The large area in red is the zone we're watching for downpour and thunderstorm development between 2pm and 8pm.  Likely starting as scattered, as more develop they may merge into clusters and pockets of downpours and thunder, meaning later afternoon and evening ones may rain longer than what you'd expect from a typical thunderstorm.  Localized flooding is possible, as are isolated bursts of damaging wind in stronger storms, but my bigger concern is cloud-to-ground lightning - there is no warning for this, so remember "when thunder roars, go indoors" - if you can hear thunder, you're close enough to lightning for it to be a threat!

Humidity continues gradually increasing across New England on a gentle but steady southwest wind, and this new atmospheric moisture combined with an energetic jet stream level disturbance aloft will prompt the development of showers, downpours and thunderstorms Tuesday afternoon.  Unlike Monday, when the focus was across Central, Western and Northern New England, this time the attention is likely to be placed on much of the southern half of New England, including Southern NH and the southern coast of Maine, points southward, except for Southern RI to Southeast MA.  Isolated downpours will develop by lunch hour, but from 2pm to 8pm our weather team has issued a First Alert for a number of storms that will develop over Hartford, Springfield, Worcester, Boston and more.  These downpours and thunderstorms, feeding off the arriving humidity, will drop heavy rain for possible localized flooding, create frequent cloud-to-ground lightning in spots (remember: when thunder roars, go indoors!  If you can hear thunder, lightning is close enough to be a threat), and may produce a few isolated strong and potentially damaging wind gusts.  As the storms become more numerous, some of them will likely merge to form pockets of rain and thunder lasting longer than the usual summertime passing storm, and it’s not impossible the early part of the Red Sox game scheduled for a first pitch at 7:10pm at Fenway Park may be delayed or in some way impacted by rain, but most storms will be exiting over Boston Harbor or fizzling by 8-8:30 pm, leaving patchy fog and a slowly clearing sky overnight.  Wednesday is unlikely to see storms, save for perhaps Northern Maine, because the entire atmosphere will be warm to hot, top to bottom, reducing any cold/warm clash in the sky that drives thunderstorm development.  Temperatures will make a run at 90 degrees Wednesday afternoon and we’re expecting to touch 90 in Boston, with humidity creating a heat index in the middle 90s.  Thursday and Friday the heat peaks: highs in the lower to middle 90s with heat index values near or around 100 degrees.  Although most of Thursday is storm-free, afternoon storms in Northern New England will attempt to build south during the evening, so it’s not impossible we see a storm all the way into Southern New England around suppertime, something we’ll keep an eye on in the coming day.  The heat continues Friday but aloft, cooler air will already be inching closer from the northwest, making conditions favorable for at least scattered late day storms, then Saturday a cold front arrives at the surface from the northwest, triggering more storms after high temperatures reach 90 degrees again for at least some of Southern New England.  Sunday brings a brand new air behind the cold front – highs near 80, lower humidity and a fair sky – an air that is expected to last through next week, even as a passing disturbance brings the chance of a few scattered showers Monday, then a shower or storm again in the latter part of the week.

It’s not saying much given the way this summer has gone, but this week certainly should end up the hottest of the season thus far with a potential heat wave and likely heat index values – “feels like temperatures,” or impact on the body – either side of 100° by Thursday and Friday.  In the meantime, a comfortable start Monday will only slowly give way to increasing humidity in Southern New England over the course of the day and this increasing moisture will first result in wispy clouds, then in increasing haze and puffy, cumulus clouds during the afternoon.  Near and north of the MA Pike, an isolated afternoon shower is a possibility but from late afternoon onward some scattered thunderstorms are possible, with the chance increasing from about 30% near the Pike to 70% and greater in the Berkshires, VT, Central and Northern NH to Western ME.  With an influx of humidity, these storms may result in isolated flash flooding in those spots that already have seen flooding over the last few weeks, and a few storms may produce locally damaging wind gusts.  Above all, remember “when thunder roars, go indoors,” as lightning is a threat in any thunderstorm.  On the water, seas of only 1-2 feet with water temperatures in the 75-80° at the South Coast and near 70° at eastern beaches make for a great day with a very high UV index.  Monday night will be a bit sticky with patchy fog in southeast New England, then Tuesday brings even more humidity - this means an earlier start to scattered storms during the afternoon into evening as temperatures continue climbing and a few communities may near 90° in the Pioneer Valley, Southern NH and the MA/NH border region and Western ME.  This will be a sure sign the air is changing and New England is breaking into the big heat we’ve heard so much about in recent weeks across the rest of the nation, and by Wednesday our First Alert Team is predicting 90° in Boston for the start of a heat wave.  Thursday and Friday should rise into the middle 90s for many in New England, with humid air resulting in heat index values either side of 100°, and our team has issued a First Alert for the impact on the body both days, with urban cooling centers likely to be needed, especially given the limited deep heat so far this season.  Our chance of storms actually drops a bit Wednesday and probably for most of us Thursday, simply because there isn’t much warm/cool clash to create those storms – the atmosphere is just hot from surface to top.  That changes Friday as cooler air starts to move in aloft, so scattered strong later day thunder is possible, then a surface cold front arrives at some point during the day Saturday, prompting more showers and thunderstorms and marking a likely end to the heat and return to our more familiar, seasonable temperature pattern for Sunday into early next week.

While Saturday turned into a great summer day, today has it beat.  No slow start with clouds, fog and sprinkles – just sunshine, save for a patch or two of valley and pond fog where temperatures cooled so comfortably overnight, thanks to comfortably low humidity levels.  That same relatively low humidity continues today, though a gentle sea breeze will allow humidity to rise ever so slightly along the coast and on Cape Cod by day’s end.  Nonetheless, tons of sun with only a few afternoon fair weather clouds will mean a gorgeous summer day from mountaintop to beach.  In fact, the beauty will continue even beyond the beaches, as only a one to two foot wave is expected on the waters today with an early afternoon high tide, and the milder water temperatures we’ve been watching just offshore have finally arrived to Eastern beaches, with ocean water now running around 70 degrees.  Although the weather pattern is about to change this week, it’s a very different change from what we’ve become accustomed to.  Rather than the jet stream “trough,” or southward dip in the jet stream winds, returning to pool energetic disturbances for numerous showers and thunderstorms, this week will feature a relaxing of that trough.  The “ridge,” or northward bump in the jet stream housing lots of hot air across the Western and Central United States, will expand east, affording an opportunity for New England to break into a chunk of the deep heat we’ve heard so much about.  As the first round of increasing humidity gradually arrives Monday, a veil of clouds will dim the sun before a few isolated afternoon and evening showers and thunderstorms are possible late Monday with temperatures in the 80s.  Tuesday brings another increase in humidity, which will mean scattered thunder, particularly during the afternoon.  Thereafter, 90 degrees or hotter seems likely Wednesday through Friday, marking a heat wave of three consecutive 90+ days for at least some of New England, and our team has issued a First Alert for Thursday and Friday, when heat index values – sometimes referred to as “feels like temperatures,” combining the impact on the body of humidity with heat – will reach to around 100°.  At this point, it looks like the heat may start to break down Saturday, prompting scattered storms later Friday and multiple storms possible with the change of air Saturday, then somewhat cooler temperatures at the end of the exclusive First Alert 10-day forecast.

A BIG pattern change is on the way this coming week - the persistent jet stream "trough," or southward dip in the jet stream winds allowing somewhat cooler air and multiple disturbances to drop into the Northeast over the last several weeks, will relax.  As a result, the jet stream "ridge," or northward bump in the jet stream winds with a dome of heat beneath it, will expand north, then east across the nation.  By Wednesday through Friday, temperatures should reach or exceed 90 degrees in New England, and this evening I issued a First Alert for New England for Thursday and Friday, when it looks like heat index values will approach 100 degrees!

I'm not sure there's anything Sunday isn't great for...except maybe cloud-watching!  :)  There will be some fair weather clouds Sunday afternoon in spots, but otherwise it's just an incredible summer day with comfortable humidity levels (only very slowly rising on Cape Cod over the course of the day), highs in the 80s, weak afternoon sea breezes and tons of sun!  Both ocean and lake water temperatures have risen nicely, too!

The round of afternoon to evening downpours and thunder expected to fire up across New England from northwest to southeast will probably be scattered and weakening by the time they arrive to the coastal plain during the evening, but inland, storms will have more impact.  Not only do I expect more storms inland, but they also should be stronger, feeding off increasing humidity, closer to the instigating jet stream level disturbance and associated surface cold front, and capable of producing damaging wind gusts and hail in addition to heavy rainfall.  Of course, recent rains have left inland ground saturated and water-logged, unable to absorb much rain, so simply a heavy downpour that lasts more than a few minutes can be enough to cause at least isolated flash flooding, and longer-lasting downpours that drop a couple inches of quick rain would exacerbate the issue.  Stay alert for warnings through the day and even where there are no warnings issued, keep thunderstorm safety in mind for outdoor plans: "When thunder roars, go indoors."

With the New York Mets in town, Red Sox Nation should enjoy great weather Saturday and Sunday for the games - though some showers and storms will be around Boston Friday evening.  After some midday sprinkles and showers, there'll be a lull during the afternoon in the City with breaks of sun between clouds and humidity.  Inland, storms will be brewing, and these will ease east during the evening, with some arriving to the Boston Metro around and after dinner into the first part of the overnight.  Because they'll be scattered, a complete rain-out seems unlikely, but a delay at some point during the game is possible if one of the storms should float over Fenway.

The decrease in humidity Thursday has eliminated the chance of thunder for nearly all of New England, and has drastically cut the chance of any showers.  Even so, some building, puffy, cumulus clouds Thursday afternoon may yield an isolated, brief shower by early evening in Eastern CT, RI or perhaps just across the state line into Southern Worcester County, MA.  Northwest Maine's mountains also may see an afternoon shower, but the vast majority of New England simply enjoys great weather and relatively comfortable air, which translates to another comfortable sleeping night Thursday night.  Friday is a different story: humidity returns with downpours arriving during the morning to Northern and Western New England (likely only an isolated shower east in the morning), then scattered and locally strong afternoon to evening thunder spreading across New England from west to east.  These storms erupt ahead of a cold front that will bring a gradual return of more comfortable air Saturday, which will really be felt for a lovely day Sunday.

After a drop in ocean water temperatures at eastern beaches early in the week, milder water is returning - and shark sightings are ticking up again, with at least four sightings along the Massachusetts coast in just the last three days.  The water had been blown east by a gentle offshore breeze, but the return of sea breezes and a light onshore wind flow over the next couple of days will bump water temperatures at the coast, as the milder surface water is blown westward once again.  In fact, that onshore wind has been sufficient to keep Cape Cod more humid than the rest of New England - though Thursday is still less humid than most recent days - and as a general southeast wind sets up Friday...and a light wind Saturday...the Cape will continue to hold onto moderate to high humidity while the rest of New England feels dropping humidity Saturday afternoon.  By Sunday, even Cape Cod feels a new, less humid air take over for what looks to be a gorgeous day.