Area Forecast Discussion
Issued by NWS Boston, MA

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204 FXUS61 KBOX 240213 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1013 PM EDT SAT JUL 23 2016 .SYNOPSIS... Hot conditions continue this afternoon/early evening with the risk of some strong to severe thunderstorms particularly in northern and eastern MA. Otherwise, excessive heat and humidity is expected at times through the middle of next week, at least away from the immediate coast. Another risk for scattered showers and thunderstorms is possible late next week with a cold front dropping south. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... 10 pm update... Outflow boundary from MCS moving S across the region well out- paced the main convection, cutting off its connection to low level vorticity and instability. This gust front is well offshore now and as such the remnant convection continues to weaken as it moves offshore as well. Otherwise, drier air already moving in and anvil CI already clearing the area leading to a relatively pleasant night. Some fog possible later, especially N and E MA where rainfall moved through this evening. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... Sunday... Shortwave ridging aloft and very dry column will bring sunshine and very warm temps, although a bit cooler than today as low level temps are cooler. Still expecting highs in the mid 80s to around 90 degrees. Best chance of 90+ in the lower CT valley but portions of RI and interior E MA will likely be near 90 degrees. Afternoon seabreezes are likely. Sunday night... Quiet night as mid level ridging in control. Weak shortwave moving over the ridge will bring some mid/high level clouds, otherwise partly cloudy. Mins mostly in the 60s with dewpoints climbing into the mid 60s toward daybreak. && .LONG TERM /MONDAY THROUGH SATURDAY/... Highlights... * Excessive heat at times through mid week at least away from the immediate coast and especially Monday * Mon/Mon night is the highest risk for scattered showers/t-storms with the threat for some severe weather and even very localized urban type flooding * Cold front may bring another risk for scattered showers/thunderstorms sometime late next week but timing uncertain Details... Upper level ridge over the southern half of the country will generate a westerly flow of air aloft and anomalously hot temperatures, especially for the first half of the week. GFS Ensembles indicate 925T between 1 and 2 standard deviations above normal for most of next week. So confidence is fairly high in above to at times much above normal temperatures. ECMWF ensembles are pretty much in agreement as well. Monday... Currently, Monday looks like it may be the worst in terms of heat and humidity. 850T near +20C should allow high temps to rise into the mid to upper 90s away from any coastal sea breezes. Surface temps may even reach 100 in a few locales if clouds do not get in the way. In addition, low level moisture may pool ahead of a pre frontal trough/cold. This may push heat index value to 100+ and decent shot will need heat advisories for portions of the region. The heat/humidity combined with frontal boundary/pre-frontal trough in the vicinity may lead to scattered showers and thunderstorms developing during Monday afternoon and night. Pretty good shot at MLCapes reaching or exceeding 1500 J/KG. 0 to 6 KM shear initially not impressive, but increase to between 25 and 35 knots during the late afternoon and especially the evening with approaching shortwave. A lot will depend on timing, but there certainly is the risk for scattered severe thunderstorms. If they are develop the primary risk would be strong to damaging straight line wind gusts. While activity may be hit and miss, will have to watch if any low level boundary washes out or becomes stationary. If this happens, there may be a very localized urban type flood threat as well with PWATS over 2 inches. Lots of uncertainty at this point, but in addition to the excessive heat/humidity potential is there for some severe weather and perhaps even a very localized flood risk later Monday into Monday night. Tuesday and Wednesday... Assuming cold front clears the region by early Tuesday morning, dry weather should prevail Tue into Wed but certainly not a guarantee this far out. High temps should still be mainly in the 90s Tue and Wed away from at least the immediate coast. Should be somewhat less humid Tue, but some more humidity may return Wed. Either way it will likely be hot away from any onshore flow. Thursday through Saturday... Above normal temps will continue over this time, but probably not quite as hot as early in the week. A frontal boundary may drop down and bring the risk for a round of two of showers/t-storms by late in the week but timing highly uncertain and by no means a washout. && .AVIATION /02Z SUNDAY THROUGH THURSDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday Night/... Tonight...High confidence. Line of convection moving through northern MA will bring strong wind gusts and brief MVFR/IFR conditions this evening, otherwise mainly VFR. Patchy late night fog possible in the normally fog prone locations. Sunday and Sunday night...High confidence. VFR. KBOS TAF...Moderate confidence. Line of storms will move over BOS 00-01z with brief gusts to 40+ kt possible and MVFR/IFR. Seabreezes likely developing by midday Sunday. KBDL TAF...High confidence. Outlook /Monday through Thursday/... Monday...Moderate confidence. Mainly VFR outside of lower conditions in scattered showers/thunderstorms mainly Monday afternoon and evening. Tuesday and Wednesday...Moderate to high confidence. Mainly VFR other than a few hours of early morning patchy fog in the typically prone locations. Thursday...Moderate confidence. Mainly VFR outside the risk for scattered showers and thunderstorms. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday Night/...High confidence. Thunderstorms with strong wind moving across the E MA waters this evening, otherwise quiet boating weather with winds and seas below SCA. Outlook /Monday through Thursday/...Moderate to high confidence. Winds and seas should generally remain below small craft advisory thresholds over this time. A period of southwest wind gusts of 20 to perhaps up to 25 knots are possible near the south coast for a few hours Monday afternoon. Otherwise...main concern is the risk for scattered thunderstorms mainly late Monday into Monday night and perhaps again on Thursday. && .EQUIPMENT... The KBOX radar is back in service but is operating in a degraded state. Radar returns are running about 10 dBZ too high. Please keep this in mind when evaluating storms. We apologize for the inconvenience. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...KJC/Frank NEAR TERM...KJC/Doody SHORT TERM...KJC LONG TERM...Frank AVIATION...KJC/Frank MARINE...KJC/Frank EQUIPMENT... is the U.S. government's official web portal to all federal, state and local government web resources and services.