Area Forecast Discussion
Issued by NWS Boston, MA
Issued by NWS Boston, MA
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160 FXUS61 KBOX 040551 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 151 AM EDT Tue Jun 4 2024 .SYNOPSIS... A back door cold front will push south from Maine and usher in cooler weather tonight and Tuesday, especially near the coast. Our weather pattern then changes to a cloudy and more unsettled outlook by Thursday and into the weekend. Thursday looks to be the wettest day with showers and storms capable of localized downpours, with more hit or miss showers or thunderstorms for Friday into the weekend. Temperatures trend a little cooler than normal. && .NEAR TERM /UNTIL 7 AM THIS MORNING/... 10 PM update... Weak backdoor front pushing west across SNE and will move through CT valley overnight as surface ridging builds south from Maine. Light E winds will develop after the front moves through. We have some mid level clouds developing across eastern MA, while area of stratus over the ocean east of Cape Cod is expanding west. As the land and marine boundary layer cools off, these lower clouds will eventually overspread Cape Cod and expand west into eastern MA and RI overnight. It still is a bit unclear how far west this stratus makes it; it could bleed over into central MA and eastern CT at worst but likely not any further given the weaker lower level flow. Radiational cooling has resulted in temps dropping into the 50s across SE MA. Lows will range from lower 50s over SE MA and Cape/Islands to upper 50s to around 60 in the CT valley. && .SHORT TERM /7 AM THIS MORNING THROUGH 6 PM WEDNESDAY/... Fairly quiet weather as upper ridge remains west of New England and weak high pressure builds in at surface. Low clouds and patchy fog should lift quickly as moisture will be fairly shallow and high June sun angle goes to work. It should take the longest near Cape Cod and Islands where this marine layer will be deepest, but even these areas should clear out by late morning. Not seeing a lot of good signals for afternoon convection as what instability there is stays to our west, or at most is tied to higher terrain areas near Berkshires. Low and mid level lapse rates are not overly impressive and we remain under large scale subsidence on eastern side of ridge. Nonetheless, we can`t rule out a spot shower/storm Tue afternoon near Berkshires. Onshore winds will keep highs in 60s/lower 70s near immediate coast but inland areas should have no problem warming well into 80s. Airmass remains fairly dry which will help temperatures fall back into 50s Tue night. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Highlights: * Pattern change toward wetter conditions and temps trending somewhat cooler than normal Thurs thru the weekend. * Wettest day looks to be Thurs with local downpours possible. More hit or miss showers and t-storms for Fri into the weekend. Possible isolated hydro issues but significant flooding not expected. Details: Wednesday: Wed projects as the final generally dry day for Southern New England as we head into a cloudy and soggy weather pattern for late week into the weekend. 500 mb heights weaken slightly and though that could support a low chance (under 20% PoP) for an afternoon shower or t-shower over northern/western MA, dry weather should result for the vast majority of the time. Increasing cloud cover for Wed night along with rising humidity levels (dewpoints into the lower-mid 60s), with a rise in PoP toward daybreak into the solid Chance range, although the bulk of the rains arrive on Thurs. As dewpoints rise, we could also see a risk for marine fog develop over the waters. Wed also to be the warmest day under full sun, with highs well into the 70s to lower-mid 80s, with lower 70s along the south coast. Lows in the low to mid 60s. Thursday through the Weekend: Heading into a period of unsettled weather with several opportunities for showers and t-storms starting Thurs into potentially a good portion of the weekend. An upper level closed low over the Gt Lakes slowly builds into the Northeast for Thurs into Fri, and remains in place through at least Sat and potentially into Sunday as well. Though this expected rain should be welcome news to wash out the clouds of pollen around our area of late, although far from ideal weather for outdoor plans. Wettest period still looks to be on Thurs; PWAT values of 1.2 to 1.4 inches along with warm cloud depths between 10000-11000 ft favor localized downpours in showers and embedded t-storms. Severe weather potential appears to be low at this time with limited instability and a general lack of stronger surface heating through abundant cloud cover. From a hydro perspective, we can`t rule out isolated issues but probably not anything more than that given the progressive nature to the rain, and we`ve also been pretty dry of late. While the international guidance lends support to this solution, did note the past couple cycles (06/12z) of the deterministic GFS are cloudy but depict a dry weather pattern. However there`s a good majority of GFS ensemble members which show rain for Thurs so we view this as a dry outlier outcome as of now. NBM probs of 24 hr rain for Thurs have increased into the the moderate to high (40-60%) range for totals at or above 0.5 inches for much of the area, and indicate moderate (30-40%) probs for rain totals at or over 1 inch in portions of RI and SE MA. PoPs were raised into the high Likely range and Categorical PoP could be warranted in later updates. For Fri into the weekend, the upper level low parks itself over or in the vicinity of Southern New England. This will maintain cloudier/unsettled weather conditions with more periodic/hit-or-miss showers or t-storms. Felt NBM based PoPs in the 30-50% range were a little too high and opted to following a more diurnal approach Fri into Sunday, with higher PoP during the daytime and lower (20-25%) at night. Here too, severe weather potential looks on the low side. Temperatures trend a little cooler than normal for this period, with cloudy weather and periods of rain, along with 850 mb temps in the upper single digits to low teens C range. Highs mainly in the lower to middle 70s and lows in the upper 50s to mid 60s. Though it will be cooler, humidity levels still looks somewhat elevated. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 06z TAFs: Through 12z... Stratus not expected to be as widespread with areas of IFR mainly confined to outer Cape and ACK 08-12z. Otherwise VFR. Today...High confidence. VFR, with sct-bkn cigs 5-7k ft developing in the interior. Low risk for an isolated afternoon shower or t-storm in the Berkshires. Coastal sea-breezes developing, otherwise SE-S wind 5-10 kt. Tonight and Wednesday...Overall high confidence, but lower confidence in stratus development. VFR, but patchy stratus may develop overnight into early Wed over Cape/Islands and possibly the south coast. Light winds tonight, then SW 10-20 kt developing Wed. KBOS TAF...High confidence. Best chance of lower cigs will be across Cape Cod so did not include in TAF. KBDL TAF...High confidence. Outlook /Wednesday Night through Saturday/... Wednesday Night: Mainly VFR, with local IFR possible. Chance SHRA. Thursday: Mainly MVFR, with local IFR possible. Breezy. SHRA likely, isolated TSRA. Thursday Night: MVFR/IFR conditions possible. Chance SHRA, isolated TSRA. Friday and Saturday: Mainly VFR, with areas MVFR possible. Chance SHRA, isolated TSRA. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Confidence: * High (80%) through Tue night. No marine headlines anticipated on MA/RI coastal waters with overall light winds and calm seas. * In the longer range, confidence is high (60%) in upcoming pattern which could bring building seas near 5 ft offshore by the end of the week. Backdoor front drops south across waters this evening and dissipates south of New England tonight, followed by weak high pressure Tue. This maintains E/NE winds which remain light enough to maintain fairly calm seas. Should see patchy fog later tonight into Tue morning with local restrictions in visibility to 1-3 miles. Winds veer to S/SW Tue as high moves offshore but weak enough to allow for coastal sea breezes again by afternoon. Outlook /Wednesday Night through Saturday/... Wednesday: Winds less than 25 kt. Wednesday Night: Winds less than 25 kt. Chance of rain showers. Thursday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers, isolated thunderstorms. Thursday Night through Saturday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Loconto NEAR TERM...KJC/Loconto SHORT TERM...JWD LONG TERM...Loconto AVIATION...KJC/Loconto MARINE...Loconto/JWD