000 FXUS61 KBOX 041418 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 1018 AM EDT Thu Jun 4 2020 .SYNOPSIS... Summer-like warmth with increasing humidity is in store through the end of the week. Showers and thunderstorms are likely Saturday as a cold front moves across Southern New England. Drier and cooler weather as high pressure builds into the region early next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 10 am update... Current forecast looks on track, with mostly sunny skies prevailing. Temperatures at 10 am were quickly rising through the 70s. Highs in the mid to upper 80s for much of the area, except along the south coast and Cape Ann where SW winds this afternoon will keep high temps a few degrees lower. Early Morning Discussion follows... * Plenty of sunshine and very warm this afternoon Patchy ground fog very early this morning should burnoff rather quickly after sunrise. Otherwise, high pressure well off the mid Atlantic coast will result in a warm west to southwest flow of air into the region today. Model cross sections indicate a lot of dry air above the boundary layer. The result should be plenty of sunshine and a well mixed atmosphere. 925T around +21C should yield high temperatures in the middle to upper 80s in many locations this afternoon. It will be a bit cooler on the south coast, but still expect highs well up into the 70s to near 80. Dry weather should prevail today with little forcing or instability available. Rip Current Risk: Long period southerly swell will result in a moderate to high risk for dangerous rip currents on many ocean exposed beaches today. The high risk for dangerous rip currents will be across the south facing ocean exposed beaches on the south coast and Islands, where we have issued a Rip Current Statement. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... Tonight... Dry weather should prevail for much of the evening. However, we will need to watch shortwave energy lifting northeast from the mid Atlantic States late this evening into the overnight hours. Model guidance once again struggling with the potential placement/coverage of precipitation overnight and there are likely some convective feedback issues. That being said, there is some elevated instability/forcing for a round of scattered showers and perhaps an embedded t-storm or two late tonight into the overnight hours. It will be quite mild tonight with clouds and increasing low level moisture. This should hold overnight low temps in the 60s across most locations. Friday... A few left over showers will be possible into Fri morning, followed by a mixture of clouds and sunshine. Another warm day is in store for the region on Friday, but it will be more muggy than today. High temperatures will once again be in the 80s, but dewpoints in the 60s will make it feel quite humid. While dry weather should dominate, we do expect 1000 to 1500 J/KG of Cape to develop. This may trigger a few showers and perhaps a t- storm or two Friday afternoon/early evening with the greatest risk across interior southern New England. Weak shortwave energy/jet dynamics and poor mid level lapse rates should limit areal coverage and keep the severe weather risk relatively low. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Highlights... * Showers on Saturday with potential for strong to severe thunderstorms * Cooler and drier on Sunday * Dry and seasonably warm early next week Details... Friday night... Southern New England remains in the warm sector overnight as the sfc trough and mid level shortwave approach keeping the risk of showers through the night. Model soundings indicate marginal elevated instability (several hundred J/kg CAPE) so some isolated nocturnal convection isn't out of the question, though forcing will lacking. The surge of dewpoints in the mid to upper 60s will keep low temperatures quite warm, in that same range. Saturday... Saturday is the day of greatest potential for impactful weather with more widespread rain and chance for strong to severe thunderstorms. At the synoptic scale we see our very zonal pattern of late breaking down as a positively tilted trough digs from the eastern Great Lakes into New England. This as a sfc low move east just out ahead. All the necessary ingredients are there for a strong thunderstorm risk, but there are a few points of question. On the positive side, there will be abundant moisture available as SW flow has been pumping it up for several days. PWATs surpass 1.5" with sfc dewpoints in the upper 60s to low 70s ahead of the cold front. This, with sfc temps rising to the mid to upper 80s will allow for ample instability. CAPE values approach 2000 J/kg with sfc LI near -6. Wind fields are also favorable for organized convection, with 0-6 km effective shear over 40 kts. Fortunately model soundings don't indicate much directional shear in the low levels. The main threat would be damaging winds, small hail, and heavy downpours. A few things that give us pause with regard to potential for a more widespread severe event; the major one being the timing of the cold front, or the main source of lift. Should it move through too early in the day it would kill our chances of realizing the instability necessary for strong storms. For now it appears strong storms are still in the cards, though the timing will be honed in as we begin to see more hi-res short term guidance. A few things which would inhibit storms that do materialize will be the meager mid level lapse rates (5-6 C/km) and too much dry air moving in aloft which could choke off the updrafts. Something to keep an eye on as we approach, but for now we recommend everyone keep an eye on the forecast and stay weather aware Saturday. Saturday night... Post frontal airmass dries out and becomes much cooler overnight. It won't be excessively dry, dewpoints remain in the 40s/50s, but will allow for slightly cooler low temps (in the 50s to low 60s). Sunday through Wednesday... Drier and cooler on Sunday with highs in the upper 60s and 70s, closer to normal for early June. Onshore flow may keep the east coast cooler than inland areas. Mostly dry conditions are expected as guidance has trended drier through the column in the last 72 hours. Early next week looks quite nice under the influence of building high pressure; seasonably cool and dry. && .AVIATION /14Z THURSDAY THROUGH MONDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 12z TAF Update: Today...High Confidence. VFR. SW winds of 5 to 15 knots developing by afternoon with some gusts up to 20 knots. Tonight...High confidence. Mainly VFR, but may see some localized lower cigs/vsbys develop after midnight near the south coast, Cape, and Islands. Also, a round of scattered showers and possibly a rumble or two of thunder may impact portions of the region during the late evening and overnight hours. Light SSW winds. Friday...High confidence. Mainly VFR conditions, but low clouds and fog patches may flirt with the south coast, Cape and Islands at times. Dry weather dominates, but a few showers and perhaps a t-storm are possible especially across the interior during the afternoon. SW winds increase to 10 to 15 knots with gusts to 20 knots during the afternoon. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Friday Night through Monday/... Friday Night: Mainly VFR, with local MVFR possible. Breezy. Chance SHRA, slight chance TSRA. Saturday: VFR. Breezy. Chance SHRA, chance TSRA. Saturday Night: VFR. Sunday: VFR. Slight chance SHRA. Sunday Night through Monday: VFR. && .MARINE... Today through Friday...High confidence. Persistent S-SW winds of 10 to 20 knots through Friday will result in 3-6 foot seas across our southern waters, where SCA are in effect. The other concern will be for areas of fog across our southern waters, especially during the overnight and early morning hours. Outlook /Friday Night through Monday/... Friday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers, slight chance of thunderstorms. Saturday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers, chance of thunderstorms. Saturday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Sunday: Winds less than 25 kt. Seas up to 5 ft. Sunday Night through Monday: Winds less than 25 kt. Areas of seas approaching 5 ft. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...High Rip Current Risk until 6 PM EDT this evening for MAZ020- 023-024. RI...High Rip Current Risk until 6 PM EDT this evening for RIZ006>008. MARINE...Small Craft Advisory until 8 PM EDT Friday for ANZ235-237- 254>256. && $$ SYNOPSIS...Frank/BW NEAR TERM...Frank/BW/NMB SHORT TERM...Frank LONG TERM...BW AVIATION...Frank/BW/NMB MARINE...Frank/BW