- Published on May 09, 2010
Reading the technology.
As Chuck mentioned in an earlier post, weather is a huge part of our daily planning. Here at Palmer Station we have two ways of evaluating weather conditions and whether they are good for diving and boating. One is the weather forecast, delivered every day by forecasters from the SPAWARS weather facility located in Charleston, South Carolina. This forecast predicts the weather and is right, mmmmm, most of the time. But weather changes quickly, so we also use the weather instruments here on station which will give you real time readings of wind, temperature, precipitation, humidity, horizontal visibility and light levels (Image 1). Using this and our eyes we can see what is really happening outside, and then plan our diving/boating.
Looking at the readings from weather on station we can tell which direction the wind is coming from, how strong its sustained force is, and what the wind is gusting to. We can also look at the wind levels for the past twelve hours to look at trends. Knowing this we look to the sea.
Using our eyes, important factors to consider are swell, which is basically wave height, and how the wind is affecting it. Diving and boating require the least amount of swell and wind we can manage. When looking at the swell you want to consider which direction it is moving and whether the wind is running with it (moving in the same direction).
When the winds are high you get white caps on the tops of waves (white caps should only be seen on breaking waves in good conditions, i.e. a beach) and if the wind is moving against the swell, you get a large amount of spray which makes it harder for the boat captain to maneuver. Wind drives swell too so when the two are combined, it may result in a significant increase in wave height. Diving should always take place in the lee of weather, which means in an area protected from weather. This is not only important for divers underwater, but for the tenders in the boat, and essential for picking up of the divers.
Rain, snow and fog conditions should also be factored into planning because they can hinder visibility during boat navigation. Here with the use of geographic markers, like islands, and a Global Positioning Device (GPS) these conditions can be worked around if they are mild.
The reason I say that the daily forecast is right, mmmmmm, most of the time is because it’s just an estimate of conditions we will experience made from afar. If you wanted to be your own meteorologist there are a few tools available to you for use. One is an isobaric analysis which is made by compiling barometric pressure readings taken at sea-level into a grid or map. The result is contour lines called isobars, which outline areas of equal pressure and are closely related to the intensity and direction of wind movement (Image 2). Low pressure is associated with warm air and storms, whereas high pressure is associated with cool air and clear skies. Where there is a quick change in pressure there is sure to be wind, no matter whether we are changing to a high or low pressure system.
Reading the sky.
So where would we be without the technology of forecasts, isobaric analyses, and weather monitoring instruments? When you look up, the most common thing you see is a cloud or a lack of clouds. Clouds are characterized by their shape and altitude and their movement is telltale of wind patterns. They may characterize what is called a ‘front’, which is a zone of interaction between cold and hot air (high and low pressure systems). A warm front may draw the clouds down in altitude, something called ‘lowering the ceiling’ and clouds will change shape, eventually becoming storm clouds. You may recognize this as a time when winds change direction and speed along with the temperature, the calm before the storm. If you had a barometer you would also notice the air pressure changing significantly.
Cloud shape can change, vertical development being the most dramatic. Clouds that do this are generally Cumulus type clouds, the small white ones often “fair weather” clouds. However if these clouds grow taller, they may turn into large stormy demons called cumulonimbus clouds. High winds will flatten the tops of these creating an anvil shape. They are often associated with heavy rain, snow, hail, thunder and lightning storms, and tornados. Helpfully the anvil points in the direction that the storm is heading, so if you see it from afar you can gauge your chances of missing it, or it missing you.
To wrap it up there are a lot of tools we can use to plan our diving and boating here at Palmer Station. My personal favorite is reading the clouds on my own, but technology often proves to be right, mmmm, most of the time. Here are descriptions of cloud shape. There is a great illustration of them and more information on the Enchanted Learning website.
High clouds are generally above 18,000 feet. These include cirrus, cirrostratus, or cirrocumulus clouds.
Cirrus clouds are the most common of the three and look long and wispy. They generally travel with the wind and are also called mare’s tails, as they curve upwards. These are fair weather clouds but if you watch them, they are travelling with the wind and will tell you which direction weather is approaching from.
Cirrostratus clouds are sheet-like, covering the entire sky. They usually approach about one day before rain or snow and sun and moon shine reaches through them.
Cirrocumulus clouds form in lines of small round puffy clouds, and indicate fair, cold weather. In the tropics this may indicate a tropical storm or hurricane because of the cold ‘front’ hitting warm tropical weather.
Clouds at a medium altitude, between 18,000 and 6,500 feet, are called alto clouds. These are used to predict weather changes that may occur in the next 6-12 hours.
Altostratus clouds cover the entire sky, and are generally gray-blue in color, creating a lens obstructing the sun or moon shine. These generally form before storms with a lot of rain or snow.
Altocumulus clouds form in groups and are grayish-white, with their heavy bellies darker than their tops. These are a sign of thunderstorms, mostly preempted by sticky, warm weather.
Low clouds are generally called stratus clouds. These range, in thick sheets or layers, at altitudes below 6,500 feet.
Stratus clouds are gray and encompass the entire sky. They are often associated with mist and drizzle, very characteristic of temperate rainforests and coastlines.
Stratocumulus clouds are lumpy, low and gray often associated with precipitation. They form rows and often have blue sky peeking out amongst them. These don’t predict weather, unless they are associated with a front.
Nimbostratus clouds are dark gray and have a jagged looking under belly. These are always associated with rain or snow.