Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 130841 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 341 AM EST Fri Jan 13 2017 .SYNOPSIS...
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High pressure slowly builds over the region late today into tomorrow, with a return of colder, more wintry temperatures. A reinforcing surge of cold dry air arrives Sunday as High Pressure exits Quebec into Maine. A cold start to the week Monday morning but a warming trend for the remainder of next week along with showery weather from time to time.
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&& .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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Latest OBS/MSAS data suggests cold front is lying from the Coastal Plain of MA through the S Coast of RI/CT and continuing it`s slide to the SSE. Timing suggests that it should be offshore save for maybe the islands by 10Z (6AM). Meanwhile, drier air is moving in quickly aloft but is lagging at the sfc with dwpts still in the low-mid 40s as far NW as portions of Worcester/Franklin Counties. However, these too should rapidly dip as OBS in NY and Berkshire county are already in the low-mid 30s. Cold advection will be the primary influence in today`s wx. H92 temps will drop to -8C to -10C by 00Z this evening. This cold advection will impact mixing but subsidence inversion will suppressthe mixing through the day. Warmest temps are likely to occur early in spite of mix of sun and clouds. Therefore, did not go with a typical diurnal trend with hourly temps/dwpts today, highlighting the warmest temps this morning. Otherwise, the cold advection/mixing should tap some of the 35-45 kt LLJ in place across the region, however the suppressed mixing will limit sfc gusts mainly to 25-35 mph, still breezy, but below wind advisory thresholds. Wind chills therefore will remain in the 30s and begin dipping below by late afternoon, in spite of ambient highs in the 40s/upper 30s early.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/...
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Tonight... Initially, breezy conditions will yield wind chills in the teens and low 20s. However, strong subsidence inversion and slackening pres gradient will lean way from wind chills and toward radiational cooling. Top of the inversion is about -12C, so plenty of room for early morning mins to drop into the teens (and even single digits in the usual cold valleys of NW MA). Only urban heat-islands remain in the 20s. Tomorrow... 1040+ high pres will settle across N New England, suppressing a weak low pres which will move off the Delmarva Sun night. This should suppress the precip shield well to the S late tomorrow afternoon and evening, for now only highlighting a low risk for flurries mainly across the Islands. This will lead to a shift in winds back to the S-SW and allow for some warming at H92, which reach -6C to -8C by tomorrow evening. However, the cold start, building CI/AC shield attendant to the low pres to the S and suppressed mixing should limit highs to the mid-upper 20s with a few low 30s. Nearly 30F colder than Thu highs.
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&& .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
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*/ Highlights... - Despite a slight chance of snow for the S-coast Saturday night, a warmer than average, more wet weather pattern for next week */ Discussion... Clash of N Hemispheric patterns signal a mild, more wet pattern into late January across the NE CONUS. Absence of wintry weather. Several features: 1) +EPO / +WPO indicating a progressive jet of mild Pacific air into the W CONUS, 2) PNA largely neutral during a weak La Nina ENSO episode supports a variable ridge-trough pattern across the W half of the CONUS, and 3) Increasing -NAO with an altering pressure pattern over the N Atlantic indicating a downstream blocking setup. Hints of a rex block. So no surprise the E CONUS / E Canada becomes a region of favorable ridging with ensemble means continuing to signal a +1-2 standard deviation in H5 heights with potential H85 anomalies on up to +20C. Leaning towards inside-runner lows with New England within the warm side of the envelope. Sorry all you skiers / snowboarders out there. After some significantly cold air over the weekend with some snow skirting the S shore Saturday night, overall light, flurries mostly, looking at mainly S winds, warmer than average temperatures, and with any disturbances outcomes will be mostly rain with a low risk of a wintry mix with onset, as is the case around Tuesday into Thursday with a leading initial warm front followed by a weak cold front. Talking highs averaging in the 40s to 50s with lows in the 30s with continued support from ensemble probabilistics. Ridging across the region, expecting emerging disturbances from the W to weaken while remaining progressive. Only noteworthy targets of opportunity may be perhaps blustery S winds with limited confidence to suggest the possibility of wind advisories. The draw of warmer, more moist air N, may also contend with low cloud / fog issues at times with wet- weather anticipated. Already this winter we`ve seen an altering WPO / EPO pattern with a variable Pacific jet during a weak La Nina ENSO event. Don`t expect this mild, wet pattern to hold for long given upstream variability. It`ll be interesting to see how the AO / NAO evolves, but aside do expect with the remaining 2+ months of winter that we`ll see the return of some colder air, but it would appear that January will end with an above-average monthly average temperature.
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&& .AVIATION /08Z FRIDAY THROUGH TUESDAY/...
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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 Saturday/... Through today...High confidence. VFR, with ACK clearing out in the next few hours. Otherwise W-NW winds, where they have not already reached 15-25 kt will pick up after sunrise, with some gusts 25+ kt. Tonight into tomorrow...High confidence. VFR. Winds drop off overnight, and remain relatively light into Sat. KBOS TAF...VFR remains in place. Winds will once again pick up especially after sunrise with gusts 20-30 kt out of the W-NW. KBDL TAF...VFR remains in place. Winds will once again pick up especially after sunrise with gusts 20-30 kt out of the W-NW. Outlook /Saturday night through Wednesday/...Moderate confidence. Saturday night... W/SW flow with gusts up to 20 kts with low-end VFR cigs, MVFR across the immediate S coast, mainly over the Islands, and -SN. Sunday through Wednesday... VFR through Monday. Lowering cigs into Tuesday down to IFR with RA and increasing S/SW winds. Low risk of LLWS impacts.
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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 Saturday/... Through tonight...High confidence. Winds across the waters will reach 25-30 out of the W-NW as seas also reach 8-10 ft on the outer ocean waters. Winds drop late this evening, and seas will take much of the overnight to subside. Therefore, small craft advisories continue today, but will be dropping this evening and overnight. Some light freezing spray is possible, mainly across the E waters and mainly this evening until winds recede. Tomorrow...High confidence. High pres will yield a period of quiet boating wx through the day. Winds will remain light, but shift from NW to S-SW by afternoon. Outlook /Saturday night through Wednesday/...Moderate confidence. An offshore area of low pressure sweeping W to E yields light snow across the S waters, perhaps some lower visibility Saturday night. Behind the low, breezy NW winds which could result in 5 foot seas on the outer waters. Seas subsiding and winds remaining light while turning S into midweek beneath high pressure will make for good boating weather. Winds increasing beginning Wednesday as does wave action as rain overspreads the region.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 2 AM EST Saturday for ANZ231>234- 251. Small Craft Advisory from 10 AM this morning to 7 PM EST this evening for ANZ230-236. Small Craft Advisory until 10 PM EST this evening for ANZ235- 237. Small Craft Advisory until 7 AM EST Saturday for ANZ250-254. Small Craft Advisory until 5 AM EST Saturday for ANZ255-256.
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&& $$ SYNOPSIS...Doody/Sipprell NEAR TERM...Doody SHORT TERM...Doody LONG TERM...Sipprell AVIATION...Doody/Sipprell MARINE...Doody/Sipprell

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