Area Forecast Discussion
Issued by NWS Boston, MA
Issued by NWS Boston, MA
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590 FXUS61 KBOX 251436 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 1036 AM EDT Tue Jun 25 2024 .SYNOPSIS... Very warm, if not hot, conditions with comfortable humidity today. Increasing humidity levels Wednesday with the risk for showers and thunderstorms, and some could become strong. Drier and less humid to end the workweek, although summerlike warmth and humidity return by late this weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 1020 AM Update: Forecast in general seems on track with a very warm day ahead but one with tolerable levels of humidity. Surface ridge to our west over the Catskills in NY is expected to shift eastward thru midafternoon. That will result in a period of easing WNW winds toward a WSW/SW windshift by later in the day. In the intervening period of time around later-morning to early afternoon, the gradient slackens enough to open the door for a possible seabreeze near the coast, indications reflected in recent NAM-3km and HRRR surface wind guidance. It`s not really set ins tone but if we do seabreeze on the eastern MA and Narragansett Bay coastlines, it ultimately may be short-lived with prevailing synoptic SW gradient developing. Tried to better show this potential by incorporating some of the HRRR wind guidance into the wind grids for the early aftn. But all in all, pretty pleasant mid-summmer conditions for Tuesday. Previous discussion: Highlights * Quiet and mild conditions across southern New England today. Could be a bit breezy at times this afternoon. Increasing mid to high clouds late. Currently caught between a a trough over the Gulf of ME and a ridge building into the eastern Great Lakes. The ridge axis will build into New England today, while a decaying MCs rides in its wake into the eastern Great Lakes late today. High pressure builds over our region today. Dry and quiet weather anticipated across southern New England today. As that decaying MCs slides into the eastern Great Lakes we will see some increasing mid to high clouds, especially late this afternoon. Otherwise weather is quite nice today with plenty of sunshine. Could be a bit breezy as the boundary layer should be able to mix to roughly 700-800 hPa per Bufkit soundings. Given the NW to W flow for much of the day should see us mixing out the dew points a bit, so blended down from the default NBM due to downsloping. Have also bumped temps up to the 75th percentile of guidance to account for downsloping. Highs in the 80s for most, but will see some lower 90s across the Merrimack and CT River Valley. Should be fairly nice with dew points comfortably in the 50s. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... Highlights * Still fairly quiet tonight into early Wed. Though there could be a few decaying spot showers across the interior tonight. * Hot and muggy on Wed. Will have late day thunderstorms. Isolated severe risk possible with the main threats of damaging wind gusts and heavy downpours, which could lead to localized flooding. Pattern becomes quasi-zonal during this timeframe. The MCs/shortwave over the eastern Great Lakes will lift through New England tonight. A more substantial trough (and our next weather maker) will dig from the Northern Plains tonight into the western/central Great Lakes by mid Wed. The trough lifts into the eastern Great Lakes by late Wed. A warm front lifts into and through much of southern New England tonight. The trailing cold front slides in later on Wed. Next shot for potentially impactful weather comes later on Wed where we could have some isolated strong to severe storms. This is the main focus of the short term. Though will note that did put in slight chances of a few spotty showers tonight across the interior as the warm front is moving through. For most should be dry tonight, but with mid/high clouds overhead. Since previous update it appears that guidance continues the trend of bringing the cold front in slower. This generally keeps our weather dry for much of the day, but there is an increasing risk for showers/storms during the afternoon/evening. Will see instability values increasing to roughly a few hundred to 1500 J/kg across. Appears at this point that would be maximized across CT and portions of the interior. Will see deep shear in the 0-6 km layer increase to 30-40+ kts, which is more than sufficient for organized thunderstorm development. Some uncertainty on timing a potential EML as some pieces of guidance showing 6-8 degree mid level lapse rates overhead during the afternoon, while low level lapse rates are roughly 7-9 degrees. The big questions at this point are we are somewhat removed from the stronger upper forcing, mid level moisture may be lacking a bit and there could be a bit of a cap to break per Bufkit soundings. Though some pieces of guidance do bring in 1.5+ inch PWATs into the afternoon/early evening, but most showing more impacts for our area Wed Night. With this all said and taking into the account the ML guidance. There are signals for strong to perhaps damaging wind gusts along with heavy downpours, which if they fall over the wrong spots could produce localized flooding. Think at this point the latest SPC Marginal Risk for Severe Weather in Day 2 and WPC Marginal Risk for Excessive Rain is fine. The HREF does show some low probs with 3-hourly PMM of 3 hr QPF greater than 3 inches late on Wed across portions of western MA/CT. This is also the area where ML guidance (CSU ML and NCAR HRRR Neural Network) indicating greatest risk for stronger storms in our area. Stay tuned for future updates on this risk. Given the increasing S to SWly flow ahead of the cold front will see oppressive dew points spreading in as we get well into the 60s for much of the region. Will also be quite warm with temps ranging from the mid 80s to the mid 90s. Should see those warmest readings across the CT/Merrimack Valley. Though it will be muggy, we fall well short of Heat Advisory criteria at this time. Still will be a good idea to take typical summertime precautions of staying hydrated and cool. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Highlights: * Couple rounds of showers and thunderstorms during this portion of the forecast. * Expecting temperatures to fluctuate between near normal and above normal. * Becoming less humid late this week into Saturday, before briefly becoming very humid Sunday. Trending less humid early next week. Looking like our region will be contending with leftover convection Wednesday night into Thursday. Latest guidance communicated a mixed message. While there are some ingredients to support stronger thunderstorms, they may not all be in place at the proper time. For example, the peak mid level lapse rates and shear may not quite line up with the peak instability. Will need to monitor the details and adjust over the next day or so. Current thinking is the most likely outcome will be diminishing/weakening convection across most of southern New England as it moves east Wednesday night. The steeper than moist- adiabatic mid level lapse rates may sustain a few stronger thunderstorms past sunset. The cold front helping to trigger these showers and thunderstorms should still be somewhere across southern New England Thursday morning, thus still a lingering risk for some showers. These would be most likely across RI and eastern MA. Once this front finally moves offshore, we should be looking at less humid conditions arriving for Friday. Drier conditions should last until another cold front approaches from the west sometime Sunday. Still too early to pin down the details. In general terms though, thinking our region gets into a brief period of very warm and humid conditions, but not like the heat we had last week. It should certainly not last nearly as long. Expecting cooler and less humid air to arrive early next week. && .AVIATION /15Z TUESDAY THROUGH SATURDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 15z TAF Update: Today: High confidence, though closer to moderate on seabreeze potential. VFR, with increasing covg of mid/high clouds later in the day into tonight. NW winds around 10 kt to start are projected to slacken a bit late this morning into the early aftn, which could open the door for a possible seabreeze on both coasts around ~16-18z; still is somewhat uncertain if it develops but if it does, it would be be pretty short-lived with prevailing WSW/SW winds by late-aftn. Tonight...High confidence. VFR with mid to high clouds continuing to increase. Winds out of the SW at 5-15 kts. Could see some 15-25 kt gusts after 06Z with the highest speeds along the immediate south coast. Wednesday...High confidence in AM. Lowers to moderate for PM. VFR conditions are anticipated for much of the day. Confidence lowers to moderate during the afternoon/evening as a cold front triggers showers and thunderstorms. Not certain at this point on coverage and exact timing, but risk seems highest across CT into interior MA. If individual storm moves over terminal could see brief MVFR to IFR conditions. Not out of the question there are strong to damaging wind gusts if a stronger storm or two can develop. Winds out of the WSW/SW at 10-15 kts with gusts of 20-30 kts. KBOS TAF...High confidence in TAF, though moderate on sea-breeze development. VFR for much of the TAF period. WNW winds arounhd 10 kt to start, though may slacken enough in the 16-18z window to allow a potential seabreeze to develop in that period of time, but this isn`t set in stone and if it develops, would be short- lived. 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 /Wednesday Night through Saturday/... Wednesday Night: Mainly MVFR, with areas VFR possible. Breezy. SHRA likely, slight chance TSRA. Thursday: VFR. Chance SHRA. Thursday Night through Friday Night: VFR. Saturday: VFR. Breezy. Slight chance SHRA. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Have extended the Small Craft Advisory for the outer waters through Wed evening. Though seas/winds will fall below SCA conditions late today into this evening, they will redevelop tonight into Wed with a strong SWly low level jet sliding in. Hoisted Small Craft Advisory for the rest of the southern waters and Cape Cod Bay due to the strong SWly low level jet previously mentioned moving in late tonight into Wed. Today...High confidence. Winds shifting from the NW to the W/WSW as the day progresses. Winds will be increasing this afternoon into the evening to 10-15 kts with some 20-25 kt gusts. Seas diminishing to 2-4 ft. 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. Outlook /Wednesday Night through Saturday/... Wednesday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Rain showers likely, isolated thunderstorms. Thursday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers, isolated thunderstorms. Thursday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Friday through Saturday: Winds less than 25 kt. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 2 AM to 8 PM EDT Wednesday for ANZ231>237. Small Craft Advisory until 8 PM EDT Wednesday for ANZ254>256. && $$ SYNOPSIS...Belk/BL NEAR TERM...Belk/Loconto/BL SHORT TERM...BL LONG TERM...Belk AVIATION...Belk/Loconto/BL MARINE...Belk/BL