Area Forecast Discussion
Issued by NWS Boston, MA

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187 FXUS61 KBOX 291959 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 359 PM EDT Mon May 29 2017 .SYNOPSIS... Weak high pres will build across the region Wednesday bringing dry weather but temperatures remaining below normal. An approaching cold front may bring a few strong thunderstorms to the northwest of a Boston to Providence corridor late Wednesday afternoon and evening. Dry and seasonable weather follows Thursday, but unsettled weather with showers at times may return Friday into early next week but plenty hours of dry weather will be mixed in too. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... Showers assocd with mid level shortwave will be exiting the region from west to east through late afternoon/early evening as the mid level dry slot moves in and the shortwave lifts to the north. Rest of the night will be dry as Maritimes sfc high builds south across New Eng. However, low clouds will persist tonight given abundant low level moisture in place along with patchy fog. Not much change in temps tonight with mins mostly in the upper 40s. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... Tuesday... Mid level trof moves into the Gt Lakes with SW flow aloft across New Eng. High pres will slowly drift offshore but SNE will remain under marine influence with onshore winds which will keep temps cooler than normal. In addition, expect clouds to linger across the region, especially in the west where low level moisture is more prevalent. Some sunshine may develop in in the afternoon across eastern New Eng where low levels dry out a bit. Highs mid/upper 60s but cooler along the coast. Models show decent instability axis developing across NY state in the afternoon which will lead to some convection developing to the west. No surface instability is forecast across New Eng due to marine influence, but instability parameters indicate some elevated instability moving into the west in the afternoon. Low risk of a few showers across western MA late afternoon, otherwise dry conditions. Tuesday night... As mid level trof moves east across the Gt Lakes, low level theta-e ridge moves into SNE. Still no surface instability, but expect a period of showers and isolated t-storms, especially interior as weakening convection from the west moves into the region, supported by deepening column moisture and elevated instability axis with subzero SWI and TT around 50. Mild night with lows in the low/mid 50s. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... Highlights... * A few severe thunderstorms possible late Wed afternoon and evening northwest of a Boston to Providence corridor * Dry and nice weather on tap for Thu * Periods of showers possible at times Fri into early next week but timing uncertain and plenty hours of dry weather expected too * Seasonable temps likely Wed into Sat but perhaps a return to unseasonably cool weather next Sun/Mon Details... Wednesday... The main concern will revolve around convective/severe weather potential Wednesday afternoon and evening. As is typically the case in southern New England, plenty of uncertainty at this point but there are certainly some ingredients there that need to be watched. Will break things down a bit more below. A shortwave and bulk of its scattered precipitation will likely have lifted east of the region by mid morning Wed. The result will be a period of subsidence with mainly dry weather into mid afternoon Wed. By late Wed afternoon and evening a potent shortwave/cold pool aloft will be approaching from the west. 500T drop to around -19C resulting in relatively steep mid level lapse rates between 6.5C and 7C/KM. 0 to 6 km shear looks impressive between 40 and 50 knots. With all that said, the biggest uncertainty is the amount of surface heating that we receive, as model cross sections do indicate the potential for lingering low clouds. If some partial sunshine develops and high temps can reach the lower to middle 70s with dewpoints in the 50s to near 60, surface instability should easily exceed 1000 j/kg. So in a nutshell, the biggest uncertainty remains do we receive enough heating to realize the potential instability/wind fields. If so, the risk for a few severe thunderstorms would exist. While locally strong damaging wind gusts would be possible, the potential for severe hail would also exist given the anomalous cold pool aloft. The main risk is to the northwest of the Boston to Providence corridor, particularly across western and northern MA closer to the better dynamics and timing for that matter. Thursday... A nice day looks to be in the cards behind Wednesday`s cold front. Plenty of early June sunshine and a dry airmass in place should allow for highs to reach into the lower to middle 70s in many locations with comfortable humidity levels. Friday through Monday... The overall weather pattern will feature an upper trough over eastern Canada and into New England with below normal height fields. This will suppress summertime heat and humidity well to our south. Seasonable temps likely Fri/Sat, but some indications that a high over eastern Canada may result in another round of unseasonably cool temps next Sun/Mon but too far out to say for sure. The upper trough nearby will make our region prone to periods of showers at times, but also extended intervals of dry weather will also occur. Timing is highly uncertain and it is really impossible to give much more information in this time range. && .AVIATION /19Z MONDAY THROUGH SATURDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday Night/...Moderate confidence. Through tonight...MVFR/IFR conditions will continue. Patchy LIFR fog developing tonight, especially near the coast. Rain will end from west to east 20-23z. Tuesday...MVFR/IFR cigs will lift to VFR/MVFR in the afternoon. A few showers or an isold t-storm possible across western MA by late afternoon. Tuesday night...More MVFR/IFR conditions with sct showers and isold t-storms moving across the region. KBOS TAF...Moderate confidence in TAF. Lowering vsbys likely as fog redevelops but timing uncertain. KBDL TAF...Moderate confidence in TAF. Outlook /Wednesday through Saturday/...Moderate confidence. Wednesday...Low to moderate confidence. MVFR-IFR conditions early may improve to MVFR-VFR by afternoon. A few strong thunderstorms possible late Wed afternoon/evening mainly northwest of a Boston to Providence corridor. Thursday...Moderate to high confidence in mainly VFR conditions. Friday and Saturday...Low to moderate confidence. A period of MVFR- IFR conditions possible in some low clouds and some showers, but timing uncertain. Greatest risk for lower cigs/vsbys late Fri into early Sat. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday Night/...High confidence. Through tonight...Winds have diminished but SCA will continue into early evening due to leftover 5-6 ft seas over southern waters. Seas will subside below 5 ft tonight. Tuesday...SE flow with speeds increasing to 15 kt in the afternoon. Vsbys may be reduced in the morning due to fog, but improving by afternoon. Tuesday night...Southerly flow with speeds mostly 15 kt or less but a few gusts to 20 kt possible across NE MA waters. Sct showers developing with low risk for an isold t-storm. Patchy fog may reduce vsbys. Outlook /Wednesday through Saturday/...Moderate confidence. Wednesday through Saturday... Wednesday and Thursday...Moderate to high confidence. Pressure gradient should be weak enough to keep winds and seas below small craft advisory thresholds. Main concern for mariners will be for some fog, especially across our southern waters during the late night/early morning hours. Also, a few strong thunderstorms are possible across our adjacent northeast MA waters late Wed/Wed evening. Friday and Saturday...Moderate confidence. Persistent long southwest wind ahead of a cold front may result in seas building to between 4 and 7 feet across our southern waters later Fri into Sat. Some showers and fog patches also may impact mariners at times. && .TIDES/COASTAL FLOODING... Expecting about a 0.5 ft surge for the high tide tonight but astronomical tides are lower than previous nights and minimal wave action so do not expect any issues. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory for hazardous seas until 10 PM EDT this evening for ANZ254>256. && $$ SYNOPSIS...KJC/Frank NEAR TERM...KJC SHORT TERM...KJC LONG TERM...Frank AVIATION...KJC/Frank MARINE...KJC/Frank TIDES/COASTAL FLOODING... is the U.S. government's official web portal to all federal, state and local government web resources and services.