Area Forecast Discussion
Issued by NWS Boston, MA
Issued by NWS Boston, MA
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928 FXUS61 KBOX 261900 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 300 PM EDT Wed Jun 26 2024 .SYNOPSIS... Hot and humid today with a risk for showers and thunderstorms especially late this afternoon into the evening. Though there is a risk for some spotty activity early this afternoon. Some storms could turn strong to perhaps severe bringing risk of strong winds and heavy downpours, which may lead to flooding. Dry and pleasant weather conditions for Friday as Canadian high pressure briefly builds in. A more humid and more active weekend is in store as a slow moving frontal system brings periods of showers and thunderstorms with localized downpours possible. Drier weather then returns for early next week with seasonable temperatures. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... Highlights: * Rest of the afternoon is warm and muggy, with a low chance of a spotty shower before sunset. * Moderate to at times heavy rainfall with localized flash flooding during the evening and overnight hours remains possible, as long as the heaviest rain develops over urban locations. * Few stronger storms with isolated severe possible, the primary threat of damaging wind gust. A warm and humid afternoon across southern New England, quick glance across the CWA and temperatures are well in the 80s and 90F reading at KBDL. Dewpoints are elevated, mid to upper 60s and a few 70F sprinkled in. The combination generated modest CAPE across the interior, between 1,500 and 2,000 J/kg per SPC meso analysis. Storms have not developed due to lack of forcing and subsidence between the showers the exited northern New England this morning and the main event which is over across northern Ohio and western New York. But a couple of spot showers have bubbled up along the spine of the Berkshires and Green Mountains due to the differential heating. The rest of the afternoon a couple of spot showers remain possible. Breaking down tonight, there are two threats, hydro likely being the primary, with secondary being severe. This is associated with a 500mb trough/shortwave and surface cold front. Hydro: There is an anomolous moisture rich airmass, PWATs are around two inches, and per SPC Sounding Climatology this is near MAX of all soundings. HREF ensembles 00z to 06z (8pm to 2am) there is between 50 and 70 percent likelihood rainfall rates across Connecticut and Rhode Island may exceed an inch over three hours. But, more concerning is the low probability (~10 percent) for three inches of rain over three hours in northwest Connecticut. Given the antecedent conditions, the marginal risk ERO for areas north and west of I-95 seems appropriated. After all, localized amounts of 3 to 5 inches of rain fell just last weekend in western Hartford County along with parts of eastern Connecticut/western Rhode Island. In addition to these locations, urbans centers will need to be closely watched tonight for the potential of flash flooding. Outside of the heaviest downpours, many should expect widespread 0.5 to 1.0 inch of rain. Severe: Wind fields are more dynamic this evening with the 850mb jet increasing after 02z, this should help to promote the development of storms across the CWA. The challenge with these storms are the poor lapse rates late this evening and overnight, low level lapse rates and mid level lapse rates are near 6C/km. But, the deep level shear is what could continue any storms that develop and move into our area. Primary threat with any storms would likely be from damaging wind gusts, though with some low level helicity in eastern New York and western Connecticut, a low risk for a spin up is there, highlighted by the 2 percent tornado contour from SPC. Thinking after 08z/4am showers begin to exit from west to east, with showers exiting the I-95 corridor during the Thursday morning commute. A few showers may linger for extreme southeast New England, Cape Cod, and the islands through mid-morning. Overnight lows are in the 60s, lower 60s along the northern border with Vermont and New Hampshire, while the southern coast the low are in the upper 60s. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/... Highlights: * Any lingering showers/storms move offshore early in the day. Will be dry for most other than perhaps a spot shower across the MA/NH/VT border during the afternoon. Caught in cyclonic flow through this period. A trough over our area will lift offshore early in the day, but will have another dig into northern New England during the afternoon. High pressure will begin to nudge in once the cold front pushes offshore during the AM. Main focus of the forecast was in the near term. Only major change made was to introduce a few spotty showers across the MA/NH/VT border during the afternoon and try to better time the AM activity exiting. Overall though for most will be a pretty nice day with decreasing humidity levels, albeit it may be a bit breezy at times. High temperatures will generally be in the 80s. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... Highlights: * Pleasant Friday with clear skies and low humidity levels. * More active for the weekend, with periods of showers and t-storms associated with a slow moving frontal system. Heavy downpours appear to be the greatest risk, but it is uncertain if any storm(s) may become strong/severe. * High pressure returns Monday and Tuesday. Details: Friday: Canadian high pressure moves into New England on Fri, moving offshore Fri night/early Sat. This will usher in a cooler and drier air mass to Southern New England with full sunshine. Add this all up and you get the makings of a spectacular Friday summer day, with highs in the 70s to low 80s and dewpoints in the mid 40s to low 50s. As high pressure moves offshore by the evening, moisture levels start to increase again but at least these rises won`t be as substantial as Sat; lows in the 50s to low 60s. Saturday and Sunday: Should be able to eke out a dry Saturday morning at least. But Sat aftn into Sun evening is looking to be an active period of weather as a surface frontal system embedded in a regime of seasonably strong westerly flow aloft will interact with rich deep moisture to favor showers and thunderstorms. Uncertainties in the forecast stem from convective details which we can`t resolve at this time range, as well as the timing, both in terms of when rain/t-storms start and also when they end. There are indications on Sun into Sun evening that the axis of a surface cold front becomes more parallel to the mid/upper flow, which could lead to a slow egress offshore. Despite the above uncertainties, there`s enough consensus in the ensembles to indicate PoPs increasing to Likely-Categorical range Sat night into Sun, then a slow decrease from NW to SE for Sun night. PWAT values rise significantly up to 2-2.25", which are 2-3 standard deviations above late-June climatology per ECMWF EPS. Unclear if we would see any storms produce severe weather - it may end up being too cloudy to really destabilize significantly - but heavy downpours and possibly hydro could be a concern at some point in this period, especially if the front slows/stalls. Did boost QPF a bit over NBM in this period to better reflect potential for heavy rains, and while it don`t expect it to be raining all the time in all areas, showers and t-storms producing downpours is a growing risk for this weekend. Temps are seasonable with readings in the upper 70s to mid 80s, but both Sat and Sun look to be quite muggy with dewpoints rising into the upper 60s to mid 70s. Monday thru Wednesday: After what is looking like a soggy weekend, early next week looks drier/lower humidity levels as we get another infusion of Canadian high pressure. Both days should feature clear skies with seasonable temps and modest northerly breezes. && .AVIATION /19Z WEDNESDAY THROUGH MONDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Through 00z... Moderate confidence. Generally dry afternoon with VFR CIGs, the low chance of an isolated and brief shower between 20z-23z across the CWA. Winds are south to southwest between 10 and 20 knots with gusts upwards of 20 to 30 knots this afternoon. Areas of coastal fog and stratus have developed south of the islands and are propagating northeast with IFR CIGs. Expecting this to expand across the Cape and Islands. Do have lower confidence in how expansive this area becomes and duration. Tonight... Moderate confidence. Risk higher for scattered showers and storms where conditions deteriorate to MVFR/IFR with localized LIFR. Some storms could be strong and produce heavy downpours between 00z and 06z. TAFs indicate this hazard with PROB30. Winds ease to between 5 and 10 knots, but will quickly shift to the west from west to east as the cold front slides through (though may not be until Thu AM for Cape terminals). Thursday...High confidence in trends, moderate in exact timing. Any lingering MVFR/IFR improves to VFR between 12z and 15z, ACK could linger below VFR through 18z. Winds out of the west between 5 and 10 knots with gusts of 15 to 20 knots. Thursday Night... High Confidence. VFR, dry, northwest to north/northwest winds 5 to 10 knots. KBOS TAF...Moderate confidence in TAF. VFR for much of today. Could have an isolated shower/storm early this afternoon, but risk higher tonight where conditions deteriorate to MVFR/IFR. Have tried to highlight best shot with PROB30. Winds remain too strong out of the SW for sea breeze to develop today. KBDL TAF...Moderate confidence in TAF. VFR for much of today. Could have an isolated shower/storm early this afternoon, but risk higher late this afternoon/tonight where conditions deteriorate to MVFR/IFR. Have highlighted best shot for thunderstorms with PROB30. Outlook /Friday through Monday/... Friday through Friday Night: VFR. Saturday: Mainly VFR, with local MVFR possible. Breezy. Chance SHRA, isolated TSRA. Saturday Night: Mainly MVFR, with areas IFR possible. Breezy. SHRA, isolated TSRA. Sunday: Mainly MVFR, with local IFR possible. Breezy. SHRA, isolated TSRA. Sunday Night: VFR. Breezy. Chance SHRA, isolated TSRA. Monday: VFR. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. 230 PM update... * SCA remains in effect thru tonight for southern waters This evening & overnight... SW winds 15-20 kt gusting up to 30kt at times. Mainly dry weather thru the daylight hours, then showers and thunderstorms over western PA/NY this afternoon, impact RI/MA waters this evening and overnight. Frequent lightning and heavy downpours with poor vsby are the main concerns. Secondary concerns is strong winds. Thursday..High confidence. Cold front enters the waters, which will shift winds to W during the AM along with improving vsbys. However, the front stalls just offshore. Seas across the outer waters diminishing to 2-4 ft during the afternoon. Thursday night...high confidence. Cold front just offshore finally accelerates out to sea, with winds becoming NW 15-20 kt, highest across the eastern MA waters. Dry weather and good vsby. Outlook /Friday through Monday/... Friday through Friday Night: Winds less than 25 kt. Saturday: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers. Saturday Night: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Chance of rain showers, isolated thunderstorms. Sunday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Rain showers, isolated thunderstorms. Sunday Night: Winds less than 25 kt. Local rough seas. Chance of rain showers, isolated thunderstorms. Monday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...High Risk for Rip Currents until 8 PM EDT this evening for MAZ020>024. RI...High Risk for Rip Currents until 8 PM EDT this evening for RIZ006>008. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ231>234-236. Small Craft Advisory until 8 AM EDT Thursday for ANZ235-237. Small Craft Advisory until 5 PM EDT Thursday for ANZ254>256. && $$ SYNOPSIS...Loconto/Dooley/Nocera NEAR TERM...Dooley SHORT TERM...Nocera LONG TERM...Loconto AVIATION...Loconto/Dooley MARINE...Loconto/Nocera