Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 201053 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 653 AM EDT Sun May 20 2018 .SYNOPSIS... A warm front warm front lifts north through the region tonight, allowing a warm and humid airmass to overspread the area. A cold front triggers scattered showers with brief heavy rainfall and isolated thunder this afternoon. Drier this evening into Monday with passing showers during the mid-week. Cooler, drier air follows for Thursday into Saturday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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700 AM Update... Upper level trough continues to approach the region from the west while surface cold front is currently draped across the eastern Great Lakes into northern New England. This front will be the focus of convection that develops today. Still a lot of clouds across the region with areas of fog and drizzle. These clouds may limit temperatures and instability today. Have noticed in area webcams that the dense fog has pushed back in across the south coast as vsbys are at or below 1/4sm. Will wait for the top of the hour obs but may issue a SPS for the patchy dense fog. Still have a good LLJ over the region and with high PWAT values cannot rule out a few isolated showers during the morning hours. Timing from the CAMs suggest that the front will approaching between 11 and 1 pm and move across southern New England through the day. As mentioned before, there is the potential for some embedded thunder but any severe weather appears unlikely at this time. The front will move offshore by 7-8 pm leading to a quick drying trend as winds will turn out of the northwest and Canadian high pressure builds into southern New England. Aside from the rain and fog, winds across southeast MA have increased to 20-25 kts. Expect these type of gusts to continue into the morning hours as low level lapse rates begin to steepen and we mix out per BUFKIT soundings. Previous Discussion... Low clouds and fog will be prevalent this morning. Widespread showers early this morning across RI and SE MA will move offshore by mid morning. Clouds will be key to the realized weather later this afternoon. A cold front will move through this afternoon and evening. Instability will be very dependent upon the amount of sunshine. Forecast CAPE values in some of the high resolution guidance of 500-1,000 J/kg persist. The longer the clouds linger, the lower the CAPE values will likely be, and the fewer thunderstorms would result. In either case, not expecting severe weather because many other ingredients are missing. Precipitable water values of 1.50-1.75 inches will mean locally heavy rainfall is possible, too. Still looks like the window for the greatest risk for showers, after daybreak, will be between 10 AM and 5 PM. Modest southwest winds will push warmer and more humid air into our region. This should make for a more summer-like feel today. High temperatures generally in the 70s away from the coasts, perhaps a little higher where sunshine breaks out for a while.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... High pressure building into the Great Lakes tonight and Monday will send drier weather our way. Mainly clear skies will permit the sunshine to boost temperatures well into the 70s Monday away from the immediate coast. Local seabreezes possible. Not nearly as humid as today, with comfortable dewpoints mainly in the 40s. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... Highlights... * Passing showers Tuesday and Wednesday * Potential for dry weather but below avg temps for the end of this week * Potential for wet weather Memorial Day Weekend Details... Monday Night...High confidence. Dry weather will prevail as high pressure slides into the Gulf of Mexico. Approaching warm front to the south will help increase dewpoints and leave temperatures cool but mild. Lows in the mid 50s. Tuesday into Wednesday... Moderate confidence. Bermuda high pressure remains while upper level trough continues over the northeast Canada. This puts the region in a more zonal pattern. Weak wave moving through the flow will slide along a stalled front south of southern New England. This could bring showers across the area and keep the region on the cool side of the front. Still a spread on how far north precip will get, but right now highest confidence is south of the Pike. Behind this disturbance, an approaching cold front will move in from the northwest. This front is associated with the upper level trough digging into the northeast. Could see some showers along this front but moisture is a bit marginal. Models are even hinting as some sb CAPE, so if showers develop cannot rule out a rumble of thunder. Temperatures will be more seasonable with highs in the mid 70s. Thursday into Saturday...Moderate confidence. Drier but breezy conditions looks to be in store for the end of the week due to a northwest flow pattern. Lots of dry air will dominate on Thursday, but appears that a weak disturbance will move through the area on Friday. For now trended the temperatures below avg and kept with a dry forecast. Sunday and beyond...Moderate confidence. Digging trough over the Great Lakes will move into the Northeast, resulting southwest flow aloft. Good moisture plume moving up from the Gulf could result in wet weather Sunday into Monday. Still a lot of uncertainty in regards to the weekend so stay tuned. && .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 Monday/... Today...High confidence in trends. Moderate confidence in timing. IFR/LIFR lifts to MVFR by midday, slightly longer south coast. Drizzle and areas of morning fog erode by midday but give way to a broken line of showers along and ahead of an approaching cold front. Low probability of isolated thunderstorms, but showers will contain locally heavy rain from about 15z-21z from west to east. Breezy southwest winds 15 to 20 kt with a few gusts up to 25 kt possible. Tonight...High confidence in trends. Moderate confidence in timing. Any leftover IFR/MVFR early evening over Cape Cod improves rapidly to VFR. Otherwise VFR and dry weather. Monday...High confidence. VFR. KBOS Terminal...Moderate confidence in TAF. Low risk for iso thunder between 17-21z. KBDL Terminal...Moderate confidence in TAF. Outlook /Monday Night through Thursday/...Moderate confidence. Monday Night: VFR. Tuesday: VFR. Chance SHRA. Tuesday Night: Mainly VFR, with local MVFR possible. Chance SHRA. Wednesday: VFR. Slight chance SHRA. Wednesday Night through Thursday: VFR.
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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 Monday/...Moderate confidence. Areas of fog will lead to restricted visibility, less than 1 NM at times. Increasing SW winds ahead of a cold front today. Gusts up to 25-30 kt. Showers with locally heavy rain this afternoon and early evening. Winds become northerly behind a cold front tonight and quickly diminish. Rough seas will take a little longer to subside, especially across the outer coastal waters. Outlook /Monday Night through Thursday/...Moderate confidence. Monday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Tuesday through Tuesday Night: Winds less than 25 kt. Chance of rain showers. Wednesday: Winds less than 25 kt. Slight chance of rain showers. Wednesday Night through Thursday: Winds less than 25 kt. Seas locally approaching 5 ft. && .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 6 PM EDT this evening for ANZ232>234-250. Small Craft Advisory until noon EDT today for ANZ230-251. Small Craft Advisory until 3 PM EDT this afternoon for ANZ231. Small Craft Advisory until midnight EDT tonight for ANZ236. Small Craft Advisory until 6 AM EDT Monday for ANZ235-237-254. Small Craft Advisory until 1 PM EDT Monday for ANZ255-256.
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&& $$ SYNOPSIS...Belk/Dunten NEAR TERM...Belk/Dunten SHORT TERM...Belk LONG TERM...Dunten AVIATION...Belk/Dunten MARINE...Belk/Dunten

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