Thursday, September 12, 2013

Crazy Monsoon Flow

The last few weeks have been pretty active. Lots of cloud development in the afternoon through evening. All of this exciting weather comes from our south and east. An upper level trough now moving up the west side of Utah has pulled a lot of the moisture from the south. With breaks in the clouds we get enough solar heating to cause some big thunderstorms. Southern Utah has had quite a bit of rain and flooding. Colorado was hit hard, as is shown later.

These are satellite images of the western states on September 12, in around 5:00 MT. These images come from the GOES-West satellite. Not all satellite images show the same things, so let me explain the difference between the two images.

This image is a Visible image. If you were an astronaut and looked down at earth, this is what you would see (except it would be in color). Notice the two areas I have circled. The blue region off the coast of California consists of widespread stratiform clouds. These are typical off the coast. The red area shows more patchy clouds. These are cumulus and cumulonimbus clouds, also known as thunderstorms. They are produced by convection, or rising motion, when the sun heats the ground.

This image is from approximately the same time, but has a little different features. This is an Infrared or IR image. Instead of looking at the visible light the instrument detects infrared radiation. Essentially it measures temperature. Dark parts of the map are warm and lighter areas are cold. Looking at a cloud free area (as indicated from the visible image) such as Southern Arizona we see a darker area, so we know the temperature is higher. No look at an area with clouds. Since the satellite can't see through the clouds, the white blotches are the cloud tops, or the temperature of the cloud top. The patches of clouds over the states are very cold. Take a look again at the blue circled off the coast of California. The clouds aren't as cold. That is because the clouds tops are lower than the tall cloud tops on the thunderstorms. Thus, this image can tell us a little more about the clouds. We can see where thunderstorms cells. But be careful! Cirris clouds are high level, cold clouds that appear white, but are not thunderstorms. Also notice the comma shape of the clouds. A low pressure is centered near the southwest boarder of Utah and winds are blowing counter-clockwise. 

This was taken from the University of Utah campus on September 11, 2013 about 5:30 PM

This is a pretty anvil topped cumulonimbus cloud. Picture taken from Provo looking north on September 12, 2013 at 7:00 PM.

The most extreme weather was dumped on our neighbors in Colorado. Some places reported up to 10 inches of rain in 24 hours! (Needless to say, there widespread flooding.) Below is the image is provided by the Advanced Hydrologic Prediction Service of the National Weather Service.

This is from MesoWest showing reported 24 hour precipitation totals for the same period.


Here are a few blog posts about this event:
The CoCoRaHS blog shows pictures of hail in Denver.
The Wasatch Weather Weenies post talks about how Utah was affected by the storm.
The Wasatch Weather Weenies also talk about the Colorado side of the storm.
Map Overlay

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