Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 171828 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 228 PM EDT Sun Mar 17 2024 .SYNOPSIS... A cold front will bring scattered showers to the region this morning with partial sunshine & breezy conditions by afternoon. A few additional showers are possible this afternoon...but the vast majority of the time will feature dry weather. Temperatures trending near to cooler than seasonable for much of the upcoming week. Isolated showers possible Monday through Wednesday along with gusty winds. Drier on Thursday and Friday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 10 AM Update... The last round of showers showers over SE MA will be moving off shore in the next hour with only lingering showers behind the front. Already seeing some sunshine break out across western MA and CT. This clearing will spread east this morning which could set off a couple of isolated convective showers this afternoon. Confidence in this occurring is low, so lowered POP`s below 25% for this afternoon. 350 AM Update... * Scattered showers this morning * Partly sunny & breezy this afternoon with a few showers * High temperatures in the middle 50s to the lower 60s Approaching shortwave trough was inducing a modest southwest LLJ early this morning. This has allowed an area of low clouds to overspread much of RI/SE MA. In addition...we expect to see scattered showers move in from the west toward daybreak as the forcing for ascent increases. These showers should be relatively short-lived in a given location and rainfall amounts will be on the light side. Behind the morning shortwave...expect to see partial sunshine develop and it also will become breezy. Enough diurnal heating will trigger some marginal instability...which will allow for a few more showers this afternoon. Not a washout though and most of the day will be dry in a given location. Given the mild start and good mixing...expect to see another day with above normal temperatures. Highs should be in the middle 50s to the lower 60s with the mildest of those readings in the CT/RI and portions of southeast MA. A west breeze of 20 to 30 mph will also develop during the afternoon with deep mixing indicated by Bufkit soundings. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... Key Points... * Gradually diminishing winds tonight with lows mainly in the 30s * Partly sunny & breezy Mon with highs in the upper 40s to lower 50s Details... Tonight... Low pressure over Quebec moves eastward into the Canadian Maritimes tonight. This will generate a westerly flow of cooler air into southern New England. Westerly winds should diminish with the loss of daytime heating and skies will become mostly clear. Winds will probably not decouple in most locations given modest winds off the deck...so expect overnight low temps mainly in the 30s. Some upper 20s are possible across the normally coldest spots of western MA. Monday... Low pressure over the Canadian Maritimes will generate a cooler westerly flow of air across the region on Mon compared to today. However...we should still have very deep mixing and with 925T near or just above 0C...expect high temps to end up still a bit above normal especially in pre-greenup. Thinking highs will mainly be in the upper 40s to the lower 50s under partial sunshine along with scattered diurnal CU. Good mixing should yield westerly wind gusts of 20 to 30 mph. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... Highlights * Dry for most on Tue with temps trending near to below normal. Isolated showers during the day. Not out of the question there is some graupel in more vigorous showers. * A quick moving front/system slides through on Wed bringing scattered showers. * Drier on Thu and perhaps through much of Fri. Could see a return to more unsettled weather late Fri into Sat. Lots of uncertainty at this point. Monday Night through Tuesday... A shortwave ridge builds into New England Mon Night, but will quickly build into the Gulf of Maine by early Tue. A shortwave trough digs into New England from Ontario during the day. A surface trough rotates through on Tue. Temperatures will be trending cooler on Tue with a fair amount of cloudiness. This is a result of the anomalously cold airmass overhead at 500 hPa. Trending cooler on Tue with more cloudiness. Should have a better shot for isolated showers across the interior. An anomalously cold airmass will be overhead at 500 hPa. The NAEFS/EPS situational awareness tables continue to indicate temps -2 to -2.5 STD below model climo. Should see those 500 hPa temps range from -25 to -35 degrees Celsius. This combined with the shortwave and diurnal heating will bring a fair amount of CU. On top of this think there could be isolated shower activity across the interior. Guidance continues to keep us dry, but have seen this set up in the past. For now have capped our chances at slight given the limited moisture. Could actually see spots where there is graupel. On top of this the other change made was to lower dew points/RH values. Looking like another day where the boundary layer will be well mixed per GFS/NAM Bufkit soundings. Shouldn`t be too difficult to mix down the -15 to -25 degree dew points at the top of the PBL. For now went with minimum RH values toward the 10th percentile of guidance. May actually need to be lowered in future updates as we tend be a bit drier than guidance indicates in pre-greenup. Wednesday through Thursday... Flow remaining somewhat cyclonic through this timeframe. A fast moving shortwave trough slides through the Great Lakes and New England on Wed. The trough lifts into the Gulf of Maine by early Thu. A ridge axis will begin building over the Low/Mid Mississippi River Valley early on Thu. This builds into the TN Valley by late Thu. A frontal system swings through on Wed. High pressure begins nudging in on on Thu. Confidence increasing in how things evolve on Wed with the frontal system sliding through. At this point the big question is will the shower activity be a bit limited due to the little moisture in place. At this point PWATs are roughly -0.5 to -1 STD below model climo. Deterministic guidance shows values ranging from 0.2 to 0.4 inches with W to WSW flow. The W to WSW flow could aid in drying things out a bit more and should have good mixing within the PBL per model soundings. The other potential hang up is the best upper forcing is more to our north. For now think that slight chance to chances of precip are fine with the best opportunity for showers north of the MA Turnpike. For most will be warm enough for rain showers, but the higher elevations could see snow showers. There are some low probs (10-30 percent chance) of 24 hr snow AOA 1 inch per the GEFS/EPS guidance. Temps may actually near to slightly milder than normal with the WSW/SW flow. Appearing drier on Thu as high pressure nudges into southern New England. Though will be quite breezy with a tightened pressure gradient in place over the region. Temps trend near to cooler than normal with highs in the low/mid 40s. Friday and Saturday... Still looking like it will be dry and quiet for much of Fri as a ridge builds into the Mid Atlantic. Our next trough lifts into the Carolinas/VA late Fri and perhaps into our region on Sat. Should see those precipitation chances increasing later on Fri into Sat, which is supported by the latest GEPS/GEFS guidance. This is actually not the case with the EPS, which is much more muted with the probs of 0.1 inches over a 24 hr period. Given there are significant differences at this point have stuck with the NBM. Temperatures still cooler than seasonable through this period. && .AVIATION /19Z SUNDAY THROUGH THURSDAY/...
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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. W winds diminishing to 5-10 knots higher near the coasts. Monday...High Confidence. VFR. W winds increasing to between 10 and 15 knots. Should see those gusts picking up to 20-25 kts by roughly 14-18Z Monday Night: VFR. West winds diminish to 10-15 knots . KBOS TAF...High confidence in TAF. VFR, gusty WNW winds at 20-25 knots. KBDL TAF...High confidence in TAF. VFR, gusty WNW winds at 15-20 knots. Outlook /Monday Night through Thursday/... Monday Night: VFR. Breezy. Tuesday: VFR. Breezy. Isolated SHRA. Tuesday Night: VFR. Breezy. Wednesday: VFR. Breezy. Slight chance SHRA. Wednesday Night: VFR. Windy with gusts up to 30 kt. Slight chance SHRA, slight chance SHSN. Thursday: VFR. Windy with gusts up to 30 kt.
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&& .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Today through Monday...High Confidence. Low pressure moves across Quebec today and into the Canadian Maritimes tonight and Monday. This will generate a westerly flow of a colder air aloft into our region into Monday with good mixing over the waters. Winds should shift from the S to the W by this afternoon with gusts between 20 and 30 knots today. Small craft headlines are posted for all our waters. These wind gusts should diminish a bit tonight...but increase again on Monday with diurnal heating/mixing. While we extended the small craft headlines for the outer-waters through Monday...we did not do that for the sounds/bays as the winds will temporarily die down tonight. But we may need additional Headlines for those waters on Monday. Outlook /Monday Night through Thursday/... Monday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Tuesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Tuesday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Wednesday: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers. Wednesday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas. Slight chance of rain showers. Thursday: Low risk for gale force winds with gusts up to 30 kt. Local rough seas. && .FIRE WEATHER... Monday and Tuesday... There are some Fire Weather concerns for Monday and Tuesday. We expect afternoon westerly wind gusts of 20 to 30 mph with minimum relative humidity values between 20 and 40 percent. Would not be surprised if RH values ended up on the lower side of those numbers too. Given we are in pre-greenup something will have to watch. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 5 PM EDT this afternoon for ANZ230>237-251. Small Craft Advisory until 8 PM EDT Monday for ANZ250-254>256. && $$ SYNOPSIS...Frank/BL NEAR TERM...Frank/KP SHORT TERM...Frank LONG TERM...BL AVIATION...KP MARINE...Frank/BL FIRE WEATHER...Frank

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