Area Forecast Discussion
Issued by NWS Boston, MA

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571 FXUS61 KBOX 202321 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 721 PM EDT Mon Mar 20 2017 .SYNOPSIS... High pressure will bring dry and mild conditions into Tuesday. An arctic front will bring near record cold Wednesday into Thursday morning along with bitterly cold wind chills. Milder weather returns Friday along with the chance of a few rain showers. A cold front crosses the region Saturday with a period or two of rain/ice and/or snow possible into early next week, but confidence is low. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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720 pm update... Previous forecast on track. Light winds/mainly clear skies and the dry airmass in place will allow temps to fall rather quickly in the typically prone locations this evening. SNE will be in between systems tonight with departing low pres to the east and weak cold front approaching from the NW. Models indicate increasing mid/high level moisture spilling into the region as upper level ridge axis moves to the east. This will result in some increase in mid/high clouds which will likely limit extent of radiational cooling. Expect low mainly in the upper 20s to lower 30s with light winds, diminishing on the Cape and Islands.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... Tuesday... Mid level shortwave passes to the north with weak front moving into the region. Cross sections show enough moisture for bkn cloud cover at times so generally ptsunny skies. Low risk of a brief shower, mainly in the Berkshires but a dry day otherwise. 925 mb temps around 2C which is a few degrees milder than today so highs should reach mid/upper 40s higher terrain and 50-55 elsewhere, except cooler Cape/Islands. Tuesday night... Digging shortwave from the Gt Lakes will result in amplifying mid level trof across the NE by 12z Wed. Arctic front expected to move across SNE around 09-12z. Marginal moisture and poor 1000-700 mb lapse rates will limit potential for squalls so only expecting a few snow showers, mainly over the higher elevations. Gusty NW winds develop late behind the front as cold advection increases. Lows will range from 20-25 over the higher elevations in northern/western MA with some teens over the Berkshires to lower 30s southern RI and SE MA. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... Highlights... * Arctic blast Wed into Thu am along with windy conditions * Milder Fri/Fri night with some rain showers possible * Low confidence next Sat-Mon with unsettled weather possible at times with some rain...ice and/or snow possible Details... Wednesday... Late season shot of arctic air invades the region on Wednesday. Depending on the exact timing of the front...early morning temps may be in the upper 20s to the middle 30s on the coastal plain. Despite very strong cold advection...the March sun angle may allow temps to hold steady into mid afternoon along the coastal plain. Less sun expected across the interior with more diurnal cumulus, so these areas should fall well into the 20s by mid afternoon. The entire region should fall quickly by late afternoon/early evening as impressive cold advection settles in with 850T dropping to between -18C and -20C. Excellent mixing should result in northwest wind gusts of 30 to 40 mph...resulting in wind chills dropping into the single digits and teens by late afternoon. Extremely well mixed atmosphere may yield a few 45+ mph gusts...so it is possible we eventually will need a wind advisory. Wednesday night... Impressive shot of arctic air for late March will be accompanied by gusty northwest winds. Low temperatures will drop into the single digits and lower teens in most locales by early Wed am. In fact...a few locations may be near record low temperatures. Wind chills will range from 0 to 10 below zero late Wed night/early Thu am. Thursday... Large high pressure builds in from the west as upper level trough lifts northeast of the region. Despite a bitterly cold early am start...plenty of sun should allow for temperatures to moderate some by afternoon. Still temps will be well below normal for late March with highs only reaching into the lower to middle 30s. It will be an improvement over Wednesday though with rather light winds. Friday... Fast moving shortwave moves across the region with a burst of warm advection aloft. May see a period of showers with this shortwave...but fast moving shortwave and limited moisture should result in light amounts. Also...duration of showers should be limited so much of Friday and Friday night may end up dry. Low risk there could be a touch of a wintry mix across the interior at the onset...but odds favor mainly just rain showers. High temps should reach well into the 40s. Saturday through Monday... Tremendous uncertainty exists in this portion of the forecast. At first glance it would appear unseasonably mild with upper level ridging off the southeast coast pumping above normal height fields into New England. However...at the surface an arctic high pressure system over eastern Canada will be nosing into the region. This will likely force a cold front south of the region. Timing is certainly subject to change but the majority of the current guidance does this on Saturday. Once this cold front crosses the region it becomes uncertain how far south it will travel. Given the upper level ridging over the southeast and that it is late March there is a decent shot the front stalls over the Mid Atlantic states. This would allow a wave or two of low pressure to develop on the front and bring the potential for a period or two of over running precipitation. Depending on exact thermal profiles...ptype may be in the form of rain...ice and/or snow. It is also possible that the front presses well south of us resulting in just a brief band of rain showers Sat...followed by mainly dry cool weather Sun/Mon. It is just too early to say much more at this time but something will need to watch. && .AVIATION /23Z MONDAY THROUGH SATURDAY/...
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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 Tuesday Night/... Tonight into Tuesday...High confidence. VFR cigs with mid/high clouds moving in tonight. Lower VFR cigs Tue with patchy MVFR and a low risk of a brief shower, mainly interior. Tuesday night...High confidence. Mainly VFR but a few snow showers possible late along an arctic front, mainly over the Berkshires and western MA. Increasing NW winds with gusts to 20-30 kt developing 09-12z. KBOS TAF...High confidence in TAF. May see a sea breeze develop Tuesday afternoon. KBDL TAF...High confidence in TAF. Outlook /Wednesday through Saturday/... Wednesday...High confidence. Low risk of brief MVFR cigs early, but otherwise VFR conditions. Northwest wind gusts of 25 to 35 knots expected with a few gusts to 40 knots possible. Thursday...High confidence in VFR conditions. Friday and Saturday...Low to moderate confidence. A period of two of showers along with some MVFR cigs are possible at times.
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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 Tuesday Night/... High confidence. Tonight...Lingering SCA seas across our eastern waters will continue to gradually diminish from west to east overnight as a weak ridge of high pres builds over the waters. Tuesday...Light NW winds becoming W/SW in the afternoon. A few gusts to 20 kt possible over south coastal waters. Seas slowly subsiding below 5 ft over eastern waters in the afternoon. Tuesday night...Increasing NW winds after midnight with gusts to 25-30 kt developing late as cold advection increases. May reach gale force by Wed morning and gale watches will be issued. Outlook /Wednesday through Saturday/... Wednesday and Wednesday night...Moderate to high confidence. Northwest wind gusts of 30 to 40 knots expected in the strong cold advection pattern. Gale Watches posted all waters. In addition...moderate freezing spray is expected across many waters Wed night into Thu am so freezing spray advisories will eventually be needed. Thursday...Moderate to high confidence. Freezing spray should diminish by mid morning. Otherwise...winds will gradually diminish but still expect small craft wind gusts for much of the day. Friday...Moderate confidence. Southwest wind gusts of 20 to 30 knots may develop ahead of a cold front. Small craft headlines may be required. Saturday...Low confidence. Winds and seas highly uncertain depending on timing of a cold front.
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&& .CLIMATE... Record cold highs for Wednesday, March 22 are below: Boston (BOS) 24/1885 Hartford (BDL) 29/1960 Providence (PVD) 28/1914 Worcester (ORH) 25/2002 Record lows for Wednesday, March 22: Boston (BOS) 8/1885 Hartford (BDL) 12/1934 Providence (PVD) 15/1988 Worcester (ORH) 8/1988 Record lows for Thursday, March 23: Boston (BOS) 6/1934 Hartford (BDL) 9/1934 Providence (PVD) 8/1934 Worcester (ORH) 4/1934 && .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Gale Watch from Wednesday morning through Wednesday evening for ANZ230>237. Small Craft Advisory until 10 PM EDT this evening for ANZ232. Small Craft Advisory until 2 AM EDT Tuesday for ANZ231. Gale Watch from Wednesday morning through late Wednesday night for ANZ250-251-254>256. Small Craft Advisory until 5 PM EDT Tuesday for ANZ250-254. Small Craft Advisory until 11 AM EDT Tuesday for ANZ251-255.
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&& $$ SYNOPSIS...KJC/Frank NEAR TERM...Frank/KJC SHORT TERM...KJC LONG TERM...Frank AVIATION...KJC/Frank MARINE...KJC/Frank CLIMATE...Staff

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