confidence in TAF. Outlook /Wednesday through Saturday/...High confidence. Wednesday: Mainly IFR, with local MVFR possible. Windy with local gusts to 30 kt. RA with isolated TSRA. Patchy FG. Wednesday Night: Mainly IFR, with local MVFR possible. Breezy. RA likely, tapering off to SHRA. Isolated TSRA possible. Patchy FG. Thursday: Mainly VFR, with local MVFR possible. Breezy. Slight chance SHRA. Thursday Night through Friday: VFR. Friday Night through Saturday: VFR. Slight chance SHRA. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday Night/...High confidence. Tonight... High pressure over the waters tonight with South winds 10 kt or less, seas 1 to 2 feet on the outer coastal waters. Good visibility. Only concern for recreational boaters continues into early this evening is for sea breezes along the coastline today with 15-20kt gusts and choppy seas near shore, especially when opposing outgoing tide. Tuesday... South wind increasing over the course of the day to 10 to 20 kts. Sea breeze along east coastal MA possible late morning/midday, then S winds should prevail as they strengthen. Seas 1 to 3 feet. Tuesday Night...SE winds less than 25 kt. Seas locally approaching 5 ft, especially on the southern outer coastal waters. SCA headlines may be needed. Rain showers becoming likely towards daybreak. Outlook /Wednesday through Saturday/...High confidence. Wednesday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Rain, isolated thunderstorms, patchy fog. Areas of visibility 1 nm or less. Wednesday Night: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 13 ft. Rain likely, chance of rain showers, isolated thunderstorms, patchy fog. Local visibility 1 nm or less. Thursday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 10 ft. Slight chance of rain showers. Thursday Night: Winds less than 25 kt. Areas of rough seas. Friday: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers. Friday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. Saturday: Winds less than 25 kt. Areas of seas approaching 5 ft. && .EQUIPMENT... The NOAA Weather Radio transmitter serving Providence is out of service due to phone line problems. The phone company has prioritized the issues and is working to get the weather broadcast back on the air as soon as possible. The transmitter serving Hyannis is back in service. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Belk/NMB NEAR TERM...NMB SHORT TERM...NMB LONG TERM...Belk AVIATION...Belk/NMB MARINE...Belk/NMB EQUIPMENT...Staff

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