Following a Storm
/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.
