Area Forecast Discussion
Issued by NWS Boston, MA
Issued by NWS Boston, MA
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547 FXUS61 KBOX 041331 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 931 AM EDT Thu Jul 4 2024 .SYNOPSIS... Increasing clouds and humidity levels today, and while there could be an isolated shower or thundershower in western MA and CT this afternoon, many stay dry. A better chance for showers or storms exists later tonight and overnight, with lesser chances for showers or storms on Friday. Very warm and humid conditions will continue this weekend through early next week. Best chance for rain comes Friday night through Saturday night. There will be dry periods, and will not rain continuously. Sunday though Monday is warm, humid, and dry. A return to more unsettled weather Tuesday and Wednesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 930 AM Update... * Considerable clouds with peeks of sunshine at times along with increasing humidity & highs in the 80s * A few showers perhaps an isolated t-storm later today...mainly across the interior but dry weather dominates Considerable mid-level cloudiness covered the region at mid- morning...but there were peeks of sunshine too. High pressure off the coast will continue to generate a southwest flow of increasing humid air into the region. Despite the considerable cloudiness...expect enough peeks of sun for highs to reach into the middle 80s away from the south coast where upper 70s to the lower 80s more common. It is even possible a few spots reach the upper 80s if enough solar insolation can be realized. Dewpoints rising through the 60s will result in increasing humidity through the day. Dry weather dominates today...but enough diurnal heating combined with a weakening shortwave will probably be enough to trigger a few showers and perhaps an isolated t-storm or two mid to late this afternoon into early this evening. This will mainly across interior southern New England as the shortwave will tend to weaken as it encounters mid level ridging. But regardless...the main story is dry weather dominating. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... 315 AM Update: Tonight: Surface trough continues to sag southward to our southern coastal areas, though it either stalls out and/or washes out as it does so. At the same time, a weak shortwave impulse over part of the mid-MS Valley early this morning will have moved into southern NY/PA by tonight. This feature will have rising moisture levels to act on (PWATs rise to 2-2.25 inches per the 03z SREF!) and with the weak boundary nearby, we should see a better chance for scattered showers tonight mainly south of the Mass Pike, with lower/lesser chances north of the Mass Pike. Best chance at showers/possible embedded thundershowers before midnight is in CT, but confidence in the timing is far from the strongest and is subject to further adjustments. Not talking heavy rain or flooding with this, but with the really juiced environment even showers could bring some brief downpours as warm cloud depths are around 14,000 ft. SW winds weaken overnight to light and variable, and creates an environment which could favor mist/fog development with the rising humidity levels. With overcast around tonight, sided temps toward warmer guidance in the upper 60s to low 70s, with dewpoints in the upper 60s. Friday: Timing uncertainties associated with the weak disturbance moving in later tonight cast lingering uncertainty for Friday too. With that said, we`ll have a stalled frontal boundary in our southern waters which will keep the immediate south coast unsettled. Further north and west, more clearing should allow for somewhat greater heating/destabilization with CAPEs around 500-1000 J/kg. With the very humid air mass, it won`t take much heating to pop up a shower or garden variety storm mainly north and west of I-95, but background weak subsidence aloft and weak 500 mb height rises in the wake of the passing weak disturbance from overnight tonight should keep coverage to a minimum. So, continued partly to mostly cloudy conditions with PoPs in the 15-20% range. Friday feels quite warm and humid with highs in the mid to upper 80s with dewpoints in the 70s, supporting heat indices in the upper 80s-low 90s. Cooler along the southeast coast where cloud cover will be slower to disperse, with highs in the upper 70s/lower 80s but still humid. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Highlights: * Few showers possible on Friday, otherwise dry, warm and muggy. * Elevated humidity Saturday along with the potential for heavier rains and an isolated afternoon thunderstorm or two. * Warm and muggy Sunday into Monday, although trends are looking drier both days. Unsettled conditions return Tuesday into Wednesday. Friday Night into Saturday Night: Unsettled and down right muggy conditions heading into the upcoming weekend. Overnight into Saturday morning shortwave energy ejects out of the Great Lakes leading to scattered rain showers overnight and ending Saturday morning as the best mid-level forcing exits east of southern New England by mid morning. Warm and quite muggy with dews in the low to middle 70s Saturday afternoon, with highs between the low and middle 80s there is enough surface based instability, around 1,000 J/kg to get a few showers to develop. Lapse rates are rather poor with the best low-level lapse rates west of the Berkshires between 7-8 C/km and the mid-level lapse rates are less than 6 C/km. Any showers or thunderstorms that do go up will have the potential to produce heavy rains. There is plenty of moisture to be had, as mentioned the past several nights PWATS are well above 2 inches, and per 04/00z guidance, those values are still on track to be between 2.0" and 2.5", daily climo max per the soundings archive is around 2.05", with the max of all soundings at 2.73" for CHH. And with a warm cloud layer of ~13,000 feet, there is the potential for efficient rain makers. Robust mid-level shortwave north of the eastern Great Lakes in Canada moves east overnight with shortwave energy breaking off and passing through New England, still looks like the best lift will be northern New England, but there could be enough lifts that makes it way south to promote showers overnight as well. Sunday trough Wednesday: Southern New England is still on the outer periphery of a mid-level ridge that is anchored over Bermuda. While not as humid on Sunday, dews remain in the upper 60s to near 70 degrees, plus temperatures in the middle and upper 80s, closer to 90 in places like Springfield to Hartford. Right now, there is little mid-level forcing to get any showers going, plus BUFKIT sounding show a firm CAP so think the day will feature mainly dry conditions. Monday looks to be a carbon copy. More unsettled conditions into mid week with the mid-level ridge shifting south and a trough approaching from the west, this will usher in the next round of rain and thunderstorms. Mid 80s to low 90s on Tuesday, then low to mid 80s on Wednesday. && .AVIATION /13Z THURSDAY THROUGH MONDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Today: High confidence, though lower on SHRA/TS development and timing. Increasing VFR cloudiness likely in multiple layers. Can`t rule out SHRA after 16z anywhere, but prospects for showers increase after 18-20z largely from ORH westward. Possible rumble of thunder but SHRA should predominate for the western airports. Indicated VCSH or SHRA for the western/central airports but left eastern TAFs dry due to lower prob of SHRA. SW winds increase to around 8-12 kt, strongest southeast MA. Tonight: Moderate confidence. General deterioration expected for most airports with at least BKN VFR-MVFR bases. Weak low pressure passing thru s`rn CT and RI/MA South Coast favors 3-6 SM visby SHRA mainly BDL-PVD-Cape airports on southward starting 01-03z, with best chance at MVFR/IFR ceilings for these airports. Less certain/lower prob on SHRA coverage north of this area. SW winds begin to decrease to 5 kt or less; best chance at mist/fog is largely south of the Mass Pike. Friday: Moderate confidence. Anticipated sub-VFR ceilings more likely for PVD and the South Coast; it could take some time for these conditions to improve if they do so at all. Should see BKN VFR ceilings elsewhere, with possible pop-up SHRA/TS in the aftn hrs; best chance from ORH westward. S to SE winds under 10 kt. KBOS TAF...High confidence in TAF. SCT-OVC VFR ceilings through at least early tonight. Better chance at MVFR bases and -SHRA after 03z Fri, with improvement toward SCT-BKN VFR after 12z Fri. SW winds around 10-12 kt today, easing to 5 kt or less thru late tonight. KBDL TAF...High confidence in TAF. VFR most of the day, though risk for SHRA/possible rumble of thunder after 20z Thu until 07z Fri. Sub-VFR possible in this timeframe. SW winds increase to around 10 kt today, then ease to around 5 kt tonight. Outlook /Friday Night through Monday/... Friday Night: Mainly VFR, with areas IFR possible. Chance SHRA, isolated TSRA. Saturday: MVFR/IFR conditions possible. Breezy. Chance SHRA, slight chance TSRA, patchy BR. Saturday Night: Mainly VFR, with local IFR possible. Breezy. Chance SHRA, isolated TSRA. Sunday through Monday: VFR. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Today through Friday: High confidence. Winds and seas below SCA thresholds. SW winds increase to 10-20 kt today, though decrease a bit into tonight. Scattered showers/possible t-storms mainly for the southern waters tonight, with a risk for fog/mist. South winds around 10-15 kt on Fri. Rain showers may continue into Fri on the southern waters too, but with lesser coverage. Seas through the period generally 3 ft or less on all waters. Outlook /Friday Night through Monday/... Friday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers. Saturday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Slight chance of rain showers. Saturday Night: Low risk for Small Craft Advisory winds with gusts up to 20 kt. Seas up to 5 ft. Chance of rain showers, isolated thunderstorms. Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers. Sunday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Monday: Winds less than 25 kt. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Loconto/Dooley NEAR TERM...Frank SHORT TERM...Loconto LONG TERM...Dooley AVIATION...Loconto/Dooley MARINE...Loconto/Dooley