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Area Forecast Discussion
Issued by NWS Boston, MA
Issued by NWS Boston, MA
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775 FXUS61 KBOX 121115 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 715 AM EDT Mon Aug 12 2024 .SYNOPSIS... Isolated to scattered shower or thunderstorm this afternoon, otherwise dry and comfortable today and Tuesday. Other than scattered showers on Thursday, much of the workweek is dry with seasonable temperatures. A frontal system brings our next best chance at widespread rains either this weekend or into early next week. && .NEAR TERM /UNTIL 7 PM THIS EVENING/... 705 AM Update: No major changes needed with this update. Mostly clear skies begin the morning with low humidity levels and current temps in the upper 50s to mid 60s. Should see at least a few hours of full sun, until we start to feel effects of a potent shortwave disturbance in mid-levels that is evident in water vapor imagery over Lake Huron. This feature and its cold pocket of air aloft has been responsible for producing a band of lake- enhanced rain seen in composite radar imagery coming off Lake Ontario. As this feature nears our area this afternoon, expect an increase in cloud cover toward partly to mostly cloudy conditions. Shallow instability in conjunction with the added dynamics should be enough to produce low-topped showers in scattered coverage during the afternoon hrs; the strongest of these could produce occasional lightning and also the potential for graupel or pea- size hail given the seasonably cold temps aloft and low wet-bulb zero heights. Overall we`re not anticipating anything necessarily impactful or significant. This activity then moves offshore by early tonight before trending drier. Not a washout, and while there will be some showers to dodge, several hrs of dry weather are also expected. Highs mid 70s to lower 80s still look on track with no changes there. Previous discussion: Updated: 2:50AM Highlights: * Few showers possible mid to late afternoon as a robust shortwave passes through the region. Otherwise it`s a dry and comfortable afternoon with highs 70s to lower 80s. A quiet start this morning with mainly clear sky conditions. Today is mainly dry, though there will be iso`d to sct`d rain/thunder this afternoon. It`s been mentioned there is a robust mid-level low pressure system centered in southwest Quebec. Shortwave ejects into southern New England this afternoon and promotes development of clouds and showers/low top thunderstorms. BUFKIT forecast soundings indicate these showers will be shallow, but thunder and maybe small pea-size hail is possible due to the cold pool aloft. The forecast sounding also showed an inverted `V` profile, which means there may be a few stronger gusts/outflow from any thunderstorms. Timing it out, generally starting 1-3 pm across western-half of southern New England and 4-6pm across the eastern-half. Not anticipating heavy rain as PWATs are near climatology to perhaps the 75th percentile which is around 1.2" to 1.4". An isolated amount of 0.25" to 0.50" is possible but most locations receive much less. Showers diminish after sunset, CAMs do show an isolated shower or two may linger through 9-11pm. A cooler afternoon with dew points in the 50s, refreshing, or is it an early fall-like feel? Recall, temperatures aloft are cooler than normal and will result in lower than normal highs. Many locations are in the upper 70s to lower 80s, but terrain AOA 750 feet are likely in the middle 70s, 73-76 degrees, coolest will be highest terrain of the east slope of the Berkshires. West to west/northwest wind today around 10 mph, with occasional afternoon gusts to 20 mph. && .SHORT TERM /7 PM THIS EVENING THROUGH 6 PM TUESDAY/... Updated: 2:50AM Tonight: Nearly a carbon copy of the previous night. Showers end and clearing sky cover, the departing shortwave provides another reinforcing shot of cooler and drier air. Light northwest winds overnight across the interior, but the boundary layer remains mixed enough to continue those winds near the coast. Where the winds are light, should have falling temperatures into the 50s, while the urban centers are still warm-ish in the lower 60s. Tuesday: All around a nice day across the region with surface high pressure building in from the southwest. Aloft, flow is out of the northwest to the north, reinforcing the lower dew points and humidity. A good amount of sunshine with fair weather clouds mixed as there is a weak shortwave moving through mid to late afternoon, but with low PWATs likely only see added clouds rather than any rain. Seasonably warm with highs in the upper 70 and lower 80s. Northwest winds 5 to 10 mph. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Updated: 2:50AM Highlights: * Other than a chance for showers on Thurs, much of the workweek is dry, with seasonable temperatures. * Next chance for widespread rains is with a frontal system moving in either on the weekend or early next week. * Monitoring developments regarding Potential Tropical Cyclone Five east of the Lesser Antilles. See NHC Advisories on this system for more details. Increasing risk for high surf and rip currents from later this weekend, but any other specifics remain too uncertain to pinpoint at this time. Details: No significant changes were noted in today`s 00z guidance through the remainder of the upcoming workweek, with pretty good consistency run-to-run and across modeling systems. Broad cyclonic flow aloft with surface high pressure will govern our weather pattern through the rest of the workweek. This should bring a mix of clouds and sun during the day, and while most of the workweek is generally dry, there is a better chance at showers on Thurs as a weak vort maxima rotating around a broad upper trough sparks shallow convective development especially in/near the higher terrain. No significant impacts are expected from any showers which develop, however. Temperatures begin around seasonable levels with a modest warming trend toward late week, but highs in the upper 70s to lower to mid 80s pretty common. Still looks as though the next best chance at more widespread rain chances is with a pretty robust frontal system moving in from the Gt Lakes either this weekend or early next week. Previously the GFS was at odds with the international guidance suite on this frontal system. There are now more members from the 00z GEFS as well as the 00z GFS which lend support to at least the existence of this frontal system nearing Southern New England. However pretty large disagreement on its timing, with the Canadian GEM holding off until early next week, the GFS late in the weekend, while the ECMWF is the most pessimistic in showing rains developing Sat and continuing through Mon. For now left a rather general broad-brushed Chance PoP for the weekend into early next week, but that will need refinement once there`s better agreement on the timing. Finally, will be continuing to keep close monitor of developments regarding what is now Potential Tropical Cyclone (PTC) Five located near the Leeward Islands. For the latest on PTC 5, see the latest advisories from the National Hurricane Center. Most available track model forecasts indicate PTC 5 - forecast to become a strong tropical storm or hurricane in the next five days, with the next named system to be Ernesto - making a northward to northeast pass well offshore east of 70W longitude late this weekend. However we need to be cognizant of adjustments in storm track as it is still very early in this system`s lifecycle. It thus remains way too early to provide specifics/effects to Southern New England, if any, due to that uncertainty. However, long-period swell well ahead of this system may stand to increase the risk for rip currents and high surf as we move into the weekend. This is supported by the ECMWF Wave guidance, which shows 5-9 ft swells reaching our southeastern coast around Sat night and Sun. && .AVIATION /11Z MONDAY THROUGH FRIDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 12z TAF Update: Today...High Confidence. VFR. Increasing clouds this afternoon, but remain VFR with clouds bases around 5,000 to 7,000 feet. Dry in the morning, then scattered brief afternoon showers, have included PROB30 for western terminals; -SHRA at BDL & BAF between 18z/22z, here is where there is highest confidence in rain. Elsewhere VCSH in the rest of the terminals, except Cape Cod and the Islands. Very low prob (5-10%) of isolated thunder, but too low to include in the TAF. WSW to WNW winds 10-15 kt. Could have some higher gusts between 18z-23z up to 20 knots. Cape and Island winds are SW 10-15 kt and gusts to 20 knots. Tonight and Tuesday...High Confidence. Dry & VFR. WNW winds are 5-15 kt. KBOS TAF...High Confidence. Mainly VFR, although risk for SHRA between 17-02z could bring MVFR visby for a brief period of time. WNW winds around 10 kt begin a slow backing to WSW with gusts 18-20 kt this aftn, before shifting to NW around 10 kt after 02z Tue. KBDL TAF...High Confidence. Mainly W to WNW winds 5-15 kt and dry weather through this morning. Then VCSH this afternoon, mainly 18z-22z. Outlook /Tuesday Night through Friday/... Tuesday Night through Wednesday Night: VFR. Thursday: VFR. Slight chance SHRA, isolated TSRA. Thursday Night through Friday: VFR. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Updated: 2:50AM Through Tuesday...High Confidence. Tranquil boating weather with persistent SW winds 5-15 kt through today, could have few stronger gusts to 20 knots for the near shore waters off of the coast of RI and southeast MA. Wind shifts to WNW tonight into Tuesday. Dry weather with the exception of a few brief showers, an isolated thunderstorm this afternoon, dissipating with sunset. Outlook /Tuesday Night through Friday/... Winds less than 25 kt. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Loconto/Dooley NEAR TERM...Loconto/Dooley SHORT TERM...Dooley LONG TERM...Loconto AVIATION...Loconto/Dooley MARINE...Loconto/Dooley