textproduct: Boston / Norton

WHAT HAS CHANGED

Rip Current Statement was issued for Sunday. Monitoring for possible heavy rain and severe weather this afternoon south of the Mass Pike, and again tonight in interior MA/CT.

KEY MESSAGES

- Showers and scattered thunderstorms with torrential rainfall along with a localized flash flood threat Sat afternoon and night. A few severe thunderstorms possible too with the greatest risk interior MA/CT and onto the south coast. Areas of smoke return late tonight into Sat but not as bad as what we had Wed.

- Drying out Sunday into the start of next week, but more active weather returns around midweek.

DISCUSSION

KEY MESSAGE 1...Areas of smoke re-developing this morning. Then two periods of storms today/tonight: one mainly south of the Mass Pike early to mid afternoon, late in the day into tonight in the interior. Torrential downpours are possible, and a lesser risk for severe weather could also occur.

Active Saturday in store as a seasonably-strong frontal system moves through Southern New England over the next 24 hours. First, on the returning smoke. Tough to remotely sense via satellite imagery with the cloud cover around, but based on AQI readings early this morning, the northern edge of the plume of near- ground smoke trails from western NY southward into central NJ. Smoke progs show this returning northward into southern New England by early to mid this morning. While the morning to early afternoon end up dry, expect skies to turn hazy again with increasing SWly winds. Air Quality Alerts remain in effect for today for PM2.5, at request of our state environmental agency partners.

Now for the shower and thunderstorm threats today/tonight. The frontal system expected to affect our area has with it pretty impressive wind fields for mid-July, which will support some severe weather potential, but will also make the storms fast- moving, which could help limit flash flooding. I'm a little skeptical on the instability ingredient though, as the smoke conditions and potential for poor recovery/limited breaks in the clouds could limit how strong storms get.

The first round of showers and thunderstorms moves in around early to mid-afternoon (1-3 PM) associated with a strong warm front, which will bring mid-70s dewpoints and PWAT values in the 2 to 2.25" range to Southern New England, with weakening stability profiles. Most of the CAMs pencil in areas south of the Mass Pike as having the most concentrated area of showers and storms, and especially the Hartford- Providence-Southeast MA corridor. Opted for high Likely to Categorical PoP for these areas, then just a generic Chance PoP north of here to make the distinction. The main risk with this first wave of storms is the risk for torrential downpours capable of street flooding. Continued QPF placement uncertainties precluded a Flood Watch with this issuance, as there are still a good number of guidance sources which shift the rain/storms into the southern waters. I still added heavy rain wording to the grids for these areas to convey that message in lieu of the Watch, and the potential for high rain rates in urbanized areas could still trigger a need for flash flood warnings this afternoon if and where any cell training occurs. There is a low risk for localized straight line wind damage or a brief tornado due to the low level windfields (300 units of 0-1 km SRH is notable), but the severe weather risk looks secondary to the heavy rain potential.

As this initial round of showers/storms shifts southward, the next period of showers and thunderstorms arrives late in the day into tonight (between 6 to 11 PM) with the cold front. Most models show a pretty extensive line of thunderstorms developing late this afternoon as the front moves southward across upstate NY and VT. We'll have to watch the northeast extent of this line as it slips south-southeast into the Berkshires, northern CT and central MA, with less of a risk into eastern MA. Straight- line wind damage, frequent lightning and torrential downpours would be the main risks with this second round. The risk for late-evening strong storms is more uncertain the further south one goes, since these areas will probably have been worked over pretty well with the afternoon heavy downpours/storms, with weakening trends more likely. Front clears into the southern waters overnight, with northwesterly breezes and turning much less humid by sunrise.

KEY MESSAGE 2...Turning drier and seasonable Sunday and Monday, but Sunday will feature a high risk for rip currents on south- facing beaches.

The cold front brings a stretch of pleasant summer weather Sunday and Monday, with low humidities and temperatures in the 70s to mid 80s, to go along with NW breezes Sunday. At the beaches though, swell directions Sunday are still oriented from SW to NE from today's storm system, with seas in the 4 to 6 ft range. This will favor a high risk for dangerous rip currents. With Sunday being a better day to go to the beach than today, issued a rip current statement for the southern beaches.

KEY MESSAGE 3...Active weather returns midweek with showers and thunderstorms.

Although there's the usual uncertainty in the details at this time horizon, most of the global ensembles show another potent northern stream upper trough interacting with a tropical Gulf moisture feed, with a risk for showers and thunderstorms Tuesday and possibly into Wednesday too. Temps warm to above average levels and we turn quite a bit humid too, so the risk for downpours is in the cards as we move into midweek.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

Forecaster Confidence Levels...

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

Through Tonight: Moderate confidence.

VFR through 16z today, although VFR-visby FU returns early today from the south. SW winds increase to 10-15 kt with gusts 25-30 kt. After 16z, categories then drop to MVFR levels with two periods of storms. First takes place 17-23z mainly BDL-PVD-Cape airports, with IFR-visby heavy SHRA/VCTS. Lesser risk north. Next round of storms occurs mainly ORH to BDL, perhaps to BOS with cold front between 22-03z, with PROB30s given uncertainty on how strong storms may get. Later TAF issuances will need to reassess the 2nd period of storms. Improvement to VFR from 02-06z NW to SE, with windshift to NW around 10-12 kt into Sunday pre-dawn.

Sunday: High confidence.

VFR. NW winds around 10-15 kt.

KBOS Terminal...Moderate confidence in TAF. 6SM/P6SM FU this morning. First round of showers/storms 18-22z stays mainly south of terminal (VCSH) with MVFR cigs, then a drier break before risk for TS after 01z (PROB30). SW winds gusting upper 20s kt range.

KBDL Terminal...Moderate confidence in TAF. 6SM/P6SM FU this morning. MVFR-IFR after 17z with initial +SHRA/VCTS, then a break before a line of strong TSRA nears terminal after 23z (PROB30). SW winds gusting mid 20s kt range.

Outlook /Sunday Night through Wednesday/...

Sunday Night through Monday Night: VFR.

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

Tuesday Night: Mainly VFR, with areas MVFR possible. Windy with areas of gusts up to 30 kt. SHRA, slight chance TSRA.

Wednesday: Mainly VFR, with areas MVFR possible. Windy with gusts up to 35 kt. SHRA likely, chance TSRA.

MARINE

Forecaster Confidence Levels...

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

Through Tonight: High confidence.

SCAs continue in effect for today and into parts of Sunday as well. Southwest wind gusts 25-30 knots are expected today with seas becoming rough, increasing to 6-8 ft offshore. Seas will also respond and become quite rough across the waters. Scattered thunderstorms later Sat and Sat night may produce localized stronger wind gusts as well...which may require the issuance of some special marine warnings.

Sunday: High confidence.

NW winds around 15-20 kt, with seas around 4-6 ft. High risk for rip currents at the beaches/surf zone.

Outlook /Sunday Night through Wednesday/...

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

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

Monday Night: Winds less than 25 kt.

Tuesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Chance of rain showers, slight chance of thunderstorms.

Tuesday Night: Low risk for gale force winds with gusts up to 35 kt. Areas of rough seas. Rain showers, chance of thunderstorms.

Wednesday: Moderate risk for gale force winds with gusts up to 35 kt. Rough seas up to 16 ft. Rain showers likely, slight chance of thunderstorms.

BOX WATCHES/WARNINGS/ADVISORIES

CT...Air Quality Alert until midnight EDT tonight for CTZ002>004. MA...Air Quality Alert until midnight EDT tonight for MAZ002>024- 026. High Risk for Rip Currents from Sunday morning through Sunday evening for MAZ020-022>024. RI...High Risk for Rip Currents from Sunday morning through Sunday evening for RIZ006>008. Air Quality Alert until 11 PM EDT this evening for RIZ001>008. MARINE...Small Craft Advisory until noon EDT Sunday for ANZ230>237-250- 251. Small Craft Advisory until 8 PM EDT Sunday for ANZ254>256.