textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes to the forecast.

KEY MESSAGES

- Dangerous heatwave continues today and Independence Day. Heat indices of 100-110 degrees today & 95-100+ on Independence Day.

- Isolated severe weather potential late today/tonight. Greatest risk interior MA/CT. Main risk will be isolated pockets of damaging straight line wind gusts.

- Low risk of severe weather and a few t-storms on Independence Day, but greatest risk for more widespread activity right now looks to be to our southwest. - Relief from the heat with cooler and more seasonable temperatures returning for the first half of next week. Also...the potential for some much need rain may occur in the late Sun-Tue time frame but that remains to be seen.

DISCUSSION

KEY MESSAGE 1...Dangerous heatwave continues today and Independence Day. Heat indices of 100-110 degrees today & 95-100+ on Independence Day.

Near record high temperatures are once again on tap for the region today. An anomalous airmass remains in place across southern New England today with 925T on the order of +27C to +29C. This coupled with a very warm start, mostly sunny skies and westerly flow will result in temperatures soaring today. High temperatures should top out in the 97 to 103 degree range and once again challenge records. This combined with high dewpoints will result in dangerous heat indices of 100 to 110 degrees. Even across the Cape highs should reach into the 90s with heat indices of 95 to 105 degrees given westerly flow.

There will be little relief tonight as low temperatures only drop into the 72-77 degree range and probably only the upper 70s to near 80 in the urban heat island of Boston.

Independence Day will still feature dangerous heat and humidity. Height falls and somewhat lower 925T will likely prevent triple digit heat on the 4th. Nonetheless...we still expect highs in the 93 to 99 degree range in most location. This will bring heat indices into the 95-100+ degree range and heat headlines remain in effect.

KEY MESSAGE 2...Isolated severe weather potential late today/tonight. Greatest risk interior MA/CT. Main risk will be isolated pockets of damaging straight line wind gusts.

The other concern will be the convective potential mainly late today/tonight. This portion of the forecast remains tricky given lack of large scale forcing but impressive instability.

We can not rule out a late afternoon isolated t-storm or two...But high resolution CAMs indicated the greatest risk may come this evening into the overnight hours. They tend to want to develop a few thunderstorms to our west and north. Given ample instability persisting well into tonight coupled with 0 to 6 KM shear of 30 to 40 knots...this activity will be capable of surviving into our region. The greatest risk for this activity appears to be across interior MA and CT where forcing is a bit more prevalent. This is also indicated by the NADOCAST and CSU machine learning guidance. This will again be more of a mesoscale/nowcast type of forecast...But the potential for isolated severe weather exists again tonight. Low risk this potential could end up a bit more widespread if a complex of storms were to organize...which always has to be a concern in this type of environment. But again the lack of overall synoptic scale forcing will be a limiting factor.

KEY MESSAGE 3...Low risk of severe weather and a few t-storms on Independence Day, but greatest risk for more widespread activity right now looks to be to our southwest.

There will a low risk for severe weather on Independence Day as a cold front works south across the region. At this time...most of the CAMs and machine learning guidance indicate that the greatest risk for more widespread thunderstorms and severe weather will be to our southwest. This is where the best instability will reside along with better forcing/shortwave energy. In our region...winds shifting to the NW early in the day may limit convergence and forcing for more widespread convection. Nonetheless...given temperatures soaring well into the 90s coupled with height falls there will be the risk for a few thunderstorms and a low risk severe weather.

KEY MESSAGE 4...Relief from the heat with cooler and more seasonable temperatures returning for the first half of next week. Also...the potential for some much need rain may occur in the late Sun-Tue time frame but that remains to be seen.

Long range ensemble guidance is in good agreement in the upper level ridge breaking down and a tendency towards lower heights next week. This will bring an end to the extreme heat, with readings more in line with typical summer. A wave of low pressure will also be approaching from the west. This may bring a period of much needed over running rain to parts of the region sometime in the Sun night to Tue time frame. Confidence in these setups is low this time of year given mesoscale convective factors and limited baroclinicity. Nonetheless...a period of two of much needed rainfall is possible for the start of the next work week.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

Forecaster Confidence Levels...

Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.

12z TAF Update...

Today through Independence Day...High confidence.

VFR conditions will dominate today through Independence Day. Low chance for fog/stratus formation across the Islands, particularly ACK, but confidence too low to include in the TAF. Otherwise...isolated thunderstorms will be possible mainly tonight and perhaps again on Independence Day. Best chance for a late evening thunderstorm today will be across western terminals, so introduced PROB30 TSRA at BDL between 01 and 05Z tonight. Shower and storm activity should decrease as any sort of storms move eastward. Later shifts should continue to monitor.

Westerly winds may gust to 20+ knots later this morning and afternoon with a few gusts near 25 knots possible. WInds shift to the NW on Independence Day with some 20 knot gusts.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...Moderate confidence in TAF, uncertainty in thunderstorm potential and timing

Outlook /Saturday Night through Tuesday/...

Saturday Night: VFR. Isolated SHRA, isolated TSRA.

Sunday: VFR. Isolated SHRA.

Sunday Night: VFR. Chance SHRA.

Monday: Mainly VFR, with local MVFR possible. Chance SHRA, slight chance TSRA.

Monday Night: Mainly VFR, with areas MVFR possible. Chance SHRA, chance TSRA.

Tuesday: Mainly VFR, with areas MVFR possible. Breezy. Chance SHRA, slight chance TSRA.

MARINE

Forecaster Confidence Levels...

Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.

Today through Independence Day...High confidence.

Winds/seas should remain below small craft advisory thresholds today through Independence Day. However...some 20+ knot wind gusts near shore later this morning and afternoon will result in some chop in some near shore sounds and Bays.

Outlook /Saturday Night through Tuesday/...

Saturday Night: Winds less than 25 kt. Scattered rain showers, isolated thunderstorms.

Sunday: Winds less than 25 kt. Isolated rain showers.

Sunday Night: Winds less than 25 kt. Chance of rain showers.

Monday: Winds less than 25 kt. Chance of rain showers, slight chance of thunderstorms.

Monday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers, chance of thunderstorms.

Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers, slight chance of thunderstorms.

CLIMATE

Record High Temperatures:

July 3: KBOS: 102/1911 KBDL: 102/1966 KPVD: 98/2002 KORH: 96/1911

July 4: KBOS: 104/1911 KBDL: 99/1911 KPVD: 99/1919 KORH: 102/1911

Record High Minimum Temperatures:

July 3: KBOS: 80/2002 KBDL: 73/2018 KPVD: 78/2002 KORH: 72/2002

July 4: KBOS: 77/2002 KBDL: 74/2018 KPVD: 77/2002 KORH: 73/2018

BOX WATCHES/WARNINGS/ADVISORIES

CT...Extreme Heat Warning until 8 PM EDT Saturday for CTZ002>004. MA...Extreme Heat Warning until 8 PM EDT Saturday for MAZ002>021- 026. Air Quality Alert from 11 AM this morning to 11 PM EDT this evening for MAZ020>024. Heat Advisory until 8 PM EDT Saturday for MAZ022-023. RI...Extreme Heat Warning until 8 PM EDT Saturday for RIZ001>007. Air Quality Alert from 11 AM this morning to 11 PM EDT this evening for RIZ003-004-006>008. MARINE...None.