Area Forecast Discussion
Issued by NWS Boston, MA
Issued by NWS Boston, MA
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698 FXUS61 KBOX 060015 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 815 PM EDT Fri Jul 5 2024 .SYNOPSIS... Warm and very humid weather expected over the next few days. Early morning showers this morning give way to brief dry weather, although scattered thunderstorms are expected to develop in the interior this afternoon. Some could produce heavy downpours. Another risk for showers and storms for Saturday. Mainly dry Sunday afternoon through early Tuesday, but more unsettled weather is on the horizon for middle of next week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... Last couple runs of the HRRR seemed to have a better grasp of the ongoing convection across southern New England this evening. Intensity was already diminishing as we approach sunset. Expecting this trend to continue late this evening. Focus for stronger thunderstorms shifting towards the immediate south coast. Also monitoring yet another round of showers and thunderstorms across northern PA and central NY state which may reach southern New England late tonight. Main concern remains heavy rainfall. So far, the stronger thunderstorms have been moving sufficiently, but will need to monitor possible training from additional rainfall. Previous Discussion... Not much change to the overall synoptic pattern tonight. Very humid air remains in place, with a frontal boundary lingering to our north. Weakly forced environment with rather poor mid level lapse rates. Latest SPC mesoanalysis showed 2,000-3,000 J/kg most-unstable CAPE values. Regional radars showed showers increasing in coverage as they moved into western southern New England late this afternoon. Still mostly concerned about downpours leading to flooding. However, given the amount of available energy, will need to monitor the storms for development. The most likely outcome is for a stronger storm to develop, then rain itself out shortly thereafter as there is not enough shear to organize these cells to separate the updraft from from the rainfall. The lack of shear also suggests these storms will most likely diminish in intensity with sunset. Although, there still could be a thunderstorm overnight, these should be more of the garden-variety type. High dew points around 70F should keep low temperatures in that same range. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... Not a lot of confidence in the details Saturday into Saturday night. Synoptic environment not really changed, except that a cold front should be closer to southern New England. Still mostly concerned about possible flooding issues, with a slightly higher chance for stronger thunderstorms due to the presence of the front. Still not likely raining the entire day, and questions remain on the impact of morning showers on the afternoon convective environment. Should at least have periods of showers Saturday afternoon into Saturday night. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Highlights: * Summer heat & humidity thru next week, with heat headlines possible Mon and Tue as heat indices of 95+ possible * Sunday: chance of morning showers/thunderstorms/coastal fog, then a drying trend likely in the afternoon northwest to southeast * Mainly dry Monday into Tue, then next chance of showers/thunderstorms late Tue into Wed * Drying trend possible late next week, but remaining warm/humid Sunday... Short wave trough moving across the St Lawrence River Valley Sunday morning will traverse east and shift the axis of the tropical PWAT plume currently over New England to the south coast and then eventually offshore. Thus, highest chance for showers/thunderstorms along with areas of fog will be in the morning over RI and southeast MA, then sliding offshore in the afternoon. Hence, drying trends for the afternoon northwest to southeast. Remaining very warm and humid, with highs 85-90, cooler along the south coast. Dew pts in the upper 60s and lower 70s. Winds SW 5-10 mph, 10-15 mph across southeast MA. Monday/Tuesday... In the wake of the departing northern stream short wave Sunday, the east coast subtropical ridge reinserts itself with height rises and 591 dam contour traversing SNE. Hence, steamy with 925 mb temps rising to +24C to +25C, warmest across northern MA. These temps combined with SW surface winds will yield highs in the upper 80s and lower 90s, with Monday likely the hotter of the two days. Some relief along the south coast and islands, with highs in the upper 70s to mid 80s. Mainly dry weather prevails. Chance of late day showers/storms western MA/CT Tuesday, pending the speed/arrival time of next upstream trough. Remaining humid both days with dew pts in the upper 60s and lower 70s. We may need heat headlines as heat indices Mon and Tue could reach the mid to upper 90s back to back days. Wed/Thu... Chance of showers/storms as upstream trough approaches. However, ensembles suggest trough deamplifies as it approaches SNE, in response to east coast subtropical ridge remaining robust. Hence, highest pops for showers/storms will be across northwest MA, lowest over southeast MA. Given cloud cover and risk of showers/storms, not quite as hot, with highs in the 80s. But remaining summery with dew pts in the upper 60s and lower 70s. Friday... Ensembles suggest mean trough axis beginning to move east of New England, followed by rising heights. Thus, a drying trend possible and remaining warm and humid, highs in the 80s and dew pts again in the upper 60s to lower 70s. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Tonight: Moderate confidence overall, but low on timing and location. Any TSRA for central/western airports to weaken through 02z. Dry weather should prevail for several hours, but we could see another round of SHRA/TSRA for these same areas late tonight. Deterioration toward a widespread IFR-LIFR, but timing uncertain. Light S winds. Saturday and Saturday Night: Moderate confidence overall, but low on timing. IFR-LIFR generally improves to SCT-BKN VFR, but seems to be a better chance at TSRA on Sat, especially ORH-PVD north and west. Timing of TSRA uncertain and subject to adjustment. SW winds 4-8 kt. KBOS TAF...Low confidence. IFR-MVFR CIGs likely to continue. Additional showers and thunderstorms are possible, but have low confidence in them reaching the terminal, and their timing. CIGs remain IFR to LIFR overnight into Saturday morning. KBDL TAF...Low confidence. IFR-MVFR CIGS likely to continue. Additional showers and thunderstorms are possible, but have low confidence in their timing reaching the terminal. CIGs remain IFR to LIFR overnight into Saturday morning. Outlook /Sunday through Wednesday/... Sunday: VFR. Slight chance SHRA. Sunday Night through Monday Night: VFR. Tuesday: VFR. Slight chance SHRA, isolated TSRA. Tuesday Night: Mainly VFR, with local MVFR possible. Chance SHRA, isolated TSRA. Wednesday: Mainly VFR, with local MVFR possible. Breezy. Chance SHRA, isolated TSRA. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Through Saturday Night: Moderate Confidence. Persistent S to SW flow with winds around 10-15 kt through the period, and seas could get near 5-ft thresholds given the long SWly fetch. Marginal Small Craft Advisories posted for the southern coastal waters. Greater risk for showers and thunderstorms reducing visibility over the southern waters Saturday, but widespread storms not expected. Outlook /Sunday through Wednesday/... Sunday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers, isolated thunderstorms. Sunday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Monday through Tuesday: Winds less than 25 kt. Tuesday Night: Winds less than 25 kt. Slight chance of rain showers. Wednesday: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers, isolated thunderstorms. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 11 AM to 10 PM EDT Saturday for ANZ235. Small Craft Advisory from 2 PM to 6 PM EDT Saturday for ANZ237. Small Craft Advisory from 2 PM to 10 PM EDT Saturday for ANZ254. Small Craft Advisory from 9 AM Saturday to 8 AM EDT Sunday for ANZ255. Small Craft Advisory from 2 AM Saturday to 8 AM EDT Sunday for ANZ256. && $$ SYNOPSIS...Belk/Nocera NEAR TERM...Belk SHORT TERM...Belk LONG TERM...Nocera AVIATION...Nocera MARINE...Belk/Nocera