Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 240149 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 949 PM EDT Sun Apr 23 2017 .SYNOPSIS... Weak high pressure remains over the area through Monday bringing dry and seasonably warm weather. Low pressure will slowly track up the east coast Tuesday and Wednesday, bringing periods of moderate to heavy rain, gusty winds and the risk of coastal flooding. Drier and warmer conditions will briefly return Thursday. A frontal system will bring scattered showers and possibly a few thunderstorms Thursday night into Friday. The front will waver close to the region, which could bring chances for showers at times into next weekend. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... 10 PM Update... Pleasant evening and overnight expected with dry weather as high pressure remains over the region. However it will become chilly as light winds, dry airmass and only thin cirrus clouds allow temps to fall into the 30s away from the coast once winds decouple. Afternoon seabreezes have resulted in onshore winds pushing dew pts into the lower 40s. This may lead to some patchy fog overnight. Some of the short term hi res guidance indicates some stratus may come onshore to the south coast after midnight. Difficult to see how much stratus is over the ocean given the canopy of high clouds masking any low level moisture. Will just have to monitor trends overnight. Previous Discussion... High pres in control will bring mainly clear skies and light winds although some high clouds will move up from the south overnight. Good radiational cooling tonight so leaned toward cooler MOS temps. Radiation fog threat appears low given the low dewpoints in the interior. && .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... Monday... High pres drifts offshore but the column remains quite dry except for increasing high level moisture moving up from the south. Sunshine will gradually give way to increasing high clouds in the afternoon, especially southern areas. Low level temps moderating so highs should be a few degrees milder than today, reaching the upper 60s and lower 70s interior but seabreezes will keep temps around 60 in the afternoon along the immediate coast. Monday night... Mid level confluence lifts north allowing deeper moisture well in advance of sfc low to slowly move north into SNE. Models have slowed the onset of moisture a bit as sfc ridging to the north hangs tough. Some light rain may overspread the region overnight with best chance south of the Pike. Increasing NE winds developing along the south coast toward daybreak. && .LONG TERM /TUESDAY THROUGH SUNDAY/... Overview... Tuesday through Wednesday night...Moderate confidence. H5 cutoff low pressure will work its way up the eastern seaboard with its surface reflection. Noting strong low level easterly jet moving ahead of this low up to 35-40 kt from H95 to H925 during Tuesday. While the low level mixing is poor due to an inversion in place, an increasing pressure gradient on the north side of the low will cause winds to increase. May see gusts up to around 30 kt with the best shot from Tue afternoon and evening, then again late Tue night/Wed as winds shift to S-SE as a low level 45-50 kt jet moves northward. Could see gusts up to 35 kt along portions of the immediate E coast Tue, then along the E and S coasts late Tue night/Wed. The persistent easterly winds along with astronomically high tides may produce some minor coastal flooding during the times of high tide Tuesday into Wednesday. Details follow in the Tides/Coastal Flooding section below. Another issue will be heavy rainfall. Excellent deep moisture transport thanks to northern feed of moisture up the east coast ahead of the low. Plume of PWATs up to 1.4 to 1.6 inches, which is close to record levels based on sounding climatology for KCHH, will bring an area of heavy rainfall across a good portion of the region. Forecast QPF amounts range from around 1 inch across the CT valley up to 1.5 to nearly 2 inches from Worcester county and NE CT eastward with the highest amounts likely along the immediate E coast where highest PWATs will lie. Expect the bulk of the heaviest rain to fall between 00Z and 18Z Wed. With this amount of rainfall, could see areas of urban and poor drainage flooding along with some upslope heavy rains possibly causing some flooding along the E slopes of the Worcester hills and possible even the Blue Hills. As the low weakens as it passes across the region Wed night, precip should taper off. However, low level moisture may be trapped near the surface so could see some spotty sprinkles or drizzle lingering along with patchy fog. Thursday...Moderate confidence. Expect a few showers and patchy drizzle to linger especially across central and eastern areas as the H5 low opens to a wave as it passes across the region. Winds will slacken, but low level moisture will remain in place as S-SW winds bring milder temps to the region. Conditions should improve by around midday, but clouds will linger. Thursday night-Friday...Low to moderate confidence. Another cold front approaches the region. Will see sct showers develop Thu night across western areas early. Some decent instability ahead of this next system. Noting CAPEs increasing to around 200 j/kg overnight Thu night into Fri. Not much to write home about, but could be enough to kick off a few isolated thunderstorms. The front moves into the region on Friday. Big question will be whether the front actually clears the region, thanks to the breakdown of the upper level ridging across the northern stream while H5 ridge builds from the Ohio valley to the SE U.S. Disagreement amongst the model suite as to whether the moisture/ instability will hold together and keep threat of showers/ thunderstorms through Friday. Have carried low chance POPs for now. Saturday-Sunday...Low confidence. Lots of questions as to the evolution of the developing steering current pattern across the lower 48 next weekend. Models are trying to signal high amplitude ridging develop generally across the eastern half of the U.S., but where the ridge axis sets up is the big question. At this point, it looks like the W-NW flow aloft could weak waves moving across a waver remnant of the front. Only carried 20-30 pct POPs mainly away from the coast, but low confidence due to wide model solution spread. && .AVIATION /02Z MONDAY THROUGH FRIDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday Night/...High confidence. 10 pm update... Not much change from the 00z TAFs...VFR and light winds. Monitoring potential low clouds/stratus coming onshore to the south coast after midnight. Earlier discussion below. ================================================================ Tonight and Monday... VFR. Light winds. Seabreezes developing along the coast around midday Mon. Monday night... VFR with cigs lowering overnight. Chance of light rain developing after midnight, mainly south of the Pike. KBOS TAF...High confidence. Seabreeze redeveloping 15-16z Mon. KBDL TAF...High confidence. Outlook /Tuesday through Friday/...Moderate confidence. Tuesday and Tuesday night... Expect CIGS to lower to MVFR-IFR with areas of -RA/RA. Areas of LIFR likely Tue night especially along the coast and over the higher terrain. VSBYS lowering to MVFR with IFR developing Tue afternoon/night in areas of fog. E winds increase, sustained at 15 to 20 kts along the coast with gusts up to 30 kts possible. Wednesday and Wednesday night... Mainly IFR CIGS Wed with isolated -SHRA/-DZ and patchy fog. Areas of LIFR conditions Wed night in any leftover showers, -DZ and fog. S-SE winds up to around 20 kt on Cape Cod and the islands Wed morning become light/variable inland and light S along the coast Wed night. Thursday into Thursday night... Conditions start out MVFR-IFR early, then should improve to VFR. CIGS/VSBYS may lower to IFR again Thu night in areas of low clouds and patchy fog. Light SW winds inland, up to 10-15 kt along the coast. Low risk of -TSRA Thu night across interior. Friday... IFR conditions early, improving to mainly VFR. May see brief MVFR CIGS during the day in scattered -SHRA. Low risk of TSRA as cold front slowly moves across. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday Night/...High confidence. Tonight and Monday... High pres south of New Eng will result in mostly light winds 15 kt or less with SW flow tonight turning SE on Monday. Easterly swell over eastern waters will erode. Monday night... Increasing pressure gradient between low pres to the south and high pres to the north will lead to increasing E-NE winds developing overnight over the south coastal waters with gusts to 25 kt after midnight. Outlook /Tuesday through Friday/...Moderate confidence. * SMALL CRAFT ADVISORIES likely for a majority of the period. Tuesday and Tuesday night... Low pressure slowly pushes N along the eastern seaboard. Long easterly fetch remains in place. Sustained winds expected from 15-25 kt, highest Tue night, with gusts up to 30 kt. Wave action across the eastern outer waters will build up to 8 to 11 feet. Rain and patchy fog will bring reduced visibilities over the waters. Wednesday into Wednesday Night... There is a low risk for gales on the outer waters for a time Wed. Winds veer to SE with with gusts up to 35 kt through midday Wed, then will begin to diminish as they shift to S late Wed/Wed night. Expect easterly swells to continue, with seas up to 11 feet on the eastern outer waters through most of the day Wed before slowly subsiding. Rain during Wed will taper to showers along with patchy drizzle and fog Wed night with reduced visibilities continuing. Thursday-Friday... Winds shift to S-SW and diminish Thu and continue Fri. Expect gusts up to 20 kt at times Fri-Fri night. Seas will remain at or above 5 feet on the outer waters through Fri. && .TIDES/COASTAL FLOODING... * Confidence continues to increase for potential minor coastal flooding during high tides from Monday night through Wednesday along the Massachusetts east coast Expect persistent easterly wind fetch to remain in place from Monday night through Tuesday night, then will start to shift to S-SE and slowly diminish during Wednesday. The strongest sustained winds at 15 to 25 mph with gusts up to around 30 mph along the Massachusetts east coast. Astronomical high tides due to the new moon will occur during this timeframe. With the continued onshore winds building the seas up to 8 to 11 feet, the possibility continues to see up to around a 1 foot surge on top of the astronomical high tides. Along with wave action, an increasing confidence of minor flooding impacts, if not at least splashover. Inundation of vulnerable shoreline roads is possible. Some minor beach erosion is also possible along the east facing beaches. Boston High Tides... 10.88 feet / Monday 10:33 pm 10.87 feet / Tuesday 10:59 am 11.47 feet / Tuesday 11:20 pm 11.15 feet / Wednesday 11:50 am With the rain falling heavily at times, there is also the possibility of poor drainage flooding issues along the entire Mass and RI coastline. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory for hazardous seas until 6 AM EDT Monday for ANZ250-254. && $$ SYNOPSIS...KJC/EVT NEAR TERM...KJC/Nocera/EVT SHORT TERM...KJC LONG TERM...EVT AVIATION...KJC/Nocera/EVT MARINE...KJC/EVT TIDES/COASTAL FLOODING... is the U.S. government's official web portal to all federal, state and local government web resources and services.