Area Forecast Discussion
Issued by NWS Boston, MA

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505 FXUS61 KBOX 281746 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 146 PM EDT Wed Jun 28 2017 .SYNOPSIS... Other than an isolated shower or thunderstorm across northern Massachusetts this afternoon, high pressure south of New England will provide mainly dry weather along with temperatures slightly cooler than normal. Thursday will be our transition day as a warm front moves across the area with the risk of showers and thunderstorms Thu night. Summer heat and humidity arrives Fri and continues into the weekend. A cold front likely breaks the heat and humidity later Sunday and will be accompanied by thunderstorms. Not as warm or humid early next week including the fourth of July holiday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 945 AM update... Current forecast on track. Expect sct-bkn cu developing with core of cold pool overhead. Still can`t rule out an isold shower/t-storm across northern MA this afternoon given marginal instability and KI increasing to near 30 along with approaching left exit region of upper jet. Previous Discussion... The morning hours will feature plenty of sunshine and temps rising from the 50s into the 60s. However scattered to broken CU/SCU clouds will develop this afternoon given the cyclonic flow and cold temps aloft (-20C at 500 mb). However with mean trough axis offshore column becomes fairly dry. This will limit any potential shower/T-storm to isolated areal coverage. Thus expecting mainly a dry day ahead. However can/t rule out an isolated shower or thunderstorm across northern MA given proximity to cold pool aloft and higher terrain of Worcester county. In addition LFQ of upper level jet streak tracks from NY state into northern MA. This will enhance forcing for ascent. Again, any shower/T-storm development will hinge on available moisture, which appears limited and will confine areal coverage to isolated. Otherwise expecting a mainly dry weather with comfortable temperatures of 75-80 and dew pts falling into the 40s in response to deepening blyr up to 750 mb. These high temperatures will average a few degs cooler than normal. More of a Sep airmass than late June. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... Tonight... Rising heights and mid level flow transitioning to anticyclonic will provide dry weather. High pressure south of New England results in light west winds. This combined with mostly clear skies and a dry airmass will yield another cool night with lows in the 50s. Thus have based mins on the cooler MOS temps. Thursday... This will be our transition day as a warm front lifts across central New England. Not expecting much if any rain here in southern New England, mainly just an increase in clouds with the greatest risk of any light rain focused across northern MA. Increasing pressure gradient will result in SSW winds increasing especially across RI and eastern MA later in the day. Highs will climb into the upper 70s and low 80s. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Highlights... * Hot and humid conditions return Friday into Sunday * Increasing risk for scatter showers/thunder Thursday PM into Sunday * Cooler and less humid Monday and Tuesday Pattern Details... Overall the deterministic models and their ensemble means have a fair handing on the evolution of the synoptic pattern for the period. However, there still remains the timing and strength difference with each shortwave. Beginning on Friday, quasi-zonal flow aloft as a surface warm front pushes through the region. The upper level pattern become more amplified as noted the previous days. This will result in a deeper trough over the northern Plains, and thus a building of the sub-tropical ridge over the East Coast. This ridge stalls an approaching cold front for the weekend before pushing through on Sunday. Pattern change aloft for early next week as the region is more in the broad trough keeping heat and humidity at bay. Overall, trended towards a blend in the guidance unless otherwise noted below. Details... Thursday night... Warm front will be north of the region by Thursday night. Any convection that does develop will ride along the mid-level flow which is parallel with the front. Higher theta-e will pool into the region as 925mb LLJ begins to develop/increase. While there is some slight height rises overnight, LLJ may provide enough lift within the warm sector will help trigger showers or thunderstorms. Current guidance is indicating the bulk of the action will remain north of southern New England. However, with increasing moisture transport in the mid-levels combined with higher K, 30-40 kts of bulk shear and lapse rates near 6C/km, cannot rule out new convection refiring along the southern edge of this system. Best location to see any precip will be north of the Pike, esp north of route 2. Aside from precip chances, increasing cloud cover and dewpoints will limit cooling during the overnight hours. Low temps will remain in the mid to upper 60s. Friday into Sunday... Heat and humidity will filter into the southern New England during this time period. Depending on how Thursday PM goes, it may have impacts to the convection potential on Friday. Surface high pressure well offshore will put southern New England in southwest flow resulting in increasing low level moisture. Plenty of heating with CAPE values over 1000 j/kg with some deep layer moisture per K values. Appear scattered showers and thunderstorms are likely especially across the western half of the region. However the potential is limited as mid-level heights rising through the day. This will limit storms from becoming widespread. Building subtropical ridge will keep the first half of Saturday dry. Southwest flow will continue across the region as PWAT values near 2 STD above normal. LLJ will begin to strengthen as Great Lakes trough begins to approach the region. Surface trough will move through upstate NY towards southern New England later in the day. This trough may be a trigger for a few strong storms. One issue is the 850 mb temps which will be near 17C. This could be a potential cap which could keep most of the area. Something to watch over the next few days. Subtropical ridge will push eastward by Sunday as cold front approaches from the west. Plenty of instability to work with as shear values increase to 30-40 kts. Anticipate scattered showers and thunderstorms, with the potential for a few strong storms. Still timing issues with the frontal passage so confidence is low. Temperatures in this period will be quiet warm compared to the past week. Expect high temps on Friday and Saturday in the upper 80s to low 90s. Cooling temps aloft on Sunday will keep high temps in the mid 80s. Sultry dewpoints reaching near 70F could result in heat headlines on Saturday. Monday into Tuesday... Upper level trough will move over the northeast by early next week. This will limit the heat and humidity. Current guidance shows seasonable temps with highs in the low to mid 80s. Northwest flow takes hold bringing in drier air in the mid-levels. Cannot rule out an isolated shower but appears that the overall period may be dry. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
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Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday night/...High confidence. Through 00z...VFR with sct-bkn cigs 050-070. Low risk for an isold shower or t-storm across northern MA. Tonight...VFR. Light winds. Thursday...VFR. Low risk for a few afternoon showers north of the Mass Pike. Increasing SW winds with gusts to 20-30 kt developing, strongest in the coastal plain. Thursday night...Mainly VFR. But a few showers/t-storms expected to move through with brief lower conditions. Gusty SW winds coastal plain in the evening. KBOS Terminal...High confidence. KBDL Terminal...High confidence. Outlook /Friday through Sunday/... Friday into Sunday...Moderate confidence. Patchy early morning fog each day. Otherwise mainly VFR, except local IFR in possible strong thunderstorms, mainly during the afternoon and evening hours through the period. Southwest winds through the period with gusts near 20 kts.
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&& .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday/...High confidence. Today... Light WNW winds this morning increasing to 15-20 kt this afternoon, strongest winds near shore. Good vsby and dry weather. Tonight... High pressure south of New England yields light WNW winds along with dry weather and good vsby. Thursday... Warm front lifts across central New England. This results in winds becoming SSW and may increase up to 25 kt late in the day across the near shore waters of RI and southeast MA. May need a Small Craft Advisory. Outlook /Thursday Night through Sunday/... Thursday night into Friday...Small craft advisories will likely be needed. Increasing SW winds with gusts to 25+ kt likely, especially over nearshore waters. Building seas may reach 6 to 8 ft. Saturday into Sunday...SW winds continue, mainly 20 kts with lingering seas. Scattered thunderstorms, some with reduced visibilities and strong gusty winds especially on Sunday. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Nocera/Dunten NEAR TERM...KJC/Nocera SHORT TERM...Nocera LONG TERM...Dunten AVIATION...KJC/Dunten MARINE...Nocera/Dunten

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