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Area Forecast Discussion
Issued by NWS Boston, MA
Issued by NWS Boston, MA
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486 FXUS61 KBOX 121935 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 335 PM EDT Mon Aug 12 2024 .SYNOPSIS... Scattered brief showers and perhaps a few thunderstorms should wind down during the first half of the evening. Otherwise...dry and very pleasant weather is on tap for Tuesday and Wednesday. Another round of scattered showers and perhaps a few thunderstorms are possible Thursday. Mainly dry weather probably returns for Friday...but a frontal system may bring some unsettled weather by the latter half of the weekend. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... 335 PM Update... * Scattered Showers/isolated t-storms end this evening * Otherwise...dry & pleasant tonight with lows mainly in the 50s Strong northern stream shortwave and cold pool aloft was dropping southward into the region at mid-late afternoon. Despite limited surface moisture...the cold pool aloft with 500T dropping to -18C was resulting in 500 to 1000 J/KG of Cape. This has allowed scattered brief showers to develop and we may also see a few t-storms. Not expecting any severe weather...but we may see small hail/graupel with a few of the stronger storms given the cold pool aloft. Localized gusty winds are possible too given a modest T/Td spread...but again not expecting severe weather. The scattered activity should wind down during the first half of the evening with the loss of diurnal heating. Otherwise...a dry and very pleasant night of weather is on tap. A ridge of high pressure to our west will allow for skies to become mostly clear and winds calm to light. This should yield a good night of radiational cooling with lows by daybreak dropping mainly into the 50s...but near 60/lower 60s expected in the Urban Heat Islands of Boston/Providence. Very localized patchy ground fog may develop in the typically most vulnerable low-lying spots toward daybreak. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... Key Points... * Beautiful & mostly sunny Tue...Highs upper 70s/lower 80s * Pleasant/Dry Tue night...lows 50s to the lower-middle 60s Details... Tuesday... Upper level trough axis will be east of us on Tue. The result will be dry/light northwest flow aloft and a very nice mid August day. 850T on the order of +11C/+12C should result in high temps in the upper 70s to the lower 80s. Most of the lower elevations away from the immediate coast should be on the warmer side of those numbers. However...dewpoints in the 50s will make for very comfortable humidity levels for this time of year. Tuesday night... A ridge of high pressure to our west will remain in control of our weather Tue night. This should allow for mostly clear skies along with light to calm winds and another good night of radiational cooling. Overnight lows should be in the 50s to the lower to middle 60s in some of the urban centers. Very localized patchy ground fog may develop in the typically most vulnerable spots toward daybreak. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... Key points: * Work week continues to look dry with seasonable temperatures, aside from the chance of showers on Thursday * Timing still not set for a frontal system moving through sometime this weekend/early next week, but starting to look more probable Saturday morning. * Continuing to monitor Potential Tropical Cyclone 5 (PTC 5) for risk of high surf and rip currents this weekend. Please see the NHC Advisories for more information on this system. Models continue to support the previous discussion`s assessment of the rest of the work week; we continue to sit under cyclonic flow aloft with high pressure at the surface. Expect to continue seeing clouds move in and out during the day with high temperatures remaining primarily in the upper 70s into the mid-80s and lower relative humidities. Thursday still looks to have a good chance at some showers this week. Some of the guidance is suggesting some favorable mid-level lapse rates and slightly elevated CAPE values for some more elevated convection, particularly in the Worcester Hills and other higher terrain. PWATs look to be seasonably normal and not indicative of any widespread downpours, so the main concern is just some isolated thunderstorms over higher terrain areas on Thursday afternoon into the evening. This weekend into early next week continues to have a good chance at more widespread showers with a strong frontal system coming in. The 12z GFS is starting to move more in agreement with the 12z runs for the Canadian GEM and the ECMWF on timing for this front: the international models favor Friday night for it to start going into western MA and through central CT, and the GFS is favoring a couple hours later into Saturday morning. Some disagreement about whether or not this rain will continue into Monday, but most of the guidance seems to favor rain continuing for most of the weekend. Did not put PoPs higher than a chance for the time being through the weekend into Monday. We are continuing to monitor PTC 5 for a chance at seeing some higher surf and strong rip currents, particularly along the South Coast and the southern coastlines of the Islands. Both NBM and ECMWF WAVE guidance seem to favor larger swells Sunday into Monday next week. This storm is still forecast to stay well offshore and far from southern New England, but it is still a bit early to get more specific regarding any possible impacts for southern New England and the forecast is very much subject to change. For more information on the latest forecast for PTC 5, please check nhc.noaa.gov. && .AVIATION /19Z MONDAY THROUGH SATURDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 18z TAF Update... This afternoon...High Confidence. VFR outside briefly lower conditions in scattered showers and perhaps a few t-storms. W winds 5 to 15 knots. Tonight...High Confidence. Scattered showers should wind down quickly early this evening. Otherwise...VFR with perhaps brief/very localized fog developing toward daybreak in the typically lowest lying locations. Calm/Light NW winds. Tuesday...High Confidence. VFR. NW winds 5 to 10 knots although winds should shift to more of a SW direction late in the day near the I-95 corridor. Tuesday night...High Confidence. VFR with perhaps brief/very localized fog developing toward daybreak in the typically lowest lying locations. Calm/Light NW winds. KBOS TAF...High Confidence. KBDL TAF...High Confidence. Outlook /Wednesday through Saturday/... Wednesday through Wednesday Night: VFR. Thursday: VFR. Chance SHRA, isolated TSRA. Thursday Night: VFR. Slight chance SHRA. Friday through Friday Night: VFR. Saturday: VFR. Chance SHRA. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Tonight through Tuesday night...High Confidence. A ridge of high pressure to our west will result in pleasant boating weather winds/seas below small craft advisory thresholds through Tuesday night. Vsbys should be quite good as well. Outlook /Wednesday through Saturday/... Wednesday through Wednesday Night: Winds less than 25 kt. Thursday: Winds less than 25 kt. Slight chance of rain showers, isolated thunderstorms. Thursday Night through Friday Night: Winds less than 25 kt. Saturday: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Frank/CH NEAR TERM...Frank SHORT TERM...Frank LONG TERM...CH AVIATION...Frank/CH MARINE...Frank/CH