Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 272015 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 315 PM EST Mon Jan 27 2020 .SYNOPSIS... Varying amounts of clouds much of the week ahead along with mainly dry conditions expected. Dry conditions with closer to seasonable temperatures for the remainder of the workweek. Still watching for the potential for a coastal storm which may impact the region for the weekend, though it remains far from a certainty. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 1015 AM Update... Mainly cloudy skies across the region at mid morning as seen on 15Z observations and GOES-East visible satellite imagery. Only area with mostly sunny skies was across most of Cape Cod, Nantucket and Martha`s Vineyard. Temps were in the upper 30s across N central and W Mass into N CT, up to the lower 40s elsewhere. Area of snow showers lingering across the Capital District of E central NY into the Berkshires, though noting -SHSN reported at KORE at 15Z. Also noting patchy light precip on the latest NE regional 88D radar imagery across portions of N central CT and just off Cape Ann and outer Cape Cod. However, in these areas, T/Td spreads remain at 6 degrees or higher, so appears to be evaporating before reaching the ground. Mid level short wave working SE across E NY into W CT and W Long Island, which could trigger a brief light rain or snow shower there. May also see brief light rain and/or snow showers across portions of the E slopes of the Berkshires through at least mid afternoon as yet another short wave wraps SE around the low across the Maritimes. Previous Discussion... Northern stream short wave approaches the region from the west today providing cyclonic flow and lots of clouds especially inland and the high terrain with less clouds across the coastal plain. Not much moisture from this feature so any snow showers/flurries should be confined to the upslope regions of the Berkshires and possibly the northern Worcester Hills. Not as mild as Sunday with 850 mb temps down to about -6C today. Although well mixed boundary layer and some downslope W-NW wind component should support highs of 40-45, except upper 30s high terrain which is still 5-10 degs above normal. A modest W-NW wind will make it feel a bit cooler. && .SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY NIGHT/... Early Morning Update... Tonight... Dry weather continues behind departing short wave along with decreasing clouds after sunset. Weak cold air advection behind the trough with 925 mb temps cooling from about -2C at 00z to -4C by 12z Tue. Brisk NW winds at sunset will diminish as boundary layer likely decouples except in the urban areas, high terrain and Cape Cod/Islands should be enough pres gradient for at least some wind. Cooler but lows still a few degs above normal with low temps in the 20s, except 30-35 in the urban areas and Cape Cod/Islands. Tuesday... Dry weather likely prevails with next potent northern short wave not approaching the region until Tue night. The only exception to dry weather may be across the outer Cape including Nantucket and Cape Ann if winds have enough northerly component to generate some ocean effect snow (OES) showers. All Hi Res guidance hints at this OES potential. 925 mb temps cool a bit more to about -3C, supporting highs from the upper 30s to lower 40s, mid 30s high terrain. Still a few degs above normal. Regarding cloud cover, breaks of sunshine in the morning likely give way to diurnal clouds with cooling temps aloft and cyclonic flow. Clouds most abundant over Cape Cod and Nantucket with winds becoming northerly and cold advection across the relatively warm ocean waters. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... Highlights... * Dry conditions with seasonal to slightly above normal temps through Fri. * Still monitoring for a potential storm next weekend, but uncertainty remains high Details... Tranquil stretch of weather for the rest of the workweek as ridging both at surface and aloft builds across Southern New England. A weak shortwave trough will dig southward from eastern Quebec through much of New England during the latter part of Wednesday; though it will be a dry passage and its only real influence will be to induce a shot of cooler air (925 mb temps -8 to -11C per ECMWF, not exactly cold but a colder airmass than seen recently) for Wednesday night into Thursday. High pressure then shifts off the coast later Thursday, affording more of a milder southerly flow Thursday night into Friday. Overall looking for seasonable temperatures with good diurnal ranges, with mostly sunny skies during the day and clear/calm nights. Highs in the mid-upper 30s for Wednesday, with the coldest day being on Thursday with the cooler thermal profiles (low to mid- 30s); warming back into the mid 30s to lower 40s for Friday. Lows on Wednesday and Thursday nights into the teens to lower 20s; while lows Friday night in the mid 20s to near freezing. Saturday into Sunday: Still a considerable degree of uncertainty on the forecast for the weekend, as models continue to simulate a coastal low pressure near the Carolinas on Saturday. While today`s guidance has shown some tendency for a south/east-of-the-benchmark track, the exact track and resulting impacts remains uncertain. Phasing of trough energy in the northern stream (digging south from the Canadian Prairies) and southern stream (South Texas into the Gulf Coast states) will prove critical in determining how close to Southern New England this potential storm system may get. Today`s deterministic model guidance from the GFS and ECMWF indicate this phasing occurs late, with resulting deepening occurring south and east of the 40N/70W benchmark. These more offshore solutions have some support (a loose majority) from their respective ensemble members (EPS, GEFS). This would verbatim bring a glancing blow to the east and southeast coasts with little if any QPF in the interior, instead supporting a colder/largely dry northwest flow. Only the Canadian GEM brings a larger extent of the precip shield back far enough west to permit some impacts across a larger spatial area later Saturday into Sunday (on the western end of the guidance). While today`s guidance indicates a more offshore track, there does remain a number of members in the 12z GEFS and 12z EPS that are closer to the benchmark; given this and the evolution of this potential system hinging on aforementioned phasing, it still is too early to lock into any solution. Lack of antecedent colder air also opens the door for continued questions on p-type. Given the above, and that were are still a good 6 days out with guidance highly probable to change in subsequent days, think it is prudent to side the official forecast fairly close to continuity, with maybe a slight decrease in PoP in the interior given the SE track. Chances for snow/rain are thus indicated for all locations. Highs in the mid 30s to low 40s, and lows in the 20s. Monday: Some uncertainty exists on Monday depending on how weekend developments transpire. Most guidance indicates dry conditions under high pressure, with temperatures remaining near to slightly above seasonal normals. Were any snowpack to be around, again contingent on what may happen over the weekend - could see some pretty chilly overnight lows. Stuck more closely to a guidance blend for this period. && .AVIATION /20Z MONDAY THROUGH SATURDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 15Z update... Short Term...High confidence. Through 00Z... VFR CIGS at 040-060 for most areas through the afternoon. Local MVFR CIGS across NW Mass, mainly across the E slopes of the Berkshires. Mainly dry conditions, except for brief light -SHRA and -SHSN across confined to higher terrain of N central and W MA. W-SW winds through midday, becoming W-NW during the afternoon. Tonight... VFR. Mid and high clouds dissipate. Modest W-NW winds. Tuesday... VFR to start but then MVFR cigs develop over high terrain and also along eastern MA coast from Cape Ann to Cape Cod to Nantucket along with isolated -SHSN. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Tuesday night through Thursday/ ... Wednesday: VFR. Wednesday Night: VFR. Breezy. Thursday through Friday: VFR. Friday Night: Mainly VFR, with local IFR possible. Slight chance SHSN. Saturday: MVFR/IFR conditions possible. Slight chance RA, slight chance SHSN. && .MARINE... Short Term /through Tuesday Night/...High confidence. Through this afternoon...W-SW winds 15-20 kt with gusts up to 25 kt through midday, becoming W during the afternoon. Dry weather. Seas 4 to 7 ft on the open waters. Good visibility. Tonight...NW winds 15-20 kt early, diminishing to around 10 kt by around midnight. Seas up to 4 to 6 ft on the outer waters then slowly subsiding after midnight. Dry weather and good vsby. Tuesday...N-NW winds 10-15 kt. Scattered rain/snow showers eastern waters from Nantucket to Cape Cod to Cape Ann. Mainly dry elsewhere. Seas lingering at around 5 ft E and S of Cape Cod, otherwise 4 ft or less. Dry weather and good vsby. Outlook /Wednesday through Saturday/... Wednesday: Winds less than 25 kt. Areas of seas approaching 5 ft. Wednesday Night through Thursday: Winds less than 25 kt. Local rough seas. Thursday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Friday: Winds less than 25 kt. Friday Night: Winds less than 25 kt. Slight chance of rain showers, slight chance of snow showers. Local visibility 1 to 3 nm. Saturday: Winds less than 25 kt. Chance of rain, slight chance of rain showers. Local visibility 1 to 3 nm. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 5 PM EST this afternoon for ANZ232>234. Small Craft Advisory until 7 PM EST this evening for ANZ235- 237. Small Craft Advisory until 6 AM EST Tuesday for ANZ250-254>256. && $$ SYNOPSIS...Loconto/EVT NEAR TERM...EVT SHORT TERM...Nocera LONG TERM...Loconto AVIATION...Loconto/EVT MARINE...Loconto/EVT

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