Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 251808 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 208 PM EDT Tue Oct 25 2016 .SYNOPSIS... Some cold unstable air will bring areas of clouds and unseasonably cool temperatures through Wednesday. Low pressure approaches from the Great Lakes Thursday, then redevelops closer to the coast and moves across our area Thursday night and early Friday. This will bring 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 /THROUGH TONIGHT/... Through evening... Upper shortwave overhead with cold pool and cold pool moisture generating clouds. The air is dry beneath these clouds, with dew point depressions of 20-25F, so any attempt at showers should dry up on the way down. Daytime heating by the sun is creating a mixed layer up to near 850 mb. Winds in the mixed layer are 20-25 knots, so expect wind gusts in this range. Temps aloft around -5C which will support max temps in the upper 40s and lower 50s. Tonight... High pressure axis remains centered to the west. North-northwest winds continue at night but the winds and diurnal sky cover will diminish with sunset. The northwest flow has been transporting colder air into the region. With this cold air in place, we expect temperatures to fall below freezing away from the coast and the mid 30s to around 40 near the coast. With these values, we expect freezing conditions in the interior including several areas that have not yet experienced a killing freeze. We will continue the Freeze Warning for those areas. For those areas that have had a freeze, the cold air tonight will be a moot point. Temps aloft around -5C to -6C with ocean temps 14-15C. This 20-degree differential with sustained winds 12 knots or higher will favor bands of ocean effect clouds, possibly a shower. But the direction will favor an offshore fetch that may clip Provincetown and parts of the Outer Cape. && .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... Wednesday... High pressure builds over the region. This should bring subsidence and mainly clear skies. Winds over the ocean will continue at 10-14 knots sustained, turning more from the north. This may keep some ocean clouds over Cape Cod, especially Hyannis and points east. Sunshine will work on -6C temps aloft to bring max temps in the mid 40s to around 50. Wednesday night... High pressure ridge will be in place surface and aloft through the night. This should provide mainly clear skies and light winds. Depending on specifics of the ridge axis, the north wind over Cape Cod could back around from the northeast, drawing ocean clouds farther west to the Cape Cod Canal. Great Lakes shortwave and associated surface low over the Midwest will approach overnight. Moisture fields show increasing potential for mid and high clouds during the night, but the lower thicker clouds hold off until near sunrise. Based on the light wind prevailing fair skies, we have stayed close to the existing min temp forecast. The coldest temps may actually be reached a couple of hours earlier than normal, with steady or slowly rising temps late at night as the clouds build in. With the dry low level air expected, the lack of any source of lift, and no forecast of measureable pcpn by this system east of the NY border... we will show nil pops through 12z Thursday. && .LONG TERM /THURSDAY THROUGH MONDAY/... Updated at 423 am... Highlights... * Cold rain and wind Thu/Thu ngt w/snow and sleet likely at the onset across the interior * Blustery with a drying trend Fri 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 /18Z TUESDAY THROUGH SUNDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Through evening... VFR. Scattered to broken sky cover from diurnal clouds, but with bases 5000-6000 feet. These should diminish with sunset. Winds in the mixed layer reach 20-25 knots, thus surface winds will gust at times to these speeds. Winds diminish after sunset. Tonight...High confidence. VFR. Diminishing NW winds. Ocean effect clouds may linger on the Outer Cape. Low risk of showers in this area. Wednesday...High confidence. VFR. Winds turn a little from the North but with gusts a little lighter than we had today. Wednesday night...High confidence. VFR. Ocean effect clouds may linger on parts of Cape Cod, especially if surface winds turn N-NE overnight. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Thursday through Saturday/...Moderate confidence. Updated 423 am... 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 Night/...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 /Thursday 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...WTB/Nocera NEAR TERM...WTB/Nocera SHORT TERM...WTB LONG TERM...Nocera AVIATION...WTB/Nocera MARINE...EVT/Nocera is the U.S. government's official web portal to all federal, state and local government web resources and services.