Area Forecast Discussion
Issued by NWS Boston, MA

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508 FXUS61 KBOX 301921 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 321 PM EDT TUE AUG 30 2016 .SYNOPSIS... High pressure over New England will move offshore tonight. Warmer and more humid weather returns Wednesday. A cold front moves through Wednesday night and Thursday, which will bring scattered showers and a few thunderstorms. High pressure will bring dry and seasonable weather Friday, then we will have to closely monitor a tropical system which will likely be lifting north along the eastern Seaboard this weekend into early next week. && .NEAR TERM /THROUGH TONIGHT/... High pressure moves offshore but will maintain dry weather across the region. Some increase in high clouds expected overnight. Temps will be milder than last night as sw flow becomes established. Mins generally upper 50s to mid 60s. Patchy late night fog possible in the normally fog prone areas. && .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... Wednesday... Cold front moves into the eastern Gt lakes and St Lawrence valley by days end with modest sw flow across New England. Low level theta-e ridge develops with higher KI values moving into the region from the west. Instability is marginal with forecast MLCAPES around 500 J/kg and synoptic forcing is weak. Can`t rule out a few showers or an isold t-storm in the interior but better chance will be to the north and west in area of greater instability and forcing. Otherwise, Pt-mosunny skies expected with increasing clouds in the afternoon. Warmer and more humid airmass moves into the region with temps reaching well into the 80s and dewpoints rising into the mid/upper 60s. Wednesday night... Amplifying mid level trof moves into the Lakes region as cold front slides south across northern New England. Subtropical PWAT plume 1.75"+ will be over the region and combined with marginal elevated instability and increasing forcing assocd with right entrance region of upper jet and approaching front will result in sct showers and a few t-storms moving across the region. It will be a mild and humid night with lows in the mid 60s to near 70. && .LONG TERM /THURSDAY THROUGH TUESDAY/... HIGHLIGHTS... * Scattered showers and thunderstorms into Thursday * Dry weather and seasonable temps into the Holiday weekend * Rough surf and rip currents could be an issue through the period due to swells from distant TD eight and TD nine OVERVIEW... The 12z guidance is in overall agreement synoptically, still some issues with timing from Thursday cold front. Also we continue to watch TD nine as the latest GFS brings it just a bit to close for comfort. Focusing on the cold front, guidance continues to slow down the frontal passage compared to yesterdays run pushing the front through late Thursday rather than Thursday morning. This lines up better with the ensembles. High pressure then builds late Friday into Saturday. Uncertainty then increases for Sunday into Tuesday with TD nine. The 12z GFS still keeps TD nine a contender for SNE. The CMC and UKMET also keeps it around, however both indicate that it is a very diffused/weak system. The 12z EC pushes it out to sea, but because of the strong block it retrogrades back to SNE on Labor day. Most of these solutions indicate just tropical rains for SNE, where the GFS could bring some wind issues. Still a large spread in all of the guidance so will continue to trend with ensembles and keep a close eye on this system. DETAILS... Thursday...Increasing confidence. A shortwave moving through central Canada and into the Great Lakes will carve out a deepening trough for Wednesday night into Thursday. The trough will then move towards the Northeast and weaken as a strong ridge builds from the central United States. Approaching cold front associated with this shortwave will continue to develop scattered showers an isolated thunder across the region on Thursday. Weak mid to surface flow aloft will allow for some of these storms to be slow moving. Some guidance continues to show an enhanced PWAT region near the I-95 corridor and points south and east of near 2 inches which may result into heavy downpours. High K values also support this idea. There is some indications for elevated thunder as showalters drop below 0 and TT are above 45. If a strong thunderstorm does develop then the main risk will be heavy rain and some gusty winds. Friday into Saturday...High Confidence. Upper level trough axis will remain over the region on Friday resulting in a cold pool aloft moving overhead. 500 mb temps near - 14 to -16C would result in another round of showers with possible thunder. The GFS is a bit more aggressive on the convection potential than the EC, as it is indicates steep lapse rates and MU CAPE values over 500 J/KG. Believe this is something to watch in the coming days. Within any strong storm, hail would be the main issue. High pressure will move in behind the upper level trough. This will allow for sunny skies and dry weather. Temperatures on each day will be near average for this time of year with highs in the upper 70s to low 80s. Sunday into Tuesday...Low confidence. Initially thinking is that high pressure and mainly dry weather will prevail for this time period. As mentioned above, we`ll have to continue to watch TD nine as it develops and move into the Eastern Seaboard. Some of the deterministic models have shifted the system west and north keeping it a player for southern New England. The latest ensembles are indicating a very low risk. We`ll have to see how the high pressure over the region and upper level ridge will drive this upcoming tropical system in the upcoming days. Right now, where the system is progged to develop and move, anticipate in another round of rough surf and rip current issues for the beaches Labor day weekend. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Through Wednesday night... Tonight...High confidence. VFR, but patchy late night fog possible in the CT valley. Wednesday...High confidence. Mainly VFR. A few showers or a t-storm possible in the interior during the afternoon with brief lower conditions. Wednesday night...Moderate confidence. Mainly VFR cigs but there is uncertainty regarding the potential for developing stratus. Sct showers and a possible t-storm which will result in briefly lower conditions. KBOS Terminal...High confidence. Seabreeze shifts to S by evening. KBDL Terminal...High confidence. Low risk for patchy fog for a few hours before daybreak. Outlook /Thursday through Sunday/... Thursday...High confidence. Mainly VFR conditions. Low probability of SCT -SHRA/ISOLD TSRA, resulting in brief MVFR conditions. Friday into Sunday...High confidence. VFR. May need to watch TD nine for aviation impacts across the Islands. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday Night/...High confidence. SE swell will bring 4-5 ft seas to the outer waters through the period with highest swell across eastern waters where we have SCA for hazardous seas. Winds will remain below SCA but sw winds will gust to 20 kt Wed into Wed evening. Outlook /Thursday through Sunday/... Moderate confidence through the period as there is a large uncertainty on TD eight and nine`s impact for southern New England waters. Conditions should be below SCA for Thursday however increasing southerly swell from TD eight may impact the southern waters into Friday. Saturday into Sunday, seas will begin to increase as TD nine will approach the Eastern Seaboard. Right now appears seas will build to at least 8 feel by sunday resulting in rough surf for the Holiday weekend. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory for hazardous seas until 4 PM EDT Wednesday for ANZ250-254. && $$ SYNOPSIS...KJC/Dunten NEAR TERM...KJC SHORT TERM...KJC LONG TERM...Dunten AVIATION...KJC/Dunten MARINE...KJC/Dunten is the U.S. government's official web portal to all federal, state and local government web resources and services.