Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 111215 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 715 AM EST Wed Jan 11 2017 .SYNOPSIS... Rainfall ends not long after sunrise with milder conditions to follow which will linger through tomorrow. Another rain event is likely tonight into early tomorrow morning. Unseasonably mild temperatures will come to an abrupt end Friday and especially Friday night behind a strong cold front. Much colder weather follows this weekend and most of it will be dry, other than a period of light snow possible late Saturday into Saturday night with the highest risk south of the Massachusetts turnpike. Moderating temperatures are expected by early next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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7 am update... Numerous reports of winds exceeding 35 to 45 mph in tandem with the band of light to moderate rain with embedded heavier showers. The crux of the low level jet combined with favorable mixing and/or precipitation drag, especially across the high terrain, is allowing the faster momentum to reach the surface. Sadly too little too late in expanding the wind advisory, but feel the impact is minimal given we`ve had a number of wind events so far this year and more than likely with those events we`ve lost a combination of weakened trees and/or tree branches. Rain pushing offshore, still concern for standing water with the AM rush as drains may be storm clogged. Poor drainage flooding, the threat of hydroplaning, just some of the other issues to address this morning. But with the rain quickly pushing offshore and the clearing line just sweeping into S New England, optimistic concerns will be brief and will swiftly improve. Otherwise, while clearing is expected behind the modest frontal passage, some mid level SC and CI could limit sunshine at times through the afternoon as moisture reloads from the top down in spite of a very dry subsidence inversion thanks to short-wave ridging. This should allow mixing to exceed expected thresholds as guidance may still be a bit corrupted by snowpack. Did lower highs a bit, but with a slight W component to the flow and H92 temps reaching between +8C and +10C by days-end, could still see a several spots approach the low 50s in spite of this snowpack. One influence expected is the mixing/snowpack which should allow for a brief dip in area dwpts, back to the upper 20s and low 30s after conditions clear later this morning.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
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Tonight... The combination of secondary low pres (which will remain well W of the region as it passes early Thu morning) and continued return S-SW flow yielding warm advection will combine with another round of deep layer moisture late tonight (pwats approach 1.25 inches which is almost above climatology by 2 std deviations), This should yield a second round of late night rainfall across much of New England as another (albeit weaker) LLJ near 40-50 kt crosses the region mainly after midnight. Given dwpts will be increasing through the overnight hours, and full loss of the snowpack today is not expected, may see another round of dense fog in areas especially before or immediately after rainfall (rainfall will mix out the lower vsbys). Will need to monitor for potential dense fog advisories due to this. Temps once again warm some overnight, dipping initially but should begin to move from the mid-upper 30s back into the 40s with the onset of the second LLJ. Thursday... Soundings suggest moisture remains locked in, particularly in the low lvls through much of the daylight hours on Thu. This should maintain cloud cover through much more of the day than Wed. Also, some fog could linger early especially if any snowpack remains by this time. Widespread rain ends as the deepest moisture shifts along a mid-lvl baroclinic zone stalled across N-central New England. SHRA remains a risk, but as the previous forecaster noted, mainly N of the Mass Pike. Other areas remain mostly cloudy. In spite of this cloud cover, the overall loss of the sfc snowpack will allow temps to better mix to the nearly +10C temps at H92. This should allow for more locations to break into the 50s, even the mid-upper 50s in spots. One note is that with these higher 2m and sfc temps, may need to monitor for another round of gusty winds which may approach advisory criteria with the onset of a 40-50 kt LLJ late in the day. S-SW flow is not a typical direction for this, and it will be limited due to colder SSTs near shore, however some inland areas may need to be watched for this risk.
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&& .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... */ Highlights... - Weak weather pattern overall, chance PoPs with forecast outcomes - Showers linger Thursday night - Chance of snow for the S-coast of S New England Sat - Sat Night - Build up of disturbed weather into next week out of the SW CONUS */ Discussion... Atmospheric teleconnections would seemingly indicate a relative flat flow over the CONUS. Less amplified, buckled pattern, the long-term forecast period is marked with rather weak weather disturbances as the NE CONUS waffles between airmasses, though with less arctic intrusion as a general W to E flow provokes higher H5 heights across the E CONUS via milder air streaming from the Pacific. Interestingly enough, this suggestion of higher heights across the region, there are greater indications of drier weather prevailing beneath the influence of stout areas of high pressure, as if S New England remains between inside-runner systems N/W and cyclogenesis emerging off the Mid-Atlantic. A zone of unfavorable development in- between beneath confluent flow aloft as noted by the prior forecaster. Of greatest uncertainty is the forecast into next week with respect to the evolution of a closed cut-off low over the SW CONUS and how, or whether, it evolves into the Plains. Some sort of impact is in the cards further out in time, but specific impacts and timing are largely unknown from the full suite of forecast guidance. As to targets of opportunity, believe the boundary layer will be uncoupled beneath stout SW flow Thursday night ahead of the cold front into Friday. Not anticipating any wind issues other than for aviation. But NW flow in wake Friday is more than likely to make for breezy conditions. Will have to watch H925-85 flow with forecast boundary layer mixing. Could really see some efficient mix-down of winds. Not yet concerned about wind advisories but will be closely monitoring given the exchange in airmasses and a near 1050 mb high building out of Canada as low pressure deepens over the SE Canadian maritimes. Impressive height rises over S Canada neighbored by the aforementioned pressure falls. It would appear per isallobaric and gradient flow that the faster low level jet max would be more N as suggested by the 11.0z NAM over all other guidance. Colder air in place, bigger issue of drier air Saturday, its influence and whether snow remains mostly offshore in association with a weak wave low emerging off the Mid-Atlantic along the aforementioned cold front now pushed S and becoming stalled well offshore. Trend as been for a more S passage and less impact on S New England. Will lower PoPs keeping them at chance around the S-shoreline. Again, as to next week, the outcomes are largely unknown. Would tend to lean a warmer- wetter solution given higher heights across the E CONUS with an inside-runner low. So overall, some lingering showers Thursday night into Friday morn, blustery NW winds friday, will continue to hint at some light snow (more than likely wet in consistency) for the late Saturday into Saturday night period, and then a build up of disturbed weather through next week ahead of the closed cut-off low emerging out of the SW CONUS. Nothing appears likely and will keep with chance PoPs throughout the long-term forecast. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
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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 Thursday/... Through 14z at the latest... MVFR-IFR lingering out on the Outer Cape with most of the RA pushed E. SW gusts up to 40 kts with LLWS roughly 23050kt 2 kft agl. Will see this diminish after 14z. After 14z... Improving to VFR W to E if haven`t done so already. S/SW flow diminishes with lingering gusts on up to 30 kts initially dropping down to 10 to 20 kts. Tonight into Thursday...Moderate confidence. VFR will give way to mix of IFR-LIFR mainly due to cigs, but also due to -RA and FG yielding MVFR-IFR vsbys as well. -RA ends Thursday, but it will take some time for improvement to VFR. Therefore, will maintain MVFR-LIFR through much of the day thanks to low CIGS hanging in. S-SW wind gusts 20-30 kt on Thursday. KBOS TAF...A diminishing trend on the winds with improvement rather quickly within the first 3 hours of the TAF. VFR should hold through the evening hours and thus the PM push. IFR moving back into the terminal shortly after midnight with winds increasing once again out of the S. KBDL TAF...Improving conditions through the day. VFR. Will see lower conditions return shortly after midnight with IFR, perhaps LIFR, anticipated. Outlook /Thursday Night through Sunday/...Moderate confidence. Thursday night... -RA lingers along with a MVFR-IFR mix. Bigger issue will be LLWS with around a 50 kt SW flow 2 kft agl. LLWS threat comes to an end as winds shift out of the W and conditions improve to VFR towards Friday morning. Friday into Saturday... Blustery NW winds with gusts up to 30 kts especially for coastal terminals mainly Friday. Winds diminishing out of the W for Saturday with increasing cigs. VFR throughout. Late Saturday into Saturday night... Chance -SN along the immediate S coast with IFR visibility, possibly VV as well. Otherwise a mix of low-end VFR to MVFR cigs. Light W winds. Sunday into Monday... VFR. Light N winds becoming W. Increasing cigs late.
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&& .MARINE...
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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 Thursday/... 7 am update...No major changes to the forecast. Through today...High confidence. Strong Gales will linger through the morning hours before dissipating as rains come to an end from W-E. Small craft advisories will follow as winds should remain elevated over the waters between 20-30 kt. Seas dissipate as well, dropping from about 10-12 ft near the Gulf of Maine early this morning. Tonight and Thursday...Moderate confidence. Occasional small craft conditions will linger, although expect increasing winds after daybreak Thu especially, reaching once again to low-end Gale force. Will not issue new Gales due to current ongoing Gales at this time, but it will need to be considered in future updates. Seas will once again build and reach 5-8 ft on the ocean waters by late tomorrow evening. Otherwise, ocean fog may yield some low vsbys beginning during the early AM hours on Thu especially. Outlook /Thursday Night through Sunday/...Moderate confidence. Heightened seas through Saturday morning as a cold front sweeps the waters Friday behind which NW winds will be blustery, potentially gale force. Late Saturday, as winds and seas remain below small craft advisory thresholds, an area of low pressure emerging off the Mid-Atlantic will bring the chance of snow, especially for the S waters, along with reduced visibility. Quiet boating weather the remainder of the period as northerly winds in wake of the wave low shift westerly, remaining light throughout.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...Wind Advisory until 10 AM EST this morning for MAZ007-020>022. RI...Wind Advisory until 10 AM EST this morning for RIZ005>007. MARINE...Gale Warning until 10 AM EST this morning for ANZ231>235-237- 251-255-256. Small Craft Advisory until noon EST today for ANZ230-236. Gale Warning until noon EST today for ANZ250-254. && $$ SYNOPSIS...Doody/Sipprell NEAR TERM...Doody/Sipprell SHORT TERM...Doody LONG TERM...Sipprell AVIATION...Doody/Sipprell MARINE...Doody/Sipprell

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