Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 182341 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 641 PM EST Sun Feb 18 2018 .SYNOPSIS... A warm front will likely bring a period of showers late Monday into Monday night. This will bringing near record high temperatures Tuesday and Wednesday. A cold front Wednesday night will bring showers and then cooler temperatures, but still at or above seasonal normals. Another weather system will pass to our west and north over the weekend bringing another period of wet weather. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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640 PM Update... High pressure is settling in overhead. Expect light and shifting wind overnight. Satellite shows high thin clouds already drifting in, and these will be with us overnight. Fair weather should persist overnight. No significant changes to the forecast. Previous discussion... A large high pressure will pass by just to the south of New England tonight. This will mean diminishing wind this evening, especially overnight. Once this high pressure approaches the Maritimes late tonight, a light south wind should develop. Decent radiational cooling conditions tonight. Expecting lows to be mainly in the 20s. This should be sufficient to refreeze any standing water into black ice on untreated surfaces.
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... Increasing south winds will boost temperatures well above normal Monday, and likely keep temperatures nearly steady or slowly rising Monday night. Morning sunshine. Increasing clouds during the afternoon as a warm front approaches. There appears to be enough forcing and moisture for a likely period of showers sometime late afternoon into Monday night. Chance for showers should decrease after midnight Tuesday as a warm front moves into northern New England. It should remain mostly cloudy, though. && .LONG TERM /TUESDAY THROUGH SUNDAY/... Big Picture... Upper ridges build over the Eastern USA and the East Pacific with a deep trough over the Western USA. Contour heights over Southern New England reach 585 dm, well above the normal 542-545 dm for February. These values lower over the Northeast USA Thursday-Friday but still remain well above normal most of the weekend. Several weak shortwaves eject from the western trough Wednesday through Sunday, with the strongest moving through the Northeast during the weekend. Model large-scale mass and thermal features are in general agreement through Friday, with some differences Saturday-Sunday. Details... Tuesday-Wednesday... With the upper ridge building so strong and with the surface front moving north to the Canadian border, a period of near record warmth is anticipated. Warm advection aloft is expected to limit mixing to about 950 mb where temps support sfc highs of 60 to 65 Tuesday and 65 to 70 Wednesday. South coastal areas will be affected by the cold ocean temps and thus stay in the 50s. Model cross sections show high moisture below 900 mb and dry air above 800 mb. If this moisture is realized as clouds, it could keep all max temps in the 50s each day. We compromised, with highs around 60 on Tuesday when there is a higher chance of clouds. Wednesday night-Thursday... A shortwave supported by a 190-knot upper jet races across Eastern Canada. New England falls under the right entrance region of the jet during this time. This will draw the front south across New England. There are differences in timing of cold fropa with the ECMWF showing a Wednesday evening passage while the GFS shows passage Wednesday night/Thursday morning. Low pressure waves forming along the front could slow the progress of the front. Expect showers during this time, and we will use the slower Wednesday night timing. The model PW fields show a band of high moisture content extending from the Western Gulf of Mexico to New England. PW values over us reach to about 1.3 inches, which is nearly record territory. Convective parameters are interesting with totals in the mid to upper 40s and mid level lapse rates 6 to 6.25C/Km. Locally heavy downpours are possible. Would not rule out some thunder, but the probability is too low to mention at this time. Friday through Sunday... High pressure from the Northern Plains moves east to New England, bringing clearing skies for Thursday night. Clouds then move back in during Friday. The next shortwave climbs out of the western trough and races northeast in the fast-moving flow. Models currently show a second shortwave on the heels of the first. The projected track of the low favors rain for Southern New England, but with concern that some low level cold air could bring a brief period of mixed precipitation Friday night. The trend is for rain everywhere by Saturday. The second shortwave would then maintain a chance of rain into Sunday. Much uncertainty remains with timing of this feature. && .AVIATION /00Z MONDAY THROUGH FRIDAY/...
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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 Night/...High confidence. Tonight...VFR. Shifting wind 5 knots or less. Washington`s Birthday: Mainly VFR, with local MVFR possible late. Breezy. Chance SHRA late. Monday Night: Mainly VFR, with areas of MVFR in -SHRA. Areas IFR possible toward the south coast, including the Cape and islands. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Tuesday through Friday/...Moderate to High confidence. Tuesday: MVFR conditions possible, especially South Coast. Breezy. Patchy BR early. Tuesday Night: Mainly VFR, with local IFR possible. Breezy. Wednesday: Mainly VFR, with local MVFR possible. Breezy. Wednesday Night: Mainly VFR, with local IFR possible. Breezy. Chance SHRA, patchy BR. Thursday: Mainly MVFR, with areas VFR possible. Chance SHRA. Thursday Night: VFR. Friday: VFR. Slight chance RA in the afternoon.
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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 Monday Night/...High confidence. Tonight...Small Craft Advisories linger south/east of Cape Cod and Nantucket. Five foot seas will subside by 10 PM. NW winds back to S. Good visibility. Washington`s Birthday into Monday night...Increasing S winds, resulting in build seas across the outer coastal waters. Small Craft Advisories will likely be needed across the outer coastal waters. Will post those, once the current set of advisories has expired. Chance of rain showers. Patchy fog possible Monday night with visibility of 1 to 3 nm. Outlook /Tuesday through Friday/...Moderate to High confidence. Tuesday through Tuesday Night: Winds less than 25 kt. Local rough seas. Slight chance of rain showers. Wednesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Wednesday Night: Winds less than 25 kt. Local rough seas. Chance of rain showers. Thursday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. Thursday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Friday: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain late.
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&& .CLIMATE... Record Highest Observed Temperature for February... (since records began) Boston.........73 (02/24/2017) Hartford.......73 (02/24/1985) Providence.....72 (02/24/1985) Worcester......69 (02/24/2017) Record High Temperatures (Tuesday 20th / Wednesday 21st)... February.......20th......21st..... Boston.........68 (1930) 63 (1906) Hartford.......69 (1930) 63 (1930) Providence.....69 (1930) 63 (1930) Worcester......65 (1930) 59 (1930) Record Warmest Low Temperature... February.......20th......21st..... Boston.........46 (1930) 45 (1994) Hartford.......50 (1981) 49 (1981) Providence.....48 (1981) 50 (1981) Worcester......47 (1981) 43 (2002) && .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 10 PM EST this evening for ANZ254- 255.
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&& $$ SYNOPSIS...WTB/Belk NEAR TERM...WTB/Belk SHORT TERM...Belk LONG TERM...WTB AVIATION...WTB/Belk MARINE...WTB/Belk CLIMATE...

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