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Area Forecast Discussion
Issued by NWS Boston, MA
Issued by NWS Boston, MA
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130 FXUS61 KBOX 290742 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 342 AM EDT Sat Jun 29 2024 .SYNOPSIS... Mainly dry weather continues today, outside a few brief spot showers across the distant interior. A slow-moving frontal system brings two potential rounds of scattered showers and thunderstorms, mainly Saturday night into early Sunday morning, and then perhaps again later Sunday into Sunday night. Drier weather with seasonable temperatures and comfortable humidity levels returns early next week as high pressure builds in from the west. This high pressure will slide east of the region late next week, allowing very warm and humid weather to return for the start of the long holiday weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Relatively quiet this morning. An approaching warm front this afternoon will bring in increasing clouds as well as some showers arriving from the west late today, mainly across the western half of southern New England. Increasing south winds should result in near normal high temperatures despite the clouds. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... Steadiest period of rainfall is tonight, especially after midnight. Could be a few thunderstorms as well, but mid level lapse rates should be mediocre at best. Not a lot of buoyancy expected tonight, but high shear is expected. It`s more likely that this shear could sustain already developed thunderstorms that move into New England, rather than having thunderstorms develop locally. Guidance continued to exhibit significant detail differences in the mesoscale. That will take more time to come into better focus. There is rather good agreement on the synoptic scale, so based this forecast on the overall consensus, realizing that further adjustments will be required with later issuances. For Sunday, thinking we will see the last of the overnight showers moving off the south coast during the morning hours. While perhaps not being completely dry, there should be at least a lull in the action across the interior. How much of a lull will be key. Very high shear values are expected. Should the clouds break enough for appreciable insolation, buoyancy could become elevated to better balance the shear, raising the stakes for more widespread severe weather. At present, thinking CAPE values between 1,000-2,000 J/kg, which is more than enough to support a few strong to severe thunderstorms. Main threats are strong gusty winds and some hail. Becoming increasingly humid and warm, if not hot, Sunday. Precipitable water values still projected to be near 2 inches, indicating a risk for localized downpours and possible flooding. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Highlights * Any lingering showers/storms Sun Night tapering off from NW to SE. Moisture laden airmass, so heavy downpours still possible. * Isolated showers/storms on Mon. Perhaps some small hail in any more vigorous storms. * Dry and quiet weather Tue/Wed with near seasonable temps. * Turning more unsettled late in the week with increasing humidity. Sunday Night through Monday... Caught in cyclonic flow through much of this timeframe. A trough will be situated over the central/eastern Great Lakes Sun Night. The trough will dig into the eastern Great Lakes/Mid Atlantic by early Mon. The trough begins to lift and cutoff over southern New England Mon afternoon/evening before lifting offshore. A slow moving cold front will still be working its way through southern New England Sun Night into early Mon, but should mostly be offshore by Mon AM. High pressure will begin nudging in from the Great Lakes on Mon. Fairly good agreement amongst guidance with showers/storms tapering off from NW to SE as the cold front slides through Sun Night into early Mon. Do wonder if synoptic guidance is a bit too slow to push this activity through as several CAMs in the latest HREF showing activity is almost completely through our region. For now have leaned on the synoptic guidance agreement vs the tail end of the CAMs, but may need to be adjusted in future forecast updates. Still think some of these storms could perhaps be strong/severe though our instability will start to wane. At this point will still have a few hundred to roughly 1500 J/kg of MUCAPE in place. Should still have plenty of deep layer shear at 40-60 kts Sun Night into early Mon. Low/mid level lapse rates not looking too great, but think there still could be some stronger activity maintaining for a bit as front slides through. Also concerned with locally heavy downpours given NAEFS SATA table still 1.5 to 2.5 STD above model climo with the 1.5- 2+ inch PWAT plume sliding offshore and warm cloud layer depths of 3.5-4.5 km. Heaviest rains during this period would be before midnight. Low temps heading into Mon will be in the 60s. Overall for most should be fairly quiet on Mon. Though will have a fair amount of CU developing given the trough cutting off over us. Expect a fairly cold airmass at 500 hPa with temps of -15 to -20 degrees Celsius. The big question will be if there will be enough moisture given the dry N/NNW flow through the day and PWATs falling to 0.75 to 1 inch. Think this is enough moisture for isolated activity, so bumped up our precip chances to reflect this. Wonder if there is also the potential for an isolated strong storm or two. Will see low level lapse rates of 6-8 degrees and given the cold pool moving in overhead will have mid level lapse rates of 6-7 to perhaps 8 degrees Celsius. Deep layer shear of 20-50 kts will slide southeastward. Though there could be a brief period, especially earlier in the afternoon where there is some overlap, which could help maintain some organized convection...provided there is enough moisture in place. Given the setup think that hail would be primary risk, but this is not supported by latest CSU ML guidance. Something to stay tuned on for future updates. Highs will be near seasonable levels. Tuesday through Wednesday... A ridge axis builds from the eastern Great Lakes early on Tue into New England by late in the day. That ridge gets pushed offshore by early Wed, while a weak shortwave lifts in. Another ridge builds in from the eastern Great Lakes on Wed. High pressure builds overhead on Tue and slides offshore to the southeast Tue Night through Wed. Dry and quiet weather expected through this timeframe with high pressure in control. Temperatures will be near to slightly warmer than normal. Humidity levels will generally be pretty comfortable, but we may start to creep up a bit on Wed as flow becomes more southerly. High temps will generally be in the 80s. Thursday through Friday... Flow becomes quasi-zonal during this timeframe. Appears that there may be one or two shortwaves lifting into/through the region. Though at this point these are quite hard to time and there is a lot of spread amongst guidance. Appears a front pushes into our region on Thu and stalls out heading into Fri. Given the spread amongst guidance have generally stuck with the NBM at this point in time. Unfortunately at this point cannot completely rule out that some showers/storms could be around. Will have increasing humidity levels as another moisture laden airmass advects in. The NAEFS guidance showing PWATs of 1.5 to 2 STD above model climo with values ranging roughly from 1.5 to 2.5 inches. Warm cloud layer depths will be roughly 3.5 to 4.5 km, which given the environment could be conducive to heavy downpours. High temperatures generally in the 80s, but we could see some low 90s across the Merrimack and CT River Valley on Thu. && .AVIATION /08Z SATURDAY THROUGH WEDNESDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Today...High Confidence. VFR, despite a fair amount of mid-high level cloudiness. S winds increasing to between 10 and 15 knots with some gusts around 25 knots. Tonight... Moderate confidence in timing, higher confidence in trends. MVFR, to eventually mainly IFR, conditions overspread the region from west to east. A round of scattered showers and perhaps a few thunderstorms possible. S winds 10 to 15 knots with gusts up to 25 knots. Sunday...Moderate confidence. Areas IFR to start should improve to mainly VFR. More showers and thunderstorms expected during the afternoon and evening, with brief MVFR conditions. KBOS TAF...Moderate confidence in TAF. Mainly due to timing of showers and thunderstorms this evening and overnight. Likely dry through the evening push. KBDL TAF...Moderate confidence in TAF. Mainly due to timing of showers and thunderstorms this evening and overnight. Evening push could be impacted by showers and thunderstorms. Outlook /Sunday Night through Wednesday/... Sunday Night: Mainly VFR, with local MVFR possible. Breezy. Chance RA, slight chance TSRA. Monday: VFR. Breezy. Slight chance RA, isolated TSRA. Monday Night through Tuesday Night: VFR. Wednesday: VFR. Breezy. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Through Sunday...High confidence. Tranquil boating conditions this morning. Increasing southerly winds by this afternoon. Small Craft Advisories continue into Sunday. Areas of rain, and even some thunderstorms, arrive late tonight into Sunday morning. Outlook /Sunday Night through Wednesday/... Sunday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain, chance of thunderstorms. Monday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain. Monday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Tuesday through Wednesday: Winds less than 25 kt. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from midnight tonight to 7 PM EDT Sunday for ANZ230-236. Small Craft Advisory from 8 PM this evening to 7 PM EDT Sunday for ANZ231>235-237-254>256. Small Craft Advisory from noon today to 7 PM EDT Sunday for ANZ250-251. && $$ SYNOPSIS...Belk/BL NEAR TERM...Belk SHORT TERM...Belk LONG TERM...BL AVIATION...Belk/BL MARINE...Belk/BL