000 FXUS61 KBOX 032037 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 437 PM EDT Wed Aug 3 2022 .SYNOPSIS... Heat and humidity will be the main weather story right through this weekend into early next week. The heat and humidity will peak tomorrow and Friday, with near record high temperatures and oppressive heat indices as well. The greatest potential for showers and thunderstorms will be on Friday into Saturday with localized heavy rainfall possible at times. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... 330 PM Update: While still rather humid across Cape Cod and the Islands, it's otherwise a warm but less humid afternoon across Southern New England, with local sea-breezes near the eastern and southern coasts. Shallow cumulus clouds dot the skies but otherwise mostly sunny skies with temperatures in the 80s to low 90s, though in the upper 70s to low 80s for coastal MA and RI. A 1016 mb high pressure area over the northern portion of Cape Cod Bay will continue to move southeastward into the offshore waters tonight. Clear skies to prevail tonight, though increasing southerly to southwest flow will transport higher dewpoints (mid to upper 60s inland, low 70s toward southern waters) northward later tonight and especially overnight. This should result in re-developing mist/fog and stratus fields initially towards the southern coastal waters and the adjacent Islands toward late evening or midnight, then tending to expand north/northwest into the south coast. Its northwestern extent is a little uncertain given S/SW winds but we could see some expansion of mist/fog toward central and northern RI into SE MA. Lows mid 60s to low 70s. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/... 330 PM Update: Thursday: Any overnight stratus/fog near southeast New England should dissipate by mid morning. Thereafter we are looking at hot and humid weather with temperatures expected to rise quickly under full sun and 850-925 mb warm advection. GFS is on the higher end of this range with 850 mb temps reaching around +21 to +22C. However in looking at the NAM and ECMWF, values are a couple degrees cooler. It really won't make much difference because southwest breezes will also add an element of downsloping and produce air temps in the mid to upper 90s and lower 80s for southeast New England. Will also mention that skies could be rather hazy as HRRR-Smoke model vertically integrated smoke shows a plume of high-altitude smoke from wildfires in the western states. Heat Advisories were maintained with this forecast package with heat indices up to 104F. A few areas have a chance to meet or briefly eclipse excessive heat warning levels, mainly in the Hartford- Springfield portion of the CT Valley and in the Merrimack Valley but confidence wasn't high enough for a large enough area to consider upgrading. Source air for dewpoints tomorrow looks to be across the central and southern Appalachians where current values are in the upper 60s to low 70s. While it still will be rather humid, WSW downsloping will help to reduce dewpoints a little, which cuts into how high heat indices get. There may be either convective cloud debris from convection over NY and/or isolated storms moving into western MA/CT later in the day. There is strong confidence in heat indices between 95 to 104 for most of Southern New England. So the message however is the same when it comes to the heat and we encourage everyone to practice appropriate heat-related precautions such as staying hydrated, taking frequent breaks in air conditioned rooms, and making sure pets and children are not left alone in cars. Thursday Night: Any isolated garden-variety thunderstorms in western MA and western CT should weaken and fizzle shortly after sundown. A warm and muggy night is in store with continued southerly flow. This will also transport tropical low to mid 70s dewpoints northward. Re-developing fog and stratus seems likely as well near south coastal New England given the rising dewpoints. Other than the higher terrain where upper 60s are forecast, lows should only drop into the lower to mid 70s. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... Highlights * Oppressive heat persists into Friday. Heat Advisory remains in effect. * Could still have oppressive heat through the weekend into early next week, but confidence is low/moderate. Additional heat headlines may be needed. * Daily shots for hit/miss showers and storms Friday through the weekend into early next week. Locally heavy downpours possible at times. Friday through Saturday... The Bermuda High will be firmly planted to the southeast of the region through this period. A weak shortwave will lift from the Mid Atlantic through New England by late Saturday. A cool front will slide toward southern New England during this timeframe, but may stall out as it is moving in. Main concern through this period is the oppressive heat. Will see 850 hPa temps of 17-19 degrees Celsius on Friday and 16-19 degrees Celsius on Saturday. More confident in the heat risk for much of the region on Friday as opposed to Saturday at this point, which is why the Heat Advisory has not been extended yet. Main concern is the cold front may be over or just through the region on Saturday. Depending on the fronts location and cloud cover will impact the temps we realize. Did bump up highs on Friday toward the 75th percentile of guidance as deep westerly mixing within the boundary layer should allow most to get into the low/mid 90s. The exception will be along the immediate south coast and Islands where highs top out in the mid/upper 80s. The catch twenty two in this situation is the deep mixing will actually dry the dew points out a bit, so have knocked them down a bit from the default NBM. By late afternoon most will see dew points in the upper 60s to mid 70s. On Saturday given the uncertainty with the front have just stuck with the NBM, which keeps dew points in the low/mid 70s. Still anticipate Heat Index values of 95-103 for much of southern New England on Friday, so Heat Advisories continue. As for Saturday, will see Heat Index values range from roughly 90-100. Some spots may need the Heat Advisory expanded into Saturday. Will have the shot for scattered showers and thunderstorms late Friday through Saturday. At this point the best shot to see any activity will be across the interior. Given the airmass in place could also have some heavy downpours at times. Will have PWATs of 1.75-2+ inches on Friday and 1.8-2+ inches on Saturday. Warm cloud layer depths are roughly 3-4.5 km with a few hundred to roughly 1500 J/kg of MUCAPE. Given the poor deep layer shear am not anticipating strong/severe storms, but there could be some locally heavy downpours with any showers/storms that develop as they will likely be slow moving. Sunday through Tuesday... Have generally stuck with the NBM guidance through this period as it seems reasonable. Will still have the Bermuda High firmly in place to the S/SE of New England through this period. Next deeper trough that lifts in is late on Monday into Tuesday. Anticipate for most that it will be dry and quiet through much of this period, but given the airmass in place will have daily shots of isolated to scattered showers and storms. Best chances will be across the interior. Expect the risk for more widespread activity comes late on Monday into Tuesday or perhaps into Wednesday with that trough lifting in. Still will see the risk for heavy downpours at times given the 1.75-2+ inch PWATs in place over southern New England. Could still be dealing with oppressive heat/humidity late in the weekend into early next week with Heat Index values ranging from 90-104 Sunday/Monday. We may finally turn more seasonable by Tuesday, but confidence at this point is low. && .AVIATION /21Z WEDNESDAY THROUGH MONDAY/... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. 18z TAF Update: Rest of the Afternoon (thru 00z Thu): High confidence. VFR. S/SE winds (more SE near the eastern MA coast) around 5-10 kt. Tonight: High confidence in trends, moderate on extent of fog/stratus. VFR early, then will start to see LIFR mist/fog and stratus develop near ACK and spread northwestward toward at least the South Coast, Cape Cod, MVY and BID. Looks like IFR fog or stratus may advance as far northward as PVD, but how far north is a question given S/SW flow. Most areas along/north of the Mass Pike to stay VFR. Thursday: High confidence. Fog/stratus dissipates by 13z. VFR with hazy skies aloft. Low prob of isolated TSRA in far western New England/Berkshires after 22z. SW winds 8-13 kt gusts to 18-20 kt. Thursday Night: Moderate confidence. Generally VFR. Status/fog may return overnight to the South Coast, Cape and Islands. KBOS...High confidence in TAF. KBDL...High confidence in TAF. Outlook /Friday through Monday/... Friday: Mainly VFR, with local MVFR possible. Chance SHRA, slight chance TSRA. Friday Night: VFR. Chance SHRA, slight chance TSRA. Saturday: VFR. Breezy. Chance SHRA, slight chance TSRA. Saturday Night: VFR. Breezy. Sunday through Sunday Night: VFR. Breezy. Slight chance SHRA, isolated TSRA. Monday: VFR. Breezy. Chance SHRA, slight chance TSRA. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. High confidence. Winds and seas to remain tranquil through the period. Winds become S/SW tonight around 10 kt with fog re-developing near the south coastal waters. SW gusts increase to 15 to 20 kt Thursday, with fog re-developing on the southern waters Thursday night. Seas continue at 3 ft or less for all waters. Outlook /Friday through Monday/... Friday: Winds less than 25 kt. Slight chance of rain showers, isolated thunderstorms. Friday Night: Winds less than 25 kt. Chance of rain showers, slight chance of thunderstorms. Saturday: Winds less than 25 kt. Slight chance of rain showers, isolated thunderstorms. Saturday Night: Winds less than 25 kt. Sunday: Winds less than 25 kt. Seas locally approaching 5 ft. Sunday Night through Monday: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers, isolated thunderstorms. && .CLIMATE... August 4th daily record maximum high temperatures... BOS - 96F  ORH - 95F  PVD - 98F  BDL - 96F  August 4th daily record maximum low temperatures... BOS - 76F  ORH - 72F  PVD - 74F  BDL - 74F  August 5th daily record maximum high temperatures... BOS - 100F  ORH - 96F  PVD - 100F  BDL - 101F  August 5th daily record maximum low temperatures... BOS - 76F  ORH - 73F  PVD - 77F  BDL - 76F  && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Heat Advisory from 11 AM Thursday to 8 PM EDT Friday for CTZ002>004. MA...Heat Advisory from 11 AM Thursday to 8 PM EDT Friday for MAZ002>021-026. RI...Heat Advisory from 11 AM Thursday to 8 PM EDT Friday for RIZ001>007. MARINE...None. && $$ SYNOPSIS...BL/Loconto NEAR TERM...Loconto SHORT TERM...Loconto LONG TERM...BL AVIATION...BL/Loconto MARINE...BL/Loconto CLIMATE...