textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes, the forecast remains on track.

KEY MESSAGES

- Summerlike warmth Today and Wednesday away from the coast, with scattered late day/early evening thunderstorms and a low risk of severe weather.

- Backdoor front may bring cooler temperatures Thu-Sat, especially in eastern MA, but uncertainty is high in exactly where it ends up.

- More seasonable temperatures early next week.

DISCUSSION

KEY MESSAGE 1...Summerlike warmth Today and Wednesday away from the coast, with scattered thunderstorms & a low risk of severe weather.

Confidence remains high in summerlike warmth Today and Wednesday away from both coasts, as strong subtropical ridge builds over the region from the Gulf. All hi res guid has highs both days easily reaching the upper 70s to lower 80s inland (+18C to +20C at 925 mph). Any early morning fog will burn off rapidly. Meanwhile, a weak pressure gradient supports cooling seabreezes for the immediate coastal areas, with temps dropping into the 50s to around 60. However, locations such as Boston and eastern MA, late morning/early afternoon seabreeze may give way to a warmer wind shift to the SSW after 18z/19z, as low level southwest jet traverses the region. This would yield a late day high temp, after 4/5pm.

We continue to monitor the potential for severe storms during late afternoon and evening both Tue and Wed, mainly 2 PM to 10 PM (highest probs 4-8pm). Low amplitude s/wvs moving through the westerly flow, only yielding weak forcing for ascent, which is evident by the lack of height falls from each of these s/wvs. However, modest mixed layer CAPE up to 1000 j/kg, modest mid level lapse rates around 6.5C/KM and 0-6km shear up to 45 kt, providing sufficient instability and shear to compensate for the lack of strong forcing. This is reflective by hi res guid offering 2-5km updraft helocity tracks into western-central MA/CT, along with highest probabilities of lightning. Convection will weaken as it traverses eastward into RI and eastern MA. Not expecting a widespread severe weather, but can't rule out a few isolates storms that approach severe in western-central CT/MA. Given the shear and instability, along with steep low level lapse rates, strong to damaging winds will be the main threat.

As previous forecaster noted, atmosphere still looks favorable for thunderstorms on Wed, although the high-res models don't show much in way of activity. Severe risk is lower on CSU and SPC HREF with axis shifted farther south into CT/RI and south of the Mass Pike. While overall severe threat remains low, we can't rule out a few storms capable of producing localized wind damage or hail.

KEY MESSAGE 2...Backdoor front may bring cooler temperatures Thu- Sat, especially in eastern MA, but uncertainty is high in exactly where is ends up.

Temp forecast becomes more uncertain later this week, as short wave energy riding up and over the top of the subtropical ridge, may be strong enough to lower heights and have a backdoor front enter SNE, especially northeast MA. However, at this time range, low predictability regarding the amplitude of individual short waves and attending surface boundaries/backdoor fronts. Thus, certainly potential for big temperature busts this far out in time.

Showers and thunderstorms could be more widespread Friday, as multi model guidance suggest a more robust mid level short wave moving across the Northeast into New England.

KEY MESSAGE 3...More seasonable temperatures early next week.

As expected, difficult to sustain temps 20+ degs warmer than normal in April, thus good multi model agreement (especially at this time range) that a strong cold front is expected to cross region sometime Sun, accompanied by some showers, that could spill into early Monday. Much cooler airmass follows behind front early next week, with temperatures returning to more typical levels for mid April, generally in 50s to around 60.

AVIATION /06Z TUESDAY THROUGH SATURDAY/

Forecaster Confidence Levels...

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

06z TAF Update:

Tuesday...High Confidence overall, moderate on exact timing and southeast extent of T-storms.

VFR with S/SW winds and coastal sea breezes 8-12 kts. Sea breezes likely shift to SSW after 18z/19z. Scattered showers and thunderstorms are possible during the afternoon and evening (20- 00Z), especially across interior southern New England. Lower confidence in thunderstorm chances into RI and eastern MA. Brief MVFR possible in any moderate showers or thunderstorms. Winds should most likely lean more SW at 10-15 kts, gusts to 22 kts in the shower/storm timeframe. Locally higher/erratic gusts in any thunderstorms.

Tuesday night...high confidence in trends, lower on exact timing of details.

Any evening scattered showers/t-storms dissipate by 02z/03z. Mainly VFR and dry thereafter. Although, we will have to watch IFR conditions just offshore, northeast of KBOS.

Wednesday...high confidence on trends, lower on exact timing of details.

Mainly VFR and dry in the morning, then isolated to scattered afternoon/evening showers/T-storms. Backdoor front may come onshore into northeast MA, including KBOS and possibly accompanied by IFR/LIFR conditions in low clouds/fog.

KBOS Terminal...High confidence in TAF. Early seabreeze develops 14z/15z, then likely shifts to the S after 18z/19z. Showers possibly 21z-02z. Probability of lightning too low to include in the TAF.

KBDL Terminal...High confidence in TAF. Brief -TSRA possible 19z- 00z.

Outlook /Wednesday Night through Saturday/...

Wednesday Night through Thursday: VFR. Chance SHRA, slight chance TSRA.

Thursday Night through Friday Night: VFR. Chance SHRA.

Saturday: Mainly VFR, with local MVFR possible.

MARINE

Forecaster Confidence Levels...

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

220 AM update...

High confidence through the end of the week, except across the northern MA waters, where uncertainty is high regarding the timing and position of backdoor front Wednesday through the end of the week.

SCA remains in effect for leftover rough seas. Weak pressure gradient will support subsiding seas along with developing seabreezes near shore beginning late Tue morning. Only other issues will be late night/early morning fog and possible late day/evening brief isolated shower/thunderstorm.

Outlook /Wednesday Night through Saturday/...

Wednesday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers, slight chance of thunderstorms.

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

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

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

Saturday: Winds less than 25 kt.

CLIMATE

Upcoming record highs:

Tue 4/14 Boston 83 in 2023 Hartford 96 in 2023 Providence 87 in 2023 Worcester 90 in 2023

Wed 4/15 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...Small Craft Advisory until 11 AM EDT this morning for ANZ235- 237. Small Craft Advisory until 2 PM EDT this afternoon for ANZ254>256.