Area Forecast Discussion
Issued by NWS Boston, MA

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524 FXUS61 KBOX 141554 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1054 AM EST Sat Jan 14 2017 .SYNOPSIS... High pressure moves E of the region today with a weak low pres sliding well S of the coast overnight. Some light snowfall is possible mainly across Connecticut, Rhode Island and Southeast Massachusetts late today and tonight. High pressure maintains dry and seasonable conditions Sunday and Monday, then milder temperatures return for the rest of the week with a wet period around midweek. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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1035 AM Update... Areas of mid and high clouds were pushing across the region at mid morning as seen on latest visible satellite imagery as well as 14Z observations. Temperatures were running up to 3 degrees below forecast at both 13Z and 14Z. Noting extensive cloud cover across NY/PA through the mid Atlantic states heading eastward, so clouds will continue to increase through the afternoon. Large 1040 hPa high pres crossing the region this afternoon, with light/variable or calm winds through midday, then will shift to light S-SW during the afternoon. Previous forecast had this well covered, but did update to incorporate current trends. Reminder of forecast in pretty good shape, but again updated to extend current trends especially for cloud cover. Temps/dewpts looked OK as well, though did tweak temps up a bit across S coastal areas as winds become more onshore off the milder ocean. Previous Discussion... The high clouds will give way to a BKN-OVC AC band in advance of weak low pres developing near the Delmarva. Have highs reaching the upper 20s and low 30s. Dry wx prevails everywhere through mid afternoon thanks to 1040+ high pres slowly sliding offshore. Winds remain light, but will back to the S-SW by afternoon.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... Late today and overnight... Weak low pres developing off the Delmarva will slide well S of the 40/70 benchmark just after midnight tonight. With center of high pres more E of S New England overnight than N, this will allow weak mid lvl f-gen band N of the developing low pres to just brush S Coastal New England during the evening hours. Sounding data suggests moisture loading from H7-sfc, but mainly S of a line through the border of MA with RI/CT and continuing E. Areas N remain under the subsidence of high pres and are not able to moisten enough to be of impact. S of this line, where PWATs reach about 0.75 inches just offshore light snowfall is possible, mainly from late afternoon into the early overnight hours. F-gen is weak and omega from this is below the primary snow growth regime but within the region saturated in respect to ice. Therefore, some light accumulations are possible below an inch, and likely even below a half inch most locations, especially as one heads N, where only flurries can be expected. Overnight mins dip mainly into the 20s, as the cloud cover associated with the wave will limit the ability for radiational cooling until late. Sunday... Secondary high pres/ridging will allow for clearing and weak pres gradient/winds and dry wx after clouds clear from exiting low pres. H92 temps hover between -6C and -8C, but once again subsidence inversion could limit mixing. In spite of sunrise, will be limiting highs to the low-mid 30s primarily. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... */ Highlights... - A warmer than average, wet weather pattern by midweek - Low confidence forecast going into the late-week */ Discussion... Signals of mild and wet-weather outcomes into late January continue. E CONUS / E Canada beneath favorable H5 ridging on the order of +1-2 standard deviations with H85 temperature anomalies in excess of +20C for portions of Canada based on a consensus of forecast N Hemisphere atmospheric teleconnections. Winter appears to be taking a vacation. Much of impacts of the nuisance variety there may be only two things to be concerned about: 1) Breezy S winds that could turn out strong, and 2) Areas of dense fog at times. Despite discrepancies among forecast solutions in handling mid-level energy emerging out of the Pacific as well as the cut-off low across the SW CONUS, there is a general trend of rain moving in on Tuesday. This subsequent of low-mid level isentropic over-running of a decent plume of sub-tropical moisture with precipitable waters in excess of an inch, brought N via a H925-85 SW low level jet of 35 to 45 mph. A risk of freezing rain with onset given lingering high pressure over SE Canada which yields undercutting cold air as low pressure sweeps across the Great Lakes. Area of concern mainly N/W MA and CT within the low-lying valleys, sheltered from S flow. Prior to the inside- runner low, it is more than likely will see some N funneling winds ahead of the aforementioned low that may keep the cold air and thus the freezing rain threat. Otherwise, storm-total rainfall consensus of around half an inch through Wednesday along a lifting warm-front prior to a sweeping cold front. Persistence the last several days, will lean towards likely PoPs. Mild temperatures. Hereafter a low confidence forecast as deterministic and ensemble solutions struggle with handling individual shortwaves. In addition there appear to be complications between preferred ridging across the E CONUS along with a potential downstream block. It`s possible high pressure and colder air out of Canada may sneak S into the area despite atmospheric teleconnections suggesting milder temperatures. Leaning with ensemble means. && .AVIATION /16Z 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/... 15z update... Through this afternoon...High confidence. VFR. BKN-OVC AOA 12Kft. Light/variable or calm winds become S-SW, but remaining light. This evening and overnight...Moderate confidence. VFR remains N of a line along the MA border with CT/RI into SE MA. S of this line, light snowfall is possible, with some light accumulations (less than an inch) possible especially near the coast and over the Islands. This could yield a period of MVFR conditions in lowered vsbys and CIGS. Conditions clear during the early morning hours Sun. Winds S-SW, but shift back to the NW after snows end. Sun...High confidence. VFR. NW flow, mainly 10 kt or less. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF overall. Low risk for very light snowfall this evening, but VFR likely to dominate. Outlook /Sunday Night through Wednesday/...Moderate confidence. Sunday night through Monday night... VFR. Increasing SW winds. Increasing cigs, lowering down to low-end VFR late. Tuesday through Thursday... Lowering to IFR with -RA. Continued breezy S winds. Potential LLWS impacts. Improving late.
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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 Sunday/... 15z update... Through this afternoon...High confidence. Winds and seas have diminished so allowed small crafts to expire at 10 AM. Expect light/variable, mainly W-NW winds to back to S-SW during the afternoon but remain AOB 10 kt. Seas 4 ft or less. Tonight into Sunday...High confidence. S-SW winds remain below small craft criteria into the overnight hours before they turn back to the NW late tonight and early Sunday morning. Even with this shift, gusts should remain below small craft. Seas should remain below 5 ft. Some rain, even mixing with snow in spots tonight will yield brief vsby restrictions. Outlook /Sunday Night through Wednesday/...Moderate confidence. Breezy NW winds shifting out of the W/SW early. Seas diminishing below 5 feet into Monday morning. Quiet into Tuesday. Will then be watching a warm front lift N across the waters with rain behind which S/SW winds will become breezy with a low risk of gales. Seas potentially building 8 to 10 feet on the S/SE waters. Will see conditions improve late Thursday.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...None.
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&& $$ SYNOPSIS...Doody/Sipprell NEAR TERM...Sipprell/EVT SHORT TERM...Doody LONG TERM...Sipprell AVIATION...Doody/Sipprell/EVT MARINE...Doody/Sipprell/EVT

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