textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes to the forecast.

KEY MESSAGES

- Showers and storms around today, especially towards the CT River Valley where an isolated strong to severe thunderstorm or two is possible.

- Drier and warmer next week before rain chances make a return sometime Thursday/Friday.

DISCUSSION

KEY MESSAGE 1...Showers and storms around today, especially towards the CT River Valley where an isolated strong to severe thunderstorm or two is possible.

Weak low pressure just off to our northeast continues to aid in continued NE low level flow this morning, keeping overcast skies over southern New England. Chances for spotty showers continue primarily towards Nantucket and the outer Cape where showers are just offshore and continuing to move off to the northeast. Aside from these, misty and foggier conditions continue this morning across the region.

The main thing to keep an eye out for today will be the chances for some showers and storms towards the afternoon. Showers tracking across New York associated with the approaching cold front will approach western MA and CT towards the late morning/early afternoon hours. The low pressure to our northeast loosens its grip over southern New England as more southerly winds take hold in the late morning/early afternoon hours, advecting in dewpoints in the 70s. Increased humidity along with diurnal instability may enhance the risk for storms in the interior turning strong to severe. Even with cloudier skies inhibiting instability a bit, model soundings and CAM guidance have MUCAPE values around 1500-1800 J/kg over the CT Valley in the afternoon, and MLCAPE values to around 1200-1300 J/kg with limited capping in the soundings. Effective bulk shear values around 40 kt will also aid in development of an isolated stronger to severe storm or two, with the main risk of these storms being damaging winds. PWAT values still around 1.25-1.5" in the afternoon ahead of the front will also keep the risk for some torrential downpours in play. The interior remains in a Marginal (1/5) risk for severe weather today considering this environment.

Outside of this risk of showers and storms, the rest of the region can expect to remain mostly dry, albeit dreary. Humid conditions prevail with highs in the upper 70s.

KEY MESSAGE 2...Drier and warmer next week before rain chances make a return sometime Thursday/Friday.

The cold front to our west passes through the region heading into Monday, clearing skies quickly in its wake. Drier post-frontal air flows into the region, noted by dew points falling into the 50s and low 60s and PWATs to an inch and lower. Temperatures return to more seasonable levels in the 70s and 80s, though it should feel more comfortable than today given the reduced humidity. High pressure steadily builds in through Tuesday into Wednesday as ridging takes place of the troughing from Quebec that will continue to shift off to the east. Clear skies and dry weather prevail through this period.

Greater uncertainty reenters the forecast towards Thursday and Friday with the approach and development of another shortwave over the Great Lakes. Ensemble and deterministic guidance does hint at the return of elevated moisture towards this time period, along with rain showers. Latest ensemble guidance has PWAT values returning to around 1.5" Thursday afternoon into Friday, along with more southerly flow towards the surface. Inconsistencies remain among the ensembles, though, regarding the track of the low associated with the shortwave. This also leads to discrepancies regarding the timing of any showers.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

Forecaster Confidence Levels...

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

18z TAF Update...

This afternoon through tonight...Moderate confidence in trends but lower confidence in specific timing.

The main cluster of showers and an occasional rumble of thunder or two will be exiting eastern MA by mid afternoon. Otherwise...a few additional showers and perhaps an isolated t-storm will be possible into mid evening with the focus across interior southern New England and particularly areas near and west of the CT River Valley.

IFR/LIFR conditions will be improving to mainly MVFR-VFR by early-mid evening in most locations although the process will be slowest across the Cape/Islands. However...a wet ground, light winds and dewpoints still in the 60s will likely result in areas of fog developing in the typically prone locations. Some of that fog may become locally dense overnight...while areas like KBOS end up going VFR. So a wide variety of conditions possible toward daybreak. Winds become calm/light SW tonight.

Monday and Monday night...High confidence.

Any leftover ground fog quickly burns off after sunrise Mon. Otherwise...VFR with SW winds of 7-13 knots. Mainly VFR conditions continue Mon night outside of any localized patches of ground fog that develop in those typically prone locations. Winds become calm/light SW Mon night.

KBOS Terminal...Moderate confidence in trends but lower confidence in specific timing.

KBDL Terminal...Moderate confidence in trends but lower confidence in specific timing.

Outlook /Tuesday through Friday/...

Tuesday: VFR. Breezy.

Tuesday Night: VFR.

Wednesday: VFR. Breezy.

Wednesday Night: VFR.

Thursday: VFR. Slight chance SHRA.

MARINE

Forecaster Confidence Levels...

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

Through Monday...High confidence.

Winds and seas are expected to remain below Small Craft Advisory criteria through tonight. However, gusts could get close to this criteria during the day Monday following the cold front passing through tonight. Patchy fog over the waters tonight will clear following the front as well.

Seas remain between 2-4 ft with 5 ft seas possible tonight in the far ocean waters. Winds shift more S to SW today, continuing through Monday.

Outlook /Monday Night through Friday/...

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

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

Wednesday through Thursday: Winds less than 25 kt.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...High Risk for Rip Currents from Monday morning through Monday afternoon for MAZ024. RI...None. MARINE...None.