Area Forecast Discussion
Issued by NWS Boston, MA

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857 FXUS61 KBOX 242315 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 715 PM EDT Mon Jul 24 2017 .SYNOPSIS...
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Widespread rain will continue to gradually move offshore this evening, but the cool and damp conditions will linger into Tuesday. High pressure will bring a return to dry and pleasant weather for Wednesday. Cold front with a surface low pressure wave approaches southern New England Thursday night and exits the area late Friday. Dry weather and seasonable temperatures expected next weekend.
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&& .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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7 PM Update... Radar at 7 PM depicted the steadier rain having moved offshore except lingering along coastal eastern MA. May continue to have measurable rain until 9 PM or so along coastal MA from Salisbury to Plymouth perhaps aided by speed convergence of NE wind due to land friction along the coast in moist air mass. Elsewhere, still see a risk of widely scattered light showers or patchy drizzle. Have tweaked POPs to reflect latest thinking. Clouds will prevent much diurnal cooling but did lower temperatures a degree or two in many locations to reflect current trends and latest guidance. Prior Discussion... Widespread rainfall was confined to the eastern half of southern New England late this afternoon, with much more spotty showers farther west. Expecting this rainfall to move offshore this evening as a low pressure moves farther from our region. Cold and damp weather will stick around through much of tonight. Cannot rule out some showers or patchy drizzle. Temperatures will continue to slowly fall through this evening.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... A little better start to Tuesday. Despite clouds lingering to start the day, we should see a drying and clearing trend during the afternoon, and especially Tuesday night, as a high pressure arrives from the north. With winds expected to be more from the north than east, max temperatures should be noticeably higher during the day than Monday, but still below normal. Below normal temperatures continue Tuesday night. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... Highlights... * Dry weather and seasonable temperatures on Wednesday * Showers and possible thunderstorms late Thu with showers likely lingering into Fri * Dry weather and seasonable temperatures likely for the weekend Overview... Ridge builds over the intermountain west while the eastern United States looks susceptible to troughing. An anomalously strong short wave trough for this time of year will cross the Great Lakes region on Thu and New England on Fri. There is considerable disagreement between the GFS and ECMWF operational runs and ensemble output regarding strength of this short wave trough. Dry weather should follow in the NW flow behind the short wave passage for the weekend when there is much better consensus among the medium range models. There is also fairly reasonable model consensus on 850 mb temperatures for the weekend time period with resultant surface temperatures likely near seasonable levels. With a few tweaks in the Thu and Fri period, have gone close to a model consensus for the longer term forecast period. Period of Focus...Thursday afternoon into Friday The one period of extra focus in the longer term period covers Thursday afternoon through Friday when operational and ensemble model disparities result in somewhat below average confidence on the outcome. All models depict the short wave trough passage but vary considerably in strength and some in timing. The ECMWF suite of model runs depict a much stronger and as one might expect slower system than the GFS suite of model runs. Timing could also play a role in convective potential on the front end late Thursday afternoon and evening. Have opted to go close to continuity with POPs and just a tad below model consensus due to model discrepancies. Nevertheless, do believe there will be enough energy to support likely POPs in most areas. Also, adjusted temperatures down just a little across northern MA from a straight model consensus due to a high probability of cloudiness and at least scattered showers. If the latest ECMWF run proves to be correct, then we will probably need to lower those high temperatures on Friday at least a little more and raise POPs. As the short wave trough approaches and the 500 mb heights begin to fall, the air mass becomes marginally unstable late Thursday, mainly across western and northern MA and do have a chance of thunder in the gridded forecast. The slower timing scenarios, however, would bring the forcing into the region well past the favorable diurnal time. There is relatively strong vertical shear as one might expect to be associated with a robust short wave trough, but the degree of instability remains something of a question mark. For now, have high chance or low likely showers and slight chance or chance thunder. We`ll be able to refine this as we get closer. && .AVIATION /23Z MONDAY 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/...Moderate confidence. Tonight...Still expect mostly IFR or low MVFR CIGs to prevail with lowest across high terrain terminals and E/SE coastal areas. Patchy -SHRA/DZ especially along E MA coast and higher terrain terminals. NE Winds gradually turn N. Winds remain strongest along E MA coast sustained around 15 kt with gusts up to 25 kt. Tuesday into Tuesday night... Improving trends. MVFR-IFR mix gradually lifting, especially Tuesday night. Still a bit breezy along the east coast with sustained winds up around 10 kt and gusts up to 20 kt Tuesday, diminishing Tuesday night. KBOS Terminal...NE winds back farther N tonight. IFR CIGS for much of the night, possibly lifting to very low MVFR at times. Moderate confidence in timing for improvement to MVFR during Tue. KBDL Terminal...IFR or low MVFR ceilings persisting through roughly midday Tuesday. Outlook /Wednesday through Saturday/... Wednesday through Thursday morning...VFR. Late Thursday afternoon through Friday...MVFR ceilings and visibilities in areas of showers. Isolated thunderstorms late Thursday afternoon and evening. Saturday...VFR.
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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/... Low pressure moves farther away from the waters tonight, backing winds from northeast to north across most of the waters. Reduced visibility in rain and fog. rain diminishes this evening, but fog and spotty drizzle likely to linger through daybreak Tuesday. Small Craft Advisory for most waters continues, concluding late Tuesday into Tuesday night as winds subside and seas diminish. Outlook /Wednesday through Saturday/... Conditions during most of the period will likely remain below Small Craft Advisory thresholds. However, this is a risk that winds and seas may approach 25 knots and 5 feet, respectively, in an increasing SW flow Thursday afternoon and a northerly flow Friday afternoon and night, depending upon the strength of a low pressure area that passes across New England and the Gulf of Maine on Friday. && .TIDES/COASTAL FLOODING... Continued strong NE flow continues tonight with sustained winds around 10 to 15 mph with gusts upwards of 30 mph. This yields a surge upwards of a foot for locations along the E MA coast N of a low sweeping W to E along the waters south of New England. A Coastal Flood Advisory continues for the evening high tide accordingly, given surge on top of high astronomical high tides. && .CLIMATE... Here is where we stand for record low maximum temperatures for the calendar day. Record Max Temperature Boston 63 - 1904 65 Hartford 67 - 1997 68 Providence 67 - 1997 66 * probable new record Worcester 60 - 1964 61 && .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...Coastal Flood Advisory from 11 PM this evening to 3 AM EDT Tuesday for MAZ007-015-016-019-022-024. RI...None. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ232. Small Craft Advisory until 2 AM EDT Tuesday for ANZ230. Small Craft Advisory until 2 PM EDT Tuesday for ANZ231-251. Small Craft Advisory until 9 AM EDT Tuesday for ANZ235-237. Small Craft Advisory until 8 PM EDT Tuesday for ANZ250. Small Craft Advisory until 3 AM EDT Wednesday for ANZ254. Small Craft Advisory until 2 AM EDT Wednesday for ANZ255-256.
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&& $$ SYNOPSIS...Belk/Thompson NEAR TERM...Belk/Thompson SHORT TERM...Belk LONG TERM...Thompson AVIATION...Belk/Thompson MARINE...Belk/Thompson TIDES/COASTAL FLOODING... CLIMATE...

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