textproduct: Boston / Norton

WHAT HAS CHANGED

Monitoring early morning shower and embedded thunderstorms across southern New England, though storms aren't anticipated to become severe.

KEY MESSAGES

- Scattered showers and thunderstorms remain possible today and Friday.

- Dry, seasonable, and comfortable weather returns for the weekend.

- Rain chances return late Sunday into Monday, followed by quieter weather into the middle of next week.

DISCUSSION

KEY MESSAGE 1...Scattered showers and thunderstorms remain possible today and Friday.

Monitoring a cluster of showers with embedded thunderstorms south of I-90 early this morning, mainly impacting Connecticut as of 0530Z. While storms remain sub-severe, they are producing lightning and localized wind gusts up to 40 mph. This complex of showers and storms will move east toward Rhode Island and southeastern Massachusetts prior to sunrise, leading to a wet start for the early morning commute. However, multiple runs of the HRRR overnight have shown the potential for a secondary cluster of showers and embedded thunderstorms to redevelop across eastern Connecticut, Rhode Island, and southeastern Massachusetts from 09Z to 12Z. Otherwise, expect a cloudy start to the day.

Clouds disperse this afternoon with daytime heating and mixing within the boundary layer, allowing temperatures to warm into the lower to middle 80s. Storm coverage this afternoon remains limited. As mentioned by the previous forecaster, the mid-levels are dry with northwest flow. Outside of a few hit-or-miss showers, the afternoon is largely dry as the better forcing remains associated with the mid- level trough and shortwave across northern New England. By late this evening, the first cold front moves offshore, with a secondary surge of drier air reinforcing on Friday. CAMs try to initiate a few pop- up storms along the edge of this boundary, but given the dry air in place, don't expect anything more than isolated coverage of garden- variety thunderstorms. The vast majority of southern New England remains dry, with lower humidity and highs in the lower 80s.

KEY MESSAGE 2...Dry, seasonable, and comfortable weather returns for the weekend.

Quiet weather-wise this weekend as an area of high pressure originating from northern Canada settles across the Northeast for Saturday and the first half of Sunday. PWATs lower quite dramatically, with values between 0.5 and 0.7 inches, or nearly one standard deviation below normal. Thus, little to no humidity is expected Saturday, and conditions may actually feel quite dry, with almost fall-like humidity. Temperatures remain near seasonable levels, ranging from the upper 70s to lower 80s. Saturday night into Sunday morning, clear skies and light winds provide favorable conditions for effective radiational cooling. Lows tumble into the mid-50s, while urban centers hover near 60 degrees. On Sunday, high pressure exits as a low pressure system approaches from the Great Lakes region. Warm air advection ushers moisture northward from the southwest with the passage of a warm front, resulting in increasing cloud cover through the afternoon. Temperatures remain seasonable and similar to Saturday, though dew points increase to near 60 degrees.

KEY MESSAGE 3...Rain chances return late Sunday into Monday, followed by quieter weather into the middle of next week.

The next opportunity for rainfall comes during the second half of Sunday into Monday. However, there remains uncertainty regarding rainfall amounts, as the best forcing is associated with the surface low and track variability makes it difficult to pin down where the greatest rainfall will occur. This is worth monitoring, as global guidance is in agreement that PWATs may exceed 2 inches, indicating the potential for heavy rainfall. This is also supported by a Marginal Risk (level 1 of 4) for excessive rainfall. Global ensembles highlight areas north of I-90 as having the greatest likelihood for measurable rainfall, with a 40-60 percent probability of at least a half inch of rain between Sunday evening and Monday evening. That said, if rainfall becomes more convective, localized totals could be higher. One positive is that this system appears progressive, with the cold front clearing east of New England on Monday. Drier air then advects in from the northwest, leading to another dry stretch from the latter half of Monday through Tuesday and Wednesday as surface high pressure builds back into the region. During this time, temperatures are expected to remain seasonable, with highs in the lower to middle 80s and tolerable humidity as dew points remain in the lower 60s.

AVIATION /12Z THURSDAY THROUGH MONDAY/

Forecaster Confidence Levels...

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

Today...Moderate confidence.

Leftover SCT/BKN VFR/MVFR decks should begin to scatter out between 15-17Z, increasing the risk for SHRA/TS, mainly north of the Mass Pike, as a sfc cold front moves through. Coverage looks spotty but will need to monitor with later updates. Winds SW to W under 10 kt, then shifting to WNW/NW at 5-10 kt after 20Z.

Tonight...High confidence.

Any lingering SHRA dissipates early, with VFR conditions prevailing thereafter. NW winds 5-10 kt.

Friday...High confidence.

VFR. Low probability of an isolated afternoon thunderstorm across interior southern New England; otherwise, dry. NW winds 8-12 kt.

KBOS Terminal...High confidence.

KBDL Terminal...High confidence.

Outlook /Friday Night through Monday/...

Friday Night through Saturday Night: VFR.

Sunday: Mainly VFR, with local MVFR possible. Breezy. Chance SHRA.

Sunday Night: Mainly VFR, with local IFR possible. Breezy. Chance SHRA, slight chance TSRA.

Monday: VFR. Breezy. Chance SHRA.

MARINE

Forecaster Confidence Levels...

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

Through Friday...High confidence.

Early morning showers and embedded thunderstorms across the southern waters off the coasts of Rhode Island and southeastern Massachusetts today will clear by mid to late morning. SW to SSW winds are expected today, with gusts around 20 kt. Winds shift to the NW tonight at 10-15 kt and continue through Friday, along with dry conditions. Seas will remain below 3 ft throughout the forecast period.

Outlook /Friday Night through Monday/...

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

Saturday through Saturday Night: Winds less than 25 kt.

Sunday: Winds less than 25 kt. Slight 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, slight chance of thunderstorms.

Monday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Chance of rain showers, slight chance of thunderstorms.

BOX WATCHES/WARNINGS/ADVISORIES

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