Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 182326 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 726 PM EDT Mon Mar 18 2024 .SYNOPSIS... Clear and cool tonight with blustery west winds. Gusty west winds again tomorrow with mainly dry conditions. Rain and snow shower chances overnight Wednesday as a moisture starved shortwave swings through. Anomolously dry conditions return Thursday and Friday before a potential precipitation maker this weekend; though the existence and the track of the low remains shrouded in uncertainty. && .NEAR TERM /THROUGH TUESDAY/...
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7 PM Update... No substantial changes made to the forecast with this update. Some minor changes so sky cover and the temperature trend after sunset were made to bring the forecast more in line with current observations. As mentioned by the previous forecaster, we are headed towards a seasonably chilly night with temps either side of freezing region wide. Previous Update... The core of the 500mb cold pool works in overhead with temperatures of -35 aloft. Strong CAA along with 925mb winds around 20-25 knots will continue to promote mixing overnight. Expecting the gusty winds from this afternoon to drop off, however, sustained winds will likely stay around 10-15 mph. Despite the non-ideal radiational cooling conditions, strong cold air advection will bring temps down below freezing for most, and mid to upper 20s across the high terrain in western MA.
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&& .SHORT TERM /TUESDAY NIGHT/... Tomorrow. The core of the cold pool moves quickly offshore bringing 500mb temps back towards -28C. With the mid to upper level warming, 700mb - 500mb lapse rates have become very meager around 4 to 6 C/km. This combined with a mid-level ridge building in should limit shower chances in the afternoon with peak diurnal heating. Still expecting diurnal cumulus to form again tomorrow afternoon. With the cold start and continued cold air advection, temperatures will only top the low to mid 40s. Winds turn gusty again tomorrow afternoon with westerly winds and a well mixed boundary layer. Peak wind gusts of 25-30mph is possible in the afternoon. Tomorrow night. Winds begin to turn southerly and diminish overnight as the pressure gradient briefly relaxes ahead of a surface low north of the Great Lakes. Skies look mostly cloudy due to mid/high level clouds out ahead of the surface low. Overnight lows look to drop near or below freezing again for most of the region with mid to upper 20s in the high terrain. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... * Light rain and snow showers Wednesday night associated with shortwave digging into the region * Dry Thursday and Friday * Increasing chances for more substantial precipitation this weekend, though uncertainty in track of low pressure remains high Persistent amplified trough across the western CONUS and broad but shallow trough across the east continues to dominate the synoptic pattern through the the period. Deep digging shortwave and associated low pressure dives into southern New England late Wednesday bringing the chance for rain and snow showers overnight into Thursday. Tranquil but seasonable weather to end the work week before shower chances increase next weekend. There is considerable uncertainty in the forecast beyond day 3, with all global guidance providing different solutions, as discussed in more detail below. Wednesday through Friday... Previously mentioned shortwave digs into southern New England increasing rain and snow chances late Wednesday evening into the overnight hours. While the shortwave appears at first to pack a punch, there will be limited moisture available to the forcing that will result in not much more than scattered showers/snow showers during the Wednesday night period as dewpoints drop from about a third of an inch to less than one quarter of an inch as flow shifts from the southwest to the west/west northwest overnight. Strong CAA will allow temperatures to drop below zero overnight into Thursday morning across the interior, which will allow for some novelty snowflakes that may yield a few tenths of an inch of accumulation across the terrain. Overall, ensembles hint at less than a tenth of an inch of QPF associated with this shortwave, so regardless of if any snow may accumulate, it will have little to no impact on the morning commute. Dry conditions work in for Thursday and Friday as PWATs drop to around -1.5 sigma of normal and PWATs continue to drop to around 0.1" by Friday. Thus, expecting a generally sunny period Thursday into early Friday ahead of our next potential precip maker. Seasonable to seasonably chilly temperatures expected. With very low dewpoints, potentially dropping below 0F by Friday, renewed fire weather concerns will develop on Thursday as gusty west winds redevelop; concerns will be less Friday as high pressure allows winds to go near calm for the better part of the daylight hours. Saturday and Sunday... There remains pretty considerable uncertainty between deterministic guidance regarding precipitation this weekend, with the 12Z GFS indicating a pretty robust inland runner will impact SNE on Saturday. The ECWMF and Canadian provide two completely different scenarios, with the ECMWF indicating scattered showers, and the CMC diagnosing a south of the benchmark low that will initiate showers across eastern MA and CT. For now, we continue to rely on the ensembles that paint a broad picture of rain chances Saturday and Saturday night with support of between a quarter and an inch of rain over the period. Depending on the existence and track of the low, there is a possibility of some mixed precipitation across the high terrain, but not placing much weight in that potential at this time as we continue to try to hone in on the potential for a storm. && .AVIATION /23Z MONDAY THROUGH SATURDAY/...
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Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High- greater than 60 percent. Tonight...High Confidence. VFR. Gusty winds drop off across the interior but remain sustained WNW at 5 to 15 knots. Gusty winds pick up over the Cape and the Islands overnight, with gusts to 20-25kt possible. Tuesday...High Confidence. VFR. WNW 10 to 15 knots with gusts of 20 to 25 knots. Another round of mid level CU with bases of 5-8 kft. Tuesday Night...High Confidence VFR. Decreasing winds turning south KBOS TAF...High confidence in TAF. VFR with gusty WNW winds KBDL TAF...High confidence in TAF. VFR with gusty west winds Outlook /Wednesday through Saturday/... Wednesday: VFR. Breezy. Chance RA. Wednesday Night: Mainly VFR, with local MVFR possible. Windy with gusts up to 35 kt. Slight chance RA, slight chance SN. Thursday: VFR. Strong winds with gusts up to 40 kt. Thursday Night: VFR. Strong winds with local gusts up to 40 kt. Friday: VFR. Breezy. Friday Night: Mainly VFR, with local MVFR possible. Breezy. Chance SN. Saturday: Mainly VFR, with local IFR possible. Windy with gusts up to 30 kt. Chance RA.
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&& .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Tonight: Moderate Confidence Marginal small craft criteria gusts overnight for both the inner and outer waters. Seas remain 2-4 feet. Tomorrow: Moderate Confidence Continued marginal small craft conditions with gusts near 25 knots esspically for the southern waters. Seas increase to 4-6 feet. Tomorrow night: High Confidence Winds turn SW overnight, but remain gusty below 25 knots. Seas of 3-5 feet. Outlook /Wednesday through Saturday/... Wednesday: Winds less than 25 kt. Areas of seas approaching 5 ft. Wednesday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas. Slight chance of rain. Thursday: Moderate risk for gale force winds with gusts up to 35 kt. Areas of rough seas. Thursday Night: Low risk for gale force winds with gusts up to 40 kt. Areas of rough seas. Friday: Winds less than 25 kt. Seas locally approaching 5 ft. Friday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas locally approaching 5 ft. Chance of rain, chance of snow. Saturday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Chance of rain. && .FIRE WEATHER... Tuesday. Minimum afternoon relative humidity values will drop into the 20 to 30 percent range Tuesday. West to northwest wind gusts of 20 to 25 mph with a few gusts up to 30 mph are anticipated by late morning/early afternoon Tuesday. In coordination with our fire weather partners, we have held off on issuing another SPS for elevated fire weather concerns, but may be reassessed overnight. Thursday... A cold front that will move through on Wednesday...will also set the stage for the potential of elevated fire weather concerns again on Thursday. Minimum relative humidity values of 20 to 40 percent are expected with WNW wind gusts of 30 to 40 mph. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 2 AM to 11 AM EDT Tuesday for ANZ231>235-237-251. Small Craft Advisory from 2 AM to 2 PM EDT Tuesday for ANZ250. Small Craft Advisory from 2 AM Tuesday to 8 AM EDT Wednesday for ANZ254>256. && $$ SYNOPSIS...KP/KS NEAR TERM...KP SHORT TERM...KP LONG TERM...KS AVIATION...KP/KS MARINE...KP/KS FIRE WEATHER...KP/KS

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