Area Forecast Discussion
Issued by NWS Boston, MA
Issued by NWS Boston, MA
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251 FXUS61 KBOX 270518 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 118 AM EDT Fri Sep 27 2024 .SYNOPSIS... Cold front brings rain this afternoon into tonight with a low chance of thunder. Drying out on Friday as high pressure builds in from the north and remains through Monday. The next chance of rain showers comes toward the middle of next week. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... 10 PM Update: Stronger line of heavy showers have formed across the south coast in response to roughly 100-250 J/kg of MUCAPE. Not expecting any thunder with this line as reflectivity values above -10C are well below 35dbz. 8 PM Update: Current surface observations show a cold front dropping southward across southern New England switching the winds north behind it. Along with it, a couple batches of showers push south and east across the region. This is a bit quicker than originally anticipated, so made some minor adjustments to the forecast to reflect this. Things will improve quicker as a result. Still can`t rule out lingering showers across the south coast and Cape early Friday morning. Highlights: * Cold front brings rain this afternoon into the first-half of the overnight. * Low risk of an isolated thunderstorm. Abundance of clouds and areas of rain continue this afternoon across the region due to a cold front and a robust mid-level northern stem shortwave. Keep the umbrella on standby if heading out this evening as showers are expected to become more numerous and cannot rule out a rumble or two of thunder. And honestly, the area with the better chance of hearing any thunder are those near the southern coast of RI and south coast of MA. There is VERY limited instability, nearly zero units of SB CAPE, but 100-200 units of MUCAPE. This area also coincides where a weak fine line could develop. Winds aloft are fairly robust, in this fine line, could see stronger wind gusts of 30 to perhaps 40 mph, sub-severe, but still notable. Otherwise, warm cloud layer is around 12,000 feet, meaning the storms are good rain makers, a few heavier downpours are possible this evening and given storm motion around 20 to 25 knots, storms are expected to be moving quickly and limits the flood threat. Lows tonight are generally in the middle 50s, could hold on to 60 degrees in urban areas like Boston, Providence, and Hartford. Given higher dewpoints overnight, patchy ground fog is possible, but not likely to become dense. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/... Highlights: * Cold front stalls south of southern New England. Generally a dry day with more in the way of sunshine north and clouds south. * Near seasonable temperatures. Today`s cold front stalls to the south of southern New England and depending how far south it reaches will dictate how much sunshine places like Hartford, Providence, and Taunton have. Current thoughts are the front is stalled south of the islands. This should keep our area fairly dry, but have left a mention of "Iso. Rain" in the grids for areas south of the Mass Pike through 18z. North of the Mass Pike have more in the way of sunshine with higher pressure building down from the north. Somewhere, a tight gradient of clouds/no clouds will develop, a shift 30-50 miles could lead to more sun all or more in the way of clouds. Feel this will be the same story heading into the overnight hours as well. Did lean on a blend for tomorrow`s temperatures, afternoon highs in the low to middle 70s. Warmest spots are in northern Massachusetts due to higher likelihood of sunshine. Nighttime lows in the 50s, with the coolest spots north, less cloud cover, and warmest south near 60F due to the higher cloud cover. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Key Points: * Dry conditions prevail through early next week * Next chance for rain arrives by mid-week Details: For the weekend, the previous upper level trough will be exited well to the east with weak ridging building in across the northeast. This will put southern New England under subsident NW flow aloft. This will support dry conditions while remnant of Helene stays to the SW. Surface high pressure positions to the northeast, bringing in onshore flow. Moisture will range around normal and with cloudy skies and breaks of sun. Temperatures range in the mid to upper 60s, with low 70s further inland in the CT River Valley. Weak upper level ridging prevails into early next week with an upper level low slowly tracking toward the northeast. Monday will likely remain dry with highs in the 60s to low 70s. Ensemble guidance is highlighting differences in the timing of this system with some members having it arriving by Tuesday and others by Wednesday. Based on ensemble means, will more likely see showers/rain chances increasing Tuesday afternoon into Wednesday. There`s a low chance for an earlier onset of showers Monday night/early Tuesday. High temperatures range in the mid 60s to near 70 in spots. Ensemble guidance shows a transition to more zonal flow aloft toward the end of the work-week next week with mainly dry conditions favored. && .AVIATION /05Z FRIDAY THROUGH TUESDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Rest of tonight...Moderate Confidence Rain continues to dissipate inland while a heavier band remains over the Cape and Islands. That band should move off shore before sunrise. Guidance is mixed on how quickly CIGS lift to VFR with some guidance hinting at radiation fog developing with all the residual moisture around from yesterdays rains. Today...High confidence. VFR with light northerly winds. Localized sea breezes develop near the coasts. Tonight...High Confidence. VFR with light and variable winds. Patchy radiation fog possible esspically in the northern CT river valley. Saturday...High Confidence VFR with east winds at 5-10 knots. BOS TAF...Moderate Confidence in TAF. VFR today with light NNW winds. Sea breeze should develop late this morning to early this afternoon. BDL TAF...Moderate Confidence in TAF. VFR today with light northerly winds Outlook /Saturday Night through Tuesday/... Saturday through Monday Night: VFR. Tuesday: VFR. Chance SHRA. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Today through Friday Night...High confidence. Showers and perhaps a rumble of thunder as a cold front moves across the waters this afternoon through the overnight hours. Rough seas and periods of stronger gusts, extended the Small Craft Advisory for the outer ocean waters through tonight, seas ease heading into Friday with improved conditions by Friday afternoon. Outlook /Saturday Night through Tuesday/... Saturday: Winds less than 25 kt. Saturday Night through Sunday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Monday through Monday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Tuesday: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 2 PM EDT this afternoon for ANZ250- 254. Small Craft Advisory until 2 AM EDT early this morning for ANZ251. Small Craft Advisory until 11 AM EDT this morning for ANZ255. Small Craft Advisory until 8 AM EDT this morning for ANZ256. && $$ SYNOPSIS...Mensch NEAR TERM...Dooley/Mensch/KP SHORT TERM...Dooley LONG TERM...Mensch AVIATION...KP MARINE...Dooley/Mensch