Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 260749 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 349 AM EDT Thu Apr 26 2018 .SYNOPSIS...
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A weak ridge of high pressure will bring a return to mainly dry weather later this morning through tonight with seasonable temperatures. Another fast moving low pressure system will bring a period of widespread showers to the region Friday afternoon and evening. Milder temperatures return Saturday, but a cold front will bring a brief shot of cooler air to the region Sunday into Monday. A significant warming trend will occur Tuesday into Wednesday with dry weather expected.
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&& .NEAR TERM /UNTIL 7 AM THIS MORNING/... 235 AM Update... Noting that visibilities have lowered to around 1/4 mile across Nantucket, and heading downward across portions of Cape Cod and S coastal Massachusetts. Expect E-SE winds to diminish as broad low pressure moves slowly N-NE through the remainder of the night. Have issued a Dense Fog Advisory for those areas, in tandem with S coastal RI and Block Island. Should see improving conditions around daybreak or so. Last of the steadier rainfall has moved offshore, though noting another batch of showers working N toward central and eastern areas as seen on latest NE regional 88D radar imagery. Per WPC surface analysis, appears this area of precip is associated with triple point/weak low pres that should push across E Mass by around 09Z or so. May also see a few brief heavy downpours with this areas as it moves ashore. Will also monitor an area of lightning flashes and C/G strokes that is well S of Cape Cod. Previous areas of in cloud and C/G lightning has tended to weaken as they moved across the cooler waters S of New England. Expect the approaching cold front across E NY state to wrap eastward around the low, pushing into western areas by around daybreak. With continued light E-SE wind flow, will see low clouds, areas of fog and even some patchy drizzle mainly across the coastal plain, while a few showers will develop and move across inland areas near the weak low along with patchy fog. Visibilities may lower to 1/2 mile or less at times through 11Z-12Z especially near the S coast with the light onshore wind. && .SHORT TERM /7 AM THIS MORNING THROUGH 6 AM FRIDAY/... Today... Upper level low will begin to pivot out of the region during the day on Thursday. Still some lingering moisture in the mid- levels with steep lapse rates which will yield to sct showers in the morning. Deep layer moisture will push northward towards Maine resulting in low precip chances by the afternoon hours. Still expect sct to broken clouds but overall trend will be dry by sunset. Gusty WNW flow expected along as the mid level shortwave passes through. Steep lapse rates and downsloping flow will result in good mixing to near 850mb. Expect wind gusts to near 25-30 MPH by the afternoon as highs reach into the mid to upper 60s. Overall a pleasant Spring day. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/...
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Highlights... * A period of widespread showers Fri afternoon/eve with localized brief heavy rainfall possible * Mainly dry and milder during the day Sat with just few showers possible across the interior * Scattered showers possible Sat night into Sun but not a washout * Mainly dry and cool Sun night into Mon * Dry with a significant warming trend Tue/Wed Details... Friday and Friday night... While much of Friday morning may end up dry...shortwave energy lifting northeastward will result in a period of widespread showers focused Friday afternoon/evening. Despite the shortwave energy gradually deamplifying a modest southerly LLJ/Pwat axis will develop ahead of it. Guidance has trended stronger and further west with the axis of the LLJ along with some elevated instability. These ingredients should combined for a period of widespread showers Friday afternoon/evening. Brief localized heavy rainfall is possible and perhaps even an isolated t-storm or two. Greatest risk for that will be across southeast New England on the nose of the LLJ. High temperatures may reach the lower to middle 60s for a time during the late morning/early afternoon...but readings should drop back into the 50s once the rain arrives and some fog should develop. The bulk of the rain should come to an end after midnight...but areas of fog may linger. Saturday... An approaching cold front will result in a milder southwest flow of air into southern New England. Partial sunshine and good mixing ahead of the front should allow afternoon high temperatures to reach into the upper 60s to the lower 70s away from the marine influence of the south coast. Mainly dry weather expected Saturday...but enough forcing/marginal instability may allow for a few showers to develop during the afternoon across the interior. Saturday night and Sunday... The guidance has trended slower with the passage of the cold frontal passage. While confidence is low...the slower movement of the front may allow for a bit better moisture return and perhaps a period of scattered showers Saturday night into Sun. The main idea is that while it does not look like a washout...a period of scattered showers is certainly possible. Highs Sun may reach well into the 50s to the lower 60s given the slower movement of the cold front. Sunday night and Monday... The latest model suite has slowed the departure of the deep upper trough across the northeast. Therefore...cool weather is on tap for Sunday night and Monday. Low temperatures Sun night probably will bottom out well down into the 30s...so some frost is possible. Highs on Monday should be mainly in the upper 50s to around 60. Mainly dry weather expected...although a few spot showers are possible on Mon given cold pool aloft overhead. Tuesday and Wednesday... A significant warmup is still in the cards for the region as the upper trough quickly departs and is replaced by upper level ridging. This should allow highs to probably break 70 across much of the region Tue and perhaps 80+ in some locations by Wed. Weak pressure gradient will likely allow for localized sea breezes at times...resulting in cooler temperatures along the immediate coast. Nonetheless...summerlike warmth is a good bet by the middle of next week away from localized marine influences. Dry weather is also anticipated Tue/Wed as upper level ridge will result in little synoptic forcing for any precipitation.
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&& .AVIATION /08Z THURSDAY THROUGH MONDAY/...
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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/...Moderate to High confidence. Through 12Z...IFR-LIFR conditions. Leftover showers with locally heavy rain through daybreak. Low CIGS and areas of fog will linger across the terminals. Today...Improving conditions to VFR with mix of MVFR north of the Pike during the day. Gusty westerly winds between 20-30 kts by the afternoon. KBOS Terminal...Moderate confidence in TAF. IFR conditions in rain and lower ceilings through the evening push. Low risk for TSRA through 05Z. KBDL Terminal...Moderate confidence in TAF. IFR conditions in rain and lower ceilings through the evening push. Dense fog is possible during the overnight. Outlook /Friday through Monday/...Moderate to High confidence. Friday: VFR in the morning will be replaced by MVFR-IFR conditions form west to east during the afternoon/early evening as rain showers move across the region with even the low risk of an isolated t-storm. Areas of fog also expected to develop late. Friday Night: Mainly MVFR-IFR conditions. SHRA mainly in the evening, but areas of fog and low clouds may persist longer. Saturday: VFR. Saturday Night: VFR. Chance SHRA. Sunday: VFR. Slight chance SHRA. Sunday Night through Monday: VFR.
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&& .MARINE...
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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/... Through 12Z...Moderate confidence. Small Craft Advisories for all waters except Boston Harbor. Winds have also diminished across Cape Cod Bay, so have ended the Small Craft there. Expect E-SE winds gusting up to 25 kt. Rough seas up to 10 to 12 ft. Rain showers along with areas of fog. Visibility locally below 1 nm at times across the southern waters. Today...Moderate to high confidence. Small craft conditions continue as winds shift to W, though winds diminish during the day. May see gusts up to 25-30 kt through midday. Seas remain at 5 feet or greater through the day across the open waters as well as the south bays and sounds. Outlook /Friday through Monday/...Moderate to High confidence. Friday: Winds less than 25 kt. Seas up to 5 ft. Rain showers develop by late afternoon with an isolated t-storm or two possible. Areas of fog. Local visibility 1 to 3 nm. Friday Night: Winds less than 25 kt. Areas of rough seas. Rain showers likely with perhaps isolated thunderstorm. Areas of fog. Visibility 1 to 3 nm. Saturday: Winds less than 25 kt. Seas up to 5 ft. Saturday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers. Sunday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Chance of rain showers. Sunday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Monday: Winds less than 25 kt. Areas of seas approaching 5 ft.
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&& .EQUIPMENT... The NOAA Weather Radio transmitter serving Providence is out of service due to phone line problems. The phone company has prioritized the issues and is working to get the weather broadcast back on the air as soon as possible. The transmitter serving Hyannis is back in service. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...Dense Fog Advisory until 8 AM EDT this morning for MAZ020>024. RI...Dense Fog Advisory until 8 AM EDT this morning for RIZ006>008. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ232>234-251. Small Craft Advisory until 11 AM EDT this morning for ANZ236. Small Craft Advisory until 8 AM EDT Friday for ANZ235-237-250- 254>256. && $$ SYNOPSIS...Frank NEAR TERM...EVT SHORT TERM...Dunten LONG TERM...Frank AVIATION...EVT/Frank MARINE...EVT/Frank EQUIPMENT...Staff

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