Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 140527 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 127 AM EDT Thu Jun 14 2018 .SYNOPSIS... A warm front will trigger scattered showers this evening. a cold front moves through overnight, followed by mainly dry weather and low humidity for the rest of this week. Warmer and more humid air arrives for Sunday and Monday. Some showers and thunderstorms are possible Monday afternoon/evening and on Tuesday, followed by drier and less humid weather Wednesday. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... 10pm update... Broken line of TSRA/heavy SHRA continues to push through the ALY CWA at the time of this writing, although it is outpacing the sfc cold front which remains across central NY and PA, about 20-30sm behind the actual convection it spawned. Have been watching sfc/ML CAPE values gradually tick up this evening, especially W of the Worcester hills. This is mainly a symptom of the EML evident of a dry layer moving in on the mid/upper lvl WV channels which continue to enhance mid lvl lapse rates. This combined with modest lower lvl shear (0-3km helicity is on the order of 150-200) should be enough to at least maintain the TSRA risk into the Berkshires and CT valley. Further E than this there are several mitigating factors at play. The persistent SW flow through the day has introduced a lower lvl marine layer which will limit further destabilization. The dry air punch mentioned above also continued to overspread and lower, providing evidence of a cap on bufkit profiles. Finally, as the convection continues to outpace its primary forcing mechanism in the cold front, all of these factors should combine to yield a gradual weakening of the convection E of the CT valley. Isolated TSRA/SHRA could make it to E CT/RI and the I-495 corridor of MA, but the downward trend is expected continue, something all latest mesoscale guidance updates continue to favor. Other than the convection monitoring, dense fog continues to develop along the SE MA coastal waters. May need to monitor some of the Cape/Island for some late night dense fog advisories. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM FRIDAY/... A mid level low should pass by close enough to our region to steer a potent mid level shortwave our way late Thursday into Thursday night. This should be enough to trigger another round of scattered showers, mainly towards NE MA, which would be closer to the mid level low. Otherwise, thinking mainly dry conditions much of Thursday. Unseasonably cool airmass associated with this mid level low. Drier air eventually moves into our region behind it, too. Near normal temperatures through this period. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Highlights... * Mainly dry Fri/Sat with pleasant temps/low humidity * Exception may be a few brief showers Thu night/Fri morning * Warmth returns Sun-Mon * Cold front brings chance for precip Mon-Tue Details... Friday...Upper trough axis in the vicinity of southern New England shifts to the east during the day. A shortwave rotating thru the base of the trough brings the chance for showers within eastern MA during the morning. Otherwise, dry airmass moving into the region during the afternoon, with clearing behind departing short wave and surface dewpoints dropping into the 40s. Afternoon sunshine should allow temps to climb into the 70s for most locales. Friday night is mostly clear and dry as surface high pressure approaches from the SW/W. Saturday...A dry day as surface high pressure moves off the Carolina shoreline. Strong upper level ridge positioned in the lower Ohio and lower Mississippi Valleys placing our area in NW flow aloft on the east side of the ridging. H850 temps increase to +12 to +15C, highs 80 to 85 forecast. Sunday... Strong upper level ridge makes some eastward progress towards/into the central and southern Appalachians during Sunday and Monday. Warm and muggy conditions as dewpoints climb well into the 60s in low level SW flow. Some uncertainty regarding the conditions on Sunday, whether there is enough subsidence to keep conditions dry, or if increasing moisture in the return flow brings the chance for showers. At this time will go with slight chance pops, highs 85 to 90. Monday thru Wednesday... A cold front approaches our area from the NW during Monday. Still several days out so uncertainty exists on timing of front`s approach, and how quickly/slowly the cold front pushes thru southern New England. For this forecast package going with a chance pop for showers both Monday and Tuesday, and chance of thunderstorms for Mon/Mon evening. Drier air should move into our area for Wednesday. && .AVIATION /05Z 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/... Through today...High confidence. Lingering IFR/MVFR CIGS/fog dissipate through about 10Z, possibly 12Z for ACK. Otherwise, trend toward VFR and W winds. Gusts 25-30 kt at times through the day. Some SCT-BKN clouds across the N this afternoon 040-060. Overnight...High confidence. Mainly VFR through 06Z. After which some MVFR conditions with low CIGS and SHRA mainly E of the Worcester Hills and the E coast of MA. VFR elsewhere. Fri...High confidence. Early MVFR/IFR conditions dissipate across the N. THen VFR all terminals for the remainder of Fri. NE winds. KBOS Terminal...High confidence in TAF overall. Mix of MVFR/IFR possible at times late tonight/early Fri in SHRA. KBDL Terminal...High confidence in TAF. Outlook /Friday Night through Monday/... Friday Night through Saturday Night: VFR. Sunday: VFR. Slight chance SHRA. Sunday Night: VFR. Breezy. Slight chance SHRA. Monday: VFR. Breezy. Chance SHRA, slight chance TSRA.
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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 Friday/... Tonight...Winds dissipate during the evening, but seas remain elevated offshore. W winds then increase during the early morning hours along a passing cold front. Thus Small Craft Advisories have been posted for tonight for the coastal waters except for Boston Harbor/Narr Bay. Thursday...Seas gradually dissipate, but once again nearshore waters winds may reach Small Craft Advisory thresholds. There may be a brief lull in the morning. SCA headlines continue during the day for the southern nearshore and outer coastal waters. Thursday Night...Winds less than 25 kt. Seas up to 5 ft across the southern outer coastal waters. Chance of rain showers across the coastal waters east of MA. Outlook /Friday Night through Monday/... Friday: Winds less than 25 kt. Seas locally approaching 5 ft. Friday Night through Saturday Night: Winds less than 25 kt. Sunday: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers. Sunday Night: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers. Monday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers, slight chance of thunderstorms.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ232>235-237. Small Craft Advisory until 5 AM EDT early this morning for ANZ231-251. Small Craft Advisory until 10 AM EDT this morning for ANZ250. Small Craft Advisory until 6 AM EDT Friday for ANZ254>256.
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&& $$ SYNOPSIS...Belk/NMB NEAR TERM...Doody SHORT TERM...Belk LONG TERM...NMB AVIATION...Doody/NMB MARINE...Belk/NMB

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