Area Forecast Discussion
Issued by NWS Boston, MA
Issued by NWS Boston, MA
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920 FXUS61 KBOX 261446 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 1046 AM EDT Thu Sep 26 2024 .SYNOPSIS... An approaching frontal system will bring showers with moderate-heavy downpours and a few embedded thunderstorms today into this evening. High pressure builds back in Friday through Monday and will bring dry and very pleasant weather. The next chance of rain showers comes toward the middle of next week. && .NEAR TERM /THROUGH TONIGHT/... Update: 10:45AM Bit of a gloomy Thursday with an abundance of clouds and areas of rain, which is concentrated across Connecticut, though spotty showers are moving into central Massachusetts. Will continue to see this trend into this afternoon before more widespread rain and perhaps a few rumbles of thunder late afternoon into the evening hours. Overall the forecast is on track, did update the POPs to reflect the latest radar trends. Previous forecast discussion: A robust northern stream trough exits the Great Lakes today, bringing several slugs of showers and possibly a rumble of thunder. With deep southwest flow aloft and southerly winds at the surface, PWATS increase up to 1.8 inches. Light to moderate rain initially expands from west to east this morning. Later in the afternoon to evening, forcing increases as the base of the northern stream trough swings through New York while a 125-knot jet streak moves over SNE. A cold front then moves through SNE late Thursday afternoon to early evening, bringing a fine line of moderate to heavy showers from NW to SE. There could be a rumble or two of thunder with the fine line, but not expecting severe weather with only 100-300 J/kg of elevated instability and less than favorable low and mid-level lapse rates less then 5C/km. With warm cloud depths around 11kft, the main threat along the fine line will be a brief period of heavy rain. The fine line will move quickly across the region, limiting the flash flood threat. The fine line moves offshore around late Thursday evening, with drying conditions overnight. When its all said and done, the highest QPF totals look north of the MA pike, with a 50 to 70% chance of one inch and a 10 to 20% chance for two inches per the HREF. The chances for one inch decrease to 20-40% south of the MA pike, but a widespread quarter to half an inch looks likely. Temperatures today warm into the upper 60s to low 70s with warm air advection. Dewpoints will also rise today into the mid to upper 60s. Winds turn NW behind the cold front, but overnight temps stay milder in the upper 50s to low 60s. && .SHORT TERM /FRIDAY/... Northern stream trough moves off to the NE Friday with rising heights behind. Guidance has trended Friday cloudier with mid-level moisture streaming north from an upper level cut off over the SE U.S. With a little bit of mid-level convergence and some shortwave energy, there could be some light sprinkles or drizzle south of the MA pike. Temperatures on Friday warm in the low to mid-70s but could end up underachieving with more clouds than the sun. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Highlights... * Dry & very pleasant weather through early next week * Next chance of rain showers comes Tue or Wed. Details... A quiet and dry stretch of weather returns for the weekend into at least the first first part of next week thanks to a building mid level ridge and surface high pressure ridge centered over southern Quebec. Subsidence should keep any precipitation chances at bay as the high keeps remnants of Helene from moving into the northeast. There`s no real change of airmass in the mid levels going into the weekend but the placement of high pressure to our northeast and the low to our southwest will direct cooler onshore surface air into southern New England once again. This means the weekend is a bit cooler than Friday, especially along the east coast where highs will remain in the mid to upper 60s. Further inland low to mid 70s are possible. Next week high pressure remains in control on Monday but some uncertainty is introduced by Tuesday with our next disturbance; a trailing frontal system approaches from the west as well as potential for a glancing blow from a coastal low to the south. Still lots of timing and placement details to work out but rain chances will increase later Tuesday into Wednesday. Ensembles indicate a 50- 60% chance of rain by Wednesday. Temperatures continue to be seasonable with highs in the upper 60s/low 70s and lows in the 50s. && .AVIATION /15Z THURSDAY THROUGH MONDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Today...Moderate confidence VFR/MVFR CIGS to start today, but become low end MVFR/IFR as light to moderate rain spreads west to east this morning. A fine line of moderate to heavy rain and IFR/LIFR conditions moves quickly west to east across region in the late afternoon through the evening. There could be some embedded thunder in this fine line, so included prob30s for the interior terminals for TSRA, even though lightning wont be frequent. Thursday Night...Moderate Confidence The fine line should clear the Cape and Islands around 06z, then rapid clearing to VFR conditions is likely. There could be some patchy ground fog overnight, but with winds turning NW, Fog shouldn`t become dense or widespread. Friday... High Confidence VFR with light northerly winds. Localized sea breezes develop near the coasts. BOS TAF...Moderate Confidence in TAF. CIGS drop down to MVFR later this morning as light rain moves in. A fine line will bring a brief period of moderate to heavy rain and IFR/LIFR CIGS late in the afternoon to early evening. There could be a rumble or two of thunder with the passage of the fine line so opted to keep the prob30 for TSRA despite confidence in frequent lightning is low. BDL TAF...Moderate Confidence in TAF. MVFR today with light rain moving in early this morning. A fine line will bring a period of moderate to heavy rain and IFR/LIFR CIGS this afternoon. There may be a rumble to two of thunder in the afternoon. Outlook /Friday Night through Monday/... VFR. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Today through Friday...High Confidence. Small Craft Advisories remain in effect for the outer waters, with wave heights still around 5-6 feet. With winds finally turning southerly today through Friday, seas begin to diminish below 5ft Friday. Outlook /Friday Night through Monday/... Friday Night through Saturday: Winds less than 25 kt. Saturday Night through Sunday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Monday: Winds less than 25 kt. Areas of seas approaching 5 ft. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...High Surf Advisory until 8 PM EDT this evening for MAZ007-019- 022-024. RI...None. MARINE...Small Craft Advisory until 8 AM EDT Friday for ANZ250-254-255. Small Craft Advisory until 2 AM EDT Friday for ANZ251. Small Craft Advisory until 8 PM EDT this evening for ANZ256. && $$ SYNOPSIS...BW/KP NEAR TERM...Dooley/KP SHORT TERM...KP LONG TERM...BW AVIATION...BW/KP MARINE...BW/KP