Hello from Southern Connecticut Weather!
Spring in Connecticut was fairly quiet, and at times characterized by very wet and warmer than normal conditions. With the exception of a few isolated severe storm days and a lot of clouds, there hasn't been a lot to talk about. Spring tends to be our quiet season, and with the warmth that arrived just before Memorial Day, it looks like we've stepped into summer, even though the humidity has been mostly absent for now.
Meteorological summer begins today and lasts through August 31st. Summer is when we ramp up from the relative quiet of spring to the peak of our heat and thunderstorm season. This time of year also overlaps with the Atlantic hurricane season, though the peak of that season arrives in September.
It's not a surprise that we're expecting summer to be warmer than normal. That tends to be the default state these days, though last summer our temperatures were about as close to normal as you could get. The tradeoff for that however was a near record wet summer.
The ENSO state changing from El Nino to La Nina informs this forecast greatly, along with some teleconnections--though they do not correlate as much to sensible weather as during the winter.
Given what we expect in the predominant upper level pattern, we do think that it will get more humid than normal and as a result of that flow, a little more active and solidly wetter than normal.
Grab an iced coffee or cold brew and settle in.
Spring in Connecticut was fairly quiet, and at times characterized by very wet and warmer than normal conditions. With the exception of a few isolated severe storm days and a lot of clouds, there hasn't been a lot to talk about. Spring tends to be our quiet season, and with the warmth that arrived just before Memorial Day, it looks like we've stepped into summer, even though the humidity has been mostly absent for now.
Meteorological summer begins today and lasts through August 31st. Summer is when we ramp up from the relative quiet of spring to the peak of our heat and thunderstorm season. This time of year also overlaps with the Atlantic hurricane season, though the peak of that season arrives in September.
It's not a surprise that we're expecting summer to be warmer than normal. That tends to be the default state these days, though last summer our temperatures were about as close to normal as you could get. The tradeoff for that however was a near record wet summer.
The ENSO state changing from El Nino to La Nina informs this forecast greatly, along with some teleconnections--though they do not correlate as much to sensible weather as during the winter.
Given what we expect in the predominant upper level pattern, we do think that it will get more humid than normal and as a result of that flow, a little more active and solidly wetter than normal.
Grab an iced coffee or cold brew and settle in.
Above: the official NOAA forecast for ENSO for the remainder of 2024. There are high probabilities that La Nina sets in shortly as sea surface temperature (SST) anomalies are rapidly cooling in the key region off the west coast of South America that measures the presence of El Nino (warmer than normal SSTs) or La Nina (colder than normal SSTs).
Below: the latest global SST anomaly analysis. There is a lot to unpack in this one image, but for the purposes of this section, you can easily see La Nina trying to build.
Below: the latest global SST anomaly analysis. There is a lot to unpack in this one image, but for the purposes of this section, you can easily see La Nina trying to build.
Connecticut Summer Temperature Climatology
Before we go to predictions, let's talk about what summer generally looks like in CT.
Before we go to predictions, let's talk about what summer generally looks like in CT.
Above: the average high and low temperatures at BDL (Bradley Airport) and BDR (Bridgeport Airport). This plot goes back to 1951 to add a longer period of record. Average temperatures rapidly rise in June, followed by the peak and plateau in July, start of a gradual decline in August, and a steeper decline that occurs with the annual march to fall in September. Image courtesy of the fantastic Iowa State University Automated Data Plotter.
The image above tells us that average highs are in the mid to upper 80s by the latter half of July, but they don't tell the full story of what's normal for us.
There is a lot of data in the graphics below--also looking at BDL and BDR, but they are very helpful in showing us the different types of summers we get here in CT.
High Heat
This type of summer is defined by relatively brief, but extreme periods of heat. For us in recent memory, 2011 is that season, where both Hartford and Bridgeport tied or set new all time record high temperatures just shy of 105. A season like this is defined by days or brief stretches where the high is 100 or greater.
Durational Heat
Another type of summer is defined by long periods of high, but not necessarily extreme heat in an absolute sense. Think of long heat waves. This is a sneaky kind of heat because the duration makes it extreme. The impact on the human body amplifies when the heat is extended out longer, even if it's not record breaking daily maximums.
For this type of summer, 2002 fit the bill in Hartford--look at the number of days that reached 95 when the yearly average is around 20 days at 90 or above. At the shoreline, 2016 was a hot one with 18 days reaching 90 when the average for the year is about half that. A season like this is defined by long heat waves or frequent short heat waves.
Ho Hum
These are increasingly rare, but they're the normal (or near normal) type of summers where there's a lot of "chamber of commerce" type days that are beautiful with lower humidity and heat, and other periods where we have a heat wave, or close to it. It's warm to hot, but not all the time or overwhelmingly so. These are seasons defined by mid-July temperatures that frequently top out at 83-85 rather than 90 and above.
The image above tells us that average highs are in the mid to upper 80s by the latter half of July, but they don't tell the full story of what's normal for us.
There is a lot of data in the graphics below--also looking at BDL and BDR, but they are very helpful in showing us the different types of summers we get here in CT.
High Heat
This type of summer is defined by relatively brief, but extreme periods of heat. For us in recent memory, 2011 is that season, where both Hartford and Bridgeport tied or set new all time record high temperatures just shy of 105. A season like this is defined by days or brief stretches where the high is 100 or greater.
Durational Heat
Another type of summer is defined by long periods of high, but not necessarily extreme heat in an absolute sense. Think of long heat waves. This is a sneaky kind of heat because the duration makes it extreme. The impact on the human body amplifies when the heat is extended out longer, even if it's not record breaking daily maximums.
For this type of summer, 2002 fit the bill in Hartford--look at the number of days that reached 95 when the yearly average is around 20 days at 90 or above. At the shoreline, 2016 was a hot one with 18 days reaching 90 when the average for the year is about half that. A season like this is defined by long heat waves or frequent short heat waves.
Ho Hum
These are increasingly rare, but they're the normal (or near normal) type of summers where there's a lot of "chamber of commerce" type days that are beautiful with lower humidity and heat, and other periods where we have a heat wave, or close to it. It's warm to hot, but not all the time or overwhelmingly so. These are seasons defined by mid-July temperatures that frequently top out at 83-85 rather than 90 and above.
We do have another type of summer however, and that's what we're predicting this summer...
SCW Summer Forecast: Temperature
Sultry Summer
These are probably the most uncomfortable kind of summers, even if the high temperatures aren't particularly memorable. They're sweaty, sticky, and plenty humid. It's far easier to achieve high heat when dew points are mixed out, but these are the kind of summers where you lose a few degrees of actual temperature and add a few degrees to the heat index because of all the moisture in the air.
This is highly dependent on the upper level pattern. If we have strong Western Atlantic Ridging (WAR), which I do expect as we move deeper into summer, that will transport moisture from the western Atlantic and potentially the Gulf of Mexico, which are running warmer than normal. The warmer the temperatures in these regions, the more moisture that can be transported. Even though our actual sea surface temperatures are much colder than further south in an absolute sense, the anomalies set the stage for periods of elevated to oppressive humidity. Our dew point peak coincides with our highest annual temperatures but are more of a plateau, with low to mid 60s dew points as part of our daily average from late June through at least mid-August.
With total 90 degree days being around 20 for BDL and 10 for BDR, I expect us to be slightly above normal in that category. The bulk of this heat will be in July and August as La Nina establishes itself right as we reach our climatological peak. It may not be hot now, but eventually it will be.
The summer will be more memorable in the humidity category than the absolute temperature category, though keep in mind Hartford averages days in the mid to upper 90s while the coast gets hot days as well, though not as frequently.
Sultry Summer
These are probably the most uncomfortable kind of summers, even if the high temperatures aren't particularly memorable. They're sweaty, sticky, and plenty humid. It's far easier to achieve high heat when dew points are mixed out, but these are the kind of summers where you lose a few degrees of actual temperature and add a few degrees to the heat index because of all the moisture in the air.
This is highly dependent on the upper level pattern. If we have strong Western Atlantic Ridging (WAR), which I do expect as we move deeper into summer, that will transport moisture from the western Atlantic and potentially the Gulf of Mexico, which are running warmer than normal. The warmer the temperatures in these regions, the more moisture that can be transported. Even though our actual sea surface temperatures are much colder than further south in an absolute sense, the anomalies set the stage for periods of elevated to oppressive humidity. Our dew point peak coincides with our highest annual temperatures but are more of a plateau, with low to mid 60s dew points as part of our daily average from late June through at least mid-August.
With total 90 degree days being around 20 for BDL and 10 for BDR, I expect us to be slightly above normal in that category. The bulk of this heat will be in July and August as La Nina establishes itself right as we reach our climatological peak. It may not be hot now, but eventually it will be.
The summer will be more memorable in the humidity category than the absolute temperature category, though keep in mind Hartford averages days in the mid to upper 90s while the coast gets hot days as well, though not as frequently.
Above: the current SST anomaly analysis. This is the kind of map that combined with a La Nina lends itself to hot and humid summer conditions. Image courtesy of TropicalTidbits.
Connecticut Summer Severe Thunderstorm/Tornado Climatology
Now let's talk about a normal CT summer when it comes to severe storms. The last 20 years have been very active on balance.
Now let's talk about a normal CT summer when it comes to severe storms. The last 20 years have been very active on balance.
Above is an accumulated line plot which shows the number of severe thunderstorm and tornado warnings combined for each year going back to 1986. On the right, you'll see the data itself, showing 11 warnings (I believe all severe thunderstorm warnings) so far in 2024, around normal. You'll see that once we get to summer, things go up dramatically, and the bulk of our warnings happen in summer and early fall.
In order for severe thunderstorms to develop you need four key ingredients: Shear, Lift, Instability, and Moisture.
Shear
In order to get a severe weather day, we need some sort of shear. You can have a high CAPE/low shear or high shear/low CAPE day, but you need shear for severe weather.
Shear—is the change in wind speed (speed shear) and/or direction (directional shear) with height in the atmosphere. Shear usually refers to vertical wind shear.
Speed and directional shear are important in severe thunderstorm development. With speed shear, a significant increase of wind with height will tilt a storm’s updraft. This allows an updraft and downdraft to occur in separate regions of the storm and reduces the risk of water loading and thunderstorm collapse.
Directional shear helps initiate the development of a rotating updraft. This is key in the formation of a supercell—the most mature and dangerous type of thunderstorm. Supercells are thunderstorms consisting of one quasi-steady to rotating updraft (I.E. storm with rotation). These are the storms most likely to produce large hail, strong winds, and tornadoes. It doesn't need to look like the picturesque Midwest supercells to be dangerous. We saw that with supercells that produced hail in eastern CT and damaging winds in Griswold recently.
What to watch for: areas of low pressure, especially tropical systems or upper level lows.
Lift
Lift is a critical ingredient for thunderstorm development, even the garden variety type. You can have moisture and instability, but if you don’t have lift, not much is going to happen. Lift provides the air the nudge it needs to rise and form convection. It happens a number of ways around the country, but in this region, we’re usually looking one major mechanism: a front.
The most common mechanism around here for thunderstorm initiation is the cold front. Fronts are the boundary between two air masses of different temperatures and air densities. When the cold front rolls through, the colder and more dense air behind the front lifts warmer and less dense air abruptly. When all the ingredients are together in the right quantities, you have showers and thunderstorms. In less frequent scenarios, we have warm fronts lifting north across the region. These are particularly noteworthy because they usually happen in an environment that is more favorable for supercells and tornadic activity. Another way in which lift can happen is along a sea breeze boundary that moves north during a summer day.
Instability
Instability is another critical element of thunderstorm production, and the more instability there is, the more potential you add to a developing storm.
Instability is the tendency for air parcels to accelerate (especially upward) when they are displaced from their original position. You don’t need a lot of instability for a garden variety thunderstorm, but you need Instability and usually significant amounts of it for for severe weather.
An unstable air mass is usually characterized by warm moist air near the surface and colder drier air aloft. This allows air that is forced upward to continue to rise on its own, which eventually will cool and develop the clouds and precip that make up a thunderstorm. High instability also contributes to prolific lightning events, which isn’t characterized as severe weather by the NWS but is deadly in its own right.
What to watch for: Convective Available Potential Energy, or CAPE—is a measure of the energy available for convection. CAPE is directly related to the maximum potential vertical speed within an updraft.
As the National Weather Service notes, observed values in thunderstorm environments often exceed 1000 joules per kilogram (J/kg), and in extreme cases may exceed 5000 J/kg. Now, 5k CAPE around here is unheard of, but If we’re talking about a high CAPE day, your ears should perk up.
There are various measures of CAPE out there, including surface based CAPE (SBCAPE), mixed layer or mean layer CAPE (MLCAPE), most unstable or maximum usable CAPE (MUCAPE), and downdraft CAPE (DCAPE).
Moisture
Think of a hazy, hot, and humid summer day. If you asked people what they remember about the end of those days, many will answer that they remember the thunderstorms. Moisture is a key element in thunderstorm development. Without moisture, you’re not going to have precipitation!
What to watch for: if you want to know what kind of moisture we’re dealing with during this time of year, look at the dewpoint—which is a measure of atmospheric moisture. A dew point is the temperature to which air must be cooled (generally) in order to reach saturation. The higher the dewpoint, the more moisture in the air.
This was a key factor in last year's storms that dumped obscene amounts of rainfall, often in very little time.
In order for severe thunderstorms to develop you need four key ingredients: Shear, Lift, Instability, and Moisture.
Shear
In order to get a severe weather day, we need some sort of shear. You can have a high CAPE/low shear or high shear/low CAPE day, but you need shear for severe weather.
Shear—is the change in wind speed (speed shear) and/or direction (directional shear) with height in the atmosphere. Shear usually refers to vertical wind shear.
Speed and directional shear are important in severe thunderstorm development. With speed shear, a significant increase of wind with height will tilt a storm’s updraft. This allows an updraft and downdraft to occur in separate regions of the storm and reduces the risk of water loading and thunderstorm collapse.
Directional shear helps initiate the development of a rotating updraft. This is key in the formation of a supercell—the most mature and dangerous type of thunderstorm. Supercells are thunderstorms consisting of one quasi-steady to rotating updraft (I.E. storm with rotation). These are the storms most likely to produce large hail, strong winds, and tornadoes. It doesn't need to look like the picturesque Midwest supercells to be dangerous. We saw that with supercells that produced hail in eastern CT and damaging winds in Griswold recently.
What to watch for: areas of low pressure, especially tropical systems or upper level lows.
Lift
Lift is a critical ingredient for thunderstorm development, even the garden variety type. You can have moisture and instability, but if you don’t have lift, not much is going to happen. Lift provides the air the nudge it needs to rise and form convection. It happens a number of ways around the country, but in this region, we’re usually looking one major mechanism: a front.
The most common mechanism around here for thunderstorm initiation is the cold front. Fronts are the boundary between two air masses of different temperatures and air densities. When the cold front rolls through, the colder and more dense air behind the front lifts warmer and less dense air abruptly. When all the ingredients are together in the right quantities, you have showers and thunderstorms. In less frequent scenarios, we have warm fronts lifting north across the region. These are particularly noteworthy because they usually happen in an environment that is more favorable for supercells and tornadic activity. Another way in which lift can happen is along a sea breeze boundary that moves north during a summer day.
Instability
Instability is another critical element of thunderstorm production, and the more instability there is, the more potential you add to a developing storm.
Instability is the tendency for air parcels to accelerate (especially upward) when they are displaced from their original position. You don’t need a lot of instability for a garden variety thunderstorm, but you need Instability and usually significant amounts of it for for severe weather.
An unstable air mass is usually characterized by warm moist air near the surface and colder drier air aloft. This allows air that is forced upward to continue to rise on its own, which eventually will cool and develop the clouds and precip that make up a thunderstorm. High instability also contributes to prolific lightning events, which isn’t characterized as severe weather by the NWS but is deadly in its own right.
What to watch for: Convective Available Potential Energy, or CAPE—is a measure of the energy available for convection. CAPE is directly related to the maximum potential vertical speed within an updraft.
As the National Weather Service notes, observed values in thunderstorm environments often exceed 1000 joules per kilogram (J/kg), and in extreme cases may exceed 5000 J/kg. Now, 5k CAPE around here is unheard of, but If we’re talking about a high CAPE day, your ears should perk up.
There are various measures of CAPE out there, including surface based CAPE (SBCAPE), mixed layer or mean layer CAPE (MLCAPE), most unstable or maximum usable CAPE (MUCAPE), and downdraft CAPE (DCAPE).
Moisture
Think of a hazy, hot, and humid summer day. If you asked people what they remember about the end of those days, many will answer that they remember the thunderstorms. Moisture is a key element in thunderstorm development. Without moisture, you’re not going to have precipitation!
What to watch for: if you want to know what kind of moisture we’re dealing with during this time of year, look at the dewpoint—which is a measure of atmospheric moisture. A dew point is the temperature to which air must be cooled (generally) in order to reach saturation. The higher the dewpoint, the more moisture in the air.
This was a key factor in last year's storms that dumped obscene amounts of rainfall, often in very little time.
As you can see above, each year we can expect a few dozen severe thunderstorm warnings and less than a handful of tornado warnings. Tornado warnings are tricky in CT, because they are often happening extremely quickly and are short track events. Images courtesy of Iowa State University.
SCW Summer Forecast: Storm Activity
Active Summer
This summer is poised to be another active one, in line with some other recent years, as we look at severe warned numbers. I think this is in large part due to the predominant upper level pattern once again, which should allow for higher humidity and thus moisture to be present in the state. It's unclear how many fronts we get during the peak of the summer, but if there is more of a "heat dome" as is expected in the central US, that could put us in a "Ring of Fire" setup periodically that would allow for more thunderstorm activity.
SCW Summer Forecast: Storm Activity
Active Summer
This summer is poised to be another active one, in line with some other recent years, as we look at severe warned numbers. I think this is in large part due to the predominant upper level pattern once again, which should allow for higher humidity and thus moisture to be present in the state. It's unclear how many fronts we get during the peak of the summer, but if there is more of a "heat dome" as is expected in the central US, that could put us in a "Ring of Fire" setup periodically that would allow for more thunderstorm activity.
Above: an old Weather Channel graphic that helps visualize a Ring of Fire setup. An expansive heat dome over the Midwest or South forces energy to move around the periphery of the ridge, bringing active weather to the east. This is a setup I expect to see a couple times this summer as the Midwest deals with significant high heat. The counter to this is that I do believe at some point we will see more ridging in Atlantic Canada, which will make the Ring of Fire less likely. We will see how quickly, if at all, that develops.
Much like the temperature forecast, I don't think this is an overwhelmingly stormy summer, but we'll have near to slightly above normal severe thunderstorms. It should be active. Tornadic activity is near impossible to predict in this region long range.
Much like the temperature forecast, I don't think this is an overwhelmingly stormy summer, but we'll have near to slightly above normal severe thunderstorms. It should be active. Tornadic activity is near impossible to predict in this region long range.
Above: thunderstorm life cycle with image courtesy of iAlert.
Connecticut Summer Precipitation Climatology
Finally, let's talk about water. We've had a lot of it in the last year, and for our corner of the country, we've been one of the wettest places in the entire lower 48 relative to normal in the last year. A lot of that started last summer, and continued straight through today. Summers usually have wet periods, but not this wet.
Connecticut Summer Precipitation Climatology
Finally, let's talk about water. We've had a lot of it in the last year, and for our corner of the country, we've been one of the wettest places in the entire lower 48 relative to normal in the last year. A lot of that started last summer, and continued straight through today. Summers usually have wet periods, but not this wet.
Above: precipitation departures dating back to this time last year. Not only are we one of the wettest spots in the country, we have seen feet of rainfall greater than normal. Images courtesy of the NRCC.
We know that summer is usually good for a few solid thunderstorms and even heavy showers. Last year kicked off a really bad series of storms that produced prolific rainfall totals and rates due to increased humidity and lack of forcing--enough to keep storms moving along.
Flash flood warnings are part of our summers, but last summer was historic.
We know that summer is usually good for a few solid thunderstorms and even heavy showers. Last year kicked off a really bad series of storms that produced prolific rainfall totals and rates due to increased humidity and lack of forcing--enough to keep storms moving along.
Flash flood warnings are part of our summers, but last summer was historic.
Above: the flash flood warning count for the state going back to when the statistic was kept. It may not look like much, but 30 summertime warnings is a significant length ahead of the other active years.
SCW Summer Forecast: Precipitation
Wet Times Continue
It would be truly extraordinary, and I daresay unprecedented, to follow up an exceptionally wet summer 2023 with an even wetter 2024. Last year was unique in that the rainfall all happened absent the influence of a tropical system.
While I think we won't be as wet as last summer, I do think we will be solidly wetter than normal, on the order of 110-130% above normal. Even this statement has me nervous for a few reasons.
First, I do think that the increased moisture in the air will lead to additional high precipitation events, some localized via thunderstorms and other more widespread due to fronts or the occasional trough. It's unclear how frequently this happens.
Second, we are expecting a historically active Atlantic hurricane season. For the purposes of this forecast, we need not assume a direct impact to receive a lot of rainfall. We only need to look at the remnants of Ida or Elsa or Fred a few years ago to see the impact remnant rainfall can be.
This is a big variable, and if I were to hazard a guess, I would say we get some significant rainfall from at least one tropical system this summer, likely in the latter part of the summer as the tropics become more active. That alone could make this forecast too low.
SCW Summer Forecast: Precipitation
Wet Times Continue
It would be truly extraordinary, and I daresay unprecedented, to follow up an exceptionally wet summer 2023 with an even wetter 2024. Last year was unique in that the rainfall all happened absent the influence of a tropical system.
While I think we won't be as wet as last summer, I do think we will be solidly wetter than normal, on the order of 110-130% above normal. Even this statement has me nervous for a few reasons.
First, I do think that the increased moisture in the air will lead to additional high precipitation events, some localized via thunderstorms and other more widespread due to fronts or the occasional trough. It's unclear how frequently this happens.
Second, we are expecting a historically active Atlantic hurricane season. For the purposes of this forecast, we need not assume a direct impact to receive a lot of rainfall. We only need to look at the remnants of Ida or Elsa or Fred a few years ago to see the impact remnant rainfall can be.
This is a big variable, and if I were to hazard a guess, I would say we get some significant rainfall from at least one tropical system this summer, likely in the latter part of the summer as the tropics become more active. That alone could make this forecast too low.
Above, a radar image of Tropical Storm Elsa in July 2021. Elsa dropped between 2-6" of rain, more than a month's worth in spots, on the state.
Overall Forecast
SCW expects to be busy this summer, as a combination of heat, storms, and wet weather will ensure an active summer.
Hopefully you found this overview and forecast to be informative and interesting! Let's see how the forecast pans out.
As always, please like, share, and interact with us on our social media--on Facebook to share our discussions, and follow us on Twitter @southernctwx to retweet our posts. Hit the buttons below to join.
Thank you for reading SCW.
-DB
Overall Forecast
SCW expects to be busy this summer, as a combination of heat, storms, and wet weather will ensure an active summer.
- There is high confidence that this is a warmer than normal summer with regard to temperature, though the most memorable aspect of the heat will be the long duration of humidity.
- There is moderate confidence that this is a more active severe thunderstorm season than normal, though only slightly above, due to the likelihood of central US and western Atlantic ridging alongside possible troughing to our west pumping moisture and potentially giving a few active storm periods.
- There is high confidence that this is a solidly above normal rainfall season, continuing the general trend of the last year. How the tropical season factors into this eventual outcome remains to be seen. It wasn't mentioned before, but I do not think this wetter than normal forecast necessarily means a continuation of the overcast skies that dominated our winter and spring. Climatology should give us sunny and dry periods.
Hopefully you found this overview and forecast to be informative and interesting! Let's see how the forecast pans out.
As always, please like, share, and interact with us on our social media--on Facebook to share our discussions, and follow us on Twitter @southernctwx to retweet our posts. Hit the buttons below to join.
Thank you for reading SCW.
-DB
