Area Forecast Discussion
Issued by NWS Boston, MA
Issued by NWS Boston, MA
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443 FXUS61 KBOX 210526 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 126 AM EDT Fri Jun 21 2024 .SYNOPSIS... Scattered strong to severe thunderstorms remain possible this evening...mainly across northern MA where a Severe Thunderstorm Watch is in effect. A backdoor cold front moves in from northeast to southwest Friday...bringing another round of showers and thunderstorms. The bulk of this activity should be across interior Massachusetts and Connecticut...where some of the storms may become severe and also result in a localized flash flood threat. Warm and muggy this weekend with rain and thunderstorm chances both Saturday and Sunday. A cold front sweeps across the region Monday with additional showers and storms, briefly less humid on Tuesday, but summer warmth and humidity returns for midweek. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... 10 PM Update The severe thunderstorm threat has ended with storms loosing strength very quickly after sunset as capping inversion developed. A few lightning strikes are still being observed, mainly over the waters, but more stratiform showers have become the more dominant precipitation mode over the last hour or so. We expect that showers will continue to dissipate over the next two to three hours, with dry conditions expected well before sunrise. Given the lack of instability/forcing after sunset, the Severe Thunderstorm Watch has been cancelled. Previous update... 745 PM Update * Strong to Severe T-Storms through late evening in areas north of the CT/RI/MA State lines * Localized damaging wind gusts & torrential rainfall which may result in a very localized flash flood threat Shortwave energy across northern New England coupled with outflow and MLCapes still over 2000 J/KG has resulted in a solid line of strong to severe t-storms to enter northwest and northern MA early this evening. We think enough outflow will result in a risk for severe storms over the next 1-3 hours in areas at last north of the CT/RI/MA state lines. This is also supported by the latest machine learning probs from the CSU to the Nadocast and HRRR Neural network...which are all showing a quite robust signal for localized damaging wind gusts. Main question is how far south this convection will survive as it out-runs the greater forcing. Given that DCapes are still over 1000 J/KG...we expanded the Severe T-Storm Watch to the CT/MA border and extended it through 11 pm. Also...these storms will be capable of producing torrential rainfall and a localized flash flood threat. Once this activity winds down later this evening...much of the overnight hours should feature dry/muggy weather. Overnight low temps will mainly be in the upper 60s to the lower 70s. We also may see some patchy ground fog develop overnight given light winds/high dewpoints especially where rain falls earlier in the evening. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/... Key Points... * Showers & t-storms anticipated Fri PM with the severe weather threat/very localized flash flood threat across interior MA/CT * Much cooler across eastern MA but still hot & humid towards the CT River Valley where Heat Advisories remain posted Details... Friday... A backdoor cold front will be moving westward across the region Friday morning and into the afternoon. This will hold high temps in the 80s across much of eastern MA and temps along the immediate coast will probably fall into the 70s by afternoon. Further inland...high temps will top off in the upper 80s to the lower 90s with the warmest of those readings in the CT River Valley. The Heat Advisory for Friday will only cover portions of southwest MA/CT...where Heat Indices are expected to top off between 95 and 100 degrees. The other concern will be for another round of showers & t- storms...which looks to be Friday afternoon/early evening. The focus for this will be along the backdoor cold front and will be enhanced by shortwave energy in west to northwest flow aloft. While a few showers & t-storms may impact the entire region...thinking the main focus for the potential of severe weather/localized flash flooding will be across western/central MA & northern CT. This is where the greater instability will reside on the order of 1500 to 2000 J/KG. These backdoor cold fronts can be a recipe for training and a localized flash flood threat. The CSU Machine learning probs highlight this risk nicely with again the focus across the interior. There also is a severe weather risk with the main concerns being locally damaging wind gusts with hail a secondary risk. This is depicted nicely by the machine learning probs as well as the HREF Updraft Helicity Swaths/Radar Simulations. Friday night... The convection should dissipate Friday evening. Otherwise...we will have to watch for areas of low clouds and fog developing. Overnight low temps will be mainly in the 60s. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Highlights: * Warm and muggy this weekend with rain chances both Saturday and Sunday. * Cold front sweeps across the region on Monday, drier and returning heat into mid next week. The mid-level ridge continues to deamplify, as 500mb heights lower from north to south, which is a consistent theme for the upcoming weekend. At the surface an area of higher pressure near Bermuda wanes and surface pressure lowers across the northeast. This area of low pressure developing over the northern Great Lakes, drives our weather conditions late this weekend into Monday, as the trailing cold front, south of the low, sweeps across the northeast sometime Monday. Beyond Monday, high pressure builds back Tuesday through Thursday, with a cold front possibly pushing across the region later on Friday/Saturday. In addition, most of next week trends warmer than normal, and at this point, next week doesn`t look to be as extreme as this current week. Though the ensemble situational awareness tables indicates Monday through Thursday, surface temperatures could be running between the 90th and 99th percentile (of climatology), with a return of average temperatures post cold front, sometime late Friday into Saturday. Saturday & Sunday: Getting closer to home, there is a quasi-stationary frontal boundary across the region, running from east to west through southern New England and through Upstate New York on Saturday. Weak area of low pressure tries to develop along the boundary, with the greatest area for showers and storms along and north of the Mass Pike during the mid to late afternoon. At this point, not expecting anything severe, and SPC has most of the region under general thunder. A slightly more elevated issue would be the potential for excessive rainfall. The ERO from WPC highlights much of central/western Massachusetts and northern Connecticut for a `Marginal` risk. Given PWATs are above two inches, isolated and locally heavy downpours could lead to urban street and poor drainage flooding. Aforementioned frontal boundary becomes a warm front Saturday night into early Sunday, lifting northeast, and placing us in the warm sector. Scattered showers into the overnight hours, though the best forcing appears to be concentrated further north. A prefrontal trough and shortwave pivot through, with showers and thunderstorms later Sunday afternoon/evening. As for temperatures, Saturday will be the `cooler` day, the warmest location will be the Connecticut River Valley, highs here are in the mid 80s. Much cooler in northwest Massachusetts where highs are low to middle 70s with the northeast flow. Nightly lows are still mild which isn`t ideal for sleeping with windows open, lows are in the middle to upper 60s to 70 degrees in the Connecticut River Valley on Saturday night, then 2-4 degrees warmer Sunday night. Next Week: Warm and muggy day ahead of a surface cold front with temperatures climbing into the 80s and dew points in the 60s. Storms develop mid to late afternoon with the surface cold front, a bit a relief behind the front with lowering dew points into the 50s and leads to a nice Tuesday with comfortable, albeit warm day, with dew points in the upper 50s to 60F. High pressure reestablishes across the northeast leading to a drier week with return of summer warmth. Highs are in the middle and upper 80s and lows in the 60s with a sign of cooler temperatures by late in the week. && .AVIATION /05Z FRIDAY THROUGH TUESDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 12z TAF Update... Friday...Moderate Confidence. More showers and thunderstorms this afternoon with more north to south coverage compared to Thursday when storms stayed north of the MA Turnpike. Anticipating VFR conditions, with the exception of patchy IFR due to fog, through 15Z after which time storms will bubble up. VFR/high end MVFR with cigs around 3500ft outside of storms. MVFR to IFR in storms with potentially torrential downpours and vsby reductions. Will be difficult to pinpoint exact storm location but terminals at greatest risk are BAF, BDL, ORH, PVD. Winds variable today, from the ENE from ORH, east, and from the NW/W across the CT River Valley as cold front pushes west towards interior southern New England. Friday night...Moderate Confidence. Bulk of storms wind down by 00Z tonight, but residual moisture and onshore ENE flow will allow pockets of fog to develop. Generally MVFR to IFR due to cigs. Saturday... moderate confidence. Another afternoon of scattered thunderstorms, though confidence on intensity and aerial coverage is low at this time. Could impact all terminals, or none at all with the best chance for tstorms coming after 17Z. Conditions improve from IFR/MVFR to VFR with perhaps the exception of east coastal MA where MVFR will persist. Locally lower flight categories likely again in storms. KBOS TAF... Moderate confidence. Expect thunderstorm activity to stay inland of Boston this afternoon, but can`t rule out a stray storm. Generally VFR this morning becoming MVFR/IFR overnight due to low stratus/fog. Winds quickly shift to the ENE this morning and will persist. KBDL TAF...Moderate Confidence in TAF. Another round of thunderstorms this afternoon with the best chance to impact BDL between 17-22Z. Storms wane quickly after sunset. VFR outside of storms, MVFR in storms, MVFR to IFR developing tonight due to fog. Winds from the West for much of the period but depending on the position of the back door cold front, could go N or ENE late in the period. Outlook /Saturday Night through Tuesday/... Saturday Night: Mainly IFR, with local MVFR possible. Chance SHRA, isolated TSRA, patchy BR. Sunday: Mainly VFR, with local IFR possible. Breezy. Chance SHRA, isolated TSRA, patchy BR. Sunday Night: Mainly VFR, with areas IFR possible. Breezy. SHRA likely, isolated TSRA, patchy BR. Monday: Mainly VFR, with local IFR possible. Breezy. Chance SHRA, isolated TSRA, patchy BR. Monday Night: VFR. Breezy. Chance SHRA. Tuesday: VFR. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Through Saturday...High Confidence. Back door cold front will move across the northeastern waters on Friday morning but likely stalls somewhere across the southern waters, which will lead to converging winds; northeast vs westerly. Afternoon showers and thunderstorms across the mainland may impact the waters very late both today and Saturday, but confidence is low as storms are expected to lose their strength after sunset. Winds and seas should stay below SCA criteria. Fog and stratus development likely tonight and will linger into the day on Saturday. Reduced vsbys should be expected. Outlook /Saturday Night through Tuesday/... Saturday Night: Winds less than 25 kt. Chance of rain showers, isolated thunderstorms, patchy fog. Visibility 1 to 3 nm. Sunday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Slight chance of rain showers, isolated thunderstorms, patchy fog. Visibility 1 to 3 nm. Sunday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Rain showers likely, isolated thunderstorms, patchy fog. Visibility 1 to 3 nm. Monday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Rain showers likely, isolated thunderstorms, patchy fog. Visibility 1 to 3 nm. Monday Night: Winds less than 25 kt. Local rough seas. Chance of rain showers, isolated thunderstorms, patchy fog. Visibility 1 to 3 nm. Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft. && .CLIMATE... All Time June High Temperature Record (Daily) BOS - 100 F (06/06/1925, 06/26/1952 and 06/30/2021) BDL - 100 F (06/26/1952, 06/30/1964) PVD - 98 F (06/25/1943, 06/15/1945 and 06/30/1945) ORH - 98 F (06/26/1952) Most recent day of 100 F (or greater) BOS - 100 F (07/24/2022) BDL - 100 F (07/21/2019) PVD - 100 F (07/28/2020) ORH - 102 F (07/04/1911)* * For ORH this is the only 100+ degree day in its period of record. Daily High Temperature Records... June 21st BOS - 96 F (2012) BDL - 96 F (1953 and 2012) PVD - 96 F (1941) ORH - 91 F (Multi-Years) Daily Warmest Low Temperatures Records... June 21st BOS - 80 F (2012) BDL - 73 F (1923 and 2012) PVD - 75 F (2012) ORH - 74 F (1923 and 2012) && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Heat Advisory until 7 PM EDT this evening for CTZ002>004. MA...Heat Advisory until 7 PM EDT this evening for MAZ008>011. RI...None. MARINE...None. && $$ SYNOPSIS...Frank/Dooley NEAR TERM...Frank/KS SHORT TERM...Frank LONG TERM...Dooley AVIATION...KS MARINE...Frank/Dooley CLIMATE...BL