Area forecast discussion National Weather Service Taunton Massachusetts 534 PM EDT Tuesday Jun 18 2013 Synopsis... another round of showers and thunderstorms is anticipated through this evening as a cold front moves across the region. Large high pressure will follow...bringing mainly dry and seasonable conditions Wednesday through Saturday. Warmer and more humid weather is expected this weekend as high pressure anchors just south of New England. Showers and thunderstorms possible Saturday. && Near term /until 6 am Wednesday morning/... thunderstorms will heavy rainfall and localized flooding will continue into this evening... Line of showers/scattered thunderstorms moving slowly but steadily S across east Massachusetts/north Rhode Island/southeast Massachusetts at 20z as seen on kbox 88d radar. Have had several reports of flash flooding...as well as reports of up to 2 inches of rain in 90 minutes or less. Noting another area of rainfall moving across north New Jersey/western Long Island...which will keep rainfall through this evening across NE CT/RI/se Massachusetts as low pressure moves along the front as it pushes offshore this evening. Pretty light pressure gradient except in thunderstorms where gusts up to 25 knots possible. Expect any thunder to end by around midnight as the low passes S of Nantucket...but showers could linger on the cape and islands through the night. May also see patchy fog develop prior to the drier air working in...but should improve from S-north as dewpoints drop. Will be a chilly night across interior S New Hampshire and north Massachusetts as temperatures fall back to the upper 40s to around 50...ranging to the middle 50s along the S coast. && Short term /6 am Wednesday morning through Wednesday night/... tonight... The cold front will slow as it pushes offshore as a weak wave lifts along the front from the mid-Atlantic. Expecting widespread rain with embedded heavier showers and thunderstorms to linger over the South Coast and adjacent waters. Concerns will still be present for localized urban flooding and ponding of water along roadways...but low confidence on severe weather threats as instability is expected to be minimal. Lows down to around low 50s. Wednesday... Cooler airmass building south should allow significant boundary layer mixing of around 4-6 kft. Subsequently...anticipating the mix- down of faster momentum and drier air. Not looking at any fire weather headlines with recent rains. Dewpoints down to around 50 degrees...some gusty northerly winds mainly across eastern New England. Expecting diurnal scattered to broken fair-weather cumulus across interior New England. && Long term /Thursday through Tuesday/... highlights... * high pressure will lead to quiet weather Thursday and Friday * high pressure S of southern New England brings warm...humid conditions this weekend * showers and thunderstorms possible Saturday There is good general agreement amongst the models through much of the long term. There are some model discrepancies regarding the strength and extent of an upper level ridge over the eastern U.S. Through this weekend. Ultimately this will affect the weather in this area mainly in where and when showers and thunderstorms are able to develop. The consensus is with the European model (ecmwf) and the upper level ridge over the southeast Continental U.S. Thursday and gradually building northward into the Ohio Valley by Saturday and into the NE Continental U.S. Sunday and sinking back south early next week. Otherwise...am expecting fairly quiet weather with more Summer like temperatures and a few humid days thrown in there as well. With thunderstorms currently moving over southern New England...will make whatever changes are necessary and base much of the forecast off the previous forecast. Thursday and Friday...high pressure crests over southern New England with a warming trend in temperatures. Saturday...best chance for showers and thunderstorms as warm...moist air builds into the region on SW winds. We will still be on the periphery of the ridge with decent instability noted in steep middle level lapse rates. Sunday through Tuesday...high pressure moves offshore as the upper ridge sinks S slowly. Warm...moist air remains in the region on southwesterly winds...and increases instability. However...not much of a trigger any of those days and models are not showing much...if any...quantitative precipitation forecast so will keep thunderstorm chances low. && Aviation /22z Tuesday through Sunday/... forecaster confidence levels... Low...less than 30 percent. Moderate...30 to 60 percent. High...greater than 60 percent. Near term /through Wednesday night/... Moderate confidence for trends...lower confidence for timing through tonight...then moderate confidence Wednesday-Wednesday night. Through 00z...MVFR-IFR ceilings/visibilities in showers/scattered thunderstorms across east Massachusetts/north Rhode Island/north CT as cold front moves slowly S. Noting brief torrential rainfall in some storms. May see local LIFR conditions. This will shift slowly S to the S coast this evening. Will also see local IFR-LIFR ceilings/visibilities along S coast with low clouds/patchy fog. Tonight...expect mainly VFR conditions across north Massachusetts/S New Hampshire...patchy MVFR-IFR ceilings/visibilities mainly in the valleys with patchy fog. Across central and southern areas...MVFR-IFR ceilings/visibilities in low clouds/showers. May see scattered thunderstorms through midnight. Brief LIFR conditions possible. Wednesday...MVFR-IFR ceilings/visibilities to start mainly S of the Mass Pike...then improving to VFR during the morning. MVFR visibilities may linger along S coast into the afternoon. Wednesday night...VFR. Kbos terminal...moderate confidence. Ra+/thunderstorms and rain possible from around 21z through 02z. Kbdl terminal...moderate confidence. Ra+/thunderstorms and rain possible through 23z-00z. Outlook...Thursday through Sunday... Thursday and Friday...high confidence. VFR. Saturday...moderate confidence. Mainly VFR. Low probability of showers and thunderstorms briefly lowering conditions to MVFR/IFR. Sunday...moderate to high confidence. VFR. && Marine... forecaster confidence levels... Low...less than 30 percent. Moderate...30 to 60 percent. High...greater than 60 percent. Near term /through Wednesday night/...moderate confidence. Tonight...winds shift to NE as cold front moves offshore...then low pressure passes S of the waters. NE winds increase...gusting to 25 knots toward daybreak across the southern outer waters and east of Cape Cod with seas up to 5 feet. Low probability of thunderstorms this evening. Wednesday...NE winds gusting to 25 knots through midday on the outer waters from Cape Cod southward. May also see gusts up to 25 knots on Nantucket Sound and Buzzards Bay mainly during the morning...so have put up small crafts there. Seas up to 5 feet...but should subside by evening. Wednesday night...winds and seas below small craft criteria. Outlook...Thursday through Sunday... High confidence. Quiet boating weather expected through Sunday with high pressure near or over the waters. The only exception is Saturday when showers and thunderstorms may limit visibilities on the waters. && Hydrology... have kept Flash Flood Watch up through this evening across the region...though may end it early across lower CT valley region. Have had several reports of flash flooding due to torrential rains from thunderstorms as the cold front slowly moves through. Have also received a couple of reports of small streams overflowing their banks. As for river flooding...the Charles at Dover remains just above flood stage. Latest guidance indicates that this river will only slowly fall and remain in minor flood through late Wednesday night. && Box watches/warnings/advisories... CT...Flash Flood Watch until 9 PM EDT this evening for ctz002>004. Massachusetts...Flash Flood Watch until 9 PM EDT this evening for maz009- 011>013-015>021. New Hampshire...none. Rhode Island...Flash Flood Watch until 9 PM EDT this evening for riz001>007. Marine...Small Craft Advisory from 6 am to noon EDT Wednesday for anz232-234. Small Craft Advisory from 4 am to 6 PM EDT Wednesday for anz254>256. && $$ Synopsis...rlg/evt near term...Frank/evt short term...evt long term...rlg aviation...rlg/evt marine...rlg/evt hydrology...evt