There will be two parts to today’s weather. The first is already underway across the region and will feature variable clouds, warm temps, and slowly but surely increasing humidity. Highs will warm into the 80’s for most with some upper 70’s along the coast. All in all, most of the day will be absolutely lovely, albeit a bit sticky. The second part of the day will begin in the late afternoon over Western NH and slowly move E into Maine by late evening. This will be the showers and thunderstorms section of today’s weather. The ingredients are not here for big severe storms, but there is plenty of moisture in the air and a period of wet weather is expected, possibly with a few rumbles. The best chance for a thunderstorm will be over western NH where a few strong wind gusts are possible. Otherwise, most areas just see showers.
HRRR Showing A Band Of Showers With Embedded Thunderstorms/Downpours. Image Credit: Weatherbell
Here’s a bit of a visual on how I think things play out this evening. A band of showers will likely impact everyone with light to moderate rain. Within that band, there will likely be pockets of heavier rain that not everyone sees. There are also likely to be a few rumbles of thunder especially over Western areas. Strong storms from NY and VT could hold on to produce a few strong wind gusts in Western NH but overall no severe weather is expected. Thunderstorms will enter NH late this afternoon between 2 and 4 PM before moving east and weakening into a band of showers that will move into Maine in the evening between 5 and 7 PM. The map shown is valid at 8 PM but is not intended to pinpoint details. I just wanted to give a sense of what the situation might look like come evening. Rain will move out early in the overnight hours and tomorrow looks like another lovely summer day.
After a wild couple days for some, everyone gets a bit of a break today as high pressure takes hold. Expect warm temps, light breezes (sea breeze along the coast), and dry air. Highs will rise into the 80’s with some upper 70’s possible along the coast and in the far north. No 90’s are expected anywhere today which will be refreshing. Even more refreshing will be the lack of humidity as dew points drop into the 50’s. Mainly sunny skies are expected.
Strong to severe storms are impacting the region currently, as forecast. The strongest storms are across SW areas which is as forecast as well. Storms will continue across the region through this evening before dying out with the loss of heating from the sun. Tomorrow will be warm and dry as high pressure builds in but the quiet weather only lasts a day and by Monday, another cold front will be at our doorstep with the chance for showers and storms, some of which could be severe.
12Z GFS Showing The Setup Aloft Monday. Image Credit: Accuweather
Another shortwave will be digging south across Eastern Canada Monday and out ahead of it, divergence aloft and convergence at the surface thanks to an approaching cold front will provide the large scale rising motion necessary for strong storms. As of now, model guidance is in agreement we will have a trigger for storms Monday. Also of note is that the large scale pattern of NW flow around the NE side of the Central US heat dome supports this shortwave crossing the area Monday. We have our trigger. Now will there be enough fuel for strong storms? Instability is the biggest question at the moment.
NAM Showing Onshore Winds Limiting Instability Monday. Image Credit: Weatherbell
Most model guidance suggests that winds will be out of the SE for most of the day Monday. A SE wind is one off the cold Gulf of Maine which would keep temps in the 70’s for most. That SE wind and those low temps would sufficiently stabilize the atmosphere so that we would stay more or less storm free. This could change, however. A peek at the Euro ensemble guidance suggests that timing remains uncertain and the potential exists for winds more out of the S or SW following the passage of a warm front. Euro ensemble mean CAPE shows this potential with values between 1,000 and 1,500 j/kg Monday afternoon. The timing of both the warm and cold fronts will be watched closely in the coming days to determine if strong storms indeed can form.
GFS Showing A Juiced Atmosphere Monday. Image Credit: Weatherbell
One thing to keep in mind is that even without typical severe storm impacts (hail, wind, etc.), there could very well be heavy rain on Monday. Guidance is pointing to Precipitable Water values (PWATs) of near 2″ which is tropical. Be aware that even without a severe thunderstorm threat, there very well may be a heavy rain threat. We do need the rain, however as southern areas are in moderate to severe drought.
Warm and dry conditions return for the middle of next week and a more substantial rain event hopefully will arrive by the end of next week into next weekend. More on that as we get closer.
I’ll have more updates on this event on Twitter tonight and tomorrow.
Today will feature slightly cooler temps, less humidity, and another chance for strong/severe thunderstorms. The thunderstorm threat will develop later this morning and continue through the early evening hours. Storms are more likely in SW areas where more energy will be available aloft. While most of the storms are not likely to become severe, some of the stronger cells do have the potential to mix down some strong wind gusts and perhaps some small hail. Frequent lightning and heavy rain are the main threats. Highs will range through the 80’s with dew points in the 60’s which is still warm and certainly not dry but far better than yesterday.
WV Imagery Showing A Disturbance Dropping SE This Morning. Image Credit: SSEC
A vigorous disturbance is currently located north of the Great Lakes and is forecast to drop SE and intensify, arriving in our area bu sunset. Storms will form out ahead of it late this morning/early this afternoon. When I talk about forecasting thunderstorms, I talk about the trigger, the organizer, and the fuel. This disturbance will be the trigger for today’s storms.
40-50 Knots Of Deep Layer Shear Will Organize Storms Into Small Clusters Capable Of Some Damaging Wind Gusts. Image Credit: SPC
A band of strong winds and powerful shear will rotate around the disturbance today. The strongest winds will be pointing at Southern New England while Northern Maine sits in the calm aloft associated with the disturbance being to their south. In southern Maine/New Hampshire, we’re a bit on the edge. We likely see enough shear to get some small clusters but large squall lines are unlikely. If that disturbance can intensify enough fast enough, it could pull some of those winds north and we could see a bit more action. If it remains a little weaker, those winds will continue screaming towards SNE. These winds will be our organizer.
Hi-Res NAM Showing Modest Instability With More Unstable Air Moving In From The West. Image Credit: Weatherbell
The biggest question today is how unstable the air will be. A cold front moved through last night (remember those storms?). That front has moved offshore and has taken the extremely soupy/unstable air with it. We are left with marginal moisture and several areas of clouds to limit surface heating. Model guidance suggests that more unstable air will try to filter in from the west later today but I have to wonder if that will make it in time. Also of note with regard to instability is wind direction. Westerly winds don’t exactly bring in the warm moist air you need for big storms. Regardless, we do still have leftover moisture and dew points remain in the 60’s which is sufficient for at least some storms. Also, wide swaths of clear skies this morning support some solid surface heating which will bring temps up into the 80’s, also plenty sufficient for storms.
All that to say, ingredients are at least sufficient for some storms, a few of which could be severe with strong winds and small hail. However, I do have doubts as to how unstable the atmosphere is. Also, we don’t have optimal winds aloft for organizing storms into lines capable of widespread wind damage. While organized severe storms are not forecast, still do keep an eye to the sky today and be prepared to duck inside for a few minutes if you plan on heading outside.
More storms are possible Monday and Thursday with two more cold fronts.
Today will feature downright hot temps, oppressive humidity, and the chance for a strong thunderstorm. Temps are currently in the 60’s but will quickly soar into the upper 80’s to low 90’s as SW winds bring hot, humid air into the area. A cold front will be pushing into the area from the west this afternoon and some showers and storms are likely to develop out ahead of it. This risk appears to be small and localized as there are indications that the setup isn’t quite as robust as initially forecast.
WV Imagery Showing Why I’m Skeptical Of Widespread Severe Weather Today. Image Credit: SSEC
Water Vapor imagery this morning highlights why I don’t see widespread severe storms in our future today. A disturbance aloft is currently causing showers over northern and western areas. I highlighted this on the map with the purple line. This disturbance will race off to the NE today and may cause some storms over Atlantic Canada. Behind this disturbance, two things are happening that will limit storm development. First, dry air is moving in aloft. Some mid level dry air is good for storms (but that’s a long story), however too much dry air will limit their development. Also of note is that there doesn’t appear to be another substantial upper level disturbance to trigger storms.
Surface Winds Currently Showing A Cold Front TO Our West. Image Credit: earth.nullschool.net
With the absence of a strong upper level trigger, we then look to the surface for a frontal system that could trigger storms. Our cold front this morning is quite unimpressive with no major temp drop behind it and only a subtle wind shift. This further lowers confidence in widespread storms. Morning cloudiness that will limit instability is another factor working against big storms. That being said, we do still have the risk for some storms this afternoon and evening. They will be scattered in nature and either you get one or you don’t. The risk for storms will be greater the farther NW you go in the area with the mountains most likely to see storms. Any storms that do form have the risk to become severe with damaging winds and small hail. This risk is even more isolated but it is something to be aware of as you go about your day. These storms are nothing to cancel plans or panic over but do be prepared to duck for cover if you’re heading into the great outdoors this afternoon.
The heat and humidity sticks around into early next week with more storms possible both tomorrow, Monday, and Tuesday. No cool weather is expected in the next 7 days.
Today begins our march up the temp ladder with high pressure moving offshore and SW return flow moving in behind it. Look for highs today in the upper 70’s north to mid 80’s south. Skies look to be mainly sunny, if not a bit hazy due to smoke from distant Canadian wildfires. Winds will be increasing slowly out of the SW but before then, a weak sea breeze could develop especially closer to the center of the high (located off the NJ coast), in southern areas.
Heat and humidity will continue to build tomorrow with highs in the 90’s and dew points approaching 70. Showers and storms are possible tomorrow and they could be severe. I won’t be able to provide detailed coverage for this threat seeing as I’m down at a weather workshop in MA. Please check with the SPC, NWS Gray, and local media for reliable information about the storm threat. I will have another update tomorrow morning.
Today will feature mainly sunny skies, comfy temps, and even comfier dew points. Current dew points this morning are in the 40’s and low 50’s which will make for a beautiful day in terms of not having to deal with humidity. Temps will be similarly pleasant with highs ranging through the 70’s and possibly hitting 80 south. Mostly sunny skies are expected today as well. Get out there and enjoy it!
Heat and humidity will start to build tomorrow with storms possible by Friday. More heat and humidity for Sunday with more storms possible Monday.
Today will feature a mix of sun and clouds, cooler temps, and drier air as a cold front has moved just offshore. Look for highs today ranging from the upper 60’s north to the upper 70’s south. Dew points will remain solidly below 60 which, combined with a light NW breeze, will make today feel fantastic especially compared to the heat and humidity of late. The one caveat of such lovely temps is that upper level disturbances racing around a trough to our north will keep clouds in the mix most of the day. The upslope/downslope regime today will keep these focused in the mountains with the coast seeing more sun than clouds but a bluebird day does not appear to be in the cards for very much if any of the area today. Enjoy the nice weather while it lasts because starting tomorrow, we begin to slowly but surely heat back up. More storms are possible by next weekend.
Today will feature the passage of a strong cold front which means some “thundah boomahs” are in store for most of the area. Look for highs today ranging through the 80’s with some low 90’s possible south. Humidity will be on the increase as well with dew points climbing through the 60’s today. Some clouds are being reported currently but should be moving out of the way shortly which will leave the strong July sun to destabilize the atmosphere. CAPE values of 1000-1500+ j/kg should be in place by mid day today. A line of convection has already formed over Western NY and this will strengthen and move east today. New storms will fire along and ahead of this line which is associated with the prefrontal trough. The cold front itself is lagging to the north west. Everything I talked about in yesterday’s update holds true for today and no big changes seemed to become apparent last night.
When thunder roars, go indoors. Keep an eye to the sky today.
A special update this evening to cover tomorrow’s severe storm threat. A cold front will approach the region from the NW tomorrow driving cool Canadian air into a tropical airmass that will be reinforced tonight by increasing southerly flow. As a result, showers and storms will fire to our west tomorrow afternoon and move east into our area tomorrow afternoon into the evening hours. Heavy rain and damaging winds will be the primary threats along with frequent lightning though some small hail cannot be ruled out. Tornadoes appear not to be an issue.
12Z GFS Showing The Setup Tomorrow With A Cold Front Trailing A Pre-Frontal Trough. Image Credit: WxBell
There will be two surface features to trigger storms, a cold front, and a pre-frontal trough. Right now, guidance is indicating that a line of storms will form along the pre-frontal trough early in the afternoon just south of the mountains. This line then looks to move SE and strengthen as it encounters more instability. There looks to be very little in the way of morning convection but a warm front won’t be too far to our north so some clouds will likely be limiting instability in the morning in the far north. Farther south, this does not appear to be a concern. Winds will be out of the SW for the most part except perhaps for the midcoast where a southerly component will be present. The SW winds will act to keep the coast more or less in play for severe weather as there does not appear to be a strong sea breeze influence.
18Z 4km NAM Showing The Two Storm Threats Tomorrow Evening. Image Credit: Wxbell
The pre-frontal trough will likely focus storms along the coast and south into SNE during the late afternoon/evening hours. Farther north, we will turn to the cold front for thunderstorms in the mountains. These storms will likely be more of a mid to late evening affair as it will take longer for that area to destabilize due to morning clouds. Storms along the cold front itself will likely be more hit or miss but could pack more of a punch as they won’t have tons of competition. These storms will fizzle as they head into the atmosphere cooled and stabilized by the pre-frontal trough convection.
There are three main ingredients needed for strong/severe thunderstorms: instability, an organizer, and a trigger. What will set the storms off, what will organize them into lines capable of damaging winds, and then what will ‘feed’ them? We already know a cold front/pre frontal trough will do that at the surface (see maps above). Now what will organize them? For organized lines of strong to severe storms to form, you need wind shear both in the low levels (0-1km) and in the upper levels (0-6km). The upper level shear will organize the storms and the low level shear will help mix down strong winds aloft so they can reach the ground.
Guidance is indicating a sufficient supply of both tomorrow as upper level energy (wind) moves in from the west associated with a short wave trough currently moving into the Great Lakes region. 25-30 kts of low level shear isn’t crazy but it will likely be enough to mix down some strong winds so be prepared for that threat. Now that we’ve established that there is sufficient low level shear, what about upper level shear?
12Z GFS Showing Sufficient 0-6km Shear For Some Organized Storms Tomorrow. Image Credit: Accuweather
That same short wave trough will bring some 0-6 km shear that is likely going to be enough to organize storms into lines capable of damaging winds. Also notice the winds heading away from each other (spreading out) as they approach the coast. This divergence aloft will aid in getting air rising tomorrow which will further assist in storm development. We now know that we’ll be able to trigger storms and get them organized but the next question is will there be any fuel for them to grow strong enough to introduce the threat for severe weather? For that we look to instability.
12Z GFS Showing Dew Points In The Upper 60’s To Low 70’s Tomorrow. Image Credit: WxBell
Instability has two components: heat and moisture. You need heat to provide enough energy for air to rise, and you need enough moisture to produce storm clouds when that air rises. Temps will climb into the 80’s tomorrow so that won’t be a problem but how about moisture? For that we turn to dew points which are forecast to be in the upper 60’s to low 70’s which is more than enough to trigger storms. Precipitable Water values (PWAT’s) will approach 2″ indicating a very moist atmosphere even well above the ground. Such high available moisture will support very heavy rain which could cause some minor flooding problems and will certainly be beneficial in easing our current drought.
12Z NAM Sounding For Portland Valid 4PM Tomorrow.
The forecast sounding for PWM tomorrow afternoon brings it all together. Notice the red and green lines (temps, and dew points) remain close to each other through the first 35kft+ of the atmosphere (as a side note for the hardcore weather geeks out there, that temp trace looks mighty close to the moist adiabat). Notice how sharply the red line goes from right (hot) to left (cold) in the first 5kft. This indicates very steep lapse rates (of up to 11c/km!) which also supports strong storms. Strong winds throughout the atmosphere will help organize the storms into line segments capable of damaging winds. All in all, a pretty solid setup especially for New England.
12Z NAM CAPE Showing Plenty Of Instability Tomorrow Afternoon. Image Credit: Weatherbell
To wrap up the instability part, we look at CAPE (Convective Available Potential Energy) which basically measures how much energy is available for thunderstorms to tap. CAPE values are forecast to exceed 1,000 j/kg which is more than supportive of strong storms. We have now established that we have the trigger (cold front/prefrontal trough), the organizer (strong 0-1km and 0-6km shear), and the fuel (70F+ dew points, 80F+ temps, 1,000j/kg+ CAPE) which means we have the green light for strong to severe storms tomorrow.
SPC Forecast For Tomorrow. Credit: SPC.
The SPC (Storm Prediction Center) agrees that the threat is there for strong to severe storms tomorrow and most of the area is under a slight risk for severe storms (a 2 on the 5 point scale). While that might not sound impressive, a slight risk is a pretty strong signal from the SPC for us. The exception is the immediate coast which is under a marginal threat (a 1 out of 5). Due to the wind setup tomorrow (mostly SW and not off the water), I wouldn’t be shocked to see that slight risk include the coast in the morning SPC update.
Is there anything that could interrupt the storms tomorrow? Yes there is bust potential. Should the pre-frontal trough move through a little early, it could trigger showers but not storms in the late morning which would limit instability leading to no fuel for any storms along the cold front. If the front is too close to the pre-frontal trough the storms along each would be prohibited from growing too big due to competition for instability. While this scenario is on the table, I would find it extremely surprising if no one in New England got a severe thunderstorm tomorrow. That doesn’t mean everyone will get one though.
I’m heading down to Mass tonight for a weeklong weather program at the Blue Hill Observatory and so won’t be quite as active this week. For more consistent updates tomorrow, be sure to check in frequently with the latest NWS forecasts as well as those from local media. Remember, when thunder roars, go indoors.
Forecasterjack 
