Area Forecast Discussion
Issued by NWS Boston, MA

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372 FXUS61 KBOX 231814 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 212 PM EDT SAT JUL 23 2016 .SYNOPSIS...
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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.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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1030 am update... Another hot day today with highs reaching the low to mid 90s across eastern MA/CT/RI although a bit cooler along immediate south coast where sw winds expected. Some of the hi-res guidance also hinting at a weak seabreeze across the immediate coast in eastern MA. Dewpoints to mix out this afternoon and likely drop into the upper 50s to lower 60s away from the immediate south coast. Main concern for this afternoon is the potential for another round of strong to possibly severe t-storms as rather potent shortwave moves into New Eng later today. Very good mid level cooling with this shortwave as 500 mb temps drop to -12 to -14C by evening which is impressive with temps into the 90s. Mid level lapse rates expected to increase to around 6.5 C/km associated with the cooling temps aloft which will allow MLCAPES to increase to around 1000 J/kg. The instability will be tempered by the decreasing dewpoints this afternoon so do not expect MLCAPES to get much higher. Hi-res guidance suggesting showers and t-storms will develop in northern New Eng and spill south into the region after 3 pm with focus across northern and eastern MA where core of cold pool moves. Currently, 0-6km shear is around 40 kt which is more than enough to support organized severe convection. However, guidance is indicating deep layer shear decreasing from the north mid to late afternoon and may drop below 30 kt which would limit organization of storms. However, very large T/Td spread and inverted V sounding profile support gusty winds and cant rule out isolated wind damage with the stronger storms. Hail is also a concern with cooling temps aloft.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/... Thunderstorms/showers should end earlier than Friday night thanks to faster movement of the forcing shortwave. Drier air will lead to some drying during the overnight but leftover convective debris cloudiness will likely keep temps from dropping too far. Expect mins mainly in the 60s. A few spots of fog possible, especially where late day rainfall is observed. && .LONG TERM /MONDAY THROUGH SATURDAY/...
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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.
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&& .AVIATION /18Z SATURDAY THROUGH THURSDAY/...
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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 Tonight/... Today...moderate confidence. VFR through at least 18Z. Then another risk for sct TSRA possible mainly E of a line from kEEN-kORH-kWST. Some strong winds possible once again in some of these storms. Otherwise, winds mainly W-SW 10-15 kt. Tonight...High confidence. Mainly VFR after any storms/showers end through the overnight hours. KBOS TAF...Moderate confidence. Another round of thunderstorms is likely this afternoon to early evening. Some of those storms could produce strong wind gusts. Low prob of a brief seabreeze developing this afternoon but it will likely remain just to the east. KBDL TAF...High confidence of VFR prevailing. There could be some patchy fog with MVFR visibility through 12Z. 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.
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&& .MARINE...
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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 Tonight/...High confidence. Seas will continue to dissipate through the morning as winds outside of thunderstorms have already dropped to or below 20 kt. Seas will also gradually dissipate this morning allowing the remaining small craft advisories to be dropped. Otherwise, another round of showers and thunderstorms are possible over the waters this afternoon and evening which could contain localized strong wind gusts. 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.
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&& .EQUIPMENT...
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KBOX RADAR IS BACK IN SERVICE AFTER GOING DOWN FOR MAINTENANCE EARLIER THIS MORNING. HOWEVER...IT IS OPERATING IN A DEGRADED STATE. RADAR RETURNS ARE RUNNING ABOUT 10 DBZ ABOVE WHAT THEY ARE. FOR EXAMPLE...RADAR RETURNS SHOWING 70 DBZ ARE ACTUALLY ABOUT 60DBZ. KEEP THIS IN MIND WHEN EVALUATING ANY STORMS. WE APOLOGIZE FOR THE INCONVENIENCE.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...None.
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&& $$ SYNOPSIS...Doody/Frank NEAR TERM...KJC SHORT TERM...Doody LONG TERM...Frank AVIATION...KJC/Frank MARINE...Belk/Frank EQUIPMENT...Staff

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