Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 232056 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 356 PM EST Fri Feb 23 2018 .SYNOPSIS... As a frontal system progresses east, rain and mixed precipitation will continue into this evening. Active weather pattern continues this weekend with more rain and interior mixed precipitation Saturday night and Sunday. A near- seasonable, quiet pattern for early next week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... *** A period of light icing likely this evening over higher elevations in central and western MA *** A Winter Weather Advisory remains in effect for the higher terrain through this evening due to the potential for freezing rain. Sounding profiles show the best chance for freezing rain/sleet to be across the higher terrain given the warm front aloft with cooler temperatures at 925mb. There still stands a low potential for ice accumulations up to a quarter inch on the eastern slope of the Berkshires. Isolated areas of freezing rain and sleet have been reported, largely along the eastern slopes of the Berkshires. Temperatures are currently between 29 and 33 degrees in the area of sleet and freezing rain. Between 21z and 00z, a warm and moist airmass will be advected over the region as winds turn southerly. With an area of high PWATs just to our south, heavy downpours are possible during this time period. Most models are suggesting precip accumulations just over a quarter inch. With temperatures rising across the region, freezing rain will transition to rain near 00z once temperatures across the region are well above freezing. Rain will be exiting around 3z this evening from west to east as mid level drying moves in and winds become westerly. Temps will continue rising through the 30s, and into the 40s in the coastal plain. Patchy low clouds and fog will develop tonight with some clearing possible before 12z. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... Saturday... Dry weather returns Saturday as a high pressure builds into the region from the NW. Lingering fog is possible after 12z along the southern coast, but should quickly burn off due to surface heating. Clouds will continue clearing, with most of the interior seeing periods of sun by midday. With NW flow, temps will reach well into the 50s across the interior and coasts. Cooler upper 40s over higher elevations NW MA. Saturday night...Rain showers expected after midnight, with a chance of higher elevation seeing freezing rain and sleet just before sunrise. && .LONG TERM /SUNDAY THROUGH FRIDAY/...
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Highlights... * Widespread precip on Sunday with wintry mix in the interior * Dry and above average for early next week * Stormy pattern emerging for the beginning of March Overview... 12z guidance is in general agreement with the extended forecast. Just some minor differences related to thermals which provide different outcomes in p-type for late Saturday night into Sunday. Deamplifying trough across the CONUS as potent shortwave moves up into the Great Lakes bringing occluded system and triple point low into southern New England on Sunday. Afterwards high pressure and strong ridge takes hold over the eastern CONUS by early next week. The GEFS and EPS continue to show anomolous high pressure building over Greenland which will influence a cut-off low to either retrograde towards the Maritimes or remain across the North Atlantic. This all due to the NAO turning negative by early March. While the pattern begins to jam up, digging shortwave out of the southern Plains on Thursday needs to be watch as it could be the first of several waves impacting southern New England. Details... Late Saturday night into Sunday...Moderate confidence. Potent wave will eject out of the desert Southwest producing a surface low pressure system up into the northern Great Lakes. Stalled front to the south will begin to lift northward as a warm front. This will result into another overrunning precip set-up as moisture from the south increases as warm front begins to lift northward. Surface high pressure will be set-up north to northeast of the region allowing for surface temps to fall. Triple point low developing along the stalled front, will reinforce the cold air especially in the 950-925mb layer leading to cooler temps at the surface, esp across the high terrain.Models are always to quick at warming temps above freezing, so trended towards cooler 2m temps and wet-bulb effects. P-type will once again be the issue as models are still struggling with the warm layer. EC continues to remain on the cold side with the 12z NAM as the warmest. GFS/CMC and now 18z NAM are in the middle of the ground and thus trended towards the ensembles guidance. As with the prev forecaster, kept a bit of snow/sleet at the onset, as cold air looks to be deep enough north of the Pike and esp Route 2. In fact with good omega in the snow growth region, could see a few inches of snowfall. Once the mid-level warm front pushes into the region, a transition to more freezing rain event will occur leading to slick travel across the interior. Highest confidence will be across the east slope of the Berkshires and the Worcester Hills as the higher terrain locations will see the coolest surface temps. This is due to warm layer remaining around 800mb. Cannot rule out northern CT and the higher terrain of RI for some wintry weather impacts, but confidence is higher across northern MA. South of the Pike and especially across RI and SE MA conditions look to warm for any wintry weather, but still will have to watch as a change in just a few degrees will impact p-type. This system continues to be quite robust resulting in more widespread precip, esp as we continue to tap into that Gulf moisture. PWAT values are around 2-3 STD above normal for this time of year. When this system is all said and done, could see about an inch across the south coast with a half of an inch near the MA/NH border. Guidance from NERFC suggest that the rivers should remain within their banks, but may need to watch some of the flashier streams. Lastly, with the surface warm front trying to push northward, may have a large gradient in surface temperatures somewhere across southern New England. While warm fronts tend to struggle to lift northward this time of year something to watch as we could see low 50s across the south coast and mid 30s across the interior. Sunday night into Wednesday...High confidence. Surface cold front will push through the region resulting in a drying trend for Sunday night. Strong high pressure over the Ohio Valley will begin to strengthen Monday into Tuesday as anomolous ridge sets-up over the Mississippi Valley. This high appears to stay in place into middle of next week before a quick moving wave from the southwest gets kick into the flow. Thanks to ridging and surface high, dry weather will prevail as temperatures turn slightly above average. Thursday and beyond...Low confidence. To many pieces to the puzzle to have confidence in the forecast for the end of the week. Approaching shortwave from the southern Plains will spawn a surface low, just uncertain on its direction and location as it will depend on large scale features downstream.
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&& .AVIATION /21Z FRIDAY 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 Saturday Night/...Moderate confidence. Through today...MVFR/IFR conditions will overspread the region this evening, with rain, pockets of sleet and freezing rain developing across interior MA. Greatest risk of FZRA over higher elevations. Tonight...MVFR prevails with rain this evening, and pockets of FZRA at higher elevations in northern MA. RA/FZRA will end by 3z along the eastern coast. Fog will settle in behind the precip, keeping conditions MVFR in the valleys. Saturday...Fog may linger along the southern coast and islands past 12z. Conditions will improve to VFR across the region by early morning. KBOS Terminal...Moderate confidence. MVFR through this evening with onset of rain near 21z. Rain ending near 3z with improving conditions around 6z. KBDL Terminal...Moderate confidence. MVFR/IFR through this evening. Patchy fog in the AM, burning off by 9z. VFR conditions to follow. Outlook /Sunday through Wednesday/...Moderate confidence. Sunday: MVFR/IFR conditions possible. Windy with gusts to 30 kt. RA, chance FZRA across northern interior. Sunday Night: Mainly VFR, with local IFR possible. Slight chance RA. Monday through Wednesday: VFR.
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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 Saturday Night/...High confidence. Today...Gusts to 20 kt over eastern waters late in the day. Vsbys lowering in rain and fog this evening. Tonight...SCA issued for our NE MA waters as a brief period of southerly gusts to near 25 kt overnight. Elsewhere, winds shifting to west with gusts up to 20 kt. Rain exits near 3z with improving vsbys, but patchy fog may develop over southern waters. Saturday...Diminishing westerly winds becoming northerly in the evening. SCA might be needed for the southern waters early Saturday where seas reach 5 feet. Outlook /Sunday through Wednesday/... Sunday: Low risk for gale force winds with gusts up to 35 kt. Areas of rough seas. Rain. Sunday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of rain. Monday: Winds less than 25 kt. Seas up to 5 ft. Monday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Tuesday: Winds less than 25 kt. Seas locally approaching 5 ft. Tuesday Night through Wednesday: Winds less than 25 kt.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...Winter Weather Advisory until 9 PM EST this evening for MAZ002>004-008-009. RI...None. MARINE...Small Craft Advisory until 6 AM EST Saturday for ANZ250.
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&& $$ SYNOPSIS...Nocera/Dunten/Correia NEAR TERM...Nocera/Correia SHORT TERM...Nocera/Correia LONG TERM...Dunten AVIATION...Nocera/Dunten/Correia MARINE...Nocera/Dunten/Correia

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