Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 210633 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 133 AM EST Sun Jan 21 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 THIS MORNING/...
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105 AM Update... Appears the southern edge of the high clouds has been slowly drifting northward across the region, with clear or mostly clear skies being reported across S CT into the NYC area at 06Z as seen on GOES-16 Nighttime Microphysics RGB composite and fog product imagery. An area of clear or few cirrus clouds will cross the region out of central and S NY/E PA/N NJ for the next few hours. However, need to watch area of low clouds moving steadily eastward from W PA/WV/W NY, which should push into the CT valley during the morning hours to midday. Noting patchy fog has developed across the normally foggy locations of KEEN and KORE at 06Z. May see more patchy fog develop across the normally prone areas of the CT valley and possibly into N central and NE Mass through the remainder of the night. Where skies have cleared, temps have fallen to the 20s to lower 30s, while holding in the mid-upper 30s along coastal areas. Light/variable (mainly W-NW) to calm winds will continue through daybreak. Have updated previous forecast to bring conditions current.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM MONDAY/...
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High pressure in place today 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 tonight. 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.
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&& .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
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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.
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&& .AVIATION /06Z SUNDAY THROUGH THURSDAY/...
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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/... Through 12Z...High confidence. Mainly VFR. Patchy MVFR-IFR CIGS/VSBYS develop in patchy fog in normally prone areas of the CT valley, possible across portions of interior E Mass for a few hours prior to sunrise. Today...High confidence. VFR. Any leftover MVFR-IFR conditions should improve by around 14Z. W-NW winds around 10 kt or less as pressure gradient relaxes. Tonight...Moderate confidence in general trends, lower in timing arrival of precip. Mainly VFR through midnight, then MVFR-IFR conditions move into the CT valley in fog and mixed snow/sleet/freezing rain. 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.
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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/...High confidence. Through 12Z... Winds have diminished below small craft levels across the near shore waters so the Small Craft Advisory ended at 10 PM. Still noting some gusts up to 20-25 kt and seas up to 5-6 ft over the open waters which will subside through the remainder of the night. Today and Tonight... 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.
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&& .HYDROLOGY... A Flood Warning remains in effect for the Connecticut River at Middle Haddam, where ice jams are causing river fluctuations. Received new data from NERFC late tonight so updated the Flood Statement to provide the latest information. Not too much change from the previous forecast. 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...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 6 AM EST early this morning for ANZ250-254>256.
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&& $$ SYNOPSIS...WTB/Frank NEAR TERM...Frank/EVT SHORT TERM...WTB LONG TERM...Frank AVIATION...WTB/Frank/EVT MARINE...WTB/Frank/EVT HYDROLOGY...Staff

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