Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 202315 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 615 PM EST Sat Jan 20 2018 .SYNOPSIS... A fast moving storm system will bring the potential for heavy rain and a period of strong winds on the coast Tuesday, but this will be preceded by a risk of a light wintry mix/ice across the interior Monday into early Tuesday morning. Blustery, dry and colder weather follows Wednesday through Friday, before above normal temperatures likely return next weekend. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... 615 pm update... A ridge of high pressure will result in mainly clear skies tonight other than some high thin cirrus. However...there might be a bit of mid level cloudiness trying to work into portions of interior southern New England after midnight. Winds will continue to diminish and allow for low temperatures in the 20s to the lower 30s. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... High pressure in place Sunday with fair skies and light wind. Moisture fields do show some increasing mid and high level moisture, so expect some increasing clouds mostly in the afternoon/evening. With mixing to 950 mb, expect max temps in the mid to upper 40s, a few spots around 50. The clouds increase Sunday night. A cold front in Northern New England dips south and may slip through Southern New England. But with the upper flow west-east we do not expect a lot of push to it, and potential that it stalls either over or near us. The net change in the airmass is nil, so min temps Sunday night should be similar to tonight. Low level southerly winds reach only to Western NY/PA by 12Z Monday...still west winds over us at that time...which means little lift to be generated Sunday night. So the probability of precip should be low. If the precipitation were to move in faster, low level temperatures would support a mix with sleet and freezing rain. But that scenario looks unlikely at this time. Our forecast shows slight chance pops in Western MA/CT by 12Z Monday, and that may be overplaying the likelihood. && .LONG TERM /MONDAY THROUGH SATURDAY/... Highlights... * Light icing risk Mon/early Tue across interior w/focus high terrain * Heavy rain Tue with a period of strong winds possible on the coast * Significant flooding issues are not expected Tuesday * Dry/blustery but turning colder Wed and especially by Thu/Fri Details... Monday and Monday night... Main concern Mon into Mon night will be the potential for a period of light icing across parts of interior southern New England with the main focus being the Worcester Hills and east slopes of the Berkshires. A cold air damming pattern appears to be setting up with Canadian high pressure in place. Meanwhile...enough warm advection aloft should result in light precipitation breaking out across the region. Timing uncertain...but potential increases Monday afternoon and night although can not rule out some light precipitation arriving Monday morning. The bulk of the precipitation that falls into Monday night should be light as stronger synoptic scale forcing/deeper moisture will remain to our west. Mainly just light rain showers expected on the coastal plain. The focus will be across interior southern New England with the main area of concern the high terrain of the Worcester Hills and east slopes of the Berkshires. Some very minor light snow/sleet accums are possible at the onset, but main issue will be light freezing rain/light icing potential. How much of the interior is impacted by a period of icing remains uncertain. Most of the guidance indicates the surface high fairly far north in Canada and it is not really nosing down into southern New England. Plus the fact that were dealing with an unseasonably mild airmass currently in place for January that needs to depart. Therefore...the main concern will be the high terrain of the northern Worcester Hills and east slopes of the Berkshires. Temps likely to be a few degrees colder in this region and most of the high resolution guidance including the SREF probabilities is targeting this region for the potential of light icing. Icy roads and walkways certainly a possibility especially later Monday into Monday night. Tuesday... The main surface low will be lifting across the Great Lakes. This will induce a southerly LLJ 3+ standard deviations above normal with Pwats 2+ above normal. While some lingering freezing rain can not be ruled out across the high terrain of MA early Tue am, any left over ice should change to rain. The main story will then be a period of heavy rain given the anomalous ingredients in place. As previous forecaster mentioned...there may even be an isolated t-storm or two as Showalter Indices drop below zero. In addition...potent southerly low level jet may result in a period of 40 to 50 mph wind gusts along the coastal plain. This is especially true if high temps climb well into the 50s and any convective elements are able to tap the stronger winds aloft. The fortunate thing is this system looks fairly progressive...so most of the heavy rain will be ending Tuesday evening. Rainfall amounts on the order of 0.75 to 1.50 inches seem reasonable...which may lead to typical nuisance/poor drainage street given much of this probably falls in a 6 hour period. However, The Northeast River Forecast Center indicates that while a few rivers may rise to action stage they are not expecting any significant problems. Wednesday through Friday... Transient trough sets up over the northeast allowing colder weather to work back into the region...but it should be dry as high pressure builds in from the west. High temps Wed will be well up into the 30s to the lower 40s on the coastal plain although a bit windy. Colder Thu and Fri with highs mainly in the upper 20s to the lower 30s. Saturday... The high pressure system moves off the coast which should allow a return flow of milder air into the region. Above normal temps look to return and right now it looks like any forcing/deeper moisture will be to the west of our region. Therefore...will maintain a dry forecast for the first part of next weekend. && .AVIATION /23Z SATURDAY THROUGH THURSDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday Night/... Tonight...High confidence. VFR with just a low risk of marginal MVFR cigs near daybreak across far western MA. Sunday...High confidence. VFR. W-NW winds around 10 kt or less as pressure gradient relaxes. Sunday night... Moderate confidence. VFR. Increasing sky cover late at night. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Monday through Thursday/... Monday: MVFR/IFR conditions possible. Chance -SHRA, chance -FZRA across the interior high terrain. Monday Night: Mainly MVFR, with areas IFR possible. Breezy. -SHRA. Pockets of -FZRA possible across the interior with the focus in the high terrain of MA. Tuesday: MVFR/IFR conditions possible. Strong winds with gusts to 40 kt. RA. Tuesday Night: Mainly VFR, with local MVFR possible. Windy with local gusts to 30 kt. Slight chance SHRA. Wednesday through Wednesday Night: VFR. Windy with gusts to 35 kt. Thursday: VFR. Windy with gusts to 30 kt. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday Night/...High confidence. Tonight... Winds have dropped below gale force thresholds and this trend will continue. Should see gusts drop below small craft thresholds overnight from west to east. Seas also subsiding tonight with the southern outer waters the last to drop below 5 feet near daybreak. Sunday and Sunday night... High pressure over the waters should provide fair weather with light winds and seas below 5 feet. Clouds will increase overnight, but support for any precipitation will remain well to our west during the night. Outlook /Monday through Thursday/... Monday: Winds less than 25 kt. Chance of rain showers. Monday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. Tuesday: Risk for gale force winds with gusts up to 40 kt. Rough seas up to 12 ft. Rain. Areas of visibility 1 to 3 nm. Tuesday Night: Risk for gale force winds with gusts up to 35 kt. Rough seas up to 11 ft. Chance of rain showers. Wednesday: Moderate risk for gale force winds with gusts up to 35 kt. Areas of rough seas. Wednesday Night: Low risk for gale force winds with gusts up to 35 kt. Areas of rough seas. Freezing spray. Thursday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas. Freezing spray. && .HYDROLOGY... A Flood Warning remains in effect for the Connecticut River at Middle Haddam, where ice jams are causing river fluctuations. For details on specific area rivers, including observed and forecast river stages, please visit the Advanced Hydrologic Prediction Service (AHPS) graphs on our website. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 10 PM EST this evening for ANZ231>235-237-251. Small Craft Advisory until 6 AM EST Sunday for ANZ250-254>256. && $$ SYNOPSIS...WTB/Frank NEAR TERM...Frank SHORT TERM...WTB LONG TERM...Frank AVIATION...WTB/Frank MARINE...WTB/Frank HYDROLOGY...Staff

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