textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

- Backdoor front brings cooling near coast but warmth continues inland through Friday.

- Rounds of showers and thunderstorms this afternoon, later tonight, and again Thursday night.

- Pattern turns cooler early next week.

DISCUSSION

KEY MESSAGE 1...Backdoor front brings cooling near coast but warmth continues inland through Friday.

Backdoor front dropping southward will bring cooler temperatures at least to eastern MA coast as winds turn onshore, but warmer temperatures will persist inland. Front itself should meander over southern New England for next couple of days, probably settling near a line from Fitchburg to Norwood and Plymouth later this afternoon, retreating back north overnight, then dropping back southward again Thursday afternoon to about the same location. This certainly presents a big challenge with the temperature forecast, less so in CT and western MA which are more likely to maintain summertime warmth through Friday, but less so across RI and eastern MA depending upon exactly where front ends up and with its timing.

KEY MESSAGE 2...Rounds of showers and thunderstorms this afternoon, later tonight, and again late Thursday.

As front remains over or near southern New England, a series of weak low pressure centers will ride along it, each bringing chances of showers and embedded thunderstorms.

First round through early tonight looks to be more scattered in nature per high-res guidance. Already seeing CU development upstream across central NY where instability is increasing so that is where convective initiation should take place.

Environment here will feature strong 0-6km shear and reasonably strong mid level lapse rates (6C/km) but best instability (1000 J/kg) is focused over western MA/CT which makes sense given that is the area to the west of the front. While we don't expect to see as much activity as we did Tuesday evening, there could still be a few storms between 4 PM and 8 PM, perhaps even a few hours later than that, capable of producing wind damage, especially in CT per HREF helicity swaths.

Farther east in the cooler airmass, there is virtually no surface instability but perhaps enough instability aloft coupled with heating to pop up a few brief showers.

Next round of showers and embedded thunderstorms arrives during the overnight hours ahead of weak short wave and weak surface low riding along front. We still have strong 0-6km shear and decent mid level lapse rates approaching 7C/km, but instability is aloft and would support more in way of elevated thunder, not surface based, so overall severe threat is low.

Once low moves offshore, it should drop front southward Thu morning before it retreats northward again in afternoon. We then remain under large scale subsidence until next stronger short wave approaches Thu night. Environment remains about same with greatest instability west of I-91 but continued presence of strong 0-6km shear and decent mid level lapse rates of 6-7C/km. Guidance shows showers and thunderstorms forming to out west during the day, which arrives here Thu night and weakens as it does so.

KEY MESSAGE 3...Pattern turns cooler early next week.

It's been said all good things must come to an end, and for those who have been enjoying this early taste of summer, a brief pattern change will bring a return to much cooler weather early next week.

A strong cold front crosses southern New England Sun followed by a deep upper trough rotating through region, bringing an anomalously cold airmass back into the region, albeit for a short time. Temperatures aloft drop to as low as -7C to -10C at 850 mb Mon morning, only supporting highs in 40s and 50s Mon.

It might not be want you want but high pressure covering much of eastern U.S. eventually shifts offshore by midweek as upper flow becomes more zonal, allowing for a slow warming trend. Highs should get back into 60s by Wed.

AVIATION /00Z THURSDAY THROUGH MONDAY/

Forecaster Confidence Levels...

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

00Z TAFs: Moderate confidence.

IFR-LIFR stratus and fog along the eastern MA coast will push a bit further inland into portions of central MA and RI overnight with lowest vsbys along the coast. Mainly VFR in the CT valley. Expecting scattered showers and embedded thunderstorms developing overnight.

Similar situation Thu. VFR inland with SW winds, and MVFR/IFR to start closer to coast with E/NE winds, but even these areas should improve to VFR Thu afternoon. Next round of scattered showers and thunderstorms should hold off until Thu night.

KBOS Terminal... Moderate confidence in TAF. LIFR fog and stratus tonight. May see some vsby improvement overnight with any showers that move through. Conditions should improve to VFR by midday Thu.

KBDL Terminal... High confidence in TAF.

Outlook /Thursday Night through Monday/...

Friday: VFR. Chance SHRA, slight chance TSRA.

Friday Night through Saturday: Mainly VFR, with local MVFR possible.

Saturday Night: Mainly VFR, with local IFR possible. Breezy. Slight chance SHRA.

Sunday: Mainly VFR, with local IFR possible. Breezy. SHRA likely.

Sunday Night: VFR. Breezy. Chance SHRA.

Monday: VFR. Breezy. Slight chance SHRA.

MARINE

Forecaster Confidence Levels...

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

High confidence through the weekend.

Backdoor front meandering over southern New England through Fri will maintain light winds and calm seas, though there will be wind shifts from SW to NE from time to time on eastern MA waters along with showers and embedded thunderstorms.

Passage of stronger cold Front Sun should bring SCA conditions to at least outer waters Sun into Mon.

Outlook /Thursday Night through Monday/...

Friday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers.

Friday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers.

Saturday: Winds less than 25 kt.

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

Sunday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers.

Sunday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Chance of rain showers.

Monday: Winds less than 25 kt. Local rough seas. Slight chance of rain showers.

CLIMATE

Today's record highs (April 15):

Boston 82 in 1896 Hartford 88 in 1941 Providence 82 in 1938 Worcester 85 in 1941

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...None.