Area Forecast Discussion
Issued by NWS Boston, MA

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176 FXUS61 KBOX 220614 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 214 AM EDT Tue Aug 22 2017 .SYNOPSIS... Southwest winds bring warm humid air Tuesday night, which will feed developing showers and thunderstorms. The wet weather will continue into Wednesday, until a cold front sweeps across Southern New England. High pressure brings dry weather Thursday through Sunday. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... 215 am update... Given dewpoints well into the 60s, temps will only drop a few more degrees through daybreak. Lows should bottom out in the 65 to 70 range in most locales with some patchy ground fog developing in the typically prone locations. Dry weather should continue, but a brief spot shower or two is possible near daybreak across the southeast New England coast with some marginal elevated instability. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM WEDNESDAY/... A cold front will approach our region from the west Tuesday. With a strong high pressure off to the east, thinking this front will be delayed from entering our region until Tuesday night. This front should not move off the coast until sometime after daybreak Wednesday morning. Despite the expected timing of this front, our region should see an increasing risk for showers and thunderstorms from west to east through Tuesday morning into the afternoon. Latest guidance suite continues to CAPE values of 1,000-1,600 J/kg during the afternoon and evening, with mid level wind speeds of 40-50 kt. These values are supportive of the risk for a few strong to sever storms. The greatest threat is across western and central MA, and northern CT. Showers and a few thunderstorms should continue into Tuesday night as a cold front pushes across southern New England. Precipitable water values are anticipated to be around 2.00 inches. Locally heavy rainfall is possible within any thunderstorms. Above normal temperatures continue through this period. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Big Picture... Long term starts off with an upper trough centered over Quebec on Wednesday. Although the upper trough center pulls somewhat northeastward on Thu, cyclonic flow remains over our region thru this weekend. Expecting temperatures to trend seasonably cool thru the period. During early next week GFS and ECMWF show signs of the upper trough moving east, placing us in upper level ridging. Thus we could see a warmup for next Mon. Details... Wednesday... Upper level short wave will push a cold front eastward during Wednesday. Depending on the exact timing of the cold front, western portions of the area could start the day off dry. However to the east and ahead of the cold front, precipitable water is 1.5 to 2 inches, allowing for locally heavy rain. Instability ahead of the cold front with LIs 0 to -2 and Cape generally 500 to 1000 J/kg, accompanied by the right entrance region of the upper jet. So some rumbles of thunder are probable ahead of the cold front Wed morning. Wed afternoon expected to bring a drying trend as the deeper moisture and better dynamics move offshore. Increasing sunshine anticipated, allowing high temps to reach the upper 70s to low 80s for most locales. Dew points will gradually dip into the 50s during the day and evening. Wednesday night... Surface ridging starts to build into southern New England and quite dry airmass in place. Thus mostly clear skies are expected. Thursday through Sunday... High pressure builds in at the surface, while upper trough lingers over southeast Canada and into our area. Not much available moisture thru this period except mainly between 700 and 850 mb. So cold pool aloft will likely allow for partly cloudy skies and mainly dry conditions. Short wave crossing the base of the trough Thu night/Fri could bring some additional clouds. Could see a few showers here or there during the long term timeframe, but again moisture looks quite limited. Temps will range from near normal to several degrees below normal. High temps ranging mainly from 70 to 80 degrees F. Dew points range mainly from the upper 40s to mid 50s, so quite comfortable from a humidity standpoint. With light winds each night, min temps in the 50s to low 60s are expected, with the warmest overnight temps near the shoreline, coolest in sheltered valleys. The light wind flow will allow sea breezes to develop each late morning and afternoon Friday through Sunday. Monday... Models indicate weak upper level ridging in our area, while surface high pressure lingers. Should be a dry day accompanied by warmer temps. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday/... Until 12z this morning...High confidence. Mainly VFR other than some patchy ground fog in the typically prone locations. Low probability that some IFR Cigs develop near the southeast New England. Today...High confidence. Mainly VFR as any early morning patchy ground in the typically prone locations quickly burns off. Otherwise...southwest wind gusts up to 25 knots expected to develop by afternoon. Low risk that some lower cigs/vsbys flirt with the southeast New England coast. An isolated shower/t-storm is possible across western MA/northern CT by late afternoon/early evening but mainly dry weather expected. Tonight...Moderate confidence. A cluster of scattered showers and thunderstorms may enter western MA/northern CT after 2 or 3z, but probably not impact the coastal plain until after 6z and perhaps closer to 12z Wed. VFR with some marginal MVFR conditions will probably dominate tonight, but some IFR CIGS/VSBYS may impact the southeast New England coast along with some LLWS from the increasing low level jet. Wednesday...High confidence in trends but lower confidence in overall timing. Scattered showers and t-storms may persist near and especially southeast of the I-95 corridor into early Wednesday afternoon. Improvement to VFR conditions expected from west to east on Wednesday, but timing somewhat uncertain. KBOS Terminal...High confidence in VFR into this evening. KBDL Terminal...High confidence in VFR today. A cluster of scattered showers and thunderstorms may approach the terminal after 2 or 3z this evening. Outlook /Wednesday Night through Saturday/... Areas of MVFR cigs/vsbys in showers/thunderstorms Wednesday morning. Otherwise, VFR all areas thru Saturday, with patchy IFR cigs/vsbys in fog Wednesday night/early Thursday and Thursday night/early Friday. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday/...High confidence. Small Craft Advisories remain posted from late Tuesday morning into Tuesday night for south coastal and outer coastal waters. Gusts should reach 25 kt, to perhaps 30 kt, along with building seas up to 6-7 ft offshore. After some more thought, decided to expand the Small Craft Advisory into Massachusetts Bay. It possible we might need an advisory in Boston Harbor, but don`t have enough confidence just yet. Winds diminish Tuesday night, although seas may take a bit longer into Wednesday morning to subside, particularly across the outer coastal waters. Outlook /Wednesday Night through Saturday/... Wednesday... Cold front moves across the waters, turning winds from the west- northwest. Gusts to 25 kt possible early in the day. Seas 3 to 5 ft on the coastal waters gradually subside during the day. Thursday through Saturday... High pressure then builds in with W/NW winds diminishing to less than 20 kt. Winds become north on Friday. Diminishing winds will bring diminishing seas, generally 3 ft or less through this period. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 11 AM this morning to 6 AM EDT Wednesday for ANZ231>234-250-254>256. Small Craft Advisory from 2 PM this afternoon to 2 AM EDT Wednesday for ANZ236. Small Craft Advisory from 2 PM this afternoon to 6 AM EDT Wednesday for ANZ235-237. Small Craft Advisory from 2 PM this afternoon to 4 AM EDT Wednesday for ANZ251. && $$ SYNOPSIS...Belk/NMB NEAR TERM...Frank SHORT TERM...Belk LONG TERM...NMB AVIATION...Frank/NMB MARINE...Belk/NMB is the U.S. government's official web portal to all federal, state and local government web resources and services.