Lexington, Massachusetts, USA
000 FXUS61 KBOX 052320 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 720 PM EDT Fri Aug 5 2022 .SYNOPSIS... Heat and humidity will be the main weather story right into early next week. Heat Advisories have been extended through the weekend and the threat of isolated to scattered thunderstorms will remain possible as well. It may be Tuesday, or later, before this heat and oppressive humidity finally breaks in a significant way. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... 720 PM Update... The threat for storms have dwindled across the region. A very isolated weak thunderstorm is possible over the next two to three hours, but that threat remains low. There is an area of light to moderate rain pushing over Cape Cod Bay and the Outer Cape, those showers continues to moves east slowly this evening. See previous forecast discussion below. ============================================================== Highlights... * Muggy with fog developing overnight...locally dense Otherwise, generally dry weather expected later tonight but it will be quite muggy with an anomalous upper level ridge off the mid-Atlantic coast. Weak surface ridging will also result in light to calm winds tonight. This coupled with the high dewpoints in place and pockets of wet ground from today/s activity will likely lead to areas of fog. In fact...some of the fog may become locally dense overnight. Low temps will only drop to between 70 and 75 in most locations with humidity too. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... Highlights... * Heat & Humidity Continue Sat...Heat Headlines Extended * Widely scattered diurnal t-storms again Sat, mainly NW of I-95 Saturday... The overall hot and humid weather pattern will continue on Saturday. This is being driven by an anomalous upper level ridge of 596+ DM off the mid-Atlantic coast. 850T are still on the order of +17C/+18C and given the warm start should see high temps top off in the lower 90s in many locations away from the very immediate south coast. A few locations may even see highs reach the middle 90s. Regardless...the main story will be the oppressive humidity given dewpoints near 70. This will allow heat indices to reach between 95 and 102 degrees. Heat Advisories have been extended for the entire region; excluding Nantucket and Block Island. The other issue will be for diurnally driven isolated to scattered thunderstorms. A weakly capped environment coupled with Cape values of 1500-2500 J/KG will support isolated to scattered activity Saturday afternoon into the first half of the evening. Main risk will probably be northwest of I-95 and especially further back to the north and west since they will be somewhat further removed from the upper level ridging off the mid- Atlantic coast. Activity will be hit or miss and many locations will remain dry given the lack of synoptic scale forcing. In addition...the overall severe weather threat will be rather limited given very weak wind fields. However, Pwats near 2 inches along with the slow movement of any activity will result in a localized heavy rainfall/very localized street flooding risk. Saturday night... Isolated to scattered thunderstorms should again wind down during the evening with the loss of daytime heating and very limited synoptic scale forcing. Otherwise...a strong upper level ridging off the mid-Atlantic coast will continue to result a very mild and muggy Saturday night. Overnight low temps will only bottom out in the lower to middle 70s. There will be a bit more of a southwest flow in the boundary layer Saturday night. This should limit the threat for much fog except near the immediate south coast. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Highlights... * Oppressive heat and humidity continues through early next week. There is the chance for isolated showers and thunderstorms daily. * A slow-moving cold front could bring much needed rainfall to portions of the region by later next week, but timing and areal coverage remain uncertain at this time. Details... Sunday... Bermuda High continues to hold strong this weekend and support a deep southwest flow pattern into southern New England. As a result, above normal temperatures and humid conditions will persist. Whether individual locations meet the criteria for a heatwave, which is three consecutive days of 90 deg, the combination of air temperature and dew points in the mid 60s to mid 70s will yield heat indices in the mid 90s to low 100s. The elevated dew points also means muggy and uncomfortable nights. Current heat headlines will likely be extended with future forecast packages for this weekend, and perhaps into Cape Cod and the Islands. Precipitation wise, weak upper level short wave will bring some cloudiness and a chance for isolated showers and thunderstorms. While there will be sufficient instability for convection, little to no deep-layer shear will suppress severe thunderstorm development. However, abundant deep layer moisture and weak boundary layer winds could support slower moving thunderstorms with localized, brief heavy downpours. Unfortunately, short of widespread soaking rainfall, there will barely put a dent in the deteriorating drought situation, where the eastern half of our CWA is now in D2 severe drought category according to the US Drought Monitor. Monday into Friday... No notable air mass change as we enter the new work week so high heat and humidity continues with a trend towards somewhat more seasonable temps later in the work week. For reference, typical highs for the second week of August are in the low to mid 80s. For those tired of the heat and humidity, we may get a reprieve sometime in the mid to late week time frame. But there remains plenty of uncertainty with regards to the timing. CIPS analog indicates that there is a somewhat better chance for stronger thunderstorms in the Tuesday or Wednesday time frame, but that is contingent on the strength and progression of the cold front. Given the plenty of uncertainty, mainly stuck to blended guidance for this part of the forecast. While there may seem to be no end in sight to this heat, the good news is that we are now past the climatologically warmest time of the year and cooler days are not far away. && .AVIATION /00Z FRIDAY THROUGH WEDNESDAY/... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. 00z TAF Update... Tonight...High Confidence. Main threat for storms has ended. Otherwise...the main concern will be for areas of fog developing later tonight which may be locally dense in the typically prone spots. The threat for widespread low clouds though will probably be confined to areas near the south coast with the best shot at Nantucket. Winds becoming Light/Calm tonight except more from the SW at 5-10 knots across the Cape and Islands. Saturday...High Confidence. Mainly VFR once the areas of fog burnoff shortly after sunrise. However, isolated to widely scattered showers/t-storms will be possible in the afternoon with the greatest risk in northern MA and interior southern New England. S-SW winds 10 to 15 knots, but there may be a couple hour window for sea breezes across the eastern and especially northeast MA coast. Any sea breezes should be overcome as the day wears along. Saturday night...High Confidence. Mainly VFR and think the main threat for low clouds/fog will be confined to areas near the south coast, Cape and Islands. Winds will be from the WSW 5-10 knots. KBOS...Moderate Confidence in TAF. KBDL...Moderate Confidence in TAF. Outlook /Sunday through Wednesday/... Saturday Night: Mainly VFR, with local MVFR possible. Breezy. Slight chance SHRA, isolated TSRA. Sunday: Mainly VFR, with areas MVFR possible. Breezy. Chance SHRA. Sunday Night: Mainly VFR, with local MVFR possible. Breezy. Slight chance SHRA. Monday: Mainly VFR, with areas MVFR possible. Breezy. Chance SHRA, isolated TSRA. Monday Night through Tuesday: Mainly MVFR, with local IFR possible. Breezy. Chance SHRA. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Tonight through Saturday night...High Confidence. Upper level ridging off the mid-Atlantic coast will maintain a S-SW wind of 10 to 15 knots with perhaps some 20 knot wind gusts developing Sat into Sat night. Thinking is though winds/seas will remain below small craft advisory thresholds through Saturday night. We will have to watch for areas of fog...mainly during the overnight into mid morning hours in the southern waters. Outlook /Sunday through Wednesday/... Saturday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers, isolated thunderstorms. Sunday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Sunday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Slight chance of rain showers. Monday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers, isolated thunderstorms. Monday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers, isolated thunderstorms. Tuesday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Heat Advisory until 8 PM EDT Sunday for CTZ002>004. MA...Heat Advisory until 8 PM EDT Sunday for MAZ002>023-026. Air Quality Alert until 11 PM EDT this evening for MAZ007-015- 016. RI...Heat Advisory until 8 PM EDT Sunday for RIZ001>007. MARINE...None. && $$ SYNOPSIS...Frank/Chai NEAR TERM...Frank/Gaucher SHORT TERM...Frank LONG TERM...Chai AVIATION...Frank/Chai/Gaucher MARINE...Frank/Chai
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