Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 180727 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 327 AM EDT Mon Mar 18 2024 .SYNOPSIS...
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Seasonable temperatures for much of the work week with mainly dry weather except for a few rain/snow showers possible sometime Wednesday and/or Wednesday night. A period of unsettled weather is also possible sometime this weekend...but confidence is low at this time.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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320 AM Update... * Partly sunny & breezy today with highs in the upper 40s/lower 50s An approaching shortwave has backed the upper level flow a bit early this morning. This has resulted in mid-high level cloudiness overspreading much of the region. There is even the risk for a brief sprinkle or two early this morning towards the southeast New England coast...but not worth inserting into the forecast at this time. We do expect this band of mid-high level cloudiness to push east of the region later this morning. This should result in skies becoming partly sunny...but colder temps aloft moving in from the west will allow a scattered to broken deck of CU to develop later today. 925T around 0C/+1C with good mixing on westerly flow aloft should allow for high temps to top off mainly in the upper 40s and lower 50s. So it will be cooler than what we saw over the weekend...but still a bit above normal for this time of year. Bufkit soundings indicate westerly wind gusts of 20 to 25 mph by late morning/early afternoon with a few gusts up to 30 mph possible.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/...
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Key Points... * Dry/Seasonable tonight with lows in the upper 20s/lower 30s * Partly sunny/breezy Tue with highs mainly in the middle-upper 40s Details... Tonight... Low pressure over the Canadian Maritimes will generate a seasonable westerly flow of air into southern New England. Although the winds will likely not decouple in most places given a modest WNW low level jet. Nonetheless...850T dropping to between -8C and -10C will result in overnight low temps mainly in the upper 20s to the lower 30s. Tuesday... Upper trough across the northeast will generate a cool west to northwest flow of air aloft again on Tuesday. Cyclonic flow along with the cold pool aloft should allow for a scattered to broken deck of diurnal CU to develop again...yielding partly sunny skies later in the day. Temperatures a few degrees colder aloft than today...so expect Tue highs mainly in the middle to upper 40s. Bufkit indicates westerly wind gusts of 20 to 25 mph with a few gusts up to 30 mph.
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&& .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
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Highlights * A quick moving front/system slides through Wed/Wed Night bringing light showers. Temps warmer than normal. * Drier on Thu/Fri, but cooler and breezy. * Could turn unsettled this weekend, but lots of uncertainty on how things evolve. Tuesday Night through Wednesday Night... Cyclonic flow in place through this period. A fast moving shortwave trough digs from the western/central Great Lakes early on Wed into the eastern Great Lakes by late in the day. The shortwave lifts into the Gulf of Maine/northern New England Wed Night. A weak warm front lifts into/through southern New England Tue Night into Wed. The trailing cold front pushes through late Wed/Wed Night. Still a tricky forecast in how wet it will be across the region, especially earlier in the day. Due to this have generally stuck with the NBM as it is mostly reasonable, but did bump up our PoPs a bit as the stronger cold front slides through later on Wed into Wed Night. The mitigating factors through this period for precip is we are fairly dry with PWATs between 0.2-0.4 inches, which is between the 25th to avg for this time of year per SPC sounding climo for CHH. On top of this we are well mixed within the PBL per Bufkit soundings, which should help mix down some drier dew points. For now have kept more spotty showers before having better chances of precip later in the day. High temps in the 40s across the higher terrain to the upper 40s to low 50s elsewhere. With the cold front and later in the day there is the better shot for more widespread showers. For most this will be rain, but the higher terrain has the potential for snow showers. There could even be a bit of accumulation. Not out of the question lower elevations see snow before things end. Right now there is discrepancy on how much QPF we can ring out in this dry airmass. Given the uncertainty stuck with the NBM. Best shot is across far northwestern MA for AOA 1 inch of snow over 24 hrs of mod to high (50-70+ percent chance) and even some low probs (10-30 percent) for 3+ inches per the GEFS/EPS guidance. The GEPS is essentially nil for the 3+ inch probs. Further east along the Route 2 corridor probs are low to mod (10-40 percent chance). Stay tuned for future updates. Anticipating it to be breezy on Wed, but especially Wed Night in wake of the cold front. Will have W to WNW flow with the LLJ increasing to 25-35 kts. Stuck with the NBM for now as its higher winds/gusts are reasonable given the cold air advection and LLJ in place. Thursday through Friday... Flow somewhat cyclonic during this timeframe. A ridge axis will be over the Low/Mid Mississippi River Valley early on Thu. This builds into the TN Valley by late Thu. The ridge axis builds into the Carolinas/Mid Atlantic on Fri, but flattens out a bit. High pressure begins to nudge in from the OH Valley/Great Lakes on Thu and just offshore of the Mid Atlantic on Fri. Dry and quiet weather expected through this period as high pressure nudges in. Anticipating gusty winds across southern New England on Thu. Will be fairly well mixed with WNW to NW flow under cold air advection and 925 hPa winds of 25-35 kts. Shouldn`t be terribly difficult to mix down given the environment. So should have gusts of 35-40 mph through much of the day. Given the well mixed boundary layer it won`t be tough to bring down -20 to -30 degree dew points near the top of the PBL. Due to this lowered dew points/RH values to the 15th percentile of guidance for now. Did bump up temps to the 75th percentile of guidance given the setup. Highs on Thu will be right around normal for this time of year in the 40s. Should still be a bit breezy on Fri, but the high will relax the pressure gradient as it builds closer to our region. Temperatures still right around seasonable levels. This Weekend... Considerable uncertainty for this upcoming weekend. A trough will be located somewhere over the Southeastern US late on Fri. This lifts northeastward toward our region on Sat and perhaps Sun depending on how things evolve. Lot of uncertainty in if a coastal system slides up our way. Given the spread in guidance have stuck with the NBM for now for this timeframe. Appears that it could be wet if the trough lifts up into our area. There are some indications that the trough cuts off to our south/southeast, which would keep us dry. At this point probs are moderate (30-70 percent) of 24 hr QPF on both days AOA 0.1 inches. There are low probs of (10-30 percent) of 1+ inch of QPF with the risk being highlighted over RI/SE MA. Can see the uncertainty quite clearly via the large spread in MSLP low pressure center tracks per the EPS/GEFS/GEPS. Temps still near to perhaps slightly cooler than seasonable.
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&& .AVIATION /07Z MONDAY THROUGH FRIDAY/...
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Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High- greater than 60 percent. 06z TAF Update... Today...High Confidence. VFR. W winds increasing to 10 to 15 knots with gusts of 20-25 knots developing by late morning/early afternoon. Tonight...High Confidence. VFR. WNW winds 5 to 15 knots. Tuesday...High Confidence. VFR. WNW 10 to 15 knots with gusts of 20 to 25 knots. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Tuesday Night through Friday/... Tuesday Night: VFR. Breezy. Wednesday: VFR. Breezy. Chance SHRA. Wednesday Night: VFR. Strong winds with local gusts up to 40 kt. Chance SHRA. Thursday: VFR. Windy with gusts up to 35 kt. Thursday Night: VFR. Windy with gusts up to 30 kt. Friday: VFR. Breezy.
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&& .MARINE...
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Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Today through Tuesday...High Confidence. Upper trough over the northeast will generate a continued cool WNW flow of air through Tuesday. Decent mixing should promote some 20 to 25 knot wind gusts at times...especially near shore during the afternoon hours. It is very borderline small craft conditions...but bulk of the time conditions will be below small craft criteria. Therefore...only opted SCA headlines for Tuesday across our southern waters. This is for marginal 5 foot seas and 20 to 25 knot wind gusts. Later shifts may need to consider additional marginal small craft headlines for Tuesday...but confidence not high enough to do that right now. Outlook /Tuesday Night through Friday/... Tuesday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Wednesday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers. Wednesday Night: Low risk for gale force winds with gusts up to 35 kt. Local rough seas. Slight chance of rain showers. Thursday: Moderate risk for gale force winds with gusts up to 40 kt. Areas of rough seas. Thursday Night: Low risk for gale force winds with gusts up to 35 kt. Local rough seas. Friday: Winds less than 25 kt. Seas locally approaching 5 ft.
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&& .FIRE WEATHER...
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Today and Tuesday... Minimum afternoon relative humidity values should drop into the 20 to 30 percent range today and 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 on both days. In coordination with our fire weather partners, we opted to issue a SPS for CT and RI due to elevated fire weather concerns today and possibly again on Tuesday. 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.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 5 AM to 8 PM EDT Tuesday for ANZ254>256.
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&& $$ SYNOPSIS...Frank/BL NEAR TERM...Frank SHORT TERM...Frank LONG TERM...BL AVIATION...Frank/BL MARINE...Frank/BL FIRE WEATHER...Frank

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