Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 141734 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 134 PM EDT Thu Mar 14 2024 .SYNOPSIS... Plenty of sunshine today with unseasonably mild highs in the 60s to around 70 across much of the region...but it will be much cooler along the immediate coast with onshore winds. Clouds increase this evening with a period of rain showers after midnight into early Friday morning along with much cooler high temperatures Friday. && .NEAR TERM /UNTIL 11 PM THIS EVENING/...
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130 PM Update Forecast remains on track this afternoon. No updates needed. 315 AM Update... * Plenty of sun today with highs 60s to near 70...much cooler coast Lingering sprinkles across the Cape/Islands exit the region before daybreak. Otherwise...upper level ridge axis moves across our region today. This will result in plenty of sunshine and unseasonably mild temperatures away from the immediate coast. 925T moderate to between +9C and +12C this afternoon...coupled with a rather dry airmass in place in pre-greenup should allow temps to overachieve. Highs should reach well into the 60s inland from the coast to near 70 in portions of the Lower CT River Valley. However...weak pressure gradient will allow for sea breezes and much cooler temperatures along the immediate coast. Highs along the immediate coast will be held in the upper 40s to the lower 50s.
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&& .SHORT TERM /11 PM THIS EVENING THROUGH 6 PM FRIDAY/... Key Points... * Period of showers overnight into early Fri AM * Much cooler Fri with perhaps some drizzle and patchy fog Details... Tonight... A shortwave and associated wave of low pressure approaches the region from the west tonight. In response...clouds will increase this evening. As the forcing for ascent increases...a period of rain showers should overspread the region from the west generally after midnight. The 850 mb low will be tracking across northern New England. This will keep the heaviest rain to the north of our region where better over running will setup. That being said...we do expect a period of showers overnight into early Friday morning across most of the region...especially north of the CT/MA border where better forcing resides. Overnight low temps will be in the upper 30s to the middle 40s. Friday... Surface wave of low pressure exits the region early Friday morning...bringing an end to the bulk of the showers. However...this will generate NNE winds and keep the region entrenched in a lot of clouds. We may also see some patchy fog/drizzle especially across eastern New England along with perhaps a few left over spot showers. Temps on Friday will be quite a bit cooler than today! Pattern recognition would suggest that the high resolution/cooler guidance is the way to go with clouds and NNE winds. Highs probably remain in the 40s across much of the region with perhaps lower to middle 50s in parts of the Lower CT River Valley. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Highlights * Spotty showers taper off late Fri into early Sat. Dry and quiet weather on Sat with a mix of sun and clouds. * A frontal system swings through Sun bringing scattered showers. * Still may be unsettled on Mon and Tue, but with spotty activity. Temps near to below normal. * Drier weather returns midweek. Friday Night into Saturday... Stuck in cyclonic flow through this period. A shortwave trough will lift from the central Great Lakes Fri Night into the Gulf of Maine by early Sat. A shortwave ridge builds into the eastern Great Lakes/western New England behind the trough. The ridge builds into New England on Sat and offshore by late Sat. A frontal boundary will initially be nearby/just south of southern New England Fri Night. This slides further offshore, while high pressure begins nudging in into early Sat. The high continues to nudge in on Sat. There still may be spotty rain shower activity Fri Night into early Sat, especially along/south of the south coast. Should be mostly dry by early Sat and through the day Sat as high pressure nudges in. Though given the cyclonic flow we will have a fair amount of cloudiness. Should see warm air advecting into the region as flow shifts from the NW to the SW as the day progresses. Will see 925 hPa temps warm to 4-8 degrees Celsius. This will result in high temps generally in the 50s, but the Cape/Islands will stay in the 40s. Sunday... Cyclonic flow persists through this timeframe. A trough lifts into/through from the Great Lakes on Sun. A frontal system moves through bringing scattered rain showers. Will be our next opportunity after Fri for more shower activity. At this point appears that this system will be pretty progressive and we actually could see some breaks of sun late in the day. Really do not have a whole lot of moisture to work with as PWATs range from 0.3-0.5 inches. This is roughly the 25th percentile to avg for this time of year. Dialed back our precip chances a bit from the NBM as it appears to be scattered activity quickly pushing through. Only other potential impacts for Sun is that there is potential for gusty winds. Though confidence is a bit lower here as guidance is all over the place on the timing, intensity and exact placement of the LLJ. Think that the risk is highest across the coastal plain based on the current suite of guidance, but would like more of a consensus. For now am advertising gusts of 20-30 mph through the day. Monday through Wednesday... Well as was the case for prior periods we will be caught under cyclonic flow. A deeper trough digs into the eastern Great Lakes/Mid Atlantic/Carolinas on Mon and through by Tue. May have a shortwave ridge build into the Great Lakes for Wed. Still appears it could be a bit unsettled through this timeframe. Anticipate a fair amount of cloudiness through this period given 500 hPa temps cool to -25 to -40 degrees Celsius. This in combination with diurnal heating should result in an ample amount of cloud cover, especially during the day. The big question will be how much moisture will we have available given the dry W to NW flow through this timeframe. At this point PWATs are roughly -0.5 to -1.0 STD below the typical values for this time of year per the NAEFS/EPS situational awareness table. Given the setup have kept the NBM slight chances as think isolated shower activity cannot be ruled out. Temperatures trending near to below normal with the colder air advecting in. Highs top out in the 40s. && .AVIATION /18Z THURSDAY THROUGH MONDAY/...
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Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 18Z TAF Update Through 00Z...High Confidence VFR. Light onshore winds near the coast and light/variable across the interior. Tonight...High Confidence in trends, moderate confidence in timing. VFR persists through about 03Z at most of the terminals. Conditions then deteriorate overnight as an area of low-pressure approaches from the west. Ceilings falling to MVFR levels across the interior, except BAF/BDL may remain above MVFR with cigs around 060 feet. Terminals near the coast likely to fall to IFR/LIFR as southeast flow advects low/marine stratus over the terminals. Low pressure system will be accompanied by -RA beginning around 06Z at BAF/BDL and eventually reaching BOS by 08-09Z. Modest 5 to 10 knot southeast winds. Tomorrow...Moderate Confidence Surface low-pressure circulation exits to the east with -RA by about 15Z. Low-level clouds continue to linger, but we should see any LIFR ceilings improve to at least IFR by mid-morning. Gradual improvements to MVFR by 18-21Z and eventually back to VFR by 00Z. Not expecting any steady periods of precipitation after 15Z tomorrow, but there may be a few spotty showers or intermittent periods of light drizzle. Winds shift to the northwest after 15Z once the surface low exits east. Speeds will be modest topping out in the 10-15 knot range. Tomorrow Night...High Confidence. VFR. Steady northwest winds 5 to 10 knots. Possibly some MVFR ceilings with cloud bases from 020 to 040 over The Cape/Islands terminals. KBOS TAF...Moderate confidence in TAF. Conditions begin to deteriorate around 06Z. Only moderate confidence in ceilings falling to LIFR levels with higher confidence of at least IFR. Low ceilings likely to persist through the morning push before some improvements after 15Z. Could be back to MVFR levels by early afternoon, but likely closer to 18Z. Improvements to VFR between 21-00Z tomorrow. KBDL TAF...High confidence in TAF. Outlook /Friday Night through Monday/... Friday Night: Mainly VFR, with areas IFR possible. Saturday: Mainly VFR, with local IFR possible. Saturday Night: Mainly VFR, with local IFR possible. Breezy. Chance SHRA. Sunday: Mainly VFR, with local MVFR possible. Breezy. Chance SHRA. Sunday Night through Monday: VFR. Breezy. Slight chance SHRA.
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&& .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Today and tonight...High Confidence. A ridge of high pressure in control of our weather today will shift east of the region tonight. This will keep winds/seas below small craft thresholds through tonight. Showers will arrive after midnight Friday...High Confidence. Winds shift to the NNE across our northern waters Fri morning and later across the southern waters. Speeds of 10 to 15 knots with a few gusts into the lower 20 knots are expected. Kept things just below small craft advisory thresholds for now. Outlook /Friday Night through Monday/... Friday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers. Saturday: Winds less than 25 kt. Seas locally approaching 5 ft. Saturday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. Sunday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Chance of rain showers. Sunday Night: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers. Monday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Frank/BL NEAR TERM...Frank/RM SHORT TERM...Frank LONG TERM...BL AVIATION...Belk/RM MARINE...Frank/BL

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