000 FXUS61 KBOX 041723 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 123 PM EDT Thu Aug 4 2022 .SYNOPSIS... Heat and humidity will be the main weather story right into early next week. The heat and humidity will peak today and Friday, with near record high temperatures today as well. The greatest potential for showers and thunderstorms will be Friday into Saturday, with localized heavy rainfall possible at times. It may be Tuesday before this heat and oppressive humidity finally breaks in a significant way. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 1 PM Update Well, it's hot out. Boston is sitting just a degree below the record for the day, at 95F, with several hours of peak heating yet to come. Importantly, the "feels like" temperature (heat index) has risen to 100 or above for many locations across southern New England. As the heat increases instability has risen with it; SPC mesoanalysis shows surface based CAPE values increasing to 1,500-2,000 J/kg. Shear is extremely weak, however, so while scattered showers and thunderstorms are possible in northwest MA this afternoon/evening they should be of the garden variety (non-severe). Previous Discussion... GOES night fog channel still showing a fair bit of patchy fog and low stratus across the south coast, Cape, and Islands. However it appears that it has been starting to become less widespread over the last hour or so. Short-term models suggest fog and low stratus lifting over the next couple of hours after sunset. Have maintained patchy fog through about 14Z. Otherwise, previous forecast remains on track and no major changes have been made. 3 AM Discussion Late night stratus and fog was readily apparent on the GOES east fog product. So far, this as constrained to be across portions of the outer Cape and Nantucket, with a smaller area just getting started across the Connecticut River valley. These areas should dissipate shortly after sunrise. Then the story becomes mostly about heat and humidity. With essentially full sunshine and near oppressive humidity, expecting heat index values to each 90 degrees by mid to late morning, and be near 100 degrees in many place for most of this afternoon. As such, Heat Advisories continue as posted. A few areas still 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 remains too low for a large enough area to consider upgrading. So the message remains the same when it comes to the heat. 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 for any length of time. As for shower and thunderstorms chances today, the greatest chance will be across western MA. Despite the heat and humidity, it appears there will just be too much dry air towards the mid levels. The synoptic forcing is also not the greatest, with a weak pre-frontal trough. Timing will be everything. At this time, expecting showers and thunderstorms to arrive a little before sunset, which will limit the chances. Expecting any storms to weaken after sunset. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... Any isolated garden-variety thunderstorms across western MA and western CT should weaken and fizzle shortly after sundown. A warm and muggy night is in store with continued southerly flow. 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. Friday will be more favorable for showers and thunderstorms as a weak cold front and mid level shortwave approaches of region. This front may linger near the Route 2 corridor by late evening. Temperatures are expected to be slightly less, due to more cloud cover, but dew points should be even higher to compensate. Thus, Heat Advisories will continue. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Highlights * Oppressive heat and humidity continues into the weekend. Additional heat headlines will likely be needed. * Chance for scattered showers and thunderstorms on Saturday with the potential for localized heavy rainfall. * Hot/humid weather continues into early next week before temperatures moderate by middle of next week. Saturday Bermuda High holds strong this weekend and continues to support a deep southwest flow pattern into southern New England. This will continue to result in above normal temperatures and humidity. Additional heat headlines, or perhaps an extension of current heat headlines may be needed in some locations. Heat indices expected to range in the 95-100 degree range or perhaps higher on Saturday and Sunday. Saturday will be a bit unsettled as a weak-upper level short- wave will bring some cloudiness and a chance for isolated showers and thunderstorms. While there will be sufficient instability for convection, little to no deep-layer shear will suppress severe thunderstorm development. However, abundant deep layer moisture and weak boundary layer winds could support slower moving thunderstorms with heavy rainfall. This will provide a chance for some isolated areas to receive some much needed rainfall. Unfortunately this wouldn't be enough to even put a dent in the current precipitation deficits and ongoing drought conditions. Temperatures on Saturday "only" expected to break into the upper 80s and low 90s, but dewpoints in the low to mid 70s will continue to support heat indices well over 95 on Saturday afternoon. Drier low-level air filters in behind the upper-level short- wave on Sunday. Drier air will support less cloud cover and more solar radiation. Thus we can expect Sunday to be the warmest of the two days this weekend with air temperatures getting into the low to mid 90s. Deep mixing of drier air to the surface will support lower dewpoints in the upper 60s to low 70s. This will translate to heat indices from 95 to 100 on Sunday afternoon. Monday through Wednesday Consensus among model guidance has been for the deep southwest flow pattern and hot/humid conditions to continue into at least Monday. By early to mid next week, there are signals for a trough to settle over the eastern CONUS. This would help bring temperatures back down closer to normal. Additionally, model guidance has suggested a frontal passage with the associated trough that would support showers and thunderstorms sometime in the Tuesday to Wednesday time frame. Confidence in timing of the front and associated trough are low at this time. && .AVIATION /17Z THURSDAY THROUGH MONDAY/... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. This afternoon...High confidence. VFR save for ACK where fog and low stratus and looking more likely to hold on throughout the day. Low prob of isolated TSRA across far western New England/Berkshires after 22Z. SW winds 8-13 kt with gusts to 18-20 kt. Tonight...Moderate confidence. Generally VFR. Stratus and fog likely return to the South Coast, Cape and Islands. Friday...Moderate confidence. Areas of LIFR to start the day. Generally VFR. Greater risk for showers and thunderstorms, especially across the western 2/3 of southern New England. Friday night...Moderate confidence. Mainly VFR. MVFR/IFR CIGS possible for some, mainly along the south coast, Cape, and islands. SHRA and TSRA come to an end after sundown. KBOS...High confidence in TAF. KBDL...High confidence in TAF. Outlook /Friday Night through Monday/... Friday Night: VFR. Slight chance SHRA, isolated TSRA. Saturday: VFR. Breezy. Slight chance SHRA, isolated TSRA. Saturday Night through Sunday Night: VFR. Breezy. Slight chance SHRA. Monday: VFR. Breezy. Chance SHRA. && .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 relatively tranquil through Friday. Areas of fog this morning, especially east of Cape Cod and Nantucket. SW gusts increase up to 20 kt today, with fog re- developing on the southern waters tonight. Any fog should dissipate during Friday morning. Outlook /Friday Night through Monday/... Friday Night through Saturday: Winds less than 25 kt. Slight chance of rain showers, isolated thunderstorms. Saturday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers. Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft. Sunday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers. Monday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. && .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...Air Quality Alert until 11 PM EDT this evening for CTZ002. Heat Advisory until 8 PM EDT Friday for CTZ002>004. MA...Air Quality Alert until 11 PM EDT this evening for MAZ005>007- 010>012-014. Heat Advisory until 8 PM EDT Friday for MAZ002>021-026. RI...Heat Advisory until 8 PM EDT Friday for RIZ001>007. MARINE...None. && $$ SYNOPSIS...Belk/RM NEAR TERM...Belk/BW/RM SHORT TERM...Belk LONG TERM...RM AVIATION...Belk/BW/RM MARINE...Belk/RM CLIMATE...