Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 261434 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1034 AM EDT Mon Jun 26 2017 .SYNOPSIS... Additional upper level disturbances move across New England this afternoon and Tuesday, bringing a few showers and isolated thunderstorms with the greater threat on Tuesday. A warming trend begins for the latter half of the week with a return to summer heat and humidity Friday and Saturday. A warm front may bring some showers Thursday night with more showers and thunderstorms possible Friday through the weekend. && .NEAR TERM /THROUGH TONIGHT/... Diurnal cumulus developing over Western and North Central Mass will spread across much of Southern New England this afternoon, with periods of more cloud than sun. Temperatures at 10 AM were in the lower 70s. Mixing is expected to reach above 800 mb with temps at that level supporting sfc max temps in the low 80s. That matches up with expectations based on the 10-11 AM temps. Will continue with the forecast of upper 70s and lower 80s. Winds in the mixed layer reach 15-20 knots, so gusts to 20 knots are possible. If the mixing were to reach above 750 mb, a few gusts to 25 knots would be possible. Other concern is for any afternoon convection. Stability parameters are marginal and this is mostly over Western/Central Mass. Airmass is dry. We will adjust pops a little, with chance pops in Western and Central Mass and slight chance across Nrn Connecticut and Nrn RI and some of Eastern Mass. && .SHORT TERM /TUESDAY/... Tonight... Any lingering convection will diminish in the evening, otherwise quiet night with light winds and a few clouds given moisture in the 850-700 mb layer. Lows in the 50s. Tuesday... Another robust shortwave will lift NE from the Gt lakes and move into northern New Eng late in the day. The mid level trof approaches SNE from the west with decent mid level cooling as 500 mb temps drop to near -20C in the west and -16 to -18C in the east. This will contribute to steepening mid level lapse rates and SBCAPES 500-1000 J/kg. Highest CAPES may end up near the I-95 corridor where higher dewpoints pool in the afternoon from increasing SW flow. Expect sct showers/t-storms developing around midday through the afternoon. Strengthening mid level flow from approaching trof will lead to 0-6km shear up to 50 kt so a few strong to severe storms are possible depending on the magnitude of instability. If CAPES can reach 1000 J/kg probability of severe will increase. Hail and gusty winds would be the primary threats. Temps will be a few degrees cooler than today given slight 850 mb cooling, with highs 75-80 degrees and continued comfortable humidity levels. Deep mixing and increasing low level winds will result in gusty SW winds in the afternoon, with gusts to 20-30 mph possible, especially coastal plain. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Highlights... * Pleasant Wednesday with low risk of a shower * Heat and Humidity return Friday into Sunday * Thunderstorm chances increase Thursday night through Sunday Pattern Details... 00z guidance is in general agreement synoptically with some difference in strength and timing for each wave late in the week. Upper level trough will move through the flow Tuesday night with southern New England on the backside Wednesday. Quasi-zonal flow will set-up across the region on Thursday with the flow with becoming more amplified by the weekend. Resulting in a broad trough over the Great Lakes and another trough over the mountain West with weak ridge between the two. Because the flow is becoming more amplified, sub-tropical ridge is also building closer to the region late in the weekend. Ridging out West by Sunday will push the Great Lakes trough towards the Northeast for early next week. Details... Tuesday night into Wednesday... Scattered shower and thunderstorms will linger Tuesday night as upper level trough continues to push through the area. Trough axis will be offshore by Wednesday putting southern New England in weak northwest flow. Depending on how quickly precip moves offshore, Tuesday night may be quite pleasant with temperatures in the low to mid 50s with low humidity. Mid level shortwave and assocd mid level cooling which brought the showers and t-storms to SNE last night has lifted to the NE. Weak subsidence behind this wave will maintain dry conditions through the morning. Another weak shortwave approaches from the SW this afternoon and will bring a few showers and isold t-storms, mainly interior. SBCAPES are marginal, 200-400 J/kg, and 500 mb temps are actually warming slightly today which should result in limited coverage of convection. Mainly dry in RI and SE MA as rather dry air in the mid levels along with very low KI values near the coast will likely keep any showers and t-storms to the north and west so we have dry conditions here. 850 mb temps around 10-11C will result in max temps in the upper 70s to lower 80s. Comfortable humidity levels with dewpoints down in the upper 40s and lower 50s. Surface high pressure will slide into the area on Wednesday as ridging builds a loft. Steep lapse rates with some moisture in the mid-levels will help develop diurnal CU by the afternoon. Mixing up to 750 mb will result in temperatures in the upper 70s with breezy westerly flow near 20-25 MPH. Guidance shows very little QPF on Wednesday, but cannot rule out a few pop-up showers by the late afternoon hours. While confidence is higher north of the region, southern New England will see instability values above 500 J/kg with K values above 25C. This may be enough for a spot shower. Winds aloft will begin to turn more to the southwest by Wednesday night with WAA. Overnight lows will remain around 60. Thursday... Dry day to start as high pressure will slide south of the region. The flow will turn more active with Zonal flow aloft and a few weak waves passing through. Impressive warming aloft as surface warm front pushes through the region. This will push southern New England in the warm sector resulting in increasingly warm and humid temperatures. Scattered showers and thunderstorms are anticipate by the latest guidance suggests not until the evening hours as mid-levels will remain quite dry. A weak shortwave moves through the flow Thursday evening/night. With zonal flow and both 850mb isotherms and winds becoming parallel, appears that anything the fires across upstate NY will ride through the flow moving into the area. In fact, guidance is indicating a lingering MCS will move through the flow overnight which could result in a few strong storms, esp north of the Pike. This region has the best area of instability and 0-6 km shear values. Still uncertainty on where this will set-up as it could still move north of the region, or south. Something to watch over the upcoming week. Friday into Sunday... Unsettled weather patter for this time period as southern New England remains in the warm sector with heat and humidity. With 850 mb temps near 2 STD above normal, appears that the potential for 90 degrees returns on Friday and Saturday. Back door cold front appears to remain well north of the region per latest GFS and EC. Thus have gone above guidance for Saturday temps. Heat headlines may be needed. Chance for showers and thunderstorms each day, but difficult to place the exact timing and location of any strong storms. Regardless, the potential for strong to severe weather appears possible through the period as frontal boundary lingers north of the region. One caveat to watch is the subtropical ridge. If this ridge moves closer, it may keep portions of the area dry. && .AVIATION /14Z 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/...High confidence. This afternoon... VFR. Scattered to broken cumulus with bases 5000-6000 feet away from the coast. Scattered showers and isold t-storms possible this afternoon in the interior, mainly Western and Central Mass. Gusty west to southwest winds with gusts near 20 knots. Tonight... VFR. A few lingering showers or an isold t-storm interior early, otherwise areas of mid level clouds. Tuesday... VFR with bkn cigs 5-7k ft. Sct showers and t-storms expected from midday through the afternoon which may bring briefly lower conditions. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Tuesday Night through Friday/... Wednesday...High confidence. Mainly VFR. NW gusts to 20 kts. Thursday...Moderate confidence. Mainly VFR. Afternoon showers possible in the interior with showers/t-storms possible all SNE Thu night. Gusty SW winds to 25-30 kt developing, especially coastal plain. Friday...Moderate confidence. Patchy early morning fog, with local MVFR. Then VFR, except local IFR in possible strong thunderstorms, mainly during the afternoon and evening hours. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday/...High confidence. Winds and seas mostly below SCA thresholds through the period with SW flow. A few gusts approaching 20 kt nearshore waters each afternoon but there is a risk of some 25 kt gusts over Boston Harbor and Narragansett Bay Tue afternoon. Outlook /Tuesday Night through Friday/... Wednesday...High confidence. Quiet boating weather with winds and seas below SCA. Gusts to 20 kt possible nearshore waters. Thursday...Moderate confidence. 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 over southern waters Thu night. Friday...Moderate confidence. SW winds continue, mainly 20-25 kt with building seas. Scattered thunderstorms, some with reduced visibilities and strong gusty winds. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...KJC/Dunten NEAR TERM...WTB/KJC/Dunten SHORT TERM...KJC LONG TERM...Dunten AVIATION...WTB/KJC/Dunten MARINE...WTB/KJC/Dunten is the U.S. government's official web portal to all federal, state and local government web resources and services.