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Area Forecast Discussion
Issued by NWS Boston, MA
Issued by NWS Boston, MA
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913 FXUS61 KBOX 141922 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 322 PM EDT Fri Jun 14 2024 .SYNOPSIS... Second round of strong to severe thunderstorms expected through early tonight ahead of a dry and pleasant Father`s Day weekend. Several days of excessive heat and humidity are likely starting Tuesday and lasting through next Friday. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... First round of thunderstorms, of which strong to severe wind gusts and small hail to the Boston metro area has move seaward, though we are not yet out of the woods with a second round of potentially severe thunderstorms building later this afternoon and evening. At present, cells are beginning to develop across southern New York and southwestern Connecticut and western MA with an agitated cumulus field bubbling ahead of the advancing cold front over the Albany metro area. MLCAPE values of >1000J/km are currently associated with the area of storm development in southern New York, which is subsequently where the strongest updrafts are being observed at this time. CAMs have really struggled to accurately depict convection today, underestimating or misplacing the geographic coverage storms, thus, they provide limited utility in diagnosing the exact timing and coverage of storms this evening. With that said, most if not all of the HREF members hint at the development of a strong line of storms after ~20Z. SPC Mesoanalysis continues to depict a recovering environment behind the first line of convection where skies have begun to clear across western MA. MUCape Values are forecast to rebound to ~2000J/kg across part with mid level lapse rates rebounding to between 6-6.5C/km while low level lapse rates remain primed around 8C/km. DCAPE, which surged to between 800-900 ahead of this afternoon`s convective line with good mixing, also look to increase this afternoon back to similar values, which will renew the damaging wind threat with any additional convection. Some small hail was also observed in mid day storms, but freezing levels to 12,000ft and meager MLLRs really put the damper on the severe hail potential, so we expect similar trends with any strong storms through this evening. The eastward extend of the severe potential with a secondary linear convective line remains in question as it will again be a race against time/sunset as instability wanes around 00-01Z. So, ultimately, we expect another line of impactful convection to traverse across southern New England between ~21Z and 02Z tonight. Unfortunately clearing will take some time behind the cold frontal passage late this evening as trailing shortwave trough will provide enough forcing, combined with residual PWATs around 1.25", to renew shower chances from approximately the Worcester to Willimantic N-S line, east. Shortwave trough axis will not move seaward of the region until between 12-15Z Saturday, so shower activity may linger across the Cape and Islands through sunrise tomorrow morning. The good news is that with little instability overnight, the severe threat really drops off as cold front moves offshore, with perhaps a few lingering rumbles of thunder possible between 11pm and 2AM. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... Departing cold front/deep digging shortwave will allow very, at least for June, dry air to filter into the region on NW/N flow tomorrow. PWATs are expected to drop to around 0.4" by 18/21Z Saturday, yielding a gorgeous, comfortable start to Father`s day weekend. Little cloud cover is expected, with dewpoints dropping into the low and mid 40s by early evening. 850mb temperatures between 8-10C will support highs in the mid 70s to low 80s. Radiational cooling will be in play Saturday night. With very dry airmass in place and mainly clear skies overhead, as well as slackening winds, it is quite possible that low temperatures drop into the low to mid 40s across northwestern MA by daybreak on Sunday. Urban heat islands, like Boston and Hartford, will remain our most mild localities, with lows around 60F expected. Temperatures across the coastal plain will fall back into the 50s. This is our last shot of cool air for quite some time as mid level ridging starts to build in to end the weekend. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Key Point: * Several days of dangerous heat/humidity Tue-Fri Big story for next week continues to be likelihood of dangerous heat and humidity starting Tue and peaking Wed-Fri. Ensembles are in very good agreement on building strong upper ridge over eastern U.S. through most of next week which lends increasing confidence. In fact, 500 mb heights nearing 600 dm is something rarely seen in the Northeast and is a very strong signal for record heat. This aligns with EPS and NAEFS Situational Awareness Tables which show several parameters outside of model climatology relating to temperature, signaling potential for a highly unusual event. We`re also seeing fairly high chances of afternoon highs well into 90s Tue-Fri, if not near 100 in some spots. More importantly, daytime heat indices may reach as high as 105 degrees and there will be little relief at night with nighttime heat indices in 70s. Upper ridge also favors dry weather for much of next week, but it`s possible we see widely scattered showers/storms, especially in Thu- Fri timeframe as cold front approaches from Great Lakes. && .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 18z TAF Update: Moderate confidence (60%) Main uncertainty is with timing of TS. First line moving through eastern MA at 17z will move offshore by 19-20z, then we are watching for a second line of TS to cross area between 20-24z ahead of cold front. Expect brief MVFR/IFR in any TS. Otherwise VFR ceilings should prevail through tonight as SW winds veer to W-NW and N overnight, except ceilings to lower to IFR around Cape Cod and Islands. Slow improvement Sat morning with VFR-MVFR ceilings gradually scattering out Sat afternoon as N winds increase to 10-20kt with gusts to 25kt near coast. KBOS TAF...Moderate confidence in TAF (60%). Best call on TS timing is now through 19z, then another possible round 22z-00z. KBDL TAF...Moderate confidence in TAF (60%). Best call on TS timing is 21-23z. Outlook /Sunday through Wednesday/... Sunday through Sunday Night: VFR. Monday: VFR. Breezy. Monday Night through Juneteenth: VFR. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Tonight: Steady light to moderate rain with embedded thunder possible. Winds shift WNW and decrease to 5-10 knots overnight. Seas 2-3 feet. Tomorrow: Rain tapers off in the morning with clearing conditions in the afternoon. Winds turn north and gust 15 to 20mph. Seas 2-4 feet. Tomorrow Night: Clear conditions and generally light winds. Seas around 2-4 feet. Outlook /Sunday through Wednesday/... Sunday: Winds less than 25 kt. Seas locally approaching 5 ft. Sunday Night through Monday: Winds less than 25 kt. Monday Night: Winds less than 25 kt. Slight chance of rain showers. Tuesday through Juneteenth: Winds less than 25 kt. && .CLIMATE... Daily Record High Temperatures... Tuesday, June 18th BOS - 94F (1929) BDL - 95F (1994) PVD - 94F (1929) ORH - 93F (1929) Wednesday, June 19th BOS - 96F (1923) BDL - 95F (1995) PVD - 94F (1923) ORH - 93F (1923) Thursday, June 20th BOS - 98F (1953) BDL - 97F (2012) PVD - 95F (1941) ORH - 93F (1953) Last Day of 100F (or greater) BOS - 100F (07/24/2022) BDL - 100F (07/21/2019) PVD - 100F (07/28/2020) ORH - 102F (07/04/1911) && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ230>237-251. Small Craft Advisory until 11 PM EDT this evening for ANZ250- 254. && $$ SYNOPSIS...KS/JWD NEAR TERM...KS SHORT TERM...KS LONG TERM...JWD AVIATION...JWD MARINE...KS/JWD CLIMATE...Dooley