283 FXUS61 KBOX 220817 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 417 AM EDT Fri May 22 2020 .SYNOPSIS... Warmest readings of the week expected today with high pressure remaining in control. Temperatures will be into the 80s today. Low pressure moves south of the region tonight and on Saturday. This will will bring the threat for showers and cooler temperatures. Not out of the question there are a few rumbles of thunder along the south coast. Dry weather expected Sunday into Monday, but with cool afternoons near the coast. Summerlike warmth arrives Tuesday and especially by Wednesday and Thursday inland from the south coast with mainly dry weather continuing. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Highlights... * Mild, dry and quiet today with increasing cloud cover late in the afternoon. The ridge axis will build from western portions of southern New England to eastern portions of southern New England. During this time a cutoff low will slowly lift northeastward from the Ohio River Valley into the Mid Atlantic. The surface high associated with the ridge will nudge into the region from the southeast. This will bring dry and quiet weather to southern New England today. Still may have some stratus/fog in place across the immediate south coast initially today, but this activity should burn off due to heating this morning. Flow aloft at 925 hPa will be westerly and become west-southwesterly late in the afternoon. This will advect 14 to 18 degree Celsius air in aloft. Expecting downsloping to occur and bring the warmest readings of the week. The previous shifts temperature forecast looked very good, but nudged things to the 95th percentile of guidance. This bumped things up a degree or two in a few locations. High temperatures range from the low 70s along the south coast to the mid 80s across the Merrimack and Connecticut River Valleys. Good agreement amongst guidance through today. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/... Highlights... * Chances of rain showers and perhaps a rumble of thunder or two tonight into Saturday. Best shot for any thunderstorms is across the south coast. * Expect cooler temperatures on Saturday due to onshore flow. Tonight and Saturday... The cutoff low will lift into PA and NJ tonight. On Saturday the broad low will slide eastward on Saturday to just south of the region. The broad surface low associated with this feature will lift into NJ and DE tonight. Expect a warm or occluded front associated with the surface low to lift into the south coast. The surface low will slide to just south of the region on Saturday. This will bring increasing cloud cover across southern New England and increasing chances of rain showers. Could even have some rumbles of thunder across the south coast. Despite only being 24-48 hours out there is a lot of spread amongst deterministic and ensemble guidance as to how far north the precipitation shield goes and QPF amounts expected. Have the most confidence in precipitation chances south of the MA Pike, but less certain further north. Did a blend of the GFS, ECMWF and HREF guidance along with the previous forecast to nudge up chances a bit. Kept chance to slight chances of precipitation for the MA pike northward. As for QPF totals did a blend of the 50th percentile of guidance along with some of the WPC guidance. Have some uncertainty in the thunderstorm chances in this somewhat weakly forced environment, but there are a few hundred J/kg of MUCAPE in place across the south coast. Am not sold there will be as much thunderstorm activity as some of the CAMs indicate, but have put an isolated thunderstorm mention in the forecast. If thunderstorm activity is more widespread than the current thinking then QPF values will need to be increased further. Winds will shift from the southwest tonight to the northeast on Saturday. The onshore flow will advect cooler air into region, so anticipating high temperatures on Saturday to occur during the morning and temperature decrease as the day progresses. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Highlights... * Mainly dry Sun & Mon, but cool afternoons near the coast * Summer-like warmth arrives Tue/Wed/Thu away from the south coast * Dry weather dominates through the middle of next week with little, if any, opportunity for rain Details... Sunday and Monday... High pressure east of the Maritimes, coupled with weak surface low pressure to our south, will generate onshore easterly low level flow. Drier weather arrives Saturday night into Sunday as this low pressure moves farther away from southern New England. Sunday will be the cooler of the two days due to the stronger east flow. Temperatures expected to be well below normal towards the east coast, then approaching near normal west of across the interior. Easterly flow weakens Monday, leading to high temperatures about 5- 10 degrees higher than Sunday. There is a risk for perhaps a few brief showers to impact the southeast New England coast Monday with ESE flow off the ocean, but that is about it. Tuesday through Thursday... With a mid level ridge building across the eastern USA, and a high pressure shifting slightly farther offshore, expecting temperatures to rise to above normal levels for late May. Dew points should also rise, leading to a summer-like feel. Still cooler towards the south coast, Cape and islands, due to onshore southerly winds. Mainly dry weather anticipated during this time given upper level ridging in place. Certainly cannot rule out the low risk for a few diurnally driven showers or thunderstorms by Wednesday and Thursday from the increasing heat and humidity. && .AVIATION /08Z FRIDAY THROUGH TUESDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Thru 12Z...High confidence VFR overnight with high confidence across the majority of the region. Still have low to moderate confidence along the south coast. Could see some IFR stratus and fog develop. Has already done so near Marthas Vineyard and Cape Cod, but this has dissipated. Am hesitant to remove this from the forecast with temp/dew point depressions around 2-3 degrees along the south coast. Only mention fog at ACK, but is possible at FMH/HYA and to a lesser extent at PVD. Have hinted at the IFR ceiling possibility. Today...High confidence Any stratus/fog that develops along the south coast will dissipate due to heating. VFR conditions expected as high pressure nudges in from the southeast. Will have southwest winds through the day. May see some gusts of 20-25 kts across Cape Cod and the Islands during the afternoon. Tonight and Saturday...Low to moderate confidence Increasing chances of rain showers as a cutoff low lifts into the Mid Atlantic tonight and just south of the region on Saturday. Still a lot of differences in how far north the shower activity reaches, but most confident along the south coast. Will see ceilings gradually lower to MVFR and IFR ceilings along the south coast. Elsewhere conditions should remain VFR. The MVFR and borderline IFR ceilings may linger across the south coast on Saturday. KBOS Terminal...High confidence in the TAF. KBDL Terminal...High confidence in the TAF. Outlook /Saturday Night through Tuesday/... Saturday Night through Sunday: VFR. Breezy. Sunday Night through Tuesday: VFR. && .MARINE... Cancelled the Small Craft Advisory issued for the south coast today as forecast wind speeds and gusts have diminished in the latest update. The Small Craft Advisory across the eastern outer water remains in effect this morning. High pressure continues to nudge into the region today. Any low clouds and fog across the south coast will diminish this morning due to heating. Southwesterly winds continue and expect speeds and gusts to increase during the afternoon. Could see a few gusts across the far outer portions of the eastern outer waters around 25 kts. Confidence was not high enough to extend the current SCA into tonight. Rain showers spreading in with reduced visibilities and fog along the south coast tonight into Saturday. Confidence lower in the rain chances across the eastern waters, but moderate to high across the south coast. Could have a few rumbles of thunder across the south coast. Outlook /Saturday Night through Tuesday/... Saturday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Slight chance of rain showers. Sunday through Sunday Night: Winds less than 25 kt. Seas up to 5 ft. Memorial Day: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers. Monday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers. Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 11 AM EDT this morning for ANZ250- 254. && $$ SYNOPSIS...Belk/BL NEAR TERM...BL SHORT TERM...BL LONG TERM...Belk AVIATION...Belk/BL MARINE...Belk/BL