Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 181044 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 644 AM EDT Tue Jul 18 2017 .SYNOPSIS... Bermuda high pressure will result in very warm and humid weather through Thursday. While dry weather will dominate for the remainder of the work week, a few diurnally driven showers and thunderstorms will occur at times. A cooler and unsettled weather pattern at times may be in store for the region this weekend into early next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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645 am update... Main concern early this morning was dense fog mainly near the south coast, Cape and Islands. A dense fog advisory remains in effect for this region through 9 am, where visibility was being reduced to one quarter of a mile at times. Otherwise, mainly dry and muggy weather early this morning besides a left over spot shower or two. Morning fog will begin to burn off late this morning as low level inversion begins to mix out. This may be a case were fog sits just off the coast into the afternoon, but flirts at times with the south coast, Cape and Islands. Once low clouds and fog burn off, temperatures will rise into the mid 80s. Cannot rule out a few sites reaching in the upper 80s, which is similar to yesterday. Upper level trough axis will swing through during the day with dry northwest flow filtering in on the backside. However, this dry air seems to lag within the mid-levels as there is plenty of moisture still across the region. Warm, moist conditions across the area will allow for precipitation to develop this afternoon. Dewpoints still in the 70s will result in CAPE values near 1500 J/KG this combined with K values near 30 should result in widely scattered showers and isolated thunderstorms. While much of the region will be at risk, biggest focus is near and south of the Pike as well as along the east coast of MA where K values will be greater. Mid- level lapse rates are quiet poor today but where the sea breeze boundary sets-up will be an area of focus for a low risk of an isolated strong to severe storm. Locations across NE MA may have the best potential for a strong/severe storm as shear values get to near 30 kts, but overall mainly looking at garden variety activity. Because of the weak flow, cannot rule out the potential for training storms leading to a low risk of very localized flash flooding.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/... Tonight... Mid-level dry air will continue to push into the region during the overnight hours tonight. However, soundings continue to show trapped low level moisture leading to another round of fog and stratus. May need another dense fog advisory for the south coast. Although left the overnight forecast dry, a spot shower or thunderstorm cannot be ruled out. Elevated instability lingers across the region which could be enough to trigger a spot shower. Dewpoints remaining in the low-mid 60s suggest this will once again be a warm night for the area. Overnight lows will be in the mid to upper 60s with a few warmer spots possible at the typical urban heat islands. && .LONG TERM /WEDNESDAY THROUGH MONDAY/...
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Highlights... * Very warm and humid Wed/Thu * Less humid on Fri but still very warm * Unsettled weather possible at times this weekend into early next week with high temps near or below normal Details... Wednesday and Thursday... Bermuda high pressure will bring very warm and humid weather to the region Wed and Thu. 850T near +16C should allow highs to reach into the upper 80s to lower 90s away from any marine influence on the immediate coast. It will be rather humid with dewpoints in the 60s to near 70. This may result in heat index values near 95 in a few locations two days in a row, which would require a Heat Advisory based on our new criteria. The majority of Wed and Thu should feature dry weather, but a few popup showers/t-storms are possible during the afternoon and evening hours. Appears to be a better chance on Thursday, given some height falls, cooling mid level temps and a weak surface boundary. However, lack of strong synoptic forcing and perhaps some mid level dry air may limit potential. Friday... Somewhat less humid air will work into the region from the west behind a weak cold front, but it still will be very warm. Highs should be well up into the 80s to lower 90s. At this point, feel weather will mainly be dry on Friday given lack of synoptic scale forcing. Saturday through next Tuesday... Strong westerly flow aloft will drop south into southern New England and allow shortwave energy to cross the region at times. This will bring a couple opportunities for showers and isolated thunderstorms this weekend into early next week. Plenty of uncertainty on when and where this activity will track and the entire period will not be a washout. All we can say at this point is that there will be a couple opportunities for showers/isolated thunderstorms over this time period. As for temps this weekend into early next week, expect them to be cooler than the next few days. This a result of more in the way of clouds, precipitation and lower height fields. In fact, high temps may end up several degrees below normal early next week if the surface boundary drops to our south and we end up with a northeast or easterly surface wind like some of the guidance currently depicts. However, still a ways out there so not much confidence at this point.
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&& .AVIATION /12Z TUESDAY 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 Tonight/... Today and tonight...Moderate confidence. Areas of IFR/LIFR will gradually improve to MVFR and then VFR from N-S in most locales by afternoon. However, low clouds and fog patches may linger across Cape/ACK/MVY through most of the day. S winds continue with weak sea breezes possible on the immediate south coast. Widely scattered showers/isolated storms expected, but many may stay dry. Overnight, another possible advancement of IFR/LIFR conditions from SE MA into SE MA/RI. KBOS Terminal...Moderate to high confidence in TAF. IFR conditions early this morning will improve to MVFR and then VFR by afternoon. Isolated thunderstorms may be in the vicinity of the terminal this afternoon. KBDL Terminal...Moderate to high confidence in TAF. IFR conditions early this morning will improve to MVFR then VFR by afternoon. Isolated thunderstorms may be in the vicinity of the terminal this afternoon. Outlook /Wednesday through Saturday/... Wednesday through Friday...Moderate to high confidence. Mainly VFR outside of an isolated to widely scattered shower/t-storm threat. There may also be some late night/early morning fog patches in the typically prone locations and especially the south coast, Cape, and Islands where it may be more widespread and persistent at times. Saturday...Low confidence. VFR probably dominates but will have to watch for a complex of showers/isolated thunderstorms moving across the region.
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&& .MARINE... FORECASTER CONFIDENCE LEVELS... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tonight/...High confidence. Winds and seas will be light enough for good boating weather. However, because of the moist atmosphere in place patchy dense fog will limit vsbys across the waters through the period. Outlook /Wednesday through Saturday/... Wednesday through Saturday...High confidence. A weak pressure gradient will keep winds and seas below small craft advisory thresholds. However, some nearshore mid to late afternoon southerly wind gusts around 20 knots at times may result in a few hours of choppy seas in the typically vulnerable Harbors and Bays. Also, areas of fog may impact the southern waters at times especially during the overnight/morning hours. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...Dense Fog Advisory until 9 AM EDT this morning for MAZ020>024. RI...Dense Fog Advisory until 9 AM EDT this morning for RIZ005>008. MARINE...None. && $$ SYNOPSIS...Dunten/Frank NEAR TERM...Frank/Dunten SHORT TERM...Dunten LONG TERM...Frank AVIATION...Dunten/Frank MARINE...Dunten/Frank

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