Area Forecast Discussion
Issued by NWS Boston, MA

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392 FXUS61 KBOX 271914 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 314 PM EDT MON JUN 27 2016 .SYNOPSIS... High pressure remains in control into Tuesday. A cool front will slowly approach the region, bringing periods of showers and thunderstorms late tonight through Wednesday. This front will push offshore Wednesday night. High pressure then brings dry seasonable weather for late this week. Another cold front may bring more showers and thunderstorms around Saturday. && .NEAR TERM /THROUGH TONIGHT/... The main issue this afternoon is the abundance of low level dry air, as evidenced by 20-25 degree F dew point depressions. A band of showers was just west of MA early this afternoon, but will likely struggle to make much progress east as a solid band. Have tweaked rainfall chances this afternoon and evening. The most likely area for showers through 4 pm will be across northwest MA. Expecting lower levels to moisten tonight. With a pre-frontal trough moving eastward, it may be enough to trigger some overnight showers, especially late tonight. Guidance continues to indicate precipitable water values between 1.50-2.00 inches. Thus, locally heavy rainfall will be possible, once the low level dry air is overcome. && .SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/... Southern New England anticipated to remain in the warm sector ahead of a cold front through Tuesday Night. This will mean a continuing southerly flow, increasing dew points, and a greater chance for showers. It appears the most likely period will be from Tuesday afternoon into Tuesday night. Besides the showers, thunderstorms will also be a concern. Model soundings are not that gung ho from an instability standpoint. If we wind up with fewer clouds than current expectations, instability could wind up becoming more potent. The timing would also be a factor against widespread strong to severe thunderstorms, with the event occurring mainly at night. Seasonable temperatures through this period, albeit humid conditions continue. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... Big Picture... Longwave scale continues to show a ridge-west/trough-east pattern over North America. This may shift east a little during the holiday weekend. One shortwave rippling through this flow moves across New England later Wednesday. A second moves down from Canada and sweeps across New England next weekend. Model mass fields are similar with the broad pattern through Friday. There are differences in positioning of the cold front associated with the first shortwave. The ECMWF is farthest west and the GGEM farthest east. This means a consensus as to the broader forecast, showers/tstms, but uncertainty regarding the details such as timing. With the second shortwave, the GFS and ECMWF are similar while the GGEM is slower and farther south. The mass field agreement and the variations in details Wednesday favor a blend of model data. Details... Wednesday... Shortwave over the Eastern Great Lakes digs over New England while the associated surface cold front moves through New England Wednesday. The upper flow through the shortwave will be SSW to NNE across our area, almost parallel to the cold front. Until the shortwave axis swings across our area and turns the upper flow across the front, the cold front will move very slowly. Upper jet flowing through the shortwave will provide dynamic support for lift. Model data shows precipitable water values pooling along and just ahead of the front with max values 1.6 to 1.8 inches. Three of four models show total-totals in the upper 40s through Wednesday afternoon in the area leading the cold front. Cross sections show the moisture will be through a deep column. All of this points to showers and possible thunderstorms. We will stay with chance pops Wednesday. Thursday through Saturday... Weak high pressure builds over the region Thursday and lingers into Friday. The second shortwave approaches with difluent flow aloft Friday afternoon/evening and increasing precip water values toward evening. Favorable instability remains to our west and northwest during Friday but then moves across Southern New England Friday night. Timing on this shortwave and surface cold front will continue to vary, but for now we will show chance pops for showers/tstms in extreme western MA Friday afternoon and chance pops for most of the area Friday night. Showers/thunder end from west to east Saturday morning. Temps aloft 13-15C should support max sfc temps in the low to mid 80s. Sunday... The Saturday cold front moves south of New England, but with long range data suggesting it may stall to our south. In this scenario, a low pressure wave would move along the front from the Ohio Valley and pass south of us. There is some potential for clouds and a chance of showers for July 3rd, mostly along our South Coast with diminishing likelihood to the north. This will need to be monitored. && .AVIATION /18Z 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/... Through 00z...High Confidence. VFR. S-SW winds continuing with gusts up to 20-25 kt. Tonight...Moderate Confidence. Mainly VFR. Scattered showers and isolated thunderstorms move into central and western areas, mainly near or after midnight with MVFR-IFR CIGS/VSBYS. Low chance for LIFR CIGS in stratus/fog across portions of western MA and northern CT. Thinking a lower risk for stratus and fog along the south coast. including the Cape and islands. The issue there will be the amount of low level dry air to overcome. Any saturated layers expected to be quite shallow. This will need to be watched closely overnight. Tuesday...Moderate confidence. Any low clouds and fog with patchy MVFR-IFR conditions should dissipate by 14Z. Will see MVFR-IFR conditions in scattered showers and thunderstorms, mainly away from the coastal plain during the afternoon. Tuesday night...Moderate confidence. VFR with areas of MVFR in numerous showers and isolated thunderstorms. KBOS TAF...High confidence. VFR. S winds increase today, gusting up to around 20 kts during the afternoon hours. KBDL TAF...High confidence. VFR. Low to moderate chance for MVFR- IFR CIGS/VSBYS late tonight in low clouds/fog. Outlook /Wednesday through Friday/... Wednesday...Moderate confidence VFR with areas of MVFR in morning showers and thunderstorms. Areas of IFR possible in fog and low clouds. South winds gusting to 20 knots will shift from the West after the cold front moves through. Thursday-Friday...Moderate confidence VFR. North winds become variable Thursday, then from the south Friday. Showers/tstms will develop over New York State, and may move into Southern New England Friday evening and night. These showers and storms would have areas of MVFR cigs/vsbys. && .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 overall confidence. Expecting relatively tranquil boating conditions across most of the coastal waters. South to southwest wind gusts should stay less than 25 kt. Seas expected to stay 4 feet or less, most of the time. Some rough seas around 5 feet possible across the outer coastal waters east of MA this afternoon. This seas should diminish some this evening. The other issue will be the possibility of poor visibility late tonight. Increasingly humid air moving over the relatively colder water, could lead to areas of fog. Not as confident in this particular aspect of the forecast. This potential will need to be watched overnight. Scattered showers, and perhaps a few isolated thunderstorms, should eventually impact the coastal waters, mainly Tuesday night into Wednesday. Outlook /Wednesday through Friday/... Wednesday...Moderate confidence. Showers and thunderstorms cross the waters with south wind gusts near 20 knots at times. Winds shift from the west as a cold front crosses the waters. Low vsbys possible ahead of the cold front in showers and storms as well as in fog. No headlines planned at this time. Thursday-Friday...Moderate confidence. High pressure builds over the waters Thursday and moves off to the east Friday. A cold front approaches from the west Friday night. Winds and seas should remain below Small Craft Advisory criteria. Scattered showers/thunderstorms possible Friday night as the cold front approaches. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 2 AM EDT Tuesday for ANZ250. && $$ SYNOPSIS...WTB/Belk NEAR TERM...Belk SHORT TERM...Belk LONG TERM...WTB AVIATION...WTB/Belk MARINE...WTB/Belk is the U.S. government's official web portal to all federal, state and local government web resources and services.