Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 200732 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 332 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 /THROUGH TODAY/... 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. && .SHORT TERM /TONIGHT 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 /07Z SUNDAY THROUGH THURSDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday/... Through 12Z...Mainly IFR/LIFR conditions in a mix of low CIGS, fog and DZ. Some improvement is possible although IFR and MVFR will dominate as winds shift to the SW and increase. Gusts to 10-20 kt at times during the early AM hours with the SW flow. 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. Very 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. 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. && .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... 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. 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 noon EDT today for ANZ251. Small Craft Advisory until 1 PM EDT Monday for ANZ255-256. && $$ SYNOPSIS...Belk/Dunten NEAR TERM...Belk SHORT TERM...Belk LONG TERM...Dunten AVIATION...Belk/Dunten MARINE...Belk/Dunten is the U.S. government's official web portal to all federal, state and local government web resources and services.