textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes with this forecast update.

KEY MESSAGES

- Significant heat and humidity continues for the rest of this afternoon and evening. Scattered showers and thunderstorms possible through the evening. A storm or two may produce strong to damaging wind gusts.

- Cooler temperatures are forecast for the first half of the week. Temperatures have the potential to be much cooler as a soaking rain is becoming more likely in the late Sunday through Tuesday time frame.

DISCUSSION

KEY MESSAGE 1...Significant heat and humidity continues for the rest of this afternoon and evening. Scattered showers and thunderstorms possible through the evening. A storm or two may produce strong to damaging wind gusts.

Hot and humid conditions ongoing across southern New England, with temperatures and heat indices alike well into the mid-to- upper 90s. Heat Advisory in effect for northern CT, majority of MA, and RI until 8 PM EDT this evening.

Elsewhere, convection is continuing across upstate NY and central/south VT. This activity is trying to "split the gap" between southern MA/northern CT/RI and northeastern MA. The northeastern MA solution is winning at the moment, with a cluster of storms crossing over into parts of Essex County as of 2:45 PM EDT.

High-resolution guidance has been rather ugly in trying to picture how the rest of this afternoon and evening unfolds. Overall, ultimately think that this splits up into two different "events" (such that they are): this afternoon between now and 5-6 PM, and another between 8-11 PM. Firework shows this evening could be dicey at times, particularly for eastern MA. Showers and storms move offshore by 2 AM EDT at the latest.

Cold front due before sunrise Sunday morning, where a wind shift from the NNE will kick in, veering to the ENE throughout the day. Highs much more reasonable in the low-to-mid 80s.

KEY MESSAGE 2...Cooler temperatures are forecast for the first half of the week. Temperatures have the potential to be much cooler as a soaking rain is becoming more likely in the late Sunday through Tuesday time frame.

High confidence remains that temps will cool down and return to more seasonable summer readings thru next week. For starters 850 mb temps are forecast to cool to between +12 to +15C. That will be enough to get temps back into the 80s on its own. Dewpoints are also forecast to cool down as well, which will make things feel more comfortable than it has been.

Temps may also be much cooler if we can get substantial cloud cover and rain into the forecast area. Overnight guidance has doubled the number of ensemble members with more than 1 inch of QPF. Now nearly all of the ECMWF ensemble members are in that camp around BDL, with roughly half of members greater than 1 inch as you move northeast to BOS. However the GEFS has also moved on board with roughly half of all members at or above 1 inch QPF across southern New England. Deterministic model guidance is forecasting mid level warm advection to produce an area of frontogenesis, giving this a little more synoptic support for rainfall than the more typical scattered summertime convective pattern to rainfall. NBM PoP looks pretty good at this range, with categorical across the southwestern forecast area and likely farther northeast, given the timing uncertainty. Rain could begin as early as late Sun night and continue thru Tue. Right now 6 hr FFG across much of the forecast area is at least 3 inches, so I am not anticipating flooding unless we see guidance really start to ramp up QPF numbers.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

Forecaster Confidence Levels...

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

00Z TAF Update...

Today through Sunday...High confidence.

VFR conditions dominate through Sunday except during any TSRA. Storms should move off the northeastern shore by 01-02z, but moving into western CT/MA 00-02z. Storms should move eastward off the Cape/Islands by 06Z at the latest tonight. Frontal passage expected before sunrise Sunday morning, where a wind shift from the NNE is expected. Winds will continue to veer towards the ENE throughout the day. KBOS Terminal...Moderate confidence in TAF. Uncertainty surrounding thunderstorm coverage and duration.

KBDL Terminal...Moderate confidence in TAF. Uncertainty surrounding thunderstorm coverage and duration.

Outlook /Monday through Thursday/...

Monday: Mainly VFR, with local IFR possible. Breezy. SHRA likely, slight chance TSRA.

Monday Night: Mainly MVFR, with local IFR possible. Breezy. SHRA likely, slight chance TSRA.

Tuesday: Mainly VFR, with local IFR possible. Breezy. SHRA likely, chance TSRA.

Tuesday Night: Mainly VFR, with local IFR possible. Breezy. Chance SHRA, slight chance TSRA.

Wednesday: VFR. Slight chance SHRA.

Wednesday Night: VFR.

Thursday: VFR. Breezy.

MARINE

Forecaster Confidence Levels...

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

Today through Sunday...High confidence.

A relatively weak pressure gradient will keep winds/seas below small craft advisory thresholds this holiday Weekend. Some 20+ knot WNW wind gusts over the land this afternoon may result in some nearshore chop...but no headlines will be needed for the waters this weekend with seas generally 3 feet or less.

Outlook /Monday through Thursday/...

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

Monday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Rain showers likely, slight chance of thunderstorms.

Tuesday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Rain showers likely, 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. Chance of rain showers.

Wednesday Night: Winds less than 25 kt. Seas up to 5 ft.

Thursday: Winds less than 25 kt. Seas locally approaching 5 ft.

BOX WATCHES/WARNINGS/ADVISORIES

CT...Heat Advisory until 8 PM EDT this evening for CTZ002>004. MA...Heat Advisory until 8 PM EDT this evening for MAZ002>023-026. RI...Heat Advisory until 8 PM EDT this evening for RIZ001>007. MARINE...None.