textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

- A cold front brings the return of heavy rain and gusty winds Sunday night and Monday. Localized flash flooding possible.

- After a quiet Tuesday unsettled weather returns mid week through the weekend with periods of showers and storms.

DISCUSSION

KEY MESSAGE 1...A cold front brings the return of heavy rain and gusty winds Monday.

An anomalously deep upper trough digging into the Ohio Valley will become cutoff as the broader longwave trough axis works its way slowly east. Its trough axis will cross over southern New England Monday night into Tuesday ushering in a much quiet and drier period. Before that, however, we'll be dealing with a very moist and dynamic system for the next 18-24 hours. This, as the shortwave and surface reflection pull copious amounts of moisture north into New England on strengthening SW flow (PWATs 2+ inches) with a 40-55 kt LLJ strengthening as it's core moves over the Cape and islands. Fortunately, even though BUFKIT soundings show 55kts down to about 925mb, the low level inversion should keep the worst aloft. Regardless, it will be a gusty day, especially over southeast MA. While some brief stronger gusts can't be ruled out, they are more than likely to top out around 40 mph on Cape Cod.

Regardless of its impact at the surface, said LLJ will certainly act as a strong forcing mechanism for our heavy rain. This together with divergence aloft/placement beneath the RRQ of an upper jet will lead to broad, deep layer ascent and widespread rain showers and thunderstorms. Continuing to expect an initial round of moderate to heavy rain showers this morning into the afternoon which has already begun to materialize. The atmosphere is primed for some heavy downpours and while we can't nail down exactly who will see these downpours, any convection would lead to a better chance of those higher rain rates hinted at by the HREF (low probability of as much as 1+/hr).

There's unlikely to be a real break in the showers and embedded thunderstorms but any pockets of clearing skies between showers may lead to increased instability parameters and a better chance for one of these thunderstorms to become severe as a final source of forcing arrives in the evening in the form of a cold front. Any storms that do get going will be in an environment with 30-45 kts of 0-6km bulk shear meaning potential for organization and some damaging wind potential.

When all is said and done (ending in western MA by 8pm, eastern MA by midnight) a widespread 0.5 to 1.5 inches of rain is expected. That being said, convective enhancement and potential for training thanks to boundary-parallel mean flow mean that localized areas could see significantly more, on the order of 3-4 inches. This amount, especially if it falls in a short period, may lead to street flooding and even isolated flash flooding situations. However, we don't expect a widespread flash flooding risk with this system.

KEY MESSAGE 2...After a quiet Tuesday unsettled weather returns mid week through the weekend with periods of showers and storms.

After a beautiful, mostly sunny, less humid day on Tuesday under high pressure ridging, unsettled weather returns Wednesday into the weekend. A broad mid level trough sets up over the eastern U.S. with several shortwaves rotating through the base of the broader trough and this will bring periodic rain and thunderstorm chances each day, especially in the afternoon/evening.

AVIATION /06Z MONDAY THROUGH FRIDAY/

Forecaster Confidence Levels...

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

06z TAF Update:

Through 12Z: Moderate confidence.

IFR/LIFR cigs continue to push north. Scattered -SHRA will expand east through 12z. Embedded thunder is possible, but low probability. LLJ pushes in from the south leading to added added wind shear in the Cape terminals, BOS, and PVD.

Monday: Moderate confidence.

IFR/LIFR in RA/+RA through the day. Embedded storms possible within the first few rounds of rain 12-21Z. Another round of scattered thunderstorms likely pushes through from west to east 19Z-02Z ahead of the approaching cold front. Wind shear likely continues in the east/southeast terminals during the day. SW winds 10-20 kts with gusts 20-30 kts. Could see period in the afternoon that winds gust 25-35 kts for the east and especially SE terminals if we clear out before the early evening round of storms.

Monday night: High confidence.

SHRA/TSRA will be pushing out of eastern terminals by 04Z leaving VFR conditions with light W wind.

Tuesday: High confidence.

VFR. Winds 5-10 kts, first W then becoming SW after 18Z.

KBOS Terminal...Moderate confidence in TAF.

KBDL Terminal...Moderate confidence in TAF.

Outlook /Tuesday through Friday/...

Tuesday through Tuesday Night: VFR.

Wednesday through Wednesday Night: VFR. Slight chance SHRA.

Thursday through Thursday Night: VFR. Breezy. Slight chance SHRA, slight chance TSRA.

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

MARINE

Forecaster Confidence Levels...

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

Winds and seas increase into early this morning across the southern and eastern waters eventually increasing across the northern waters. Seas 5-9 ft for the outer coastal waters, especially south. 5-7 ft seas stretch into portions of the inner souther waters. SW winds 15-20 kts with gusts around 30 kts. Can't rule out a few isolated gusts near Gale-force late morning-afternoon if winds mix down from the low level jet overhead. SCAs are in effect for all the coastal marine zones. Elevated seas will keep SCAs around through Tuesday for the southern waters.

A high surf advisory is in effect for the south coast and islands Tuesday. A strong 35-45 kt southerly low level jet will help build waves 5-9 ft across the waters of RI and south of MVY-ACK Monday. Rough surf and strong rips are likely to linger into Tuesday. Will have to watch this as Tuesday is shaping up to be an ideal beach day.

Outlook /Tuesday through Friday/...

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.

Wednesday Night: Winds less than 25 kt.

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

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...High Surf Advisory from 7 AM this morning to 9 PM EDT this evening for MAZ023-024. RI...High Surf Advisory from 7 AM this morning to 9 PM EDT this evening for RIZ006>008. MARINE...Small Craft Advisory until 5 PM EDT this afternoon for ANZ230- 236. Small Craft Advisory from 8 AM this morning to 5 PM EDT this afternoon for ANZ231-251. Small Craft Advisory from 8 AM this morning to 2 AM EDT Tuesday for ANZ232>234. Small Craft Advisory until 2 PM EDT Tuesday for ANZ235-237. Small Craft Advisory from 8 AM this morning to 2 PM EDT Tuesday for ANZ250-254. Small Craft Advisory until 8 PM EDT Tuesday for ANZ255-256.