textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

- Areas of light rain showers this morning with another round developing this afternoon. More widespread rain arrives for the Cape and Islands tonight.

- Turning drier and sunnier with a warming trend Monday and Tuesday.

- Increasing chance for showers and even thunderstorms mid to late week.

DISCUSSION

KEY MESSAGE 1... Areas of light rain showers this morning with another round developing this afternoon. More widespread rain arrives for the Cape and Islands tonight.

Shortwave impulse provides enough lift for a round of scattered showers early this morning across much of northern and central Massachusetts. After a bit of a lull in the morning, the chance for showers increases again this afternoon as a weak surface boundary moves from west to east. CAMs show about 150-300 J/kg of surface CAPE and low level lapse rates steepening to 8-9 C/km, sufficient values for another wave scattered showers and perhaps a rumble of thunder or two.

Attention turns to a sub-990 mb cyclone as it takes a track NE to a path east of the 40N/70W benchmark for late this afternoon and continuing northward into Sunday. There will be a sharp gradient on the northwestern edge of the precip shield as drier air behind a weak front makes its way into interior southern New England. The latest NBM still has the western edge of steadier rains across the MA/RI coastal plain to around I-495, where the GEFS and EPS ensembles have a 60-80 percent chance of at least a half inch of rain.

All told, not really a great weekend if your plans bring you to Cape Cod or eastern MA and RI, but conditions in CT and western MA should be quite a bit better. Highs mainly in the 50s on Saturday with clouds and periods of showers, cooler lower 50s in southeast New England; on Sunday, highs have a decent shot at reaching the low 60s in western interior Southern New England, but are in the mid 50s near the eastern coast as it will take quite a bit longer before we can see peeks of sun develop.

KEY MESSAGE 2...Turning drier and sunnier with a warming trend Monday and Tuesday.

Southwesterly flow advects a much warmer airmass in from the Mid Atlantic Monday and Tuesday. 850 mb temperatures climb to +5C Monday and then +12-14C Tuesday. These values bring highs in the 60s to lower 70s on Monday, but diurnal mixing of lower dewpoints (RHs down to around 30 percent) to go along with breezy southwest winds could warrant fire weather concerns on Monday. Temperatures on Tuesday are even warmer with most areas away from the southeast coast well into the 70s, except SW winds look to be a little lighter and relative humidities aren't quite as low. Will assess how much rain actually falls and then consider fire weather partner input before weighing a decision on fire weather headlines, but they could be possible on Monday and possibly Tuesday.

KEY MESSAGE 3...Increasing chance for showers and even thunderstorms mid to late week.

500 mb pattern amplifies by midweek, with a pronounced upper trough over the nation's midsection and an amplifying ridge associated with above normal temperatures over the eastern and southeast US into the western Atlantic. A slow-moving frontal boundary will be progressing eastward with low pressure developing along it at some point late in the week - guidance varies on when this happens but loose consensus around Thursday. Pretty robust dynamics and decent moisture plume could favor several opportunities for showers and even a few thunderstorms around late in the week. We do need the rain so this should be more beneficial than necessarily hazardous, but either way, expect temperatures to remain slightly above normal but with chances for rain on the increase. Will have to watch this boundary for the development of a more significant low pressure by weeks end but details are unclear at this time.

AVIATION /06Z SATURDAY THROUGH WEDNESDAY/

Forecaster Confidence Levels...

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

06Z Update

Rest of tonight: Moderate confidence. VFR for most, though risk for -SHRA and low-end VFR/MVFR ceilings at BDL and ORH between 06z and 12z. VFR ceilings outside of any -SHRA activity.

Today: Moderate confidence on the timing and coverage of -SHRA.

OVC low-end VFR/MVFR ceilings with passing -SHRA over interior CT/western MA advancing east through 17z to BOS. Looking for SHRA to redevelop across interior Southern New England airports by afternoon with patchy MVFR ceilings and NW winds around 5-10 kt. Better chance for 4-6 SM -RA and MVFR ceilings comes in after 21z for BOS, PVD and the Cape airports as coastal low pressure begins to approach. S winds become SE/ESE Sat afternoon for eastern airports around 5-10 kt.

Tonight: Moderate confidence.

VFR from ORH westward, but MVFR ceilings and steadier -RA continues for PVD, BOS, and the Cape airports. Winds come around to NW around 10 kt Sat night.

KBOS Terminal...High confidence in TAF. Winds to go light late in the day, around 22-04z, which could allow for a period of light onshore winds to develop before becoming S around 5 kt.

KBDL Terminal...High confidence in TAF.

Outlook /Sunday Night through Wednesday/...

Sunday Night: VFR.

Monday through Tuesday: VFR. Breezy.

Tuesday Night: VFR. Windy with gusts up to 30 kt. Slight chance SHRA.

Wednesday: VFR. Windy with gusts up to 30 kt. Chance SHRA.

MARINE

Forecaster Confidence Levels...

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

Overall high confidence.

Winds and seas should remain below small craft advisory levels through today and tonight. Winds increase to 10-15 kt this afternoon, with seas 4 ft or less all waters. Mainly dry weather, though rain begins to increase on the southern waters later tonight into Sunday.

Winds and seas then increase to small craft levels late Sunday morning as winds turn NW with gusts 20-25 kt and seas building to 4-6 ft on the outer waters. Rain could also locally reduce visibility.

Outlook /Sunday Night through Wednesday/...

Sunday Night: Winds less than 25 kt. Local rough seas.

Monday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft.

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

Tuesday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas.

Tuesday Night: Strong winds with gusts up to 35 kt. Local rough seas.

Wednesday: Strong winds with gusts up to 35 kt. Seas up to 5 ft. Chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 11 AM Sunday to 2 PM EDT Monday for ANZ250-254>256.