Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 190821 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 421 AM EDT Fri May 19 2017 .SYNOPSIS... Cold front will move slowly south across southern New England and then south of the areaby early tonight. A strong high pressure area for this time of year centered over south central Canada will spread into New England tonight and Saturday. More seasonable pattern is expected for the weekend into early next week. Dry initially then turning wet Monday ahead of a sweeping cold front. A brief reprieve Tuesday prior to more rain expected mid to late week along with continued near-seasonable conditions. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Primary issue for today is the potential for any thunderstorms across Rhode Island and southeast Massachusetts early to mid this afternoon. Most stability indices support a chance of thunderstorms, but the moisture profile is marginal and may serve to limit deep convection. Winds at the 500 mb level will be 40-45 kt and this sets the stage for fairly strong vertical shear and suggests a risk of isolated strong wind gusts if deep convection becomes initiated. There looks to be some low level moisture convergence along the frontal boundary and around 1500 j/kg of surface based CAPE may be enough to fire a few thunderstorms. The HRRR, which verified reasonably well with respect to last evening`s convection, was depicting scattered deep convection across Ri and SE MA this afternoon but has just backed off of that solution. Temperatures today look to be cooler than yesterday by some 10 degrees or so but still on the warm side compared with normal for this time of year. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/... Friday night and Saturday look to be dry and much cooler as fairly strong surface high pressure for this time of year expands into New England, and 850 mb drop about 10C degrees between Friday and Saturday. Onshore winds will result in even cooler high temperatures for Boston and other east coastal MA locations during Saturday afternoon. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... */ Highlights... - Seasonable and dry for Sunday - Rain with embedded heavier showers for Monday - Dry on Tuesday - Wet for the mid to late week period, remaining near-seasonable */ Overview and Discussion... Not much change in the long-term forecast. While unclear as to the circumstances leading up to, enhanced H5 ridging over the NE Pacific gradually transitioning E into the W CONUS promotes downstream gyre across the Central and E CONUS through which individual disturbances rotate. Averaged out and generally speaking, an active weather setup with periods of wet-weather while being near-seasonable throughout. Pretty decent consensus we`ll salvage the weekend, comfortable and dry. Yet beginning Monday morning we`ll see a pattern of successive areas of low pressure and accompanying periods of rain through the remainder of the week inbetween which there will be lulls of drier weather and likely sunshine. Only main concern is how efficiently each individual disturbance is able to capture sub-tropical air and drag it N into S New England, as to whether there is the chance for thunderstorms and/or effective warm-rain processes. In addition the magnitude of the S draw and both the depth and richness of moisture involved. Some anomalous signals per SREF/GEFS on the order of +1-2 standard deviation with S low-level inflow and precipitable waters. Could be contending with both low cloud and/or fog issues as well as blustery S winds. Perhaps Monday and then again on Thursday. High chance to likely PoPs with a slight chance mention of thunder. Some stronger gusts and a hint of fog. All in all, seasonable conditions throughout for late May with highs in the upper 60s to low 70s and lows down into the upper 40s to low 50s. && .AVIATION /09Z 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 Saturday/... Today...High confidence. With the exception of local MVFR/IFR conditions in stratus/fog along the south coast and patchy fog in a few interior river valleys early this morning, VFR conditions should prevail. Risk of widely scattered to scattered thunderstorms along and south of a IJD- PVD-PYM line during early/mid afternoon. An isolated thunderstorm or two could produce gusty surface winds. Tonight...High Confidence. VFR conditions expected with mostly clear skies. Saturday...High confidence. VFR conditions. Onshore wind expected along east coastal MA. KBOS TAF...High confidence. VFR expected through the period. Note wind shifts to be from the east on Saturday afternoon. KBDL TAF...High confidence. VFR expected through the period. Outlook /Saturday Night through Tuesday/... Saturday night through Sunday night... S winds into Sunday as CIGs lower and thicken. A mix of MVFR-IFR into Monday morning W to E with onset of -RA/RA. Monday into Monday night... MVFR-LIFR. Lowest conditions likely for the S-coast with potential fog impacts. Increasing S winds ahead of a line of widespread -RA with embedded RA/+RA late and into evening. Gusts up to 25 kts. Low risk TSRA. Possible LLWS impacts with S/SW winds 2 kft AGL 40-50 kts. Tuesday into Tuesday night... VFR. Clearing. Possible SKC if not SCT-BKN low-end VFR CIGs and possible mid-level CIGs late. NW winds initially turning S. May be light enough to allow onshore sea-breezes.
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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 Saturday/... High confidence. Have opted to continue the Small Craft Advisory as originally construed. It may be possible to cancel the Rhode Island Sound portion by around noon but will let next shift monitor conditions there first. The wind has begun to diminish but enough fetch remains in place to keep seas near 5 feet in the advisory area. Outlook /Saturday Night through Tuesday/... Great boating weather continues into Sunday with light S winds and waves 1-2 feet. Going into Monday, S winds on the increase with gusts up to 25 kts ahead of a cold front along with a widespread line of rain with embedded heavier showers beginning Monday morning and dissipating late afternoon into evening. A low risk of thunderstorms. Clearing out after midnight into Tuesday morning though waves build 5 to 6 feet and are slow to diminish under NW winds. Winds are light through Tuesday turning S so this should allow seas to subside. && .CLIMATE... Records were broken in Boston, Providence, and Hartford yesterday and tied at Worcester. Refer to the latest Record Event Reports which were issued on Thursday. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 6 PM EDT this evening for ANZ235- 254>256. && $$ SYNOPSIS...Sipprell/Thompson NEAR TERM...Thompson SHORT TERM...Thompson LONG TERM...Sipprell AVIATION...Sipprell/Thompson MARINE...Sipprell/Thompson CLIMATE...

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