textproduct: Boston / Norton

WHAT HAS CHANGED

Chances for some brief scattered showers late Saturday night into very early Sunday morning. Confidence increasing in near record high temperatures possible by Tuesday and/or Wednesday along with the potential for a round of strong to severe thunderstorms.

KEY MESSAGES

- Fog possible overnight before warm-up kicks off Saturday.

- Unseasonably warm temps Sun through Wed with near record high temps into the 90s possible Tue and/or Wed.

- Strong to severe thunderstorms possible by Tue with perhaps a better potential by Wed but a lot needs to be sorted out.

- Seasonable temperatures return by next Thu and Fri.

DISCUSSION

KEY MESSAGE 1...Fog possible overnight before warm-up kicks off Saturday.

The closed low aloft will continue shifting offshore through tonight, being replaced by more zonal flow to kick off the weekend. The associated surface low currently located off to our east that is providing the moisture plume around NE MA will also progress east through tonight and pull away from the region. Latest mesoanalysis indicates some surface-based CAPE along the south coast that's helping fuel some pop-up showers. These will likely continue through this evening, ending around sunset. Cloud cover will linger before winds start to shift more NW then SW, and with the moist ground conditions, patches of fog may develop across southern New England, extending beyond the usual areas in the river valleys and other frequently foggy areas. Lows will once again be mostly in the 40s with dew points not far behind them.

Southwest flow closer to the surface really kicks up Saturday morning as the quasi-zonal flow aloft takes hold. Skies clear out and with the full sun along with warmer air aloft, highs will rise into the 70s across southern New England. Spots in the CT Valley may also approach 80. Winds may gust between 20-25 MPH in the afternoon. A weak shortwave passing just to our north overnight may also bring the chance for some light showers late Saturday night into Sunday, but not much else expected in the way of precipitation tomorrow. With warmer air remaining aloft and SW flow starting to shift more W, lows overnight Saturday will likely only fall into the mid to upper 50s.

KEY MESSAGE 2...Unseasonably warm temps Sun through Wed with near record high temps into the 90s possible Tue and/or Wed.

High confidence continues in a pattern change to unseasonable warm temperatures for the first half of next week and potentially flirting with record highs on Tue/Wed. GEFS/EPS guidance continue to show a building Bermuda High pressure system resulting in above to well above normal height fields.

W-SW flow should push high temps into the 80s on Sun away from the Cape and Islands. A weak backdoor cold front may bring briefly cooler temps Mon...mainly on the immediate coast. Highs Mon on the immediate coast probably in the upper 60s and 70s while 80+ risk will be confined to the interior. The hottest days look to be Tue and/or Wed depending on the timing of a cold front. 925T near +24C should result in the potential for high temperatures to climb into the 90s away from any modified marine influences. This may result in record high temperatures being challenged at least in areas away from the south coast.

KEY MESSAGE 3...Strong to severe thunderstorms possible by Tue with perhaps a better potential by Wed but a lot needs to be sorted out.

Quite the ways out there...especially for a convective forecast. That being said...there are some signals for potentially strong to severe thunderstorms later Tue and perhaps a better chance by Wed. This will be dependent upon the timing of a cold front...but given anomalous/near record warmth the potential is there. In fact...much of our machine learning guidance indicates some modest severe weather probabilities for a Day 4-5 forecast...so this is certainly something to watch.

KEY MESSAGE 4...Seasonable temperatures return by next Thu and Fri.

The long range guidance is in good agreement in the return of seasonable temperatures by Thu and Fri behind the mid-week cold front.

AVIATION /00Z SATURDAY THROUGH WEDNESDAY/

Forecaster Confidence Levels...

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

00z TAF Update...High confidence in trends with moderate confidence in timing.

Lingering MVFR with some localized IFR conditions across eastern MA will continue to improve to VFR as the evening wears along. Most locations should be VFR by midnight...except across parts of the Cape and Islands. However...we will need to watch for localized patchy ground fog developing overnight in the typically prone locations given light/calm winds and wet grounds from the recent rain.

Any fog patches quickly burn off by early to mid morning Sat. Otherwise...VFR with SW wind gusts of 20 to 25 knots developing by Saturday afternoon. Mainly VFR conditions continue Sat night with SW winds of 5 to 15 knots and some 20-25 knot gusts persisting near the coast. Some LLWS possible late Sat night along with perhaps a brief passing shower or two.

KBOS...High confidence in trends with moderate confidence in timing.

KBDL...High confidence in TAF.

Outlook /Sunday through Wednesday/...

Sunday: VFR. Breezy.

Sunday Night: VFR.

Monday: VFR. Breezy.

Monday Night: VFR.

Tuesday through Tuesday Night: VFR. Breezy.

Wednesday: Mainly VFR, with local IFR possible. Breezy. Scattered SHRA, scattered TSRA.

MARINE

Forecaster Confidence Levels...

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

SCAs remain in effect on most waters as easterly swell brings elevated seas in the 4-7 ft range tonight. Winds shift more SW tonight into Saturday, getting up to around 15 kt sustained Saturday afternoon. Gusts to 25 kt possible then as well. Fog possible again tonight over the waters.

Given the continued elevated seas and increase in winds tomorrow, SCAs have been extended through Saturday into part of Saturday night. Winds and seas are expected to remain elevated then, and possibly into Sunday morning.

Outlook /Sunday through Wednesday/...

Sunday through Monday Night: Winds less than 25 kt. Areas of seas approaching 5 ft.

Tuesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft.

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

Wednesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Scattered rain showers, isolated thunderstorms.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 2 AM EDT Sunday for ANZ235-237-251. Small Craft Advisory until 4 AM EDT Sunday for ANZ250-254>256.