Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 231807 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 207 PM EDT SAT JUL 23 2016 .SYNOPSIS... Hot conditions continue today, along with another risk for thunderstorms this afternoon, some of which may become severe. An approaching cold front will bring another round of scattered showers and thunderstorms from Monday into early Tuesday. More warm weather follows midweek. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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2 PM update... Scattered showers and t-storms developing to the north and west of SNE this afternoon where deeper moisture and higher KI values are present. MLCAPES generally around 500 J/kg, limited by lower dewpoints which have dropped into the 50s. 0-6km shear around 40 kt, but lower shear values present to the north. Mid level cold pool near the Canadian border will drop south across SNE later this afternoon with increasing mid level lapse rates. Expect sct showers/t-storms to move into SNE as shortwave approaches with increasing synoptic forcing. MLCAPES expected to peak around 500-1000 J/kg and not likely much higher due to lower dewpoints while deep layer shear will decrease from the north mid to late afternoon. This will limit organization and areal coverage of convection but there are still some concerns. Specifically the very dry air in the low levels with pronounced inverted V profile supports strong gusty winds with any storms. Downdraft CAPES up to 1200 J/kg which is impressive. Seabreeze boundary moving into eastern MA could become a focus later on. Previous discussion... 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 /SUNDAY THROUGH FRIDAY/... Overview... Not much change from the previous model cycle. High pressure covers much of the southern USA for most of next week. This will mean any fronts will struggle to get very far south of our region next week. Mid level flow transitions to a near zonal flow by early next week, then to a broad trough by mid week. Temperatures should generally be above seasonable levels most of this portion of the forecast. Details... Sunday... High pressure in place through the day. Winds appear to be light enough where seabreezes may develop along both coasts. Moderate confidence in seabreezes. Above normal temperatures continue for most of southern New England. Monday... A mid level shortwave moves across our region late Monday into Monday night. Most of the day should be rain-free. Some signs of marginal instability crossing during the morning, which may be a warm front with a couple of light showers. Greater instability moves in from the west during the afternoon and evening, in the warm sector ahead of a cold front. Precipitable water values remain high, so locally heavy rainfall is still possible in stronger thunderstorms. Scattered showers and thunderstorms should continue into Monday night as a cold front passes by. Tuesday and Wednesday... High pressure takes control and brings fair weather. Above normal temperatures continue. Thursday and Friday... Latest operational guidance continues to indicate some potential for showers, largely due to a stalled front to our south, and another cold front approaching from the north. Still have low confidence in the details. Will continue to mention a chance of showers and thunderstorms due to the presence of these boundaries. && .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/... Through 00z...Mainly VFR, but widely sct showers/t-storms developing will result in briefly lower conditions, mainly north of a KBAF-KTAN line. Some strong winds possible in some of these storms. Otherwise, mainly NW winds 10-20 kt with a few higher gusts CT valley and higher terrain. Tonight...High confidence. Mainly VFR. Patchy late night fog possible in the normally fog prone locations. Sunday and Sunday night...High confidence. VFR. KBOS TAF...Moderate confidence. A brief t-storm is possible 4-7 pm. Some of those storms could produce strong wind gusts. Seabreeze just east of BOS may briefly move onshore shifting winds. KBDL TAF...High confidence. Outlook /Sunday night through Wednesday/... Monday...Moderate confidence. Mostly VFR. Possible IFR in early morning fog. Brief MVFR/IFR cigs/vsbys in afternoon and early night showers/thunderstorms. Tuesday and Wednesday...High confidence VFR.
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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 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 /Sunday through Wednesday/...Moderate confidence. Winds less than 20 knots and seas less than 5 feet through this period. A cold front will bring scattered showers/thunderstorms Monday afternoon and night, with potential for strong wind gusts and brief poor vsbys in heavy downpours. && .EQUIPMENT...
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The KBOX radar is back in service but is operating in a degraded state. Radar returns are running about 10 dBZ too high. .
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 2 PM EDT this afternoon for ANZ255- 256. && $$ SYNOPSIS...Belk/Doody NEAR TERM...KJC SHORT TERM...Doody LONG TERM...Belk AVIATION...Belk/KJC MARINE...Belk/Doody EQUIPMENT...

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