To purchase our 24” x 36” full color cloud chart, go to our online store. It is suitable for framing in a standard 24” x 36” frame.
Learn how to identify clouds by following the Clouds of the Day posts below.
Nimbostratus - This mid-level cloud has its base in the low levels but extends through a deep layer vertically. It is a thick gray layered cloud with rain and snow falling from it.
The outcome from a nimbostratus cloud.
This post is in progress throughout today as a storm system spreads lowering clouds and rain across the area into Easter Sunday.
10:23 a.m. - Cirrus and Cirrostratus
10:24 A.m. - Cirrus, Altocumulus, Altostratus
10:25 A.M. - Cirrus, Altocumulus, Altostratus
12:18 p.m. - Cirrostratus with darker and lower Altostratus bottom
12:19 p.m. - Close-up of Altostratus, bottom half of photo
12:20 p.m. - Cirrostratus top, altocumulus wave clouds bottom
Photos above taken from Cedar Falls, Iowa, which is located just northwest of Waterloo. All photos, except last one of wave clouds, are looking south toward rain shown here on Des Moines NWS Radar. The Darker altostratus clouds in photos are north of this area of rain. Rain cells are moving northeast but the entire area of clouds and rain is shifting to the north.. This image is courtesy of Radarscope software. Radar image from screen grab at 12:35 p.m. CDT.
1:18 p.m. - Altocumulus - looking southeast, ceiling 7000 ft
1:19 p.m. - Altocumulus - looking southeast, ceiling 7000
1:20 p.m. - altocumulus - Looking souteast, photo zoomed in, ceiling 7000
2:32 P.M. - Nimbostratus; light rain began at 2:27 p.m.
2:33 p.m. - Nimbostratus; light rain
2:34 P.M. - Nimbostratus; Light Rain; note the fragmented cloud in foreground forms by condensation of evaporating light rain
5:34 P.M. - Cumulus, Stratocumulus, Altostratus after .02 inches of rain
5:35 p.m. - Cumulus, Stratocumulus, Altostratus after light rain
The wild blue yonder - Polar Air equals clear sky - for awhile
Altocumulus
Alto Cumulus
Altocumulus
Altocumulus
Altocumulus
Altocumulus
Altocumulus
Altocumulus
Today was a busy weather day. No, there weren’t major storms here. It was just a blustery day, typical for this time of year. But it turns out that it was an interesting study in how our weather works. In this case the weather was very busy behind the scenes.
Strong winds from an invading polar high pressure, gusty winds, updrafts, downdrafts, and snow showers made for a fun-filled day - if you like that sort of adventure. Between Noon and 8:00 p.m. today increasing air pressure pushed the general wind speeds to about 20 mph. However, air descending to the surface from higher altitudes brought 50 mph gusts to ground level. Solar heating causes the atmosphere to mix with updrafts and downdrafts. These motions created the gusty winds, bringing higher altitude wind speeds to the surface.
When the solar heating waned in the late afternoon all the fun came to a halt. The gusts stopped and general wind speeds decreased. The heating and a storm system aloft had supported the development robust cumulus clouds with snow showers. They dissipated as the sunshine decreased.
The following meteographs and the photos in the previous post paint an interesting picture. The graphs for temperature, dew point, relative humidity, barometric pressure, wind direction, wind speed, and solar radiation from our weather station tell the story. While the graphs cover the previous 48-hours, the time period of interest is from Noon to 8:00 p.m on the 9th. The tracings show a period of very unsteady changeable weather. It is a great example of how an automatic weather observing station picks up subtle and not so subtle weather changes.
The temperature (red line), dew point (green dotted line), relative humidity (blue dashed line), and air pressure were all unsteady. At the same time, the wind speed increased and became very gusty with snow showers. The solar radiation was very unsteady.
Passing showers with gusty winds caused small changes in air pressure that show up as small bumps in what is a steady pressure increase during the day. Approaching high pressure was responsible for the general all day rise in pressure. Temperature and dew point were very unsteady as the up and down motion of gusty winds were mixing air with different temperature and dew points. The relativity humidity was unsteady because it is directly related to changes in temperature and dew point - which were unsteady. Wind speed and wind gusts increased as stronger winds mixed down to the surface. The solar radiation was changing wildly as clouds covered and uncovered the Sun.
The solar radiation graph is revealing. The overall increase in solar heating is shown very well in the general shape of the graph. Within the general shape there are many large short-term swings in intensity caused by clouds blocking and unblocking the Sun. It was the changes in solar radiation which was behind the changes in the weather. It changed the heating, which changed the air mixing, which changed the wind gusts and development of cumulus clouds and snow showers. As the graphs show, all of the readings smoothed out as the Sun set.
Cumulus
Cumulus
Cumulus
Cumulus
Cumulus
Cumulus
Clouds looked wind blown as colder air and winds more than 40 mph swept the area.
Late afternoon snow shower
Snow streaks falling from large cumulus
One more view of snow showers
Graupel on The Deck - The snow showers contained graupel - also called soft hail or snow pellets. Graupel forms when super-cooled water droplets freeze on falling snow flakes. Surface temperatures were near 40 F during the snow showers. Temperatures aloft were below freezing.
Cumulus with Sprinkles - Looking South-Southwest
Developing Cumulus with Fractus - looking North
Developing Cumulus - Looking North
Altocumulus - Looking South. Clear Skies north and west at end of day
This morning dawned with fog but after a couple of hours visibility improved leaving these clouds behind. The clouds are all that remained after the fog dissipated.
As temperature increases, the relative humidity decreases - the fog evaporates. We see the fog thinning until all that remains are the clouds you see in the photos. Fog is a stratus (flat/layered) cloud at ground level. Cumulus puffy or lumpy clouds caused by rising air currents. The clouds in the photos have both flat and lumpy shapes; hence the name stratocumulus.
For the scientific explanation of what happened scroll down below the photos. View the pictures below and then scroll down to see the temperature, relative humidity, and dew point traces from our weather station this morning. The traces illustrate what happened. When reading the explanation keep in mind that dew point is a measure of the amount of moisture in the air. If it increases (decreases) then moisture is increasing (decreasing) in the air. Relative humidity is the relative amount of moisture in the air compared to the capacity of the air to retain moisture. As temperature or dew point rise the air gets closer to saturation - the point at which the relative humidity becomes 100%. Clouds form when relative humidity approaches 100%.
Stratocumulus from dissipating fog
Stratocumulus from dissipating fog
Stratocumulus from dissipating fog
Stratocumulus from dissipating fog
Looking South at 12:15 p.m. after mixing evaporated most of the clouds.
Looking North at a cumulus cloud formed by rising warm air currents.
End of the Day - Cumulonimbus (thunderstorm) southeast
Cumulonimbus (thunderstorm) - Hiding behind the trees - Evening
What happened last night and this morning demonstrates how temperature, dew point, and relative humidity are related. Temperature is a measure of heat energy in the air. Dew point is a measure of the moisture in the air. Relative humidity is a measure of how much moisture is in the air compared to its capacity of contain moisture.
For example, if moisture remains steady and temperature increases (decreases), the relativity humidity decreases (increases). If dew point increases (decreases) the relative humidity increases (decreases). If temperature increases (decreases) and dew point increases (decreases) combinations of relative humidity are endless. Relative humidity depends on the values of both temperature and dew point which may exist together in any combination. Relative humidity depends on both temperature and relative humidity but temperature and dew point do not depend on each other.
Follow the traces on the chart. Temperature is red. Dew point is the green dotted line. Relative humidity is the blue dashed line. Temperature and dew point were almost identical all night which meant the relative humidity was near 100%. The air was nearly saturated and fog (a cloud near the ground) formed. After sunrise the temperature increased and relative humidity decreased. Notice how the temperature and dew point lines diverged. As the difference between temperature and relative humidity increases relative humidity decreases. As relative humidity decreased the fog began to thin - it evaporated.
What ultimately happened was sunlight began to heat the earth increasing the temperature. That caused the air to rise which began to mix the air. Warmer air near the ground began to rise and drier air aloft descended. This mixing warmed and dried the air enough to cause evaporation of the fog. The layer of moist air near the ground was very shallow. In the end the moist air became mixed and the relative humidity in the lower levels of the atmosphere dried enough for the fog and most clouds to dissipate.
The entire process takes place in front of our eyes. The bottom left photo, taken at 12:15 p.m. shows only a few remnants left over from the mixing process that evaporated the fog and finally the left over stratocumulus. The rising air currents and sinking air currents stirred the air, mixing in drier air. The rising motion is not being sustained because the air is stable after mixing so the sky is clear. On the other hand, looking north at the bottom right photo, there is a band of cumulus clouds partly explained by a storm system to the north that is sustaining rising motion in a slightly unstable air mass. This is maintaining upward motion and cumulus clouds. Clouds do have a story to tell.
From the unusual to the usual the sky brings an unending stream of variety to a backyard near you.
The unusual: A lone cloud streaming ice crystals.
Nothing but blue - backdrop for the wind sensors.
The usual: Cirrus and cirrostratus.
More cirrostratus…
The day ended with bands of cirrostratus.
NASA Photo - Mariner
Venus, Earth’s nearest planetary neighbor is putting on quite a show in the western evening sky. f you would like to follow the latest on Venus here are three links that may interest yoo. Venus is visible beginning before sunset high in the western sky and then for the remainder of the eveing. It will be brightest on April 27th. Don’t miss the chance to see it in the evening sky before and after sunset. Through April and into May.
Links:
https://theskylive.com/venus-tracker
http://www.skymarvels.com/infopages/vids/Venus%20-%20Current%20001.htm
Stratocumulus - looking south-southwest
Stratus with stratocumulus lower right - looking north
Stratocumulus with higher cirrocumulus behind
ANother view of stratocumulus with higher cirrocumulus behind
Stratus (R), Stratocumulus (L), Cirrus & Cirrocumulus behind
Cirrostratus - looking south-southeast
Altocumulus - looking south
Altocumulus
Altocumulus with Sun visible
Altocumulus, (Top R) Cirrostratus (R)) and cirrocumulus (Center).
Altocumulus - unusual wave pattern Right
Closeup of unusual Altocumulus wave Pattern
Stratus - looking southwest
Nimbostratus about 30 minutes later - looking southwast
The difference between stratus and nimbostratus is the presence of rain. Since rain was not falling at our location the cloud is classified as stratus. Rain was likely falling in the distance - based on how the cloud looked. However it is classified as stratus until precipitation (rain or snow) is observed. Other than possibly drizzle, true stratus do not produced precipitation. The presence of rain indicates a much thicker cloud and confirms the cloud is nimbostratus. Nimbostratus often form in the mid-levels and lowers as the rain saturates lower layers. Nimbostratus can easily be more than 10,000 feet thick.
Altocumulus, Looking southeast
Cirrostratus, altostratus, and cumulus west
Altocumulus, altostratus, looking north
Altostratus and cumulus, looking south-southwest
Altocumulus, altostratus, looking south
Altostratus (right)) with a few altocumulus (Left)
Altocumulus
Altostratus with a few altocumulus
Altostratus and altocumulus
Altostratus (top) and SCUD (bottom) - SCUD is StratoCumulus Under Deck
Cirrus that look like fibers or hair
Cirrostratus (top half)) cirrus like fibers (lower left)
Cirrus in fibers and strands, Cirrocumulus (top center)
Cirrostratus (upper right) and cirrus fibers in bands, streaks, and streamers
Cirrostratus (top) and cirrus streamers below
Primarily Cirrostratus but with patches of opaque cirrus left
These photos of cirrus clouds were taken within a 30 minute time period this afternoon - all from our backyard. Clouds of ice and the winds aloft create unusual patterns ranging from filaments to streaks to streamers and smooth locks of hair. Step outside and look up to see a free show put on by Mother Nature.
This post is in progress.
Photo by Craig Johnson, 3-29-2020
This is what the sky looked like moments before sunset this evening. If the old saying, “Red sky at night, sailors delight. Red sky in morning, sailors take warning” is correct then tomorrow should be a pleasant day.
This post began on March 27th and is being added to here in order to keep all related posts with the original.
March 29, 2020, 12:15 p.m. CDT
Gravity waves are common in the atmosphere. The waves form when moving air disturbs stable layers in our atmosphere. Once disturbed these layers will oscillate up and down. The up and down motions continues until the energy dissipates. Think of waves on a lake or ocean. They can move long distances. The same happens in the atmosphere.
For example thunderstorms push air aside as rising air expands up and outward. This disturbs any stable layers that are in the way and causes waves to move away from the storms. We all have made waves while swimming. Boats make waves while moving through the water. The waves are similar to gravity waves in the atmosphere. Speed boats bounce over waves. Airplanes encounter turbulence caused by waves. If clouds are in the way, the waves become visible. Waves that come from different directions create complex patterns in the clouds.
Below are two photos showing waves that formed when thunderstorms moved through central Iowa on Saturday, March 28th. The waves created by the storms and waves caused by winds aloft created the formations you see in the photos.
clouds associated with gravity waves, Photo by Craig Johnson
Close-up of clouds created by gravity waves, Photo by Craig Johnson
March 29, 11:00 a.m. - Sequence of Surface Maps
A sequence of 5 maps beginning yesterday (Saturday, March 28th at 7:00 a.m. CDT) was added to this post today. The sequence shows the progression of a surface low that developed over the Southern Plains and moved north to northern Lake Michigan by 11:00 a.m. CDT this morning (Sunday, March 29th). by using the station model plots on the maps watch how the weather changed for any location plotted on the map. Pick out a station and notice the following as you move from map to map:
How did the cloud cover change?
How did the wind direction and speed change?
How did the temperature and dew point change?
How did the cloud ceilings change?
How did the weather change? Was there fog, rain, or thunder, at any stations?
How did the pressure change?
What was the path of the low center?
What is the visibility?
Notice that winds are strongest where the isobars are closest together.
This map includes station model plots, isobars (lines showing of constant pressure), and the low center. The plotting was limited to simplify the maps.
Station model plots pack a lot of data into a small space. There were reports of at least 5 tornadoes touching down from southwest to northeast Iowa during the afternoon and early evening. The tornadoes formed near the low center where a boundary between warmer and cooler air created changes in wind direction with height. Temperatures across the boundary ranged from 40s on the north side to 60s on the south. Wind shear and upward motion was sufficient to spin up tornadoes. The boundary is visible extending east from the low center noting the difference in temperature, dew point, and wind change across the boundary. It’s the difference in readings that matters.
Severe weather reports are available here.
Surface Map, 11:00 a.m., Sunday, March 29, 2020; Map plotted by Digital Atmosphere, www.weathergraphics.com
Surface Map, 7:00 p.m., Saturday, March 28, 2020; Map Plotted by Digital Atmosphere, WWW.weathergraphics.com
Surface Map, 4:00 p.m., Saturday, March 28, 2020; Map Plotted by Digital Atmosphere, WWW.Weathergraphics.com
Surface Map, 1:00 p.m. CDT, Saturday, March 28, 2020; Map Plotted by Digital Atmosphere, www.weathergraphics.com
Surface Map, 10:00 a.m., Saturday, March 28, 2020; Map Plotted by Digital Atmosphere, WWW.Weathergraphics.com
March 28, 2020, 11:00 a.m. CDT - Low Pressure Moves North
Be sure to scroll down to see the earlier posts. This post is an exercise in reading the station model plots. Learn more about stations model pots on our home page. Hints are included below.
The low pressure center has moved into central Kansas as of 7:00 a.m. CDT this morning. Using the station model plot format you can see the following:
A warm front from Kansas to Ohio is dividing cool air to the north from warmer air to the south. Temperatures south of the front are in the 60s and 70s. To the north readings are in the 40s. Reminder: The temperature is the number plotted to the upper left of the station location. For example St. Louis, Missouri reports 69 degrees. Chicago is 46.
Cold front with cooler temperatures and drier air extends from Kansas south into Oklahoma. Ahead of the front temperatures are in the 60s and 70s. Behind the front temperatures are in the 50s, 40s, and 30s. There 20s, teens, and single digit readings in Colorado. Dew points ahead of the front are in the 60s while behind the front dew points are in the 50s, 40s, 30s, and 20s. The dew point is plotted below the temperature.
Looking at the weather symbols, fog is reported in Kansas, Nebrasksa, and Iowa. Rain is reported in Michigan, Illinois, Wisconsin, Iowa, South Dakota, and Nebraska. Look at the station location symbols (circles and squares) for cloud cover. Every station located north of the warm front reports overcast skies; their station location symbols are 100% filled in black. To find examples of stations reporting clear skies look at Wyoming and Colorado.
Light snow is reported in western Nebraska and northeastern Colorado.
Notice how the wind is circulating counterclockwise around the low center in Kansas. Colder air is already flowing in behind the storm from Wyoming and Colorado into western Kansas, Nebraska, and the Texas Panhandle. See the streamline map below. Air is flowing northward into Missouri and the Ohio Valley. Another cold front is dropping south into South Dakota, Minnesota, and northern Wisconsin. Note the temperatures in the 30s behind the front.
The low is expected to move north into Nebraska today.
March 27, 2020 - Large Storm Headed for the Upper Midwest
A strong storm is expected to develop over the Southern Plains and move northeastward across Iowa on Saturday and Saturday night. Clouds are increasing across the state this morning (Friday, March 27th). We will follow this storm using a variety of information including maps, satellite images, and radar.
Our first map is a weather depiction chart. It uses part of the Station Model Plot format to display current weather. The chart displays sky cover, cloud ceiling, current weather, and visibility. It also includes the current position of fronts, low and high centers, and isobars.
Sky Cover is indicated by the amount of the station location circle or square that is filled with black.
Cloud ceiling is indicated with the letter “C” followed by 1, 2, or 3 digits. Add two digits to the number and you will know the cloud height in thousands of feet.
Current weather symbols are located just left of the station location circle or square.
Visibility is indicated to the left of the current weather symbol. It may be a whole number or a fraction.
The map below shows a low pressure system developing over northeastern New Mexico to the Texas Panhandle. Fog is widespread over Kansas, southeastern Nebraska, central South Dakota and western Iowa.
We will watch this storm develop and move northeastward.
Clouds are increasing from the southwest at Cedar Falls, Iowa.
Looking South from Cedar FAlls, IA, 11:45 a.m. CDT, 3-27-2020
Looking SSW from Cedar Falls, IA, 11:45 a.m. CDT, 3-27-2020
Pressure trace from Cedar Falls, Iowa. The pressure began falling at 11:00 p.m. on March 26th and has been unsteady since 2:20 a.m. March 27th. Watch the live weather station trace that can be accesses on our home page.
Stratocumulus, Photo copyright by Craig Johnson 3-24-2020
This cloud above was one of three clouds shaped like long parallel tubes lined up in northwest to southeast oriented rows. In between the rows there were nearly cloud-free rows of blue sky. The cloud rows were caused by waves rippling through the air.
The pattern of waves is similar to waves that form on lakes and the ocean. The clouds form where the waves crest (upward motion) and disappear where air sinks (downward motion). The entire system was moving to the northeast.
Because the clouds have both cumulus (lumpy) and stratus (flat) characteristics it is called stratocumulus.
The photo below was taken looking to the northwest underneath one of the cloud rows. Sometimes the cloud rows may be much more distinct and have sharper edges.
Stratocumulus; Photo by Craig Johnson, Copyright 3-24-2020
Read the signs and you will learn about your weather.
For the weatherwise, storms send out signs. Today was one of those days. Cirrostratus (Cs) is often a storm’s calling card. This is especially true if cirrostratus is widespread and increasing across the sky. In the photo below Cs is covering more of the sky than it appears. Even the blue sky in this photo is covered by cirrostratus. Cs is usually thin, sometimes almost invisible. Except for the “thicker” Cs on the left and bottom of this photo, the Cs might be entirely missed, especially at night. Look closely when you look at the sky. You may see very thin filaments of Cs.
The thing is, in this photo the Cs is extensive and it is thickening to the west (left) and north. The sky should be reported as overcast with thin Cs. Patchy Cs usually does not herald a storm. But if Cs is increasing in thickness and steadily overspreading the sky it is worth watching. If a storm is coming the Cs will likely thicken and overspread the sky before lower clouds appear.
Cirrostratus 3-17-2020, Photo by Craig Johnson
The Cs in the next photo is more prominent. It is spreading over the sky from right to left. The increasing coverage and thickness indicates there may be a storm approaching.
Ciirrostratus increasing from right to left. Photo by Craig Johnson 3-17-2020.
About 6 hours after the Cs first appeared, the clouds thickened and lowered. The photo below shows a middle cloud layer that appeared underneath the Cs. This cloud deck is altocumulus (Ac). The lumpy nature of the clouds indicates a layer of instability overhead caused by warmer moist layer aloft being lifted. It is also a sign of an approaching storm.
Altocumulus approaching from the west. Photo by Craig Johnson 3-17-2020.
Next in the progression is the altostratus below. The cloud streaks indicate precipitation falling aloft. Notice the streaks below the cloud layer - a classic sign of precipitation. Because the air below the cloud base is very dry (surface dew points were in the upper 20s) it will take 6 to 8 hours for the precipitation to saturate the air and allow rain to reach the ground. By then surface temperatures will be above freezing so freezing rain is not expected.
Altostratus, Precipitation is falling aloft but not reading the ground, Photo by Craig Johnson, 3-17-2020.
I promised to occasionally write about the value of an automatic weather station. This is one of those occasions.
The first two graphs below show the wind speed and wind direction, in that order, from our weather station in Cedar Falls. The dates are March 6th and 7th. The 2 minute average wind speeds on both days were mostly less than 10 mph with a few periods exceeding 10 mph (blue line). But there were higher gusts (stars). The gusts exceeded 20 mph
Note a couple of things. First the winds were gusty during the evening of the 5th and early morning of the 6th (stars) before dying down during the day on the 6th. After the Sun came up on the 7th wind speeds increased again and became gusty (stars). Winds were from the WNW on the 6th but gradually decreased and became southeasterly during the day of the 6th. On the 7th winds increased from the south, becoming gusty after sunrise. This is a common pattern for wind speeds. Stronger winds aloft are not always felt at the surface at night because nighttime cooling separates the near surface air from the strong winds aloft. If winds (as in this case) begin to suddenly increase after sunrise it is likely that solar heating is mixing the air allowing stronger winds aloft to drop to the surface.
Let’s look at the temperature (red), dew point (green), and relative humidity (blue) lines on the graph below and the pressure change on the bottom chart. Lets just look at March 7th beginning at 8:00 a.m. Notice how the temperature (red) started rising quickly after sunrise. The sharp rise was due to solar heating but enhanced by the mixing down of air aloft. As the air sank toward the ground it warmed at 5.5 degrees F for every 1,000 feet it descended. Temperatures warmed to near 60 in the afternoon.
At the same time the relative humidity decreased. As air warms its capacity for water vapor increases. Since more water could be in the air at 60 degrees than at 40 degrees, the relative humidity decreased from 60% in the morning to less than 30% in the afternoon.
Finally, the dew point increased slight during the day. The dew point is one way to measure the amount of water vapor in the air. It increase slightly because the southerly winds were bringing slightly higher dew points into the area.
While all of that was going on the air pressure was decreasing as chilly high pressure was moving away from Iowa and lower pressure to the west was inching eastward. The pressure change chart shows this clearly.
All of the factors measured and shown on these charts are related to each other and to changes in the atmosphere over the United States. Forecasters use these changes, along with other data, to create daily weather forecasts. Data from automatic weather stations is one tool that is used to make those forecasts.
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Cedar Falls, IA 50613, Phone: 319-215-2634, Email: craig@weatherbriefing.com
