textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

- Last round of showers and thunderstorms pushes through this afternoon and evening with the arrival of a cold front. Dry and seasonable day expected Tuesday.

- Summer heat and humidity slowly returns later Wed, then peaks Thu/Fri and likely lingers into the weekend. Diurnal scattered thunderstorms each day, but many hours of dry weather too, hence, not a washout.

DISCUSSION

KEY MESSAGE 1...Last round of showers and thunderstorms pushes through this afternoon and evening with the arrival of a cold front. Dry and seasonable day expected Tuesday.

Expect widespread showers with pockets of moderate to heavy rain possible through the late afternoon. A cold front approaches from the west with a leading line of scattered showers and thunderstorms. Originally this posed a threat for some strong to severe thunderstorms. We are still in a marginally unstable airmass with SPC mesoanalysis SBCAPE values around 500-1,000 J/kg accompanied by rich moisture. Enough to support thunderstorms in the mix of that line. The risk for severe will be on the lower side as we didn't have enough clearing to allow the to re- bound/destabilize enough. Given the deep moisture, brief downpours are also possible within these cells. This line will push through western MA this afternoon then clearing the east coast by 8 PM. Winds decrease and shift to the west with the cold front accompanied by scattering and clearing clouds. Dry conditions expected tonight. Can't rule out some patchy fog in the valleys and the Cape/Islands once they areas clear if there is any residual moisture.

Quiet day for Tuesday with a weak mid-level ridge building over the region. This will support dry conditions and seasonable temperatures in the low to mid 80s.

KEY MESSAGE 2...Summer heat and humidity slowly returns late Wed, then peaks Thu/Fri and likely lingers into the weekend. Diurnal scattered thunderstorms each day, but many hours of dry weather too, hence, not a washout.

Summer heat and humidity slowly returns later Wed and then peaks Thu/Fri and likely continuing into the weekend, as ensembles are in good agreement on 597+ dam 500 mb subtropical ridge/Bermuda high building across the Western Atlantic. This will circulate a very warm and humid airmass into SNE, with dew pts 70-75 Thu/Fri and possibly lingering into the weekend. With 925 mb temps 22C+ each afternoon, highs 85-90 are likely and combined with dew pts of 70- 75, heat headlines are possible late this week and possibly into the weekend.

Synoptic scale forcing is very weak Thu and Fri,thus, many hours of dry weather. However, short wave energy will eject northeast from remnant closed low currently over the southeast states into SNE. Then over the weekend, mean trough axis sets up from central Canada into the Western Great Lakes, with broad cyclonic flow into New England. This combined with heat/humidity/instability will be sufficient for typical summer, scattered diurnal convection Thu/Fri and into the weekend. With PWATs +1.5 to +2.0 sigma, any storm will have the potential for tropical/torrential downpours. Again, many hours of dry weather too during this time period. Thus, not a washout.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

Forecaster Confidence Levels...

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

00Z Update...

Tonight: High confidence.

Expect a trend of improving conditions with ceilings improving to VFR between 22Z(west) and 02Z (Cape/Islands). Patchy fog possible in valleys and for Cape and Islands once they clear. Winds shift to the W/WNW behind the front (22-02Z) at 5-10 kts.

Tuesday: High confidence.

VFR. Winds 5-10 kts, first W then becoming SW after 18Z. Potential for a late-day sea breeze for BOS.

KBOS Terminal...High confidence in TAF.

- VFR 23-01Z behind FROPA as winds shift toward the W by 03Z. Winds become more SW tomorrow morning with potential for a late-day sea breeze.

KBDL Terminal...High confidence in TAF.

Outlook /Tuesday through Saturday/...

Tuesday through Wednesday Night: VFR.

Thursday: VFR. Breezy. Slight chance SHRA, isolated TSRA.

Thursday Night: Mainly VFR, with local IFR possible. Chance SHRA.

Friday: Breezy. Chance SHRA.

Friday Night: Breezy. Slight chance SHRA.

Saturday: Breezy. Chance SHRA.

MARINE

Forecaster Confidence Levels...

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

Seas and winds slowly decrease tonight into Tuesday. Seas will be slowest to fall across the southern waters with seas 5-9 ft gradually falling to 5-6 ft toward sunrise. SW winds 15-20 kts with gusts around 30 kts. Can't rule out a few isolated gusts near gale force for the remainder of the afternoon. Winds decrease after 00Z and below 25 kts by 06Z. Seas remain elevated Tuesday keeping up SCAs for the southern and eastern outer coastal waters.

A high surf advisory is in effect for the south coast and islands through tonight with seas 5-9 ft across the waters of RI and south of MVY-ACK. Rough surf and strong rips are likely to linger into Tuesday from the prolonged strong SW flow/swell. With Tuesday being a nice beach day, issued a Rip Statement for the south coast and Islands for Tuesday with the high risk for rip currents. There is a moderate risk for rip currents for the east-facing beaches along the outer Cape.

Outlook /Tuesday through Saturday/...

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

Tuesday Night: Winds less than 25 kt. Areas of seas approaching 5 ft.

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

Wednesday Night through Thursday Night: Winds less than 25 kt. Areas of seas approaching 5 ft.

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

Saturday: Winds less than 25 kt. Areas of seas approaching 5 ft.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...High Risk for Rip Currents from 5 AM EDT Tuesday through Tuesday evening for MAZ020-023-024. High Surf Advisory until 9 PM EDT this evening for MAZ023-024. RI...High Risk for Rip Currents from 5 AM EDT Tuesday through Tuesday evening for RIZ006>008. High Surf Advisory until 9 PM EDT this evening for RIZ006>008. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ231- 251. Small Craft Advisory until 2 AM EDT Tuesday for ANZ232>234. Small Craft Advisory until 2 PM EDT Tuesday for ANZ235-237-250- 254. Small Craft Advisory until 8 PM EDT Tuesday for ANZ255-256.