textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes to the forecast.

KEY MESSAGES

- Dangerous heatwave continues through this afternoon and Independence Day. Heat indices of 100-110 degrees expected this afternoon, and 95-100+ on Independence Day. - A welcomed break from the heat with cooler and more seasonable temperatures returning for the first half of next week. There is also some low confidence potential for some much need rain may occur in the late Sunday though Tuesday time frame.

DISCUSSION

KEY MESSAGE 1...Dangerous heatwave continues through this afternoon and Independence Day. Heat indices of 100-110 degrees expected this afternoon, and 95-100+ on Independence Day.

Stout summer ridge continues to spin over the Carolinas and VA. Dangerous heat is ongoing across New England. Hourly METAR observation at KBOS registered a temperature of 100F at 2:54 PM EDT, marking two consecutive days of triple digits.

Heat indices across the region are hanging well in the 100-110 range. Extreme Heat Warning continues until 8 PM EDT Saturday for all of southern New England except for the Cape/Islands (Heat Advisory in those parts). Heat indices Saturday will range from 95F to at or above 100F during the afternoon.

Meanwhile, isolated to scattered convection is popping up over western and southern NY. These storms may try to make their way into western MA late this evening into the overnight hours, but it'll get harder after sunset with instability dropping off. Convection chances look slightly better Saturday afternoon and evening with a cold front approaching, but guidance has come down on the coverage with each forecast update, so this may not be as much of an issue as once thought. Good news for Independence Day festivities. Stay cool and hydrated!

KEY MESSAGE 2...A welcomed break from the heat with cooler and more seasonable temperatures returning for the first half of next week. There is also some low confidence potential for some much need rain may occur in the late Sunday though Tuesday time frame.

There is high confidence that temps will cool down and return to more seasonable readings thru the middle of next week. Some of that is due to modeled cloud cover and rain, but even in the absence of those factors 850 mb temps around +15C would give surface temps in the 80s rather than the 90s to 100 degrees we have been seeing. In addition there is pretty good consensus that dewpoints may even fall back into the 50s for some parts of the Worcester Hills and Merrimack Valley. So overall much more comfortable temps are forecast in the extended.

The rainfall chances on the other hand remain uncertain. There is growing ensemble support for at least a widespread light rain event, which is much needed. The NBM 10th percentile QPF is still zero for the forecast area, but 25th percentile values have climbed to 0.10 to 0.05 inches from southwest to northeast. 75th percentile QPF has also increased to near 1 inch, mainly across western Mass. So I don't feel that likely to categorical PoP is unreasonable at this time. There does appear to be a bit of a bimodal structure with QPF across ensemble guidance. One less than 0.50 inches, and another at or above 1 inch. Around BDL about 25 percent of members are greater than 1 inch QPF, vs around 15 percent as you move towards LWM. It is also notable that many of these rainy member are from the ECMWF ensemble. That's why I'm leaning more light rain at this time than a true soaker.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

Forecaster Confidence Levels...

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

18z TAF Update...

Today through Independence Day...High confidence.

VFR conditions will dominate this afternoon 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 kept in the PROB30 TSRA at KBDL between 01 and 05Z tonight. Shower and storm activity should decrease as any sort of storms move eastward. Threw in another PROB30 group at KBDL to address potential convection concerns heading towards 00Z Sunday.

Westerly winds may gust to 20+ knots later this 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 Wednesday/...

Sunday: VFR. Slight chance SHRA.

Sunday Night: VFR. Chance SHRA.

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

Monday Night: MVFR/IFR conditions possible. SHRA likely, slight chance TSRA.

Tuesday: VFR. Breezy. Chance SHRA, chance TSRA.

Tuesday Night: VFR. Chance SHRA.

Wednesday: VFR. Slight chance SHRA.

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 still look to remain below Small Craft Advisory thresholds this afternoon through Independence Day. However, some 20+ knot wind gusts near shore this afternoon will result in some chop in some near shore sounds and Bays. A similar story is in store for Saturday.

Outlook /Saturday Night through Wednesday/...

Sunday: Winds less than 25 kt. Slight chance of 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. Rain showers likely, chance of thunderstorms.

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

Tuesday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers, slight chance of thunderstorms.

Wednesday: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers.

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 until 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 until 11 PM EDT this evening for RIZ003-004- 006>008. MARINE...None.