Marine Weather and Tide Forecast for Smith Mills, MA

NEAR TERM /UNTIL 6 PM THIS EVENING/
410 AM Update:

Key Messages:

* Dry and seasonably warm, with modest west winds. Possible coastal seabreezes.

* Highs in the mid to upper 80s, with low levels of humidity.

Details:

High pressure with cyclonic flow aloft (a broad northwest flow)
governs SNE early this morning. Heights slowly rise through today, which will favor seasonably warm temperatures, along with a modest rise in humidity level but should be on the tolerable side of the ledger. Will have to watch for a possible cooling seabreeze near the eastern MA coast today, but all in all, relatively benign weather is expected to kick off the weekend. However today will likely be the last relatively seasonable day in terms of temperatures and humidity levels. Highs generally in the mid 80s.

SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY NIGHT/
410 AM Update:

Key Messages:

* Monitoring for possible overnight to early morning cluster of thunderstorms, which could become strong to severe. Although the chance of occurrence is increasing, location and exact timing are still highly uncertain.

* First day of an extended spell of dangerous heat and humidity begins Sunday. Extreme Heat Warnings and Heat Advisories (Berkshires) issued. Highs into the 90s, with heat indices around 100-105F.

* Mainly dry weather, but couldn't rule out an isolated thunderstorm, which could become strong to severe if it develops.

Tonight:

The main forecast issue for tonight revolves around the track of what is currently a severe mesoscale convective system (MCS) seen in early-Saturday-morning satellite imagery over NE MN. This feature and its convectively-augmented shortwave disturbance is rotating around a building heat ridge over the mid-MS Valley with a plume of mostly capped but extreme convective instability over the mid/northern MS Valley associated with the northeastward advection of an elevated mixed layer coming off the Rocky Mtns.

Models over the last few days have hinted at this for the past few days, although the track of this feature is still a bit uncertain. There is a pretty apparent split in outcomes between the global models and the convective-allowing models; the global models (GFS, ECMWF, NAM- 12) all take this feature across far northern New England or adjacent Quebec late tonight with little to no impact to SNE. On the other hand, the majority of the CAMs have trended further SW, essentially backbuilding the southern end of the MCS into the considerably more unstable air, with a potential MCS moving over parts of or all of SNE during the pre-dawn to early Sunday morning hours (approx 3 to 8 AM).
Although surface based instability progs at that time of day are essentially nil, steepening lapse rates aloft support nearly 1500 J/kg of MUCAPE with increasing effective shear to around 40-45 kt, a shear/instability space which could support embedded elevated supercells above more stable sfc layer.

There still is quite a bit of uncertainty regarding this feature's track and how strong it may become, were it to affect our area. The outcomes here range from passing us by to the north, to an overnight to early-day MCS capable of hail, wind damage and torrential rain. I ended up following the trends in the CAMs, which increase PoPs into the 15-25% range for the southern coast, and increasing to around 30- 50% for northern MA. After coordinating with the neighboring WFOs, also included enhanced wording for gusty winds, hail and heavy downpours. While not set in stone, there has been an uptrend in at least some overnight/early-Sunday impact from this convective complex. Stay tuned on this situation.

Sunday:

While not the hottest day in the stretch, Sunday nonetheless is the first day of a multi-day stretch of dangerous heat and humidity, that looks to last well into Tuesday. While there are uncertainties on some days if we'll truly meet extreme heat criterion, the cumulative effect of at least three days of dangerous heat indices with no significant relief at night could compound the potential for developing heat illnesses. Given this, and in an effort to keep the messaging simple, we opted to make the decision now to change the existing Extreme Heat Watch over to an Extreme Heat Warning starting Sunday through Tuesday, while also adding a Heat Advisory for significantly high heat indices for the Berkshires for the same timeframe.

More specifically for Sunday, the main question mark on the forecast pertains to the effect cloud cover/rain from the early part of the day holds on. As 500 mb heights rise to anomalously high levels even for late June, it's likely any cloud cover should dissipate to full sun by mid to late morning. 850 mb temps warm significantly to around +18 to +20C. In a full-sun setting, that will push highs well into the 90s, with highs in the lower 80s for the Cape and Islands.
Increasingly muggy air will lead to heat indices around 100 to 105 degrees, with a few areas possibly reaching the upper-100s. Lows Sunday night will be very warm and muggy, in the 70s, and areas in the CT Valley have the potential to stay above 80 degrees!

The other potential issue for Sunday is if we can see any afternoon thunderstorms. The strong subsidence from the heat ridge and extremely warm low-level temps leading to capping should make that less likely. Some model solutions however are showing some re- development along residual boundaries/outflow from the MCS from earlier in the day; not sure how realistic that may end up being and though I think dry weather wins out, any storm that can break the cap would have an environment more typical of central Plains instability rarely seen in New England: as much as 4500 J/kg of CAPE, steep lapse rates of 8 C/km albeit with weak shear. Thus any storm could become severe quickly, and while I did leave a 15-20% slight chance mention for thunderstorms, there's probably better chances the day ends up being dry.

LONG TERM /MONDAY THROUGH FRIDAY/
Key Messages:

* Dangerous heat and humidity continues Mon and Tues, with daytime high temperatures approaching the low 100s away from the coast on Tuesday. Heat indices as high as 110 degrees!

* Gradually cooling off Wed thru Fri, although shower and storm threats then return.

Details:

Monday and Tuesday:

Dangerous heat and humidity are expected to continue for both Monday and into Tuesday. Extreme Heat Warnings (Heat Advisories for the Berkshires) will remain in effect. Potential exists for record high temperatures, possibly approaching some of the warmest temperatures ever observed in the month of June for some of our climate sites, with no relief at night. There also won't be much help from Mother Nature to cut into the heat from thunderstorms, with dry weather expected.

For Monday, the question revolves around a possible seabreeze for the eastern MA coast, as a weak high pressure cell builds offshore.
If that develops, it could lead to less-hot conditions for the eastern MA coast until late in the day. While areas away from the eastern coast see highs soar into the upper 90s to lower 100s, with heat indices around 105-110.

The hottest day looks to be Tuesday, as 850 mb temps warm to as much as 21 to 23C. Full sun would support daytime highs temperatures well into the 90s to the lower 100s, with upper 80s for the Cape. Heat indices should reach well into the 100s to 110F.

Wednesday through Friday:

It looks as though the heat ridge shifts southward into the Carolinas on Wed, which would bring less-hot temperatures to SNE. We may still eke out another 90+ degree day in the CT valley, but we should otherwise see highs in the 80s. Heat indices in the 80s to lower to mid 90s. A steadier cooldown toward more seasonable conditions with an easterly wind component taking hold for late in the week.

The risk will increase for daily shower and thunderstorm chances in this period, as the ridge shifts southward and allows for the more active storm track to become more aligned across the mid-Atlantic and Northeast states. More specific details are uncertain regarding this late week shower/storm threat at this time.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/
Forecaster Confidence Levels...

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

12z TAF Update:

Through Tonight: High confidence, though moderate on daytime seabreeze potential.

VFR. West winds around 5-10 kt; seabreeze will likely struggle to develop this morning and may take until 18z to push inland.

Tonight: Moderate confidence.

VFR generally dominates much of the period. Monitoring for a potential cluster of t-storms that may impact the northern/northeast part of Southern New England during the 07-12z period. Indicated PROB30s for TSRA at BAF, BDL, ORH, BED and BOS to hint at this. Exact track of this feature and its southwest extent, were it to develop, is still uncertain but could see a need to hit this potential harder and across the remaining TAFs. Period of wind shear of 40kts also possible from 09-12z as low-level jet moves over the region. Winds become south around 5-10 kt, though could become more variable and potentially quite a bit stronger in any TSRA.

Sunday: Moderate confidence.

Any potential early-day cluster of t-storms moves eastward. VFR generally the rule. An isolated t-storm could develop during the afternoon, and if it does, it would likely become strong to severe quickly. Location is highly uncertain and odds favor dry weather. Winds to become SW around 5-10 kt.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Monday through Wednesday/...

Monday through Tuesday Night: VFR.

Wednesday: VFR. Slight chance SHRA.

MARINE
Forecaster Confidence Levels...

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

Through Sunday...High confidence.

Anticipating mainly sub-SCA conditions through Sunday with west winds today around 10-15 kt and mainly southerly on Sunday at similar speeds, though they increase to near-SCA level late in the day.

Main concern for mariners in this period is the potential for strong thunderstorms affecting the waters overnight tonight into early Sunday.

Outlook /Monday through Wednesday/...

Winds less than 25 kt.

BOX WATCHES/WARNINGS/ADVISORIES
CT...Extreme Heat Warning from 11 AM Sunday to 8 PM EDT Tuesday for CTZ002>004.
MA...Extreme Heat Warning from 11 AM Sunday to 8 PM EDT Tuesday for MAZ003>007-010>021-026.
Heat Advisory from 11 AM Sunday to 8 PM EDT Tuesday for MAZ002- 008-009.
RI...Extreme Heat Warning from 11 AM Sunday to 8 PM EDT Tuesday for RIZ001>007.
MARINE...None.