000 FXUS61 KBOX 021731 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 131 PM EDT Tue Aug 2 2022 .SYNOPSIS... Becoming hot, muggy, with brief widely scattered showers and isolated thunderstorms develop ahead of an approaching cold front Tuesday afternoon. Dry and very warm again Wednesday albeit noticeably cooler along portions of the immediate coast. This will be followed by near record high temps and oppressive humidity Thursday some of which may linger into Friday. The threat for scattered showers and thunderstorms increases Friday and may persist at times this weekend into next Monday, but a washout is not expected. Above normal temperatures continue as well, but not at the potential record breaking levels of Thursday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 1030 AM Update: Earlier stratus has eroded in entirety giving way to full sun and increasingly more humid weather on SW breezes. May have to consider raising high tempratures a couple degrees in later updates especially eastern MA/RI away from the coastline. Pre-frontal trough trailing through central NY should be a focus for widely scattered SHRA/TSRA this afternoon, particularly in the interior. Expect any convection to be very pulse-like in character given weak low to mid-level wind fields. CAPE values tend to vary between the drier RAP at around 1000-1500 J/kg (due to lower dewpoints from a mixing PBL), while the NAM doesn't mix its surface dewpoints (a known bias) and contributing to 2000+ J/kg of CAPE. Suspect the RAP may be closer to reality, leading to generally garden-variety, perhaps SPSable type storms with gusty outflow and likely development of cold pools/outflow for new storms to develop upon. Think the main risk for scattered TSRA is across interior MA/CT, but do have to watch for the Route 6 corridor in CT-RI where both RAP and NAM show higher CAPEs and potentially greater storm vigor around 22-00z. Perhaps a stronger, marginally SVR storm in this corridor with gusty winds. Downdraft CAPEs are also closer to the 800-1000 J/kg range in this general area too, which can be a good predictor of strong gusts in weak shear/pulse-storm environs. Previous Discussion: Rather expansive area of stratus was located over the eastern 2/3 of southern New England this morning. This stratus should dissipate rather quickly after sunrise, only to be replaced with higher clouds later today. Expecting another rather warm and humid day today, with the risk for some showers and a few thunderstorms as a cold front approaches. Given the timing of this front, these are more likely across the western half of southern New England. There is not a lot of shear to organize to modest CAPE values of 1,000-1,500 J/kg. Thus, not expecting a widespread severe weather event today, but cannot rule out a strong storm or two. These storms should weaken after sunset. Expecting max temperatures to be about 5 degrees higher today due to a persistent southwest wind ahead of a cold front. This will also lead to much higher dewpoints. At this time, thinking we will stay just under the threshold for a Heat Advisory, but it will be close. This will need to be monitored by the day shift, as a subtle increase of only a degree or two in either temperatures or dew points from the current forecast could make all the difference. If you must work outdoors today, please drink plenty of fluids and take frequent breaks out of the sun. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... A cold front will move offshore late this evening and overnight, leading to less humid conditions Wednesday. A few locations across eastern MA could also be slightly cooler, with seabreezes developing by afternoon. Across the interior, max temperatures should be similar to today. Once showers dissipate this evening, rain-free weather should persist through Wednesday. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Highlights * Potentially record setting heat on Thursday with heat indices over 100. * Oppressive humidity Friday with scattered showers and thunderstorms Friday afternoon. * Above normal temperatures continue this weekend Thursday and Friday Deep southwest flow is forecast to advect an anomalously warm and humid air mass into southern New England for Thursday and Friday. Temperatures at 850 hPa are expected to rise above 20 Celsius on Thursday. With persistent 15-20 knot southwest winds expected in the boundary layer, we can expect diurnal mixing to 850 hPa which will support high temperatures in the upper 90s to perhaps 100 degrees across much of interior southern New England. Lower temperatures forecast across southeastern MA and the south coast in the upper 80s to low 90s. Dewpoints in the upper 60s to low 70s will result in heat indices in the low 100s at some locations. Heat advisory headlines are likely at this time. Dry air in the mid-levels will keep the region dry on Thursday afternoon, but a spot shower/thunderstorm Thursday night can't be ruled out across the western zones. Deep southwest flow continues into Friday and supports surging dewpoints into the low to mid 70s. Temperatures remain above normal, but increasing cloudiness Friday afternoon should limit high temperatures to the upper 80s and low 90s. Nonetheless, the oppressive humidity will have us flirting with heat advisory criteria with heat indices in the upper 90s likely. Weak upper-level disturbance and surface frontal boundary moves across the region late Friday. This will bring the potential for a few thunderstorms and some much needed rainfall across portions of southern New England. Weak boundary layer winds and PWATs close to 150 percent of normal will be supportive of locally heavy downpours. Not expecting any severe storms to develop as both deep-layer shear and synoptic forcing for ascent will be very limited. This Weekend Southwest flow continues to support above normal temperatures this weekend. No strong signals for advisory level heat this weekend, but still hot with highs in the upper 80s to low 90s. Dewpoints remain elevated in the low to mid 70s making for some very uncomfortable sleeping weather. Can't rule out a few isolated convective showers or thunderstorms during the afternoon. Next Week Consensus among long-term models and ensembles if for the southwest flow pattern and above normal temperatures to continue into Monday. Beyond Monday there is a signal for a frontal passage early next week that would bring the next opportunity for substantial rainfall. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... 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 Wed): High confidence. VFR, though SCT SHRA/TSRA develops in western MA/CT and moves ESE between 18-00z. Main risk is the interior airports and into PVD; less clear if BOS or Cape airports see this activity. Since storm type should be more cell type storms, have carried VCSH in for airports with greatest risk and will TEMPO for a more obvious risk. Storms capable of brief downpours with visby reduction to MVFR-LIFR, lightning and brief strong wind gusts. SW winds around 10-15 kt, gusts to 22-25 kt with shift to W late for the western airports. Tonight: High confidence. VFR for most; LIFR fog/stratus re-develops between 00-03z at ACK and expands northward towards Cape airports. W winds 5-8 kt shift to NW by daybreak. Wednesday and Wednesday Night: High confidence. VFR, with stratus/fog for Cape airports/ACK diminishing by mid morning. Probable sea-breezes for the coastlines ~15-17z, otherwise winds become WSW 4-8 kt late. Continued VFR for most, though re-developing mist/fog and stratus for the evening for at least the Cape and Islands but also possible towards SE MA and PVD. S/SW winds 4-8 kt. KBOS...High confidence in TAF. SHRA/TS possible 22-00z but too low confidence to include in TAF. Will tempo if a direct hit looks imminent. KBDL...High confidence in TAF. Outlook /Wednesday Night through Saturday/... Wednesday Night: VFR. Thursday: VFR. Breezy. Thursday Night: Mainly VFR, with local MVFR possible. Breezy. Slight chance SHRA. Friday: Mainly VFR, with areas MVFR possible. Chance SHRA, slight chance TSRA. Friday Night: Mainly MVFR, with areas VFR possible. Chance SHRA, slight chance TSRA. Saturday: Mainly MVFR, with areas VFR possible. Breezy. Slight chance SHRA. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Monday evening into Tuesday night...High confidence. Poor visibility early this morning will improve during the day. A cold front brings another chance for showers and slight chance for thunderstorms this afternoon and early evening. A cold front will move across the waters tonight, with fair conditions expected Wednesday. Outlook /Wednesday Night through Saturday/... Wednesday Night through Thursday: Winds less than 25 kt. Thursday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers. Friday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers, slight chance of 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. && .CLIMATE... August 4th daily record maximum high temperature. BOS - 96F  ORH - 95F  PVD - 98F  BDL - 96F  August 4th daily record maximum low temperature. BOS - 76F  ORH - 72F  PVD - 74F  BDL - 74F  && .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...Belk/RM NEAR TERM...Belk/Loconto/RM SHORT TERM...Belk LONG TERM...RM AVIATION...Belk/Loconto/RM MARINE...Belk/Loconto/RM CLIMATE...