Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 251111 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 711 AM EDT Tue Oct 25 2016 .SYNOPSIS... West to northwest winds will continue to bring unseasonably cool but dry conditions across the region through midweek. Some of the coldest air of the season will push across the region Wednesday into Thursday. Low pressure will track across the region Thu into early Friday and will be accompanied by a cold rain...possibly heavy at times and gusty winds along the coast. A period of snow and sleet is likely at the onset across the interior. A drying trend develops Fri in the wake of the low, but blustery northwest winds develop. Another round of showers is possible sometime over the weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 7 am update... Not much change from previous forecast. Cold but dry NW flow continues across New England. SPC mesoanalysis indicates 850 temps currently -5C to -6C across the area at 7 am with -9C upstream just across the NY/VT Canadian border. Thus robust cold air advection for late Oct with 850 mb temps anomalies running around -2 standard deviations colder than climo. Winds will increase later this morning as solar heating increases blyr mixing. This will only exacerbate the chilly conditions. Expect a mix of sun and clouds in this flow regime. Previous discussion below. =================================================================== Low pressure at the surface and aloft continues to spin across the Maritimes with W-NW flow in place. Strong H85 cold air advection in place on the NW flow aloft, with temps falling back to -5C to -8C through midday before leveling off. Also noting an H85 jet of 30-35 kt to pass across the region by mid-late morning. Lapse rates will increase up to 10C/km through H85, will see low level mixing increase. This will bring gusts up to 25-30 mph, though may be higher across the higher inland terrain. Will still see good downsloping on the NW flow, so expect skies to be mostly sunny, though clouds may linger across the east slopes of the Berkshires as well as near the Mass/NH border through late morning. Some diurnal clouds may develop away from the coast. As the low across the Maritimes start to slowly shift E this afternoon, winds will diminish from W-E, though will remain gusty across Cape Cod and the islands. The winds will also slowly veer to a more northerly direction toward sunset, which will allow for low clouds to form across the warmer ocean waters near and east of Cape Cod. Some question as to whether some ocean effect showers may develop toward sunset as well. RAP and 4km NAM Bufkit soundings signaling some ocean effect precip may develop on the outer Cape. The big question will be whether the winds shift to a more northerly direction to allow the ocean effect precip to work in, or if it remains more NW and keep it offshore. With the excellent cold air advection in place, will be a very chilly day today. Expect highs only in the lower-mid 40s across the higher inland terrain, ranging to around 50 along the coast. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... Tonight... N-NW winds will drop off, but not completely diminish except possibly the low inland valleys tonight. However, with the cold air in place, temperatures will plummet. Expect temps to fall below freezing away from the coast, but should hold in the upper 30s to mid 40s along the immediate coast. Some of our inland areas have not experienced a killing freeze yet, but should tonight. Have issued freeze warnings for those areas. Another question for tonight will be whether frost will form. Noting relative humidities up to 75 to around 90 percent after midnight in the areas where the freeze will take place. Can not rule out some patchy frost, especially where the winds drop off after midnight. Will also ocean effect clouds across portions of Cape Cod as well as Nantucket. There will also be a low chance for some showers there. Have only carried slight chance POPs mainly for the outer Cape and Nantucket. Wednesday... Any leftover clouds and isolated showers across the outer Cape should end by mid morning, though clouds will linger there through most if not the remainder of the day. Otherwise, high pressure will slowly push into the region, allowing for lighter N-NW winds. Skies will average out mostly sunny, though high clouds will filter in from the W during the afternoon. It will remain chilly though with highs in the 40s to around 50, mildest along the immediate south coast. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Updated at 423 am... Highlights... * Coldest temperatures of the season possible Wed ngt/Thu morning * Cold rain and wind Thu/Thu ngt w/snow and sleet likely at the onset across the interior * Blustery with a drying trend Fri Wednesday Night... 1034 mb high over Quebec will nose southward into New England providing one of the colder nights this season. 850 temp anomalies are about -2 standard deviations colder than climo by days end Wed. This cold/dry airmass will combine with light winds and mostly clear skies to allow temps to plummet with sunset Wed evening. Northerly flow over Cape Cod and the islands will preclude temps from free falling given SSTs still in the upper 50s to low 60s. In addition this air/sea temp difference on northerly flow will likely yield ocean effect clouds and limit temps from being as cold as across the interior. Any ocean effect showers on Wed will diminish as subsidence inversion lowers Wed night with surface high cresting over New England. Also some uncertainty on exact timing of mid/high clouds arriving into western portions of CT/MA. This will impact temp forecast. Otherwise just a cold/dry night with diminishing winds. As for mins...used a blend of the colder MOS guidance to derive low temps. Thursday into Friday... Interesting setup with cold airmass lingering over the region early Thu in response to 1035 mb high over Quebec. Meanwhile Robust northern stream short wave energy diving southeast into the Great Lakes/OH valley. Differences in deterministic guidance with 00z EC colder than 00z GFS on the front end with airmass over the region early Thu. This results in the EC driving the baroclinic zone/storm track farther southward. In addition EC is stronger with jet energy diving into the Great Lakes/OH valley and also mergers energy quicker than GFS...although not as robust as its prior 12z run. This results in mid level flow digging farther southward to our latitude...which would delay warming in the mid levels. In addition this also results in cyclogenesis developing farther south than the GFS...with EC forming secondary low along the south coast. This scenario would linger low level cold air longer across the interior. Both GEFS and EPS ensembles provide support for the deeper/colder solution of the ECMWF. Thus will blend the stronger/colder ECMWF solution into this forecast. However not expecting a high impact event here given system is progressive and doesn/t really intensify until it moves northeast of the region into coastal ME and Gulf of ME. So for now expecting a period of snow and sleet Thu at the onset across northwest CT/MA...possibly as far east as the Worcester Hills with a risk of a minor accumulation across the higher terrain of the East slopes of the Berkshires. Otherwise...with mid level low tracking west-northwest of the region mid level warming overspreads the entire region with a changeover to all rain by late in the day. For the remainder of the region a cold rain is expected and possibly heavy at times given strong jet dynamics and moisture advection. Could also have a period of brief strong onshore winds Thu ngt across Coastal eastern MA as secondary low intensifies over RI/southeast MA before exiting into Gulf of ME. System is fairly progressive so should see a drying trend Fri along with brisk northwest winds on the backside of the low. Weekend... Models differ on next bundle of northern stream energy. Good agreement that there will be a period of showers sometime this weekend. GFS is of lower amplitude with progressive system and risk of showers late Sat into Sat night. ECMWF more dynamic with risk of showers Sat night thru Sun night. Early next week...uncertainty on timing of departing system Sun/Mon. However thereafter both deterministic and ensemble guid suggest pattern deamplifying next week...suggesting not as cold as this week. && .AVIATION /11Z TUESDAY THROUGH SATURDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Updated 7 am... Not much change from 06z and 09z TAFs. Any cigs will be in the VFR range. Main issue today will be gusty WNW winds from late morning into the afternoon. Earlier discussion below. ===================================================================== Short Term /through Wednesday/...High confidence. Today...VFR. Mainly FEW-SCT clouds at 5-7kft across NE Mass and outer Cape Cod through midday. W-NW winds gusting up to 20-25 kts across higher terrain and coastal terminals. Tonight and Wednesday...Mainly VFR. May see MVFR CIGS move into outer Cape Cod and Nantucket with N-NW winds around or after 00Z through 14Z-15Z. Low risk of isolated showers. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Wednesday Night through Saturday/...Moderate confidence. Updated 423 am... Wednesday night... VFR and diminishing north winds. Thursday into Friday... IFR-LIFR likely. Initial SN/IP possible with potential accompanying LLWS transitioning to -RA/RA with embedded +RA, possible TSRA mostly S/SE. Blustery S/SE winds. Gusts up to 30 kts along the immediate shoreline terminals. Improving Friday with winds turning out of the WNW. Saturday... Brief period of VFR before conditions return low-end VFR to MVFR with another chance of -RA/RA. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday/...High confidence. NW winds will continue to gust up to 25-30 kt today, then gradually diminish tonight. Seas will remain up to 5-8 ft. Small craft advisories remain in effect. Winds and seas will diminish below small craft criteria along the near shore waters tonight, but will linger on the outer waters into Wednesday. Outlook /Wednesday Night through Saturday/...Moderate confidence. Wednesday night... North winds diminishing. Vsby may lower in rain and snow showers offshore. Thursday into Friday... Rain on the increase through Thursday, moderate to heavy at times with the possibility of thunderstorms. S/SE winds strengthening ahead of a deepening area of low pressure across the region. Seas building 8 to 10 feet the height of which will be on Friday, slowly dropping off thereafter as winds turn out of the W behind a cold front but remain breezy. Saturday... Breezy W winds continue as there is a brief lull in the weather. Seas remain above 5 feet on a good chunk of the waters as winds increase once again along with wet-weather late Saturday into Saturday night. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Freeze Warning from 2 AM to 9 AM EDT Wednesday for CTZ003. MA...Freeze Warning from 2 AM to 9 AM EDT Wednesday for MAZ006-007- 013-014-018. RI...Freeze Warning from 2 AM to 9 AM EDT Wednesday for RIZ001-003- 006. MARINE...Small Craft Advisory until 2 AM EDT Wednesday for ANZ232. Small Craft Advisory until 8 PM EDT this evening for ANZ230- 233-234-236. Small Craft Advisory until noon EDT Wednesday for ANZ231. Small Craft Advisory until 1 AM EDT Wednesday for ANZ237. Small Craft Advisory until 9 AM EDT Wednesday for ANZ235. Small Craft Advisory until 6 PM EDT Wednesday for ANZ250-254- 255. Small Craft Advisory until 8 AM EDT Wednesday for ANZ251. Small Craft Advisory until 2 PM EDT Wednesday for ANZ256. && $$ SYNOPSIS...Nocera/EVT NEAR TERM...Nocera/EVT SHORT TERM...EVT LONG TERM...Nocera AVIATION...Nocera/EVT MARINE...Nocera/EVT is the U.S. government's official web portal to all federal, state and local government web resources and services.