Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 221406 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1006 AM EDT Mon May 22 2017 .SYNOPSIS... Cooler today. Some showers early this morning give way to a lull from mid morning into at least early afternoon before more widespread showers move in from the south later this afternoon and evening. Mainly dry and seasonable weather is expected Tuesday. A coastal wave of low pressure may bring a period of rain to the south coast Tue night into early Wed. However by Wed afternoon a brief drying trend develops behind the departing wave along with pleasant temperatures. However the risk of more rain returns Thu and Fri as low pressure approaches. The holiday weekend begins with dry weather but there could be a period of showers Sunday or Monday. Temperatures look to be near seasonable through the period. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 10 am update... Increased pops slightly for late am/midday based on radar trends, to account for some lingering isolated/scattered showers associated with lead short wave. Additional showers will be possible later this afternoon/evening as a second short wave is expected to cross our area, no changes in forecast for that timeframe. Forecast temps look on track. Early morning discussion follows... ================================================================== Modest upper lvl shortwave linked to warm frontal movement, increased PWATS around 1.25 inches and unorganized warm advection is generating SHRA across the region this morning. These will continue through about 8AM (12Z) until the wave moves E of the region and allows for reinforced ridging and drying of the lower lvls (which still have not completely recovered from the low dwpts this past weekend). Therefore, after this first round of wetting (although not significant) rainfall, expecting a lull across the region through the remainder of the morning hours as the synoptic system reloads in favor of convection linked to the cold front well S and a LLJ sliding up along S coastal locations by late this afternoon and evening. Latest model runs support this, showing much lower overall QPF totals, supported by a fairly dry period in mesoscale model radar depictions through the day. Therefore, have lowered POPs widespread until mid-late afternoon, then raised them from SW-NE into the evening. In fact, it now appears bulk of the rainfall will be focused across SE MA/RI with lower totals further inland. This is along the core of a modest LLJ around 30-40 kt which crosses the region after 00Z. PWATs not overly impressive either, with highest (1.5+) remaining well to our S, and more closely associated with convection off the mid-Atlantic which is likely to usurp some of the higher Gulf Moisture. Risk for TS is low, however noting soundings supporting some modest conditional instability late this evening/early overnight, so will continue a mention for an isolated rumble of thunder. Otherwise, although guidance shows upper lvl warm front lifting across the region in advance of the weakened cold frontal passage tonight, am concerned sfc warm front may struggle, as it typically does through spring. Will be capping highs mainly in the mid-upper 50s given that even with a break in showers, skies should remain mostly cloudy through the day, with S to SE winds carrying cooler onshore flow. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... Tonight... Banded precipitation becomes more closely focused on a weakening cold frontal passage through the late evening and early overnight hours. Highest theta-e plume, along with modest conditional instability becomes focused along the Sly LLJ mainly across SE MA and extreme SE RI. Will be focusing POPS there. Also final QPF totals above 0.5 inches (including any rainfall today) will be focused on this area as well as precip is likely to end across the interior late this evening. Therefore, expect gradual improvement thanks to reinforced subsidence from NW-SE through the overnight hours such that precip should be ending even over the islands between 10Z and 12Z tomorrow morning. Some clearing inland is likely as well. The one fly in the ointment here, will be that as winds shift to the W-NW through the column and the subsidence inversion develops, there is still plenty of low-lvl trapped moisture especially areas E of the Worcester hills. This should leave, even as rainfall ends. Fog and low clouds in its wake. May even need to watch for some patchy dense fog in areas as precip ends. Temps will be tricky thanks to the risk for clearing in the far NW interior. Some cooling there could allow temps to drop back into the 40s while areas further E remain in the mid to upper 50s with the low lvl moisture remaining in tact. Tue... Continued improvement through the morning thanks to reinforced high pres building in from the NW. Most locations should see at least a bit of sunshine through the day. The one caveat will be S coastal locations as cold front will be settling to the S and a secondary shortwave suggests the development of a coastal wave off the mid-Atlantic. At the very least, this will reinforce cloudiness across the S, limiting the sunshine and warming. However, worst case scenario if the wave is strong enough it will bring another round of light-mod rainfall mainly across the immediate S coast/Cape/Islands by late afternoon. Latest trends suggest a lower risk for this, as ECMWF, which was the most robust has backed down somewhat on its QPF across the land. Something to watch over the next 24 hours or so as mesoscale guidance better captures this feature. Otherwise, a much nicer day as H85 temps should remain averaging +9C through the day. Inland areas that see the most sun will see highs in the low-mid 70s. Coastal areas will be cooler due to sea breezes, but as mentioned above, the increased risk for clouds will limit S coastal locations even more. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Highlights... * Dry and seasonable Wednesday Afternoon * Showers likely Thu and Fri * Holiday Weekend Likely begins Dry and Seasonable Tuesday night... Deterministic and ensemble guidance beginning to coverage on next chance of rain Tue night into Wed morning across CT/RI and southeast MA especially the immediate south coast and islands, as next mid level wave approaches and spawns weak cyclogenesis just south of New England. Remainder of the region especially along and north of the MA pike likely remains dry. However these small scale frontal waves can be tricky on the exact track of its precip shield. Wednesday... Could be the pick of the week as any lingering rain early over southeast MA scoots out to sea with good subsidence on backside of departing wave. This should support at least partial sunshine during the afternoon along with seasonable temps, mid 70s CT River Valley to 60-65 across eastern MA coastline due to light onshore flow. Thu & Fri... Mid level trough and broad area of low pressure approach the region from the southwest. Parent low over the eastern lakes gives way to secondary low pres along the south coast of New England Fri. This setup will support periods of rain regionwide & cool onshore winds for eastern MA. Holiday Weekend... Rising heights and increasing anticyclonic flow will yield dry and pleasant weather Saturday. Models then differ on timing of next upstream trough with ensembles leaning toward Monday and GFS/EC more toward Sat. Given the time range leaned toward the ensembles. Temps looks seasonable with highs in the 70s. && .AVIATION /14Z MONDAY THROUGH FRIDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday/... 10 am update... Through today...Moderate confidence, mainly due to some uncertainty in timing. Mainly VFR through midday today, with isolated to scattered showers mainly affecting ORH/BED/BOS and vicinity. Then, afternoon into evening CIGS gradually drop through MVFR to IFR, along with more widespread SHRA/RA after 18Z. Winds remain mainly S, although with slight SE shift possible. Minor LLWS possible mainly across the S coast late this afternoon/evening. Overnight...Moderate confidence. IFR/MVFR with low CIGS/fog/SHRA mainly S and E of a line from HFD-ORH-PSM, meanwhile some improvement is possible N and W of this line especially during the early morning hours. Otherwise a damp night. Some S-SW winds gust 20-25 kt mainly Cape/Islands. Otherwise, winds shift to the NW by sunrise Tue. Tue...Moderate confidence. Improvement to VFR everywhere during the morning. Winds begin out of the N-NW then back again to the S by late evening. Sea breezes expected on coastlines. Will need to watch another weak low pressure system south of the region which could maintain wet weather and lower categories mainly for SE MA/RI terminals. Right now will feature mainly an improvement all locations. KBOS TAF...High confidence in TAF trends, lower confidence in exact timing for the lower categories this afternoon which may be off by a couple of hours. On and off light showers between 10 am and noon, with additional showers probable later this afternoon and evening. KBDL TAF...High confidence in TAF trends, lower confidence in exact timing for the lower categories this afternoon which may be off by a couple of hours. A few showers between 10 and 11 am may lead to wet runways, but should be short lived. Additional showers probable late this afternoon and evening. Outlook /Tuesday Night through Friday/... Moderate forecast confidence this period. Tue night...VFR except MVFR possible south coast in risk of showers. Wed...VFR except period of MVFR showers possible early over southeast MA. Thu & Fri...MVFR and/or IFR in periods of rain. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday/... Late this morning into tonight...High confidence. Mainly quiet to start although with isolated to scattered showers over the waters. By afternoon, more widespread rainfall will combine with stronger southerly winds reaching around 25 kt, which will linger into the overnight hours. While seas should generally remain at or below 5 ft, will be issuing a small craft advisory for these winds beginning late this afternoon and continuing until the winds shift to the W-NW early tomorrow morning. These will mainly be fore the open waters, rather than the sheltered bays/sounds. Fog/showers will reduce visibility mainly late this afternoon through the overnight. Tomorrow...High confidence. Improvement across the waters expected. Winds and seas will remain below small craft advisory thresholds. Winds will be shifting from the W, back to the S by late in the day. Outlook /Tuesday Night through Friday/... Weak wave of low pres tracks just south of New England Tue night and Wed morning. Then a stronger low may pass just south of the coast Fri. Could be a brief burst of WNW winds up to 30 kt Fri night as storm intensifies over Gulf of Maine Fri night. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 8 PM this evening to 4 AM EDT Tuesday for ANZ231>234. Small Craft Advisory from 2 PM this afternoon to 4 AM EDT Tuesday for ANZ235-237-256. Small Craft Advisory from 5 PM this afternoon to 4 AM EDT Tuesday for ANZ250. Small Craft Advisory from 5 PM this afternoon to 8 AM EDT Tuesday for ANZ254-255. && $$ SYNOPSIS...Nocera/Doody NEAR TERM...Nocera/Doody/NMB SHORT TERM...Doody LONG TERM...Nocera AVIATION...Nocera/Doody/NMB MARINE...Nocera/Doody/NMB is the U.S. government's official web portal to all federal, state and local government web resources and services.