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
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KBOX 200752 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 352 AM EDT Thu Apr 20 2017 .SYNOPSIS...
-- Changed Discussion --
A weak frontal boundary moves across the region today with a period of rain showers along the S coast this morning. The frontal boundary slips south of the area this afternoon followed by a drying trend and temperatures milder than yesterday. This frontal boundary lifts northward as a warm front late tonight into Friday morning and will be accompanied by another round of rain. Dry and quiet for Saturday. Skirting rain from the S around Sunday and another shot around late Tuesday, otherwise near- seasonable conditions as temperatures moderate up against E onshore flow.
-- End Changed Discussion --
&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
-- Changed Discussion --
345 am update... Northern stream short wave trough over southern Quebec and northern New England beginning to exit eastward. Anticyclonic flow and associated subsidence behind this feature beginning to advect into northern MA with back edge of rain shield from coastal CT-RI- southeast MA at 330 am. This drying trend will continue during the predawn hours from northwest to southeast. However weak wave on the frontal boundary over PA will advect another round of light rain across the immediate south coast and islands around daybreak. Thus rain will be slow to clear this region. Good mid level drying behind this wave this afternoon as K indices drop into the negative numbers. However low level moisture will be difficult to completely scour out. So expecting clouds to lift as the day progress along with a few breaks of sunshine. This may especially be true toward sunset as daytime heating wanes. Milder than yesterday with highs in the low to mid 60s except 50s along the immediate coast including Boston with light onshore winds.
-- End Changed Discussion --
&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
-- Changed Discussion --
Tonight... Dry evening but progressive upper air pattern results in overrunning precip redeveloping 03z-06z across the region from west to east as parent low enters the Great Lakes. This results in frontal boundary that slipped south of the region later today to return as a warm front. Thus rain should become widespread second half of the night. This portion of the forecast was based on a non NAM solution given its wind fields/jet dynamics were considerably stronger than any other guid source. Increasing SE winds in return flow will provide damp/chilly/raw conditions across the region. Not much of a temp change along with uniform conditions give widespread clouds/rain. Friday... Good overrunning precip during the morning and possibly lingering into early afternoon as parent low tracks into southern Quebec along with triple pt low trying to form over eastern PA. Forcing for ascent is modest and instability aloft is very marginal. Therefore decided to leave out any mention of thunder. However with PWATs climbing to +2 SD above climo rain could be moderate to perhaps briefly heavy for a time. It will be a chilly/damp/raw day with increasing southeast winds off the chilly ocean waters. Could see winds gusts up to 30 mph at times from Cape Cod to Cape Ann. Drier air invades the region 21z-00z from west to east as K indices drop into the negative values. Thus rain should taper off during this time.
-- End Changed Discussion --
&& .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
-- Changed Discussion --
*/ Highlights... - Drying out Friday night into Saturday - Chance of rain Saturday night into Sunday morning, esp S/E - A gradual warming through the week up against onshore flow - Another chance of rain in-between late Tuesday / Tuesday night */ Overview... Series of Pacific disturbances undergoing cyclogenesis to the lee of the Rockies while being steered via a larger N Canada gyre. Fairly decent agreement of mid-level features within the global models into early next week, diverging in their handling of individual impulses thereafter especially off the E CONUS by late week. Yet at this time there are indications of perhaps a sub-tropical connection related to the MJO resulting in stronger H5 ridging between HI and CA ahead of deep troughing extending S from Aleutians. Downstream H5 trough- ridge promotion over the CONUS signaled broadly per ensemble means. Trend towards anomalous NE CONUS ridging with potential +15C H85 temperature anomalies. Corroborating signs within 20.0z deterministic guidance with surface high pressure N/E lending to an onshore, cool flow, while uncertainty on a possible cut- off low. Thus will stick with ensemble means given increasing spread in solutions for late week. Consensus blend prior to Wednesday. Will hit the highlights in the discussion below. */ Discussion... Friday night into Saturday... Drying out. Increasing subsidence and drier air through the column, low level moisture becoming trapped. Thinking we`ll see broken to overcast cloud decks throughout. Perhaps a lid on temperatures. If more sunshine were allowed to filter through we`d see seasonable conditions with highs up into the 60s, otherwise cooler under a light NW flow. A blend of all available guidance weighting towards seasonable averages, highs in the upper 50s to low 60s. Saturday night through Sunday night... Possible rain overnight into Sunday, otherwise dry. Noting a consensus blend of elongated mid-level energy extending SW-NE across the NE CONUS parent with sufficient low to mid level moisture and isentropic ascent, especially over S/SE New England incorporating CT, RI, and SE MA. Leaning with chance PoPs, NW-SE gradient, holding away from likely given some uncertainty. Through the day, drier air and down-sloping motions, as well as subsidence mid-level features, leaning more so with the 20.0z GFS, expecting drier conditions in advance of an approaching N-stream cold front, but not ignoring the 20.0z EC nor it`s 19.12z EPS/ECens counterparts which lean heavy on the wet side of solutions. Given this, could end up notably warmer on Sunday with scattered to broken cloud decks in believe the GFS and its H925-85 temperature profile. Again, the EC cooler and wet. Light winds throughout, somewhat variable between low to mid level features. Monday through Wednesday... Periods of dry weather with potential of some rain for late Tuesday into Tuesday night. Additional Pacific energy emerging from the W potentially draws cut-off energy and sub-tropical moisture off the SE CONUS, ascending it N across the region. Sufficient low to mid level moisture along with lifting mechanisms and perhaps some attributable forcing per a consensus of deterministic guidance. A decent signal of light rain outcomes discerned from the GEFS/ECens. Will lean with chance PoPs, highest S/E. Return of milder air aloft, leaning seasonable for Monday, clouds at the very minimum Tuesday which will keep conditions cool, while milder Wednesday. However, a tricky temperature gradient SW to NE with likely surface wedge of high pressure from the N/E brought on by potential enhanced ridging across the region ahead of a developing broad trough over the W CONUS. So in summary, leaning a slow, moderating temperature trend with E onshore flow hampering a faster warm-up, with the chance of some over-running rains late Tuesday into Tuesday night in-between. Forecast solutions flopping on a potential coastal low setup so will steer away from the 20.0z EC with this forecast leaning with more dominant wedging ridge, slower pattern, and possible cut-off energy that the 20.0z GFS suggests. Thursday onward... Keeping it dry under the dominance of mid-level ridging and surface high pressure. Preference to ensemble means over considerable spread within deterministic guidance. Continued influence of E onshore flow wanes lending to a moderating temperature trend over time.
-- End Changed Discussion --
&& .AVIATION /08Z THURSDAY THROUGH MONDAY/...
-- Changed Discussion --
Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 2 am update... Short Term /through Friday/...Moderate confidence. Thru 12z... Rain shield over CT/RI and southeast MA will continue moving southeast and should be confined to the immediate south coast of MA/RI at daybreak. Cigs mainly a mix of IFR/MVFR with vsbys mostly VFR. After 12z... Back edge of rain shield may continue to clip the south coast of RI/MA at 12z...otherwise trend will be for precip to move offshore and drier air to overspread the region. IFR/MVFR cigs slowly lift to VFR by afternoon. VFR vsbys continue. Winds fairly light and variable today. Tonight... Dry to start but rain redevelops after 03z from west to east with some rain moderate to briefly heavy toward 12z Fri. VFR conditions to start the evening but then lowering to a mix of IFR/MVFR late. Friday... A mix of IFR/MVFR in rain with a drying trend 18z-00z from west to east. Southeast winds becoming gusty across eastern coastal MA from Cape Cod to Cape Ann during the afternoon. KBOS TAF...high confidence on trends but somewhat lower on exact details including timing. KBDL TAF...high confidence on trends but somewhat lower on exact details including timing. Outlook /Friday night - Monday night/...Moderate confidence. Friday night into Saturday... BKN-OVC MVFR/IFR mix lingering especially across E New England with the chance of -RA overnight, improving through the day from the W with SCT-BKN cigs lifting low-end VFR / MVFR. N winds. Saturday night through Sunday night... Another shot of -RA Saturday night with BKN-OVC MVFR/IFR cigs, improving through the day Sunday into Sunday night, becoming SCT. N winds becoming E. Monday into Monday night... N/E winds with perhaps some SCT low-end VFR cigs. Low risk MVFR for high terrain.
-- 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 Friday/...High confidence. Today... Leftover Small Craft Advisory conditions as southerly winds of 20-25 kt ease later this morning and will result in seas subsiding. Morning showers across the southern waters will give way to dry weather and improving vsbys this afternoon. Tonight... Southeast winds increasing late across eastern MA waters. Could see wind gusts up to 30 kt eastern ma waters...not as strong westward. Showers lower vsby 1-3 miles late. Friday.. southeast winds 20-30kt with strongest winds eastern MA waters. Vsby 1-3 miles in showers with an improving trend late in the day especially western waters. Outlook /Friday night - Monday night/...Moderate confidence. Friday night into Saturday... Rain lingering as a broad area of low pressure sweeps across the waters, clearing out during the day Saturday. N winds more stout across the E waters with gusts up around 15 kts. Waves subside however hold around 5 feet for the E waters. Saturday night through Monday night... Elongated area of low pressure to the S with high pressure situated N/E. Breezy NE winds with gusts up to 20 kts possible. Will keep wave heights 4-5 feet on the E waters. Could see some rain for the Saturday night into Sunday morning timeframe.
-- End Changed Discussion --
&& .BOX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 AM EDT this morning for ANZ250. Small Craft Advisory for hazardous seas until 8 AM EDT this morning for ANZ254. Small Craft Advisory for hazardous seas until 5 AM EDT early this morning for ANZ255.
-- End Changed Discussion --
&& $$ SYNOPSIS...Nocera/Sipprell NEAR TERM...Nocera SHORT TERM...Nocera LONG TERM...Sipprell AVIATION...Nocera/Sipprell MARINE...Nocera/Sipprell

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