textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes to the forecast.

KEY MESSAGES

- Scattered showers this afternoon into early morning Monday.

- A sharp temperature drop is then expected for the start of the week followed by a return to dry, fall-like conditions.

DISCUSSION

KEY MESSAGE 1...Scattered showers this afternoon into early morning Monday.

High pressure south of the Maritimes no longer had enough influence to prevent clouds and scattered showers from overspreading southern New England this afternoon. The trend of the latest guidance suite was slightly farther south, quite close to the 40N/70W benchmark just after midnight. Based on this, kept the highest rainfall chances towards the Cape and islands, while simultaneously lowering those chances farther inland. Thinking there should be a rather sharp gradient on the northwest edge of this storm, but there is lower confidence on where exactly that will be. Overall, rainfall totals should remain less than one half inch across the Cape and islands, and generally less than one quarter inch north and west of the Cape Cod Canal.

Thinking that most of the showers will be well offshore shortly after midnight, and even past the southern New England coastal waters around daybreak Monday.

KEY MESSAGE 2...A sharp temperature drop is then expected for the start of the week followed by a return to dry, fall-like conditions.

A deep low continues tracking eastward across Quebec to start the week, with latest guidance indicating the 540dam thickness line reaching northern New England, generally across Maine at its southernmost pass. The 560dam thickness line may extend through central MA. High pressure follows this low, which will aid in drying out the region and remains the main story for this week.

With the passage of this low, colder, drier Canadian air will plunge south, with 850 mb temperatures reaching 0C and lower across the higher elevations late Monday night/early Tuesday morning. 925 mb temperatures may also approach 0C in these same areas and generally remain below 10C through Tuesday night as well. This environment will be supportive of lows Monday night in the low 40s and upper 30s. Tuesday night looks to be cooler given some radiational effects possible with diminishing winds overnight and clear skies as another high pressure passes just to the south of southern New England.

The flow aloft shifts more WSW to SW as the low exits and high pressure centered to our south midweek tracks east. With the return of SW flow and drier conditions, more seasonable temperatures take hold for the back half of the week. Ensembles also hint at the chance of high temperatures getting back to the low 70s towards Thursday afternoon, generally across the CT Valley, Merrimack Valley, and the coastal plain. Probabilities currently range between 20 and 60 percent, with the highest probabilities in the GEFS and lowest in the ECMWF ensemble. Overall, though, highs are expected to be more so in the 60s for the second half of the week into the weekend.

AVIATION /00Z MONDAY THROUGH FRIDAY/

Forecaster Confidence Levels...

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

Tonight...High confidence in trends, moderate confidence in timing of showers.

MVFR with pockets of VFR early, then degrading to IFR over SE MA, RI, and the Islands overnight with showers. Lowered visibilities more likely over ACK and Cape terminals tonight where scattered showers should persist through around 05z-06z tonight. VFR expected to persist west of a line from BOS-PVD- WST, outside of some brief MVFR early for BOS and ORH this evening. Winds become light to calm.

Monday and Monday Night...High confidence.

Lingering IFR across the Cape and Islands Monday morning. Otherwise, VFR. Gusty W to WNW winds developing by early afternoon. Gusts should diminish towards sunset with skies clearing, though breezy WNW winds continue at 5-15 kt overnight.

KBOS Terminal...High confidence in trends, moderate confidence in timing. MVFR not expected to last very long outside of the 00z-03z timeframe this evening, though it could fluctuate between SCT/BKN.

KBDL Terminal...High confidence in TAF.

Outlook /Tuesday through Friday/...

Tuesday: VFR. Breezy.

Tuesday Night: VFR.

Wednesday through Thursday: VFR. Breezy.

Thursday Night through Friday: VFR.

MARINE

Forecaster Confidence Levels...

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

Through Monday Night...High confidence.

A low pressure passes southeast of the waters tonight, with another cold front to pass by during Monday. Widespread showers tonight, especially across the southern waters. Gusty west winds then develop with the frontal passage Monday afternoon. Posted Small Craft Advisories for marginal wind gusts up to 25 kt. In addition, seas should build to 5-7 feet across the outer coastal waters.

Outlook /Tuesday through Friday/...

Tuesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft.

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

Wednesday: Winds less than 25 kt.

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

Thursday through Friday: Winds less than 25 kt.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 9 PM Monday to 1 AM EDT Tuesday for ANZ232. Small Craft Advisory from 10 AM Monday to 1 PM EDT Tuesday for ANZ250. Small Craft Advisory from 8 AM Monday to 1 PM EDT Tuesday for ANZ254. Small Craft Advisory from 3 PM Monday to 1 PM EDT Tuesday for ANZ255-256.