Area Forecast Discussion
Issued by NWS Boston, MA

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989 FXUS61 KBOX 241541 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1041 AM EST Fri Feb 24 2017 .SYNOPSIS... High pressure over the Atlantic Ocean will maintain dry and unseasonably warm conditions through Saturday. A warm front near northern Massachusetts may bring a few showers across that area this morning before moving off to the north. A strong cold front will cross the region Saturday night, bringing showers and areas of fog. There will be a low chance for isolated thunderstorms as the front passes. Near seasonable temperatures will return Sunday and Monday, with blustery conditions. Wet weather returns to the area for the Mid- week. Another shot of cold air moves back into New England on Thursday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Trended temperatures up a little higher from the previous forecast. Fog has largely dissipated across southern New England already, although there were a few lingering spots in the CT River Valley. Expecting fog there to dissipate before noon, with a warm front now mainly north of southern New England. Also increased wind speeds slightly. These south to southwest winds will also help to boost temperatures from present levels. Previous Discussion... A 40-50 knot southwest low level jet is riding up and over the top of the stalled front...out over the Eastern Great Lakes. This has generated an area of showers which is sliding northeast up the front. Meanwhile an upper ridge builds through the day over New England with a southwest upper flow in place. This should nudge the stalled front farther north and steer most of the showers across VT and NH. Northern MA could get clipped during the mid to late morning, but even this chance should slide north with the departing warm front. Forecasting sky cover in New England in a wintertime southwest flow is always dangerous. Most of the sky cover in place over our area is either fog or convection moving with the front. Satellite shows many clear spots over us, and partly to mostly clear skies upstream to the southwest. Expect morning clouds to diminish with partly to mostly sunny skies in the afternoon. Mixing yesterday overachieved, reaching 700 mb on the evening Albany sounding while other sites showed mixing to between 800 and 850 mb. Mixing to 850 mb would support max temps today in the mid 70s! Meanwhile mixing to 900 and 925 mb would support max temps in the mid to upper 60s. This is still several degrees warmer than model guidance. With sunshine and an eye to yesterday, we will favor max temps in the mid and upper 60s...values of 62 to 68 inland and 50s along the south coast. Winds in the mixed layer show a max potential of 30 knots, but mixed values more favor 25 knots. We will again bump guidance up a bit to the favored values. Records for max temp and high min temp are listed in the climate section at the end of this discussion.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY NIGHT/...
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Tonight... With Southern New England deep into the warm sector, we expect another mild dry night with areas of fog. Dew points in the warm sector remain in the 40s, which should keep temperatures no lower than that. Saturday and Saturday night... Shortwave ejecting into the Central Plains this morning is digging a surface low along the stalled front. This low is moving northeast into the Midwest. Models are consistent in moving this low northeast into Canada Saturday, eventually swinging a cold front through New England Saturday night. Low clouds and fog linger first thing Saturday morning, but should break and allow higher clouds to take over. There could be some breaks of sun with all of this, which would allow for a period of mixing especially around midday. Three forecasting concerns will be temps, winds, and precip. Even with modest mixing, temps aloft should again allow temps to climb to at least 60. With a period of dry weather and some sun late morning/midday, we opted to again forecast higher than guidance by several degrees. Temps in the mixed layer do support max sfc temps in the low to mid 60s. A south-southeast wind may take shape, which could hold down temps below these values in the coastal plain. Winds in the mixed layer show gust potential of 25 to 30 knots, and so we bumped gust values up a little from guidance. The cold front crosses NY and PA during the day, with the best upper dynamics in that area through the day. This suggests much of the daytime will be rain-free with increasing chance of showers later in the day. A strong primary low level jet is indicated just ahead of the cold front, with 40-50 knot winds. Also, appreciable instability is noted. for example there is a zone of Totals at 50-52 just ahead of the front. Finally, as the front sweeps through early Saturday night it will be accompanied by the right entrance region of the upper jet. We will continue to mention slight chance of thunder. Potential for strong wind gusts with any convection. Precipitable water values continue to show just over an inch, 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 late Saturday night following the 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. Wind gusts will have a potential late Saturday night of reaching 30-40 knots. One other aspect after this system passes will be rising water levels across the watershed into early next week. Much if not all the snowpack has or will have melted across this region, but still much more upstream that will push into the headwaters and head downstream. Will need to monitor in case some river levels approach action stage.
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&& .LONG TERM /SUNDAY THROUGH THURSDAY/...
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Highlights... * Blustery and more seasonable temperatures Sun and Mon * System on Tuesday will bring some snow/rain showers to the area * Widespread showers possible Wednesday/Thursday Pattern Overview... 00z guidance is in general agreement with some mesoscale differences especially in regards to timing. Synoptically, the ensembles show rather good agreement in the medium range for next week. This includes the Western trough lifting northeastward as upper ridging over the southeast US continues to build by Mid-week. Towards the end of the week, troughing will move into the eastern half of the CONUS bringing temps back to average. Confidence level was increasing until the new 24.00z EC. The EC is more amplified and develops a couple of surface lows along the warm and cold front as it passes over New England. This deviation has resulted in issues with precip timing, type and temperature profiles. While normally the deterministic appears an outlier, the GEFS and previous GFS runs were also indicating this potential. Because of this increasing spread, will continue with moderate confidence in the overall forecast. Details... Sunday into Monday...High confidence. Upper level trough axis begins to push towards the Maritimes as surface high pressure builds across the southeast. This will put the region in CAA and northwest flow. Temperatures on Sunday will feel quite chilly compared to the previous few days as high remain in the 40s. True mixing up to 850 mb where a 40-45kt LLJ will develop. Expect blustery conditions with gusts near 30-35 mph. Weak shortwave will move through the flow on Monday but with building high pressure to the south, the region should remain dry. However this will tighten the pressure gradient resulting in a LLJ of 35-45 kts. Again another blustery day for southern New England. Temperatures will be a bit warmer however with highs into the 50s. Tuesday and Wednesday...Moderate confidence. Guidance begins to diverge on this portion of the forecast resulting in low confidence. High pressure south of the region will help increase low level moisture into the area due to southerly winds. Approaching low pressure system across the Great Lakes will extend its warm front near the region as well. This may result in overrunning of precipitation and with thermal profiles near freezing, could see some snow showers on Tuesday morning. As temperatures rise precipitation will turn more to rain. However the more amplified EC is developing a low along the front where as the GFS/CMC and UKMET are more progressive and this low develops over the Atlantic. Latest ECENS develops this low further east than deterministic guidance. Therefore will trend towards the ensembles resulting in a cloudy and wet day on Tuesday. Surface low pressure over the Great Lakes will move towards southern Canada, dragging a cold front through the region. Timing appears to be the bigger issue with the more amplified EC several hours slower then the GFS. Right now appears that the CMC is in the middle of guidance. There is also the potential for a secondary low to develop along this front which could increase rainfall amounts. Spread is still to great to nail down amounts etc. However confidence is increasing the precip will move through the region later Wed into Thursday morning. In fact both the ECENS and GEFS continue to show high probability or qpf after 12z Thursday, so the timing may slow down a bit. Lastly, large temperature spread amongst the guidance during this time period with the GFS indicating upper 50s and the EC in the mid 40s. All dependent on the placement of the low and how quickly will the warm front move northward. Trended towards the warmer side of the guidance with support from the GEFS/GFS and ECENS. Thursday...Low confidence. Still a chance for showers across the region but overall should be a dry day on Thursday. Reinforcing arctic air will drop temperatures back to seasonable with blustery conditions.
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&& .AVIATION /16Z FRIDAY THROUGH TUESDAY/...
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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 Saturday Night/... Today...Moderate confidence. Generally VFR. Patchy IFR/LIFR in fog will continue to improve to VFR by 17-18Z. Tonight...Moderate confidence. VFR with areas of IFR/LIFR developing in areas of fog. Saturday...Moderate confidence. Lingering IFR in morning fog, otherwise VFR. Showers approach from the west and are most likely between 21Z and 03Z in the west, and between 00Z and 06Z in the east. Conditions may briefly lower to IFR in any rain showers. Isolated thunderstorms are possible as this band of showers moves through. Rain may chance to snow in the higher terrain as it tapers off. Low level wind shear is possible in the evening with S-SW winds at 40-50 knots at 2000-3000 feet AGL. Winds shift from the west during the early night as a cold front sweeps through from west to east. WNW winds will become gusty overnight with gusts to 30 to 35 knots possible. KBOS TAF...Moderate confidence in TAF due to variable cigs in fog areas. Confidence improves after 14Z. KBDL TAF...Moderate confidence in TAF due to variable cigs in fog areas. Confidence improves after 14Z. Outlook /Sunday through Tuesday/... Sunday and Monday...High confidence. VFR with blustery NW wind gusts near 30-40 kts. Tuesday...Moderate confidence. MVFR conditions possible in -SHRA or -SHSN.
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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 Saturday Night/...High confidence. South-Southwest winds today with brief gusts near 25 knots possible. Areas of poor vsbys in fog through mid morning. Winds diminish tonight. Seas remain below 5 feet through tonight. Saturday...Moderate confidence. Winds shift a little from the south-southeast and increase with gusts of 25-30 knots possible. Seas also build with heights 5-7 feet on the southern waters in the afternoon/evening. A cold front sweeps across the waters Saturday evening and early night with showers and isolated thunderstorms. Strong winds aloft may produce a couple of strong wind gusts in showers and storms. Winds shift behind the cold front. Winds from the west after midnight will have potential gusts of 30 to 35 knots. This would be borderline conditions for gales toward Sunday morning. A Gale Watch may be needed. Outlook /Sunday through Tuesday/... Sunday and Monday...High confidence. Northwest winds will keep seas up and increase wind gusts near 30-35 kts. Low probability for gales across the waters. Improving conditions on Monday with gusts near 20 kts and seas beginning to relax as high pressure builds over the southern waters. Tuesday...Low confidence. Wind and seas will be below SCA for the day. With approaching system to the west could see lower vsbys in rain and fog. && .CLIMATE... RECORD HIGH TEMPS FOR TODAY BOS 70/1985 PVD 72/1985 BDL 73/1985 ORH 67/1985 RECORD HIGH MIN TEMPS FOR TODAY BOS 49/1930 PVD 45/1984 BDL 43/1981 ORH 46/1985 RECORD HIGH TEMPS FOR SATURDAY BOS 65/1930 PVD 69/1976 BDL 70/1976 ORH 64/1976 RECORD HIGH MIN TEMPS FOR SATURDAY BOS 46/1891 PVD 45/1930 BDL 45/1930 ORH 37/1996, 1984, 1976 && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...WTB/Dunten NEAR TERM...WTB/Belk/Dunten SHORT TERM...WTB LONG TERM...Dunten AVIATION...WTB/Dunten MARINE...WTB/Dunten CLIMATE...

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