Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 200547 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1247 AM EST Tue Feb 20 2018 .SYNOPSIS... A warm front will bring showers tonight. This will set the stage for near record high temperatures Tuesday, and especially Wednesday, so long as enough sunshine is realized. A cold front moves through Wednesday night, followed by an additional disturbance on Thursday. This will bring showers followed by cooler temperatures, but still at or above seasonal normals. Another weather system will pass to our west and north over the weekend bringing another period of wet weather. && .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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1245 AM update... Last band of showers moving across northern MA will lift to the north next hour or 2, then much of the rest of the overnight period will be dry. Areas of fog developing along the CT coast and HWRF indicates fog will expand along the RI and MA south coast and Cape/Islands. Fog may be locally dense. Previous discussion... Pre warm frontal showers in warm advection pattern moving through SNE this evening. Upstream, showers are becoming more scattered across western NY and expect a decrease in coverage overnight as warm front lifts north into the region and mid level drying moves in from the southwest. Areas of low clouds and fog will likely develop late tonight, especially near the south coast as the higher dewpoint air moves in over colder water with SW flow. Locally dense fog is possible. Temps steady or slowly rising in the 40s.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM WEDNESDAY/... Tuesday... A few showers and patchy fog may linger along south coastal areas early, then should push offshore by around midday. However, clouds will likely linger across most areas through the day. The big question will be whether the clouds will dissipate during the midday and afternoon hours across the interior. If the clouds do break more than currently forecast, max temperatures will likely be higher than current forecast, too. Tuesday night... Anomalous southwest flow will continue across southern New England. Low temperatures expected to be about 10 degrees above the normal high temperature for this time of year. Still thinking some low clouds and fog are possible, especially near the Cape/Islands with high dewpoint air moving over the relatively cool ocean. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Big Picture... Upper ridge lingers over the Eastern USA while a deep trough holds over the west. The ridge relaxes south a little Thursday, then a little more over the weekend. Even so, 500-mb heights remain above normal through the period. The ridge relaxes as several shortwaves eject out of the western trough and erode the heights on the north side of the ridge. Contours are forecast to be well-packed. The trough axis will be positively tilted. Expect the shortwaves to be fast-moving. Good agreement among the model mass fields through Saturday morning. Differences in shortwave detail, most notably on Sunday and Monday, but the overall pattern is similar and suggests three disturbances moving through during the long term period. Just differences in timing. Details... Wednesday... Upper ridge over the Eastern USA brings deep warm advection into New England. The question will be how deeply mixing will be able to tap that warm air. The GFS shows mixing in the interior to 925 mb and possibly 900 mb, while areas closer to the South Coast may be buffered by the flow of the southwest wind off the ocean. Temps at 925 mb will be equiv to 5-9C at 850 mb, while temps at 900 mb will be equiv to 8-11C. This suggests max sfc temps in the upper 60s and lower 70s inland. Any locations that could eke out a mixed layer to 900 mb should reach low to mid 70s. Model cross sections of moisture continue to show a layer of high- moisture air below 925 mb. This could be indicating a low cloud layer over the region that would reduce or eliminate sunshine and resulting mixing. That would keep temperatures several degrees lower. This will need to be monitored. Mixing will also tap stronger winds aloft. Winds at 850 mb will be 40-50 knots. Within the mixed layer winds will be 25-30 knots, with gusts to those speeds possible Wednesday afternoon. Wednesday night-Thursday... Shortwave and associated surface low pass across Quebec and push a cold front south across New England. Consensus between the GFS and ECMWF brings the front across our area during the evening hours. The ECMWF does so briskly with no hesitation, while the GFS shows similar initial timing but then forms a couple of waves on the front and slows its departure off the south coast. Moisture cross sections from both models show low level moisture with minor lift Wednesday night, then deep moisture and strong lift Thursday...overlying a dry layer near the surface. Precip Water values continue to show well above normal levels. So some contradictions that cut back on confidence. But sufficient elements to indicate a chance of showers, especially on Thursday as the strong forcing moves through. Expect cooling behind the cold front Wednesday night with temps falling to the upper 30s and 40s. Mixing to 950 mb supports max sfc temps Thursday in the 40s. Friday through Monday... High pressure from the Northern Plains moves east to New England, bringing clearing skies for Thursday night. Clouds then move back in during Friday. As noted above, model consensus shows a couple of shortwaves moving through the flow over the weekend. But the fast-moving pattern reduces confidence in exactly timing the passage of each across New England. The first should move through anywhere from Friday afternoon to early Saturday, the second on Sunday. High pressure over the Maritimes Friday is in position to hold cold air over New England at the start of the first event. This would mean a brief period of snow or ice before changing to rain Friday afternoon. If timing goes as forecast, high pressure builds Monday with dry weather and near seasonable temperatures. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/...
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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 Wednesday/...Moderate confidence. Through 12z...Widespread MVFR/IFR. Areas of LIFR in fog, locally dense, developing along the south coast. Showers will lift north of the region. Today...IFR/MVFR stratus and patchy fog improving to VFR by midday. LIFR fog may linger into early afternoon over the islands. SW gusts to 20-25 kt. Tonight...Stratus and patchy fog redeveloping with MVFR/IFR conditions. Areas of LIFR along the south coast. Patchy drizzle. Wednesday...IFR/MVFR to start, improving to VFR by afternoon. KBOS Terminal...Moderate confidence in TAF. KBDL Terminal...Moderate confidence in TAF. Outlook /Wednesday Night through Saturday/...Moderate confidence. Wednesday Night: Mainly VFR, with local MVFR possible. Breezy. Chance SHRA. Thursday: Mainly VFR, with areas MVFR possible. Chance SHRA. Thursday Night: VFR. Friday: Mainly VFR, with areas MVFR possible. Chance RA, slight chance FZRA. Friday Night: MVFR/IFR conditions possible. Chance RA, chance FZRA, patchy BR. Saturday: Mainly MVFR, with local IFR possible. Chance RA, slight chance FZRA, patchy BR.
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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 Wednesday/...High confidence. Rough seas still expected to develop across the ocean-exposed waters with the arrival of southerly swells. Will need to continue the Small Craft Advisories across those waters. Scattered showers and patchy fog will bring reduced visibility tonight, then should improve on the eastern waters Tuesday. Reduced visibility lingers Tuesday into Tuesday night on the southern waters in patchy fog and isolated showers. Outlook /Wednesday Night through Saturday/...Moderate to High Wednesday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Slight chance of rain showers. Wednesday Night: Winds less than 25 kt. Local rough seas. Slight chance of rain showers. Thursday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers. Thursday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers. Friday through Saturday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain.
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&& .CLIMATE... Record Highest Observed Temperature for February...(since records began) Boston.........73 (2/24/2017) Hartford.......73 (2/24/1985) Providence.....72 (2/24/1985) Worcester......69 (2/24/2017) Record High Temperatures... February.......2/20......2/21 Boston.........68 (1930) 63 (1906) Hartford.......69 (1930) 63 (1930) Providence.....69 (1930) 63 (1930) Worcester......65 (1930) 59 (1930) Record Warmest Min Temperature... February.......2/20......2/21 Boston.........46 (1930) 45 (1994) Hartford.......50 (1981) 49 (1981) Providence.....48 (1981) 50 (1981) Worcester......47 (1981) 43 (2002) Extreme High Dew Points... Dew Point forecast has values in the 50s Tuesday and Wednesday. February.......2/20......2/21 Boston.........54 (1991) 56 (1953) Hartford.......53 (1981) 55 (1989) Providence.....58 (1939) 56 (1989) Worcester......53 (1981) 54 (1953) && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 6 AM EST Wednesday for ANZ235-237- 250-254>256. && $$ SYNOPSIS...WTB/Belk NEAR TERM...KJC SHORT TERM...Belk LONG TERM...WTB AVIATION...WTB/KJC MARINE...WTB/Belk CLIMATE...

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