textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes to the forecast.

KEY MESSAGES

- Warm and pleasant conditions today.

- Hotter on Wednesday before a bit of a cool down Thursday into Friday. Slight risk of isolated afternoon showers/t-storms Wednesday afternoon and showers Thursday afternoon.

- Temperatures trend near or below normal heading into the weekend as rain chances return.

DISCUSSION

KEY MESSAGE 1...Warm and pleasant conditions today.

Big improvement in the near term forecast compared to the dreary holiday weekend we just left behind. This, as southern New England is placed beneath largely zonal mid-level flow with surface high pressure to start on Tuesday. Subsidence and a much drier airmass (PWATs down near 0.5" briefly) will give us a dry Tuesday with plenty of sun filtered through high cirrus. Warm advection in the low/mid layers coincident with good mixing to near 850 mb will push high temperatures back into the 80s. For reference, normal highs this time of year are in the upper 60s to mid 70s.

KEY MESSAGE 2...Hotter on Wednesday before a bit of a cool down Thursday into Friday. Slight risk of isolated afternoon showers/t- storms Wednesday afternoon and showers Thursday afternoon.

Further low level warm advection Wednesday pushes temps into the mid to upper 80s while moisture advection kicks in with dewpoints rising well into the 60s, especially along the south coast. This contributes to a decent amount of instability (focused again over the south coast) with 1000+ J/kg CAPE while low level lapse rates are 6-7.5C/km; limitations, however, include drier air in the mid levels and poor mid level lapse rates which would limit updraft development. Even so, given a cold front dropping through providing some lift, can't rule out some scattered showers and thunderstorms in the afternoon and evening if frontal timing is right. Behind that front on Thursday the airmass is cooler as the first in a series of shortwaves rounds the base of an eastern Canada trough directly over SNE. This means cooler temps (highs in the 70s) and little to no instability, so while some diurnal showers are expected, thunderstorms aren't a risk.

KEY MESSAGE 3...Temperatures trend near or below normal heading into the weekend as rain chances return.

A deeper, cut-off low then rounds the base of the previously mentioned trough in the Friday night/Saturday time period which would bring an unusually cold airmass overhead depending on how deep it ends up being. Still uncertain as to how cool and wet this system is in SNE but models are in agreement with the occurrence of the deep trough, if not the exact placement and who gets a bulk of the wet weather. Ensemble guidance continues to favor northern New England for the wettest weather. Not seeing a quick improvement in this cooler/unsettled pattern in New England early next week as the synoptic pattern features a decent omega block well into the extended forecast period.

AVIATION /06Z TUESDAY THROUGH SATURDAY/

Forecaster Confidence Levels...

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

06z TAF Update:

Through 12Z...High confidence in TAF.

Generally VFR except IFR to MVFR ceilings likely across the Cape and Islands. Areas north and west of I-95 will be most favorable for the development of radiational fog, with localized dense fog possible; however, confidence in exact placement remains low.

Tuesday...High confidence.

VFR after fog burns off 12-15z. Winds become SW 8 to 12 kt.

Tuesday Night...Moderate confidence.

VFR. Marine stratus may develop south of the Islands overnight and drift toward the south coast. Winds remain SW less than 10 kt.

Wednesday...Moderate confidence.

Generally VFR, though there will be a chance for afternoon SHRA/TSRA. Winds will be WNW at 5 to 10 kt inland and 10 to 15 kt along the coast.

KBOS...Moderate confidence in TAF.

Low confidence regarding fog development early this morning, though current thinking favors less restrictive conditions than suggested by LAMP/GLAMP guidance.

KBDL...Moderate confidence in TAF.

Localized fog remains possible early this morning, though confidence in occurrence and exact timing remains moderate.

Outlook /Wednesday Night through Saturday/...

Wednesday: VFR. Breezy. Isolated SHRA, isolated TSRA.

Wednesday Night: VFR. Isolated SHRA.

Thursday: VFR. Breezy. Isolated SHRA, isolated TSRA.

Thursday Night through Friday: VFR. Slight chance SHRA.

Friday Night: Mainly VFR, with local MVFR possible. Chance SHRA.

Saturday: Mainly VFR, with areas MVFR possible. Chance SHRA.

MARINE

Forecaster Confidence Levels...

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

Through Wednesday...High confidence.

Marginal Small Craft Advisory conditions continue this morning across the outer ocean waters, with seas of 4 to 6 ft. These seas gradually subside by daybreak, followed by tranquil boating conditions through Wednesday, with seas mainly 2 to 4 ft. Winds remain light and somewhat variable on Tuesday as high pressure moves overhead. By Wednesday, winds become more southwesterly around 15 kt, with occasional gusts up to 20 kt possible over the nearshore waters south of the coast. Both Wednesday and Thursday afternoons feature the chance for isolated pop-up showers or thunderstorms, though a washout is not expected.

Outlook /Wednesday Night through Saturday/...

Wednesday Night through Thursday: Winds less than 25 kt. Isolated rain showers, isolated thunderstorms.

Thursday Night through Friday: Winds less than 25 kt. Slight chance of rain showers.

Friday Night: Winds less than 25 kt. Chance of rain showers.

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 AM EDT this morning for ANZ250- 254>256.