Area Forecast Discussion
Issued by NWS Boston, MA

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317 FXUS61 KBOX 301149 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 749 AM EDT Sun Apr 30 2017 .SYNOPSIS... Strong high pressure over southern Quebec will build southeast across New England today, bringing drier and much cooler air. This high pressure moves off the coast this evening, and a warm front moves north into our region Monday. A cold front will move through Tuesday. Another storm moves toward southern New England late Thursday or Friday, and could linger nearby into Saturday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... No major changes to the forecast this morning. Brought the forecast back in line with observed trends. Previous Discussion... Colder air continues to filter in on northwest to north winds early this morning. Temperatures had cooled to 50 to 55 in western and central MA and Provincetown with 55 to 60 elsewhere. It was in the 40s in the Berkshires and in Cheshire County, NH. Dewpoints reflected dry air...in the 30s to lower 40s across the region. The gradient, which was still supporting some gusts to 20 mph along the coast early this morning, will weaken and winds will diminish during the day. The wind direction will become northeast, then east. It will be much cooler than yesterday, with highs ranging from the low/mid 50s along the eastern MA coast to the low/mid 60s in the CT Valley. Sunshine to start the day will give way to increasing clouds from SW to NE as mid level moisture spills over the ridge. There is a low risk for a brief shower in the northwest hills as warm advection develops late in the day...otherwise it will be dry. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... Tonight... As high pressure moves offshore, a warm front will approach SNE from the south and west. SREF probabilities are near 100 percent for low cloudiness to rapidly develop across the entire region. Expect patchy fog along the south coast as higher dewpoint air moves in over colder sea surface temperatures. Models are generating some light QPF which is likely some drizzle given the abundant low level moisture and dry air aloft. As the night progresses, there could also be some scattered showers, as a southwesterly low level jet of 40 kt develops, accompanied by an increase in K Indices...to near 30. Lows will be mainly in the mid 40s. The astronomical tide will be on the high side again...11.45 feet at Boston at 3:35 AM, but little in the way of storm surge is expected, with southeast winds less than 20 kt, so am not expecting much in the way of splashover. Will keep an eye on this possibility. Monday... The warm front will continue moving northeastward but may have trouble making it all the way into the Merrimack Valley. Have gone with a model blend of temperatures...which are mainly in the 60s but range from near 70 in the CT Valley to the upper 50s in Essex County, MA and over outer Cape Cod and the Islands. The day will start will start with low clouds, fog, and areas of drizzle. The surge of higher K indices exits northern MA by mid- morning, and the risk of any showers will end from south to north along with it. Much drier air aloft moves in from the south, actually, for a time, allowing for some breaks of sunshine through mid-afternoon. Then, clouds will increase and there is a chance of showers late in the afternoon, well in advance of an approaching cold front. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... Overview... Still seeing variations in the model solutions for later this week, although some details are starting to emerge with greater confidence into Thursday morning. 30/00Z operational GFS continues to be out of step with the GEFS mean, as well as the ECMWF and CMC. Favored a consensus approach through Wednesday, then leaned a bit more toward a non-GFS solution Friday into Saturday. Lower than average confidence in the Friday-Saturday forecast. Details... Monday night-Tuesday...Moderate confidence. Low pressure will push across the Great Lakes into Ontario and western Quebec during this timeframe. Strong SW low level jet will result in excellent moisture transport, and help to organize modest instability ahead of a cold front. Not expecting severe weather, since the primary time period would be Monday night, but with 45-55 kt winds, cannot completely dismiss the possibility. Showers move out of our region Tuesday morning, but the cold front will lag a bit longer. Gusty southwest winds should continue through the day. Once the sunshine breaks out, expecting another day of above normal temperatures. Wednesday...Moderate confidence. This is still looking like a mainly dry period. Cyclonic flow aloft will mean a period of diurnal clouds, mostly toward NW MA. Any isolated showers which might develop would be confined to far western MA. Near normal temperatures. Thursday-Friday...Moderate confidence. Have greater confidence early Thursday morning will start out dry. Lots of ingredients lining up for a period of wet weather, the question which is harder to pin down is the timing. Have increasing rainfall chances from SW to NE through the day Thursday, leading into the more likely period of rainfall Thursday night into Friday. Rainfall could be heavy at times. Saturday...Low confidence. This period remains complicated. GFS still has a very wet solution, while the CMC, ECMWF, and GEFS suggest a closed 850 mb low passes by to our west, which would force a dry slot into southern New England during the. As previously mentioned, favored the drier non-GFS solutions, but did not go with a completely dry forecast. It will likely be another day or two before this discrepancy start to get resolved. && .AVIATION /12Z 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. Today...High confidence. VFR. Low risk for a brief shower in northwest hills late in the afternoon. Easterly winds 5-15 kt. Tonight...Moderate confidence. Conditions deteriorating to MVFR/IFR around midnight as stratus and patchy drizzle develops. Areas of fog along the south coast. Monday...Moderate confidence. MVFR-IFR CIGS through mid to late morning in areas of drizzle and fog. Some improvement to VFR mainly south of the Mass Pike from late morning through mid afternoon. Becoming MVFR again with scattered showers late in the afternoon, mainly in western sections, well out ahead of an advancing cold front. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Monday Night through Thursday/... Monday night...High confidence. CIGS lower to mainly MVFR across most of the region, with local IFR in heavier SHRA. Scattered TSTMS. SW LLWS up to 45-55 kt at 2000 ft AGL along the south coast, including the Cape and islands. Tuesday...High confidence. MVFR-IFR conditions linger early morning in leftover showers, then improving to VFR through midday. LLWS with SW winds 45-55 kt across south coastal areas possible through 16Z, highest across the islands. Wednesday...High confidence. VFR. Wednesday night-Thursday...Moderate confidence. VFR expected through the period, although CIGS lower during Thursday. Increasing coverage of rain from SW to NE Thursday, with MVFR VSBYs in heavier rain during the afternoon. -RA and patchy fog lingers with areas of MVFR CIGS/VSBYS into Thursday night. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday/...High confidence. Today into tonight...NW-N winds may gust to near 20 kt early this morning. Winds then become N/NE later this morning and veer to the E/SE by mid-late afternoon. Speeds will diminish to 15 kt or less. Winds become SE to S tonight. Seas below Small Craft Advisory thresholds. Vsbys lowering to below 3 miles in fog developing after midnight over the southern coastal waters. Monday...Moderate confidence. Warm front moves across the waters Monday. SE winds ahead of the front become S-SW behind the front, mainly over the southern waters. Visibility restrictions in areas of drizzle and patchy fog through early Monday afternoon. Seas could build to 5 ft over the southern waters late in the afternoon. May need to issue Small Craft Advisories...but still a little too early. Outlook /Monday Night through Thursday/... Monday Night...Moderate confidence. Increasing SW winds ahead of a cold front approaching the waters, with gusts up to 30 kt. Rough seas building across the outer coastal waters, too. Showers likely with scattered thunderstorms. Visibility restrictions in precipitation. Small Craft Advisories likely. Tuesday...Moderate confidence. Improving conditions as showers move out of the area during the morning. Gusty SW winds up to 30 kt continue, before diminishing Tuesday night. Rough seas linger across the outer coastal waters. Small Craft Advisories likely for the southern coastal waters. Wednesday...Moderate confidence. Winds continue to diminish through Wednesday night, but seas will take a while longer. Thursday...Moderate confidence. Winds expected to remain less than 20 kt, with seas less than 4 feet. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Belk/GAF NEAR TERM...Belk/GAF SHORT TERM...GAF LONG TERM...Belk AVIATION...Belk/GAF MARINE...Belk/GAF

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