Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 271339 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 939 AM EDT Mon Jun 27 2022 .SYNOPSIS... A cold front will bring increased clouds today along with a period of widespread rain showers. Locally heavy downpours are possible. Rain ends early tonight as cold front moves offshore. Dry conditions, cooler temperatures and low humidity levels then return on Tuesday and Wednesday. Increasing temperatures late in the week with more unsettled weather by the weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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940 AM Update... KBOX radar currently revealing scattered showers across southern New England this morning. A few light showers moving over portions of the south coast right now. Further west there are a additional scattered showers with pockets of moderate to heavy rainfall. Expect showers to expand in coverage and intensity this afternoon as a cold front pushes through the region. Forecast remains on track, have only made minor adjustments in this update to reflect latest observations and more recent short-term model guidance. See 3AM discussion for additional details. 300 AM Update: Warm sector air mass regime in place over Southern New England early this morning, with south winds and current temps in the 60s to low 70s. Mostly clear skies generally prevail, but increasing clouds are anticipated over the next couple of hours in association with a cold front analyzed over western New York. Several clusters of rain showers were noted along and just ahead of the boundary; these rain showers are being infused by PWATs in the 2 inch range. Cold front will continue to progress eastward, into western MA and CT between 8 and 10 AM, into central MA/western RI/eastern CT around noontime/early-afternoon, toward eastern MA/RI by mid to late in the afternoon and approaching Cape Cod late in the day. Besides the high- PWAT airmass which is expected to advect over our area before the front arrives, warm cloud depths in the 13k range are very favorable for heavy downpours. However rather fast individual storm motions should keep these locally heavy rains from sitting over any one area. Thus, not anticipating any significant flooding risks but there will nonetheless be some reduced visibility in heavy downpours. On the thunder potential, abundant cloud cover will significantly limit destabilization. Though I`ve maintained a mention of isolated thunder in the forecast, the lack of instability makes prospects for thunder pretty limited. I did want to maintain the mention of heavy rain but opted for rain heavy at times wording versus the heavy downpours in thunder mention, because thunder should be the exception vs the rule. While rain will continue across Cape Cod into the early evening, behind the front expect a much drier air mass and a windshift from S/SW to W and eventually NW. Highs rise only a few degrees into the 70s today under considerable cloud cover.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... 300 AM Update: Tonight: Moderate-intensity rains may still be ongoing early tonight across Cape Cod and the Islands but the cold front will gradually progress offshore. Rain should be ending areawide by midnight. As an upper- level trough moves into eastern NY, NW flow will induce a cooler and much drier air mass, with dewpoints falling from the 60s into the upper 40s to lower 50s. While leftover cloudiness should be peeling away from Cape Cod and the Islands, most areas will see mostly clear skies and lows in the 50s. Tuesday: Mostly sunny skies prevail on Tuesday, though a cool pocket of air aloft associated with upper level trough passage could lead to some shallow-based fair weather Cu fields. Expect lots of sunshine, and with 850 mb temps around +7 to +9C and dewpoints in the 40s to lower 50s, looking at pleasant weather conditions. Highs in the 70s to low 80s but with much lower humidity levels ideal for any outdoor activities. Modest NWly breezes. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Highlights * Dry and quiet for much of the week with temperatures trending upward. * Spotty showers possible late Wed into Wed evening. More unsettled weather for this upcoming weekend. Tuesday night through Friday... Caught up in somewhat cyclonic flow Tuesday night into late Wednesday before flow becomes more zonal. Will have a trough lift from the Great Lakes region Tuesday night into New England by late Wednesday. Behind the trough a ridge axis builds into and through New England late in the week. Generally anticipating dry and quiet weather across southern New England through much of this period. High pressure moves offshore on Wednesday, which allows a weak cold front/trough to slide through the region late in the day. Think this combined with diurnal heating will result in isolated showers late Wednesday into Wednesday evening. Think for most it will be dry as there is not a whole lot of moisture in place over our area. Precipitable Water values get up to roughly 0.75-1 inch, which is around the 25th to 50th percentile for CHH per SPC Sounding Climatology for this time of year. High pressure reasserts itself for the rest of the week as it nudges in offshore/well east of the Mid Atlantic coast. Given the position of the high will see increasing heat and humidity. Bumped up highs to the 80th percentile of guidance for Thursday and Friday due to W and WNW downslope flow. On Thursday, temps at 850 hPa increase to 11- 15 Celsius. The result will be highs well into the 80s for most, but it should be a bit cooler along the immediate coastline due to local seabreezes. As for Friday we get into 16-19 degree Celsius air at 850 hPa. The result is fairly widespread low/mid 90 degree readings. Coastal locations generally range from the upper 70s to the upper 80s. Late Friday through and Sunday... Flow over our area becomes more cyclonic as a cutoff digs into Hudson/James Bay and northern Quebec. A shortwave trough lifts into and potentially through southern New England on Saturday. There may be another wave that lifts into the region for Sunday, but confidence not as high in this next wave moving in. A cold front slides into and through southern New England bringing showers and thunderstorms. At this point appears to be mostly on Saturday, but not completely out of the question the front is still over us on Sunday. Per WPC Cluster analysis the most variance at this point deals with the amplitude of the trough. At this point all clusters show precipitation on both days. Deterministic guidance paints the cold front pushing completely through the region and being dry on Sunday. However, am going to lean toward the ensemble guidance at this point. Have slight chances to chances of precip through the weekend. Could see some thunder as there is at least a few hundred J/kg of CAPE per GEFS/GEPS/EPS probabilities of CAPE AOA 500 J/kg. On top of this will have increasing deep layer shear. Cannot completely rule out there could be some stronger storms, but really need to time when the front moves in and convective parameters. Stay tuned as we will hone in on more specifics/details as we get closer. Stuck with the NBM which keeps temps in the 80s and low 90s in Saturday. As for Sunday appears a bit cooler with highs ranging from the mid 70s to the mid 80s. && .AVIATION /14Z MONDAY THROUGH FRIDAY/... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Today...High confidence in trends but moderate in exact timing. VFR to start for most. Expect ceilings and visibilities to lower to MVFR/IFR levels as showers with perhaps some embedded thunder as a cold front pushes in. Should have efficient rainfall processes today, so will likely have heavy downpours at times bringing visby down to IFR range. Thinking that the thunder risk is highest for BDL/BAF/ORH/PVD, but have held off from including the latest update. Gusty S/SW winds shifting to the W once the front passes. Gusts of 20-30 kts with the highest gusts over the Cape terminals. Tonight...High confidence in trends but moderate on timing. Conditions improving to VFR as showers come to an end. May not be until roughly 06-09Z for the Cape/Islands. W to NW winds 5-10 kt, trending lower end of that speed range by Tue morning. Tuesday...High confidence. VFR. NW winds 4-8 kt; sea-breeze possible at BOS. KBOS Terminal...High confidence in TAF/trends but moderate on timing. KBDL Terminal...High confidence in TAF/trends but moderate on timing. Outlook /Tuesday Night through Friday/... Tuesday Night through Wednesday: VFR. Wednesday Night: VFR. Isolated SHRA. Thursday through Thursday Night: VFR. Friday: VFR. Breezy. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Continued small craft advisories into today as southerly winds gusting to the low to mid 20s kt range and seas building into the 3- 6 ft range (highest offshore). In addition, there is a high rip current risk today for Block Island, Martha`s Vineyard and Nantucket. South facing shores could see rip currents due to these seas and SW winds. Decreasing winds and seas with a wind shift to NW as a cold front moves over the waters tonight. Periods of rain, perhaps heavy at times could reduce visibility tonight. By Tuesday, NW gusts around 10 kt with seas in the 2-3 ft range should lead to favorable boating conditions. Outlook /Tuesday Night through Friday/... Tuesday Night through Wednesday: Winds less than 25 kt. Wednesday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Isolated rain showers. Thursday through Thursday Night: Winds less than 25 kt. Friday: Winds less than 25 kt. Areas of seas approaching 5 ft. && .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...High Rip Current Risk until 8 PM EDT this evening for MAZ023- 024. RI...High Rip Current Risk until 8 PM EDT this evening for RIZ008. MARINE...Small Craft Advisory until 11 PM EDT this evening for ANZ231>235-237-250. Small Craft Advisory until 7 PM EDT this evening for ANZ236- 251. Small Craft Advisory until 2 AM EDT Tuesday for ANZ254>256.
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&& $$ SYNOPSIS...BL/Loconto NEAR TERM...RM SHORT TERM...Loconto LONG TERM...BL AVIATION...BL/Loconto MARINE...BL/Loconto

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