Using GOES-16 to view clouds over snow

May 1st, 2017 |

GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing.

A late-season snow storm dropped a band of heavy snow over Colorado, western Kansas and western Nebraska on 29-30 April 2017. In the visible image above from sunrise on 1 May 2017, it is difficult to guess where the cloud features sit on top of the snow (Click here for a visible image with a map), even with the knowledge that they are casting shadows in this early morning imagery. GOES-16 includes a 1.61 µm channel, however; radiation at that wavelength is absorbed strongly by ice — either in the form of cirrus clouds, or snow, so that reflectance is small over ice features. The toggle below between the 1.61 µm “Snow/Ice” Channel and the 0.64 µm “Red Visible” channel shows ice and snow as dark. Clouds that are made up of water droplets are highly reflective in the 1.61 µm and in the 0.64 µm channels; such water clouds (there are only a few of them!) show up as very bright against the dark background of snow in the 1.61 µm channel.

Note in the toggle above that shadows are much darker in the 1.61 µm channel. Why?

Atmospheric scattering is stronger at shorter wavelengths in the atmosphere; there is more scattering of 0.64 µm radiation than of 1.61 µm radiation. In the shadow regions, more 0.64 µm radiation than 1.61 µm is being scattered back towards the satellite for detection. Shadows in the 0.47 µm “Blue Visible” band should be even less distinct. Non-annotated versions of imagery are available here for 0.64 µm and here for 1.61 µm.

During the subsequent late morning and early afternoon hours, the edges of the long swath of snow cover were seen to melt quickly — due to heating from the high May sun angle — on GOES-16 Visible (0.64 µm) and Snow/Ice (1.61 µm) images, below. The Snow/Ice images helped to highlight bright cumulus clouds (composed of supercooled water droplets) drifting southeastward across the snow cover.

GOES-16 Visible (0.64 µm, left) and Snow/Ice (1.61 µm, right) images [click to animate]

GOES-16 Visible (0.64 µm, left) and Snow/Ice (1.61 µm, right) images [click to animate]

Animations of GOES-16 Visible vs Snow/Ice images from the previous day (when the southwestern portion of the swath of fresh snow cover first became evidentt as clouds from the parent storm departed) are available here: Animated GIF | MP4.

Winter storm from the Upper Midwest to the Northeast US

March 15th, 2017 |

GOES-16 Water Vapor (6.9 µm) images, with hourly plots of surface weather [click to play MP4 animation]

GOES-16 Water Vapor (6.9 µm) images, with hourly plots of surface weather [click to play MP4 animation]

** The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing. **

A winter storm produced heavy snow across parts of the Upper Midwest on 13 March 2017, and then merged with subtropical jet stream energy to help develop an intense and rapidly-deepening storm which affected much of the Northeast US during 14 March15 March (WPC storm summary). GOES-16 ABI Water Vapor (6.9 µm) images covering the 13-15 March period (above) showed the development and motion of this complex storm. .

A closer view of the Northeast US on 14 March (below) displayed some of the complex banding structures associated with the deepening storm, and also showed the sharp gradient of precipitation type along the coastal areas. Notable weather impacts included a storm total snowfall of 48.4 inches at Hartwick, New York, a new all-time 24-hour snowfall accumulation of 31.1 inches at Binghamton, New York, 0.4 inch of freezing rain accumulation at Chesilhurst, New Jersey and a wind gust of 77 mph at Plum Island, Massachusetts.

GOES-16 Water Vapor (6.9 um) images, with hourly surface weather symbols [click to play animation]

GOES-16 Water Vapor (6.9 um) images, with hourly surface weather symbols [click to play animation]

Some interesting features were also seen in the wake of the large Northeast US component of the storm. For example, a GOES-16 Mesoscale Sector provided 1-minute interval  0.5-km resolution Visible (0.64 µm) imagery of lake effect snow bands streaming southward off Lake Michigan on 14 March, which produced heavy snow in parts of southeastern Wisconsin, northeastern Illinois and northwestern Indiana (below).

GOES-16 Visible (0.64 µm) images, with hourly surface plots [click to play MP4 animation]

GOES-16 Visible (0.64 µm) images, with hourly surface plots [click to play MP4 animation]

GOES-16 6.2 µm, 6.9 µm and 7.3 µm Water Vapor images (below) revealed widespread mountain waves downwind of the southern Appalachians on 15 March.

GOES-16 Water Vapor images: 6.2 µm (top), 6.9 µm (middle) and 7.3 µm (bottom) [click to play animation]

GOES-16 Water Vapor images: 6.2 µm (top), 6.9 µm (middle) and 7.3 µm (bottom) [click to play animation]

These mountain waves were responsible for a few pilot reports of moderate turbulence, two of which are highlighted below.

GOES-13 Water Vapor (6.5 µm) image, with pilot report of turbulence [click to enlarge

GOES-13 Water Vapor (6.5 µm) image, with pilot report of turbulence [click to enlarge]

GOES-13 Water Vapor (6.5 µm) image, with pilot report of turbulence [click to enlarge]

GOES-13 Water Vapor (6.5 µm) image, with pilot report of turbulence [click to enlarge]

GOES-16 Multispectral views of the eastern United States

March 14th, 2017 |

GOES-16 Snow/Ice (1.61 µm) animation, from 1100 UTC on 12 March through 1800 UTC on 14 March [click to play mp4 animation]

The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing.

The ABI on GOES-16 includes a Snow/Ice Channel at 1.61 µm and a Cirrus Channel at 1.38 µm. These bands offer different perspectives on the evolution of the atmosphere before and during the strong 13-14 March 2017 winter storm on the East Coast of the United States. The Snow/Ice channel, above, is dark in regions where ice clouds or snow on the ground are present because ice is a strong absorber of radiation with a wavelength of 1.61 µm. Water clouds, in contrast, readily reflect such radiation and appear brighter white. Consider the mp4 animation above (available here as a 150-megabyte animated gif). At the start of the animation, on 12 March, snow is indicated over Tennessee, a dark stripe that erodes on that day under the strong March sun. Cirrus retreating southward over the southeastern United States (cloud signals that are grey in the 1.61 µm imagery) reveal much brighter low-level stratus clouds (made of water droplets). Cirrus contrails are apparent above those low clouds. The Mesovortex over the Great Lakes is bright white — water clouds — and is gradually obscured by high-level cirrus clouds from the west and northwest. Terrain-induced wave clouds are also present over Pennsylvania. Their bright color suggests they are composed of water droplets.

On 13 March, low clouds are moving northward over the Piedmont of North Carolina and Virginia as Cirrus clouds spread northeastward from the Deep South. By 14 March, a well-developed wave cyclone is apparent with a large cirrus canopy outlining a warm conveyor belt.

What does the Cirrus Channel, below show? (Click here for a large animated gif.) Strong absorption by water vapor molecules occurs at 1.38 µm. Note, for example, that on 12 March the mesovortex is not apparent in the Cirrus Channel — but the wave clouds over Pennsylvania are. The conclusion is that the atmosphere over the northeast is much dryer than that over the western Great Lakes. On 13-14 March, lake-effect clouds are apparent downwind of Lake Superior in the Upper Peninsula of Michigan and over Wisconsin. The airmass has dried over the Upper Midwest in two days, allowing the Cirrus Channel to view features closer to the surface. In general, the cirrus channel provides outstanding delineation of cloud-top structures over the developing and mature extratropical cyclone.

GOES-16 Cirrus Channel (1.378 µm) animation, from 1100 UTC on 12 March through 1800 UTC on 14 March [click to play mp4 animation]

The Cirrus Channel and the Snow/Ice Channel rely on reflected Solar energy to provide a signal. As such they are useful primarily during the day.

Added: Animations showing the evolution of the three GOES-16 Water Vapor bands during part of the East Coast storm’s lifecycle are available here. A water vapor animation from a CONUS perspective is available here. A better-quality animation centered over the northeast US is available here. Here is an animated gif/mp4 with 6.9 µm brightness temperatures and surface observations. A blog post on this storm is here.

Mesovortex over Lake Michigan

March 12th, 2017 |

http://cimss.ssec.wisc.edu/goes/blog/wp-content/uploads/2017/03/170312_0740utc_suomi_npp_viirs_DayNightBand_rtma_surface_winds_Lake_Michigan_mesovortex_anim.gif

Suomi NPP VIIRS Day/Night Band (0.7 µm) image, with RTMA surface winds [click to enlarge]

** The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing. **

A Suomi NPP VIIRS Day/Night Band (0.7 µm) image (above) revealed the formative stage of a mesoscale vortex over Lake Michigan at 0740 UTC or 2:40 AM Central time on 12 March 2017.

During the subsequent daylight hours, GOES-16 Visible (0.64 µm) images (below) showed the continued development and motion of the mesovortex.

GOES-16 Visible (0.64 µm) images, with hourly surface reports [click to play animation]

GOES-16 Visible (0.64 µm) images, with hourly surface reports [click to play animation]

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As was shown in a Tweet from NWS Marquette (above), beginning at 1741 UTC one of the GOES-16 Mesoscale Sectors was moved far enough northward to provide 1-minute imagery of the mesovortex (below; also available as an MP4 animation).

GOES-16 Visible (0.64 µm) images, with hourly surface reports [click to play animation]

GOES-16 Visible (0.64 µm) images, with hourly surface reports [click to play animation]

At South Haven, Michigan (KLWA), the surface visibility was reduced to 5 miles with light snow at 2014 UTC (below) as one of the more well-defined cloud elements associated with the mesovorex moved inland over that location.

Time series plot of South Haven, Michigan surface observations [click to enlarge]

Time series plot of South Haven, Michigan surface observations [click to enlarge]