Area Forecast Discussion

271 FXUS61 KBOX 302324 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 724 PM EDT Mon Jun 30 2025 .SYNOPSIS... Cloud cover increases tonight, with a risk for showers and thunderstorms overnight to early Tuesday morning. Tuesday is very warm and humid with heat indices in the mid 90s. Another period of showers and storms redevelops Tuesday afternoon, some with torrential downpours, before clearing out for Tuesday night. Very warm Wednesday and Thursday then drying out with more seasonable temperatures heading toward the 4th of July. An upper level disturbance may bring scattered showers and thunderstorms Thursday, otherwise dry through the end of the week. Heat and humidity return later next weekend. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... 315 PM Update: Key Messages: * Increasing cloudiness tonight, with fog and low clouds over southeast New England. Turning more humid too. * Overnight to early Tue showers and embedded storms, timing approximately 3-9 AM. Although severe weather isn`t expected, storms could be capable of downpours and lightning which could impact the Tue AM commute. Details: Overall not too bad a day as we close out the month of June with weak high pressure in control. At least through the early part of the overnight, the vast majority of Southern New England should end up being dry albeit with increased cloud cover. RI and southeast MA will start to see fog and low clouds/stratus return northward starting by early evening. Forecast then starts to change during the latter half of the overnight into the early Tue morning period. A warm front associated with a very humid and conditionally-unstable airmass to its south will be moving ENE approx. during the 3-10 AM timeframe. In tandem with this warm front, active convective activity currently taking place over the mid-Atlantic to parts of the OH Valley should begin to approach our western MA/CT areas closer to 3-4 AM, which then generally moves ENE towards the eastern coast around early Tue AM. In a weakly-forced setting like this one as is customary, high-res model guidance still remains frankly scattershot as far as where and when the best risk for thunderstorms could lie in the overnight. Some risk for storms could exist virtually anywhere, but think the better shot for storms is mostly south of the Mass Pike. Severe weather is not expected from this activity with weak windfields and still pretty stable low-levels, but could still produce lightning and heavy downpours, which could coincide with Tuesday morning commute periods. While this activity should be coming to an end toward daybreak in western MA/CT, it may still be ongoing for eastern MA, RI and the Cape and Islands. Turns quite muggy tonight with lows upper 60s to lower 70s. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... 315 PM Update: Key Messages: * Early-day showers/embedded storms end by mid-morning, with dry weather thru midafternoon. * Thunderstorms likely re-develop Tue late afternoon to early evening, soonest interior (after 3 PM) which then conglomerate and move southeast by sundown and offshore early Tue night. Main risk is from torrential downpours capable of urban and street flooding, with possible flash flooding where storms re- develop. More limited localized wind damage threat possible but secondary to the heavy downpours threat. * Very warm and humid, feeling like the mid 90s Tue aftn. Details: Quite a bit of moving parts for Tuesday, due in part to the early- day shower/thunderstorm risk and the recovery/destabilization potential in the wake of this activity. This leads to a still lower than average forecast confidence as it pertains to the timing of re- developing showers and thunderstorms during the afternoon and early evening, as well as to how warm temperatures and heat indices may get. We think leftover cloud cover from morning activity begins to scatter out closer to noontime. So after the early morning shower/storm activity ends, we should see a period of relatively dry weather. How long that dry period holds on for is still a question mark, but we think there should be some subsidence and relatively drier period thru at least 3 PM. The risk for showers and thunderstorms then increases more substantially around/after then as a cool front interacts with a heated and humid airmass. starting in interior Southern New England, then lurching southeast towards the I- 95 corridor around sundown, and then move towards the southern coastal waters early Tue evening. Regarding thunderstorm parameters for Tue, lapse rates in mid-levels are barely moist- adiabatic if that, and wind fields in the lowest few km of atmosphere are quite weak. However precipitable water values are sizable at over 2", warm cloud depths around 12,000 ft with CAPEs around 1500-2000 J/kg but is of a tall-skinny type of profile. But I think the greatest risk, given the above, in any thunderstorms which develop is from instances of street and flash flooding. This is especially the case where storms can re- develop over the same areas with the synoptic pattern favors storms backbuilding and re-developing. And it could potentially be a problem for the Tuesday afternoon/evening commuters. A more limited risk for severe weather in the form of water-loaded outflows/wind damage could develop but think this is a more secondary risk than to the lightning and heavy downpours threat. Included enhanced wording for heavy downpours and gusty winds in the forecast, but of the two, I think heavy downpours/instances of street flooding would be the main risk. Activity should begin to move offshore by late Tue evening before most if not all areas trend dry by early Wed. Tue should end up being very warm to hot and also quite humid, which will bring elevated heat indices. Tempering that to an extent will be some degree of cloud cover. High temps in the mid to upper 80s and dewpoints in the mid 70s would favor it feeling closer to the mid 90s. This doesn`t meet the threshold for heat advisory criteria but it still will be quite warm and humid nonetheless. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... Key Messages: * Very warm Wed-Thu. Scattered showers and t-storms possible Thu * Drying out with more seasonable temperatures and less humidity for the 4th of July * Heat and humidity return Sun-Mon Details... Weak trough/cold front appears to get hung up in the coastal plain Wed with elevated PWAT axis near 2 inches near the south coast, before drier air pushes southward across the region during the afternoon. Can`t rule out a few lingering showers near the south coast Wed morning within the moisture plume, otherwise dry and very warm conditions with highs well into the 80s. 70+ dewpoints linger near the south coast but less humid airmass will begin to move south across the region during the afternoon. Upper trough amplifies over the NE Thu-Fri as upper low digs southward through Quebec and into northern New Eng Fri. Increasing forcing for ascent ahead of the trough will lead to chance of showers/t-storms Thu afternoon, especially interior. Given increasing mid level wind field and favorable mid level lapse rates approaching 6.5 C/km, we think there will be a conditional severe wx threat if there is enough moisture/instability. The magnitude of instability is uncertain and SREF probs are rather meager with CAPES. Instability will be the key for Thu, but CSU and NCAR ML guidance is indicating some risk for severe. Very warm temps are expected Thu but dewpoints may mix out and fall through the 50s which would be a inhibiting factor. Stay tuned. Then cold front is expected to move offshore by Fri with NW flow bringing less humid airmass and more seasonable temps for the 4th of July. Looking ahead to next weekend into early next week, upper trough exits followed by rising heights and ridging building back into the region. This will result in increasing heat and humidity, especially by Sun and Mon. && .AVIATION /23Z MONDAY THROUGH SATURDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 00z TAF Update: Tonight: High confidence in TAF/trends but moderate on timing. IFR-LIFR stratus and fog advances northward from Cape Cod and immediate south coast overspreading RI and SE MA to south of BOS by 06z, with MVFR further inland. SHRA/possible embedded TSRA moves in from eastern/southern NY after 07z, TS possible anywhere but somewhat better chance for the BDL/HFD-PVD/SE MA area. These storms would not become strong were any to develop but could still pose risk for lightning and brief IFR visby downpours. Tuesday: High confidence in TAF/trends but moderate on timing. Early-day SHRA/possible TS thru 14z then trends to VFR. Another period of TS more likely late in the day (after 20z), but could start as soon as 18z in interior Southern New England. Storms could produce torrential downpours and brief gusty winds. SW winds around 5-10 kt with occasional gusts. Tuesday Night: High confidence. SHRA/TS moves southeast towards the southern waters thru 02z, with gradual improvement to VFR thereafter. Possible BR/FG south coast until SHRA/TS clears the southern waters. KBOS Terminal...Moderate confidence in TAF. Stratus will approach the airport from the south after 06z. Confidence is not high in IFR so added a BKN010 in the TAF and will re- evaluate at 06z. Early-morning SHRA from 09-14z Tue, outside chance at TS but better chance south and west. VFR thereafter approx 14-22z with SW breezes but risk for SHRA/TS returns by 22z (indicated with PROB30s). KBDL Terminal...Moderate confidence in TAF. VFR thru 07z, SHRA with embedded TS 09-12z Tue. VFR thereafter approx 13-19z with S winds but risk for SHRA/TS returns by 19z (indicated with PROB30s). Outlook /Wednesday through Saturday/... Wednesday through Wednesday Night: VFR. Thursday through Thursday Night: VFR. Slight chance SHRA, isolated TSRA. Independence Day: VFR. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Tonight: High confidence. Dry weather with SE to S winds around 10-15 kt and seas 2-4 ft. Main risk for mariners tonight is fog over the waters, and a potential risk for thunderstorms early Tue AM. Tuesday and Tuesday Night: Moderate confidence. SCA remains valid for Tue as SW winds increase to around 25 kt, with seas building to 4-6 ft. Early-morning showers and thunderstorms possible, then dry weather for most of the afternoon. The risk increases for showers and thunderstorms again for late in the day into the mid Tuesday evening hours, some could be capable of frequent lightning, heavy downpours and locally rough seas. Outlook /Wednesday through Saturday/... Wednesday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. Wednesday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Thursday: Winds less than 25 kt. Thursday Night: Winds less than 25 kt. Slight chance of rain showers, isolated thunderstorms. Independence Day: Winds less than 25 kt. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 11 AM Tuesday to 6 AM EDT Wednesday for ANZ250-254>256. && $$ SYNOPSIS...KJC/Loconto NEAR TERM...Loconto SHORT TERM...Loconto LONG TERM...KJC AVIATION...KJC/Loconto MARINE...KJC/Loconto NWS BOX Office Area Forecast Discussion