Severe thunderstorms are the most dangerous kind of thunderstorms. You hear about them in the news, but what exactly makes a severe thunderstorm different from a regular thunderstorm?
Many believe that the amount of lightning in a thunderstorm is how storms are classified as severe or not. While lightning is a significant threat, all thunderstorms contain lightning and some weaker thunderstorms can still contain a high amount. Rainfall rate is also not a factor in classifying a storm as severe or not, though severe thunderstorms typically do have higher rainfall rates.
There are three things that can cause a thunderstorm to be classified as severe. If a severe thunderstorm warning is issued, the National Weather Service is doing so because they have been notified or suspect that one or more of the following is present:
1. Hail One Inch in Diameter or More
Not so long ago, the requirement for a severe thunderstorm was hail that was only 3/4" in diameter. More research proved that while hail this size or smaller can destroy some crops, it really doesn't damage buildings or vehicles. Once hail reaches an inch in diameter though (about the size of a quarter) it can begin to dent cars and damage roofs. Hail that size falls from the sky at about 50mph, so it can certainly hurt you as well!
2. Wind Gusts of 58 mph or More
This may seem like a random number, but there is something to it. Studies have shown that this is about the wind speed that branches begin to break off from tree trunks. It is also important to note that the winds don't have to be sustained at 58 mph or greater; they just have to be gusting up to that speed. It's very unlikely to have winds constantly at this speed in a thunderstorm unless...
3. Tornado
Any thunderstorm that produces or is suspected of producing a tornado is automatically classified as severe. When this occurs however, you won't see a severe thunderstorm warning issued, but a tornado warning. This means that if you are under a tornado warning, you are also experiencing a severe thunderstorm.
Any of the above three conditions can be very dangerous, so do not take severe thunderstorm warnings lightly!
Got anymore questions about severe weather? Let me know in the comments below!
Wednesday, February 27, 2013
Saturday, February 16, 2013
Top Five Tornado Myths
With winter winding down, temperatures are warming up and the likelihood for severe weather and tornadoes is also increasing. We've already had an EF-4 tornado go through a heavily populated area (Hattiesburg) this month, so I'm taking the time now to debunk some myths about tornadoes and tornado safety. The number of myths is surprisingly large, but we can't get too lengthy and since I like countdowns, I'm going to focus on the five myths that stand out to me as being the most flagrantly wrong.
5. You Can Rate a Tornado Just by Looking at it.
I blame the movie Twister for this one. Throughout the movie, they constantly look at tornadoes and say, "That's a F-3," or "There's a F-5 heading our way!" This is all wrong. The width of a tornado gives a general idea of the intensity, but there are plenty of examples of relatively skinny tornadoes that had higher winds than other wider ones. It is nearly impossible to measure the wind speed of a tornado as they are happening as the instruments would likely be destroyed. The F or Fujita Scale was developed as a way to estimate the wind speed of tornadoes based on the damage they left behind. To evaluate the damage, the tornado has to already have passed, which is why the official Fujita Scale rating of a tornado is usually not announced by the National Weather Service until a day after the storm. So you might not know how strong a tornado is before it hits, but it doesn't matter. Every tornado is dangerous and requires your immediate action. Also, to be correct, it's not the F Scale anymore but the EF or Enhanced Fujita Scale. The original scale was tweaked back in 2007 to make it more accurate. The image below shows you how the scale breaks down:
4. It's Better to Stay Inside a Mobile Home Than Leave.
While it is almost always better to be indoors than outdoors during a tornado, there is an exception when it comes to mobile homes/trailers/manufactured homes. Mobile homes are much more likely to be destroyed by a tornado than a permanent building. Most mobile homes are only designed to sustain winds up to 70 mph; the strength of an EF-0 tornado. Mobile homes also frequently flip over in tornadoes, because it is so easy for winds to get underneath the home and lift it. If you are in a mobile home and a tornado warning is issued, get out! If a permanent building is nearby, go there and seek shelter on the lowest floor. If there is not one close by, you're still better off getting in your vehicle and driving to another location or seeking shelter in a low lying place outside the mobile home than remaining inside.
3. A Highway Overpass is a Safe Place to be.
It's no mystery that a car is not the safest place to be in a tornado. They can be flipped over relatively easily and outrunning a tornado only works under ideal circumstances. The idea that stopping your car under a highway overpass and taking shelter underneath it is a better option though is a misconception. There are documented cases of people surviving a tornado under an overpass, but there are more cases of people not surviving. Overpasses often act like a wind tunnel, enhancing the speed of the wind and providing a location for debris to gather. If you find yourself in a car during a tornado warning, do not stop under an overpass, but continue driving to the closest permanent building. If you see the tornado and have no direction to escape in, then you're still better off getting out of your vehicle and taking shelter in a ditch or other low lying area than taking shelter under an overpass.
2. Tornadoes Do Not Cross Rivers or Hills.
Some believe that if they can get to the opposite side of a river from a tornado they will automatically be safe. This is just not true, as tornadoes have been documented crossing rivers and continuing on the other side. A tornado is just as likely to occur over water as land; over water they're known as waterspouts instead of tornadoes. The image below is of a waterspout that formed at sea. Another common belief is that tornadoes only occur in flat areas and cannot cross over hills. This too has been proven false. While most tornadoes do form over flat terrain, they have also occurred in the mountains and have tracked for miles over hilly terrain.
1. Opening the Windows in a House Before a Tornado Hits Will Help Protect it.
This may be the biggest tornado safety myth that's still widely believed. The idea is that opening all the windows in a house will help equalize the pressure between the inside and outside of the house and keep it from being crushed. While tornadoes are associated with lower atmospheric pressure, research has shown that it is the winds and debris being carried by the tornado that destroy homes, not the pressure change. Taking the time to open all the widows in your home only wastes valuable minutes when you could be taking shelter in the safest part of your home. A strong tornado will break the windows anyway and should the tornado not pass over you, you will avoid having rain and debris blown into your house.
So there you have my top five tornado myths. If you want more information on tornadoes and tornado safety this is a great website to check out: http://www.ready.gov/tornadoes
And as always if you have any other weather questions, be sure to comment below!
5. You Can Rate a Tornado Just by Looking at it.
I blame the movie Twister for this one. Throughout the movie, they constantly look at tornadoes and say, "That's a F-3," or "There's a F-5 heading our way!" This is all wrong. The width of a tornado gives a general idea of the intensity, but there are plenty of examples of relatively skinny tornadoes that had higher winds than other wider ones. It is nearly impossible to measure the wind speed of a tornado as they are happening as the instruments would likely be destroyed. The F or Fujita Scale was developed as a way to estimate the wind speed of tornadoes based on the damage they left behind. To evaluate the damage, the tornado has to already have passed, which is why the official Fujita Scale rating of a tornado is usually not announced by the National Weather Service until a day after the storm. So you might not know how strong a tornado is before it hits, but it doesn't matter. Every tornado is dangerous and requires your immediate action. Also, to be correct, it's not the F Scale anymore but the EF or Enhanced Fujita Scale. The original scale was tweaked back in 2007 to make it more accurate. The image below shows you how the scale breaks down:
4. It's Better to Stay Inside a Mobile Home Than Leave.
While it is almost always better to be indoors than outdoors during a tornado, there is an exception when it comes to mobile homes/trailers/manufactured homes. Mobile homes are much more likely to be destroyed by a tornado than a permanent building. Most mobile homes are only designed to sustain winds up to 70 mph; the strength of an EF-0 tornado. Mobile homes also frequently flip over in tornadoes, because it is so easy for winds to get underneath the home and lift it. If you are in a mobile home and a tornado warning is issued, get out! If a permanent building is nearby, go there and seek shelter on the lowest floor. If there is not one close by, you're still better off getting in your vehicle and driving to another location or seeking shelter in a low lying place outside the mobile home than remaining inside.
3. A Highway Overpass is a Safe Place to be.
It's no mystery that a car is not the safest place to be in a tornado. They can be flipped over relatively easily and outrunning a tornado only works under ideal circumstances. The idea that stopping your car under a highway overpass and taking shelter underneath it is a better option though is a misconception. There are documented cases of people surviving a tornado under an overpass, but there are more cases of people not surviving. Overpasses often act like a wind tunnel, enhancing the speed of the wind and providing a location for debris to gather. If you find yourself in a car during a tornado warning, do not stop under an overpass, but continue driving to the closest permanent building. If you see the tornado and have no direction to escape in, then you're still better off getting out of your vehicle and taking shelter in a ditch or other low lying area than taking shelter under an overpass.
2. Tornadoes Do Not Cross Rivers or Hills.
Some believe that if they can get to the opposite side of a river from a tornado they will automatically be safe. This is just not true, as tornadoes have been documented crossing rivers and continuing on the other side. A tornado is just as likely to occur over water as land; over water they're known as waterspouts instead of tornadoes. The image below is of a waterspout that formed at sea. Another common belief is that tornadoes only occur in flat areas and cannot cross over hills. This too has been proven false. While most tornadoes do form over flat terrain, they have also occurred in the mountains and have tracked for miles over hilly terrain.
1. Opening the Windows in a House Before a Tornado Hits Will Help Protect it.
This may be the biggest tornado safety myth that's still widely believed. The idea is that opening all the windows in a house will help equalize the pressure between the inside and outside of the house and keep it from being crushed. While tornadoes are associated with lower atmospheric pressure, research has shown that it is the winds and debris being carried by the tornado that destroy homes, not the pressure change. Taking the time to open all the widows in your home only wastes valuable minutes when you could be taking shelter in the safest part of your home. A strong tornado will break the windows anyway and should the tornado not pass over you, you will avoid having rain and debris blown into your house.
So there you have my top five tornado myths. If you want more information on tornadoes and tornado safety this is a great website to check out: http://www.ready.gov/tornadoes
And as always if you have any other weather questions, be sure to comment below!
Tuesday, February 5, 2013
Partly Cloudy vs. Partly Sunny
There are lots of terms in meteorology that are very similar and that's part of what leads to the confusion that exists out there. The two terms in the title of this week's blog post are a great example. Partly cloudy and partly sunny are two terms that pop up in weather forecasts a lot, but what's the real difference between the two?
To try and answer this, let's start by looking up the definition given by the federal organization that sets the standards for the field of meteorology in the United States: the National Oceanic and Atmospheric Administration (NOAA). In the Federal Meteorological Handbook, NOAA describes five categories of cloud cover that should be documented at all weather observing stations. The list includes the following:
Clear = No visible clouds
Few = 1/8 - 2/8 of sky covered by clouds
Scattered = 3/8 - 4/8 of sky covered by clouds
Broken = 5/8 -7/8 of sky covered by clouds
Overcast = 100% cloud cover
Though these five terms are all the description NOAA deems necessary to describe sky cover, there's a lot of room for interpretation. A big problem is that unless you're in the meteorology field, most people don't look at the sky in eighths and the difference between scattered and broken could be large. To try and relate to the public better and keep forecasts more interesting, forecasters at the National Weather Service (which is a part of NOAA) decided to come up with their own categories for sky cover. Here's the list they use:
Cloudy = 90-100% sky cover
Mostly Cloudy = 70-80% sky cover
Partly Cloudy/Partly Sunny = 30-60% sky cover
Mostly Clear/Mostly Sunny = 10-30% sky cover
Clear/Sunny = 0-10% sky cover
Fair = Less than 40% cloud cover, no
precipitation and no extreme weather
They too only have five categories (not counting fair), but they added different terms to describe the same conditions. As far as the NWS is concerned, partly cloudy and partly sunny are the same thing. The only difference is that partly sunny is used to describe daytime cloud cover and partly cloudy is used to describe nighttime cloud cover. Same goes with mostly sunny/mostly clear and clear/sunny.
So case closed right? Not so fast. Because the terms are so similar, the nighttime and daytime terms often get used interchangeably by most forecasters. If skies are expected to be partly sunny for the next five days, it's highly likely the forecaster will switch between saying partly sunny, partly cloudy, and fair just to spice up the forecast some.
The difference between partly cloudy and partly sunny though has really taken on a life of its own; so much so that many forecasters now separate the two terms to have a total of six categories of sky cover instead of five. The most common order of these six categories of sky cover, from least to greatest, is as follows:
Sunny = 0-10%
Mostly Sunny = 10-30%
Partly Cloudy = 30-50%
Partly Sunny = 50-70%
Mostly Cloudy = 70-90%
Cloudy = 90-100%
This is the scale I personally go by, but even this is not agreed upon by all meteorologists. Some argue that partly sunny and mostly cloudy mean the same thing while others use partly sunny when cloud cover is expected to dissipate later and partly cloudy when cloud cover is expected to increase later.
The bottom line is that it depends on the person who made the forecast for what partly cloudy or partly sunny actually means. While you're more likely to see more clouds when the forecast calls for partly sunny skies compared to partly cloudy skies, get to know your favorite source for weather and see what the sky looks like when it says partly cloudy or partly sunny. You should be able to figure out what category the meteorologist who made the forecast falls in!
Big thanks to "The Media Mind" who provided the inspiration for this post after asking about this in the comments of my last blog post. If you have a weather question you want answered, comment below and I'll do my best to answer it in a future post!
To try and answer this, let's start by looking up the definition given by the federal organization that sets the standards for the field of meteorology in the United States: the National Oceanic and Atmospheric Administration (NOAA). In the Federal Meteorological Handbook, NOAA describes five categories of cloud cover that should be documented at all weather observing stations. The list includes the following:Clear = No visible clouds
Few = 1/8 - 2/8 of sky covered by clouds
Scattered = 3/8 - 4/8 of sky covered by clouds
Broken = 5/8 -7/8 of sky covered by clouds
Overcast = 100% cloud cover
Though these five terms are all the description NOAA deems necessary to describe sky cover, there's a lot of room for interpretation. A big problem is that unless you're in the meteorology field, most people don't look at the sky in eighths and the difference between scattered and broken could be large. To try and relate to the public better and keep forecasts more interesting, forecasters at the National Weather Service (which is a part of NOAA) decided to come up with their own categories for sky cover. Here's the list they use:
Cloudy = 90-100% sky coverMostly Cloudy = 70-80% sky cover
Partly Cloudy/Partly Sunny = 30-60% sky cover
Mostly Clear/Mostly Sunny = 10-30% sky cover
Clear/Sunny = 0-10% sky cover
Fair = Less than 40% cloud cover, no
precipitation and no extreme weather
They too only have five categories (not counting fair), but they added different terms to describe the same conditions. As far as the NWS is concerned, partly cloudy and partly sunny are the same thing. The only difference is that partly sunny is used to describe daytime cloud cover and partly cloudy is used to describe nighttime cloud cover. Same goes with mostly sunny/mostly clear and clear/sunny.
So case closed right? Not so fast. Because the terms are so similar, the nighttime and daytime terms often get used interchangeably by most forecasters. If skies are expected to be partly sunny for the next five days, it's highly likely the forecaster will switch between saying partly sunny, partly cloudy, and fair just to spice up the forecast some.
The difference between partly cloudy and partly sunny though has really taken on a life of its own; so much so that many forecasters now separate the two terms to have a total of six categories of sky cover instead of five. The most common order of these six categories of sky cover, from least to greatest, is as follows:
Sunny = 0-10%Mostly Sunny = 10-30%
Partly Cloudy = 30-50%
Partly Sunny = 50-70%
Mostly Cloudy = 70-90%
Cloudy = 90-100%
This is the scale I personally go by, but even this is not agreed upon by all meteorologists. Some argue that partly sunny and mostly cloudy mean the same thing while others use partly sunny when cloud cover is expected to dissipate later and partly cloudy when cloud cover is expected to increase later.
The bottom line is that it depends on the person who made the forecast for what partly cloudy or partly sunny actually means. While you're more likely to see more clouds when the forecast calls for partly sunny skies compared to partly cloudy skies, get to know your favorite source for weather and see what the sky looks like when it says partly cloudy or partly sunny. You should be able to figure out what category the meteorologist who made the forecast falls in!
Big thanks to "The Media Mind" who provided the inspiration for this post after asking about this in the comments of my last blog post. If you have a weather question you want answered, comment below and I'll do my best to answer it in a future post!
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