First off, what is a jet stream? A jet stream is a fast flowing river of air in the upper atmosphere that steers our storms. Within the jet stream, there are pockets of air that are moving fast. The faster moving pockets are called jet streaks. We usually look at the 250 mb level to detect where the jet stream and its associated jet streaks are located.
Next, how does the jet streak influence storm strength? When a strong jet streak is positioning itself correctly over a surface low pressure, upward vertical motion is enhanced. The enhanced motion can lead to explosive storminess. Many times, a relatively innocuous storms explodes into a monster that means business when the strong jet streak comes to town.
Showing posts with label General. Show all posts
Showing posts with label General. Show all posts
Friday, January 11, 2008
What does pressure have to do with storm strength?
I recently was asked why a 960 mb storm means that the storm is strong. Before fully answering the question, we need to understand the definition of air pressure. Air pressure is the weight per unit area of the air in the column above our head. Therefore, as we go up in elevation, less air is above our heads, and hence, we see a corresponding decrease in air pressure. At the surface, low pressure indicates inclement weather whereas high pressure is more commonly associated with fair weather.
Next, we need to understand why a low pressure would be a favorable location for inclement weather. In order to understand this, we need to know something about the pressure gradient force. The pressure gradient force is the force that acts from high to low pressure. In other words, air flows from regions of high surface pressure to regions of low surface pressure. Many of us have seen the pressure gradient force in action when we fly. When you open your water bottle to take a sip when flying, you fill the bottle with lower air pressure. Once the plane lands, we are at ground level where pressure is higher than it was in the cabin when the plane was aloft. We notice that the bottle appears to be crunched together. This crunch occured because the pressure inside the bottle is lower than the pressure outside the bottle, and effectively squeezes int he bottle. The same thing happens in the atmosphere. As air flow in from all sides of the low pressure region, it converges. Because air cannot enter the ground, it is forced to rise. This rising motion leads to stormy weather.
So when we ask what pressure has to do with storm strength, the simple answer is that a lower surface pressure causes stronger convergence, which means we have more vigorous upward motion. The more vigorous upward motion creates stormier weather. Of course, this is a simple explanation to a more intricate phenomenon.
Next, we need to understand why a low pressure would be a favorable location for inclement weather. In order to understand this, we need to know something about the pressure gradient force. The pressure gradient force is the force that acts from high to low pressure. In other words, air flows from regions of high surface pressure to regions of low surface pressure. Many of us have seen the pressure gradient force in action when we fly. When you open your water bottle to take a sip when flying, you fill the bottle with lower air pressure. Once the plane lands, we are at ground level where pressure is higher than it was in the cabin when the plane was aloft. We notice that the bottle appears to be crunched together. This crunch occured because the pressure inside the bottle is lower than the pressure outside the bottle, and effectively squeezes int he bottle. The same thing happens in the atmosphere. As air flow in from all sides of the low pressure region, it converges. Because air cannot enter the ground, it is forced to rise. This rising motion leads to stormy weather.
So when we ask what pressure has to do with storm strength, the simple answer is that a lower surface pressure causes stronger convergence, which means we have more vigorous upward motion. The more vigorous upward motion creates stormier weather. Of course, this is a simple explanation to a more intricate phenomenon.
Thursday, January 3, 2008
Humidity
I just got off the phone with my friend Tressana, and told her to check out the latest observations in Rhode Island. She is sitting in her warm apartment looking out the window at 55 degree weather while I sit here freezing. I think God is answering menopausal women's prayers, because there is no way anyone could sweat in this cold. Anyways, Tressana noticed that the relative humidity is high in Rhode Island. She asked me how that could be true if the temperatures are so cold.
The answer is that relative humidity is a relative number. In other words, the higher the temperature, the more moisture that air can hold before the airmass is saturated. The opposite also holds true, in which lower temperatures are able to hold much less moisture. As a result, we could have a lot of moisture in the air, but a very high temperature would mean the air could hold a lot more moisture. Hence, the air is dry relative to the amount of water the air could actually hold. In this case, we would see a LOW relative humidity. In the case where the temperature is very cold (as in Rhode Island tonight), the air can only hold very little moisture. As it turns out, there is some moisture in the air, but only a small amount. The truth is that this cold atmosphere couldn't hold much more. In this case, we have a HIGH relative humidity because the air is already holding almost as much moisture as it possibly can.
The answer is that relative humidity is a relative number. In other words, the higher the temperature, the more moisture that air can hold before the airmass is saturated. The opposite also holds true, in which lower temperatures are able to hold much less moisture. As a result, we could have a lot of moisture in the air, but a very high temperature would mean the air could hold a lot more moisture. Hence, the air is dry relative to the amount of water the air could actually hold. In this case, we would see a LOW relative humidity. In the case where the temperature is very cold (as in Rhode Island tonight), the air can only hold very little moisture. As it turns out, there is some moisture in the air, but only a small amount. The truth is that this cold atmosphere couldn't hold much more. In this case, we have a HIGH relative humidity because the air is already holding almost as much moisture as it possibly can.
Wednesday, January 2, 2008
Welcome!
Welcome to a blog devoted to my love for all things weather related. I have been visiting my family in Rhode Island for the past couple of weeks, and storm after storm has been hitting the area. Because I live in southern California, I forgot how excited I get when I know a new storm is heading in my direction. My focus on this blog will be to discuss upcoming, present and past storm events and anything that is related to severe weather phenomena. If you ever have a weather related question, please feel free to ask. I may not always know the answers, but I am sure I can try to at least find one.
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