Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 131214 AFDBOX Area Forecast Discussion 713 AM EST Tue Feb 13 2018 .SYNOPSIS... High pressure brings dry but chilly weather to southern New England today. Unseasonably mild weather is anticipated Wednesday into Friday afternoon with scattered rain showers from time to time ahead of an approaching cold front. A brief shot of cold but dry weather follows Friday night into Saturday...but above normal temperatures return Sunday and especially by Monday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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713 am update... A 1045 mb high was building in from the west early this morning and skies were mainly clear other than a touch of high cloudiness. Cold advection has allowed early morning temperatures to drop into the upper teens to the middle 20s. This chilly start, combined with relatively weak mixing will keep temps mainly below normal. Highs progged low-mid 30s, but with plenty of sunshine and just a bit of high cloudiness. Although the high pres itself is quite strong, a function of the influence of subtropical ridging, the mean jet is also very strong as a result of competing S and N streams. Therefore it is likely to crest before the end of the day across New England, even though it is starting well W.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... Tonight.. High pres shifts E with return flow developing. This will allow the lower lvls to gradually moisten through the evening. In fact, by 12Z Wed, soundings show nearly saturated profile beneath H8 with drier air above. Therefore, expecting increasing cloud cover from S-N, especially as a very weak shortwave and attendant warm front approaches from the S. Also, given very weak lift, and moisture below H8, could see the development of some late night/early AM very light precip, drizzle or snow flurries with little to no accum. The lift will be weak, and lacking any form of sfc/low lvl convergent boundary. In fact, will continue with NIL POPs, but add it to weather as a possibility mainly S of the Mass Pike, where moisture is peaked. Temps will be key at this point, as there is a risk for sfc temps to drop near or below freezing before or as precip starts if it does. Could see localized flurry/freezing drizzle which will need to be watched for the Wed AM commute. Wed... Aside from the early AM ice risk, warm front should be able to shift N of the region thanks to enhanced S flow through the day. This allows H85 temps to reach a full standard deviation above normal, or nearly +2C to +4C by late afternoon. There is a modest damming signal which could slow this progression. However, will likely see highs reaching mid 40s to around 50F especially if some later day sunshine is observed. Rising heights through the day support this possibility, before a stronger wave arrives Wed evening/overnight. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
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Highlights... * Brief showers possible late Wed night/early Thu am, otherwise mainly dry with unseasonably mild temperatures Thu afternoon * Cold front likely brings some showers Thu night/Fri am followed by a brief shot of dry but cold weather Fri night/Sat * Above normal temps return early next week but there is a low risk for a period of ice/snow during the transition Details... Wednesday night and Thursday... Anomalous upper level ridging over the Gulf coast will result in unseasonably mild westerly flow across southern New England. We may have a brief round of showers late Wed night/early Thu with a burst of marginal elevated instability/moisture. The low level jet has mainly a westerly component...so uncertain if these brief showers will impact most of the area or pass to the south of most locations. Regardless...mainly dry weather anticipated by late Thu morning and afternoon. Given well mixed atmosphere and 850T between +4C and +6C...high temps should be well above normal. High temps will likely climb well into the 50s. However...if we end up with more sunshine than expected it is not out of the question that a few locations in the lower elevations could break 60! Thursday night and Friday... Weak wave of low pressure and approaching cold front will likely bring a period of showers to the region Thu night into Fri morning. Mild/above normal temperatures will continue over this time period. Temps should remain above freezing Thu night with highs well up into the 40s to lower 50s on Fri. Friday night and Saturday... Dry weather but a brief shot of cold air moves into the region behind the cold front. Low temps Fri night in the teens to lower 20s with highs Sat mainly in the 30s. Sunday and Monday... Upper level ridging builds across the southeast coast resulting in the return of unseasonably high height fields into southern New England. Above normal temperatures will return early next week. Some guidance is indicated the risk for a bit of snow or ice during the transition back to milder temperatures Sat night/Sun. Will call that a low risk for now but something will have to watch.
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&& .AVIATION /12Z TUESDAY THROUGH SATURDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday/...High confidence. Through tonight... Mainly VFR, although some SCT-BKN MVFR CIGS (020-030) could impact the outer Cape/Nantucket late this afternoon and evening. N winds with a few gusts to around 20 kt across SE MA this morning. The winds then shift around to the SE by evening. Wed... More clouds with CIGS gradually lowering to low VFR with occasional MVFR conditions from S-N. Winds mainly SSW around 10 kt. KBOS Terminal... High confidence in TAF. KBDL Terminal... High confidence in TAF. Outlook /Wednesday Night through Saturday/...Moderate Confidence. Wednesday Night: Mainly VFR, with local MVFR possible. Breezy. Chance SHRA, patchy BR. Thursday: Mainly VFR, with areas MVFR possible. Breezy. Thursday Night: Mainly MVFR, with local IFR possible. Chance SHRA. Friday: MVFR/IFR conditions possible. Windy with local gusts to 30 kt. Chance SHRA. Friday Night: VFR. Windy with areas gusts to 30 kt. Saturday: VFR. Breezy. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday/...High confidence. Through today... Winds diminish through mid morning, but lingering seas near 5-6 ft on the outer waters will require the Small Craft Advisory conditions to continue. Tonight into tomorrow... Winds shift to the S, then SW late tonight. Gusts could reach around 25 kt with a slowly building swell into Wed. Another round of early AM-Wed Small craft advisories may be needed. Outlook /Wednesday Night through Saturday/...Moderate to High Confidence. Wednesday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. Thursday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers, patchy fog. Local visibility 1 to 3 nm. Thursday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. Friday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas. Chance of rain showers. Friday Night: Low risk for gale force winds with gusts up to 35 kt. Rough seas up to 11 ft. Saturday: Winds less than 25 kt. Local rough seas. && .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 10 AM EST this morning for ANZ231- 250-251-256. Small Craft Advisory until 1 PM EST this afternoon for ANZ254- 255.
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&& $$ SYNOPSIS...Doody/Frank NEAR TERM...Doody SHORT TERM...Doody LONG TERM...Frank AVIATION...Doody/Frank MARINE...Doody/Frank

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