Lexington, Massachusetts, USA
000 FXUS61 KBOX 021932 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 332 PM EDT Tue Aug 2 2022 .SYNOPSIS... Heat and humidity will be the main weather story right through the weekend and into early next week. The heat and humidity will peak on Thursday and Friday with near record high temperatures and oppressive heat indices as well. The greatest potential for showers and thunderstorms will be on Friday with even some localized heavy rainfall possible. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... 330 PM Update: Very warm to hot temperatures and humid dewpoints (upper 60s to mid 70s!) continue as of mid-afternoon. Some modest relief is anticipated later tonight as a cool front moves eastward. In the interim, scattered showers and thunderstorms continue to develop on a pre-frontal trough moving through central MA into eastern/east- central CT, with more shallow convection tied to the cold front now moving into the western Berkshires and eastern NY. Ongoing storms have been slow to develop given weak mid-level lapse rates that are at less than moist-adiabatic levels. A few have produced several instances of lightning across western MA along with short-lived, localized downpours. Environment is very much a weak shear/pulse environment with cores developing, then dissipating within about a half hour or so of time. Surface based CAPE values range from 1500- 2000 J/kg, and while downdraft CAPE values are generally 500 J/kg or less across most of MA, they are nearly double that across CT and RI into SE MA. Will have to watch CT-RI and SE MA as widely scattered cellular storms move eastward through sundown for locally stronger wind gusts, possible isolated SVR, but anticipate most convection to remain at sub-severe levels with lightning, brief downpours and sub- severe gusts. Cool front moves through tonight, which should bring clearing skies and a drop in dewpoints into the low-mid 60s especially in the interior. Across the Cape and Islands, will still be quite humid with dewpoints upper 60s/locally near 70F. BUFKIT soundings showing radiation inversion developing near the South Coast, Cape and Islands with conditions favoring stratus and fog development for the overnight hrs. Lows mid 60s to lower 70s. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... 330 PM Update: Wednesday through Wednesday Night: High pressure ridges into SNE as cool front moves offshore. Still will be quite warm but northerly flow as well as heating/mixing of drier air aloft should support lower to middle 60s dewpoints for most. So a little less humid, but plenty of sun and 850 mb temps in the mid teens C range should support highs at least as warm as today with mid 80s to low 90s in the interior and coastal plain. Should see local sea-breezes develop which will keep coastal areas a couple degrees cooler. Winds will shift from N/NW to S/SW as high pressure moves offshore later in the day. Dewpoints rise again back to uncomfortable levels (upper 60s/low 70s) later Wed aftn into Wed night. As indicated by several guidance sources and the 12z HREF, developing fog/stratus near the South Coast/Cape and Islands looks to expand northwestward; it's not clear how far north and west fog may make it but could expand at least to the I-95 corridor and potentially into eastern CT/southern Worcester County. Lows mid/upper 60s to lower/mid-70s. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Highlights... * Oppressive Heat & Humidity Thu and Fri with Heat Headlines Posted * Heat Indices in 100 to 105 degree range Thu & Fri * Main threat for showers & thunderstorms will be Fri with localized heavy rainfall possible * Heat and humidity continue this weekend into early next week with a few showers & thunderstorms possible Details... Thursday and Friday... Excellent model agreement in oppressive heat and humidity for both Thursday & Friday. The 500 MB height fields are on the order of 590 to 594 DM which is outside the ECMWF climatological database. That is an excellent signal for an anomalous weather event; in this case being oppressive heat & humidity. 850T will be on the order of +19C to +21C over this time period along with southwest flow. Plenty of sunshine Thursday with good mixing should yield near record high temps in the 96 to 101 degree range. Dewpoints well into the 60s should bring Heat Indices on the order of 100 to 105 degrees. By Friday...the surface cold front will be dropping down from the north. While high temps may end up a few degrees lower than Thu; the dewpoints will be higher as moisture should pool along the cold front likely in the 70 to 75 degree range. High temperatures should still come up well into the 90s and it is not out of the question that a few spots hit 100 on Friday. Heat Indices should be on the order of 100 to 105 degrees. Given the above we have opted to issue Heat Advisories for our entire region...except for the Cape and Islands. We eventually may need to include the Cape in the Heat Advisory for Friday. Lastly, given the potential for those very high dewpoints Friday...a few spots may see Heat Indices on the order of 105 to 107 so an upgrade to an Excessive Heat Warning is not out of the question. Either way oppressive heat and humidity is on tap for the region. Dry weather should prevail for much of Thursday given lack of synoptic scale forcing/deeper moisture. However, a few showers & t-storms can not be ruled out late Thu across our western zones. However, the main threat for scattered showers and thunderstorms will be on Friday as the cold front drops south into our region. The severe weather threat will be rather limited by weak wind fields. However, Pwats of 2+ inches coupled with a slowing frontal boundary may result in localized heavy rainfall. This Weekend Into Early Next Week... Upper level ridging will remain anchored off the mid-Atlantic coast. This will result in continued above normal height fields and temperatures as well. In addition...this setup will result in quite a bit of humidity too. Highs in the upper 80s to the middle 90s along with humid conditions may result in the need for additional Heat Headlines. Perhaps some relief arrives by Tuesday. There also will be the potential for a few showers/t-storms at times, but not expecting a washout with dry weather dominating. && .AVIATION /19Z 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 /Thursday through Sunday/... Thursday: VFR. Breezy. Thursday Night: Mainly VFR, with local MVFR possible. Breezy. Slight chance SHRA, isolated TSRA. Friday: Mainly VFR, with areas MVFR possible. Breezy. Chance SHRA, slight chance TSRA. Friday Night: Mainly VFR, with areas MVFR possible. Chance SHRA, slight chance TSRA. Saturday: Mainly VFR, with areas MVFR possible. Breezy. Slight chance SHRA, isolated TSRA. Saturday Night: Mainly VFR, with local MVFR possible. Breezy. Sunday: Mainly VFR, with areas MVFR possible. Breezy. Slight chance SHRA, isolated TSRA. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Overall high confidence. Winds and seas to stay at sub-SCA levels through the period. SW winds near 20 kt late today shift to W and decrease early tonight, then becoming NW around 10 kt. Biggest concerns for tonight are potential for isolated/scattered thunder early tonight, then fog with significant reduction in visby overnight near the south coastal/nearshore waters. NW winds 10 kt shift to onshore with sea-breeze development Wed afternoon; then will trend S/SW Wed night with fog re-developing. Seas 3 ft or less all waters. Outlook /Thursday through Sunday/... Thursday through Thursday Night: Winds less than 25 kt. Friday: Winds less than 25 kt. Chance of rain showers, slight chance of thunderstorms. Friday Night: Winds less than 25 kt. Slight chance of rain showers, isolated thunderstorms. Saturday: Winds less than 25 kt. Saturday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers, isolated thunderstorms. && .CLIMATE... August 4th daily record maximum high temperatures... BOS - 96F [1928] ORH - 95F [1944] PVD - 98F [1944] BDL - 96F [1944] August 4th daily record maximum low temperatures... BOS - 76F [1930] ORH - 72F [2002] PVD - 74F [2010] BDL - 74F [2006] August 5th daily record maximum high temperatures... BOS - 100F [1955] ORH - 96F [1944] PVD - 100F [1944] BDL - 101F [1955] August 5th daily record maximum low temperatures... BOS - 76F [1938] ORH - 73F [1938] PVD - 77F [1938] BDL - 76F [1938] && .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...Loconto/Frank NEAR TERM...Loconto SHORT TERM...Loconto LONG TERM...Frank AVIATION...Loconto/Frank MARINE...Loconto/Frank CLIMATE...Simpson
Meta data:
ID: 7421835f-51e2-4843-9e5c-d214b5cc82cb
Link:
https://api.weather.gov/products/7421835f-51e2-4843-9e5c-d214b5cc82cb