Area Forecast Discussion
Issued by NWS Boston, MA

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KBOX 212043 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 343 PM EST Sun Jan 21 2018 .SYNOPSIS... Warm air aloft moves north tonight and brings clouds to Southern New England. Some light precipitation is possible Monday. Most of it will be rain, but some light icing is possible in the interior. A fast moving storm system will bring a period of heavy rain to the region Tuesday along with strong winds on the coast. Blustery, dry and colder weather follows Wednesday through Friday, before above normal temperatures likely return next weekend. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... High pressure is situated to provide dry weather much of the night. Low level flow remains light most of this time, but shows signs of overrunning after midnight. Meanwhile, satellite images and sfc observations show a cloud deck over Eastern PA edging northeast. Between this and the favorable development of lift overnight, expect increasing clouds through the night. Can not rule out some light precip late, especially in Western MA and CT, but the chance before 12Z is rather low so we used slight chance pops. If any precipitation were to form late tonight, temperature profiles suggest rain in the south and a snow/sleet/freezing rain mix north. Clouds will limit the overnight cooling, and cold air damming signal does not show much until late night. We maintain a range of upper 20s north to mid 30s south coast. && .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
-- Changed Discussion --
Monday... High pressure over Quebec Monday and increasing cold air damming into New England. The damming seems focused on Northern New England, but could further expand into our area as well during Monday morning. Our temperature profiles support rain most places, but a rain/snow mix north of the Mass Pike. The GFS and ECMWF bring a front south into Southern New England or just to our south. This shows increasing lift potential, thus increasing pops. We show chance pops all areas Monday morning and likely pops in the afternoon in Western and Central Mass and adjoining CT. An east wind should be enough to keep ptype as rain, but it may be marginal in Western Mass/Northern Worcester County. Even with better lift, the focus of southerly low level winds and moisture remains to our west across New York State through the day. So we continue to expect QPF amounts up to 0.1 inches. Monday night... Evening cooling and the stalled front to our south may allow a brief period of freezing rain in Central and Western Mass, especially along and north of the Route 2 corridor. The front moves north during the night with winds shifting from the south. This will bring slowly rising temperatures overnight ending the icing risk. South-southwest winds 35-40 knots move up over the region during the late night. This transports 1 inch PW values into the area. Expect increasing chance of rain toward morning with categorical pops...75 pct or higher...over Western Mass and Western CT.
-- End Changed Discussion --
&& .LONG TERM /TUESDAY THROUGH SUNDAY/...
-- Changed Discussion --
Highlights... * Heavy rain Tue with a period of strong winds SE New Eng * Some minor flooding issues are possible * Dry/blustery and turning colder Wed and especially Thu/Fri Overview and model preferences... The medium range will feature gradual breakdown of strong positive height anomalies as ridging shifts offshore, allowing an opening cutoff to phase with the northern stream. This transition, and the fact that the cutoff will have tapped subtropical moisture will feature a widespread rainfall event Tue, until the drier CP air associated with the N stream filters in mid week. This colder airmass is not significantly cold, as low and mid lvl temps anomalies are barely 1 full standard deviation below normal, but colder wx can be expected to follow the rainfall. As a PACNW wave deepens in the lee of the Rockies late week, this will force yet another rise in height anomalies with strong ridging into the weekend, which would favor another moderation in temperatures and suggests that any precip associated with low pres attendant to the wave moving E of the Rockies is likely to remain warm at least initially. Overall, both ensembles and deterministic guidance are in fairly good agreement with these synoptic scale features, so will use a consensus guidance blend as the baseline for this forecast. Details... Tue... Low pres, moving out of the Great Lakes will initially slide along the Canadian border into N Canada. The fact that this system is continuing to deepen on Tue suggests the lack of an occlusion processes yet and favors a more progressive passage. Several factors point to periods of moderate and occasional heavy rain as the cold front slides through mid day Wed into early Wed evening. With the influence of subtropical moisture allowing PWATs to reach near 1.00 inches (almost 3 std deviations above normal) combined with deep warm rain processes, conditionally unstable profiles supporting some modest elevated CAPE and LLJ approaching +60 kt all should act in accordance. Therefore, expecting widespread rain with periods of rainfall approaching 0.5-1.00in/hr on occasion, especially as any convective elements develop. These rainfall rates do suggest a lingering risk for urban and poor drainage flooding, as well as some flashier river flooding especially where any lingering ice is involved. Area hydrographs, particularly in NW MA continue to show the influence of ice. This may require the hoisting of a flood watch in the future. Final QPF totals generally range between 0.75 and 1.50 inches, although a few spots may approach 2.00 inches before all is finished. Low risk for occasional TSRA, especially along the LLJ core across SE MA/RI, but there is a low risk across most of S New England. Aside from the heavy rain/flood risk. The core of a 60+ kt (H92) LLJ will slide across SE MA/RI during the afternoon and early evening hours. Conditionally unstable soundings support some mixing of this momentum on its own, but as previous forecaster noted, the addition of warmer sfc temps (if they reach near 60F) will enhance the lower level mixing. Also, convection will also enhance this mixing. Therefore, will continue to yield about 60-70 percent of this momentum to the surface in this area, which is likely require wind advisories if realized. Near shore locations may be slightly inverted thanks to cooler SSTs, but these could be overcome by the mechanical and frictional forces mentioned above. Mild, thanks to warm H92 temps in place into the overnight hours. Expecting highs mainly in the 50s across most of S New England. Wed through Fri... Cooling trend expected as lower height anomalies associated with a gradually opening trof settles across New England. This will also be associated with high pres and generally dry conditions thanks to strong subsidence inversion, especially as the high crests above 1035hPa. Wed, the delay in cold advection should keep highs near seasonal normals, mainly the upper 20s to mid 30s, although a few spots mainly across E MA/RI could reach around 40F thanks to some downsloping. Otherwise, the cooler days are expected on Thu and Fri as H92 temps settle to -10C and -7C on average respectively. This will keep highs in the mid 20s to low 30s each day. The best chance for radiational cooling appears to be Thu night into Fri, thanks to a slackening in the sfc pres gradient which will be too strong Wed night. This will likely allow mins to fall into the single digits and teens. Next weekend... Gradual transition as high pres and associated ridging move E, allowing for another deepening trof to impact the region. Initially, the warming signal with rising heights for Sat favors mainly a warm solution for low pres passage on Sun, but given the possibility of some entrenched lower level cold air in the NW at precip onset, as well as uncertainty with the N stream influence does hint at the possibility of a colder solution. Will lean more heavily on ensemble means, which, for the most part yields a warmer (rain) solution, but this will have to be watched as all of the players become better sampled.
-- End Changed Discussion --
&& .AVIATION /21Z SUNDAY THROUGH FRIDAY/...
-- Changed Discussion --
Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday Night/... Tonight...High confidence in general, moderate confidence in timing of lower conditions. VFR through midnight. MVFR cigs after 06Z. Low probability toward morning for rain/sleet/freezing rain in Western Mass and Hartford County CT. This could affect the morning commute, especially in the CEF-BDL-HFD area. Monday...Moderate confidence. MVFR cigs with areas of IFR cigs developing in the afternoon. Increasing chance of light rain through the day. Generally MVFR vsbys in rain and some mixed rain/snow. Light wind becomes light East-Northeast. Monday night...Moderate confidence. MVFR conditions with areas of IFR. Rain most places with a chance of freezing rain early in northern areas of Massachusetts such as vicinity of FIT and ORE. Winds turn from the Southeast and South toward morning. KBOS Terminal...Moderate to high confidence in TAF. KBDL Terminal...Moderate to high confidence in TAF. Outlook /Tuesday through Friday/... Tuesday: Mainly MVFR, with local IFR possible. Strong winds with gusts to 40 kt. RA, slight chance TSRA. Tuesday Night: Mainly VFR, with local MVFR possible. Strong winds with local gusts to 40 kt. Wednesday through Friday: VFR. Breezy.
-- End Changed Discussion --
&& .MARINE...
-- Changed Discussion --
Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday Night/...Moderate confidence. Tonight and Monday... Light winds shift from the south late at night and from the southeast Monday. Speeds remain below 15 knots. Seas 2 feet or less. Vsby lowers to 3-5 miles in rain during Monday afternoon. Monday night... Southeast to south wind increasing, but remaining below 25 knots. Seas building to 4 feet. Rain with vsbys 3-5 miles. Outlook /Tuesday through Friday/... Tuesday: Moderate risk for gale force winds with gusts up to 40 kt. Rough seas up to 11 ft. Rain, slight chance of thunderstorms. Tuesday Night: Moderate risk for gale force winds with gusts up to 40 kt. Rough seas up to 10 ft. Chance of rain showers. Wednesday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 10 ft. Wednesday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Thursday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Thursday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Friday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas.
-- End Changed Discussion --
&& .HYDROLOGY... A Flood Warning remains in effect for the Connecticut River at Middle Haddam, where ice jams are causing river fluctuations. No significant change from earlier forecasts. 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...
-- Changed Discussion --
CT...None. MA...None. RI...None. MARINE...Gale Watch from Tuesday morning through late Tuesday night for ANZ232>235-237-250-254>256. Gale Watch from Tuesday morning through Tuesday evening for ANZ230-236. Gale Watch from Tuesday morning through late Tuesday night for ANZ231-251.
-- End Changed Discussion --
&& $$ SYNOPSIS...WTB/Doody NEAR TERM...WTB SHORT TERM...WTB LONG TERM...Doody AVIATION...WTB/Doody MARINE...WTB/Doody HYDROLOGY...staff

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.