AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 1045 PM EDT Tue Jun 25 2024 .SYNOPSIS... Generally dry and quiet weather overnight, but there could be a few spotty showers across the interior. Hot and humid on Wednesday with a risk for showers and thunderstorms later in the afternoon into the evening. Some storms could turn strong Wednesday afternoon and evening. Drier weather for late in the week along with decreasing humidity levels. However we enter a warming trend with increasing humidity into the weekend, which will also increase our chances for showers and thunderstorms this weekend. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... 1030 PM Update... Have made a few changes in the latest update. Most notably is generally for the Wed timeframe where have hoisted a Rip Current Statement. Seas will be elevated and given our flow am anticipating a high risk for rip currents across south facing beaches. In addition, have bumped up to slight chances of precip across portions of the interior. Several CAMs depicting light precip sliding through roughly 09Z as a shortwave trough lifts through. Should be quite spotty given the high ceilings, but there are a few spots reporting light rain across Upstate NY at the time of this issuance. 650 PM update... High clouds are moving across the region with thicker mid level cloud cover to the west poised to move in tonight. Despite high res guidance insisting otherwise, this guidance is too bullish in showing any rain with this shield of cloud cover as it is (1) too high in the sky to generate any precipitation and (2) quite dry in the lowest few thousand feet AGL to support precip. So really just expecting an increase in midlevel cloud cover but looking for dry weather for the balance of the evening and overnight. It will however start to bring humidity levels back up some with dewpoints in the lower 60s by daybreak Wed, but still fairly tolerable overall. Sided lows toward the milder end of guidance since SW winds should stay up all night and the advancing canopy of midlevel cloud cover should mitigate much radiational cooling. Opted for lows in the mid 60s, with upper 60s/around 70 possible in the urban areas. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... The most active period of the forecast continues to be centered on a shortwave and associated cold front that will move from the Midwest to the Great Lakes and into the Northeast on Wednesday. At the mid levels we`ll see zonal flow become more meridional through the day on Wednesday as the neutrally tilted trough axis digs into NY/PA. The progression of the trough and cold front has been slowing down over the last few days and with it the severe threat decreasing for our area thanks to misalignment of the best forcing and axis of max instability/shear. CSU machine learning probs of severe winds are in line with this trend, continuing to back west where we expect the better chance of severe weather. The warm, moist air that is advected into SNE during the day on Wednesday behind a warm front will lead to much more humid conditions and destabilization, especially for areas south of a Hartford-Worcester-Boston line. This is because hi-res guidance is indicating a weak shortwave and cold front ahead of the main front which may keep dewpoints lower in northwest/north central MA as it stalls overhead. Convergence associated with this boundary may be the focus for a few isolated thunderstorms Wednesday evening ahead of the main line, but the bulk of the action should be overnight, between 8pm and 4am as the cold front crosses the region. Confidence in the placement of this boundary is low to moderate, however. Strengthening mid level flow in the 500-700 mb layer will increase the 0-6 km bulk shear to 30-40 kts in the afternoon/evening so if there is enough lift to kick off a storm in the 1500 J/kg CAPE environment there is potential a storm could be organized enough to become severe. However, odds are low, and by the time the best lift arrives overnight the instability will have waned substantially making severe weather unlikely. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Highlights: * Showers and a few t-storm lingering SE New Eng Thu AM, otherwise improving conditions * Dry and seasonable Fri with low humidity * Another round of scattered showers/t-storms Sat afternoon into Sun. Becoming rather humid Sun * Dry and less humid Mon & Tue Thursday and Friday... Expect improving conditions from west to east on Thu as deep moisture axis will be moving offshore. Still some timing differences with how quickly the moisture moves to the east but consensus of the deterministic and ensemble guidance suggests showers and a few t- storms lingering Thu morning across SE New Eng near the cold front, then should see at least partial sunshine developing from west to east as good mid level drying moves in. Mid level shortwave will be passing to the north Thu afternoon so can`t rule out a spot shower but better chance will be across northern New Eng closer to the cold pool aloft. Highs should reach into the 80s with decreasing humidity in the interior, but it will remain humid in the coastal plain as weak front hangs up near the coast. The mid level trough moves to the east Thu night with high pres building into New Eng through Fri. This will result in clear skies Thu night and abundant sunshine Friday. Highs Fri will be in the upper 70s to near 80, with coastal sea-breezes developing. Humidity levels will be rather low as dewpoints drop into the 40s and lower 50s. Saturday into Sunday... Next mid level trough will be moving east across the Gt Lakes and approaching New Eng Sun evening. Deeper moisture axis with high PWATs exceeding 2 inches will be moving into SNE, especially during the afternoon and Sat night. Risk for showers and a few t-storms will be increasing in the west Sat afternoon, but better chance will be Sat night into Sunday across entire region as forcing for ascent and instability increases ahead of the mid level trough along with the cold front moving into SNE Sun afternoon. Given rather high PWAT airmass, heavy rainfall will be the primary threat, but as surface instability increases on Sunday will have to watch the potential for a few strong storms. A lot will depend on timing of drier air moving in from the west which is uncertain at this time range. Temps will be close to seasonable norms but humidity levels will begin to increase late Sat-Sat night, peaking on Sunday with oppressive humidity possible as dewpoints potentially reach the low to mid 70s. Monday and Tuesday... Cold front moves offshore Sun night followed by high pres and much drier airmass Mon into Tue. Will set the stage for sunshine, seasonable temps and low humidity early next week. && .AVIATION /03Z WEDNESDAY THROUGH SUNDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 00z TAF Update: Tonight: High confidence. VFR, although with an increasing canopy of mid to high clouds (at/above 11kft) tonight. SW winds around 7-10 kt. Wednesday and Wednesday Night: High confidence in the morning, then becomes moderate for the afternoon/evening. VFR with SW winds around 10-12 kt (gusts 23-27 kt) during the morning to at least the early aftn. Scattered t-storms are still anticipated, better shot along/south of I-90, but the timing is uncertain. Storms could begin in the 18-21z timeframe but seem more likely after 21z and into the evening hours. Some storms could be strong, especially if they develop on the earlier end of that timing window. SW winds ease to around 5-10 kt for the evening while shifting a bit to W late. KBOS TAF...High confidence in TAF, though moderate on sea-breeze development. VFR for much of the TAF period. WNW winds around 10 kt to start, though may slacken enough in the 18-20z window for a possible seabreeze. By late-aftn, winds shift to SW/WSW around 10 kt. Possible TS after 21z Wed but timing is still uncertain. KBDL TAF...High confidence in TAF. VFR for most of the TAF period. Winds to become SW around 10 kt this aftn/tonight with increasing covg of mid/high clouds. Possible TS after 18z Wed though timing is still uncertain. Outlook /Thursday through Sunday/... Friday through Friday Night: VFR. Saturday: VFR. Breezy. Chance SHRA. Saturday Night: MVFR/IFR conditions possible. Breezy. SHRA likely, chance TSRA. Sunday: Mainly MVFR, with local IFR possible. Breezy. SHRA likely, chance TSRA. Sunday Night: VFR. Breezy. Slight chance SHRA. Monday: && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Small Craft Advisories have been extended for the most of the southern waters through Wed night. Though seas/winds will fall below SCA conditions this evening, they will redevelop tonight into Wed with a strong SWly low level jet sliding in. Tonight...High confidence. Increasing SW to SSW winds with gusts of 20-30 kts. Seas building 3-6 ft across the southern and eastern outer waters. Wednesday...High confidence. Winds remain out of the SW/SSW at 15-25 kts with gusts of 20-30 kts. Seas 4-6 ft across the southern waters and eastern outer waters. Scattered thunderstorms could spread into the waters late in the afternoon/evening. Wednesday night...High confidence. Winds SW 15-25 kts with gusts of 20-30 kts. Seas 5-7 ft. Scattered showers and thunderstorms continue into the morning. Outlook /Thursday through Sunday/... 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: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Chance of rain showers, slight chance of thunderstorms. Sunday: Low risk for Small Craft Advisory winds with gusts up to 20 kt. Seas up to 5 ft. Rain showers likely, chance of thunderstorms. Sunday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. Monday: Winds less than 25 kt. Seas locally approaching 5 ft. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...High Risk for Rip Currents from 6 AM EDT Wednesday through Wednesday evening for MAZ020>024. RI...High Risk for Rip Currents from 6 AM EDT Wednesday through Wednesday evening for RIZ006>008. MARINE...Small Craft Advisory until 8 PM EDT Wednesday for ANZ231>234. Small Craft Advisory until 8 AM EDT Thursday for ANZ235-237- 254>256. Small Craft Advisory from 2 AM to 8 PM EDT Wednesday for ANZ236. && $$