Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 310133 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 933 PM EDT SAT JUL 30 2016 .SYNOPSIS... An area of low pressure will move slowly eastward from the lower Great Lakes Region towards southern New England. The warm front extending from this low is expected to remain to our south during tonight and Sunday, which will allow for scattered showers and isolated thunderstorms across our area. This low will pass south of New England during Sunday night and Monday, then move offshore during Tuesday. High pressure will build out of northern New England during Wednesday through Friday, bringing dry conditions. Temperatures will warm up toward the end of next week. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... 930 pm Update... Rainfall rates have decreased over past hour and were no more than 1"/hour across parts of CT Valley. This activity formed in an area of marginal instability (CAPES up to 500 j/kg) but on nose of moisture axis which extends from mid Atlantic states into central MA. High-res models keep showers around southern New England overnight, and want to weaken activity as it passes E of Worcester Hills, focusing most of it near the Berkshires after midnight. This looks reasonable based upon radar trends so have adjusted PoPs accordingly (highest in W New England). That`s not to say there won`t be a stray shower or two farther E as well. Warm/muggy night ahead with lows in 60s to around 70 and patchy fog, which will be dense in spots near South Coast. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... During Sunday the warm front is expected to remain draped just south of our area, as the weak low pressure gradually moves eastward. Thus a continued modest overrunning setup is anticipated. For Sunday have the highest (likely) POPs in the western MA/north central CT where the models suggest better forcing. Chance pops to the east. With K indices in the lower 30s, cannot rule out isolated thunder during Sunday. Skies are expected to be mainly cloudy through the day. The combination of clouds and generally onshore flow is expected to keep temperatures in the mid to upper 70s on Sunday. During Sunday night models show the weak low pressure passing south of New England. This will bring continued cloudiness to the area, along with scattered showers/isolated t-storms. Lows mainly in the 60s are expected. With abundant low level moisture expecting some areas of fog. && .LONG TERM /MONDAY THROUGH SATURDAY/... Highlights... * Unsettled weather through early Tuesday with scattered showers, mainly over northern and western areas * Isolated thunderstorms possible across central and western areas Monday afternoon/evening * Mostly dry weather expected Tuesday afternoon through Friday, with a warming trend toward the end of next week Overview and model preferences... 30/12z guidance continues to shower decent overall agreement with synoptic trends over this portion of the forecast. Agreement on some of the more significant details, not so much. Latest guidance continues to show an open wave of energy in the mid levels passing the northeast USA early next week. Then the mid level flow transitions to a nearly zonal flow for the second half of next week. One question which still needs to be answered is how close does another mid level open wave get to southern New England toward next weekend. This nearly zonal flow should lead to much quieter weather during the middle of next week. At the surface, there is some disagreement at how close a pair of low pressures get to our region early next week. This will be key to determining how quickly the risk for showers winds down Tuesday. The majority of the guidance keeps these low pressures to our south Monday into Tuesday. So while not expecting a washout, have low confidence with this portion of the forecast, especially with timing. Used a blend of available model and ensemble guidance for this portion of the forecast. Details... Monday through early Tuesday... Expect a couple of low pressures to slowly ride along a stalled front just off the southern New England coast into early Tuesday. This will keep a good low to mid level moisture feed across the region thanks to an E-SE wind flow that will slowly back to NE late Monday night into Tuesday as the final low pressure pushes offshore. The greatest risk for showers still appears to be Monday, gradually diminishing Monday night into Tuesday. Greatest risk for showers should be across the interior, but really anywhere in southern New England has a shot at some showers or thunderstorms. Will see the final low push offshore early Tuesday as it becomes better organized. The last of the showers should start to dissipate during the morning. With the mainly onshore flow, expecting temperatures to run several degrees below seasonal normals, especially toward the coasts. Tuesday afternoon through Friday... This still looks like a mainly dry period of the forecast. Cannot rule out a stray, isolated shower. There may be just enough instability and moisture to generate one or two, especially across the higher terrain of interior southern New England. Temperatures should return to seasonal levels Wednesday, then will warm further as winds become more S-SW as the high crests across the region, then slowly pushes offshore. Humidity levels will also slowly increase. Saturday...A cold front is currently expected to cross our region. This should lead to a chance of showers. Still lots of time to work out the timing details. && .AVIATION /02Z SUNDAY THROUGH THURSDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday Night/... Tonight...Moderate confidence. Mainly VFR ceilings are expected to start, except localized IFR cigs/vsbys in fog possible Cape/Islands. Then areas of MVFR cigs/vsbys developing overnight in scattered showers and areas of fog. Localized IFR cigs/vsbys possible. Sunday...Moderate confidence. MVFR ceilings/vsbys to start with scattered showers and patchy fog. There is a chance for IFR ceilings/vsbys in stratus/fog near the coastline. Ceilings should become mostly VFR for afternoon although some MVFR ceilings will be possible in vicinity of showers. Sunday night...Moderate confidence. MVFR/IFR cigs/vsbys with scattered showers and areas of fog. KBOS TAF...Moderate confidence through Sunday. VFR conditions expected through this evening. Occasional MVFR ceilings possible in vicinity of showers and fog late tonight/Sunday. Weakening thundershower south of the terminal through 01Z. KBDL TAF...Moderate confidence through Sunday. VFR conditions expected through this evening, except brief MVFR cigs/vsbys possible in an isolated shower or t-storm. Occasional MVFR ceilings possible in vicinity of showers and fog late tonight/Sunday. Outlook /Monday through Thursday/... Monday through Monday night...Moderate confidence. Mainly VFR. Scattered showers possible at any time. Cannot rule out a heavier shower or thunderstorm with local MVFR-IFR conditions, mainly from central Mass into N Connecticut Monday afternoon and evening. Areas of late night/early morning fog with IFR CIGS/VSBYS Monday night. Tuesday...High confidence in trends. Moderate confidence in timing. Mainly VFR. Scattered showers across the CT Valley through north central and northeast MA Tuesday morning, then improving. May see brief local MVFR conditions in any showers. Patchy late night/early morning fog with MVFR-IFR conditions Tuesday night in the normally prone areas. Wednesday and Thursday...High confidence. VFR. Just a few areas of MVFR possible in patchy late night/early morning valley fog and in the usual fog prone locations. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday Night/...High confidence. Winds and seas are expected to remain below Small Craft Advisory thresholds through Sunday Night. Areas of visibilities 1 to 3 nm in areas of fog are possible at times tonight along the waters around Nantucket, and isolated to scattered showers are possible over the waters later tonight and Sunday. For Sunday night, visibility restrictions possible in scattered showers and fog patches. Outlook /Monday through Thursday/...High confidence. Monday through Tuesday...Relatively light winds and seas. Visibility restrictions in patchy late night/early morning fog both nights, and in scattered showers Monday and Monday night, slowly improving on Tuesday. Isolated thunderstorms possible off the RI coast Monday into Monday evening. Tuesday night through Wednesday...Persistent onshore winds continue. A passing low pressure may generate rough seas across the eastern coastal waters. Local visibility restrictions continue Tuesday night in patchy fog, mainly after midnight through mid morning Wednesday. Thursday...Tranquil boating conditions with light winds and seas expected. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Belk/NMB NEAR TERM...JWD SHORT TERM...NMB LONG TERM...Belk AVIATION...Belk/NMB MARINE...Belk/NMB

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