textproduct: Boston / Norton

WHAT HAS CHANGED

Rainfall coverage and amounts have trended lower for late tonight into Monday.

KEY MESSAGES

- Widespread showers expected tonight into Tuesday although the overall rainfall totals have continued to trend down.

- Scattered showers and a few storms possible later Tuesday. Increased chances for showers arrive for late-week.

DISCUSSION

KEY MESSAGE 1...Widespread showers expected tonight into Tuesday although the overall rainfall totals have continued to trend down.

A low pressure system off the southern Long Island waters will move east tonight bringing a widespread wave of rain showers to southern New England, some of which is already beginning to slowly push into northern NJ/ southern NY. Dewpoints have been steadily rising throughout the day, and will continue to do so into the night as prolonged southwesterly flow advects PWATs of 1.8-2.0 inches into the region. Latest guidance has indicated the low will remain far enough south to keep the heaviest rainfall along the south coast, Cape & Islands, southern RI, and southern CT. Showers will slowly push east and overspread the region around sunset, with highest chances for heaviest rainfall between midnight and sunrise Monday morning. The commute Monday will likely be wet as showers linger across RI and eastern MA through the morning and early afternoon, with the Cape and Islands seeing the rain hang on into the early evening. Rainfall totals have continued to trend lower with each round of model guidance... latest trends indicate between 0.10" and 0.33", with Nantucket and the outer Cape possibly seeing near 0.50". Dewpoints will remain higher (near 70) even once the rain stops, so looking at a muggy and overcast evening/night Monday.

KEY MESSAGE 2...Seasonably warm temperatures and moderate humidity return through the middle of next week, followed by increasing shower chances late in the week.

High pressure slowly builds in Tuesday supporting increasing sunshine and dry conditions for much of the day. A mix of diurnal heating, residual moisture, and a weak shortwave in the flow may help trigger scattered showers in the afternoon/evening. Instability will likely be marginal, but enough to support the potential for a few thunderstorms in the mix as well. Temperatures range in the upper 70s to low 80s perhaps a little warmer for the CT Valley.

Flow aloft stays zonal Wednesday through Friday. A stronger shortwave trough moves through eastern Canada later Wednesday through Thursday accompanied by a cold front. There is potential for a leading shortwave to trigger a few showers late Wednesday night, otherwise Wednesday is likely to remain dry. The main shortwave moves through Thursday accompanied by better ascent and plume of slightly above normal moisture. This will bring an increased risk for showers Thursday. Ensemble probabilities range 50 to 80 percent with higher end of probabilities over the south coast, southeast MA, and Cape/Islands.

We'll be in a post-frontal airmass Friday resulting in slightly cooler temperatures in the mid 70s to low 80s and a downtick in humidity. Overall, high pressure is likely to push in from the west bringing mainly dry conditions. However, there are indications across model guidance of a boundary stalling offshore with a series of embedded shortwaves riding that boundary Friday through the weekend. This may bring periodic chances for showers, perhaps some thunderstorms if the waves align with diurnal heating. The higher risk for showers will the for south coast extending to Cape Cod/Islands.

AVIATION /19Z SUNDAY THROUGH FRIDAY/

Forecaster Confidence Levels...

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

18z TAF Update...

Today...High confidence.

VFR. Seabreezes along the coastal plain. Otherwise, SSW winds near 10 kts with a few gusts 15-18 kts possible.

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

Mainly VFR conditions persist this evening. MVFR with localized IFR ceilings over spread the interior between 04z and 08z and reach the I-95 corridor by 12z. Scattered showers may also accompany the low clouds. S winds generally 6-12 knots.

Monday...Moderate confidence.

Low end MVFR to IFR ceilings should dominate Monday with perhaps even some localized LIFR conditions. Scattered showers especially in the morning but not a washout of a day. An isolated t-storm or two is also possible...but nothing widespread is expected. SE winds 8-16 knots may shift to light N-NE across the interior as the day wears along.

KBOS Terminal...High confidence in TAF. Seabreeze should kick out 20z-22z time frame. VFR persists today and most of tonight...but MVFR with localized IFR conditions should arrive toward the Monday morning push.

KBDL Terminal...High confidence in TAF.

Outlook /Tuesday through Friday/...

Tuesday: Mainly VFR, with local MVFR possible. Slight chance SHRA.

Tuesday Night through Wednesday: VFR.

Wednesday Night: VFR. Slight chance SHRA.

Thursday: VFR. Chance SHRA, slight chance TSRA.

Thursday Night: VFR. Slight chance SHRA.

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.

South-southwesterly winds increase to around 20 kt tonight, then shift to southeast Monday morning then east by late afternoon, with gusts of 20 to 25 kt. Seas build to 5 to 8 ft by early Monday morning as the low approaches. Small Craft Advisories remain in effect through Monday night.

The risk for rip currents increases Monday along south-facing beaches, then Tuesday along east-facing beaches, as rough seas and long-period swells settle in behind the departing system.

Outlook /Tuesday through Friday/...

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

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

Wednesday through Wednesday Night: Winds less than 25 kt.

Thursday through Thursday Night: Winds less than 25 kt. Chance of rain showers, slight chance of thunderstorms.

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 8 AM to 11 PM EDT Monday for ANZ231- 232-250-251-254. Small Craft Advisory from 2 AM Monday to 2 AM EDT Tuesday for ANZ233>235-237-255-256.