Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 292316 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 716 PM EDT Sat Apr 29 2017 .SYNOPSIS... After a cold frontal passage tonight, high pressure builds over New England Sunday with mainly dry but much cooler air. A warm front moves into the region on Monday, followed by a cold front on Tuesday. Another storm moves toward southern New England late Thursday or Friday, and could linger nearby into Saturday. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... 7 PM Update... Secondary front clearing the region from N-S, with winds shifting to NW and gusting up to 25-30 kt at 22Z. Several reports of gusts over 30 kt, including 38 kt at KBOS, 37 kt at KOWD, 34 kt at KBED and 29 kt at KTAN. Still noting gusts to 30-35 kt at 23Z across central and eastern areas. Gusts up to around 30 kt also noted on the coastal waters ahead of the front. Have extended the small crafts to Cape Cod Bay, Nantucket Sound through 02Z, as well as the eastern outer waters from Cape Ann to Plymouth through 06Z. Have updated near term to bring conditions current and incorporated trends through around 06Z. Previous Discussion... Cold front moving into western New Eng will push off the coast this evening followed by a wind shift to NW then N as high pres builds to the north. Cooler and much drier will advect into SNE with dewpoints falling into the 30s overnight. Debris clouds from decaying MCS upstream will move into the region this evening, otherwise expect ptcldy and dry conditions tonight. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... Sunday... High pres builds across Gulf of Maine to east of Cape Cod bringing low level easterly winds. Much cooler airmass with temps up to 20 degrees cooler than today and possibly up to 30 degrees cooler along the eastern MA coast. Highs ranging from low/mid 50s eastern MA coast to mid 60s 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 interior in the developing warm advection pattern, but most of the day will be dry. Sunday night... As high pres moves offshore, warm front will approach SNE from the south and west. Expect low clouds to develop overnight along with patchy fog along the south coast as higher dewpoint air moves in over colder SST. Models are generating some light QPF which is likely some drizzle given the abundant low level moisture and dry air aloft. Lows will be mainly in the mid/upper 40s. && .LONG TERM /MONDAY THROUGH SATURDAY/... Overview... Overall medium range guidance remains in good agreement through the middle of next week as long wave H5 high sets up off the SE U.S. coast. However, changes see on the 12Z guidance for late next week, as both the ECMWF and GFS have tended keep the H5 long wave cutoff low meandering across the SE U.S., while the GGEM broadens it from the Carolinas northward to western Quebec. This lends to even less confidence during the Fri-Sat timeframe. Went along with consensus forecast amongst the models, then trended closer to blend without the GGEM for the latter portion of this period, but with low confidence. Details... Monday-Tuesday...Moderate confidence. Low pressure will push across the Great Lakes into Ontario and western Quebec during this timeframe. Will see associated warm front lift across the region, but low level moisture will get trapped so will areas of drizzle and patchy fog forecast through at least midday Monday across most of the region. This should lift N as S-SW winds begin to pick up Mon afternoon. Will see lingering showers through the afternoon mainly across N central and western areas. Low level SW jet, up to 50-60 kt along the S coast Mon night, will combine with some decent instability (SLIs at zero to -1, K indices in the lower 30s and CAPEs up to 200 j/kg) ahead of the approaching cold front to kick off some convection. Have put in a chance for thunderstorms as the front crosses the region through the night. Also noting good PWAT moisture plume along this front, up to 1.5 to 1.6 inches, so have also mentioned possibility of heavy rainfall. Should see precip start to taper off during the early morning hours across N CT into W Mass as dry slot wraps in behind the passing front. Even though a mainly SW winds continues, will see mild temps and gusty winds in place. Diurnal clouds will linger across N central and western areas with enough cold pooling aloft. Expect highs across the coastal plain and lower CT valley reach the lower 70s. Wednesday...Moderate confidence. Cyclonic flow continues across the region, so could see some diurnal clouds develop across N central and western areas during the day. A weak H5 short wave moves across but expect little if any precip except possibly across the E slopes of the Berkshires. Temps will run close to seasonal normals across the coastal plain but down to 5 degrees below normal over the higher inland terrain. Thursday-Friday...Low to moderate confidence. Continue to see another moisture plume working NE out of the SE states toward the region for this timeframe. Kept likely POPs going, with area of moderate to possibly heavy rainfall. Current forecasted QPF suggests up to 1.5 inches possible, but will monitor as noted wide solution spread amongst the suite over the last several runs. Saturday...Low confidence. 12Z GGEM appears to be the outlier this go-round, keeping cutoff low pres spinning across the mid Atlantic states, while GFS and ECMWF push high pres ridging SE out of the Great Lakes. With the change on this package, have kept CHC POPs in for now, but improving late Sat/Sat night. && .AVIATION /23Z SATURDAY THROUGH THURSDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short term...through Sunday. Through 00z...High confidence. VFR. Any lingering IFR VSBYS in fog near and over the islands will quickly improve by around 02Z. W-NW wind gusts 25 to 35 kts through 01Z- 02Z with frontal passage, then diminishing. Tonight...High confidence. Any lingering IFR fog over the islands rapidly improving, otherwise VFR. Diminishing winds becoming north. Sunday...High confidence. VFR cigs. Low risk for a brief shower in the interior. Easterly winds 5-15 kt. Sunday night...Moderate confidence. Conditions deteriorating to MVFR/IFR after midnight as stratus and patchy drizzle develops. Areas of fog along the south coast. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Monday through Thursday/... Monday...Moderate confidence. MVFR-IFR CIGS through mid to late morning in areas of drizzle and fog. Some improvement across central and portions of eastern areas from late Mon morning through Mon evening, then will lower to MVFR- IFR again Mon night with areas of fog and scattered showers. MVFR- IFR CIGS linger along the S coast Mon, then lower to mainly MVFR across most of the region Mon night. Scattered TSTMS Mon night. SW LLWS up to 45-50 kt at 2000 ft AGL along the S coast Mon night. Tuesday...Moderate to high confidence. MVFR-IFR conditions linger early Tue morning in leftover showers, then improving to VFR through midday. LLWS with SW winds 45-55 kt across S coastal areas, highest across the islands through 18Z. Wednesday...Moderate to high confidence. VFR. Wednesday night-Thursday...Moderate confidence. VFR early Wed night, then CIGS lowering to MVFR in areas of -RA. Patchy fog with local IFR VSBYS after midnight Mon night through around 12Z-14Z Thu. -RA and patchy fog lingers with areas of MVFR CIGS/VSBYS into Thu night. && .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. Through tonight... UPDATE...Have added Cape Cod Bay, Nantucket Sound and the eastern outer waters from Cape Ann to Plymouth to Small Craft. Gusts up to 25-30 kt will diminish from 03Z (nearshore) to 06Z (outer waters). Previous Discussion... Winds shift to north overnight as high pres builds to the north. Reduced vsbys in fog over south coastal waters through early evening, then improving. Sunday into Sunday night... N/NE winds will veer to the E/SE Sunday then eventually to SE/S Sunday night with speeds mostly 15 kt or less. Seas below SCA. Vsbys lowering in developing fog after midnight Sunday night over south coastal waters. Outlook /Monday through Thursday/... Monday...Moderate confidence. Warm front moves N of the waters late Mon night. SE winds along the E coast shift to S-SW by Mon night, while remaining S-SW on the southern waters. Gusts up to 30 kt develop on the outer waters Mon night. Seas build up to 7-9 ft Mon night on the southern waters and E of Cape Cod. Visibility restrictions in areas of drizzle and patchy fog Mon through early afternoon, then in showers through Mon night. Scattered thunderstorms Mon night. Small crafts likely. Tuesday...Moderate confidence. SW winds gusting to 25-30 kt through Tue, then shift to W and diminish Tue night. Seas remain up to 5-9 ft over the open waters Tue, then slowly subside Tue night. Local brief visibility restriction in patchy light rain and patchy fog Tue through midday. Wednesday...Moderate to high confidence. W winds may briefly gust to 25 kt on the southern waters with seas lingering at 5-6 ft during Wed. Winds diminish as they shift to N Wed night and and seas should subside Wed night Thursday...Moderate confidence. Light N winds shift to SE and increase, gusting to 25-30 kt Thu night. Seas will build after midnight to around 4-5 ft on the southern waters. && .TIDES/COASTAL FLOODING... * Isolated minor splashover possible during astronomically high tide tonight and Sunday night along the east coast The astronomical high tides remain elevated this weekend. Low risk and low impact for tonight/s high tide as winds will be offshore during time of high tide with little or no surge. The Sunday night tide is a bit lower but onshore flow may result in minor splashover along the most vulnerable shoreline roads. Boston High Tides (flood stage at Boston 12.5 feet)... 11.88 feet / Sunday 2:39 am 11.45 feet / Monday 3:35 am && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 10 PM EDT this evening for ANZ231- 232. Small Craft Advisory until 8 PM EDT this evening for ANZ230- 236. Small Craft Advisory until 2 AM EDT Sunday for ANZ250-254>256. && $$ SYNOPSIS...KJC/EVT NEAR TERM...KJC/EVT SHORT TERM...KJC LONG TERM...EVT AVIATION...KJC/EVT MARINE...KJC/EVT TIDES/COASTAL FLOODING...KJC is the U.S. government's official web portal to all federal, state and local government web resources and services.