Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 282306 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 706 PM EDT Tue Mar 28 2017 .SYNOPSIS... Wet weather continues through tonight. Improving into Wednesday into Thursday as high pressure delivers cool and dry weather. Low pressure from the Ohio Valley Friday will redevelop south of New England Friday night into Saturday. This bring snow, mixed precipitation and rain Friday into early Saturday, followed by dry weather Sunday and Monday. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... 7 PM update... Low pres near NJ coast tracks south of New Eng tonight. One area of rain assocd with mid level deformation zone moving across northern MA, with convective showers and isold thunder south of LI and moving NE. Hi-res guidance indicates rain will consolidate along the coastal plain later this evening through midnight as decent low level frontogenesis develops, then gradually move east across SE New Eng and Cape/Islands through 06-09z. Rainfall may be briefly heavy near the south coast with low risk of an isold t-storm mainly over the islands. Current forecast on track. Made some minor adjustments to pops to reflect current radar and near term forecast trends. Previous discussion... Widespread rain with a low risk of thunderstorms. If any, mainly isolated. Anomalous deep-layer moisture with precipitable waters in excess of an inch undergoing deep layer forcing ahead of a low emerging out of the Mid-Atlantic and sweeping E immediately S of New England. Watching closely attendant frontal boundaries including that of the kink across our region for focused areas of frontogenetical convergence and subsequent moderate to perhaps heavy rain, as well as any instability that creeps N as indicated by the latest SPC mesoanalysis into S New England. Latest HRRR / RAP model trends seem to be highlighting trends well enough. A blend is preferred. Continued thinking of a decent slug of rain. Amounts of 0.50 to 0.75 with the heavier amounts focused S/E. Some locations, especially along the S coast may see higher amounts where there is a greater risk for convection. Otherwise low clouds, dreary, light E flow. With the increasing moisture across the region, will see clouds lower resulting in patchy dense fog redeveloping across the region, especially over the high terrain. Visibility down to a quarter mile or less in spots. More than likely holding through midnight, a gradual W to E progression of fog erosion as winds turn NW ushering into the region cooler and drier air towards morning. Temperatures mainly holding in the 40s but dropping into the 30s via cold air advection, either via N/E winds with initial high pressure damming, or behind the departing low late with the aforementioned N/W cool, dry winds. Temperatures should remain above freezing across all of S New England, so no concerns at the moment for black ice developing on area roadways. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... Wednesday and Wednesday night... Drying out and turning breezy. Departing low pressure deepens out across the Georges Bank as a 1030+ high pressure builds S out of Canada. Combination of the tight gradient and pressure rises, cold air advection proceeding with an increasing component of isallobaric flow, will see winds increase out of the NW with gusts up to 30 to 35 mph late in the day into evening, especially out across E/SE MA, given stronger winds aloft at times during efficient boundary layer mixing up to H85. Conditions clearing during the morning. A mix of sun and clouds thru the remainder of the day and clearing overnight. Given the late- March sunshine with a warm airmass aloft lingering, albeit cold air advection will be ongoing, temperatures warm up around the upper 40s to low 50s around midday. Dropping down into the 20s overnight. Dry air and breezy winds through the day, roads should dry out. && .LONG TERM /THURSDAY THROUGH TUESDAY/... */ Highlights... * Dry and seasonable Thursday * Snow and rain developing Fri and continuing into early Sat * Plowable snow likely over higher elevations * Dry and seasonable Sunday and Monday */ Discussion... Thursday... High pressure builds across New Eng which will bring sunshine and seasonable temps. It may be a bit breezy in the morning across eastern New Eng given the pressure gradient in place, but trend will be for diminishing wind during the day. 850 mb temps around -5C in the afternoon supports highs mid 40s to around 50 degrees. Thursday night through Saturday... Complex forecast evolving as potent southern stream trof approaches Fri into Sat and interacts with northern stream energy. Result will be a primary low lifting through the Ohio valley and eastern Lakes Fri with deepening secondary low expected south of New England Friday night into Sat. As is typical at this time range there are model differences in track and intensity of the low pres which will affect QPF, thermal profile and potential snow accum. There will be two periods of precip, the first assocd with the warm advection ahead of the primary low during Fri, with a second pulse Fri night into early Sat and this may be heavy at times depending on the track and intensity of low pres to the south. Expect precip to overspread SNE from west to east after midnight Thu night to daybreak Friday. With strong high pres to NE the column will be sufficiently cold for most areas to begin as snow. However, due to marginal boundary layer temps snow may mix or even change to rain at times when precip intensity is light, especially near the coastal plain. During heavier periods, the precip will likely be snow given cold temps aloft. Minor accum are possible all the way to the coastal plain but any accum during the day will be confined to colder surfaces with most roads remaining wet. Exception is across higher elevations in interior MA and northern CT where colder temps may result in some accum on roadways. The second period of precip will be Fri night into early Sat assocd with comma head from intensifying low pres to the south. There are differences in the track which will impact intensity of precip but a period of heavy precip is possible. The uncertainty is temps will be warming aloft from SW to NE so ptype is very much uncertain, especially north of the Pike. Expect mainly rain possibly mixed with sleet at times south of the Pike. To the north, expect snow changing to sleet, freezing rain and rain but this is uncertain and subtle changes in the thermal profile and timing would yield different outcomes. Several inches snow accum possible north of the Pike with best chance of warning level snow over the east slopes of the Berkshires and northern Worcester Hills. There is also a risk of some ice accretion over the higher elevations as precip transitions to rain with temps hovering around freezing. Precip should taper off Sat morning with improving conditions in the afternoon. Sunday... Showers may linger late Saturday evening into Sunday morning as the low pressure system moves offshore. With the low offshore and a high pressure area building into the region, skies will clear throughout the day. Winds will continue to diminish along the coast, with winds gusting to 20 mph throughout the day. As the high pressure moves in, northerly winds will become westerly. Temperatures will be seasonable Sunday with high temperatures in the upper 40s to low 50s across the region. Monday and Tuesday... Both days will be seasonable with temperatures ranging in the upper 40s to mid 50s. Monday will be dry as the high pressure remains overhead. Skies will be mostly sunny throughout the day with near calm winds. A low pressure approaches from the southwest Tuesday, bringing widespread precipitation to the area. Precip will move into the area after midnight, moving from west to east across Southern New England. Rain accumulations around a quarter inch are expected, with locally high amounts of a half inch. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday Night/... 00z update... Tonight..High confidence. Hold with IFR/LIFR cigs with vsbys lowering MVFR-IFR in areas of fog developing. Low risk TSRA, mainly over the islands. N/E flow. Improving to VFR CT valley toward morning however rest of SNE likely to remain beneath IFR-LIFR. Wednesday into Wednesday night...High confidence. Improving conditions through morning with VFR everywhere by 18Z, lingering longest over the Cape and Islands. NNW winds. Gusts to 20-25 kt at times. KBOS TAF...Will hold with IFR through 12z Wednesday. Cigs 800 feet or less. -RA/RA moving through 20z-6z. Some variability in visibility during this time frame, though a lowering trends prior to N/E winds shifting out of the W. KBDL TAF...Will hold with IFR through roughly 9z Wednesday with cigs 800 feet or less. -RA moving in presently becoming RA late afternoon into evening, improving shortly before midnight. VSBYs variable though a downward trend overnight with N/E flow before winds become W. Outlook /Thursday through Sunday/... Thursday...High confidence. VFR. Winds diminishing. Friday-Saturday...Moderate confidence. Conditions lowering to IFR with areas of LIFR with snow and mixed rain/snow transitioning to rain south of the Pike Fri evening. Snow changing to rain and freezing rain north of the Pike Fri evening. Precip ends Sat morning with improving conditions in the afternoon. Sunday... MVFR conditions becoming VFR in E Massachusetts as showers linger in association with a low pressure area moving offshore. VFR conditions for the remainder of the area. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday Night/... Through Wednesday night... Rain and some visibility restrictions will impact the waters overnight as an area of low pressure passes over the S waters. Exiting E out over the Georges Bank as high pressure builds S out of Canada, NW flow increases with the potential for gusts up around 30 kts developing Wednesday evening and continuing over- night with a low risk of gales. Seas build towards 6 to 8 feet on the outer waters. Small craft advisories issued accordingly with the increasing N winds beginning Wednesday into Wednesday night. Outlook /Thursday through Sunday/... Thursday...High confidence. SCA northerly gusts 25-30 kt in the morning eastern waters diminishing in the afternoon. Friday into Saturday...Moderate confidence. Easterly winds below SCA Fri. Increasing SE winds Fri night with SCA gusts likely then shifting to NE Saturday. Vsbys reduced in rain and fog mixed with snow Friday. Sunday...Moderate confidence Low pressure area moving off the coast of New England will result in diminishing winds along the SE waters. Small Craft Advisory may be needed. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 11 AM Wednesday to 8 AM EDT Thursday for ANZ231>234-251. Small Craft Advisory from 5 PM Wednesday to 8 AM EDT Thursday for ANZ230. Small Craft Advisory from 8 PM Wednesday to 8 AM EDT Thursday for ANZ235>237. Small Craft Advisory from 5 AM Wednesday to 8 AM EDT Thursday for ANZ250-254>256. && $$ SYNOPSIS...KJC/Sipprell/Correia NEAR TERM...KJC/Sipprell SHORT TERM...Sipprell LONG TERM...KJC/Correia AVIATION...KJC/Sipprell/Correia MARINE...KJC/Sipprell/Correia is the U.S. government's official web portal to all federal, state and local government web resources and services.