Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 020712 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 312 AM EDT Sat Jul 2 2022 .SYNOPSIS...
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Two rounds of showers and thunderstorms Saturday. First round early this morning, then a break with a period of dry weather mid to late morning into early this afternoon, followed by a second round of showers and thunderstorms mid to late afternoon into early this evening. A few storms may contain strong to damaging winds, large hail and with torrential downpours. A cold front will sweep across the region later this evening and overnight, ushering in drier and less humid air across the area. This will lead to beautiful warm weather, along with comfortable humidity Sunday and 4th of July Monday. Then unsettled Tuesday through Thursday with chances of showers and cooler than normal temperatures.
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&& .NEAR TERM /THROUGH TODAY/...
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300 AM update... * Two rounds of showers & thunderstorms today, early this morning and again mid/late afternoon into early this evening * Some storms may contain strong to damaging winds, large hail and torrential downpours Today/Saturday... Impressive warm sector over the region early this morning, with dew pts 65-70, and will rise into the low 70s across CT-RI and up to the Pike in MA later this morning and this afternoon! Hence, oppressive humidity. More clouds than sunshine today, but very warm airmass aloft (+20C to +22C at 925 mb) will support highs in the low to mid 80s. But given dew pts in the low 70s, it will feel closer to 90. Hence, very warm and humid today. Current temps in the 70s and dew pts in the upper 60s to lower 70s, is yielding MLCAPEs of 500-1000 j/kg across SNE. This instability coupled with weak forcing from an approaching short wave exiting the eastern Great Lakes, was supporting convection across PA/NY/western MA/CT. A few of these storms have a history of producing strong winds and large hail across NYS into western MA. This convection will continue to advect eastward and impact CT/RI and southeast MA, possibly up to the Mass Pike. Some of the CAMs have the convection peaking around/toward sunrise across CT/RI and southeast MA. In addition, HREF max updraft and UH swaths occur across this area. This seems reasonable, as short wave trough approaches, deep layer shear begins to increase after 08z/09z across this region. Therefore, expecting greatest risk of a few strong to perhaps a severe storms roughly 09z-12z across this area. Strong winds, large hail and torrential downpours are possible. Then as this initial short wave exits offshore, a period of dry weather is likely, or just disorganized showers, from mid to late morning into early afternoon. Then the question becomes, how much deep layer moisture is available for trailing short wave mid to late afternoon and early evening. Given column begins to dry out from NW to SE, greatest risk for storms to refire would be across CT/RI and southeast MA, possibly up to the MA Pike, with lower risk northward to the MA/NH border. This matches up well with HREF area of max updraft and UH swaths. Deep layer shear is not as impressive this afternoon as this morning, but instability is greater (MUCAPE 1000-2000 j/kg), thus another round of strong to severe storms appears likely. Threats remain the same, strong to damaging winds, large hail and torrential downpours. Given anomalous PWATs (150 percent of normal), including dew pts in the low 70s, storms will have the potential to produce 1-2" of rainfall. Given the break in convection between the two rounds of storms, this should preclude any significant flooding. However, isolated street/highway flooding can`t be ruled out. Given the above attributes, SPC continues a slight risk of severe storms across most of the region today, along with WPC maintaining a marginal risk of excessive rainfall across CT/RI and south of the Pike (I-90) across MA.
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&& .SHORT TERM /TONIGHT THROUGH 6 PM SUNDAY/...
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3 AM update... * Dry, warm but much less humid Sunday Tonight... Early evening convection across CT/RI/southeast MA, especially along the south coast, will exit offshore as FROPA sweeps across the area. Turning drier and less humid overnight with the wind shift to the NW. Just before sunrise Sunday, morning lows will be in the upper 50s across northwest MA, with low to mid 60s elsewhere. Still humid along the south coast with dew pts in the low to mid 60s at daybreak Sunday. Sunday... Absolutely a beautiful summer day, with dry WNW flow promoting lots of sunshine, warm temperatures (low to mid 80s), but very comfortable humidity as dew pts crash into the upper 40s and lower 50s. A nice west breeze at 10-15 mph, this will keep beaches warm as well.
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&& .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Highlights * Dry and quiet weather for the rest of the holiday weekend with high pressure in control and near seasonable temps. * Unsettled Tue-Thu with chances for showers. More confident in precip chances on Tue. Cooler than seasonable temperatures. Sunday and Independence Day... Ridge axis builds over the Northern Plains/Upper Mississippi River Valley on Sunday into the Great Lakes by early Monday. The ridge flattens out over the eastern Great Lakes/New England late on Monday. High pressure nudges into southern New England from the eastern Great Lakes on Sunday. The high builds over our area Sunday night before sliding offshore on Independence Day. Dry and quiet weather expected through this period with high pressure in control. Did opt to bump up temps to the 75th percentile of guidance for both days as we will have W/NW flow at 850 hPa resulting in downsloping. Along the immediate coastline went with the 50th percentile of guidance to cool things down a bit as am anticipating the sea breeze to develop. Temps at 850 hPa on Sunday will be roughly 10-14 degrees Celsius and 12-14 degrees Celsius on Monday. Expect temps to top out generally in the upper 70s to mid 80s. There may be a few spots across the CT and Merrimack Valley where they get into the upper 80s. Fortunately will be more comfortable than today and Saturday with dew points in the 50s. Tuesday through Thursday... Unsettled through this period with a ridge set up across the western US and a trough over the east. During this timeframe a few shortwaves slide into and through southern New England bringing opportunities for showers. Confidence at this point is highest in rainfall chances early Tuesday morning through Tuesday as a cold front slides through the region. Did dial back precipitation chances from Monday evening as the NBM appears to be bringing in precip much too quickly based on deterministic and ensemble guidance. Could see things coming into western areas after 06Z, but more likely during the day Tuesday as the front is moving through. Could have some thunder as well with a few hundred J/kg of MUCAPE along with 0-6 km shear in the 30-40 kt range. Not completely out of the question there is a strong storm or two, but mid level lapse rates look quite poor at this point. While low level lapse rates are around 6-9 degrees Celsius per km. Thinking the risk will largely be dependent on how much instability we can get ahead of the front. Could also see there being some heavy rain with PWATs of 1.5-2 inches and warm cloud layer depths of 3-4 km. Will be something to keep an eye on in the coming days. Have leaned on the NBM for the rest of the forecast despite the drier solutions from the deterministic guidance mid/late in the week. Lots of uncertainty for the Wed-Thu timeframe given there are still shortwaves sliding into our region. Deterministic guidance at this point shows high pressure nudging into the region keeping us dry, however WPC Cluster Analysis/Ensembles paint a wetter/more unsettled picture. For both days the main variance is the amplitude of the trough over New England and its positioning. All clusters at this point feature it being wet over our region, but just a question on how much precipitation we receive. Though I will point out that one cluster for Thursday does keep us completely dry, which contains 25 members. Given the uncertainty, have just leaned on the NBM bringing chances of precipitation through this period. Will need to see how things evolve in the coming days on if we will be drier or not. Temperatures will fall to cooler than seasonable readings with highs in the 70s to the lower 80s during this timeframe. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
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Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. 06z update... Saturday...High confidence in trends, lower in exact details. Two rounds of showers and thunderstorms today, first round this morning until about 14z, then a lull in the activity. Showers and thunderstorms redevelop around 18z-19z and continue until about 00z. Most of the activity this morning and afternoon will be across CT/RI and southeast MA, possibly up to the Pike. A few storms (this morning and afternoon/early evening) may contain strong winds (up to 50 kt), large hail and torrential downpours. Highest probability of IFR/LIFR will be this morning along the south coast. SW winds 10-20 kt. Saturday Night...High confidence in trends, lower on exact details. Any lingering showers and thunderstorms along the south coast at 00z, move offshore by 03z followed by a wind shift from SW to NW overnight. Any MVFR/IFR conditions improve to VFR with the wind shift. Sunday...high confidence. VFR, dry weather and WNW winds 10-15 kt. KBOS Terminal...High confidence in TAF. Most of the thunderstorms may remain south of the terminal. KBDL Terminal...High confidence in TAF. Outlook /Sunday Night through Wednesday/... Sunday night thru Monday Night: VFR. Tuesday: Mainly VFR, with local MVFR possible. Breezy. Chance SHRA, isolated TSRA. Tuesday Night: Mainly VFR, with local MVFR possible. Chance SHRA. Wednesday: VFR. Slight chance SHRA.
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&& .MARINE...
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Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. 300 AM Update Overall high forecast confidence on trends, lower on exact details. Saturday... SW winds 10-20 kt. Showers and thunderstorms this morning, then a brief break in the action from late morning into the early afternoon. A 2nd round of showers and thunderstorms expected later this afternoon and early evening. Frequent lightning but also a few strong storms, with isolated wind gusts up to 50 kt possible, large hail and torrential downpours. Saturday night... Early evening storms exit offshore, followed by a drying trend and a FROPA with winds shifting from SW to WNW overnight. Sunday... Beautiful boating weather, with dry weather, sharp vsby and WNW winds 10-15 kt. Outlook /Sunday Night through Wednesday/... Sunday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Independence Day through Monday Night: Winds less than 25 kt. Tuesday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers, isolated thunderstorms. Tuesday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers, isolated thunderstorms. Wednesday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 9 AM EDT this morning for ANZ231- 251. Small Craft Advisory until 5 PM EDT this afternoon for ANZ232>234. Small Craft Advisory until 2 AM EDT Sunday for ANZ235-237. Small Craft Advisory until 5 AM EDT early this morning for ANZ236. Small Craft Advisory until 1 PM EDT this afternoon for ANZ250. Small Craft Advisory until 6 AM EDT Sunday for ANZ254>256.
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&& $$ SYNOPSIS...Nocera/BW NEAR TERM...Nocera SHORT TERM...Nocera LONG TERM...BL AVIATION...Nocera/BL MARINE...Nocera/BL

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