337 FXUS61 KBOX 020157 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 957 PM EDT Mon May 1 2023 .SYNOPSIS... Any diurnally driven activity diminishes this evening. Clouds increase late as another disturbance moves in. This will bring a period of showers and perhaps a rumble of thunder late tonight into Tuesday. Cooler and unsettled conditions will continue through the end of the week with showers at times as low pressure aloft moves from into New England. There are signs of a change to a drier and milder weather by the weekend. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... 10 PM Update Forecast remains generally on track at this hour. KBOX radar is detecting an area of showers over western MA that has lost steam over the past hour or so. Expect this shower to taper off as it continues NNE toward Orange before fizzling out near the MA/NH border. Another more widespread round of showers will begin early tomorrow morning as we approach day break. Previous Discussion Highlights * Diurnally driven showers/storms taper off this evening. Increasing clouds late with more widespread activity pushing in toward late. Broad cutoff rotates across the eastern Great Lakes this evening and tonight. Will have a shortwave rotating around the cutoff, which will lift into southern New England toward daybreak from the OH Valley. Broad sfc low over the eastern Great Lakes through this period. Will have a weaker secondary low develop across the Mid Atlantic and lift into E NY toward daybreak. Will have isolated to scattered shower activity mainly across the interior into this evening that is diurnally driven. This is a result of the -20 to -25 degree Celsius 500 hPa cold pool pushing in aloft. Cannot completely rule out an isolated thunderstorm or small hail. Have leaned toward the HREF/HRRR guidance as it is doing well based on latest observations. Should see any diurnally driven showers taper off during the evening. Clouds increase late tonight with more shower activity spreading in late tonight/toward daybreak. Could see a few rumbles of thunder, especially across the S/E coast as a low level jet pushes in. Low temps bottom out in the 40s. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... Highlights * Unsettled with fairly widespread showers and perhaps a few thunderstorms on Tue. Still may have some showers lingering into Tue night. Broad cutoff over the eastern Great Lakes will gradually rotate eastward into the Mid Atlantic by late Tue. This will keep a broad low over/nearby the region. The weather remains unsettled through this period, but am not anticipating a washout. Will have fairly widespread hit-or-miss shower activity across the region on Tue. Thinking that the thunder risk is greatest across eastern areas as indicated by the latest HREF guidance, which is also where the strongest low level jet is at 925 hPa. Given the cold pool in place aloft along with some CAPE within the hail growth region do not think it is out of the question we get some graupel/small hail. Have not added a hail mention at this point, but it may be necessary in future forecast updates. Will be a bit cooler given the significant amount of cloud cover across the region Tue. Highs top out in the 50s. Will see shower activity diminish Tue night, but not completely shut off given the upper low nearby. Will have relatively light winds and given the moisture we just got and are expecting through this period, could see fog in the typical fog prone areas. Low temps in the 40s. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... Highlights * Cool wet weather through Friday * Milder and drying out for the weekend Upper level trough will slowly break down and exit the region by the end of the week. Until then, cyclonic flow and cold temperatures aloft will bring scattered rain showers with graupel occasionally mixed in through Friday. As for rainfall amounts, Wednesday shouldn't be a washout with GEFS and Euro ensembles having less then 10% chance for greater then a half inch of rain. Thursday looks to be the wettest day of the week due to better forcing as an embedded shortwave traverses the back side of the trough. Ensembles have 10- 30% chance for a half inch of rain. There is a bit of elevated CAPE thursday meaning there could be a rumble of thunder. Temperatures Thursday will also be the coolest of the week running well below average due to onshore NE flow. Highs Thursday likely struggle to reach 50F. Friday looks a bit drier with only low chances for scattered showers. Highs Friday will likely remain below average with northerly flow and mostly cloudy skies. The upper level pattern finally begins to change Saturday as the upper level trough finally kicks off the east. An upper level ridge begins building in helping clear out the showers and clouds. Although winds will remain northerly, with the sunny conditions and warming 850mb temps, high temps will be begin to moderate back towards normal to even above normal by Sunday. The start of the work week looks to start off dry with continued above normal temps from the weekend. Rain chances come back into the forecast mid next week as a short wave trough works its way over the region. && .AVIATION /02Z TUESDAY THROUGH SATURDAY/... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. 00Z Update... Tonight into Tuesday...High confidence in trends lower in exact timing. VFR for much of tonight. Will lower to MVFR levels, especially across the interior into Tue AM as showers spread in. Could have some isolated thunder into the AM push, especially across the S/E coast, but have not added to TAF due to uncertainty on the coverage. Ceilings lifting to VFR in the afternoon across the interior with showers persisting. Diminishing SW winds this evening becoming S/SE 5-10 kt overnight, then S 5-15 kt Tue. Tuesday night...High confidence. VFR with rain showers lingering, especially across the MA/NH/VT border. Winds becoming relatively light, so may see patchy fog development across the typical fog prone areas. MVFR ceilings spreading into the interior toward daybreak. KBOS Terminal...High confidence in TAF. VFR with gusty winds subsiding 00-02Z. Low shot for an isolated thunderstorm for the Tue AM push as showers move in. KBDL Terminal...Moderate confidence in TAF. VFR with scattered rain showers around. MVFR ceilings spreading in late tonight. Outlook /Wednesday through Saturday/... Wednesday: Mainly MVFR, with areas VFR possible. Chance SHRA. Wednesday Night through Thursday: Mainly MVFR, with local IFR possible. Breezy. SHRA likely. Thursday Night: Mainly VFR, with local IFR possible. Breezy. Chance SHRA. Friday: Mainly VFR, with areas MVFR possible. Breezy. Slight chance SHRA. Friday Night: Mainly VFR, with local MVFR possible. Breezy. Saturday: VFR. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Tonight and Tuesday...High confidence. S/SW winds 10-20 kt tonight and southerly gusts to 20 kt Tue. Seas gradually subsiding but remaining above 5 ft over open waters. Showers spreading in late tonight and could have a few rumbles of thunder especially earlier on Tuesday. Tuesday night...High confidence. S/SW winds diminishing below 10 kts after midnight. Seas remain above 5 ft across the outer waters. Outlook /Wednesday through Saturday/... Wednesday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers. Wednesday Night: Winds less than 25 kt. Local rough seas. Chance of rain showers. Thursday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Chance of rain showers. Thursday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Chance of rain showers. Friday: Winds less than 25 kt. Local rough seas. Slight chance of rain showers. Friday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Saturday: Winds less than 25 kt. Seas locally approaching 5 ft. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 2 AM EDT Tuesday for ANZ232>234. Small Craft Advisory until 2 AM EDT Wednesday for ANZ235-237- 250. Small Craft Advisory until 2 PM EDT Tuesday for ANZ251. Small Craft Advisory until 8 AM EDT Wednesday for ANZ254>256. && $$ SYNOPSIS...BL/KP NEAR TERM...RM SHORT TERM...BL LONG TERM...KP AVIATION...BL/KP MARINE...BL/KP