textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes to the forecast since the last update.

KEY MESSAGES

- Unseasonable warmth and dry weather continues Wednesday

- Wet and unsettled weather returns Thursday through the weekend with continued warmer temperatures to start before cooler temps arrive Sunday and beyond.

DISCUSSION

KEY MESSAGE 1...Unseasonable warmth and dry weather continue Wednesday

Mid-level ridging and surface high pressure continue to dominate the pattern through early Thursday. A thermal ridge with 925mb temperatures +14 to +17C positions across southern New England. Mainly sunny skies, fairly dry soils, and SW flow will typically support better mixing than most guidance anticipates. This will likely favor temperatures warmer than what model guidance projects. High temperatures Wednesday are likely to be in the upper 60s to low 70s range, with mid 70s possible in the valleys. Can't rule out temperatures overperforming reaching the upper 70s. NBM probabilities show low to moderate probabilities (20-50%) for greater than 75 degrees in portions of the CT Valley and Boston Metro. If this does happen, records have potential to be met or broken. Record at BOS is 78, PVD 77, ORH 74, BDL 78.

A warm day will be followed by a warm night. Overnight temperatures fall into the 50s which is about average for our high temperatures this time of year. Some locations may have a shot at meeting/breaking the high min record.

KEY MESSAGE 2...Wet and unsettled weather returns Thursday through the weekend with continued warmer temperatures to start before cooler temps arrive Sunday and beyond.

Ensemble guidance continues to herald the end of our highly anomalous stretch of dry weather by Thursday, kicking off a period of 36-48 hours of periodic rainfall, sometimes heavy. This comes courtesy of a few things; first is an approaching front extending from a trough of low pressure crossing the Great Lakes. After moving through NY the front stalls draped across New England from SW to NE late Thursday. This brings the initial round of rain chances for Thursday, mainly for western areas of SNE while much of the region southeast of a BDL-ORH line may stay dry. A better shot of widespread and heavier rainfall then arrives for Friday into early Saturday as a secondary wave of low pressure forms along the front. It deepens as it lifts north in the vicinity of Cape Cod Saturday and then even moreso over the Gulf of Maine on Sunday by which time we'll be on the drier side.

There will be a lot of moisture for this system to work with as persistent moist SW flow ahead of the upper trough pulls in PWATs over 1.5" and dewpoints into the low 60s! This will lead to very warm low temps Friday morning (in the low 60s) but more importantly, fuel for the good dynamics to work with. Those elevated dewpoints will make for some instability allowing for some convection to contribute to localized downpours, while convergence around the low and placement beneath the RRQ of a 105kt upper jet will provide more lift in the meso/synoptic scale. Exact placement of the swath of heaviest rainfall will unfortunately not be nailed down until we get closer to the event as it will be determined by where exactly the front stalls. Generally ensemble guidance is calling for a 1-3" rainfall with EPS and GEFS calling for a 50-60% and 30-40% chance of AOA 1" of rainfall respectively, centered over central and eastern SNE. Fortunately, we've been very dry and Flash Flood Guidance is high. Thus, not expecting flash flooding to be an issue though some poor drainage/urban flooding is possible especially given the leaves blocking drainage this time of year.

Beyond Saturday we'll see some scattered showers continuing as the upper trough is slow to exit overhead; nothing like Friday/Saturday, though, as the atmospheric column begins to dry out going into next week. Behind the trough colder NW flow ushers in a colder (closer to normal) airmass for early next week as high temperatures return to the 50s.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

Forecaster Confidence Levels...

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

18z TAF Update:

Today and Tonight...High confidence.

VFR. Mid level ceilings this afternoon and tonight. Low chance for development of a low stratus deck across the south coast and Cape/Islands 06-12Z. Not high enough confidence to include in TAFs. Winds generally SW at 5-15 kts this afternoon. Light SSE winds for a period early this afternoon before shifting to the S/SSW by 21Z.

Wednesday...High confidence.

VFR. SCT higher decks possible during the day. Areas of lower FEW/SCT cloud decks can't be ruled out along the south coast/Cape terminals. Winds SSW/SW at 5-15 kts. Few gusts to 18 kts for ORH and Cape/Island terminals in afternoon.

KBOS Terminal...High confidence in TAF. Lighter winds have resulted in a weak sea breeze early this afternoon. SSE winds possible until winds mix out a little more and increase above 06 kts (by 21Z).

KBDL Terminal...High confidence in TAF.

Outlook /Wednesday through Sunday/...

Wednesday: VFR. Breezy.

Wednesday Night: Mainly VFR, with local IFR possible.

Thursday: Mainly VFR, with local IFR possible. Breezy. Chance RA.

Thursday Night: Mainly VFR, with local IFR possible. Chance RA.

Friday: Mainly MVFR, with local IFR possible. RA, slight chance TSRA.

Friday Night: MVFR/IFR conditions possible. RA, slight chance TSRA.

Saturday through Saturday Night: VFR. Chance RA.

Sunday: VFR. Slight chance RA.

MARINE

Forecaster Confidence Levels...

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

Through Wednesday Night...High confidence.

Surface high pressure stays positioned across southern New England through Thursday. This will favor seas 1-3 ft and winds less than 25 kts out of the SW. Winds become breezy by Wednesday afternoon with 20 kt gusts. A few gusts up to 20-25 kts are possible with the greatest chance for the SE coastal waters near the Cape/Islands. Gusts likely aren't consistent enough 25kt+ over a period to warrant SCAs at this time.

Outlook /Wednesday through Sunday/...

Wednesday: Winds less than 25 kt.

Wednesday Night: Winds less than 25 kt. Patchy fog. Local visibility 1 to 3 nm.

Thursday: Winds less than 25 kt.

Thursday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain.

Friday: Winds less than 25 kt. Areas of seas approaching 5 ft. Rain, slight chance of thunderstorms.

Friday Night: Winds less than 25 kt. Seas up to 5 ft. Rain, slight chance of thunderstorms. Local visibility 1 to 3 nm.

Saturday: Winds less than 25 kt. Seas up to 5 ft. Rain, slight chance of thunderstorms.

Saturday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of rain.

Sunday: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain.

CLIMATE

Persistent unseasonable warmth over the next several day will challenge calendar-day record highs and record high minimums across southern New England climate sites.

Daily Record Highs to Watch:

Boston (BOS): Wednesday 78F (1987)|Thursday 79F (1994)

Hartford/Bradley (BDL): Wednesday 78F (1987)|Thursday 75F (2022)

Providence (PVD): Wednesday 77F (1987)|Thursday 75F (1994)

Worcester (ORH): Wednesday 74F (1987)|Thursday 73F (1994)

Daily Record Lows to Watch:

Boston (BOS): Thursday 56F (1994)|Friday 57F (2020)

Hartford/Bradley (BDL): Thursday 55F (1994)|Friday 56F (2020)

Providence (PVD): Thursday 56F (1994)|Friday 58F (2020)

Worcester (ORH): Thursday 55F (1994)| 55F (2020)

BOX WATCHES/WARNINGS/ADVISORIES

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