Area forecast discussion National Weather Service Taunton Massachusetts 503 PM EDT Thursday may 23 2013 Synopsis... a cold front will move slowly into New England Friday. Low pressure will develop on this front...causing the system to linger across the region through the weekend. This will bring showers and cooler conditions...with a few thunderstorms possible. Some of the rainfall will be heavy at times. Conditions should improve on Monday. Dry weather and seasonable temperatures are expected into the middle of next week. && Near term /until 6 am Friday morning/... numerous showers and isolated thunderstorms with locally heavy rainfall moving NE across western new eng. Environment is marginally unstable with MLCAPES around 500 j/kg while middle level lapse rates are less than 6 c/km. Instability is a limiting factor for severe weather despite 30-40 knots 0-6km shear. Near term forecast of significant severe parameter also supports limited severe potential. Still cant rule out an isolated severe storm...but heavy rainfall is primary concern into this evening across the interior with precipitable waters near 1.7". Tonight...cold front moves slowly east from central New York and will approach western new eng toward daybreak as middle level trough amplifies over the Great Lakes. Southern New England will be under the right entrance region of the upper jet which will provide good forcing acting on high precipitable water airmass to bring locally heavy rainfall to southern New England. Showers and isolated thunderstorms will be ongoing across the interior in the evening...then focus will shift to the coastal plain after midnight as low level jet strengthens across southeast new eng. Instability will be weakening overnight and even elevated instability parameters are marginal. Still cant rule out isolated thunderstorms given deep synoptic forcing...but lack of instability should limit rainfall rates. Areas of urban and poor drainage flooding likely overnight in eastern new eng. && Short term /6 am Friday morning through 6 PM Friday/... high amplitude trough forecast to close off over the middle Atlantic region on Friday with southerly flow aloft. Surface low develops on the front which will slow its eastward progress across southern New England. Low level jet will be situated just east of Cape Cod in the morning with axis of heavy rainfall confined to the cape/islands...before moving east in the afternoon. However...showers will persist all day across much of the region with deep moisture axis in place and surface wave moving along frontal boundary. In fact...this has a winter look to it with decent low level frontogenesis and deformation axis setting up across western new eng northwest of surface low. Temperatures will likely fall into the 50s over northwest higher terrain as front moves to the east...but should reach well into 60s to around 70 across southeast new eng which will remain east of the boundary for most of the day. The front should reach the i95 corridor by late afternoon. && Long term /Friday night through Thursday/... highlights... * slow moving upper level system will keep showers and cooler temperatures for the weekend * improvements begin on Monday...with drier but cool conditions * moderating temperatures arrive by late next week Overview and model preferences... all operational models now on board with developing amplified upper level pattern across the lower 48...with digging troughs on the east and west coasts with building ridge across the central U.S. Through a good portion of this period. 500 mb cutoff low develops across the middle Atlantic then slowly moves into the region this weekend...with surface low developing along slowly moving cold front. Lowered confidence on timing the exit of the low... however. By early next week...though...should see improving conditions but cool temperatures. Temperatures start to moderate by middle week. Went along with 12z GFS/00z European model (ecmwf) and their ensembles...which is pretty close to the wpc guidance. Details... Friday night through Sunday...continued cloudy skies with showers and cool temperatures will continue through most of the Holiday weekend. Surface low pressure trapped with its upper level cutoff low will slowly move across the region...with periods of heavy rainfall anytime during this timeframe. Current quantitative precipitation forecast forecast suggests possibility of 1-2 inches of general rain with the highest amounts across the CT valley and SW New Hampshire. However...with the chance of thunder...could see localized flooding especially across central and western areas with good low level moisture inflow. Will continue to monitor for potential of flooding along rivers and low lying areas. Temperatures will become rather chilly across S New Hampshire/west Massachusetts Sat night as low pressure spins across east Massachusetts...with north-northwest winds in place. MOS guidance suggests readings falling back to the middle-upper 30s across the higher terrain. Can not rule out the remote possibility of some mixing over the highest terrain of SW New Hampshire. For now...looks like the low and upper level system will slowly move NE during Sunday...but precipitation will linger into Sun night before tapering off from SW-NE overnight sun. Daytime highs will only be in the 50s through the weekend. Monday...transition day as high pressure builds out of central Canada. May still see some widely scattered showers across S New Hampshire/NE Massachusetts early but will push NE. Will continue cool...but readings should reach the 60s. Tuesday-Thursday...high pressure will shift to the middle Atlantic coast then offshore during this timeframe. Expect a dry forecast with slowly moderating temperatures. && Aviation /20z Thursday through Tuesday/... forecaster confidence levels... Low...less than 30 percent. Moderate...30 to 60 percent. High...greater than 60 percent. Overview...moderate confidence. Variable MVFR/IFR ceilings this afternoon will trend to widespread IFR/LIFR tonight into Friday with areas of fog developing. Showers and scattered thunderstorms CT valley and western new eng this afternoon will expand east across rest of southern New England tonight into Friday...with focus for heavy rainfall shifting to the coastal plain late tonight and Friday morning. Localized low level wind shear possible late tonight cape/islands as low level jet strengthens across the region. Kbos terminal...moderate confidence. Expect lowering ceilings to IFR tonight with showers increasing. Scattered thunderstorms possible. Kbdl terminal...high confidence. Widespread showers and a few thunderstorms this afternoon and evening. Outlook...Friday night through Tuesday... Friday night through Sunday...low to moderate confidence. Very unsettled pattern with variability between VFR conditions and MVFR/IFR conditions in rain showers/scattered tsra/fog. Improving conditions during Sunday night from SW to NE. Monday-Tuesday...moderate to high confidence. VFR. Low probability of MVFR ceilings across S New Hampshire/north Massachusetts early Monday then improving. Low confidence on sea breeze development. && Marine... forecaster confidence levels... Low...less than 30 percent. Moderate...30 to 60 percent. High...greater than 60 percent. High confidence through Friday. Low level jet will bring near Small Craft Advisory gusts on the waters through tonight...diminishing west of the canal later tonight as the low level jet moves to the east. Strong low level inversion will limit gusts so gales not expected. Persistent SW flow will result in building seas through Friday. Winds will diminish on Friday as the low level jet moves east of the waters. Expect low visibilities in fog and locally heavy showers. Isolated thunderstorms are also possible. Outlook...Friday night through Tuesday... Friday night...low to moderate confidence. Low pressure and cold front will slowly cross the waters...then stall along the eastern near shore waters. Expect SW gusts up to 20 knots early...then will diminish. Low probability for thunder. Areas of low visibilities in heavier showers and patchy fog. Seas will remain at or above 5 feet mainly over the open waters. Saturday-Sunday...low confidence mainly for timing. As low pressure stalls across east Massachusetts/mass Bay...will see light/variable winds except north-northwest over the western waters later Sat...which will shift toward the eastern waters during sun. Seas remain high. Low chance of thunderstorms Sat-Sat night. Low probability of gusts up to 25 knots sun. Monday-Tuesday...low to moderate confidence. Winds become west with gusts up to 20 knots Monday...then diminish Monday night-Tue. Seas around 5 feet on the outer waters Monday...then subsiding. && Tides/coastal flooding... Rhode Island South Coast this evening... a moderately strong southerly fetch of surface wind and increasing low level jet is expected to drive enough water into Narragansett Bay for a surge around or even just above a foot at the time of the evening high tide...about 2330z. This will be on top of a particularly high Spring tide. Both the estofs and etss surge guidance depict essentially no surge this evening but seems like too much of a S to SW wind to avoid some surge...and at 15z pvd was already showing a .4 feet surge and climbing. In addition... shoreline flooding could be exacerbated some by any heavy rain producing fresh water runoff that struggles to drain at the shoreline during high tide. East Coast of Massachusetts this weekend... astronomical high tides will occur this weekend into early next week. With surface low wobbling over southern New England Saturday and into Sunday...expect gusty northerly to northwest winds especially during the daytimes hours. At Boston...a high tide of 11.9ft will occur on Friday night at 11:21 PM and 12.2 feet early Sunday morning at 12:12 am. Expect a light southerly winds during the Friday high tide so this is less than a concern. Looking at the Sunday morning high tide...northerly to northwesterly winds may help increase the surge especially for Cape Cod Bay. Right now only expect minor splashover across north facing beaches. Will need to continue to monitor and update with the latest forecast guidance. && Box watches/warnings/advisories... CT...none. Massachusetts...none. New Hampshire...none. Rhode Island...coastal Flood Advisory until 9 PM EDT this evening for riz002- 004>007. Marine...Small Craft Advisory until 10 am EDT Friday for anz232. Small Craft Advisory until 6 am EDT Friday for anz233-234. Small Craft Advisory until 10 PM EDT this evening for anz230- 236. Small Craft Advisory until 4 am EDT Friday for anz231-251. Small Craft Advisory until 6 PM EDT Friday for anz235-237. Small Craft Advisory until 8 PM EDT Friday for anz250. Small Craft Advisory until 6 am EDT Saturday for anz254>256. && $$ Synopsis...kjc/evt near term...kjc short term...kjc long term...evt aviation...kjc/evt marine...kjc/evt tides/coastal flooding...Thompson