Area Forecast Discussion
Issued by NWS Boston, MA

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828 FXUS61 KBOX 272323 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 723 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 /UNTIL 6 AM TUESDAY MORNING/...
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7 am update... Areas of low clouds have advanced from offshore ahead of deck of mid-upper clouds associated with a weakening rain shield. This suggests mainly cloudy conditions overnight. Risk for rain is non-zero everywhere as the weakened pre-frontal trof moves through. Will highlight mainly chance pops from W-E through midnight local. Otherwise, higher dwpts suggest a slightly more sticky night and higher risk for areas of fog to develop later, especially where any rain falls. Previous discussion... 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.
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&& .SHORT TERM /6 AM TUESDAY MORNING 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 MONDAY/... Highlights... * Showers/thunderstorms end Wednesday * Seasonable Thursday and Friday. * Another risk for showers and storms, late friday and the weekend. Overview and model preferences... PNA remains strongly positive through much of the long term with negative EPO. Therefore, the reflection across the CONUS remains nearly unchanged through the period. This is also partially thanks to a rex-type block with PACNW vortex leading to building ridge across the northern prairies, culminating in persistent longwave trof across the northeast. An initial shortwave will be exiting Wed along with an attendant cold front leading to a brief period of weak ridging until secondary shortwave from Hudson Bay reinforces the longwave trof by late in the week. This trof does take on a slight negative tilt suggesting a slightly stronger system, however the bulk of the jet forcing shifts into the Boreal forest regions of Canada. Therefore, the generally dry with only a risk for spot showers/storms are expected to continue through this long term cycle. Deterministic guidance is generally in good enough agreement that a blend should still work fine as a starting point. Details... Wed... Cold front will be moving through the region and continuing to weaken as it parallels steering flow aloft. Remnant shra and even an isolated T-storm can`t be ruled out until the front clears the region fully, however noting a significant drop in PWATs from 1.5 inches to an inch or less through the day. The sounding reflects this drying and suggests some stabilization with subsidence inversion development. Therefore, in spite of the slow movement of the front, precip chances will wain through the day. H85 temps near +12C should still lead to temperatures in the mid 80s. Thu... Dry wx prevails under weak ridging with front settling offshore. H85 temps still near +12C, so another day with highs in the 80s and lows dropping back into the upper 50s and low 60s is expected. Fri into Sun... More significant differences here between available guidance, including the ensembles. Cold front will sweep through the region connected to low pres moving across ON/QC. Best forcing remains N, however decreased stability coincident with increase in PWATs back to nearly 1.5 inches suggest increasing risk for diurnally driven shra/tstorms. How quickly and ultimately how far the front moves offshore will define how long into Saturday this risk lasts. Secondary frontal wave development also possible, with the ECMWF leading the charge for Sun, suggesting some rain across the region from the S. Will maintain a low risk, but with settling trof, it may remain far enough offshore for little impact. Either case, a relatively unsettled period. Early next week... Another round of weak ridging within the longwave trof suggests a return to dry wx and seasonable temperatures. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/...
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Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday Night/... Tonight...Moderate Confidence. Mainly VFR. Scattered showers and isolated thunderstorms move into central and western areas through 04Z, with MVFR-IFR CIGS/VSBYS. Low chance for LIFR CIGS in stratus/fog across portions of western MA and northern CT. Some stratus expansion likely overnight, moving north from the south coast where it currently resides. 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 Saturday/... Wednesday...Moderate confidence VFR with areas of MVFR in morning showers and thunderstorms. Areas of IFR possible in fog and low clouds especially in the morning. South winds gusting to 20 knots will shift from the West after the cold front moves through. Thursday-Saturday...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.
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&& .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 Saturday/... 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-Saturday...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...Belk/Doody NEAR TERM...Belk/Doody SHORT TERM...Belk LONG TERM...Doody AVIATION...Belk/Doody MARINE...Belk/Doody

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