Area Forecast Discussion
Issued by NWS Boston, MA
Issued by NWS Boston, MA
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912 FXUS61 KBOX 081122 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 722 AM EDT Mon Jul 8 2024 .SYNOPSIS... Oppressive heat and humidity are expected today and tomorrow, and could continue into Wednesday as well. Dry weather is expected today, but there is a chance for thunderstorms north and west of Interstate 95 Tuesday afternoon. Still fairly humid late week, though temperatures are slightly less hot, along with periods of rain and thunderstorm activity as the remnants of Beryl moves towards the northeast. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Updated: 7:15 AM Fog is quickly lifting across portions of Rhode Island and southeast Massachusetts, a Dense Fog Advisory will be allowed to expire for those locations at 8AM, but will continue for Cape Cod and the Islands through noon. But, places like Nantucket could be stuck in the fog much of today. Forecast remains well on track with minimal changes. See the previous forecast below. 345 AM Update: Our weather pattern continues to be little changed from the last couple days. Weak sea-level pressure gradient in place along with a continued stream of subtropical moisture maintaining dewpoints in the mid 60s to lower to mid 70s, highest over southeastern New England. Most areas in RI and eastern/southeast MA near and southeast of I-95 are socked in with low clouds and fog. There`s been an increasing number of sites with visbys down to one quarter mile in RI and southeast MA, with Providence reporting a visibility of less than a quarter mile for several hrs. Given that it`s the Monday after the Fourth of July holiday weekend and there could be more traffic volume on the roads in addition to the typical commute traffic, we opted for a Dense Fog Advisory for RI and southeastern MA, Cape and Islands. Since it looks like visbys will improve into the morning for RI and adjacent southeast MA, this segment of the advisory runs until 8 AM Monday; with anticipated delayed improvement for the Cape and Islands, this segment is slated to expire at noon. There have been patches of fog elsewhere in portions of the CT Valley and into Metrowest, but it is more patchy here. As we`ve seen over the past couple days, low clouds and fog should gradually retreat into the waters in all areas by late morning/noontime. A very warm and humid day is expected with several hours of sunshine for much of Southern New England. There also won`t be any relief from breezes away from the coastlines, and large- scale subsidence should suppress, literally, the risk for thunderstorms today. Expanded the Heat Advisory to include the Greater Springfield metro area (eastern Hampden County forecast zone) as well as Kent County in RI. Although dewpoints should be in the low 70s in eastern and southeast New England, further inland in interior MA, models show mixing taking place and that could reduce dewpoints into the low to mid 60s. That could keep some areas in the Advisory from reaching Advisory criteria, but we felt it was marginally close enough. Heat indices in the Advisory area should reach into the mid 90s, with some upper 90s popping up in the Merrimack and CT Valleys. Highs should reach into the mid 80s to the lower to mid 90s, with upper 70s to mid 80s Cape and Islands with a shorter period of full sun. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... 345 AM Update: Tonight: Persistence forecast again for tonight. Stratus and fog that shifted into the waters again looks to return back northward/landward tonight into the overnight. The exact northward areal extent of this fog and stratus layer is still a bit unclear but in general it should be roughly similar to this morning (near/southeast of I-95). Lows in the upper 60s to the mid 70s. Tuesday: SSW flow on Tuesday looks to be a little stronger than the last couple days, and that will allow for a greater transport of lower to middle atmospheric moisture. Dewpoints should return back into the middle 70s for much of the area - resembling bathwater out there tomorrow. Heat Advisory was maintained for Tuesday as well, and the higher dewpoints than today means that we won`t need as much heating to reach Advisory levels. Some minor reservations in that compared to today, there should be more cloud cover around in the SW flow aloft, even as morning low clouds and fog scatter/disperse into the waters again. There is also the potential for thunderstorms on Tuesday afternoon as well as a weak ripple in the 500 mb flow rotates ENE from the mid- Atlantic, with areas north and west of I-95 being a little more favored. SPC has designated a large portion of Southern New England into portions of NH in a Marginal risk for severe thunderstorms on Tuesday. If storms indeed develop, localized straight line wind damage would be the primary risk, along with torrential downpours. But specific to the heat, both of the above factors cast a little uncertainty on how warm temperatures may get. But humidity levels Tuesday still will be really oppressive. Brought highs into the mid 80s to low 90s, producing maximum heat indices in the mid to upper 90s in the Heat Advisory area, with upper 80s to lower 90s surrounding it to include remaining portions of northern MA and the Cape and Islands. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Highlights: * Warm and humid conditions Wednesday through the upcoming weekend with no relief from the tropical-like humidity. * Periods of rain and storms midweek into this upcoming weekend with the potential for heavy rains and stronger storms on Wednesday and Thursday. Little change to the forecast with the synoptic pattern featuring a mid-level ridge of high pressure centered over Bermuda. Persistent southwest flow continues to funnel abnormally high moisture into southern New England with no breaks from the high humidity for the foreseeable future. Additionally, 850mb temperatures remain at or above climatological normal through this coming weekend, which boils down to a warmer than normal daytime and night time temperatures. Getting caught up in the deep southwest flow are bursts of shortwave energy riding the outer periphery of the subtropical ridge, plus the moisture associated with Beryl may lead to periods of heavy rainfall and potential for flash flooding mid to late week, highlighted by WPC`s ERO. Temperatures: By midweek, there is a slight `cool off` in temperatures, there is good agreement amongst the 08/00z guidance the 925mb have lowered to 20C to 22C for much of the forecast period. What may cause a few headaches this week is the amount of cloud cover and how that will influence high temperatures. In general, afternoon highs are in the 80s, with Wednesday being the warmer of the days, highs in the upper 80s across much of the region. Southwest winds do keep the south coast of Rhode Island and southeast Massachusetts cooler in the lower 80s. As for dew points, still down right tropical in the lower 70s. During this update did not have the confidence to extend the `Heat Advisory` into Wednesday, but if there were an area it would most likely be Hartford County. The summer warmth and humidity continues Thursday, albeit a few degrees less than Wednesday, right through this upcoming weekend. Afternoon highs are in the low and middle 80 and overnight lows in the lower 70s. Still fairly humid, dew points hold steady in the lower to middle 70s. Precipitation: Mid-level energy from Beryl will be transported from Texas to the northeast. While there is uncertainty with exact location and timing of the shortwaves, it will be moving over a loaded atmosphere. As of now, the better forcing does appear north and west of southern New England, but any storms will have the potential to produce tropical downpours and possibly flash flooding. Per the 08/00z guidance, forecast PWATs are 2"+, with outsiders indicating 2.5" for Wednesday and slightly higher PWATs on Thursday. These are significant PWATS, 2-3 standard deviations above what is normal for Wednesday, and 3.5 standard deviations above what is normal on Thursday. Another way of looking at this, these forecast values may reach near the highest record PWATs per the climatological soundings done at CHH, OKX, and ALY. For reference, the MAX PWATs per the sounding climatology at ALY, OKX, and CHH are 2.75", 2.62", and 2.73" respectively. WPC has Slight (at least 15%) ERO for Wednesday and Thursday across northwest Massachusetts and points north and west, while much of the CWA has a Marginal (at least 5%) ERO. These two days will need to be closely watched for flash flooding potential. Stronger storms are possible Wednesday and Thursday as well. SPC has generally thunder, with a small Marginal risk of severe weather just west of southern New England. With the dynamic remnants of Beryl in the vicinity of the region there is plenty of ingredients for storms to develop, SREF indicates on Wednesday MUCAPE is 1000 to 1500 J/kg, 30 to 40 knots of 0-6km shear, and 100 units of 0-1km helicity. CSU has most of southern New England highlighted for thunderstorm winds, around 5% to 15%, and even low risk for an tornado, around 2% to 5%. Unsettled conditions do continue late week and into this upcoming weekend with shortwave energy continuing to ride the periphery of the subtropical ridge. This will lead to periods of rain and storms Thursday into the upcoming weekend. && .AVIATION /11Z MONDAY THROUGH FRIDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 12z Update: Today: High confidence, though moderate on improvement for Cape Cod. Similar general trends to past couple days, with areas currently affected by stratus and fog should see improvement thru 12-16z Mon. Thus VFR for most. Less certain on clearing for the Cape and Islands and even where it does improve to VFR at FMH and HYA, IFR stratus will likely be in the vicinity and could require AMDs. There is high confidence that ACK remains IFR- LIFR all day. Light south winds, with seabreezes at BOS and PVD. Tonight: High confidence in trends, moderate confidence on the timing and northward coverage of sub-VFR. ACK will still be dealing with LIFR. Initial VFR then degrades as stratus and fog at IFR-LIFR levels will again return landward/northward. Exact timing and how far north the IFR-LIFR layer makes it is still uncertain; generally should follow a similar 00-09z timing as the last few nights, with gradual improvement from NW to SE during the 09-12z Tue timeframe. VFR outside of these areas, with higher confidence near/north of the Mass Pike. Light winds. Tuesday: Moderate confidence. Any sub-VFR stratus/fog conditions improve to VFR for most, though still some degraded conditions anticipated for the Cape and Islands. Potential for SCT TSRA from an HFD-ORH-LWM line north and west after 18z Tue. S-SW winds 8-12 kt, possible seabreeze at BOS. KBOS TAF...High confidence in TAF. VFR; overall high confidence that BOS doesn`t see stratus/fog that is developing at OWD early this morning, but left SCT015 for a couple hrs 09-11z Mon in case it does. Seabreezes develop around 14-15z, turning light S by 00-01z. Will have to monitor stratus return tonight from southern coast but thinking stays far enough south again. KBDL TAF...High confidence in TAF. VFR, though TEMPO radiational fog thru 11z Mon. Could be a better chance that stratus makes it to BDL late tonight. S winds around 5 kt today, becoming light tonight. Outlook /Tuesday Night through Friday/... Tuesday Night: Mainly VFR, with local IFR possible. Areas FG, slight chance SHRA, isolated TSRA. Wednesday: Mainly VFR, with areas MVFR possible. Breezy. Chance SHRA, isolated TSRA. Wednesday Night: MVFR/IFR conditions possible. Breezy. Chance SHRA, isolated TSRA. Thursday: Mainly MVFR, with local IFR possible. Breezy. Chance SHRA, isolated TSRA. Thursday Night: MVFR/IFR conditions possible. Breezy. Chance SHRA, isolated TSRA. Friday: Mainly VFR, with local IFR 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 Tuesday: High confidence. Winds and seas to remain below SCA criteria in this forecast period. Southerly winds will be on the light side today and tonight, around 10 kt or so. Southwest winds pick up a little more on Tuesday, into the 15-20 kt range on all waters. Seas 3 ft or less on all waters. The main concern for boaters continues to be reduced visibility from fog, which looks to continue even into Tuesday night. Outlook /Tuesday Night through Friday/... Tuesday Night: Winds less than 25 kt. Areas fog, slight chance of rain showers, isolated thunderstorms. Areas of visibility 1 nm or less. Wednesday: Winds less than 25 kt. Areas fog, slight chance of rain showers, isolated thunderstorms. Wednesday Night: Winds less than 25 kt. Chance of rain showers, isolated thunderstorms. Thursday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Chance of rain showers, isolated thunderstorms. Thursday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Slight chance of rain showers, isolated thunderstorms. Friday: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers, isolated thunderstorms. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Heat Advisory from noon today to 8 PM EDT Tuesday for CTZ002>004. MA...Heat Advisory from noon today to 8 PM EDT Tuesday for MAZ005- 011>013-017-018. Dense Fog Advisory until 8 AM EDT this morning for MAZ017>021. Dense Fog Advisory until noon EDT today for MAZ022>024. RI...Heat Advisory from noon today to 8 PM EDT Tuesday for RIZ001>004. Dense Fog Advisory until 8 AM EDT this morning for RIZ001>007. Dense Fog Advisory until noon EDT today for RIZ008. MARINE...None. && $$ SYNOPSIS...Loconto/Dooley NEAR TERM...Loconto/Dooley SHORT TERM...Loconto LONG TERM...Dooley AVIATION...Loconto/Dooley MARINE...Loconto/Dooley