Sometimes the rain seems like it will never stop, so it’s natural to ask, ‘Does scattered thunderstorms mean rain all day?’
Before answering that question, let’s start by parsing what scattered thunderstorms mean for the layperson.
Scattered rain typically means it will be patchy and may travel quickly. But what about scattered thunderstorms?
Scattered thunderstorms mean that you should expect thunderstorms that start and stop. Assuming the forecast is accurate, it can make planning your day challenging because you need to time trips outside so that they fall between storms.
So, Does Scattered Thunderstorms Mean Rain all Day?
The short answer to ‘Do scattered thunderstorms mean rain all day?’ is NO.
Scattered thunderstorms mean intermittent storms. Depending on your forecast area, you may see no rain or more rain than anticipated.
Crucially, meteorologists distinguish between scattered and isolated thunderstorms based on the amount of area they cover.
Scattered thunderstorms are the specific designation for storms covering between 25-and 50% of a radar image or forecast area.
What are isolated thunderstorms if scattered thunderstorms have to cover up to 50% of a forecast grid?
These are thunderstorms that cover less than 25% of a weather forecast map.
So, that’s the difference between isolated and scattered thunderstorms.
One deals with spotty, sporadic rain across a significant area, while the other covers less ground and lasts a more measurable period.
But which is worse, scattered or isolated thunderstorms?
At a glance, scattered thunderstorms sound less threatening. If the rain is intermittent, it can’t be that severe.
However, that’s not how it works. The unpredictability of scattered thunderstorms means that if you get caught out in one without an umbrella, there’s more at risk than getting a bit soggy.
Partly that’s because they cover more area, so they do more damage. But it also has to do with the conditions that cause the storm.
Several factors affect thunderstorm severity, and an important one is what causes the updraft.
Tip: if you know it will storm, keep a spare pair of dry socks in your bag.
Updrafts are the result of different air masses colliding. These masses come from atmospheric pressures called cold and warm fronts.
Even though they share several common factors, they have different densities.
Consequently, when cold and warm fronts combine, they don’t mix. Instead, they compete for dominance.
Since warm air is lighter, when it collides with a cold front, it rises up and over the top of it.
As the warm front rises higher up in the stratosphere, its moisture coalesces and produces nimbus clouds that, in the right conditions, create moderate but persistent rain.
Conversely, when a cold front hits a warm front, it sinks underneath it. It forces the warm air upwards much faster than usual, and the resulting cloud is called a cumulonimbus.
These kinds of clouds generate sudden, sharp bursts of heavy rain.
It’s harder to sustain a cold front than a warm front, and that goes a long way to deciding whether your weather forecast will involve isolated showers or scattered thunderstorms.
The other variable at play is wind. It picks up the updraft generated by colliding weather fronts and blows it through various weather forecast sectors.
How far it propels it and for how long makes a difference in whether you experience scattered or isolated thunderstorms.
It’s also responsible for distributing those clouds, whether cumulonimbus or nimbus.
However, the cloud base itself affects the severity of your isolated or scattered showers.
Tip: Use a poncho rather than an umbrella in the wind.
Moisture also plays an integral role in the severity of scattered thunderstorms.
The degree of moisture present in the atmosphere drastically affects the cloud-base.
When there is limited moisture, you get a high cloud-base, and the resultant rainy weather features the kind of microbursts that cause thunderstorms.
When there’s a high degree of moisture, the cloud-base sits lower in the atmosphere. So, even though you get more rain, the downdraft is weaker and the showers more persistent.
Although these storms with low cloud-bases tend to be isolated, they come with their own problems.
Instead of the lightning, thunder, and tree damage associated with scattered thunderstorms, isolated storms are more likely to result in flash-flooding.
The other factor that affects whether your weather forecast predicts scattered thunderstorms or isolated ones is vertical wind shear.
At its simplest, vertical wind shear is the change in wind direction as it rises through the atmosphere.
When it is low, the updraft phase of a thunderstorm is short-lived. That means the downdraft becomes dominant sooner, and you are likely to get scattered thunderstorms across a significant area.
The updraft persists for more extended periods when vertical wind shear is high.
Updraft affects the time it takes for the storm to dissipate and tends to create isolated thunderstorms.
Tip: Use a tightly fitting ball cap to keep your head dry and rain from your eyes.
So, that’s what causes scattered thunderstorms. But if not all day, how long should you expect scattered thunderstorms to last?
Like many other things in nature, thunderstorms have life cycles, and several factors affect them.
Typically, scattered thunderstorms last between one and two hours. The conditions that cause the storm usually dissipate when the downdraft redistributes the clouds.
However, we mentioned thunderstorms start with updrafts. These cause the precipitation, and that, in turn, triggers a downdraft.
Whether scattered or isolated, the updrafts and downdrafts coexist at the height of a thunderstorm. However, the downdraft begins to dominate at a certain point, which helps move the storm on.
One of the reasons you get scattered thunderstorms is because as the downdraft of a thunderstorm redistributes the clouds, it catches a new warm front.
When that happens, the storm cycle starts over again.
The scattered thunderstorms may resume, either in your area or further afield, but it won’t be all day.
If your forecast anticipates scattered thunderstorms, you may have other weather conditions to consider.
For instance, it may be persistently overcast rather than sunny, resulting in cooler temperatures.
Alternatively, while the thunderstorms may resolve, you could still see the rain return in a gentler but more persistent manner later.
Scattered thunderstorms can be disruptive, so much so that occasionally they interrupt air traffic.
That’s because they usually come with high winds and, if the conditions are right, lightning.
Depending on the severity of the rain, you may see flash-flooding. And if high winds are present, you can expect damage to trees or dead branches.
The dangers that come with scattered thunderstorms tend to be short-lived since they don’t last all day.
Even if the rain continues, the severer elements of scattered thunderstorms abate before they can cause extreme damage.
Tip: if you are out and you hear thunder, count the seconds until you see lightning. If you don’t hit 30 seconds, you could be in danger and should find shelter.
The presence of lightning in a thunderstorm relies on a rising warm front. The ground cools as the hot air rises, and the competing temperatures create thunderclouds.
These thunderclouds fill with ice pellets in the right conditions, and these rattle around, accruing electrical charge as the thunderstorm escalates.
Whether or not scattered thunderstorms include lightning depends on whether they result from a cold front hitting a warm front or the other way around.
Typically, scattered thunderstorms result from a cold front colliding with a warm front and forcing the warm air high into the atmosphere. That means you may see lightning.
Do scattered thunderstorms mean rain all day? Not necessarily.
Scattered thunderstorms have a lot of ground to cover, so they are unlikely to stay in one place all day. Still, if you hear thunder, it’s best to get under cover to avoid the lightning that may follow.
Keep in mind that just because the thunderstorm moves on doesn’t mean the rain will stop.
So, when making plans for your day, keep an umbrella or poncho nearby. The law of contraries says that if you have it with you, you’ll probably escape the rain, but it also pays to be prepared!