Area Forecast Discussion
Issued by NWS Boston, MA

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675 FXUS61 KBOX 222308 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 708 PM EDT Fri Jun 22 2018 .SYNOPSIS... High pressure continues to move offshore tonight, but it will remain dry. Scattered showers and a few thunderstorms are expected at times this weekend...but it is uncertain if any activity will linger into Monday. Mainly dry weather with seasonable temperatures anticipated Tuesday and Wednesday with a ridge of high pressure in control. Summer heat and humidity should return by the end of next week as this high moves east of the region. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... 7 pm update... The center of high pressure will continue to gradually slide east of our region. Mainly expect increasing/thickening cloudiness across our area overnight with dry weather prevailing. May see a few spot showers arrive near daybreak...but there is initially some dry air to overcome. Low temperatures will mainly be in the middle to upper 50s. Also...we did update Saturday to include categorical pops and the potential for localized heavy rainfall. While the entire day will not be a washout...most locations should see a period of two of rainfall with isolated t-storms possible. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... Saturday... A warm front lifts NE-ward during the day, and may reach the south coast of New England around 00Z. Increasing moisture is expected throughout southern New England, with precipitable water increasing to 1.5 inches or higher. The approach of the front will provide lift, allowing for the development of showers across our area. Planning on going with likely pops. While it doesn`t look to be a washout for the full day, hi-res guidance is in agreement on areas of showers moving thru the region. Model thermal profiles show a low level inversion which makes sense given warm front to the S, and an onshore/E wind providing a cooler marine influence near the surface. However some elevated instability is anticipated, which should yield isolated thunderstorms and the potential for brief locally heavy rainfall. Plan to go with likely pops and considerable cloudiness. High temps will be on the low side, only reaching into the 60s. A few spots might reach 70. Saturday night... Warm front lingers in our vicinity Sat night, accompanied by a 30-40 kt low level jet. This will continue to provide a lifting mechanism for showers. Precipitable water values remain at or above 1.5 inches, so brief locally heavy rainfall is possible. Model soundings showing continued elevated instability. Will continue with likely pops, with isolated thunderstorms. Best chance for thunder is probably along south coastal MA/RI, closer to the low level jet. Areas of fog developing. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Highlights... * Warmer with scattered showers and t-storms on Sunday * Mainly dry/seasonable temps with comfortable humidity Tue and Wed * Summer heat/humidity should return by the end of next week Details... Sunday... The warm front will lift north of most locations Sunday morning...allowing a warmer and more humid airmass to move into the region. High temps should reach into the upper 70s and lower 80s despite potential for a fair amount of clouds. We may see a period of partial sunshine though and if that does occur a few middle 80s would be possible. The main concern will be Sun afternoon/evening when a pre-frontal trough/cold front approach from the west. There probably should be enough instability for scattered showers and a few thunderstorms during that time. If we can muster 1000 J/KG of MLCape...which is dependent on solar insolation and amount of low level moisture return a few strong thunderstorms would be possible. 0 to 6 km shear is on the order of 30 to 40 knots...but mid level lapse rates are weak and we will not have the anomalous environment that we saw last Monday. Nonetheless...a few strong thunderstorms with gusty winds and heavy rainfall are possible if enough instability can be realized. Monday... A vigorous shortwave/cold pool aloft will drop southeast into the Northeast on Monday. The GFS is most aggressive showing the anomalous cold pool dropping furthest south into our region with 500T dropping below -20C. This scenario would likely produce scattered showers and thunderstorms along with some hail given such cold temperatures aloft. While this solution is possible, appears to be a low probability at this time given the rest of the guidance is further north and east with the cold pool...resulting in mainly dry weather. Therefore...will just include some low pops for now and see how the models trend over the next 24 hours. Tuesday and Wednesday... Mainly dry and pleasant early summer weather with a ridge of high pressure in control. High temperatures will mainly be in the upper 70s to the middle 80s along with comfortable humidity levels. Thursday and Friday... A pattern change to more summerlike warmth and humidity expected Thu and Fri as upper level ridging builds to sour south...resulting in rising height fields in southern New England. Highs should be well up into the 80s to perhaps over 90...but specific details this far out remain uncertain. Dry weather probably dominates...but a few showers/t-storms can not be ruled out. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday Night/...High confidence thru tonight, then moderate confidence. Tonight...VFR conditions continue despite thickening mid level cloudiness overnight. Saturday...Bands of SHRA across the region, with isolated TSRA and localized heavy rainfall. VFR in most locations at 12z...but MVFR-IFR overspread the region from south to north later in the morning through the afternoon. Saturday night...Mainly IFR with even some LIFR conditions in areas of showers and fog. Isolated TSRA. KBOS Terminal...High confidence in TAF thru tonight, then moderate confidence. VFR thru tonight, deteriorating to MVFR Sat morning then IFR during the afternoon. KBDL Terminal...High confidence in TAF thru tonight, then moderate confidence. VFR thru tonight, deteriorating to MVFR Sat morning then IFR during the afternoon. Locally lower conditions may occur earlier in heavier showers. Outlook /Sunday through Wednesday/...Moderate confidence. Sunday: Mainly VFR, with local MVFR-IFR possible. Chance SHRA, isolated TSRA. Sunday Night: Mainly VFR, with local MVFR possible. Chance SHRA, slight chance TSRA, patchy BR. Monday: Mainly VFR, with local MVFR possible. Slight chance SHRA, isolated TSRA. Monday Night: VFR. Tuesday through Wednesday: VFR. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday Night/...High confidence. Tonight and Saturday...E-SE winds in place. A few gusts approaching 25 kt on the southern outer waters late tonight into early Saturday. Visibility restriction in areas of fog along the southern waters late tonight, then in showers and areas of fog moving in from S-N during Sat. Isolated thunderstorms possible during Sat. Saturday Night...SW winds less than 25 kt. Seas approaching 5 ft on the southern outer coastal waters. Showers likely with isolated thunderstorms. Areas of fog visibility 2-3 nm or less. Outlook /Sunday through Wednesday/...Moderate confidence. Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers, isolated thunderstorms, patchy fog. Sunday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers, isolated thunderstorms, patchy fog. Local visibility 1 to 3 nm. Monday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Slight chance of rain showers, isolated thunderstorms. Monday Night: Winds less than 25 kt. Seas up to 5 ft. Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft. Tuesday Night: Winds less than 25 kt. Seas up to 5 ft. Wednesday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...NMB/Frank NEAR TERM...Frank/NMB SHORT TERM...NMB LONG TERM...Frank AVIATION...NMB/Frank MARINE...NMB/Frank

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