FXUS61 KBOX 250710 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 310 AM EDT Sun Jul 25 2021 .SYNOPSIS... Warm front lifts through New England this morning bringing increasing clouds, humidity and showers. A weak cold front brings showers through the day with scattered thunderstorms possible mainly this afternoon and evening. The cold front moves offshore tonight. High pressure then brings fair humid weather for Monday. Unsettled pattern returns with the risk for showers and a few thunderstorms each afternoon and evening Tuesday into Friday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Upper shortwave pushes a warm front through the region today. One 50- kt low level jet pushes up through VT into Canada, while a second 40- kt low level jet moves up the coast and across SE Mass. Plenty of moisture being moved into Srn New England by the latter jet, with PW values of 1.5 to 1.75 inches. By afternoon, this moisture concentrates along the South Coast and adjacent parts of CT-RI-SE Mass. This is above average for mid-late July although not excessive. Still... could be some local downpours. Convective parameters are modest but supportive. CAPEs of 1000-1500 J/Kg build along the NY border this afternoon, with 700 J/Kg moving across the region this afternoon/evening. LI values will be minus 1 to minus 2, mostly in the afternoon. Expecting showers, with a thunderstorm possible. If the storms are able to draw upon that 40- kt jet then there could be strong wind gusts. Best chance for this would be in Western MA and adjacent parts of CT. Note that SPC has these western areas in a Marginal Risk, meaning isolated severe tstms possible but limited in duration/coverage/intensity. With a developing southwest wind and increasing moisture, expect increasing dew points this morning. Early morning values were 60 to 65, but values of 65 to 69 noted in SW CT and Long Island. Data continues to suggest mixing will reach just to 925-mb. Winds in the layer suggest gusts to 25 kt, possibly 30 kt. Temperatures at 925-mb climb to 16-18C this afternoon...equiv to 8-10C at 850-mb. So expect max temps mostly in the mid 70s. So to sum up...a cloudy muggy day with showers and scattered thunderstorms, some with local downpours and gusty winds. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... Overview... Weak cold front slides south of New England tonight. West-northwest flow behind the front will bring drier air and clearing...although South coast areas may hold on to the showers later into the night. High pressure then builds over the region for Monday, bringing warmer air. Details... Tonight... Showers/thunder will taper off early in the night in the interior. Showers/thunder will linger through midnight along the South Coast before tapering off. A west-northwest upper flow will bring clearing skies to the region. Dew points remain in the mid 60s along the NH border and upper 60s/around 70 along the South coast, so expect at least some humidity through the night. Clearing skies and light wind will allow areas of fog to form, especially in the usual favored spots. Based on expected dew points, expect min temps in the 60s, except around 70 along the South coast. Monday... Upper trough maintains a weak cyclonic flow over the Northeast USA. Moisture cross sections continue to show a brief moist layer between the 800-mb and 700-mb levels. With mixing reaching into that layer, expect diurnal cu to once again develop, although limited in coverage. So a mostly sunny day, with wind gusts 15 kt or less. Temperatures at 800-mb show readings of 10-11C, equiv to 15-16C at 850-mb. This would support max sfc temps in the mid to upper 80s, except 80 or low 80s along the Berkshire East Slopes. West winds will be persistent enough to limit sea breezes to the South Coast. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... Highlights... * Periodic rain and thunderstorm chances through the period, first on Tuesday then again Thursday into Friday * Near to slightly above normal temperatures continue Tuesday, then trend below normal Wednesday through the weekend Details... Tuesday through Wednesday... The broad trough that remains overhead through the end of the week reloads on Tuesday bringing the return of rain and thunderstorm chances. Zonal steering flow Monday night becomes more amplified by Tuesday afternoon as the shortwave rounds the base of the trough. At the surface a weak warm front is followed quickly by a trailing cold front Tuesday night into early Wednesday morning, while placement of a 300 mb jet favors large scale ascent. With PWATs near 1.75" and instability on the order of 1000 J/kg of CAPE some embedded thunderstorms are expected. Guidance is divided on how favorable or not the shear will be, but the higher resolution NAM would favor a poor shear, weaker thunderstorm environment; something to watch as we approach. By Wednesday high pressure returns with dry and partly sunny conditions. Behind the front temperatures will top out in the 70s compared to upper 80s on Tuesday. Thursday through Saturday... For the second half of the week ingredients come together for a more potent period of unsettled weather followed by a break by the weekend. A deeper shortwave digs in from the Great Lakes region Thursday into Friday bringing a surge of moisture in the form of more clouds, rain, and thunderstorms. Timing of the wettest period is uncertain but at this point Thursday evening into Friday morning look like the best shot at heavier rain. Beyond that high pressure may return bringing a drier start to the weekend. Temperatures remain below normal through the extended forecast period, in the 70s for most, low 80s in the typical warmest locations. && .AVIATION /07Z SUNDAY THROUGH THURSDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Today...High confidence in trends, moderate in timing. Ceilings/vsbys lower to MVFR this morning from west to east as a warm front brings showers and humid air. A few areas, such as the Central Hills, may lower to IFR for a time. The showers may be joined by scattered thunderstorms, especially in Western Mass and Hartford County CT this afternoon. Southwest winds will be 10-15 kt with gusts to 25 kt possible especially across CT-RI-SE Mass. Tonight...Moderate confidence. The risk of scattered showers and isolated thunderstorms will diminish most places early tonight, but may linger along the South Coast until just after midnight. Expect improving ceilings and vsbys as skies clear from northwest to southeast. Light wind and wet ground may favor patchy fog late tonight, with IFR cigs/vsbys where it occurs. Monday...High confidence. High pressure builds over Southern New England, bringing light wind and mostly clear skies. VFR. KBOS TAF...High confidence in TAF. VFR conditions overnight with showers arriving around 7-9AM and continuing through the morning. There may be a break, but showers return during the afternoon and possibly a thunderstorm. KBDL TAF...High confidence in TAF. VFR conditions, lowing to MVFR in showers 5-7AM continuing through the morning. There may be a break, before scattered showers/thunderstorms develop during the afternoon. Outlook /Monday Night through Thursday/... Monday Night: VFR. Tuesday through Tuesday Night: VFR. Chance SHRA, slight chance TSRA. Wednesday: VFR. Chance SHRA, isolated TSRA. Wednesday Night: VFR. Slight chance SHRA. Thursday: Mainly VFR, with local MVFR possible. Breezy. Chance SHRA, slight chance TSRA. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Today... South winds turn more from the southwest, with gusts increasing to 25-30 kt. Seas build to 5-6 feet on the southern waters and outer eastern waters. Showers develop this morning from west to east, and may be accompanied by a thunderstorm. Scattered showers and thunderstorms will move across the waters this afternoon and evening, with best chance over the southern waters as well as the waters around Cape Cod. A Small Craft Advisory is in effect for all waters today. Tonight... Cold front moves offshore tonight, stalls for a time, then slowly moves out to sea overnight. This will maintain a chance of showers/thunder until the front moves off. Gusty winds and 5-foot seas linger on the Southern waters overnight, but winds/seas will diminish on the waters farther north. Monday... Winds less than 15 kt all waters. Seas near 5 feet on the Southern Outer waters, where a Small Craft Advisory will continue, but less than 5 feet on most of the waters. /Outlook /Monday Night through Thursday/... Monday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Tuesday: Winds less than 25 kt. Slight chance of rain showers, isolated thunderstorms. Tuesday Night through Wednesday: Winds less than 25 kt. Chance of rain showers, slight chance of thunderstorms. Wednesday Night: Winds less than 25 kt. Slight chance of rain showers. Thursday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers, slight chance of thunderstorms. && .HYDROLOGY... No active river flood warnings are in effect for rivers and waterways across southern New England. However, after having a tremendous amount of rainfall from early to mid July, many rivers and streams are running much higher than normal. This is resulting in swift currents that would not typically be seen in the summer. These swift currents can catch those swimming or tubing/kayaking on area waterways off guard. There have been 3 total reports of drownings in the last week on the Farmington River in CT and Squannacook River in MA given the higher than usual flows and swift currents. Through this weekend, those with interests swimming, tubing or kayaking on area rivers and waterways should be aware that swift currents due to high flows are occurring. This can result in dangerous conditions, and it is generally discouraged to swim, inner-tube, or kayak until flows decrease. && .TIDES/COASTAL FLOODING... Tides reached their monthly astronomical peak and will now trend lower each day. Tides will not flood, but could still cause minor splashover with the evening high tide tonight. Minor splashover is possible on typically vulnerable shoreline roads. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 11 AM this morning to 4 AM EDT Monday for ANZ231-232. Small Craft Advisory from 11 AM this morning to 11 PM EDT this evening for ANZ233-234-250-251. Small Craft Advisory from 11 AM this morning to 8 PM EDT this evening for ANZ230-236. Small Craft Advisory from 11 AM this morning to 8 AM EDT Monday for ANZ235-237. Small Craft Advisory from 11 AM this morning to 10 PM EDT Monday for ANZ254>256. && $$ SYNOPSIS...WTB/BW NEAR TERM...WTB SHORT TERM...WTB LONG TERM...WTB AVIATION...WTB/BW MARINE...WTB/BW HYDROLOGY... TIDES/COASTAL FLOODING...