Area Forecast Discussion
Issued by NWS Boston, MA

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814 FXUS61 KBOX 251149 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 649 AM EST Sat Feb 25 2017 .SYNOPSIS... Mild air remains over the region today. A strong cold front will cross the region tonight, bringing showers and a low chance for thunderstorms as this front passes. Blustery conditions with temperatures close to seasonal normals expected for Sunday and above average on Monday. A couple of weather systems will bring periods of wet weather Tuesday into Thursday. Colder air looks to return late next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Patchy dense fog remains over the region this morning. Went ahead and continued the advisory until 10 AM as southerly low will continue to pump in high moisture keeping the fog around. Also expanded the advisory to coastal Plymouth County per latest obs and webcams showing that region pretty socked in. Will continue to monitor the area for any changes. Aside from the fog, most of the forecast remains on track for today. Previous Discussion... Digging shortwave over the Great Lakes will eject northeast into Canada. The digging turns the upper flow more northerly. A cold front over the eastern Great Lakes will sweep east across NY and PA during the day. Precipitation along the front will mostly move north/northeast into Canada and only slowly shift east. Best chance of showers from this front will be late afternoon and in Western MA/Western CT. Model guidance has been consistantly cool compared with verification the past couple of days. Temps at 925 mb support max sfc temps in the mid to upper 60s. The warmer guidance members also aim at this range.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... The cold front arrives in the Hudson Valley around 6-7 pm and crosses into western New England around 8-9 pm...Central sections 9-10 pm...and eastern New England 10 pm to midnight. This front will be supported by the sharp upper shortwave. Airmass stability will decrease through the evening...for example, Totals will climb into the lower 50s. This supports the concept of sufficiently unstable conditions for a few thunderstorms as the cold front approaches and moves through. The greatest risk for tstms would be in Western MA and Western CT where the low level inflow is least maritime. Low level southerly winds will increase during the afternoon, so that by evening we expect a 50-knot jet at or below 5000 feet. Confidence is not high as to how much of that wind may be brought to the surface in gusts during showers/tstms, but its presence suggest a chance of strong wind gusts this evening...possibly isolated damaging wind. Greatest risk would again be in western areas early tonight. Precipitable water fields continue to advertise values a little over an inch, which is well above normal. But this is a narrow and fast- moving zone, so while showers may be briefly strong, total amounts should be 0.50 inches or less. Colder air rushes in behind a cold front. It will be a race between the cold air and the departing showers, but a brief changeover to snow is possible at the end. Any accumulations should be limited, generally less than an inch and mainly over the higher terrain of the Berkshires and Worcester Hills. Finally, the colder air advection behind the front will bring mixing of strong WNW winds aloft to the surface late at night. Wind gusts at that time will have a potential of reaching 30-35 knots. Sunday...High confidence. The shortwave trough moves offshore Sunday morning. The last of any pcpn should end by that time. So Sunday shapes up to be a dry day as high pressure builds in from the west. Cold advection continues during the day. Mixing due to this advection will tap winds aloft of 25-35 knots and possibly a few areas of 40 knots. These winds will diminish during the afternoon as the high pressure area approaches. Temps aloft chill behind the front, but hover on Sunday at levels that support sfc max temps around 40 or the lower 40s. Given the morning temps starting in the 30s, we have forecast max temps in the upper 30s to mid 40s. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Highlights... * Above average temperatures for next week * Widespread showers possible Wednesday/Thursday * More seasonable conditions return on Friday Pattern Overview... The 00z models and their ensembles have been in generally food agreement through the period with the GFS just a bit displaced. Therefor used a blend of the ensembles for the bulk of the forecast. Overall, zonal flow over the region as Bermuda high begins to build in the mid-levels. By mid-week the western trough is forecast to transition into the east as a surface front will move from the Great Lakes towards the Northeast around Wed/Thurs. Still some issues with the timing of the front as a surface wave may develop along it, which could slow it down a bit. This appears to be more inline with the EC/GEFS and ECENS. Otherwise, northwest flow behind the front could result in several clippers for next weekend. Details... Monday... High confidence. Westerly flow across the region as high pressure builds south of the region. Developing LLJ of near 40 kts will develop with high pressure to the south and quick moving wave to the north. This will make conditions a bit gusty at times. As surface high pressure moves farther to the east, winds will begin to back resulting in WAA. Surface temps could reach into the mid 50s on Monday with full mixing. Otherwise dry weather will prevail. Tuesday...High confidence. More of a transition day for Tuesday as high pressure moves eastward as upper level trough approaches. Southwest flow aloft will help saturate the profile. Guidance does show a weak wave developing a coastal low but appears to be just to far east to bring significant rainfall to the region. Depending on when this occurs, we could see a few flakes north of the Pike but confidence is low on this occurring. For now expect a few showers and clouds on Tuesday. Wednesday into Thursday... Moderate confidence. Main weather produce for the long term will occur Wed into Thursday as upper level trough approaches the region. Warm front ahead of the system will bring some showers to the area as temperatures rise well above average. Upper level low will move from the Plains towards northern Maine. This will drag a potent cold front through the region. Good agreement amongst the guidance with this system, just some issue`s with the exact timing of the front. Trended towards the slower side as there is the potential for a secondary low to develop along the front. This is more inline with the ensembles. This is an anomolous system with PWATs 3 STD above normal as Gulf moisture is tapped out ahead of the frontal passage. Heavy precip is a possibility if secondary low does develop bringing the better dynamics over southern New England. Also have noticed that there is a potent southerly LLJ out ahead of this system with 925 mb LLJ increasing to near 50-60 kts. If heavy rain does develop then we could tap into these stronger winds as the system moves through. Lastly appears that there is some elevated instability so have kept with iso thunder in the forecast. Still a lot of details to work out, but a system to watch in the coming days. High confidence in above average temperatures with a non-diurnal trend Wednesday night. Went several degrees above guidance and could still be a bit low. Friday and beyond... Moderate confidence. As the cold front passes through, northeast winds take a hold of the region. Models appear to be inline with a few shortwaves/clipper systems moving through the flow. So some snow showers are certainly possible as temps drop back to seasonable. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
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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 Sunday/... Today...Moderate confidence. Generally VFR to MVFR across the area with IFR/LIFR across the south coast in dense fog. Fog and stratus will remain over the region the morning before lifting by the afternoon. Conditions could improve to MVFR by this afternoon. Cannot rule out a few showers during the day. Tonight...Moderate confidence. A cold front sweeps west to east across the region between 6 pm and midnight. Showers and widely scattered thunderstorms are possible. This means conditions may briefly lower to IFR in any showers or thunderstorms. We continue to expect low level wind shear as well as a chance of strong wind gusts with showers/storms as that 50 knot low level jet sweeps across ahead of the cold front. The best chance for this will continue to be in Western MA and CT early in the night. Behind the cold front, winds will shift from the west and west- northwest. Colder air moving in behind the front will allow strong WNW gusts to work in by late night, with speeds of 30 to 35 knots possible. The colder air may also bring a brief change from rain to snow at the western edge of the precipitation. Sunday...High confidence. VFR. West-Northwest winds will continue to gust 25-35 knots. There are pockets of 40 knots shown in our forecast guidance, so a few of these stronger winds are possible. Winds will diminish by mid to late afternoon. KBOS TAF...Moderate confidence in TAF. Low probability in fog development this morning. KBDL TAF...High confidence in trends, lower confidence in timing. Outlook /Sunday Night through Wednesday/... Monday...High confidence. VFR with westerly wind gusts near 20-30 kts. Tuesday...Moderate confidence. Generally VFR with MVFR conditions possible south of the Pike. Wednesday...Moderate confidence. MVFR to possible IFR in -SHRA.
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&& .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday/...High confidence. Today...High confidence. Increasing southerly winds through the day, with gusts to 25 knots mid to late afternoon. Seas will increase through the day with 5 to 6 foot heights on the southern waters by mid to late afternoon. Tonight...Moderate confidence. A cold front sweeps across the waters the first part of the night. This will bring showers and a widely scattered thunderstorm. The showers may tap strong winds at 2000 to 4000 feet above the surface and bring them to the surface in strong southerly wind gusts. Seas build to 5-8 feet on the exposed waters of the south and the outer waters of the east. Behind the front, winds shift from the West or West-Northwest and bring cooler air. Winds late tonight should gust 30 to 35 knots. Seas will continue at 5 to 8 feet. Sunday...High confidence. West-Northwest winds continue to gust 30 to 35 knots during the morning and early afternoon. Winds may slowly diminish during the later afternoon. Seas will linger at 5 to 8 feet on the exposed waters. Outlook /Sunday Night through Wednesday/... Monday...High confidence. Improving conditions on Monday with gusts near 20 kts and seas beginning to relax as high pressure builds over the southern waters. Tuesday into Wednesday...Low confidence. Wind and seas will be below SCA for Tuesday. Approaching system to the west could see lower vsbys in rain and fog. Seas build late Tuesday night into Wednesday as low pressure system approaches. There is the potential for southerly gales across the waters. && .HYDROLOGY... We will need to monitor rising water levels across southern New England into early next week. Much, if not all, of our snowpack has, or will have, melted. There is still much more snowpack upstream, over northern new England, that will push into the headwaters and head downstream. Some river levels could approach action stage. && .CLIMATE... RECORD HIGH TEMPS FOR YESTERDAY BOS 73/2017 - previous record 70/1985 PVD 72/1985 - topped off at 71 degrees (no record) BDL 73/1985 - topped off at 72 degrees (no record) ORH 69/2017 - previous record 67/1985 RECORD HIGH MIN TEMPS FOR YESTERDAY BOS 49/1930 - bottomed out at 46 (no record) PVD 45/2017 - ties previous record of 45/1984 BDL 43/1981 - bottomed out at 42 (no record) ORH 48/2017 - previous record 46/1985 RECORD HIGH TEMPS FOR TODAY BOS 65/1930 PVD 69/1976 BDL 70/1976 ORH 64/1976 RECORD HIGH MIN TEMPS FOR TODAY BOS 46/1891 PVD 45/1930 BDL 45/1930 ORH 37/1996, 1984, 1976 DEW POINTS OF NOTE FOR YESTERDAY BOS Max Dew Point 54 ties highest for date set in 1985 PVD Max Dew Point 53 is highest for date. Previous high 50/1990 BDL Max Dew Point 54 is highest for date. Previous high 49/1990 ORH Max Dew Point 53 is highest for date. Previous high 48/1985 && .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...Dense Fog Advisory until 10 AM EST this morning for MAZ019>022. RI...Dense Fog Advisory until 10 AM EST this morning for RIZ002>008. MARINE...Gale Warning from midnight tonight to 7 PM EST Sunday for ANZ231>235-237-250-251-254>256. Small Craft Advisory from midnight tonight to 7 PM EST Sunday for ANZ230-236.
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&& $$ SYNOPSIS...WTB/Dunten NEAR TERM...WTB/Dunten SHORT TERM...WTB LONG TERM...Dunten AVIATION...WTB/Dunten MARINE...WTB/Dunten HYDROLOGY... CLIMATE...

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