Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 260017 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 709 PM EST Sun Feb 25 2018 .SYNOPSIS...
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The rain has ended but areas of ground fog and patchy black ice may impact motorists later tonight into early Monday morning. High pressure will then bring dry weather with cool nights and mild afternoons through mid week. The potential continues for a significant coastal storm late this week with several possible weather hazards...but it is not a certainty this far out.
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&& .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... 710 pm update... Tricky forecast overnight into early Monday morning regarding the extent of fog and potential for patchy black ice developing. Early this evening...the rain has exited the region as departing low pressure has taken the deeper moisture/forcing with it. However...there has not been a real push of dry low level air so an abundance of low clouds remained in place. Some data suggesting that enough drier air will eventually work into the region to allow some breaks in the low clouds. If this occurs...given wet ground/boundary layer moisture areas of fog will become more widespread and perhaps dense in the typical spots. Greatest risk for this is after midnight through around daybreak Monday. In addition...that would also allow many locations to drop into the upper 20s to the lower 30s leading to the risk of patchy black ice for the early Monday morning commute. Greatest risk for that will be northwest of the Boston to Providence corridor. A lot of the fog/patchy black ice potential hinges on how much of the lower clouds scour out. This remains uncertain...but motorists planning travel overnight into early Monday morning should be prepared for locally dense ground fog and patchy black ice. && .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... Mon... Low and mid lvl baroclinicity wedged between the low pres moving E of the Maritimes and sfc 1030hPa high pres slackens through the early AM hours. This both raises the H92 temps in the NW interior and cools these same temps across the SE, yielding a nearly uniform +1C to +2C. Early AM lingering clouds should dissipate through mid day, so expect that mixing should reach and more likely exceed H92, allowing temps to reach the mid-upper 40s. Highs may peak out in the low 50s however across portions of E MA/RI thanks to a W-downsloping component to the flow. Overall dry but a bit breezy with winds gusting to 20mph at times. Mon night... High pres in control with continued clearing overnight. Although still not perfectly ideal for radiational cooling as pres gradient remains elevated enough to keep some light winds at the sfc. Only caveat may be the more sheltered valleys of NW MA. Seasonably cool overnight, mins mainly in the upper 20s and low 30s. Slightly cooler where isolated decoupling occurs. && .LONG TERM /TUESDAY THROUGH SUNDAY/... Highlights... * Dry/mild with above normal temperatures Tue and especially Wed * Significant coastal storm possible late this week with several "potential" weather hazards but it is not a certainty this far out Details... Tuesday and Wednesday... Westerly flow aloft with above normal height fields coupled with a surface high pressure to the south will keep our weather dry and mild. High temps should reach into the upper 40s to lower 50s Tue afternoon. Even milder temperatures on Wed as the high moves off the mid Atlantic coast allowing high temps to recover well into the 50s to near 60...away from the cooling marine influence of the south coast. Thursday through Saturday... The potential continues for a significant/long duration coastal storm late this week...but there remains plenty of uncertainty. This event is still 4-5 days out in the model world...where track errors over 150 miles are quite common. Therefore...it really is impossible to lock in any particular solutions or outcomes. Nonetheless...there are several ingredients in place that still have us concerned for the threat of a significant/long duration coastal storm with several weather hazards possible. What exactly unfolds late this week will have to do with timing/strength of many features. A couple main players involve shortwave energy emerging from the southwest and another across the north central plains. Their specific strength/timing will have a large impact on the developing storm that will occur in the Ohio Valley. A strong -NAO/Greenland Block should prevent the storm from cutting to our west and force it eastward...at least secondary coastal development. As previous forecaster mentioned...a highly anomalous -NAO can sometimes suppress the storm track well south of our region but that is not always the case. There have been plenty of big storms in New England with very strong -NAO/s...but a lot of that is a function of where the block sets up along with where exactly the storm develops and intensifies. While it is way too early to get into specifics about this potential strong coastal storm...there are several possible weather hazards. These include significant amounts of rain and/or snow depending on thermal profiles...which are impossible to say at this point. If ptype favored rain there would be a concern for fresh water flooding. A period of strong to damaging winds especially along the coast. The GEFS ensembles are already indicating an easterly LLJ 4+ standard deviations above normal at 12Z Friday...which is quite a strong signal to see in an ensemble 120 hours out. Lastly...a persistent and potentially strong onshore flow may result in significant coastal flooding/beach erosion during several high tide cycles along the eastern MA coast given high astro tides. In a nutshell...the potential hazards listed above are if this storm comes to fruition but we are still 4 to 5 days out. If shortwave timing/strength changes a weaker storm suppressed further to the south could spare the region many issues. Nonetheless...this system does have significant potential and bears watching. Sunday... Low confidence this far out...but looks like bulk of the precipitation will have departed with seasonable temperatures. && .AVIATION /00Z MONDAY THROUGH FRIDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday Night/... Through 11Z Mon morning...Low to Moderate confidence. Mainly IFR to low end MVFR conditions across the interior early this evening. Ceilings may lift a bit or even scour out from a time...especially from west to east after midnight. However...this may lead to more fog perhaps becoming locally dense in spots late. Therefore...a wide variety of conditions may be seen in the terminals after midnight. Some areas may lower LIFR conditions in fog developing which may be locally dense with the best chance in low lying areas. Other locations may see MVFR to even localized VFR conditions develop near overnight. After 11Z and into Mon night...High confidence. Winds settle NW around 10 kt. Lingering IFR/fog conditions dissipate through the early AM, with VFR then remaining through Mon night. KBOS Terminal...Moderate confidence in TAF. IFR conditions early this evening may improve to MVFR conditions after midnight and perhaps even VFR towards 12z. KBDL Terminal...Low confidence. MVFR conditions early this evening may see brief improvement to VFR. However...if this occurs areas of fog perhaps locally dense may develop. This remains uncertain...but if any dense fog develops it should scour our shortly after daybreak Monday. Outlook /Tuesday through Friday/... Tuesday through Wednesday...High confidence in mainly VFR conditions. Thursday: Increasing threat for MVFR to perhaps even IFR conditions as the day wears on Thu...but that will depend on the timing of a developing coastal storm. Thursday Night and Friday: MVFR-IFR conditions likely. Windy with gusts to 40 to 50 knots possible along the coast depending on track/timing/strength of coastal storm. RA and/or SN likely. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday Night/...High confidence. Through tonight... All gales have been converted to small craft headlines. While the winds dissipate and back to the N-NW, seas remain elevated through the early AM hours. Therefore small craft advisories may have to linger through early Mon across the outer most waters. Otherwise, fog through the evening expected with reduced vsby. Mon and Mon night... Brief lull in conditions Mon morning. By Mon afternoon, wind gusts should once again reach around 25 kt offshore out of the NW and linger through the evening, seas only build to about 5 ft, but some Small Craft Advisories will likely be needed even for the marginal conditions. Outlook /Tuesday through Friday/... ***Potentially dangerous storm for Mariners late Thursday into Saturday with strong winds and high seas which are dependent on the track/strength of a potential strong coastal storm*** Tuesday: Winds less than 25 kt. Seas locally approaching 5 ft. Tuesday Night: Winds less than 25 kt. Wednesday: Winds less than 25 kt. Areas of seas approaching 5 ft. Wednesday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Thursday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain. Thursday Night and Friday: Gale to storm force wind gusts between 40 and 50 knots may develop depending on track/strength timing of coastal storm. Seas may approach or exceed 20 feet! && .TIDES/COASTAL FLOODING... Thursday through Saturday... The potential exists for significant coastal flooding/beach erosion over several high tide cycles late this week...particularly along the eastern MA coast. While this is far from a certainty given the potential event is 4 to 6 days in the future...there are several ingredients in place coupled with high astronomical tides that this will need to be watched closely. && .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 10 PM EST this evening for ANZ235- 237. Small Craft Advisory until 7 AM EST Monday for ANZ250-251- 254>256.
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&& $$ SYNOPSIS...Doody/Frank NEAR TERM...Frank SHORT TERM...Doody LONG TERM...Frank AVIATION...Doody/Frank MARINE...Doody/Frank TIDES/COASTAL FLOODING...Frank

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