13:14 Mon May 18, 2020
When Hail Freezes Over
To coincide with this week’s Virtual Classroom topic of thunderstorm types, I wanted to explore a type of precipitation that is commonly found alongside thunderstorms – hail. It’s a fascinating phenomenon in meteorology, and, if you think about it, it seems a little strange to see pieces of ice falling from the sky on a hot summer day. Let’s start by taking a look at the interesting formation process of hail and what kind of conditions are needed to begin the process.
Hail is frozen precipitation that occurs when a strong updraft within a storm pushes rain drops higher within the cloud, where they freeze. This droplet is also pushed to different parts of the cloud by horizontal winds as it is kept aloft by the updraft. As it collides with water droplets (or other hailstones) that freeze onto it, it grows. The temperature in the cloud is the main factor that governs the appearance of the hailstones. When water freezes immediately upon contact with the growing hailstone, air bubbles don’t have time to escape, leaving a cloudy appearance to the ice (similar to why rime ice appears cloudy). If the water takes longer to freeze, air bubbles escape before the new layer is solid, leave a clear new layer of ice. With difference of temperature and other conditions within a storm cloud, hailstones may have multiple different-looking layers as they move within the cloud. When the hailstone is heavy enough for gravity to be stronger than the updraft, it falls to the earth.
The process of hail formation. Taken from the Australian Bureau of Meteorology.
The speed of the fall depends on several factors, including size. Hail that is between 1 and 1.75 inches in diameter may fall around 25-40 mph, but those greater than 4 inches may fall at speeds over 100 mph! In 2010, the largest hailstone recorded in the US fell in Vivian, South Dakota. It was 8 inches in diameter and just shy of 2 pounds in weight – that’s almost as big as a volleyball! Here on the summit, the hail we receive is small, typically around ¼ inch or pea-sized. We don’t usually see hail much larger than that because the mountainous terrain is unfavorable for the extremely tall thunderstorms with strong updrafts needed for large hail to develop.
Small hail piled up outside the Observatory.
A hailstone several inches in diameter, that clearly shows the aggregation of smaller stones as it moved through the cloud. Photo taken from NOAA.
Hail is dangerous for a few reasons. Besides its association with a severe thunderstorm, risks of lightning and high winds, significant damage can be caused by larger hailstones. They frequently damage crops, and often take a toll on vehicles (including airplanes) and buildings. Even small hail can accumulate on the ground, leading to slick driving conditions just like driving on ice. When a thunderstorm is approaching, you want to seek shelter immediately not only because of lightning, but to ensure you aren’t caught outside when the ice starts falling. To check out more on thunderstorms, including Tom’s presentation on the different types of thunderstorms, head to our Virtual Classroom page at mountwashington.org/classroom and stay tuned for more thunderstorm topics coming soon!
AJ Grimes, Weather Observer
14:41 Mon May 11, 2020
Something's Abuzz...Lightning Safety!
For this week’s observer post, I wanted to continue the theme of this week’s virtual classroom topic – lightning and lightning safety. This topic warrants some extra attention because of how dangerous lightning is, and how crucial it is to understand what to do (and what not to do) when lightning is nearby. Weather observers will go outside into some pretty crazy conditions to do our hourly readings, but we will never go out if there is a thunderstorm near the summit due to the danger of lightning.
Lightning is an immense electrical discharge ranging from 100 million to 1 billion volts delivered over a few milliseconds. Within just a few millionths of a second, it heats the surrounding air to about 50,000⁰F – about five times hotter than the surface of the sun. Though the majority of people struck by lightning survive, they may suffer significant and lifelong disability. Fortunately, there are a number of things you can do to stay safe during a thunderstorm.
Lightning bolts over Wildcat B.
Lightning can strike 10-12 miles from its parent thunderstorm – and strikes have even been documented more than 25 miles away. Since thunder is only heard for about 10 miles, you should seek a safe shelter as soon as you hear it, and wait about 30 minutes after the last rumble before you head out. A safe shelter is an enclosed building with plumbing and electricity or a metal-topped vehicle with the windows rolled up. A building’s plumbing and electrical wiring are excellent conductors, so they will conduct the electricity to the ground if the structure itself is struck. Small and less robust buildings or those with open sides, like dugouts, porches or sheds, or vehicles like convertibles or golf carts do not offer adequate protection.
Lightning to the southeast, with the Stage Office and Tip Top House in the foreground.
Once you’re inside, there are still steps to take to be sure you’re safe. After all, the plumbing and electrical wiring can also conduct the charge to you! So, while you can use a cell phone that is not plugged in, anything plugged into electrical outlets can conduct the charge. Surge protectors do not provide adequate protection from the magnitude of surge from a lightning strike, so while you can protect electronics by unplugging them before a storm, it’s best not to risk yourself once there’s lightning in the area. Also keep clear of water: Electricity travels well in water, whether you are swimming outside or taking a bath inside, or even doing dishes or laundry.
If you can’t get indoors, there are still some things you can do to lower your risk. Electricity takes the “easiest” path as it travels, and the shorter paths are easier. So, it’s safer to be lower (and not to be on hills, mountaintops, and ridges where you are higher up and the path to you is shorter). Keep clear of things that conduct electricity like water, and do not take cover under large trees, rocky outcroppings, or metal structures. Being near a tall object (like under a tree) can cause a “side splash” whereby lightning hits the tree, then jumps to the person next to it for the rest of the journey to the ground.
An impressive thunderstorm to the northwest over Vermont.
Lightning makes a thunderstorm an awe-inspiring event to watch, but it is also extremely dangerous. We take lightning safety seriously at the Observatory and you should too. For more information on the creation of lightning and lightning safety, check out Ian’s excellent presentation on our Facebook page or on our Virtual Classroom page at mountwashington.org/classroom
AJ Grimes, Weather Observer
12:47 Mon May 04, 2020
Like a Breath of Fresh Air - Only Thinner
Here at the Observatory, we get a lot of questions regarding altitude and the lack of oxygen on the summit. I thought we could continue last week’s theme of high altitude, but instead of baking tips, this week we will investigate the effects on the body as one ascends through the atmosphere and the changes it automatically makes to adjust. Since the air is thinner at the height of Mount Washington (6,288 feet), less oxygen is available with each breath – about 20% less than at sea level. In order to meet your body’s oxygen demands, it must make some changes to continue to get what it needs.
A breathtaking morning view from the summit.
If you were to climb to the summit of Mount Washington, you might notice the lesser oxygen content by getting “winded” more quickly. This means your oxygen demand is harder to meet with less oxygen coming in with each breath. You would compensate immediately by increasing the volume and frequency of breathing by taking deeper breaths and breathing faster. Your body makes short-term accommodations like these when you do any aerobic exercise. The problem is that doing this over a long period of time takes a lot of energy, so this mechanism really acts like a bridge while your body does some other things to acclimate to the altitude.
Red blood cells carry oxygen from your lungs out to your body, and carbon dioxide from your body back to the lungs. So, more red blood cells means more carrying capacity. To make this happen, your body produces a signaling protein called erythropoietin, which stimulates the production of red blood cells. The more red blood cells available to circulate oxygen and carbon dioxide, the more effective each breath is. The body also makes each red blood cell more efficient by creating a molecule called 2,3-DPG. This molecule is in red blood cells and changes how their hemoglobin binds oxygen. You want the red blood cells to pick up oxygen where there is a lot of it (in the lungs) and drop off oxygen where there is little of it (at the tissues). In order to do that, hemoglobin must let go of oxygen more readily at the tissues. Even with less oxygen available in the lungs, there is still enough for this mechanism to ensure that red blood cells pick up enough oxygen in the lungs, but also that the 2,3-DPG makes them dump more oxygen in the tissues. Other factors can affect oxygen delivery similarly - for instance, lactic acid from anaerobic exercise like weight lifting, and increased temperature.
In spite of these changes, don’t worry – Mount Washington is a tall mountain, but not tall enough to reach the altitude where people can no longer acclimate, called the “death zone”. This altitude is generally considered to be around 26,000 feet above sea level, where peaks such as Mount Everest and K2 reach. However, if you climb Mount Washington or do any sort of work up here (such as climbing up and down stairs and ladders to de-ice instruments), you will notice a difference in how your body reacts to the altitude!
AJ Grimes, Weather Observer