Area Forecast Discussion

932 FXUS61 KBOX 151113 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 713 AM EDT Thu May 15 2025 .SYNOPSIS... Weakening low pressure will bring scattered showers or thunderstorms at times through the end of the week as it reaches New England, but a majority of the time will be dry. Scattered showers or thunderstorms will be a possibility to start the weekend before a cooling trend and drier conditions move into the region to start next week. && .NEAR TERM /THROUGH TONIGHT/... 330 AM Update: Key Messages: * Scattered showers early in the morning move offshore. * Overcast and on the humid side. * Isolated to widely scattered aftn showers/t-storms in the interior if clouds can break, some which could be slow-moving and be a localized heavy-downpour risk. Details: The axis of showers and embedded thunderstorms over interior SNE will be gradually shifting eastward into eastern MA and RI and Cape/Islands over the next couple hours. Could be some localized downpours in some of this activity but it should just make for difficult travel/reduced visby for morning commuters vs yield any street flooding concerns. This axis of rain showers continues moving offshore by mid-morning; in its wake is left a rather cloudy and humid warm sector in an amorphous/weak/"blah" sea-level pressure pattern. This occurs as an upper level disturbance works its way northeast into eastern NY and opens up as it does so. The main forecast challenges for today are related to the extent to which we can shake free of cloudiness, or if we can at all. BUFKIT profiles from the RAP/HRRR suggest that cloudiness should hang tough in eastern MA and RI, and it would also lead to more convectively-stable thermo profiles. It wouldn`t take much mid- May sun angle to disperse this layer of cloudiness but I`m more pessimistic we`ll see much of any breaks in eastern New England. There is more optimism we`ll scatter out during the afternoon in interior Southern New England; and if that does occur then the risk for diurnally-driven scattered showers and thunderstorms could develop. There isn`t much in terms of a lifting source given the above-described pressure pattern, other than weak upslope convergence against the interior hills. CAPEs are progged around 700-1200 J/kg from HFD-ORH-BED north and west but would be of the tall, skinny type of CAPE profile with poor mid- level lapse rates. Some of the convective-permitting model output simulates some popup cells in that weakly unstable airmass. Severe weather is not expected. But since mid-upper flow weakens to under 20 kt thru a deep depth of atmosphere with the approach of the upper disturbance, and that warm cloud depths are around 10-11kft favoring precip efficiency, any storm which develops would be slow moving and be capable of heavy downpours and local heavy rain footprints, falling in an area which has been soaked of late. Probabilistic HREF 3-hourly QPF progs show some solid probs (up to 50%) of 1" rainfall in 3 hrs from Worcester west. In a nutshell, could be some minor hydro issues in slow moving cells but shouldn`t rise to the level of significant/flash flooding. Should see highs in the mid 60s coastal areas to the low-mid 70s, with better chance at mid 70s in the Berkshires and interior SNE with sustained breaks in cloudiness. && .SHORT TERM /FRIDAY/... 330 AM Update: Key Messages: * Stratus and areas of fog tonight, locally dense in some locations. * Should clear out Friday, and while generally dry, will watch for possible scattered thunderstorms in western New England late in the day. Better potential exists in NY. Details: Tonight: Diurnally-driven showers or storms should dissipate by early evening. Weak sea-level pressure pattern continues, with light to calm winds, a humid airmass with recent rainfall having occurred. Though I don`t have the strongest conviction in ceiling/visby guidance of late, this is a favored setup for development of areas of fog and stratus. There`s also been a history of fog/stratus in the mid-Atlc states overnight tonight, which is where our airmass is coming from. NBM visby progs actually sock all of SNE in dense fog, so it`s possible later shifts could consider doing fog statements or advisories if needed. Rather mild, but generally dry and on the humid side with lows in the mid 50s to lower to mid 60s. Friday: We probably will have quite a bit of stratus and fog to open Friday. Background weak subsidence owing to 500 mb height rises could lead to more uncertainty on when we can scatter out. Tried to show some optimism in clearing during the mid to late morning to a partly sunny look, and temps warming to well into the 70s to a few spot 80 degree readings; if clearing is delayed until the afternoon, we`ll probably struggle to reach 80. Later in the day our western areas start to get into stronger height falls with the approach of a midlevel warm front. This front will really help steepen lapse rates in the 850-500 mb layer, and there`s some potential for a few rumbles of thunder during the late-afternoon stemming from a more active convection pattern in the Gt Lakes. Think a better chance for more robust convection develops in central/southern NY with weakening activity if any here in SNE, and that`s the more likely outcome, but a few solutions such as the high- res WRF windows offer potential for scattered storms after 21z working over the Berkshires. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Key Messages: * Severe thunderstorms are a possibility on Saturday * Drier and cooler to start next week Details... A warm front is expected to move through the region Saturday morning, and we will be in the warm sector behind it before a cold front moves through. Ensembles still showing some probs for some elevated surface CAPE across western and central MA that would favor some thunderstorms. Timing on the cold front`s passage could affect just how favorable the environment could be for severe storms and their mode. Even with some of the higher res guidance starting to reach this period hinting at some more organized convection in the evening hours Saturday, it`s still far enough out that this could change. Probs for higher shear across the interior are soundly above 50 percent, so a high shear low CAPE environment could be what these storms develop in. CSU ML guidance does indicate some slightly higher chances for severe weather in southern New England, though, so this will continue to be monitored. A cold front moving through is expected to usher in a drier airmass following the exit of the mid-level low. Mid-level ridging pushes its way in heading into midweek with surface high pressure shifting into southern New England, which should keep the region dry. Winds shift more to the NW and N. Guidance shows temperatures aloft cooling by around 10C from Saturday afternoon by Monday, continuing into Wednesday. Saturday and Sunday highs are expected to be primarily in the 70s, although Sunday is slightly cooler with the highest temperatures in the low to mid 70s. Once the cold front moves through, highs to start the week may settle more into the mid to upper 60s. && .AVIATION /11Z THURSDAY THROUGH MONDAY/... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 12z TAF Update: Today: Moderate confidence. Should see widespread MVFR-IFR cigs early with early-day SHRA/embedded TS moving offshore. It looks like moisture gets trapped and struggles to mix out east of ORH, and maintained at least MVFR bases for most of the day. Wouldn`t rule out a SHRA at times but majority of the time will be dry. For ORH, BAF and BDL, there`s more optimism in bases lifting to VFR, but that will increase the risk for SCT slow-moving SHRA/possible TS indicated in TAFs with PROB30s from 17-23z. Although severe weather not expected, lightning and downpours could affect these western terminals if a direct hit occurs. Continued SE to S winds around 5-10 kt. Tonight: Moderate confidence. Areas of IFR to LIFR fog and stratus develops after daytime SHRA/TS eases after sundown. Showed most airports around 1/2 to 5SM, but fog could become locally dense and visbys could be as low as 1/4SM, especially western airports. Light to calm winds. Friday: High confidence in trends, but moderate on timing. IFR-LIFR from overnight should start to improve to VFR 13-16z, perhaps longer across the Cape/Islands. Some risk for SHRA/TS possible west of ORH after 18z but stronger activity seems more likely west of the Berkshires. Light S winds. KBOS TAF...Moderate confidence. VFR for another couple hrs until SHRA moves in around 08-09z with ceilings then trending to MVFR/IFR. SHRA ends around 12z although MVFR ceilings likely continue into early afternoon. Categories could trend MVFR-VFR range during the afternoon, then start to lower again to IFR- LIFR levels late-afternoon to tonight. KBDL TAF...Moderate confidence. MVFR with 3-6 SM SHRA. SHRA ends around 11z although MVFR-IFR bases continue into the early afternoon. Scattering to VFR around early-midaftn, but potential for slow-moving TS 17-23z. IFR-LIFR in fog/stratus tonight, locally dense fog possible. Outlook /Friday Night through Monday/... Friday Night: Mainly VFR, with local IFR possible. Chance SHRA, isolated TSRA. Saturday: MVFR/IFR conditions possible. Chance SHRA, isolated TSRA. Saturday Night: VFR. Chance SHRA. Sunday through Sunday Night: Mainly VFR, with local MVFR possible. Breezy. Slight chance SHRA. Monday: VFR. Breezy. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. 330 AM Update: High confidence overall. E/SE winds remain below SCA levels Thu and Fri. Seas will be building on the southern ocean waters where SCAs still continue. Few showers or a thunderstorm possible early this morning, with areas of marine fog developing tonight and could linger into a good part of Fri. Outlook /Friday Night through Monday/... Friday Night: Winds less than 25 kt. Slight chance of rain showers, isolated thunderstorms. Saturday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers, isolated thunderstorms. Saturday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers. Sunday Night through Monday: 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 4 PM EDT this afternoon for ANZ235- 237. Small Craft Advisory until 1 AM EDT Friday for ANZ254>256. && $$ SYNOPSIS...Loconto/Hrencecin NEAR TERM...Loconto SHORT TERM...Loconto LONG TERM...Hrencecin AVIATION...Loconto/Hrencecin MARINE...Loconto/Hrencecin NWS BOX Office Area Forecast Discussion