Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 251055 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 655 AM EDT Thu May 25 2017 .SYNOPSIS... Low pressure and its attending warm front will bring a steady rain and drizzle to the region today along with cool northeast winds. The rain will be heavy at times tonight into Fri as the low tracks along the southern New England coast to just east of Cape Ann Friday. Big improvement to start of the holiday weekend as weak high pressure delivers dry weather with mild days and cool nights both Sat and Sun. However by Sunday night and into Monday another coastal low may bring the risk of showers, although a washout is not expected. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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7 AM update... High amplitude mid level trough along the eastern seaboard and beginning to take on a negative tilt. This deep mean trough tapping tropical moisture with its source region from Cuba and the Bahamas with PWATs up to 2.0 inches just off the mid Atlc coast! This will act as a firehose of atlantic moisture into southern New England from later this morning into Friday morning. Initial band of rain overspreading CT at 7 am and this is associated with mid level warm front/warm conveyor belt. Steady rain overspreads the region from south to north this morning then tapering off to drizzle late today and evening as dry slot overspreads the area. As rain intensity increases temps will drop a few degrees closer to wet bulb values. In addition ENE winds will increase as low level jet develops. Thus a cool/damp/raw day today with coolest temps along the eastern MA coast. Previous forecast captures these details so no wholesale changes to the forecast. Earlier discussion below. ================================================================== Active pattern is shaping up for the region over the next few day. Anomolous closed low over the Ohio Valley and digging trough in the southeast will continue its eastward progression through the day. Overall flow across the eastern seaboard is southerly aiding in deep moisture advection from Gulf. This has pushed PWAT values to 2 inches off the Virgina coast. Upper level shortwave combined with a southerly LLJ has resulted in widespread showers just south of Long Islands as of 330 AM. Dry weather will prevail for the reminder of the overnight hours. The upper level disturbance will approach the region early this morning resulting in widespread showers moving from south to north during the morning commute. Locations south and east of the I-95 corridor has the potential in seeing the heaviest amount of rainfall due to higher theta-e plume and the orientation of the Jet. The latest HRRR is a bit more on the western envelope of guidance compared to the HI-res ARW/NMM, GFS and RAP but there is the potential for a few locations to see near an inch of rainfall this morning. After the first surge of precipitation from the mid-level warm front, the bulk of the guidance is indicating a potent dry slot moving into the region by late morning into the afternoon hours. This will limit rainfall intensity to more of light showers and/or drizzle. Easterly 925 mb will strengthen during this time to near 30 kts, however stout inversion will limit the winds from truly mixing down. Cannot rule out a few rogue gusts, but confidence it low on hoist a wind advisory. Persistent easterly flow at the surface will also keep the low levels quiet moist. This may enhance any fog development and limit temperatures from warming. High temps for today will stay in the 50s, which is below normal for this time of year. Overall a cool and dreary day is on tap. Heavy rainfall for the morning hours; with showers, drizzle and fog for the afternoon.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... Tonight into Friday... Anomolous low pressure system will continue its eastward progression during the overnight hours. A potent pv-anomaly will round the base of the trough and develop a surface low over the middle Atlantic region. This low will trek right over southern New England bringing widespread rainfall. Some of it will be heavy at times as the system becomes vertically stack resulting in deep moisture through the entire column. PWAT values are also near an inch to 1.5 inches with increasing LLJ aiding in moisture advection. This will result in another chance for locations south and east of the I-95 corridor of seeing an inch of rainfall. This much rain combined with the King high tide may result in urban flooding as the water will have trouble receding. Guidance is also hinting as some elevated convection with a few models having some surface CAPE late tonight into tomorrow morning. Therefore continued with the mention of isolated thunder. This may also enhance precipitation amounts. Widespread heavy rainfall will begin to wind down by Friday morning as the low begins to move offshore. However, pretty good comma head signature with a deformation zone in the mid-levels could set up. This will keep the dreary weather going through much of the day before beginning to let up by nightfall. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Highlights... * Mainly dry weather w/mild days and cool nights Saturday and Sunday * Risk of rain returns Sun night into Monday * Seasonably warm Tue & Wed but low risk of scattered showers Details... Friday night... Improving weather as closed mid level low over the Gulf of Maine exits seaward and allows rising heights along with mid level anticyclonic flow to move across New England. This will promote a drying trend overnight. Temps will be seasonably cool with lows in the upper 40s and low 50s. Saturday... WNW flow aloft with mid level mean ridge axis across the eastern Great Lakes will provide dry weather and seasonable temps across southern New England. Models do differ on cloud cover Sat with GFS showing much more low level moisture. Given the WNW flow aloft thinking at least partial sunshine will verify. This combined with light winds will provide very pleasant conditions with highs 70-75 CT river valley and 60s elsewhere. Weak pressure gradient will support cooling afternoon seabreezes for the coastline. Sunday... Deep layer ridging lingers across the area promoting dry weather much of the day. However model time sections and moisture profiles indicate lots of clouds likely on Sunday. 00z deterministic and ensemble guidance in good agreement that rain/showers associated with upstream system should arrive into southern New England either late in the day or after sunset. So as of now the bulk of the daylight hours of Sunday appear dry, especially across RI and eastern MA. Given the expected cloud cover highs should be a few degs cooler than Saturday. Fortunately SSE winds should be fairly light but will keep the immediate coastline cooler. Monday... Weak coastal low may pass south of New England along with its precip shield impacting the area. Doesn`t look like a washout but enough support to keep showers in the forecast. Somewhat cool with highs in the 60s given cloud cover and light onshore winds. Tuesday/Wednesday... Not as cool as parent low pressure over the Great Lakes provides warmer southwest flow into New England. With the milder temperatures comes the risk of scattered showers as mid level flow becomes increasingly cyclonic. && .AVIATION /12Z THURSDAY THROUGH MONDAY/...
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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 Friday/...Moderate confidence. 7 AM update... Not much change from 06z and 09z TAF issuance. Steady rain along with MVFR-IFR conditions overspreads CT/RI/MA as the morning progresses from south to north. Steady rain transitions to drizzle later this afternoon. Modest ENE winds today with highest speeds along the eastern MA coastline. Earlier discussion below. =================================================================== Today...Deteriorating to MVFR/IFR cigs and vsbys in rain and fog. Heaviest rainfall in the morning with -SHRA and drizzle in the afternoon. Easterly winds could gust to 20 knots. Tonight...IFR cigs and vsbys will continue in rain and fog. Could see an iso thunder but confidence is low. Rain will be heavy at times. Easterly winds will continue to gust to near 20 knots. Friday...IFR/MVFR cigs will continue with persistent on and off showers through the day. Conditions may improve to VFR across western terminals in the late afternoon. Northwest winds for all terminals. KBOS TAF...High confidence in trends, moderate confidence on timing. KBDL TAF...High confidence in trends, moderate confidence on timing. Outlook /Friday Night through Monday/...moderate to high forecast confidence. Friday night...a mix of MVFR-VFR but a trend toward dry weather overnight as surface winds become WNW. Saturday and Sunday daytime... VFR. Light winds Sat with seabreezes at the coast. Winds Sunday more from S-SE direction at fairly light speeds. Sunday night-Monday... Cigs/vsbys trending to MVFR/IFR in showers. Winds from the southeast, trending from the south Monday.
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&& .MARINE... 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...Approaching system from the west will help increase winds and seas through the day. SCA continues where confidence is highest for seas above 5 feet. Also went ahead an issued SCA for near shore waters for the potential for gusts near 25 kts. Rain and fog will limit vsbys through the day. Tonight... Poor vsbys in rain and fog Thursday night. Easterly winds around 25 knots eastern coastal waters with strongest winds during the evening. These winds then lift north of the waters. Seas building up to 10 feet across the Cape Ann waters, less elsewhere. SCA continue. Cannot rule out an iso thunderstorm over the waters tonight. Friday... Potent low pressure system still over the region will keep seas and winds up through the period. SCA will be needed. Outlook /Friday Night through Monday/... Friday night... Low pressure over Gulf of Maine moves seaward with WNW winds developing across the MA/RI waters resulting in a drying trend and improving vsby. Saturday and Sunday... Fairly light winds and tranquil seas as high pres crest over the area. Dry weather and good vsby too. Sunday night and Monday... A series of weak lows may develop and pass south of New England, near the 40N/70W benchmark. && .TIDES/COASTAL FLOODING... Combination of a very high astronomical tide and onshore flow will result in widespread minor coastal flooding tonight. Persistent easterly flow yesterday and today will help aid in a storm surge around .7 to 1.0 which will push many sites above flood stage. The Salisbury to Cape Ann stretch of coastline continues to be the most at risk, since the low level ENE jet would have just moved north of this area just a couple of hours before high tide with a moderately significant NE wave fetch in place. However, the expected total water level looks to be high enough to support areas of minor coastal flooding along the coastline south of Gloucester to Plymouth as well as Provincetown. Thus, went ahead an issued a Coastal Advisory for much of the MA east coast including Cape Cod and Nantucket for tonight`s high tide. Waves will not be a major factor but looks like enough low level wind gradient to produce 6 to 10 foot waves in the near shore waters in Ipswich Bay, about Cape Ann, and Massachusetts Bay. Some erosion is likely along the Salisbury and Plum Island shorelines where wave action will be somewhat more significant. Elsewhere along the MA and RI coasts, the combination of the high astronomical tide and a tidal departure near a half foot may be enough to cause pockets of minor coastal flooding as has become more common during such king tide cycles. A statement may be needed for the Islands, and both the MA and RI south coasts, including Narragansett and Buzzards Bay shorelines, for the Thursday evening/night high tides. Right now confidence is to low. Little to no storm surge is expected at the time of the late Friday night or very early Saturday AM high tide. This as well as offshore flow may limit the potential. Will have to continue to watch as we cannot rule out the potential for isolated pockets of minor coastal flooding. && .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...Coastal Flood Advisory from 10 PM this evening to 3 AM EDT Friday for MAZ007-015-016-019-022-024. RI...None. MARINE...Small Craft Advisory until 4 PM EDT this afternoon for ANZ231>234. Small Craft Advisory until 6 PM EDT Friday for ANZ235-237-250- 254>256. Small Craft Advisory until 6 PM EDT Friday for ANZ251.
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&& $$ SYNOPSIS...Nocera/Dunten NEAR TERM...Nocera/Dunten SHORT TERM...Dunten LONG TERM...Nocera AVIATION...Nocera/Dunten MARINE...Nocera/Dunten TIDES/COASTAL FLOODING...staff

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