textproduct: Boston / Norton

WHAT HAS CHANGED

A Flood Watch has been issued for Connecticut.

KEY MESSAGES

- Cooler/seasonable temps return today with highs mainly in the upper 70s to the middle 80s. Mainly dry today outside a few showers across western MA/CT and near the south coast.

- Confidence growing in the potential for bands of heavy rainfall & even the risk for localized flash flooding late tonight into Tue. Greatest risk for this right now is in northern CT...where a Flood Watch has been issued.

- Summer warmth & humidity return for the latter half of the week. A few showers and thunderstorms possible by Fri-Sat.

DISCUSSION

KEY MESSAGE 1...Cooler/seasonable temps return today with highs mainly in the upper 70s to the middle 80s. Mainly dry today outside a few showers across western MA/CT and near the south coast.

The upper level ridge has finally broken down across the region...which will bring a return to cooler/seasonable temperatures today. We do expect a scattered to broken deck of mid-level cloudiness across the region as a weak surface boundary slowly lifts north across the region. Dry weather will dominate today...except for a few showers across western MA/CT and near the south coast given their proximity to deeper moisture and forcing.

KEY MESSAGE 2...Confidence growing in the potential for bands of heavy rainfall & even the risk for localized flash flooding late tonight into Tue. Greatest risk for this right now is in northern CT...where a Flood Watch has been issued.

Confidence is growing in the potential for bands of heavy rainfall and even the risk for localized flash flooding late tonight into Tue. This is a rather complex forecast in trying to determine the location and greatest risk for torrential rainfall/localized flash flooding which we will discuss more below.

Weak high pressure over eastern Canada will help to focus a shallow boundary at the surface. Just above that a modest ESE low level of 25 to 35 knots at 925 mb will impinge on this surface boundary. This will combined with Pwats of 1.5 to 2+ inches and set the stage for bands of heavy rainfall late tonight into Tue with some embedded thunder possible. We are essentially combining synoptic scale forcing with summertime moisture and instability...which is a good setup of for bands of torrential rainfall and potential for localized flash flooding. The models do quite a good job these days in indicating the potential for torrential rainfall/localized flash flooding. However...they often struggle to depict the location given various mesoscale parameters in play. Currently, the models seem to be favoring our southwest zones where the best moisture and Pwat plume are located.

Given the above...we have gone ahead and issued a Flood Watch for our CT zones. This is for a widespread 1-3 inches of rainfall...But the potential for localized narrow bands of 4-6 inches of rain inside 6 hours. If this were to occur...the potential would exist for both urban and small stream flash flooding late tonight into Tue. Later shifts may need to expand the Flood Watch further north and east...But we felt this was a good starting point for now. It is also possible that the heavy rain/flood threat remains to our southwest...But either way felt a Flood Watch for CT was reasonable to just highlight the potential.

KEY MESSAGE 3...Summer warmth & humidity return for the latter half of the week.

Drier weather works into the region by Wed as the shortwave trough departs. Westerly flow will develop by late in the week bringing typical summertime warmth and humidity back into the region...But fortunately not the extreme heat we have dealt with the last few days. There will also be the risk for a few showers and thunderstorms by Fri-Sat as the next shortwave works into the region.

AVIATION /08Z SUNDAY THROUGH THURSDAY/

Forecaster Confidence Levels...

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

06z TAF Update...

Today through Monday...Moderate confidence.

Mainly VFR today but some lower MVFR conditions possible at times today in a few showers across western MA/CT and near the south coast. MVFR conditions become more widespread across western MA/CT later tonight and Mon along with periods of showers with locally heavy rainfall.

Light ESE winds today and tonight becoming E at 6 to 13 knots on Mon.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Monday Night through Thursday/...

Monday Night: Mainly MVFR, with areas IFR possible. Breezy. SHRA, slight chance TSRA, patchy BR.

Tuesday: MVFR/IFR conditions possible. Windy with local gusts up to 30 kt. Chance SHRA, slight chance TSRA, patchy BR.

Tuesday Night: Mainly VFR, with areas MVFR possible. Breezy. Chance SHRA.

Wednesday through 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 and tonight...High confidence.

High pressure over eastern Canada combined with a wave of low pressure passing to our south will result in ESE winds today and tonight...But the winds/seas should remain below small craft advisory thresholds.

Monday...Moderate confidence.

Wave of low pressure passing to our south should result in E wind gusts increasing to around 25+ knots across our southern waters. Later shifts will likely need to issue small craft advisories for our southern waters and we may need to expand them further north Monday night.

Outlook /Monday Night through Thursday/...

Monday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas. Rain showers, slight chance of thunderstorms, patchy fog.

Tuesday: Moderate risk for Small Craft Advisory winds with local gusts up to 30 kt. Rough seas up to 10 ft. Rain showers likely, slight chance of thunderstorms, patchy fog.

Tuesday Night: Winds less than 25 kt. Rough seas up to 10 ft. Chance of rain showers, slight chance of thunderstorms.

Wednesday: Winds less than 25 kt. Rough seas up to 9 ft. Slight chance of rain showers.

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...Flood Watch from late tonight through Tuesday afternoon for CTZ002>004. MA...None. RI...None. MARINE...None.