Area Forecast Discussion
Issued by NWS Boston, MA
Issued by NWS Boston, MA
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991 FXUS61 KBOX 031736 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 136 PM EDT Wed Jul 3 2024 .SYNOPSIS... High pressure brings dry weather and seasonably warm temperatures today. Cloud cover increases later tonight and especially on Independence Day, with scattered showers to dodge for the holiday along with rising humidity levels. Very warm weather with increasing humidity this weekend and into early next week. Saturday will have the highest humidity levels. While there is a risk of rain and thunderstorms throughout the weekend and early next week, it won`t rain continuously. There will be significant dry periods, with Saturday into Saturday night having the greatest chance for heavier rains. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 9 AM update... High pres across SNE will shift to the south this afternoon with S-SW flow developing. Other than some high clouds expect mostly sunny skies with seasonably warm temps. Highs will reach low- mid 80s, but cooler along the south coast due to southerly winds. A brief sea-breeze is expected to develop along the eastern MA coast but winds should turn southerly by mid-late afternoon. Dewpoints in the 50s today keeps humidity levels in the comfortable range. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... 332 AM Update: Tonight: Upper level ridge flattens/weakens later tonight in response to broad cyclonic flow/height falls moving into the Northeast states into the early morning hrs. While most of the first part of the night should see mostly clear to partly cloudy skies (high clouds), increasing cloud cover overspreads for the overnight hours from NW to SE associated with a significant surge in deep moisture (e.g. PWAT values increasing to around 1.5-1.8"). Dewpoints then start to rise into the lower to mid 60s for the overnight; that should offer development of patchy fog over the southern waters, then expanding slightly landward into the RI/MA South Coast. These are trends indicated both in BUFKIT sounding profiles but also on some of the LAMP MOS progs. With southerly winds increasing a bit, its northward coverage probably will be pretty limited to the immediate coast. So, turning a little more humid tonight but the increase in clouds also will allow for lows to run some 10 degrees warmer than tonight, in the mid to upper 60s. Independence Day: A weak frontal system approaching from the west, associated with a surge in deep moisture, will slowly sag its way southward through Southern New England during the holiday. This spells increased cloud cover, although BUFKIT profiles showing several layers of saturation indicate cloud cover could be more of a multi-layered look (mix of low and mid clouds). The sagging boundary would ordinarily serve as a focus for showers, and while there is quite a bit of deep moisture around with PWATs nearly 2", there is hardly any instability to speak of (less than 200 J/kg of MUCAPE). Couldn`t really rule out a shower anywhere or anytime, so I opted to phrase it in the zone forecast as scattered showers vs chance shower phrasing. Despite the semantics, it is generally dry most of the time, but I couldn`t say no to a shower to dodge. Although temperatures probably will be slower to rise amid cloud cover (highs upper 70s to mid 80), it gets quite humid as dewpoints reach into the upper 60s. Will have southerly breezes around 10-15 mph too. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Highlights: * Few showers possible on Friday, otherwise dry, warm and muggy. * Humidity becomes oppressive for Saturday along with the potential for heavier rains and thunderstorms. * Unsettled period continues Sunday though early next week, although there will be dry periods, and continued heat and muggy conditions. Thursday Night and Friday: Signals marine stratus and fog could develop along the south coast and the adjacent waters of Rhode Island and Massachusetts as BUFKIT forecast soundings have the lowest thousand feet saturated. Not out of the question it may lead to pockets of drizzle and as well as areas of patchy fog. Will say, there is low confidence in how widespread fog could become, but felt it was worth mentioning due to the numerous recreational boaters on the water for the Independence Day holiday. If this were to develop, think it would occur overnight into the predawn hours of Friday. Heading into Friday, there are subtle height rises along with weak shortwave energy traversing through the zonal mid-level regime. The best forcing remains to our northwest, over the Great Lakes, though bouts of shortwave energy does break off and travel east because of the near zonal mid-level pattern. Given a moisture rich atmosphere, PWATS are 1.5" to 1.8", and 2.0" plus along the southern coast a few showers cannot be ruled out. Timing out the is difficult, will have to utilize the high-res guidance to sort it out. With anomolously high PWATs, dew points are elevated, it is the type of humidity you can feel. Dew points climb into the low 70s and is accompanied by highs in the low to middle 80s. Saturday: Unsettled conditions heading into the upcoming weekend. Shortwave energy ejects out of the Great Lakes for Saturday, and with several hundred units of MUCAPE, convective showers are possible. The warm cloud layer is from 12,000 feet to 15,000 feet, meaning there is the potential for efficient rain makers, with PWATs near max of climo, with forecast values as high as 2.0 to 2.5", daily climo max per the sounding archive is around 2.05", with the max of all soundings at 2.73" for CHH. Heavy rains are possible. WPC mentioned the western CWA in day four excessive rainfall outlook, most of Connecticut and central to western Massachusetts. Saturday afternoon is warm and very muggy with dew points in the low to potentially the mid 70s, down right tropical! Highs are between the low and middle 80s. Sunday through Tuesday: Southern New England is still on the outer periphery of a mid-level ridge that is anchored over Bermuda. Model guidance continues to show bouts of shortwave energy riding the ridge, leading to a daily chance for daily chances for convective showers. While the risk continues into early next week, it won`t rain continuously. There will be significant dry periods as well. Guidance continues to indicate warm and muggy conditions with highs well into the 80s to 90 degrees and lows in the 60s to low 70s. High PWATs linger as well, likely leading to dew points in the upper 60s to 70 degrees. && .AVIATION /18Z WEDNESDAY THROUGH SUNDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Through 00z: VFR. S wind 10-15 kt with gusts to 20 kt. Sea-breeze along eastern MA coast kicks out 21-22z with wind shift to S. Tonight: High confidence. VFR cigs. Low risk of a shower 09-12z in the interior. SW wind 5-15 kt. Thursday: High confidence. Mainly VFR cigs, but patchy MVFR possible over higher elevations. Isolated morning shower possible, then a few showers or a t-storm possible in the afternoon in the interior. SW wind 10-20 kt. Thursday night: Moderate confidence. Cigs gradually lowering to MVFR with IFR possible near the south coast. A few evening showers possible, then scattered showers and possibly a t-storm near the south coast after midnight. KBOS TAF...High confidence in TAF. Sea-breeze kicks out 21-22z with wind shift to S. KBDL TAF...High confidence in TAF. Outlook /Friday through Sunday/... Friday: VFR. Chance SHRA. Friday Night: Mainly VFR, with local IFR possible. Chance SHRA. Saturday: MVFR/IFR conditions possible. Breezy. Chance SHRA, isolated TSRA. Saturday Night: Mainly VFR, with areas IFR possible. Breezy. Chance SHRA, isolated TSRA. Sunday: VFR. Breezy. Slight chance SHRA, isolated TSRA. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Today through Thursday: High confidence. Tranquil boating conditions expected today, with light southerly winds around 10 kt and easterly seabreezes nearest the coast. SW winds increase tonight to around 10-15 kt, although there will be a risk for patchy fog overnight on the southern waters and southern nearshore bays and harbors. Visbys could turn as low as one quarter mile. Winds then increase to around 15-20 kt on most waters for Independence Day, although gusts near shore could get to near-SCA levels during the daytime hrs. Scattered showers possible later in the day but shouldn`t restrict visby. Seas through the period generally 3 ft or less on all waters. Outlook /Thursday Night through Sunday/... Thursday Night: Winds less than 25 kt. Isolated rain showers. Local visibility 1 to 3 nm. Friday: Winds less than 25 kt. Slight chance of rain showers. Friday Night: Winds less than 25 kt. Chance of rain showers. Saturday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers, isolated thunderstorms. Saturday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers, isolated thunderstorms. Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers, isolated thunderstorms. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Loconto/Dooley NEAR TERM...KJC SHORT TERM...Loconto LONG TERM...Dooley AVIATION...KJC/Dooley MARINE...Loconto/Dooley