Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 240820 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 320 AM EST Fri Nov 24 2017 .SYNOPSIS... Quiet weather through Friday with dry and cool conditions. Milder air returns Saturday ahead of a cold front. The cold front moves through southern New England Saturday night accompanied by scattered showers. Blustery weather follows on Sunday. Milder temperatures may return for Tuesday and Wednesday of next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Mid and high level clouds continue to dissipate as they move east across southern New England this morning. The thicker mid level clouds towards the Berkshires will be more stubborn to erode as there is some connection to the Great Lakes to keep the humidity higher, along with the upslope over the Berkshires themselves. Adjusted the forecast through daybreak to reflect observed trends. For today, high pressure to our south will dominate our weather. Dry conditions with relatively light west winds shifting southwest as the day progresses. Abundant sunshine with only a few higher clouds from time to time. This sunshine will permit higher temperatures than Thursday, and close to normal values for late November. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/... Southwest winds should increase slightly tonight, setting the stage for a warmup Saturday. As noted by prior shift, dewpoints also increase with the southwest flow, but not expecting fog to be an issue. Low stratus is likely across the Cape and islands late tonight. Dry conditions continue. Saturday should be above normal temperature-wise as modest southwest winds continue ahead of a cold front. Latest model suite continues to show pretty good lift and humidity within the 850-700 mb layer, but more drier air beneath it to be overcome. Envisioning a scenario where clouds increase through the day, with dry weather into mid-late afternoon. Since this is a cold frontal passage, and BUFR soundings continue to show the column saturating from the top down, will continue the idea of a slight chance for showers, becoming a greater risk towards the east coast very late in the day Saturday due to proximity to more humid low levels. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Highlights... * Scattered showers Saturday night and then mainly dry rest of the forecast period * Blustery behind cold front on Sunday * Milder temperatures may be in store for Tuesday and Wednesday Discussion... Forecast area will be subject to a series of fairly low amplitude upper short wave trough passages for the next 7 days. At the surface, these will be reflected by mainly dry frontal passages. After Sunday and Monday, it looks to be mainly dry, but some uncertainty in temperatures due to uncertainty in whether the southern and northern stream flow is the more dominant over the region. As is typically the case in a pattern with progressive short wave troughs, there are uncertainties especially in the timing. However, the impact on the forecast is mitigated by the fact that there is limited moisture available. Most of the focus for this forecast period is early on with the cold front passage Saturday night followed by a rather blustery day on Sunday. A fairly sharp upper short wave trough and moderately strong surface cold front affect the region Saturday night. Moisture is expected to be fairly limited given the trajectory of this feature, but bufkit soundings do show a brief period of fairly deep moisture especially closer to the coast where there is some marine influence in the lower levels. This looks to be enough to support at least scattered light showers. Moderately strong cold air advection follows on Sunday with 850 mb temperatures +2C to +4C Saturday evening dropping to about -5C to - 8C by midday Sunday. Upper trough axis probably does not pass through southern New England until midday Sunday and so cannot rule out a few flurries at least across the higher terrain. The surface pressure gradient and cold air advection will likely produce mixing of 25 knots or slightly higher gusts to the surface during the day Sunday over land and perhaps closer to 30 knots over the water. Medium range models suggest another upper short wave trough in the NW flow moving across New England Sunday night. This looks to be dry other than a chance of a few flurries over the east slopes of the Berkshires. For Tuesday through Wednesday, 500 mb heights rise in response to a southern stream trough ejecting from the 4 corners area, and this should be reflected in milder temperatures. A fly in the ointment, however, could be a northern stream short wave trough that may hold back warm air advection in to New England. For now have gone with a model blend with a somewhat greater temperature gradient than average from north to south. Given uncertainty in timing and strength of this northern shortwave, there is below average confidence in mid week temperatures. Operational and ensemble runs suggest upper level ridging over our area ahead of a somewhat more amplified trough moving across the Mississippi Valley on Thursday with possibly an approaching warm front late in the day or Thursday night. && .AVIATION /08Z FRIDAY THROUGH TUESDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday/...High confidence. VFR. W/NW winds diminish overnight, turning S/SW into today. BKN-OVC MVFR CIGs possible for SE New England into tonight into early Saturday morning. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Saturday Night through Tuesday/... Saturday night...High confidence. Mostly VFR with local areas of MVFR ceiling and visibilities in scattered showers. Sunday...High confidence. VFR but surface wind gusts 25 to 30 kt. Sunday night through Tuesday...High confidence. Mainly VFR. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday/... Small Craft Advisories adjusted to account for trends in observed seas. Expecting all advisories for the outer coastal waters to be down by daybreak this morning. Will adjust timing as needed. High pressure in control with good boating weather for a time today. Increasing southwest winds tonight into Saturday will likely build seas once more across portions of the outer coastal waters. Additional Small Craft Advisories may be needed for marginal rough seas. Outlook /Saturday Night through Tuesday/... Confidence...Moderate NW winds will likely gust to between 25 and 30 kts across the waters on Sunday. Isolated gale gusts, especially east of Cape Cod and Nantucket, cannot be ruled out. May be enough gradient and lingering seas to result in Small Craft Advisory conditions persisting through the early part of next week across the outer waters. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory for hazardous seas until 7 AM EST this morning for ANZ254. && $$ SYNOPSIS...Belk/Thompson NEAR TERM...Belk SHORT TERM...Belk LONG TERM...Thompson AVIATION...Belk/Thompson MARINE...Belk/Thompson

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