Area Forecast Discussion
Issued by NWS Boston, MA

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558 FXUS61 KBOX 220545 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 145 AM EDT Tue May 22 2018 .SYNOPSIS... Dry and tranquil weather continues overnight. Rather cloudy skies are anticipated Tuesday along with cooler temperatures. A warm front will bring some showers to the region...generally Tuesday afternoon and evening. Mainly dry weather Wednesday through Saturday. Moisture increases through the weekend with the best chance of showers on Sunday. Much warmer Friday into the weekend. && .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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145 AM update... Still just some thin cirrus cover across the region. Thicker high cloudiness was moving into the Berkshires at 145 AM. Showers were steadily progressing across southwestern NY state and a few thunderstorms had developed in north-central PA. No changes to the current overnight forecast.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM WEDNESDAY/... Tuesday and Tuesday night... A rather cloudy day is on tap for Tuesday ahead of a warm front. There appears to be enough forcing/moisture along with a modest low level jet for some showers Tuesday afternoon/evening. Not expecting a complete washout...but most locations should see a period of wet weather during this time. There is even a low risk for a rumble or two of thunder...mainly near the south coast with some marginal elevated instability. High temperatures will be held in the upper 60s to around 70 in most locations given the clouds along with the afternoon/evening showers. The bulk of the showers should come to an end Tuesday evening...but a few will remain possible after midnight as a weak cold front crosses the region. Clouds will probably hang tough for most of the night and may see some fog develop given ample low level moisture. This should hold overnight low temperatures in the lower to middle 50s. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Highlights... * A spot shower lingers Wednesday * Cool Thursday but much warmer into the weekend * Risk of showers increases by Sunday Overview... Through the mid term, the N stream dominates, mainly in the form of a longwave trof settling across the Maritimes which is linked to a Baffin Sea vortex. However, with the mean trof axis to the W, central CONUS ridging will lead to rising heights and generally cyclonic flow through the latter half of the week. It is not until the tropical disturbance in the Gulf of Mexico gets caught up with shortwave energy moving out of the Pacific that there is a transition for New England. These impacts, particularly with a plume of tropical moisture, could yield a wet latter half of Memorial Day weekend. Overall, enough agreement between guidance to use a consensus blend for this forecast update. Wed... Cold front slows as it begins to parallel mid lvl flow. However, soundings support rapid influx of drier air through the column, reducing PWATs to below 1.00in by mid day. Although this does steepen lapse rates, the overall lack of moisture may limit convective potential. Near NIL QPF supports this thinking. Still enough to warrant at least slight chance POPs. Delayed cold advection suggests highs should reach the mid 70s to around 80, especially as some clearing is observed. Thu through Sat... Mainly dry thanks to implied ridging through mid and upper lvl height rises and sfc high pres as a response. Thu looks to be the coolest day, but with H85 temps avg around +8C, it still should yield low 70s across much of the region. Milder Fri and Sat with temps in the upper 70s and low 80s thanks to a gradual increase in mid lvl temps. These are best observed inland however, as weak pres gradient suggests local sea breezes at area coastlines. Sun into early next week... Echo previous forecasters concern and lack of overall confidence as guidance widely diverges during this period. This is not surprising, as models often struggle with complex tropical interactions. At odds for New England, is a resurgence in N stream forcing trof out of the Arctic with its sfc response, a N-S moving cold front front which makes temperatures rather uncertain. From the S stream, is tropical moisture plume with PWATs potentially reaching near 2.00 inches just to the S. If this dominates a period of wet and very unsettled conditions are possible, keeping the front to the N. For now, will lean most heavily on ensemble means for this period as it takes into account the potential solutions. This will come into focus better as the feature players, particularly the tropical wave become better sampled. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/...
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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 Wednesday/... Overnight...High confidence. VFR. Light and variable wind. Today and tonight...Moderate to high confidence. Mainly VFR conditions into this afternoon. It probably will take until evening especially along the coast for MVFR to localized IFR ceilings and visibilities to arrive. These lower cigs/vsbys will likely persist Tuesday night. Some showers expected especially Tuesday afternoon and evening. A low risk for a rumble or two of thunder mainly near the south coast Tue evening. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Wednesday Night through Saturday/...Moderate confidence. Wednesday: Mainly VFR. Wednesday Night: VFR. Breezy. Thursday through Thursday Night: VFR. Friday through Friday Night: VFR. Breezy. Saturday: Mainly VFR, with areas MVFR possible. Chance SHRA.
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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 Wednesday/... Overnight through Tuesday night...High confidence. Weak pressure gradient will keep winds and seas below small craft advisory thresholds through Tuesday night. Biggest concern for mariners will be the potential for some fog developing Tuesday night along with the low risk for a rumble or two of thunder across our southern waters. Outlook /Wednesday Night through Saturday/...Moderate confidence. Wednesday: Winds less than 25 kt. Slight chance of rain showers, patchy fog. Local visibility 1 to 3 nm. Wednesday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Patchy fog. Local visibility 1 to 3 nm. Thursday through Thursday Night: Winds less than 25 kt. Friday: Winds less than 25 kt. Local rough seas. Friday Night: Winds less than 25 kt. Areas of rough seas. Saturday: Winds less than 25 kt. Areas of rough seas. Chance of rain showers.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Frank/Doody/Field NEAR TERM...Field SHORT TERM...Frank LONG TERM...Doody AVIATION...Frank/Doody/Field MARINE...Frank/Doody/Field

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