Area Forecast Discussion
Issued by NWS Boston, MA
Issued by NWS Boston, MA
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719 FXUS61 KBOX 051731 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 131 PM EDT Wed Jun 5 2024 .SYNOPSIS... Rather warm and mainly dry today outside the risk for an isolated afternoon shower or thunderstorm across northeast MA. Our weather pattern then changes to a cloudy and more unsettled outlook by Thursday and continuing into early next week. Widespread rain showers and embedded thunderstorms are expected on Thursday with locally heavy rainfall possible. Shower and thunderstorm coverage for Friday into Monday then becomes more scattered with some dry periods at times. Temperatures trend slightly cooler than normal. && .NEAR TERM /UNTIL 6 PM THIS EVENING/.. 125 PM Update... * Plenty of sunshine & very warm this afternoon with highs well into the 80s away from the south coast * Low risk for a few showers/isolated t-storm late this afternoon/early this evening across northeast MA The initial shortwave has departed the region and was allowing for plenty of sunshine to develop. Still some clouds across eastern MA...but we do expect more sunshine to develop in this region too over the next couple hours. 850T around +15C/+16C with southwest flow should allow highs to reach well into the 80s away from the south coast and a few spots may flirt with 90. Southwest flow will keep highs mainly in the 70s on the immediate south coast, Cape and Islands with a modified marine airmass. Another shortwave coupled with diurnal heating was resulting in scattered showers/t-storms to develop in northern New England. The brunt of this shortwave energy and its associated forcing will stay to our northeast...keeping most of the convection to our north. That being said...there is a low risk for a few showers/isolated t-storm to spill into far northeast MA late this afternoon/early this evening. But generally a dry afternoon and evening is in store for the region. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... Key Points... * Widespread showers and a few t-storms move across the region late tonight into Thu * Another round of showers and t-storms develop in western New Eng during the mid-late afternoon Thu * A few strong storms are possible Thu afternoon but the greater risk is for localized heavy rainfall capable of flash flooding Tonight... Dry this evening, although expecting stratus and patchy fog to develop along the south coast and expand north overnight as higher dewpoint air advects northward. A subtle shortwave approaches late tonight as the mid level ridge slides to the east. Good moisture transport and modest forcing for ascent will result in an area of showers and perhaps and isolated t-storm overspreading the region from SW to NE toward daybreak. It will be a mild night with lows in the 60s, and humidity levels will be increasing as dewpoints climb into 60s. Thursday... Widespread showers and a few t-storms assocd with this shortwave will lift NE across SNE during the morning, lingering into early afternoon across eastern MA. Given PWATs increasing to 1.5-2.0" locally heavy rainfall is possible. A dry slot will move in behind the shortwave during the afternoon which will result in a lull in the rainfall. However, a more potent shortwave rotating around the Gt Lakes upper low will be approaching toward evening. It is possible a few breaks of sunshine may develop in western New Eng during the afternoon which will help to generate up to 1000 J/kg of SBCAPE. As a result, all the CAMs are indicating another round of showers/t-storms moving into western New Eng later in the afternoon. 0-6km shear up to 30 kt so can`t rule out a few strong storms although low and mid level lapse are not favorable. However, HREF is indicating some updraft helicity swaths and CSU ML probs and HRRR Neural Network are indicating low probs of severe wx in western New Eng with wind the main threat. While we can`t rule out a strong to severe storm, heavy rainfall will likely be the greater threat given high PWAT airmass. HREF localized PMM indicating potential for localized rainfall amounts of 3+ inches and WPC ERO has a slight risk of rainfall exceeding flash flooding across interior MA. Highs will be mostly in the 70s and it will be rather humid with dewpoints 65-70. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Highlights: * Unsettled through early next week with daily chances for showers/thunderstorms * Many locations should experience dry/pleasant weather but with some cloud cover and slightly below normal temps * Unsettled pattern breaks sometime early next week Friday A broad upper-level low approaches The Northeast from The Great Lakes region on Friday. This will continue to support a period of unsettled weather for southern New England. Available moisture and forcing ahead of the upper trough axis on Friday will be limited, but should be enough to trigger a few scattered showers and possibly a rumble of thunder on Friday afternoon. With muggy conditions and dewpoints in the mid 60s there should be a few hundred J/kg of CAPE available, but not enough to make severe thunderstorm development a concern. Latest suite of model guidance actually supports a bit of dry air in the lower levels with most of the available moisture in the mid-levels around 700 hPa. Because of this, many locations in southern New England will experience a decent spring day on Friday with a mix of sun and clouds and temps in the low 80s. The greatest risk for showers/storms looks to be focused along and north of I-90 where there should be more moisture available. We should have more details for Friday as we enter the window of hi-res model guidance in the next 24 to 36 hours. Saturday and Sunday Upper-low remains parked over The Northeast this weekend. A surface cold front pushes through The Northeast Friday night into Saturday which will bring cooler temperatures to the region into early next week. Dewpoints come down to more comfortable levels behind the front, falling into the mid 50s by Saturday afternoon. The air mass behind the front will be characterized by 925 hPa temps around 15C, give or take a few degrees. This will support high/low temps in the mid-upper 70s and mid-upper 50s respectively this weekend. The presence of the upper-low and cold air aloft will support more clouds than sun for most of southern New England and continued chances for afternoon showers/thunderstorms, though no washouts look to be in the mix this weekend, mainly just hit or miss showers/storms. Early Next Week Forecast becomes fuzzy early next week, but it looks like we`ll have at least one more substantial rainfall event before the quasi- stationary upper-low over The Northeast finally departs over The Atlantic. Model guidance differs in the timing of when this will happen, but it could be as early as Monday evening or as late as Tuesday evening. The timing of the departure of this feature will govern what kind of weather we experience early next week. Stay tuned for more details. && .AVIATION /17Z WEDNESDAY THROUGH SUNDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 18z TAF Update... This afternoon...High Confidence. VFR. A low risk of a late day shower/t-storm in far northeast MA...but the bulk of that activity will remain to our north. S-SW winds around 10 knots. Tonight into Thursday night...High Confidence on trends but lower confidence on specific timing. Light moist southerly flow will allow for low stratus and areas of fog to overspread the region tonight from south to north. Specific timing uncertain...but do expect most locales to see IFR-LIFR conditions develop overnight. These conditions will continue through much of Thursday. Improvement will occur Thu night across the interior...but lower conditions will persist for most of Thu night across the eastern half of the region. The other concern over the next 36 hours will be for a band of widespread showers and perhaps isolated t-storms that will cross the region from southwest to northeast Thu morning. Brief downpours are expected with this activity too. A second area of scattered showers & t-storms will impact the region from the west late Thu afternoon/evening. Winds will be from the S generally 10 kts or less...but will shift to the E on Thu across northern MA. KBOS TAF...High confidence in trends, but lower confidence in specific timing. KBDL TAF...High confidence in trends, but lower confidence in specific timing. Outlook /Friday through Sunday/... Friday: VFR. Chance SHRA, isolated TSRA. Friday Night: VFR. Saturday: VFR. Chance SHRA. Saturday Night: VFR. Slight chance SHRA. Sunday: Mainly VFR, with local MVFR possible. Breezy. Chance SHRA. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Through Thursday...High Confidence. Increasing SW winds today into this evening with gusts to 20 kt developing. Winds become more S-SE during Thu with gusts to 20 kt. Seas may build to near 5 ft over southern waters Thu afternoon. Patchy fog may reduce vsbys over southern waters today, with greater risk of fog tonight and Thu morning. A round of showers and embedded t-storms will move through late tonight and Thu. Outlook /Thursday Night through Sunday/... Thursday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. Friday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers. Friday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Saturday through Saturday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers. Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...KJC/RM NEAR TERM...Frank SHORT TERM...KJC LONG TERM...RM AVIATION...Frank/RM MARINE...KJC/RM