Area Forecast Discussion
Issued by NWS Boston, MA

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830 FXUS61 KBOX 231733 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 133 PM EDT MON MAY 23 2016 .SYNOPSIS... An area of low pressure will wobble north along the coast later today into this evening and through Tuesday bringing with it showers and the chance of thunderstorms. Warmer weather follows beginning Wednesday. A weak front will move south of the region Wednesday night with dry, warm weather for Thursday. The front will move north toward southern New England as a warm front on Friday bringing scattered showers and thunderstorms. The front will continue to drift slowly north over the Memorial Day weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 130 pm update... Cumulus emerging especially along the ridges of high terrain as the boundary layer becomes well-mixed with diurnal heating. Per mesoanalysis, an environment is evolving primed for shower and possible thunderstorm activity especially to the N and W. Deeper cumulus developing where the convective temperature of 76 degrees is being exceeded in a region of steep lapse rates up to H7 beneath decent mid-level lift with SW-NE stretched vortex energy inverted from the Mid-Atlantic low. Subsequent surface convergent reflection noted within the local observations. Marginal instability and weak shear, any thunderstorm activity should be non-severe with the main threats being lightning and heavy rain. Thinking most of this activity will be W of our region but can not rule out some of it occurring over the CT River Valley where highs will reach the 80 degree mark. Otherwise, the previous discussion below is still valid... Cutoff mid to upper level low spins across the Mid-Atlantic this morning with its surface reflection just E off the coast. A fair amount of convective energy associated that will bear watching as the low undergoes its mature to dying phase as it begins to stack and ingests drier air during its wobble N. Have this energy getting in closer to evening, but not absolutely sure. A decent amount of variance between the near-term high-res solutions lends to lower confidence with respect to specific outcomes going into evening. There is some decent low level convergent flow into S New England although not impressive. What is more significant is the attendant mid level vortex lobe pushing into our region towards evening. It is likely along the leading edge we`ll see a band of showers sweeping W/NW with some decent venting aloft albeit weak. But it is enough to warrant the likely PoPs going into tonight. Will leave it at that. It does appear E/SE portions of New England will remain dry today, mild initially but turning cooler much like yesterday with increasing clouds and onshore NE flow. Highs topping into the mid 70s with 60s along the immediate coasts, across the Cape and Islands. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... Tonight... Instability moving up from E PA may reach W CT this evening and bring a few showers. The more significant feature will be low pressure surface and aloft that will move north toward New England. This feature will bring colder temps aloft over our area, supporting greater instability. Upper jet moving around the low will be just east of MA with the lift-supporting left exit region over RI and eastern MA. For both reasons, expect showers moving up from the south tonight with sufficient instability for a couple of thunderstorms too. Will use likely PoPs, but on the lower side of this range. Clouds and the northeast flow off the water point to min sfc temps near the dew point, in the lower 50s. Tuesday... Core of the upper low moves over RI and Eastern MA. Similarity among the models gives some confidence to this positioning. Core of the cold pool aloft also moves over our area, so instability will linger through the day. Concern remains for the chance of a couple of thunderstorms due to the unstable airmass. We will mention slight chance of thunder. POPs will be at high-end chance or low-end likely much of the day. Tuesday will be much cloudier than today so more limited mixing, probably to 925 mb or 900 mb. Temps at these levels would support max surface temps in the 60s. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Highlights... * Significantly warmer Wednesday and Thursday * Cooler on Friday with Scattered showers and thunderstorms * Warm for Memorial Day weekend with a few showers/thunderstorms Overview and Model Preferences... At upper levels...a persistent upper low moves northeast over the Canadian Maritimes by late Wednesday afternoon. A strong upper level ridge of high pressure will develop from the mid-Atlantic coast to New England late in the week and next weekend. At the surface...a weak front will slip south of the region Wed night bringing a wind shift to the north and drier air for Thu. That front will strengthen and move northward as a warm front by Fri...bringing increasing chances of showers and thunderstorms and cooler weather. The front will slowly edge northward next weekend allowing summerlike temperatures to return for the Memorial Day weekend but with a few showers and thunderstorms possible each day. Tuesday night... As the upper low finally moves northeast away from the region, any lingering light showers will end in the evening and skies will clear out after midnight. Lows mainly 50-55. Wednesday... Brief ridge of high pressure to our south takes over, leading to westerly downslope air flow, drier conditions, and more summer- like temperatures away from the coast...mainly 80 to 85.There could be seabreezes, but it appears the synoptic flow could be just strong enough to prevent lower temperatures along parts of the MA east coast. Cape Cod and the islands, as well as Cape Ann, however, will likely remain as cool as the south coast of New England, where southwest winds should prevail...upper 60s to mid 70s there. Wednesday night and Thursday... Weak low pressure passes by to our northeast Wed evening and an associated weak front will move across our region. The front will usher in very dry air aloft and light west winds will turn northerly. With a good deal of sunshine on Thu, high temperatures will again reach the 80 to 85 degree mark over the interior. But there will be a better chance of sea breezes along the entire east and southeast coastline, with temperatures only reaching mid 60s to mid 70s at the immediate coast. Thursday night and Friday... The front that moved through Wed night will strengthen to our south and begin to head northward Thu night. Winds will turn to the east and southeast, bringing an increase in moisture and a chance of showers and isolated thunderstorms later Thu night. Friday now looks like a much cooler day than earlier anticipated, with a warm front in our vicinity and a continuation of E to SE flow. It will be on the cloudy side with a chance of showers and thunderstorms, especially in western sections. Highs only in the 70s...cooler at the immediate coast. Saturday and Sunday... This far out...there is still a fair amount of uncertainty. However, it looks like the warm front will drift slowly northward on Saturday and be completely north of the region on Sunday. The Memorial Day weekend should feature a return of summer-like temperatures with highs in the mid 80s. Upper 80s are possible in the Connecticut River valley on Sunday. There is a possibility of scattered diurnally-driven afternoon and evening showers or thunderstorms, but most of the time it should be dry. && .AVIATION /17Z MONDAY THROUGH FRIDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday Night/... 18z update... Today...High Confidence. Mostly VFR. SHRA/TSRA potential over CT Valley terminals into this afternoon and towards evening to which could produce TEMPO MVFR/IFR. E/NE winds with gusts up around 15 kts. Tonight...Moderate Confidence. Specificity difficult to nail down. Will prevail VCSH with uncertainty while -RA with confidence. Anticipate scattered SHRA with chance TSRA with greater confidence of impact over W terminals. With respect to cigs and vsbys, confident widespread MVFR/IFR impacts with fog and mist especially over E/SE terminals. NE winds with gusts upward of 15 kts. Tuesday...Moderate Confidence. SHRA and chance TSRA continue with greatest confidence over W terminals. Widespread MVFR/IFR impacts begin to shift E with the usherance of winds backing out of the W/NW. Gusts of around 15 kts possible. Tuesday Night...Moderate confidence. Continued clearing trend W to E with W/NW winds. Improving to VFR. It is perhaps at the start of the period that MVFR/IFR will only linger along the E coast of MA. KBOS TAF...Wet weather likely to be either approaching or in the area during TAF periods of VCSH. -RA prevailed where there was greater confidence of rain impacting the terminal. -RA could become more widely scattered into Tuesday with much of the activity focused W. Can not rule out SCT-BKN cigs and TEMPO VFR before conditions clear out Tuesday evening. KBDL TAF...Confident the terminal will see a fair share of -RA beginning around midnight and continuing through much of Tuesday before clearing out late. There is the possibility of TSRA, in the vicinity to the N/W this afternoon, and again overnight. With the anticipated isolated nature, opted not to prevail TSRA. TAF will be amended accordingly should confidence increase and conditions warrant. Outlook /Tuesday Night through Friday/... Tuesday night... Moderate confidence. Any lingering MVFR improving to VFR after midnight. Could be isolated IFR in patchy fog late. Wednesday through Thursday...High Confidence. VFR. Thursday night and Friday... Low to Moderate Confidence. Mainly VFR early Thu night...becoming MVFR with areas of IFR in showers and possible fog patches. Isolated thunderstorms late Thu night. Mainly MVFR throughout the region on Fri with scattered showers and thunderstorms. Isolated IFR possible in heavier showers or in patchy fog mainly near the coast. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 130 pm major changes. Today...Moderate Confidence. Low pressure moves up the coast from Virginia and the Carolinas. Most of the day will be fair with North winds turning from the Northeast. Speeds will be 15 knots or less. Lingering 5 to 7 foot seas will slowly subside through the day. Small craft advisory for hazardous seas is in effect, mostly for the outer waters, through the day. Tonight and Tuesday...Moderate Confidence. Coastal low pressure moves across the waters. This will bring showers and widely scattered thunder with lower visibility in showers and fog. Winds will remain 15 knots or less, and seas will mostly be less than 5 feet. A few 5 foot readings could show up on the southern outer waters Tuesday. Outlook /Tuesday Night through Friday/... Tuesday night into early Wednesday... Moderate Confidence. A small craft advisory may be needed for seas of 5 to 6 feet over the southeastern outer waters Tue night...subsiding to below 5 feet by Wed afternoon. Otherwise...light southwesterly winds. Wednesday night and Thursday... Moderate confidence. Light winds from the southwest will shift to the northwest Wed night and to the northeast to east on Thu. Seas mainly well below small craft criteria...but could reach 5 feet over the waters southeast of Nantucket late Thu afternoon. Thursday night and Friday... Moderate confidence. Southeast winds on the order of 10-15 kt and seas 1 to 3 feet. Just a slight chance of showers or a thunderstorm. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory for hazardous seas until 11 PM EDT this evening for ANZ250-254-255. && $$ SYNOPSIS...WTB/GAF NEAR TERM...Sipprell SHORT TERM...WTB LONG TERM...GAF AVIATION...Sipprell/GAF MARINE...WTB/GAF is the U.S. government's official web portal to all federal, state and local government web resources and services.