Area Forecast Discussion

286 FXUS61 KBOX 201737 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 137 PM EDT Tue May 20 2025 .SYNOPSIS... Cloudy with unseasonably cool high temperatures for the remainder of the work week that will run 10 to 20 degrees below normal! A late season Nor`eater likely brings a cold windswept heavy rain to the region late Wednesday into early Friday. The brunt of this storm appears to be Thursday, when wind gusts of 40-50+ mph will be possible along the coast with pockets of minor coastal flooding also possible. The soaking rain will likely come to an end Friday morning, but a few showers will remain possible at times through the holiday weekend. Temperatures will slowly moderate, but still remain below normal into this weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Key Messages: * Some peeks of sun early in western New England, but it`s a continued overcast day for most of Southern New England. * Sprinkles or patchy drizzle as onshore flow increases this afternoon, though most areas are dry. * Highs low 60s western New England, and in the mid 50s for most of eastern MA and RI. Details: By late-May standards, it`s a really chilly early morning! Current temps are in the mid 40s to around 50, with air temps being kept up by a blanket of overcast, along with northwest winds running around 10-15 mph with gusts to 25 mph. Wind chills in interior Southern New England have been into the low to mid 30s too. Just underscores how chilly it is out there, now only a few days away from Memorial Day Weekend. The main synoptic features really haven`t changed much over the last 24 hours, with a well- developed upper level low located near Nova Scotia, making little eastward progress amid a blocky pattern in the North Atlantic. Maritime-polar origin moisture from Atlantic Canada continues to be advected in from the northeast, which is contributing to the overcast cloud cover. A ridge of high pressure over NY early this morning should move into western New England this morning, which will help in easing northerly winds to around 10 mph, and should allow for some sun and comparatively milder temperatures in western MA and Tolland/Hartford Counties in CT (highs in the low 60s). Eventually here, overcast rebuilds in but that should hold off until late this afternoon or even early evening. For eastern/central MA and RI, it`s more of a question mark how much (if any?) diurnal warming we can generate today. The moisture associated with this ongoing overcast is somewhat shallow so it could be prone to some peeks of sun, but that moist layer becomes a little deeper per BUFKIT cross sections as we move into late morning to afternoon. Winds will also be turning northeasterly around 5-10 mph in central and eastern MA and RI. Some of the model QPF guidance shows "speckles" coming in as the moist onshore flow increases this afternoon, so there could be some sprinkles or patchy drizzle then, although the vast majority of time will be dry. This is not a scenario which leads to much warming. Leaned toward maintaining overcast and I`ve built highs off the hourly raw guidance temps, which only brings highs in the mid 50s. It`s not as cold as the NAM guidance, but it`s also on the colder end of forecast guidance. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... Key Messages: * Overcast, periods of drizzle or sprinkles and strengthening northeast winds tonight and continuing into Wednesday. * Anomalously cold high temperatures Wednesday in the low to mid 50s, which will feel even colder with northeast breezes. Normal highs in the upper 60s to low 70s. Details: Conditions won`t really change very much through this period, as a strong sfc ridge of high pressure builds southward into Wed. Model thermal fields indicate a cold-air damming type look, with 925 mb temps dropping to an unseasonably cold +2 to +4C! The sfc ridge will also keep the leading edge of steadier rains associated with a rather strong late- season Nor`easter suppressed to the northern mid- Atlantic states thru Wed aftn. Expect onshore NE flow and overcast conditions to continue. There could be some patchy drizzle or very light rain showers that should make greater inroads into interior Southern New England into early Wed, but the vast majority of the time is dry. NE winds start off at relatively modest levels through tonight (around 5-10 mph), but then becomes more of a moderate NE breeze into Wed with speeds around 10-15 mph and some gusts to 20 mph especially near the coast. The story is the unseasonably cold temperatures, especially with regard to the Wednesday highs. There won`t be much change to temperatures tonight, with lows in the mid to upper 40s. The cold advection, overcast and increasing NE breezes on Wednesday will mean highs also won`t rise much if at all, especially near the coast. The CT Valley has the best chance at seeing highs Wed into the middle/upper 50s. But the majority of Southern New England otherwise should stay in the lower 50s. I did take a peek at daily record lowest maxes and we`re not close to those but it will nonetheless feel quite chilly. FWIW...with a high temp in Boston of 52 degrees, Boston has experienced a high temp of 52 degrees or colder on May 21st 9 times in its period of record, most recently in 1990. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Key Messages... * Unseasonably cool for the remainder of this week, with some improvement this weekend into Memorial Day * Nor`easter will bring a cold, windswept rain late Wed into early Fri, with Thu afternoon temps in the mid 40s to lower 50s * ENE wind gusts of 40-50+ mph possible along the coast Thu, with perhaps some pockets of minor coastal flooding during high tide * The widespread rain comes to an end Fri morning, but a few showers will remain possible at times for this holiday weekend Details... Not much change to the idea of a widespread rainfall arriving Wednesday night and continuing into at least part of Friday. While the guidance has started to come into better agreement with the track and overall timing, it`s still a bit early to set this forecast in stone. Latest guidance consensus still favors a track just inside the 40N/70W benchmark, although there remained some guidance, like the global GEM, that are hinting at a more offshore track. Rainfall totals between 1-2 inches is still possible, but not a guarantee. Latest NationalBlend probabilities for 48-hour rainfall ending 8 AM Friday in excess of 1 inch was only about 35-55% across southern New England. The highest probabilities were in the Worcester Hills, where some upslope could enhance rainfall. Another concern from this storm will be strong winds as this low pressure passes bu our region. The latest NationalBlend probabilities for 24-hour max wind gusts in excess of 40 mph ending 2 AM Friday were only 40-60%. Will keep an eye on this as the track will be critical. Should we achieve better mixing, peak wind gusts could approach 50 mph. With leaves on the trees, there may be a little more impact than a similar storm during the winter. Lastly, while astronomical tides are not that high, the potential exists for 1.5 to 2.5 foot storm surge. If this occurs, we may see some minor coastal flooding along the eastern MA coast onto Nantucket during the Thu high tide cycle depending on specific timing and the magnitude of the winds/wave heights. This low pressure system will lift off into the Canadian Maritimes Fri into this holiday weekend. This will bring an end to the threat for the widespread rain Fri morning. However, a deep upper level anomalous trough will be slow to depart. This will bring us the risk of a few showers at times through this weekend, but it will not be a washout. Below normal temperatures expected into late this week. High temperatures only anticipated to be a few degrees higher than our normal low temperatures for late May. We should start to warm up more substantially later this weekend, but perhaps not approach normal temperatures until Sunday into Monday. && .AVIATION /18Z TUESDAY THROUGH SATURDAY/... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 18z TAF Update: This afternoon: High confidence in trends, moderate on timing. SCT-OVC VFR bases for most terminals, with NW/N winds around 10 kt. Ceilings then deteriorate to MVFR soonest in northeast MA and then gradually spreading southwest. This will also occur with a windshift to NE with speeds 5-10 kt. Tonight and Wednesday: High confidence. Widespread MVFR cloud bases with little change. NE winds around 5-10 kt tonight, which then increase to around 10-15 kt with gusts to 25 kt. Wednesday Night: Moderate confidence. IFR with increasing rain chances as heavier precipitation moves in from the southwest. E/ENE winds 10-20 kts, increasing toward 12Z. BOS TAF...High Confidence in TAF. BDL TAF...High Confidence in TAF. Outlook /Thursday through Saturday/... Thursday: Mainly MVFR, with areas IFR possible. Windy with areas of gusts up to 30 kt. RA. Thursday Night: MVFR/IFR conditions possible. Breezy. RA. Friday: MVFR/IFR conditions possible. Breezy. Chance RA, chance SHRA. Friday Night: Mainly VFR, with local IFR possible. Chance SHRA. Saturday: Mainly VFR, with areas MVFR possible. Chance SHRA. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Today Through Wednesday: High confidence. NW winds around 20-25 kt early today decrease into early this morning, then become NE late morning to afternoon. NE winds 5-10 kt this afternoon and tonight, increasing to 10-15 kt with gusts 20-25 kt Wed. Seas may still be near 5 ft in southeast waters today through Wed. Outlook /Wednesday Night through Saturday/... Wednesday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Chance of rain. Thursday: Strong winds with gusts up to 30 kt. Rough seas up to 12 ft. Rain, isolated thunderstorms. Thursday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 13 ft. Rain likely. Friday: Winds less than 25 kt. Rough seas up to 13 ft. Chance of rain, slight chance of rain showers. Friday Night: Winds less than 25 kt. Local rough seas. Slight chance of rain showers. Saturday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Gale Watch from Thursday morning through late Thursday night for ANZ230-236. Gale Watch from late Wednesday night through late Thursday night for ANZ231>235-237-254>256. Small Craft Advisory until 8 AM EDT Wednesday for ANZ250-254- 255. Gale Watch from late Wednesday night through late Thursday night for ANZ250-251. && $$ SYNOPSIS...Belk/Loconto NEAR TERM...Loconto SHORT TERM...Loconto LONG TERM...Belk AVIATION...Frank/BW MARINE...Belk/Loconto NWS BOX Office Area Forecast Discussion