Area Forecast Discussion
Issued by NWS Boston, MA

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
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
-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KBOX 192121 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 521 PM EDT Wed Apr 19 2017 .SYNOPSIS...
-- Changed Discussion --
Weak low pressure area will approach New England this evening, crossing the region overnight. A weak area of high pressure will bring a brief period of dry conditions Thursday. Low pressure from the Plains redevelops along the New England coast Friday afternoon/evening. This means rain Thursday night and Friday. Weak high pressure builds drier weather for Saturday and early Sunday. Another low pressure area moves to the Carolina coast and passes well offshore of Nantucket Sunday night. High pressure in Canada brings dry weather early next week.
-- End Changed Discussion --
&& .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... Afternoon Update... Afternoon temps were several degrees warmer than forecast thanks to gusty winds that shifted to S-SW beginning across the CT valley around 18Z then moved E across most areas. Winds remained from the S- SE across Cape Cod and the islands and into southern Plymouth county where temps remaining in the mid-upper 40s. Wind gusts up to 25-27 kt reported at KMQE, KOWD and KBVY at 19Z. Noted 3 hr pres falls of 2-3 mb as high pres ridge shifts E into Mass Bay and the Gulf of Maine. Mid and high clouds have been pushing steadily E this afternoon across the region. Noting lower clouds moving into portions of the CT valley, with leading edge of light rain into the mid and upper Hudson Valley. Already noting some light rain at KORE and KAFN at 20Z, but visibility at 10SM so remaining spotty. Some more sprinkles will move into the CT valley through 22Z, even with dewpt depressions rather high (temps in the lower 50s and dewpts in the lower-mid 30s). Will take some time to saturate the lower layers before steady rain arrives. Area of -RA/RA across most of NY state into N PA at 19Z, moving steadily E at around 30 kt. Current timing suggests that the back edge of steady precip may reach the CT valley by around midnight as the best lift shifts E. Could still see some leftover spotty showers lingering through most of the night, but somewhat drier air may begin to push into central and northern areas from 10Z-12Z. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...
-- Changed Discussion --
Tonight... Weak, flat H5 short wave will work eastward across the region. Short range models signaling H85 jet at 40-45 kt moving across helping with decent lift. With the fast flow aloft, the best dynamics (which is not all that much of to begin with) will remain N of the region as it weakens further overnight. QPF amounts will range from a tenth of an inch of less N of the Mass Pike, up to around 0.2 inches across southern areas where precip will slow overnight especially along the S coast. With clouds across the region and S-SW winds in place, temps will only fall back to the lower-mid 40s by around midnight before slowly rising during the pre-dawn hours. Thursday... Leftover showers across S coastal areas should push offshore by mid-late morning. Weak ridge at the surface and aloft moves quickly across, but low level moisture will be trapped in light wind field so expect clouds to linger through the day. 12Z MOS and model guidance continues to signal rather mild temps considering the cloud cover. Could realize the milder readings across the interior with light winds. However, will be cooler along the coast as winds, which start off below 10 mph as front moves across during the morning, will shift to N-NE by afternoon then eventually to E. Carried temp ranges from the 50s along the immediate coast to lower-mid 60s inland. With fast flow aloft, leading edge of light rain will start to approach western areas by late afternoon. Carried chance POPs with this approaching system moving into the CT valley by evening. Thursday night... Models signaling rather strong H5 short wave moving across the Great Lakes late Thu night, along with good H5 difluence moving across ahead of this system as the H5 ridge moves offshore by around 06Z. Noting decent PWAT moisture plume working across the region mainly after midnight, on order of 1.1 to 1.2 inches. So, could see some downpours. Best shot of precip will be across central and northern areas as low passes across northern New England. Also noting decent instability moving across N CT into W RI after midnight, with K indices around 30 and TQ values in the upper teens. So, can not rule out some isolated thunder with some of the rain as it moves across. Have mentioned it in the forecast for those areas, even though it looks like better instability works across after 12Z. Expect temps to bottom out in the mid-upper 40s.
-- End Changed Discussion --
&& .LONG TERM /FRIDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
Big Picture... Longwave flow pattern trends from zonal late this week to weakly cyclonic over the Central and Eastern USA by early next week. Contour heights remain at or above normal values. The shortwave scale shows one shortwave moving across Canada and passing north of New England Friday night and Saturday. A southern stream shortwave moves ashore from the Pacific today, forms a closed low over the Plains Friday night, and then shifts to the Florida coast late Monday. A portion of this shortwave eject east through the Mid Atlantic states Monday. Mass fields are similar among the models through early next week, which increases confidence. Details... Friday... Northern stream shortwave starts the day over the Great Lakes with supporting 135-knot jet aimed at Buffalo. These move east, with the upper jet reaching the coastline in the afternoon. Meanwhile low level southeast jet feeds in off the ocean into Eastern MA, riding up over the stalled front south of New England. All models show the surface system redeveloping near NYC and Long Island late afternoon and moving off to our east Friday night. The resulting lift combined with precip water values over an inch and southeast flow should bring rainy weather to most of Southern New England until the system moves past on Friday evening. The high precip water values suggest potential for locally heavy downpours embedded in the rain area. Stability parameters are marginal (TT is 46-48) and mostly favor CT. We note that guidance pop values diminish quickly by midday while the moist southeast flow lingers through the afternoon and evening. We have manually maintained likely pops through the afternoon and diminish west-to-east as the surface system moves past. Winds shift from the north- northwest bringing in partial clearing during the night. One other change regards the temperatures. With a steady onshore flow over water temps in the mid 40s, we lowered temps a couple of degrees with max values along the coast in the upper 40s and low 50s and temps inland in the mid to upper 50s. Saturday... Weak high pressure in Canada builds south with drier air. Meanwhile, a second trough axis associated with the northern shortwave moves through New England. Most of the forcing and moisture with this system is focused over Northern New England, but close enough to us to expect areas of daytime clouds, especially in Northern MA. Sunday... Southern stream upper low and trough feed moisture up the coast and generate another area of overrunning south and southwest of New England. The GFS and ECMWF show the surface level easterly jet and low level southwest jet remaining south of our area. This brings into question whether we would get any rain. Meanwhile cross sections show deep lift and deep moisture over southern areas such as Providence and less moisture and lift over northern areas such as Boston. Worcester and Hartford are in between. We will feature chance pops for most areas with the bulk of pcpn Sunday afternoon and evening. South Coastal areas, closest to the offshore low, will feature likely pops at the height of the storm. The shortwave Monday through Wednesday... Canada high pressure reasserts control from the Maritimes much of this period. The ECMWF and GGEM take the low off Florida and eject it northeast and pass it just off Nantucket Tuesday night or Wednesday. The GFS keeps the system well offshore. Not much confidence in the solutions at this time. We will feature slight chance pops in RI and Eastern MA Tuesday and await a consensus to form.
-- End Changed Discussion --
&& .AVIATION /21Z WEDNESDAY THROUGH MONDAY/...
-- Changed Discussion --
Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday Night/...Moderate confidence. Through 00Z...Any leftover MVFR CIGS along S coastal areas should improve to VFR as S-SW winds pick up. Low risk of brief MVFR CIGS across CT valley after 22Z in any steady -SHRA. SE winds shift to S, gusting up to 20-25 kt along immediate coast. Tonight...Mainly VFR, but areas of MVFR conditions will move E across the region with -SHRA/SHRA. Low chance for brief IFR in any heavier showers, mainly through 04Z-08Z. Any -SHRA should end by 10Z-12Z near and N of the Mass Pike, but MVFR CIGS will likely linger. Thursday...Areas of MVFR to local IFR conditions early Thu morning, then should improve to VFR. Sct -SHRA may linger along S coast through midday before moving off the coast. As next system approaches, will see spotty light rain move into western areas around or after 22Z. Should remain VFR. Thursday night...Generally VFR in -RA early, then CIGS lowering to MVFR-IFR from W-E mainly after midnight. Low risk of -TSRA across N CT/W RI around or after 08Z. E-SE winds KBOS TAF...Moderate confidence. Mainly VFR into this evening. CIGS may lower to MVFR around 03Z-05Z. Low risk for period of IFR CIGS/MVFR VSBYS toward daybreak Thu. -SHRA move across from 03Z-08Z, then push S of KBOS around 12Z-14Z Thu. S winds around 15 kt this aftn will diminish tonight. CIGS improve to VFR Thursday light/variable becoming onshore. KBDL TAF...High confidence. VFR through around 00Z, then CIGS lower to MVFR with scattered -SHRA. May see brief IFR CIGS after 06Z-12Z Thu. S wind gusting to 20-25 kt into this evening, then diminishing overnight. Conditions should improve to VFR CIGS by mid morning Thu. Light/variable winds shift to E Thu afternoon. Outlook /Friday through Monday/... Friday...Moderate confidence. IFR in rain and fog, improving to VFR from west to east Friday night. East to southeast winds may gust near 30 knots at times along the east coast of Massachusetts Friday. Winds shift from the north and diminish during Friday night. Saturday...Moderate-high confidence. VFR Saturday with potential for MVFR cigs along the east coast of Massachusetts. Sunday-Monday...Low-Moderate confidence. VFR cigs Sunday morning lower to MVFR by Sunday afternoon. Areas of MVFR/IFR in rain and fog late Sunday and Sunday night. Best chance of lower conditions will be near the South Coast and Islands. Conditions improve to VFR Monday.
-- 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 Thursday Night/...High confidence. Tonight...Small crafts continue on the eastern waters, mainly for seas E and S of Cape Cod and Nantucket and for both wind and seas E of Cape Ann to Plymouth where gusts will be up to around 25 kt. Seas around 5 ft mainly on the outer waters. Conditions should diminish after midnight on Mass and Ipswich Bays as winds diminish, but seas may linger through the remainder of the night on the eastern outer waters. Thursday...Expect light winds and seas below 5 ft Thu as weak high pres builds across the waters. Thursday night...Winds shift to E-SE as low pressure passes N of the waters. Winds and seas will increase after midnight mainly on the eastern waters, with gusts up to 25-30 kt and seas building to around 5 ft. Small crafts will likely be needed. Outlook /Friday through Monday/... Friday...Moderate confidence. East to southeast winds to the north of a warm front Friday. Some southern waters may slip south of the front, with winds becoming more from the south. Wind speeds will increase east of Massachusetts during the day with gusts 25 to 30 knots and a low potential for 35 knot gusts. These winds will help build seas east of Massachusetts with 5-8 feet in the afternoon/evening. Poor visibility at times in rain and fog during the day. A cold front swings across the waters early Friday night, with winds shifting from the north and northwest behind the front with speeds to 20 knots. Seas will diminish overnight as winds become offshore. Visibility will improve with the wind shift. Saturday...Moderate confidence. Winds from the north-northwest with speeds up to 20 knots. Low potential for 25 knots. Lingering 5 foot seas on the eastern outer waters will diminish later in the day. Winds diminish Saturday evening. Sunday-Monday...Moderate confidence. Winds turn from the east Sunday as low pressure passes well offshore. Winds up to 20 knots are possible with the best chance on the southern outer waters. Seas remain below 5 feet on our waters, but build to 5 feet just south of our southern outer waters. Winds turn from the north on Monday but remain below 20 knots.
-- End Changed Discussion --
&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 AM EDT Thursday for ANZ250. Small Craft Advisory until 2 AM EDT Thursday for ANZ251. Small Craft Advisory for hazardous seas until 8 AM EDT Thursday for ANZ254. Small Craft Advisory for hazardous seas until 5 AM EDT Thursday for ANZ255. && $$ SYNOPSIS...WTB/EVT NEAR TERM...EVT SHORT TERM...EVT LONG TERM...WTB AVIATION...WTB/EVT MARINE...WTB/EVT

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