Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 250733 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 333 AM EDT Wed Apr 25 2018 .SYNOPSIS...
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Low pressure approaching from the southwest will bring a soaking rain today and into this evening. Locally heavy downpours may result in some brief nuisance poor drainage street flooding with an isolated thunderstorm or two possible. Seasonable temperatures follow for the remainder of the week with mainly dry weather other than a brief period of rain showers likely Friday. A cool down will occur Saturday night and Sunday, but this will be short lived as unseasonably warm temperatures appear to be in store for the region by the middle of next week.
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&& .NEAR TERM /UNTIL 6 AM THIS MORNING/... 955 PM Update... Temperatures have been very slowly decreasing hours while dewpoints have slowly increased as seen on surface observation trends since 22Z. Still noting rather wide T/Td trends, though they are lower across the immediate S coast and especially on the islands from the 01Z observations, down to 3 degrees at KACK. Weak ridging extending westward from high pressure SE of Nova Scotia keeping precip at bay this evening with the continued dry airmass, though noting reports of -RA at KJFK at 01Z. With mainly cloudy skies across the region, along with winds becoming generally E-SE, should see temps continue to fall slowly overnight. Have updated near term forecast to bring conditions current, but not a whole lot of changes from the previous update. Previous Discussion... Model trends have slowed the timing just slightly for the onset of the warm advection rainfall. This is due to such a dry airmass in the mid-levels (700-800mb). BUFKIT soundings moisten the profile out west by 06z and over the east around 10z. Thus went ahead and slowed the timing. Aside, expect clouds to thicken and lower during the overnight hours before the precipitation begins to fall. Anticipate showers to start due to isentropic lift and in the WAA pattern. Heavier precip will fall by 09-12z from west to east towards the morning hours. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM THURSDAY/... Wednesday into Wednesday night... *** Heavy rainfall and isolated thunder for Wednesday *** Southern stream surface low will approach the region on Wednesday as northern stream trough swings into the area from southern Canada. This surface low will move across the region, allowing for the southern half of SNE to become warm sectored. This upper level trough will continue to dig and go negatively tiled pushing the surface low up into the Gulf of Maine by Thursday morning. Rainfall... Steady rainfall will stream into the region by Wednesday morning as PWAT values increase to 1.3 inches, 1-2 STD above normal. Associated with this system, strong LLJ nearing 3 STD above normal will allow for strong moisture transport into the region. Right now appears that widespread 1-2 inches of rainfall will occur through Wednesday night. Think the highest amounts will occur across the Worcester hills and the east slope of the Berks where upslope flow will help create a bit more lift. Cannot rule out the potential for 2+ inches in that region, which is indicated by the ARW. Still with this much rainfall, appears the the main stem rivers will remain in their banks per NERFC`s forecast and MMEFS. Still, we will have to watch some of the flashy streams. Right now believe that urban and poor drainage flooding will be the main threat. Precip will come to an end by late Wednesday into the overnight hours as main jet lifts farther north. Models also show some drying into the mid to upper levels which could result in showery weather towards Thursday morning. Wind... As mentioned before, strong LLJ increases during the day on Wednesday reaching close to 3 STD above normal. In fact, 925mb winds increase between 50-60 kts. Believe that most of this wind will remain elevated as soundings show a strong inversion across the area. However, could see some mixing near the southeast coastal plain where the potential for thunder could bring down a few strong winds gusts. Also appears to be a narrow window where lapse rates may be steep enough. Believe that we could see somewhere near 25-35 MPH across the southeast coastal plain. Will hold off in any adv for this time as confidence is not that high. Thunder... A low risk for thunder during the day on Wednesday as we warm sector just a bit by the afternoon hours. Models indicate that showalters drop below 0 and there is some elevated CAPE nearing a few hundred joules. Like the timing of the SPC HREF MU CAPE so tried to incorporate that into the forecast. Biggest risk would be heavy rainfall and some gusty winds within any thunderstorm. Fog... As the system begins to wind down late Wednesday night into Thursday morning, we may have to watch for the potential for fog. High dewpoint airmass will still be over the region Wednesday night and with some drying in the mid-levels, low levels appear to remain saturated. Winds also appears to be light. So aside from some showers moving across the region, may have to watch for patchy dense fog, especially across the south coast. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
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Highlights... * A 1-3 hour period of rain showers likely Fri * Milder Sat with just a few brief afternoon/evening showers possible * Dry and noticeably cooler Sun with frost potential late Sun night * Dry weather Mon/Tue/Wed with a significant warming trend and the potential for 80+ in some locations by the middle of next week Details... Thursday night... A ridge of high pressure will result in a dry/tranquil night. Low temperatures should bottom out in the upper 30s to the middle 40s in most locales. Friday... Shortwave trough remains to our west and it will eject a piece of energy into our region on southwest flow aloft. Appears there will be enough forcing for a 1 to 3 hour period of rain showers sometime Friday into early Friday evening. Certainly not looking at a lot of rain...but appears the likelihood that most locations do see a brief period of rain showers. Clouds and the likelihood of a brief period of wet weather should hold high temps mainly in the lower 60s. Saturday and Saturday night... A milder day is on tap for Saturday ahead of an approaching cold front. Southwest flow and partial sunshine should allow high temperatures to recover well into the 60s to possible around 70 in a few locales. While dry weather should dominate...an approaching cold front may trigger a few brief showers during the afternoon/evening. Greatest risk will be across western MA...where forcing/moisture will be a bit deeper. Turns cooler Sat night behind the cold front. Low temps by daybreak Sun should be down into the upper 30s and lower 40s. Sunday and Sunday night... Deep trough sets up across the Northeast with anomalously low height fields. It will be noticeably cooler...but highs should still top out well into the 50s with good mixing in northwest flow along with the benefit of the increasing spring sun angle. The dry airmass in place will allow for chilly temps late Sun night into early Mon am. Lows should bottom out in the upper 20s to the middle 30s in many locations. Frost headlines may eventually need to be considered where the growing season has officially started. Monday through Wednesday... The northeast trough quickly moves east of the region Monday and will be replaced by strong upper level ridging by the middle of next week. The result should be dry weather with a significant warmup. High temps should recover into the lower to middle 60s Mon...probably well into the 70s by Tue...and the potential for some 80 plus degree readings on Wed. A weak pressure gradient will likely allow for sea breezes and cooler conditions along the coast at times. Nonetheless...at least a taste of summer afternoon warmth appears to be in the cards for much of the region.
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&& .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
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Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday/...Moderate to High confidence. Overnight...Expect mainly VFR. Winds will shift to the E-SE between 06Z and 09Z. Wednesday...MVFR lowering to IFR, moving in from SW to NE generally between 10Z and 14Z. Rain will quickly overspread the region as winds remain E-SE. IFR-LIFR conditions possible during the late morning into the afternoon with +RA and isolated thunder. Low risk for 35 kt gusts across the southeast coastal plain. Otherwise strong LLWS through much of the day. Wednesday night...IFR with possible LIFR across the area. Improving to MVFR towards dawn on Thursday. +RA remains trending towards showery weather after midnight. Could be low vsbys along the south coast in Fog through much of the night. KBOS Terminal...High confidence in TAF. May get the first part of the morning rush through in VFR, albeit lowering cigs. However, E to SE wind accompanied by rain likely keep cigs/low late morning into Wed night. Low risk for TSRA after 21z. KBDL Terminal...High confidence in TAF. Morning rush could be impacted with +RA. Outlook /Thursday Night through Sunday/...Moderate to High confidence. Thursday Night: VFR. Friday and Friday night: A period of MVFR to localized IFR conditions likely in a round of rain showers sometime Friday into early Friday evening. Saturday through Saturday Night: VFR. Breezy. Slight chance SHRA. Sunday: VFR. Breezy.
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&& .MARINE...
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Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday/... Tonight...High confidence. Approach surface low will switch winds to the ESE and gusts to near 25kts. Seas will build as a response resulting in SCA. Wednesday and Wednesday night...Moderate confidence. Small Craft Advisory winds with gusts up to 30 kt and a low risk for a few 35 knot gusts early in the evening across the southeast waters. Rough seas up to 13 ft. Chance of rain showers, areas fog, isolated thunderstorms. Visibility 1 to 3 nm. Outlook /Thursday Night through Sunday/...Moderate to High Thursday Night: Winds less than 25 kt. Areas of rough seas. Friday: Winds less than 25 kt. Seas up to 5 ft. Rain showers likely. Friday Night: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers. Saturday: Winds less than 25 kt. Seas up to 5 ft. Saturday Night: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers. Sunday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft.
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&& .EQUIPMENT... The NOAA Weather Radio transmitter serving Providence is out of service due to phone line problems. The phone company has prioritized the issues and is working to get the weather broadcast back on the air as soon as possible. The transmitter serving Hyannis is back in service. && .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 9 PM EDT this evening for ANZ231- 232. Small Craft Advisory from 7 AM this morning to 9 PM EDT this evening for ANZ233-234. Small Craft Advisory from 1 PM this afternoon to 8 PM EDT this evening for ANZ230. Small Craft Advisory from 9 AM this morning to 6 PM EDT this evening for ANZ236. Small Craft Advisory until 9 AM EDT Thursday for ANZ235-237- 254. Small Craft Advisory from 8 AM this morning to 9 AM EDT Thursday for ANZ250-251. Small Craft Advisory until 9 AM EDT Thursday for ANZ255-256.
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&& $$ SYNOPSIS...Frank NEAR TERM...EVT/Thompson SHORT TERM...Dunten LONG TERM...Frank AVIATION...EVT/Frank MARINE...EVT/Frank EQUIPMENT...Staff

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