330 FXUS61 KBOX 161901 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 301 PM EDT Mon May 16 2022 .SYNOPSIS... Strong to severe thunderstorms possible this afternoon and especially late this afternoon/evening across western Massachusetts and northern Connecticut as a cold front slides through. Any stronger storms could bring damaging winds, hail and heavy downpours. Cooler but seasonable temperatures return Tuesday through Thursday. Summertime warmth arrives Friday with the potential for our first 90 degree temperatures Saturday. && .NEAR TERM /THROUGH TONIGHT/... 245 PM Update... Highlights * Isolated strong to severe storms possible across western MA/northern CT into central MA this afternoon. * Risk of more widespread strong to severe storms across western MA/northern CT between 5-9 PM as a line moves in from the west. Per coordination with SPC have hoisted a Severe Thunderstorm Watch across western MA/northern CT this afternoon into the evening. Weak forcing for ascent due to the incoming trough coupled with an uncapped environment and dew points in the low/mid 60s has resulted in showers/storms developing within the warm sector well ahead of the cold front. In the latest update have leaned more toward the NSSL WRF, which is doing well compared to observations. Should see this initial activity lift northwards with a bit of a lull in the activity before a disorganized line moves in late this afternoon into the evening. At the moment per SPC Mesoanalysis have 500-1500 J/kg of MLCAPE with no CIN. Low level lapse rates are 6-9 C/km with poor mid level lapse rates and effective shear of 20-30 kts. As mentioned think this afternoons activity will lift northward, but will be tough to sustain itself until the stronger forcing/better shear comes in later. Not out of the question a few storms are severe with the main risk being damaging winds and perhaps some large hail along with heavy downpours. As for later this afternoon/evening am thinking that our previous forecast was pretty good, though things could come in a touch sooner than previously forecast. Timing wise am thinking roughly 4-9 PM range as the cold front swings in. The upper trough becomes negatively tilted as it lifts into the eastern Great Lakes/New England tonight. A strong cold front will sweep into eastern NY late this afternoon/evening and into/through southern New England this evening/tonight. The main question for this evening will be if any line that comes in from the west is able to tap into the waning instability. Most CAM guidance shows the activity weakening as it progresses eastward tonight, but will need to keep a close eye on it due to the strong forcing in place along with more than sufficient shear. Will have deep layer shear increasing to 30-40 kts ahead of the line. MLCAPE around 500-1000 J/kg, but should decrease as time goes on. Low level lapse rates initially nearly adiabatic with mid level lapse rates approaching 6 C/km. The focus of this will be across western MA/northern CT. Again timing wise looked pretty good from previous shift, but maybe just a touch sooner with the latest HREF 4/5 PM advancing eastward to the CT Valley by 5-7 PM and weakening as it pushes into central MA/NE CT 7-9 PM. Think given the strong forcing there still could be a few rumbles of thunder as it moves into eastern areas, but the stable marine layer should continue to weaken the activity as it progresses eastward this evening. At this point as the line moves in the main risk will be damaging winds, perhaps some large hail and heavy downpours. An isolated tornado is not out of the question, but think the risk will be higher to the SW/W of the region due to the better instability along with more favorable low level shear profiles. Should see most of this activity out of the region around 10 PM to 12 AM. Dry and quiet weather expected behind the front with temps cooling into the 50s. && .SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/... Highlights * Dry and quiet weather with more seasonable temps. A bit breezy in wake of the cold front. Given the activity across the region this afternoon did not spend a whole lot of time looking at this period. Cyclonic flow aloft will lead to lots of diurnal clouds across southern new England, but may be dry enough in the lower levels to keep any shower activity at bay. Have removed precipitation chances at this point, but not out of the question there could be a sprinkle or two. Will be breezy due to a deep mixed layer as colder W/WNW flow advects into the region. Think there could be some 25-35 mph gusts during the afternoon and 15-25 mph gusts Tuesday night. Again will be more seasonable with temps ranging from the mid 60s to mid 70s. Low temps will generally be in the 40s, but there will be some 50 degree readings along the coastal plain. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... Highlights... - Temperatures and humidity on the uptick by mid-week - Hot and humid conditions forecast for next week - Afternoon Thunderstorms possible next weekend Wednesday and Thursday... Pick of the week? I think so. Deep northwest flow will support seasonable temperatures and dry conditions across southern New England on Wednesday afternoon. High pressure will keep the skies clear. Seasonable temperatures this time of year fall into the upper 60s to low 70s for highs on Wednesday afternoon. Humidity will not be an issue as dewpoints are expected to be in the 20-40 F range. By Wednesday night however, a mid-level ridge builds in from the west resulting in a wind shift to the southwest. Increasing moisture and warm advection from the south/southwesterly flow may produce some scattered showers across the region Wednesday night into Thursday. Southerly flow continues to advect more warm/moist air into southern New England on Thursday. Cloud cover keeps high temperatures in the low 70s on Thursday, but increasing low-level moisutre will support higher dewpoints and thus higher humidity on Thursday. Overall a decent day with no rainfall or impactful weather expected. Weak short-wave aloft traversing over southern New England Thursday night may produce another round of scattered rainfall. Friday... Upper-level ridge begins to amplify over the east coast on Friday. Deep southwest flow and strong WAA will raise temperatures at 925 hPa close to 20C. This will support high temperatures at the surface in the upper 70s to low 80s on Friday. Dewpoints continue to climb into the low-mid 50s supporting more humid conditions than what is expected mid-week. Saturday and Sunday... Hot and humid conditions expected next Saturday and Sunday. Could see temps in the low-mid 90s at some locations Saturday afternoon per ensemble guidance. A deep upper-level trough will be approaching from the west, and with an unstable air mass in place, there exists the possibility for afternoon thunderstorms. Quite a bit of spread in the models with respect to time of arrival of the upper-level trough axis and associated front. EURO brings the front through Sunday morning, while the GFS has the front arrive nearly 24 hours later. Given the great uncertainty, have leaned on NBM which appropriately assigns the highest PoPs to Sunday evening. Stay tuned for more. && .AVIATION /18Z MONDAY THROUGH SATURDAY/... Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Through 00Z...Moderate confidence, mainly due to uncertainty in exact timing. Generally have VFR conditions across southern New England with scattered showers and thunderstorms due to weak ascent well ahead of the incoming cold front. Have tried to add a VCSH/VCTS to account for this activity, but this initial round should lift northwards. Not out of the question there are gusty winds and some hail if a storm passes over a terminal. Think the risk is greater between 21-03Z as the cold front slides in bringing a disorganized line from west to east. Anticipate MVFR with brief IFR/LIFR conditions as the line slides through for CT Valley to ORH. Anticipate this activity to weaken as it progresses further east due to the waning instability, but could see some 40 kt gusts. Further east the marine layer should weaken the activity, but still could have a few rumbles of thunder. Winds out of the S at 10-15 kts with gusts up to 20 kts outside of thunderstorm activity. Could have some higher gusts if a thunderstorm moves over a terminal. Cold front pushes through SNE later tonight with wind shift to W/NW and improvement to VFR, which continues into Tue. Will be breezy across the region. KBOS TAF: Medium confidence due to timing in category changes. KBDL TAF: Medium confidence due to timing in category changes. Outlook /Wednesday through Friday/... Wednesday Night: VFR. Thursday: VFR. Slight chance SHRA. Thursday Night through Friday: Mainly VFR, with local MVFR possible. && .MARINE... Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. High confidence through Tuesday. Main concern tonight is areas of dense fog until the cold front crosses waters, shifting winds to W/NW and bringing improving visibility. May also see a few showers perhaps a rumble of thunder or two as front passes. Winds and seas should reach SCA later this evening with increasing W/NW flow and have continued SCA for outer waters where we are more confident. Still uncertain for SCA across the nearshore waters as winds appear to be marginal. Outlook /Wednesday through Friday/... Wednesday: Winds less than 25 kt. Seas up to 5 ft. Wednesday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Thursday: Winds less than 25 kt. Slight chance of rain showers. Thursday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers. Friday: Winds less than 25 kt. Areas of seas approaching 5 ft. && .TIDES/COASTAL FLOODING... We will be in a period of high astronomical tides this week, the first of which occurs with tonight's high tide along both the east and south coasts. Some coastal sites are forecast to crest just below or right at flood stage. Keep in mind no storm surge or wave action is expected since winds will be blowing offshore most of the week. Only shallow inundation (less than 1 foot) is expected from still water elevation in the most vulnerable locations, such as some shoreline roads. This will be more in the way of nuisance flooding and should not present any significant impacts. We handle situations like this by issuing Coastal Flood Statements. These will be updated periodically during the week as necessary. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 8 PM this evening to 8 AM EDT Tuesday for ANZ250-254>256. && $$ SYNOPSIS...BL/RM NEAR TERM...BL SHORT TERM...BL LONG TERM...RM AVIATION...BL/RM MARINE...BL/RM TIDES/COASTAL FLOODING...