Weather in Motion

As we know, weather moves! Our atmosphere is an ever moving cauldron of many processes acting at once. The purpose is to balance temperature differences, water the earth and sustain our  environment. Without weather life would not be possible on Earth.

Weather forecasting is the part of meteorology where the public gets to see the fruits of meteorologists labor on a daily basis. While there is much scientific research going on behind the scenes the weather forecast is where the rubber meets the road. If forecasts are dependable the science looks good. When forecasts are wrong it doesn't look so good. Fortunately the science has advanced to the point where forecasts are reasonably dependable even though there is considerable of room for improvement. 

Some of the tools used to create your daily weather forecast are forecast models. There are many models - many nations do their own modeling for their own purposes. The United States, Canada, the European Union, China, Japan, Russia and many others have their own models. 

None of the models are perfect. The models lack sufficient data and the ability to process the available data to make the models perfectly mimic the weather. None the less, the models are very useful.

One of the models is the American GFS (Global Forecast System). To give you an idea of what a model looks like here is a link to an animated version of the GFS. Link to it and just watch it move. It runs for a two week period and is updated several times a day. Keep in mind that this is just 1 of many forms of output available to forecasters. You are seeing a very tiny, but significant, part of what the model does. Occasionally this blog will show you some of our other tools. 

Click on the link below to see the GFS run. Pick the 1000_500_Thick to see an animation of the surface pressure systems forecast for the next two weeks. Don't worry about understanding everything you see. The point is to notice the movement that is forecast. You are watching one model's interpretation of what may happen. Forecasters pick and choose between the models based on their experience of watching models perform. There are other animations available. 

GFS Forecast Animation

If you want browse through other American models click the link below. 

U.S. Model Home Page

Weather Maps and Radiosondes

Map plotted by Digital Atmosphere which is available at www.weathergraphics.com. 

The surface map above shows weather observations shortly before 10:00 p.m. this evening. It is a little difficult to read the plots because of the small font. Look at Omaha, Nebraska. The plotted ceiling height is C31 which is code for 3100 feet above ground level. The sky is overcast. If you look at the station model plots and observation coding which are accessed on our home page you will see the Omaha sky is overcast. 

Now, look at the chart below. This is the radiosonde (weather balloon) plot from Omaha, Nebraska as of 6:00 p.m. local time. The red line is the temperature in degrees F while the green line is the dew point. wherever the lines are close together the relative humidity is high and the probability of cloud cover increases. On the far left the chart shows conditions are favorable for cloud formation - see the small gray boxes at the left side of the chart. You can see a small gray box on the left side marking the 3000+ altitude. This confirms a layer of low level moisture that is creating the overcast skies at Omaha. Notice that the layer is less than 2000 feet thick. Above it the  red and green lines diverge indicating a deep layer of dry air. There are several layers in which clouds are also possible - see if you can find them. These areas indicate the possibility of up to 3 layers of moisture that may be producing cloudiness. 

The Radiosonde plot is made by RAOB, a program available at RAOB.com.

What does the instrument package look like? Learn more by clicking here.

Odds of a White Christmas

What are the odds of a White Christmas? The National Center for Environmental Information has the answers. Click the button below to learn  more.

Hartman Reserve, Cedar Falls, Iowa;  Photo by Craig Johnson

Northeast vs the Southwest

Map plotted by Digital Atmosphere which is available at weathergraphics.com.

It's a tale of two weather regimes. The northeast is getting another taste of winter while parts of southern California are facing more fires.

A winter storm is organizing over the Great Lakes tonight and will spread moderate to heavy snow from the lower Great Lakes to New England during the next two days. Behind the storm lake effect snows are for areas western Lower Michigan and central Upper Michigan.

Then there is the west. Large high pressure centered over the Great Basin is creating strong winds in Southern California. The weather is favorable for continuing fires with the wind and single digit relative humidity. 

In between, gusty northerly winds along a cold front are bringing colder air to the Upper Midwest. The colder air is wrapping around the backside of the developing low over the Great Lakes.

Cirrus spissatus - a unique cloud.

Photo Copyright by Craig Johnson, 12-2-2017

Cirrus spissatus is a unique cloud type. It is the only cirrus cloud dense enough to hide the the disk of the Sun. Other cirrus allow the disk to be at least faintly visible. Most spissatus form by the breakdown of the anvil of a thunderstorm. Spissatus not formed by remnants of a thunderstorm anvil often appear as multiple patches of dense cirrus, often at different levels, like the cirrus in this photo. 

Variety's the very spice of life, that gives it all its flavor. - William Cowper

Variety in the sky raises many questions. Why are there multiple cloud types in the sky at the same time? What processes are causing these cloud types? Why do some of the clouds look like tufts of wool (floccus) while others are a hybrid of stratus and cumulus types. Why do some look like waves? (Hint: They are waves.) When looking at clouds - look closely. The shapes reveal the processes and air motions overhead. 

This morning we had three distinct different types of altocumulus in the sky. The first photo was taken looking to the southeast, the second was to the north, and the third was looking to the south. The photos were all taken within a few minutes of each other. Prairie skies are very interesting indeed!

Photo Copyright by Craig Johnson, 12-2-2017

The photo above is a good example of altocumulus floccus. The floccus form is concentrated in the right half of the photo.

Photo Copyright by Craig Johnson, 12-2-2017

The second photo is altocumulus stratiformis and altocumulus floccus. The floccus are identified by their puffy 'tufts of wool' look while the stratiformis are a flatter version of altocumulus. These types are mixed together in the photo above. It is easy to see that identifying cloud types is not always a clear-cut decision. Cloud processes and air motion are often part of a continuum rather than discreet structures. We often need to identify what are the dominate cloud types because cloud structures do not always fit into nice neat packages.

This tells us something about the complexity of our atmosphere. It is fluid with its motions transitioning in an infinite variety of ways. Many times we can look at clouds and see basic identifiable structures. However - don't stop there! Look closer and notice what is in the fine details. Try to imagine the type of flow that is creating the shapes you see. Sometimes the flow is what it seems to be. Other times the shapes are the result of secondary flow which requires more study. I will try to point out some of these differences in future posts. 

Photo Copyright by Craig Johnson, 12-2-2017

The third photo is altocumulus undulatus. There are several formations working together. The first are the clumps of cumulus that make up the overall structure. These clumps are arranged in bands caused by

Photo by Craig Johnson, 12-01-2017

The last photo is looking south. Note the unusual very thin altocumulus undulatus extending from the center to the right. These wavy clouds are subtle waves moving from right to left (west to east). These clouds were at a lower level than the more predominate clouds elsewhere in the photo.  Wave type clouds are typically caused by gravity waves.

From cirrostratus to altocumulus

The dominant cloud type in the sky often changes in a hurry in the middle latitudes. This photo was taken less than an hour after the cirrostratus photo posted yesterday. Instead of cirrostratus the sky was now dominated by altocumulus. The altocumulus here are wave clouds, caused by ripples in the flow. Flying through these clouds would provide a bumpy ride - much like a boat ride on a lake that is covered by waves. The waves are created by the wind friction as it contacts the water surface.

Cirrostratus

This is a photo of a classic cirrostratus sky. Taken at Cedar Falls, Iowa on 11-26-2017 at 3:15 p.m. CST,  it shows diffused sunlight and the classic "milky" sky of cirrostratus. The photo also reveals several CONTRAILS (condensation trails) left by passing aircraft. The hint of a halo is visible in an arc right of the Sun. Halos are caused by sunlight being refracted as it passes through ice crystals contained in the cirrostratus. The halo was only visible in the photo - not with the naked eye. 

November Prairie Sunset

Life on the prairie includes seeing for miles and miles and miles. Sunsets can be spectacular with vivid colors and a variety of cloud shapes. The three images in this post were taken near sunset at Fort Dodge, Iowa, 11-16-2017. The sky was dominated by altocumulus clouds. These images show a few different forms of altocumulus that were in the sky at the same time. 

Notice the ripples (waves) traveling in different directions at different altitudes. The waves creating these clouds are  gravity waves - waves generated at the interface between two media. Watch the wave action on a lake and you get an idea of how these waves form in the atmosphere. They occur along the interface between layers of different air density. Like a lake, which has considerably different density between the water and the air, the air motion across the lake creates waves. The same thing is happening here only the waves are occurring between layers of air. 

The altocumulus are prominent in this  photo with the most distinctive wave action near the center. Temperatures were in the 40s and the sky definitely has the chilling look and feel of mid-November.

The leafless trees and the setting Sun set up a picturesque November sky. Red light bathed the altocumulus cloud base with red light. The coloration brings out the three dimensional structure of the cloud formation. Notice two large birds cruising below the clouds and above the trees. The trees have lost their leaves in preparation for winter.

Asperitas - A New Cloud Type

Asperitas Cloud Photo by Craig Johnson

Sometimes a gray day requires being a little creative with a post. Today is one of those days. So let's go back the spring of 2017 to view an unusual cloud type. Asperitas is Latin for roughness. This is one of 11 new cloud types that have been added to the newest edition of the International Cloud Atlas published by the World Meteorological Organization (WMO). The cloud type was first "discovered" at Cedar Rapids, Iowa in 2006 and features chaotic ripples and small divots. The formation did not fit into the existing cloud type system. The photo above was taken in Cedar Falls, Iowa on April 25, 2017. 

Check out the new International Cloud Atlas here: https://cloudatlas.wmo.int/search-image-gallery.html

Following a Cold Front

Yesterday's post showed a cold front from Hudson Bay into southcentral Canada and then northwestward parallel to the mountains in western Canada. Today that front has moved to eastern Hudson Bay to Lake Superior, South Dakota, then northwestward across Montana into southwest Canada. The polar front we were watching was stretched across the southern United States.

These fronts form in the middle latitudes where temperature contrasts from north to south create traveling cyclones (low pressure) and anti-cyclones (high pressure). The flow of these systems is a major part of managing the Earth's heat budget, bringing warm air north and cold air south to dissipate the middle latitude temperature differences. More about that in a different post.

For now we can say the arctic front continues to move southeastward with its air mass being modified by warmer ground, longer days, and mixing with warmer air. Ahead of the front warmer air is moving north to be cooled by colder land and water, shorter days, and mixing. 

Surface Weather Map, Wednesday, November 8, 3:00 p.m. CST. Map plotted by Digital Atmosphere  available here: http://www.weathergraphics.com/

For those of you who like to delve in to the science of all this, below you will find what is called a RAOB (RAwinsonde OBservation). It is a sounding of the atmosphere made by an unmanned balloon which radios data back to earth as the balloon ascends. This sounding is from Davenport, Iowa at 6:00 a.m. CST today. It shows a dry air mass with the red line (temperature plot) and green dashed line (dew point). The spread between the two lines is substantial, indicating dry air. The greater the difference between the temperature and the dew point temperature the lower the relative humidity. In this case the dry air is sufficient to prevent precipitation as the cold front moves southeast across eastern Iowa. There is a lot more to this chart so I am going to leave it at that for now but it is one tool used by meteorologists to gauge what is happening in the air over our heads. 

RAOB Sounding Plotted by the  RAOB Program available here: http://raob.com/

How often are balloons launched? Weather balloons are launched twice per day, 6:00 a.m. and 6:00 p.m. CST (7:00 a.m. and 7:00 p.m. EST and so on around the world). The balloons are launched simultaneously worldwide, at least twice daily, to measure upper air conditions including temperature, dew point, and wind. More than 200 other parameters are computed and plotted from these basic measurements. The chart about shows the temperature, dew point, and wind profiles (changes with height).

.Learn about weather balloons and how they are launched by clicking here. Where are the weather balloons launched i the USA? Check this website from NOAA. The launches are scheduled twice daily. Additional launches may be requested as the weather demands.

Mid-day Weather Map

The map was plotted by Digital Atmosphere: http://www.weathergraphics.com/

The seasons are changing. The surface weather map at 1900Z (1:00 p.m. CST) shows the polar front stretched from California to Colorado, south to Texas, east through the Gulf States, then northeast off the cost of Canada and east of Greenland. An Arctic front is backed up against the mountains in western Canada south and east to Lake Winnipeg and northeast across northern Hudson Bay. The coldest air is behind the Arctic front where temperatures fall into the teens, single digits, to below zero. North of the polar front is a broad area of high pressure covering much of the United States. The polar high pressure connects to high pressure with arctic characteristics over the Yukon. Weak low pressure systems are moving along the polar front with  clouds and precipitation. The Arctic front is forecast to spread southeastward into the Upper Midwest, across the Great Lakes, to New England. 

Altostratus

Above: Altostratus
Below: Altostratus with a hint of the cumulus cloud type.

Look closely and notice the slight hint of cumulus in the cloud photo above. The lighting reveals little lumps scattered through the cloud. Cloud names are based on a cloud shape, size, and texture. Some clouds may have several structures embedded in the main cloud type. The cloud above would likely be categorized as altostratus even though there are very small cumulus textures. The texture is easier to see in this photo than with the naked eye. Overall, it is part of a broad sheet of altostratus covering the sky. The cloud has formed in an area of cold advection (cold air replacing warmer air) over the Midwest.

Altocumulus Family: Altocumulus becomes altostratus.

Altocumulus floccus (like tufts of wool) cover the sky over Cedar Falls, Iowa during the afternoon of November 6, 2017. The cloud ceiling was measured at 11,000 ft. at the Waterloo, Iowa Airport. A combination of a moist layer and turbulence likely created the altocumulus which spread in to an altostratus layer. 

Altocumulus floccus Photo by Craig Johnson

There were several variations of altocumulus floccus. Notice the more diffuse version below. Organized bands of waves are seen rippling through the layer creating alternating cloud bands with clear strips in between. 

Altocumulus Floccus Photo by Craig Johnson

Altocumulus dominate the upper right quadrant of this photo with altostratus visible across the bottom.

Altocumulus floccus Photo by Craig Johnson

Altocumulus and altostratus mixed together as the altocumulus flattens into altostratus.

Altocumulus and Altostratus photo by Craig Johnson

Clouds that look like stratus and cumulus.

Photo by Craig Johnson on I-35 north of Ames, IA, 10-30-2017

Strong northwest winds gusting to 35 mph and a stratocumulus cloud deck made for a chilly windy day. Stratocumulus clouds have stratus and cumulus cloud characteristics, as seen here. The lumpy cloud pattern is the cumulus form while the general flat look to the clouds is the look of stratus, hence the name - stratocumulus.

All Storms Come to an End

Photo by Craig Johnson

Cirrostratus and cirrus fibratus at sunset, Cedar Falls, Iowa. After several days of overcast skies and rain the end of the storm was finally visible on the western horizon. The storm's cloud shield had a sharp cutoff on its western edge. The gradual transition from a low overcast finally culminated in this dramatic sharp edge from clouds to clear sky. The cirrus edge marked a southwest to northeast jet stream that extended from the Midwest to Lake Superior and onward to Canada. The surface low by this time was northeast of the Great Lakes. Much drier air and colder air at low levels had already wiped out low and middle clouds - only the cirrus remained.

Storms begin and they have an end. This marked the end.

Mare's Tails

Photo by Craig Johnson

"Mare's tails and mackerel scales make tall ships carry low sails;" so says weather lore. In the early days of ocean going ships there were no weather forecasts. Ship's crews needed rely on their own observations and past experience to make decisions. Many times they were wrong but their forecasts were not always busts. The sky does give indications of what's coming next but given the complexity of our atmosphere sometimes similar clouds did not lead to the same result. That's because cloud altitudes and shapes are not always associated with the same weather outcome.

The scientific name for the above clouds is cirrus uncinus. Uncinus is from the Latin, meaning "curly hooks." These clouds are certainly have curly hooks! Most people know them by a different name; mare's tails. In this case the mare's tails remind us of the locks of hair on the lower hind legs of a girl horse. You can almost see the locks of hair blowing in the wind when you see cirrus uncinus. It is said that mare's tail clouds indicate approaching strong winds and suggesting ships should lower their sails because winds aloft could lower to the surface. Is it true? Not always but they are often associated with strong winds aloft that may eventually descend to the surface as a storm system gets closer.

You can try this out yourself to see if the weather lore is right. Watch the sky for mare's tails and then see observe your winds to see if they increase over time? If the winds increase how long did it take for it to become noticeable and how strong were they? Maybe the winds were already strong when you noticed the clouds. It is possible that the situation was already right for strong winds or there wasn't a storm coming after all. Or, as the weather lore states, "Mare's tails and mackerel scales make tall ships carry low sails!"

Do you want to read more about the science of high clouds? Link to a NASA web page on the subject by clicking here.

 

Photo by Craig Johnson

This photo was taken on December 30, 2016, just after sunrise. The sky was full of wavy clouds. There were waves superimposed on waves and the pattern was especially evident in the southeast where the Sun was rising. Elsewhere the sky was not nearly so dramatic which shows how important light is to photographers. It can make or break a picture. Without the low Sun angle these clouds would appear "ho-hum," even though they are not.

Southwest Iowa Sunset

Photo by Craig Johnson

A yellow and orange glow backlights an Iowa wind farm at sunset. 

More Mammatus

An evening thunderstorm is retreating and in its wake is this mammatus formation. The setting sun illuminates the sky in red. orange, and yellow. Mammatus form on the underside of the thunderstorm anvil. Pilots report at flight level that mammatus appear transparent. The form as heat pours out of the thunderstorm top and sinks to create the pouches seen in these photos.