November 11-15, 2021 Atmospheric River event over the Pacific Northwest and British Columbia

By Sheldon Kusselson

Click on the image below:

 

 

 

 

Posted in Heavy Rain and Flooding Issues, POES | Leave a comment

ALPW analysis for the New York City and vicinity flood event of September 1, 2021

By Sheldon Kusselson

Posted in Heavy Rain and Flooding Issues | Leave a comment

ALPW analysis for the 21 August 2021 flood event in central Tennessee

By Sheldon Kusselson and Dan Bikos

The following shows the Advected Layer Precipitable Water (ALPW) product just prior to the significant flood event in central Tennessee on 21 August 2021:

ALPW animation

Posted in Heavy Rain and Flooding Issues | Leave a comment

How far north can we see sun glint in GOES satellite imagery?

By Bernie Connell and Erin Sanders

Sun glint is an optical phenomenon that can be seen in visible and near-IR satellite imagery over water features such as ocean, lakes, and rivers.  Its presence depends on the geometry between Sun, Earth, and satellite viewing angle.  When sunlight is reflected off water features towards the satellite sensor at nearly equal angles, this type of reflection is called specular reflection.

How far north can we see sun glint? Sun glint is a common occurrence in the tropics and is typically seen in daytime satellite imagery between 30ºN and 30ºS.  The following examples show sun glint at latitudes higher than 30ºN during northern hemisphere summer using visible imagery in the red part of the spectrum (0.64 μm).  The first animation shows imagery from the GOES-17 satellite located at 137.2°W in the early hours between sunset and sunrise on July 21, 2021.  From this perspective, a seasoned eye may discern the pattern of sun glint areas appearing to travel north and eastward with the changing angle of the sun.

GOES 17 – Arctic sunset and sunrise on July 21, 2021 from 8:30-10:30 UTC.

Let’s zoom in on a few of these regions and take a closer look.  From this perspective the regions of sun glint are easier to spot.  As the Sun, water surface, and satellite geometry changes, areas of brightness appear and then disappear in less than an hour.

GOES 17 – Arctic sunset on July 21, 2021 from 8:10-9:20 UTC.

These areas of sun glint indicate relatively calm waters with a smooth surface to reflect sunlight, much like a mirror.  The increase in reflected solar energy that reaches the satellite sensor can saturate the image as seen by the bright white swaths.  However, not all water surfaces reflect sunlight equally.  Winds cause rougher water and waves that will scatter sunlight in multiple directions and appear darker, as less sunlight will be directed to the satellite sensor.  Cloud cover will also obscure any water surface below.  Both of these can lead to patchy areas of sun glint in satellite imagery.  Can you differentiate between calm water, rough water, and cloud cover in the next two examples?

GOES 17 – Arctic sunrise on July 21, 2021 from 9:00-9:50 UTC.

GOES 17 – Arctic sunrise on July 21, 2021 from 9:20-10:20 UTC.

The following set of animations show sun glint detected by GOES-16 located at 75.2°W on July 26, 2021.  We will again start with the full view from sunset to sunrise, and then focus on two examples.

GOES 16 – Arctic sunset and sunrise on July 26, 2021 from 3:30-6:30 UTC.

Zooming in over the Pacific Ocean off the western coast of the United States shows the contrast between the extensive bright glint area and darker surrounding areas of cloud.  The sun glint can be seen well above 40ºN.

GOES 16 – Arctic sunset on July 26, 2021 from 3:30-4:20 UTC.

Sun glint highlights areas of calm water and can reveal details about the water surface and its reflective properties.  In this next example, it also shows the ocean-land boundary with Greenland to the north.  Sun glint appears on the water surface but not land, although land can certainly influence wind patterns over the water surface and affect how the light is reflected.

GOES 16 – Arctic sunrise on July 26, 2021 from 4:40-5:30 UTC.

So how far north can we see sun glint in GOES satellite imagery?  It is clearly seen above 75ºN on this day!  The latitudinal extent of where sun glint can be seen has a seasonal dependence.  In the northern hemisphere it can be spotted between the vernal equinox (~20 March) and the autumnal equinox (~22 September).  The summer solstice (~20 June) is when we would expect sun glint to be seen the farthest north of the equator based on the positioning of the Sun, Earth, and satellite.

Notice the unexpected.

Posted in GOES, Satellites | Leave a comment

Flooding in Utah – 26 July 2021

By Sheldon Kusselson and Dan Bikos

The North American monsoon has been in full swing during the summer of 2021, bringing much needed moisture to the Southwest.

 

At times though the abundant moisture has resulted in heavy rain and flash flood events.

See the 4 panel Advected Layer Precipitable Water (ALPW) animation

Upper left: ALPW in the Surface to 850 mb layer

Upper right: ALPW in the 850 to 700 mb layer

Lower-left: ALPW in the 700-500 mb layer

Lower-right: ALPW in the 500-300 mb layer

When viewing this product in the west, keep in mind that data is missing over higher elevations. This effect is easily observed in the Surface to 850 mb layer, and even shows up in localized regions of the 850 to 700 mb layer.  The 700-500 mb layer is very useful for the monsoon season with the typically high moisture values observed in mid-levels over regions of higher elevation.  The relative maximum in moisture across southern Utah can be easily observed in this layer.  The 500-300 mb layer can depicts regions of higher moisture at that level highlighting regions where the moisture is particularly deep which can enhance precipitation efficiency.  Compare the animation with the slide above that denotes with arrows the direction moisture plumes are moving in the different layers.  Source regions of moisture can be readily identified along with when these moisture layers become vertically aligned leading to a deep moist profile typically associated with excessive precipitation events.

See the 4 panel 700-500 mb ALPW, GOES-16 6.2 um water vapor band and 2 TPW products

Upper left: ALPW in the 850 to 700 mb layer

Upper right: GOES-16 6.2 um (upper-level) water vapor band

Lower-left: Blended TPW product (operational), (missing before 1400 UTC)

Lower-right: Merged (GOES + POES) TPW product (experimental)

Compare the animation of the water vapor imagery with the annotated water vapor image on the slide above that denotes short waves.

Compare the TPW products with the ALPW animation above, how do they complement and supplement each other?

See the 4 panel 700-500 mb ALPW, MRMS composite reflectivity and GOES-16 IR (10.3 um) and upper-level water vapor (6.2 um) imagery

Upper left: ALPW in the 850 to 700 mb layer

Upper right: MRMS composite reflectivity

Lower-left: GOES-16 IR (10.3 um)

Lower-right: GOES-16 upper-level water vapor (6.2 um)

Again, the water vapor imagery depicts the short wave.

Note how the ALPW seems to increase at certain times.  If the increase is occurring over a large area, it is likely due to a new polar pass becoming available or a pass with a different sensor.

Detailed information on the flooding in southern Utah

 

 

Posted in Heavy Rain and Flooding Issues, Hydrology | Leave a comment