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Area Forecast Discussion
Issued by NWS Boston, MA
Issued by NWS Boston, MA
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026 FXUS61 KBOX 060603 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 203 AM EDT Sat Jul 6 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 THIS MORNING/... 1000 PM Update: Most persistent area of thunderstorms current are coming off southeast Litchfield County CT into far southern Hartford Counties in CT and adjacent portions of southern CT. Radar all- tilts and cross-sectional reflectivity trends continue to indicate these storms are still capable of producing frequent lightning but otherwise the main risk with these is from torrential downpours. Fortunately they are moving along at a fair clip; they should still be capable of lightning and downpours as they move into southern Tolland and southern Windham Counties but general weakening trends are expected as they`re moving into a more stable air mass. Further north into western/north-central MA, earlier line of storms in has really fallen apart over the last hour and that should also continue. It`s a quite humid night and it won`t take much to pop a shower at any time but drier weather should then prevail for most of the night. Early look- ahead at pre- dawn/early Sat indicates another round of storms is possible, as activity over central PA and southern NY moves ENE, but this isn`t well agreed upon. Will continue to monitor these trends with incoming guidance. Otherwise, much of the area is blanketed in stratus and expect that to continue to expand north and west over the next few hours of the night. A very warm and muggy night given dewpoints are in the low to mid 70s, and temps are already close to those values. Lows should also range in the low to mid 70s. 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 THIS MORNING THROUGH 6 PM SUNDAY/... 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 NIGHT 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 /06Z SATURDAY THROUGH WEDNESDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 06Z TAF Update: Through 12z Saturday: Moderate confidence. MVFR-IFR due to stratus, with not much categorical change. Wouldn`t rule out 3-6 SM BR at times but shouldn`t be persistent. Best chance for showers thru 09z Sat at PVD, FMH and HYA. SW winds around 10-15 kt with gusts 20-23 kt for the Cape and Islands, with lighter SW winds (5-10 kt) elsewhere. Today: Moderate confidence overall, low on timing and areal coverage of SHRA/TS. Somewhat stronger confidence in ceiling trends, with MVFR-IFR ceilings being more persistent/stubborn to improve in RI and southeastern MA today. Elsewhere, MVFR-IFR to start but offering one-category improvement to BKN VFR/MVFR north and west after 14z. SW winds around 10-15 kt today. On SHRA/TS...given available guidance, confidence in timing and coverage of showers and thunderstorms and their evolution today is poor. Message is that SHRA/TS are expected today, more so than currently reflected in the TAFs, but really couldn`t get specific given this low confidence. Proactive use of TEMPOs will be needed today to highlight more specific timing. In general, airports to the north and west have a somewhat better chance at seeing SHRA/TS and less so for PVD and the Cape airports, but they can`t be ruled out anywhere and virtually at any time. Tonight: Moderate confidence overall, low on timing of SHRA/TS. Sub-VFR likely thru midnight for most airports, as weak frontal boundary sags SE toward the coastal waters. SHRA/TS likely to be ongoing somewhere in the airspace, with trend being for a gradual SE shift towards the south coast. Should see gradual improvement in flight categories from NW to SE, but sub-VFR likely to continue into early Sun AM for the south coast. Winds continue SW around 5-10 kt, though will turn WSW late. Sunday: High confidence. Improvement to VFR expected on Sunday for most, but can`t rule out periodic SHRA and sub-VFR at ACK (more so in the morning) as frontal boundary stalls. WSW winds 5-10 kt. KBOS TAF...Moderate confidence overall, low confidence on SHRA/TS timing and coverage. MVFR to begin, with some scattering/lifting of cloud bases into VFR/MVFR range late this morning. SHRA/TS possible virtually anytime today, and will need TEMPOs to provide more specifics as current fcst confidence on those aviation parameters are low. Better chance tonight as boundary sags southward. SW winds around 10 kt. KBDL TAF...Moderate confidence overall, low confidence on SHRA/TS timing. IFR ceilings to start, but should see improvement toward VFR-MVFR range. Better chances for SHRA/TS here today, but the timing is uncertain and could occur virtually anytime. Will need TEMPOs to provide more specific timing. S winds around 10 kt, shifting to WSW late tonight. Outlook /Sunday Night 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 Night 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 this morning to 10 PM EDT this evening for ANZ235. Small Craft Advisory from 2 PM this afternoon to 6 PM EDT this evening for ANZ237. Small Craft Advisory from 2 PM this afternoon to 10 PM EDT this evening for ANZ254. Small Craft Advisory from 9 AM this morning to 8 AM EDT Sunday for ANZ255. Small Craft Advisory until 8 AM EDT Sunday for ANZ256. && $$ SYNOPSIS...Belk/Nocera NEAR TERM...Belk/Loconto SHORT TERM...Belk LONG TERM...Nocera AVIATION...Loconto/Dooley MARINE...Loconto/Dooley