Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 200202 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 1002 PM EDT Thu Apr 19 2018 .SYNOPSIS...
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An upper level disturbance moves east of Massachusetts overnight, ending any remaining rain and snow showers. Drier air moves in on Friday as high pressure over the Great Lakes Region moves eastward. Building high pressure will bring gradually warming temperatures and dry weather into early next week. Storm system expected for mid to late week.
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&& .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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Upper level low and cold pool pver New England early in the night with clouds covering the region and radar showing scattered light rain/snow showers over the region. The trough moves east of Southern New England by morning, taking with it the support for any showers. Moisture aloft trends less with time, so expect partial clearing from the south overnight. Gusty northwest winds observed around 22 knots. Mixing continues overnight as the cold pool and strong lapse rates continue to bring some winds to the surface overnight.
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&& .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... Friday... Cyclonic flow around the upper low continues on Friday. Models continue to show a decrease in overall moisture over the course of the day, however sufficient moisture in the low levels for diurnal cumulus/stratocu. Mainly dry conditions expected, though could see some spot showers along the east slopes of the Berkshires, and a few sprinkles elsewhere. The cold advection and cold temperatures aloft should allow mixing to at least 850 mb. Models continue to show winds in this layer around 25 knots, so NW gusts of 25-30 mph anticipated for the afternoon. Highs generally in the mid 40s to low 50s, except for low 40s along the east slopes of the Berkshires. For most of the region this is a good 10 degrees or so below normal for mid April. Friday night... Upper trough lifts east of the area while surface high pressure over the Great Lakes Region moves eastward. This allows for drier air and skies becoming mostly clear. Diminishing NW winds become light, with lows in the upper 20s and 30s. && .LONG TERM /SATURDAY THROUGH THURSDAY/... Highlights... * Moderating temperatures and dry weather will prevail through the weekend and into next week * Next batch of rainfall will occur during the mid-week Overview... Longwave wave trough over the Northeast will lingering through the weekend before mid-level ridging pushes through for early next week. At the surface, strong high pressure leaning towards 2-3 STD above normal will lead to dry weather. However with the upper level trough, temps will slowly moderate out through next week. By Tuesday/Wed, both the GFS and EC indicate a cut-off 500mb low associated with the southern stream. This southern stream could interact with an approaching northern stream wave, developing a system for mid next week. This is supported by ensemble guidance which has between 50-70 percent probs of seeing 0.5 inches of rainfall. Details... Temperatures...Moderate confidence. Spring will make an appearance during this medium range forecast as temperatures will begin to moderate through the weekend and into next week. Longwave trough over the region will slowly begin to exit towards the Maritimes by early next week. This will keep the weekend below average for temperatures as both 925 and 850mb are near 1-2 STD below normal. Still plenty of sunshine across the area for the weekend with fairly light winds so it will feel pretty warm compared to this past week. Mid-level ridge will build into the area by Monday/Tuesday. This will help increase temperatures back into the low to mid 60s. Near the coastline, temperatures will feel cooler due to potential sea breeze develop as high pressure is situated right over the area. Approaching system for the mid-week will drop temperatures back down below average, especially behind the system. Precipitation...High confidence. Dry weather will prevail from Saturday into Tuesday thanks to surface high building in from the west. Model guidance indicates this high will near 2-3 STD above normal. A good break to dry out the soils. However, approaching surface low that develops near the Carolinas will track towards southern New England between Wednesday and Thursday bringing wet weather to the area. As mentioned above, ensemble guidance has between 50-70 percent probability of seeing 0.5 inches of rainfall. Chances are this amount will go up especially since this event is still 6+ days out and there is strong agreement amongst the ensembles and deterministic guidance. && .AVIATION /02Z FRIDAY THROUGH TUESDAY/...
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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 Friday Night/... Overnight...Moderate confidence. Lingering MVFR cigs over Cape Cod and Islands will improve to VFR overnight. VFR over the rest of Southern New England overnight. Sky cover diminishes from the south and southwest overnight. Friday...High confidence. VFR. Northwest winds will gust to 25 knots during the day. Isolated -SHRA/-SHSN possible along the east slopes of the Berkshires, this could briefly cause MVFR cigs/vsbys. Elsewhere patchy sprinkles possible. Friday night...High confidence. VFR. KBOS Terminal...High confidence in TAF. VFR. Gusty NW winds on Friday preclude sea breeze development. KBDL Terminal...High confidence in TAF. VFR. Outlook /Saturday through Tuesday/...High confidence. 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 Friday Night/...High confidence. Overnight... A low pressure system moves off south of Nova Scotia overnight. Increasing northwest winds expected tonight, gusting 25 to 30 kts at times. Seas will build overnight, with 5-8 foot seas on the southern outer coastal waters overnight. Small craft advisory continues for all waters. Friday...Northwest winds gusting to 25 knots, with seas 5-7 feet on the outer coastal waters. Small Craft Advisory in effect. Friday night...Northwest winds gust 20-near 25 kts with seas gradually subsiding. A Small Craft Advisory may be needed for the outer coastal waters. Outlook /Saturday through Tuesday/...Moderate Saturday: Winds less than 25 kt. Seas locally approaching 5 ft. Saturday Night through Tuesday: Winds less than 25 kt.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 2 AM to 3 PM EDT Friday for ANZ231>234-251. Small Craft Advisory from 4 AM to 6 PM EDT Friday for ANZ230. Small Craft Advisory from 4 AM to 11 AM EDT Friday for ANZ236. Small Craft Advisory until 5 PM EDT Friday for ANZ235-237. Small Craft Advisory until 6 PM EDT Friday for ANZ250. Small Craft Advisory until 8 PM EDT Friday for ANZ254>256.
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&& $$ SYNOPSIS...WTB/Dunten/NMB NEAR TERM...WTB/Dunten/NMB SHORT TERM...NMB LONG TERM...Dunten AVIATION...Dunten/NMB MARINE...WTB/Dunten/NMB

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