2018 Nor’Easter and NCC!

To kick of the new year, 2018, we start off with a Nor’Easter that has developed over the East Coast and has brought freezing rain, sleet, snow, and high winds to the coastal areas, ranging from northeast Florida, the Carolinas to the New England areas. This particular storm experienced rapid cyclogenesis: a significant decrease in pressure of the low-pressure system (i.e. nor’easter) within a short period of time, producing high amounts of precipitation and high winds for the states along the East Coast.

The latest Near-Constant Contrast (NCC) imagery (shown below) highlights the magnitude of this storm as of this morning, 4 January 2018 @ 0614Z (~0114 local time). The NCC imagery product, is a derived product of the Day/Night Band (DNB) which utilizes a sun/moon reflectance model that illuminates atmospheric features, senses reflected and emitted light sources and monitors the distribution of clouds during the nighttime. At the time the satellite image was taken, the center of the storm appears to be located just east of the state of North Carolina, as it makes its way north to the New England states. What one can also see is the corresponding snow fields that were produced after the storm passed, seen in the red rectangle. The snow fields stretch from southern Georgia all the way to the Carolinas in this image. In complement to the imagery, in the top-right corner, is the moon percent visibility and moon elevation angle, implying the moon provided adequate moonlight and was above the horizon when the satellite image was taken.

NCC @ 0614Z, 4 January 2018

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4 January 2018 explosive cyclogenesis event

GOES-16 imagery captured the spectacular explosive cyclogenesis event on the eastern seaboard on 4 January.  First, we’ll look at the 3 GOES-16 water vapor channels along with the air mass RGB product:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/4jan18/4panel_wv&loop_speed_ms=60

During this loop we see an instant occlusion type of cyclogenesis.  We also see the development of a sting jet, annotated on the 0852 UTC image:

Next, we’ll look at 1-minute imagery of the visible band (0.64 um), Day Cloud Phase Distinction RGB product, IR (10.3 um) and True Color RGB (only available at 5 minute intervals):

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/4jan18/4panel_vis&loop_speed_ms=30

The loop is zoomed in over the surface low.  The Day Cloud Phase Distinction product adds additional value in terms of variable cloud heights, with colder clouds being glaciated which shows up from the 1.6 um band contribution and even colder clouds from the 10.3 um band contribution.

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High cloud obscuration during a lake-effect snow event

When analyzing satellite imagery during lake-effect snow events, one is interested in looking at the low-level clouds associated with the snowbands.  However, sometimes high clouds obscure the low-level clouds making analysis from a satellite imagery perspective more challenging.  An example of high cloud obscuration can be seen in this GOES-16 loop from 2 January 2018:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/2jan18&loop_speed_ms=60

Upper left panel: Day Cloud Phase Distinction RGB product (R: 10.35 um, G: 0.64 um, B: 1.61 um)

Upper right panel: Visible (0.64 um)

Lower left panel: IR (10.35 um) with default color table

Lower right panel: IR (10.35 um) with alternate color table for winter

In the first half of the loop, there exists considerable high cloud cover which shows up quite well in the IR imagery as the colder cloud tops, and in the visible imagery as cirrus clouds moving in a different direction than the low-clouds over the lakes.  In the later half of the loop, there is less high cloud obscuration over Lake Erie where the lake-effect snow band can be easily seen.  Over Lake Ontario, there is much more high cloud cover to obscure the band, however by late in the loop the high cloud coverage is less over the western and south central portions of Lake Ontario.  This can be most easily seen in the Day Cloud Phase Distinction RGB product since high clouds stand out as red (colder, thus more red gun (10.35 um) contribution).  The low clouds associated with the lake-effect snowbands show up well in the visible band, thus appear light color in combination with the 1.6 um band.  The RGB product gave indications of the presence of the lake-effect snowband, which can be confirmed with this radar reflectivity image which shows a significant lake-effect snowband:

At times during lake-effect snow events, the clouds of most interest can be obscured with high clouds, therefore it is important to know what other satellite products are available and may be of use in determining where lake-effect snowbands exist.  Also, be aware of alternative techniques for viewing the imagery, on the animation above, click on rock and turn up the loop animation speed.  Can you delineate the low-clouds associated with the lake-effect snowband more easily?

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Snow in the southeastern US!

Due to strong, cold, upper-level low that swept through the southeastern United States last weekend (8-9 December 2017), there were variable snow totals that accumulated from southeastern Louisiana, all the way to the Appalachian Mountains.  Snow totals varied from a trace of snow to 10 inches plus in some areas.  The local NWS-Atlanta, GA, has some updated snow totals from this uncommon December snowstorm.

Even more fascinating, the large swaths/fields of snow that impacted the southeastern United States can be seen via satellite. The Suomi-National Polar-orbiting Satellite (SNPP), in which, the Visible Infrared Imaging Radiometer Suite (VIIRS), an instrument on-board SNPP is utilized here. VIIRS has 22 spectral channels, and the following satellite imagery is produced from one of those spectral channels; the Imagery Band (I-1) (0.64um) visible channel. This channel is at a high spatial resolution (375-m) and can see the snow swaths extending from Louisiana, Mississippi, Alabama, Georgia to the Carolinas, during the daytime (i.e. afternoon) hours.

Three separate, daily, visible images (9-11 December 2017) are provided showing the areal extent of the snow, and how the snow diminishes, due to solar heating, throughout the following days. It is important to note, that for 9 December 2017, the snowstorm just passed through the area hours before the satellite image was taken.

9 December 2017 @ 1906Z

10 December 2017 @ 1843Z

11 December 2017 @ 1826Z

For more information on the December snowstorm, click the flowing NWS -Peachtree City, GA link.

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