Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 232052 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 352 PM EST Fri Feb 23 2018 .SYNOPSIS...
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As a frontal system progresses east, rain and mixed precipitation will continue into this evening. Active weather pattern continues this weekend with more rain and interior mixed precipitation Saturday night and Sunday. A near- seasonable, quiet pattern for early next week.
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&& .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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*** A period of light icing likely this evening over higher elevations in central and western MA *** A Winter Weather Advisory remains in effect for the higher terrain through this evening due to the potential for freezing rain. Sounding profiles show the best chance for freezing rain/sleet to be across the higher terrain given the warm front aloft with cooler temperatures at 925mb. There still stands a low potential for ice accumulations up to a quarter inch on the eastern slope of the Berkshires. Isolated areas of freezing rain and sleet have been reported, largely along the eastern slopes of the Berkshires. Temperatures are currently between 29 and 33 degrees in the area of sleet and freezing rain. Between 21z and 00z, a warm and moist airmass will be advected over the region as winds turn southerly. With an area of high PWATs just to our south, heavy downpours are possible during this time period. Most models are suggesting precip accumulations just over a quarter inch. With temperatures rising across the region, freezing rain will transition to rain near 00z once temperatures across the region are well above freezing. Rain will be exiting around 3z this evening from west to east as mid level drying moves in and winds become westerly. Temps will continue rising through the 30s, and into the 40s in the coastal plain. Patchy low clouds and fog will develop tonight with some clearing possible before 12z.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
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Saturday... Dry weather returns Saturday as a high pressure builds into the region from the NW. Lingering fog is possible after 12z along the southern coast, but should quickly burn off due to surface heating. Clouds will continue clearing, with most of the interior seeing periods of sun by midday. With NW flow, temps will reach well into the 50s across the interior and coasts. Cooler upper 40s over higher elevations NW MA. Saturday night...Rain showers expected after midnight, with a chance of higher elevation seeing freezing rain and sleet just before sunrise.
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&& .LONG TERM /SUNDAY THROUGH THURSDAY/... */ Highlights... - Wintry mix transitions to freezing rain Saturday night into Sunday - Quiet, dry, near-seasonable early week period - Stormy pattern emerging for the beginning of March */ Overview... Upstream Pacific flow flattening, SE CONUS sub-tropical H5 ridge weakening, SW-NE thermal wind axis and storm track along the better baroclinic zone shifts S/E along which mid-level impulses eject out of a preferred H5 trof pattern across the W CONUS. An active weather pattern with a series of disturbances delivering mixed precipitation events thru the weekend. Building up over the N Atlantic signaled by a strongly -NAO, initial omega-block transitions to a rex-block, retrograding W. The preferred region of storm development shifting, a quiet early week period looks to turn stormy for the beginning of March. Preference to high-res guidance through the weekend capturing 2m temperatures in more detail, with ensemble means thereafter. Hit on targets of opportunity below. */ Discussion... Saturday night into Sunday... An over-running precipitation event associated with a classic warm occlusion into S Canada. Transitioning precip-types as a warm nose around H8 becomes pronounced, deepening above a shallow surface cold airmass, maintained by interior S funneling ageostrophic flow aided by a secondary coastal surface low invoked by strong synoptic lift / forcing as cold surface high pressure is situated N/E. Whew. Overall a favorable synoptic setup for an initial onset of snow and/or sleet before changing over to freezing rain, mainly across the interior. Change-over if not already rain towards the coast. No surprise consensus forecast guidance edged colder, more high-res guidance becoming available. CIPS analogs a higher probability of a >6 hour freezing rain event, yet notably a large spread in the top 5 analogs. While leaning N/W MA holding below freezing throughout, and that sub-freezing wet bulb conditions could extend as far S as N CT and NW RI, hesitation given a decent slug of precip falling through an ever increasing warm layer above a shallow cold layer. Forecast trend accordingly, entrenching cold overnight but chipping away into Sunday morning with increasing warm air advection aloft through which precipitation intensity reaches its peak. A retreat of mainly freezing rain outcomes N/W over time, reiterating that areas in N/W MA are likely to see freezing rain throughout after a brief burst of snow and/or sleet. Ice accretion amounts upwards of 0.1 to 0.2 inches given less dry air intrusions and deeper lift / forcing. This an precipitable waters in the 0.75 to 1.00 inch range, looking at storm-total precipitation amounts that can be well up around 0.50 to 0.75 inches, locally higher along SW facing high terrain slopes and along the anticipated kinked surface warm front. Early next week... Continued preference to ensembles. N Atlantic traffic build up, an omega-block evolves lending to a strongly -NAO. Evolution towards a rex-block retrogressing as energy continually emerges from upstream out of a W CONUS H5 trof pattern, indications the initial region of preferred storm development off SE Canada alters W closer to the E CONUS. The slowed pattern allowing cyclones to mature and later occlude in our neighborhood, forecast model consensus trending with a deep, strong storm in our vicinity for the beginning of March. Way out in time, can hardly touch on details and specifics, continued ensemble member spread. However can`t ignore such robust signal when tides are reaching their peak (Boston around 11.5 feet). Until then will keep it dry and near-seasonable right on up through Thursday. Then all eyes are upon a potential storm system. && .AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
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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 Night/...Moderate confidence. Through today...MVFR/IFR conditions will overspread the region this evening, with rain, pockets of sleet and freezing rain developing across interior MA. Greatest risk of FZRA over higher elevations. Tonight...MVFR prevails with rain this evening, and pockets of FZRA at higher elevations in northern MA. RA/FZRA will end by 3z along the eastern coast. Fog will settle in behind the precip, keeping conditions MVFR in the valleys. Saturday...Fog may linger along the southern coast and islands past 12z. Conditions will improve to VFR across the region by early morning. KBOS Terminal...Moderate confidence. MVFR through this evening with onset of rain near 21z. Rain ending near 3z with improving conditions around 6z. KBDL Terminal...Moderate confidence. MVFR/IFR through this evening. Patchy fog in the AM, burning off by 9z. VFR conditions to follow. Outlook /Sunday through Tuesday/...Moderate confidence. Saturday: VFR. Breezy. Saturday Night: Mainly VFR, with local MVFR possible. Breezy. Chance RA, FZRA, chance SN. Sunday: Mainly IFR, with areas MVFR possible. Windy with local gusts to 30 kt. RA, FZRA, patchy BR. Sunday Night: Mainly VFR, with local IFR possible. Breezy. Patchy FG. Monday: VFR. Monday Night: VFR. Breezy. Tuesday: VFR.
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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 Saturday Night/...High confidence. Today...Gusts to 20 kt over eastern waters late in the day. Vsbys lowering in rain and fog this evening. Tonight...SCA issued for our NE MA waters as a brief period of southerly gusts to near 25 kt overnight. Elsewhere, winds shifting to west with gusts up to 20 kt. Rain exits near 3z with improving vsbys, but patchy fog may develop over southern waters. Saturday...Diminishing westerly winds becoming northerly in the evening. SCA might be needed for the southern waters early Saturday where seas reach 5 feet. Outlook /Sunday through Tuesday/... Saturday: Winds less than 25 kt. Saturday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas locally approaching 5 ft. Chance of rain. Sunday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Rain, patchy fog. Local visibility 1 nm or less. Sunday Night: Winds less than 25 kt. Areas of rough seas. Chance of rain, patchy fog. Local visibility 1 to 3 nm. Monday through Monday Night: Winds less than 25 kt. Seas up to 5 ft. Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...Winter Weather Advisory until 9 PM EST this evening for MAZ002>004-008-009. RI...None. MARINE...None. && $$ SYNOPSIS...KJC/Nocera/Sipprell/Correia NEAR TERM...KJC/Nocera/Sipprell/Correia SHORT TERM...KJC/Nocera/Correia LONG TERM...Sipprell AVIATION...KJC/Nocera/Sipprell/Correia MARINE...KJC/Sipprell/Correia/Nocera

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