Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 191957 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 357 PM EDT Sun Mar 19 2017 .SYNOPSIS...
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Departing ocean storm will result in some left over non-accumulating snow showers across the Cape/Islands this evening...but the bigger story will be the strong winds. High pressure building in from the west will result in partly to mostly sunny skies and milder weather on Monday continuing into Tuesday. An arctic front will bring near record cold temperatures Wednesday and Thursday along with bitterly cold wind chills. A warming trend then develops Friday and Saturday.
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&& .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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Lingering low level moisture and forcing will allow snow showers to continue into early this evening across the Cape/Nantucket. Temps will remain above freezing though...so no additional accumulations are expected. May see a few flurries even back into the Boston to Providence corridor early this evening...but will be of little consequence. Should see the bulk of the snow showers across the Cape/Nantucket wind down by late evening...although a few flurries may linger a bit longer. Good mixing on northerly winds should yield wind gusts of 40 to 50 mph across the Cape/Islands for a good portion of the night. We went with wind advisories for this region...but maintained the high wind warning for Nantucket as a few gusts over 55 mph will be possible this evening. The strongest winds should gradually diminish after midnight but it still will remain windy through daybreak. Otherwise...skies are already becoming mostly sunny across western MA into northwest CT. Should see skies become mostly clear in most locations as the night wears on except for the Cape/Islands. Lows by daybreak Monday should range from the middle to upper teens across the normally coldest outlying locations of western MA...to mainly the 20s elsewhere. Wind and warming mid level temps will probably keep the outer Cape/Nantucket above freezing all night.
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
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Monday... Partly to mostly sunny skies and milder temps will usher in the first day of spring. 850T near 0C and good mixing should result in many locations seeing high temps recover into the upper 40s to the lower 50s Monday afternoon. The exception will be the Cape/Nantucket where gusty northerly winds blowing off the cold ocean will hold high temps in the lower 40s. Wind chills across the Cape/Nantucket will be in the upper 20s to middle 30s with the gusty winds so a typical early spring day in southern New England.
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&& .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
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Highlights... * Moderating temps Mon and Tue with 50 possible for some Tue! * Arctic blast with near record cold returns middle of next week * Warming trend Friday and Saturday with some precipitation likely Overview and model preferences... Noting enough agreement between deterministic guidance through at least Fri that a blend can be used as a baseline. Given uncertainty with a S stream cutoff developing Fri into the weekend will lean more heavily on ensemble means to account for the full envelope of possibilities. Modest meso ridging Mon night into Tue gives way to another arctic wave and attendant arctic front by late Tue into Wed, with below normal cold Wed and Thu. This gives way to warm ridging by Fri and Sat, but a meandering S stream cutoff could allow for precipitation in the form of an inside runner. Timing somewhat uncertain, but by leaning on ensemble means, it appears mainly the weekend will be wet. Details... Mon night into Tue... Relatively warm period thanks to modest ridging yielding H85 temps near +2C by 12Z Tue. Although mid lvl temps will gradually decrease through the day it`s still likely that with downslope flow in areas of little to no snowpack (SEMA and S RI) will see highs in the low 50s, but still holding in the 40s inland in spite of the snowpack. Mainly sunny skies, although some days- end clouds possible ahead of the approaching arctic front. Tue night through Thu... Arctic front will slide through Tue evening. Right now it appears there will be little fanfare but with the robust upper lvl cold advection, could see a few SHSN or even an isolated squall developing especially during the daylight hours on Wed when the low lvl lapse rates will be steepest. Moisture is somewhat lacking, hence the low confidence and limited areal coverage potential. Strong pres gradient Wed will enhance the squall threat, but at the very least lead to cold N winds. Otherwise, still monitoring an offshore frontal wave moving off the mid Atlantic and along the front stalled to the S. As previous forecaster noted, not seeing enough backing in the flow to suggest precip shield impacting S New England, however as noted yesterday, there continues to be a slight northerly shift each run of the peak F-gen/deformation that suggests maybe enough low-lvl trofing for some precip outside of the SHSN or isolated squalls. Still worth watching for Wed. Below normal temps are expected as H85 temps drop between -18C and -20C which may be record breaking for CHH sounding per SPC climatology. The late March sun angle will likely still allow highs into the low-mid 30s each day, but assuming a break in the pres gradient Wed night and Thu night, mins could drop into the single digits and teens, potentially approaching some records. Fri... Gradual warming thanks to a rebound in ridging with the arctic wave moving E. This does have some connection to Gulf of Mexico moisture/warmth as H85 temps warm rapidly back to an average of +2C by Fri afternoon. This suggests highs once again back into the 40s and potentially even near 50. Will also be watching a warm front approaching from the W, but looking at the associated LLJ and dry soundings in the the low lvls, so not expecting much in the way of precip at least during the daytime Fri given these mitigating factors. Sat and Sun... Modest baroclinic zone is stalled across or just N of S New England with a weak low pres traversing it sometime on Sat. This suggests increased risk for rainfall as ensemble average PWATs are around 1.00 inches. This gradual southward progression suggests a risk for rainfall both Sat and into Sun, although some improvement is possible as timing will be better worked out as we approach. One other note of uncertainty is the placement of an arctic high pres to the N, which as the precip shield shifts S may allow for some changeover to a wintry mix. This is highlighted in some ensembles and bears watching as we approach.
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&& .AVIATION /20Z SUNDAY THROUGH FRIDAY/...
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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 Monday/... Tonight...Moderate to high confidence. Lingering IFR conditions in some snow showers/low clouds should improve to mainly MVFR across the Cape/Nantucket early this evening. The bulk of the snow showers in this region should come to an end by late this evening. Across the rest of southern New England...MVFR cigs will continue to improve to VFR from west to east this evening. Northerly wind gusts of 20 to 30 knots are expected along the coastal plain with 30 to 45 knots across the Cape and Islands tonight. Strongest of those winds will be across Nantucket. Monday...High confidence in VFR conditions. Northerly wind gusts of 25 to 35 knots into mid afternoon across the Cape and Nantucket. KBOS TAF...Moderate to high confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Monday Night through Friday/... Mon night through Tue...High confidence. Mainly VFR. Winds light out of the W. Wed and Thu...High confidence. Mainly VFR although isolated SHSN possible mainly Wed with brief lower categories. Winds gusting 20-25 kt on Wed out of the NW. Lighter Thu. Fri...Moderate confidence. Winds shift to the SW. Mainly VFR, but a MVFR CIGS may begin to filter in from the S late in the day.
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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 /Tonight and Monday/... Tonight...Moderate to high confidence. Pressure gradient between departing ocean storm and high pressure building into the mid Atlantic will result in strong winds and high seas tonight. Gale Warnings posted for 35 to 45 knot wind gusts across the open waters with strong small craft for Boston Harbor/Narragansett Bay. We did maintain marginal Storm Warnings across our extreme southeast outer- waters for a few gusts up to 50 knots. 10 to 15 foot seas expected across our easter outer-waters with the longer fetch. Monday...High confidence. Northerly Gale Force Wind gusts should diminish to between 25 and 30 knots by late morning and continue into the afternoon. Nonetheless...pressure gradient will remain strong enough that will need small craft headlines. Outlook /Monday Night through Friday/... Mon night into Tue...High confidence. Winds and seas gradually diminish Mon night dropping below small craft advisory thresholds by early Tue morning after starting around 25-30 kt and 5-7 ft respectively. Quiet boating weather follows for the daytime on Tue. Wed and Wed night...Moderate confidence. Winds shift to the NW with gusts potentially reaching low end gale force. Gale warnings may be needed, however at least small craft advisories will be needed. Seas peak late Wed around 8-10 ft on the ocean waters. These conditions linger into Wed night but any Gales may be turned over to small craft advisories by late Wed night. Risk for light freezing spray begins late day Wed and continues into early Thu. Thu...High confidence. Mainly quiet boating weather after winds and seas recede early. Fri...Low confidence. Winds shift to the SW. May reach low end Gale force by Fri afternoon, but more likely small craft advisories may be needed. Timing somewhat uncertain.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...Wind Advisory until 2 AM EDT Monday for MAZ022-023. High Wind Warning until 2 AM EDT Monday for MAZ024. RI...None. MARINE...Gale Warning until 8 AM EDT Monday for ANZ231>235-237-250-251- 256. Small Craft Advisory until 8 AM EDT Monday for ANZ230-236. Storm Warning until 2 AM EDT Monday for ANZ254-255.
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&& $$ SYNOPSIS...Frank/Doody NEAR TERM...Frank SHORT TERM...Frank LONG TERM...Doody AVIATION...Frank/Doody MARINE...Frank/Doody

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