Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 151155 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 755 AM EDT Sun Apr 15 2018 .SYNOPSIS... Quite a chilly day which will be accompanied by periods of sleet and freezing rain. Low pressure will push across the region Monday, swinging a front across the region which will bring rain, locally heavy at times, along with isolated thunderstorms. Showers will linger into Tuesday across interior portions of the region. Another low pressure may approach Thursday, bringing another round of showers. Temperatures will continue to run below normal early this week, then moderate to more normal levels later this week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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745 AM Update... Weak ridge of high pressure and low level dry air has thus far been sufficient to keep precipitation to our north. Temperatures were also slightly higher. Once precipitation arrives, evaporational cooling should permit temperatures to fall slightly. Made major updates to the forecast to slow down the timing of any precipitation this morning. If anything does fall it will be in the form of very light precip as temp/dewpoint spread remains large. Contemplated canceling portions of the Winter Weather Advisory. A complication will be the arrival of precipitation later this afternoon, where sleet and or freezing rain would be possible. Rather than dropping the advisory, only to maybe put it back in place later, will wait it out a bit longer. The longer we remain precipitation free, the less likely we would see wintry precipitation, particularly across the coastal plain of RI and SE MA. Previous Discussion... * Unseasonably cold day with rain, sleet and pockets of freezing rain across much of SNE * Quiet a change of airmass compared to 24 hours ago. High pressure to the north will continue to push cooler temps into the region today. In fact, 925 mb temp will fall to about 2 STD below normal, quite an anomolous airmass. Since highs will reach in the upper 20s to mid 30s it appears that all of the climate sites could break their low max temps. Precipitation chances have been tricky for today. Boundary well to the south of the region with southerly winds in the mid- levels will indicate some overrunning precip. However, still a strong temp/dewpoint spread across the area this morning. BUFKIT soundings also show that the profile will take its time to moisten and with PWAT values actually weakening today feel that on and off showers or just spotty precip will occur. Since temperatures continue to fall, p-types will vary across the area. Light rain will occur across areas where the temperatures are above 32F. However as we go through the day and temps fall, strong subfreezing layer will establish itself below 900mb. This will help transition any precip to sleet despite the strong warm layer at 800mb. One issue to watch is the lack of ice in the snow growth region, so may have to contend with drizzle, freezing drizzle or even snizzle. Overall, appears that a mix bag of wintry precip will occur today, but more in the way of on and off showers or pockets of precip. Finally, winds out of the northeast will remain gusty. Strong enough jet at 925mb and with mixing up to that level expect wind gusts near 25-35 MPH.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/... * Wintry Mix will impact the region Tonight Tonight... Better chance for precipitation to occur will be this evening and into tonight. Ridge axis will begin to move offshore as strong surface low will approach the region from the west. PWAT values will be on the increase reaching above 1.3 inches (2-3 STD above normal). This combined with strong 850mb jet will help bring widespread precipitation to the region. Temperature tonight will be cold to start so any precip that forms will once again be in the freezing rain/sleet mix. However surface temperatures will be on the rise thanks to WAA. This will help transition any wintry precip to more of a rain event towards dawn. However, the high terrain may take their time to flip over resulting in wintry precip lingering into the morning. This could impact the beginning of the morning commute. The WAA will also help erode the subfreezing layer below 900mb, so p-types may switch more to freezing rain than sleet before flipping over to rain. The combination of the high moisture airmass and good dynamics will bring more QPF to the region. Thus we could see a light glaze of ice across most of southern New England with near 0.1-0.25 inches of ice accretion across the high terrain. Have adjusted the winter weather adv to last into tonight to account for the potential for ice. This could result in slippery conditions across elevated areas. Aside for the temperatures and precip, gusty winds will also be of concern. Anomolous LLJ at 925mb will increase to 40 kts towards the morning. Mixing does appear to be somewhat limited, but with pressure dropping ahead of the surface low and some heavy precip moving through, we could tap into the jet resulting in gusts closer to 40 MPH. One area to really watch is downsloping from the Worcester Hills. A Wind Advisory may be needed. && .LONG TERM /MONDAY THROUGH SATURDAY/... Overview... 15/00Z guidance remains in rather good agreement with the synoptic pattern into Wednesday. Thereafter, differences arise in their handling of a potent shortwave over the northern plains, which will have implications on our forecast later this week. Have above normal confidence in the forecast through Tuesday, then a moderate confidence in the forecast for Wednesday and beyond. Details... Monday through Wednesday... Cutoff mid level low will slowly move over the Great Lakes Monday night, reaching the Maritimes sometime Wednesday. This will generally keep our region within a synoptic cyclonic flow aloft. This would support at least a slight risk for periods of wet weather, depending on available moisture, as well as near to slightly below normal temperatures. Main period of wet weather will be Monday into Monday evening. A triple point low pressure is still expected to move across southern New England during this time. This will help to enhance low level convergence, and make rainfall processes more efficient. Lots of moisture expected to be in place, with precipitable water values 2-3 standard deviations above normal. Instability remains marginal, but also persistent, for several model cycles, now. Maintained the mention of isolated thunderstorms for Monday. Significant anomalies with the 925 mb wind, both for advecting moisture north, as well as colder air from the North Atlantic. Besides the potential for strong gusts towards the east coast, thinking temperatures will also struggle to rise much Monday morning. High temperature MOnday may be later in the day than usual. Will need to consider a Wind Advisory with later forecasts. Thinking it is rather marginal at this point. Will let the next shift get another look. Drier air in 850-700 mb layer punches into our region from the SW-NE behind the triple point low and a cold front Monday night. This should at least cause any remaining rain to taper off for a time. As this low lingers across southern Quebec Tuesday-Wednesday, could see some patchy showers redevelop during the daylight hours, especially across northern MA. Mid level moisture will also keep clouds across much of region through part of Tuesday night. Anticipate mainly dry conditions on Wednesday, though some diurnal showers may still develop across the E slopes of the Berkshires. Wednesday night through Saturday... Another fast moving mid level shortwave approaches, along with a surface low pressure. Timing and track are still the big questions. Model solutions are converging, but still some wiggle room in their solutions. At this time, thinking the window for the greatest risk of showers is Wednesday night into Thursday, but this could change. Also a possibility showers linger into Friday, with a mid level trough still to move past our region. Lower confidence forecast for this timeframe. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/...
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Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tonight/... Today...Moderate confidence. VFR/MVFR with pockets of IFR for the day. Light wintry mix developing for the interior with a mix of rain/sleet near the coast. Precip will be on and off. E gusts 25-30 kt, strongest along the coast. Tonight...Moderate confidence. Widespread MVFR/IFR. Rain, sleet, freezing rain trending toward all rain overnight, but pockets of freezing rain persisting over interior MA. E/NE gusts 20-30 kt, up to 35 kt Cape/Islands. Worcester hills could see gusts near 40 kts. KBOS Terminal...Moderate confidence in TAF. Spotty wintry precip today and more widespread impact for the evening push tonight. KBDL Terminal...Moderate confidence in TAF. Spotty wintry precip today and more widespread impact for the evening push tonight. Outlook /Monday through Thursday/...Moderate confidence. Monday: Mainly IFR, with areas MVFR possible. Strong winds with local gusts to 40 kt. RA, FZRA, isolated TSRA, patchy FG. Monday Night: Mainly VFR, with local IFR possible. Windy with local gusts to 30 kt. Chance RA, slight chance SHRA, patchy FG. Tuesday: Mainly VFR, with local MVFR possible. Breezy. Slight chance SHRA. Tuesday Night through Wednesday: VFR. Breezy. Wednesday Night: Mainly VFR, with local MVFR possible. Slight chance SHRA. Thursday: Mainly VFR, with local IFR possible. Chance SHRA.
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&& .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tonight/...High confidence. Increasing NE winds today with gusts 25-35 kt, increasing to 35-45 kts tonight as winds veer to the east. Gale warnings are in effect. Vsbys reduced at times in rain and fog today, with lower vsbys possible tonight as fog becomes more widespread. Outlook /Monday through Thursday/...Moderate Confidence. Monday: Moderate risk for gale force winds with gusts up to 45 kt. Rough seas up to 17 ft. Rain, isolated thunderstorms, patchy fog. Areas of visibility 1 nm or less. Monday Night: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 16 ft. Chance of rain, patchy fog. Local visibility 1 nm or less. Tuesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 9 ft. Tuesday Night through Wednesday: Winds less than 25 kt. Areas of rough seas. Wednesday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers. Thursday: Winds less than 25 kt. Local rough seas. Chance of rain showers. && .TIDES/COASTAL FLOODING... Strong South winds over the west Atlantic Monday will build a storm surge up to 2 feet that may reach the south coast. This will need to be monitored for possible minor splashover along the south coast late Monday night along south facing beaches. && .CLIMATE... Record lowest max temperatures for Sunday April 15 BOS 40 in 1881 PVD 42 in 1972 BDL 41 in 1943 ORH 39 in 1943 Record lowest min temperatures for Sunday April 15 BOS 28 in 1943 PVD 27 in 1923 BDL 24 in 1957 ORH 19 in 1940 && .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...Winter Weather Advisory until 2 AM EDT Monday for CTZ002>004. MA...Winter Weather Advisory until 9 PM EDT this evening for MAZ013- 015>017. Winter Weather Advisory until 2 AM EDT Monday for MAZ005>007- 010>012-014. Winter Weather Advisory until 8 AM EDT Monday for MAZ002>004- 008-009-026. RI...Winter Weather Advisory until 9 PM EDT this evening for RIZ001>003. MARINE...Gale Warning until 7 PM EDT Monday for ANZ232>235-237-255-256. Small Craft Advisory until 7 PM EDT Monday for ANZ230-236. Gale Warning from midnight tonight to 7 PM EDT Monday for ANZ231. Gale Warning from midnight tonight to 10 PM EDT Monday for ANZ250-251. Gale Warning until 10 PM EDT Monday for ANZ254.
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&& $$ SYNOPSIS...Belk/Dunten NEAR TERM...Belk/Dunten SHORT TERM...Dunten LONG TERM...Belk AVIATION...Belk/Dunten MARINE...Belk/Dunten TIDES/COASTAL FLOODING...Staff CLIMATE...Staff

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