Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 160714 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 314 AM EDT Sat Mar 16 2024 .SYNOPSIS...
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A mixture of clouds and sunshine with unseasonably mild temperatures today, but it will be noticeably cooler along portions of the immediate coast with sea breezes. A round of brief showers overnight into Sunday morning will be followed by another mild Sunday afternoon along with breezy conditions developing. Temperatures trending near to cooler than seasonable for much of the upcoming week. Isolated showers possible Monday through Wednesday along with gusty winds. Drier on Thursday and Friday.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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315 AM Update... * A mixture of clouds/sun today with highs upper 50s/near 60, but it will be cooler along parts of the immediate coast with sea breezes Lingering cyclonic flow continued to result in an abundance of low clouds across central/eastern New England very early this morning. There was also some very localized patchy ground fog in the typical low-lying locations where some partial clearing has occurred...but any of this should burnoff quickly after sunrise. Guidance indicates some subtle upper level ridging building into the region today. This should allow some of the stratus to dissipate across central/eastern New England later this morning. That being said...expect more strato- cu to develop with diurnal heating. So overall...a mixture of clouds and sunshine are on tap for today. 925T on the order of +5C/+6C by this afternoon should yield afternoon highs mainly in the upper 50s to near 60 inland from the coast. These temps are about 10 to 15 degrees above normal for this time of year. A weak pressure gradient will allow for localized sea breezes and cooler high temps in the upper 40s to the lower 50s along parts of the immediate coast.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
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Key Points... * Brief scattered showers after midnight into Sun AM * Partly sunny & breezy Sun afternoon with perhaps a spot shower * Highs Sunday in the upper 50s/near 60...cooler high terrain/Cape Details... Tonight into Sunday... An approaching shortwave trough will induce a modest southwest LLJ overnight into Sun am. While we expect dry weather to prevail this evening...the forcing for ascent will increase along with low level moisture overnight. This should result in a brief band of showers crossing the region after midnight into Sunday morning. Overnight low temps will only drop into the upper 30s to the lower 40s. These showers will be short-lived in a given location with the bulk of them over by Sunday afternoon. Still may have a few spot showers Sunday afternoon with some diurnal heating...but generally Sunday afternoon will be dry & unseasonably mild. Highs should top out mainly in the upper 50s to near 60...but cooler in the high terrain as well as the Cape/Islands. It will be a bit breezy too with southwest winds shifting to the west with some gusts of 20 to 30 mph.
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&& .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
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Highlights * Dry for most on Mon and Tue with temps trending near to below normal. Could have some isolated showers in western MA/CT on Mon. Should see a bit more coverage in the shower activity on Tue. * A quick moving front/system slides through on Wed bringing more spotty showers. * Drier on Thu and perhaps for much of Fri. Monday through Tuesday... Will have cyclonic flow in place through this timeframe. An elongated trough digs into the eastern Great Lakes/Mid Atlantic on Mon. This lifts into the Gulf of Maine/Nova Scotia by early Tue. In its wake a shortwave ridge builds into New England, but quickly shifts offshore on Tue. Another shortwave digs into New England on Tue. A weak cold front slides through on Mon and a surface trough rotates through on Tue. Think out of these two days that Mon will be dry for most of the region. The only exception is across western MA/CT where could see some PoP up showers as a -20 to -30 degree 500 hPa airmass slides in. Think we remain a bit drier and warmer further to the E/SE given the W to WNW flow at 850 hPa and PWATs of roughly 0.2 to 0.25 inches. Looks also like we will have excellent mixing within the boundary layer perhaps mixing down -20 to -30 degree Celsius dew points at the top of the PBL during the day. Due to this have lowered our RH/Td values to account for mixing down drier air. Given the W/WNW flow will be near to slightly warmer than seasonable on Mon until that front slides through. Trending cooler on Tue with more cloudiness. Should have a better shot for isolated showers across the interior. An anomalously cold airmass will be overhead at 500 hPa. Both the NAEFS/EPS situational awareness tables indicate -2 to -2.5 STD below model climo, which are values of roughly -30 to -40 degrees Celsius. Given the core is parked more over us will have a fair amount of cloudiness, especially with diurnal heating. Have kept slight chances of precip given limited moisture, but based on experience have seen these setups result in spotty shower activity. Could actually see spots where there is graupel. Wednesday through Thursday... Bit of a pattern change setting up as flow shifts from cyclonic to quasi-zonal. A fast moving shortwave slides through the Great Lakes and New England on Wed. A ridge axis begins building over the Low/Mid Mississippi River Valley on Thu. A frontal system swings through on Wed through on Wed before high pressure nudges in on Thu. Still a bit of uncertainty on how things exactly evolve for the middle of the week, but models are a bit more consistent with a shortwave digging in. Though there are questions on how strong a wave digs in. A frontal system slides through, which will bring spotty showers. Still thinking that the NBM slight chances of precip handles this well, so have stuck with it. High temps range from the mid 30s across the high terrain to the 40s elsewhere. Dry on Thu as high pressure nudges into the region. Temperatures still trending cooler than seasonable. Highs top out in the mid 30s across the higher terrain to the 40s elsewhere. Friday... At this point still appears dry and quiet on Fri with a ridge axis building into the Mid Atlantic. Could have our next trough lift in from the Mississippi/TN Valley later in the day, but there are timing/intensity differences. At this point appears the risk is greater more for Sat than Fri, but have stuck with the NBM for now given the run to run differences.
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&& .AVIATION /07Z SATURDAY THROUGH WEDNESDAY/...
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Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 06z TAF Update... Today...High Confidence. Any lingering MVFR ceilings should dissipate across eastern New England through 12z...but may persist a few hours longer across the Cape/Nantucket. Otherwise...VFR with winds becoming SW at 5-10 knots and localized sea breezes developing in the afternoon along parts of the very immediate coast. Tonight and Sunday...Moderate Confidence. Mainly VFR conditions this evening. A period of MVFR with brief localized IFR conditions possible overnight into Sunday morning with a few brief showers also possible. Conditions will tend to improve to mainly VFR by the middle of Sunday afternoon...but this process may be delayed several hours across parts of the Cape/Islands. S winds up to 10 knots or so tonight with some 20 to 25 knot gusts developing toward daybreak across the Cape/Islands. Winds shift to the west by mid afternoon Sunday with gusts of 20-25 knots. KBOS TAF...High confidence in the overall TAF...but uncertainty if we do see an period of ESE sea breezes during the afternoon. KBDL TAF...High confidence in TAF. Outlook /Sunday Night through Wednesday/... Sunday Night through Monday: VFR. Breezy. Monday Night: VFR. Windy with local gusts up to 30 kt. Tuesday: VFR. Windy with local gusts up to 30 kt. Isolated SHRA. Tuesday Night: VFR. Breezy. Wednesday: VFR. Breezy. Slight chance SHRA.
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&& .MARINE...
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Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Today through Sunday...High Confidence. Lingering 5 foot seas across our southeast outer-waters will diminish by daybreak. Therefore...will let the small craft headlines expire at 10z for these locations. Winds/seas will then remain below small craft advisory thresholds today into this evening. Approaching shortwave trough will induce a modest southwest LLJ overnight into Sunday. This should generate SW wind gusts of 20 to 30 knots overnight into Sunday eventually shifting to more of a W direction. A new set of small craft headlines will be needed once the current headlines over our southeast outer-waters expire. Outlook /Sunday Night through Wednesday/... Sunday Night through Monday: Winds less than 25 kt. Areas of seas approaching 5 ft. Monday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Tuesday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Tuesday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Wednesday: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 7 AM EDT this morning for ANZ254- 255.
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&& $$ SYNOPSIS...Frank/BL NEAR TERM...Frank SHORT TERM...Frank LONG TERM...BL AVIATION...Frank/BL MARINE...Frank/BL

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