Lake effect snow bands seen in water vapor imagery

February 12th, 2016 |

GOES-13 Visible (0.63 µm) images [click to play animation]

GOES-13 Visible (0.63 µm) images [click to play animation]

GOES-13 Visible (0.63 µm, 1-km resolution) images (above) showed the development of lake effect snow bands across the Great Lakes region following the passage of a strong arctic cold front on 12 February 2016. As a result of the atmospheric instability (due to the advection of very cold air aloft), several distinct convective elements could be seen developing within a few of the lake effect bands —  especially over Lower Michigan where moderate to heavy snow was reported at some locations during brief snow squalls.

Many of these lake effect snow bands could also be seen on the corresponding GOES-13 Water Vapor (6.5 µm, 4-km resolution) images (below).

GOES-13 Water Vapor (6.5 µm) images [click to play animation]

GOES-13 Water Vapor (6.5 µm) images [click to play animation]

A comparison of 1-km resolution Aqua MODIS Visible (0.65 µm) and Water Vapor (6.7 µm) images at 1854 UTC (below) revealed much better detail of the lake effect cloud band features in the water vapor image.

Aqua MODIS Visible (0.65 m) and Water Vapor (6.7 µm) images [click to enlarge]

Aqua MODIS Visible (0.65 m) and Water Vapor (6.7 µm) images [click to enlarge]

Conventional wisdom states that water vapor imagery generally portrays features located within the middle to upper troposphere, due to the altitude of the peak of the water vapor channel weighting function calculated using a relatively warm and moist “US Standard Atmosphere” (plot). However, in air masses that are very cold and/or very dry, the altitude of the water vapor channel weighting function peak is shifted to much lower altitudes, allowing a look at features that are located in (or at least rooted within) the lower to middle troposphere. Such was the case on this day, with the flow of very cold and dry arctic air behind the cold front. A comparison of the GOES-13 imager* water vapor channel weighting function plots at 12 UTC for Green Bay WI (behind the cold front) and Detroit MI (ahead of the cold front) showed the dramatic drop in the peak altitude over Green Bay (below).

GOES-13 imager Water Vapor (6.5 µm) weighting function plots for Green Bay WI and Detroit MI at 12 UTC on 12 February [click to enlarge]

GOES-13 imager Water Vapor (6.5 µm) weighting function plots for Green Bay WI and Detroit MI at 12 UTC on 12 February [click to enlarge]

Similarly, a comparison of GOES-13 imager water vapor channel weighting function plots for Detroit MI at 12 UTC (before the passage of the cold front) and 00 UTC on 13 February (after the passage of the cold front) showed a sharp drop in the altitude of the weighting function peak. This allowed radiation emitted from the tops of the more pronounced and vertically-developed lake effect cloud bands to reach the water vapor detectors on the satellite.

GOES-13 imager Water Vapor (6.5 µm) weighting function plots calculated from Detroit MI rawindsonde data at 12 UTC on 12 February and 00 UTC on 13 February [click to enlarge]

GOES-13 imager Water Vapor (6.5 µm) weighting function plots calculated from Detroit MI rawindsonde data at 12 UTC on 12 February and 00 UTC on 13 February [click to enlarge]

*Note: there are also 3 unique water vapor channels on the GOES sounder instrument (6.5 µm, 7.0 µm, and 7.4 µm) — however, due to an ongoing problem with the GOES-13 sounder, said water vapor imagery was not available (as it was for this example). However, the ABI instrument on GOES-R will provide imagery from 3 separate water vapor channels that are similar to those found on the current-generation sounder (but at much higher spatial and temporal resolution).

Hat tip to @turnageweather for the suggestion to blog about this case!

“Lake effect” snow in northern Alabama

February 10th, 2016 |

Aqua MODIS Sea Surface Temperature product [click to enlarge]

Aqua MODIS Sea Surface Temperature product [click to enlarge]

Wheeler Lake is a reservoir along the Tennessee River in northern Alabama. The Aqua MODIS Sea Surface Temperature product (above) showed that water temperatures along the axis of the lake were as warm as the lower 50s F (cyan color enhancement) on 07 February 2016.

Following the passage of a strong cold front on 08 February, the northwesterly flow of air with surface temperatures in the 30s F on 09 February allowed for a narrow “lake effect” (or in this case, river effect) snow band to form over Wheeler Lake, which created accumulating snowfall to the southeast (downwind) of the lake. This lake effect snow band could be seen in a RealEarth composite of Suomi NPP VIIRS / Aqua MODIS true-color Red/Green/Blue (RGB) images and radar reflectivity (below). The lake effect plume began to shift northward during the afternoon hours, as surface winds briefly backed to a more westerly direction.

Suomi NPP VIIRS and Aqua MODIS true-color images, combined with radar refectivity [click to enlarge]

Suomi NPP VIIRS and Aqua MODIS true-color images, combined with radar refectivity [click to enlarge]

On 10 February, the northwesterly flow of cold air was less pronounced, but was still enough to allow for a narrow lake effect plume to be seen early in the day on 1-minute interval GOES-14 Super Rapid Scan Operations for GOES-R (SRSO-R) images (below; also available as a large 89 Mbyte animated GIF). As the clouds cleared during the afternoon hours, small patches of white snow cover could be seen just southeast of Wheeler Lake.

GOES-14 Visible (0.63 µm) images [click to play MP4 animation]

GOES-14 Visible (0.63 µm) images [click to play MP4 animation]

In a comparison of Terra MODIS true-color and false-color RGB images (below), the presence of snow cover (cyan in the false-color image) could be seen between the lines of cumulus clouds.

Terra MODIS true-color and false-color images [click to enlarge]

Terra MODIS true-color and false-color images [click to enlarge]

Data from NOHRSC (below) showed that as much as 3.0 inches of total snowfall was measured downwind of Wheeler Lake (in the higher elevation of the Union Hill area) during the 09-11 February period, and the snow depth on the morning of 10 February was 2.5 inches at that location (enough to be seen on the GOES-14 visible images above).

24-hour snowfall amounts ending at 12 UTC on 09, 10, and 11 February [click to enlarge]

24-hour snowfall amounts ending at 12 UTC on 09, 10, and 11 February [click to enlarge]

Snow depth during the 24-hour period ending at 12 UTC on 09, 10, and 11 February [click to enlarge]

Snow depth during the 24-hour period ending at 12 UTC on 09, 10, and 11 February [click to enlarge]

Additional information and images of this event can be found here.

GOES-14 SRSO-R: aircraft “hole punch clouds” in North and South Carolina

February 9th, 2016 |

GOES-14 Visible (0.63 µm) images [click to play MP4 animation]

GOES-14 Visible (0.63 µm) images [click to play MP4 animation]

1-minute interval GOES-14 Super Rapid Scan Operations for GOES-R (SRSO-R) Visible (0.63 µm) images (above; also available as a large 71 Mbyte animated GIF) revealed the formation of clusters of aircraft “hole punch clouds” over central North and South Carolina on the morning of 09 February 2016. These types of cloud features form when aircraft fly through a layer of clouds composed of supercooled water droplets; cooling from wake turbulence (reference) and/or the particles from the jet engine exhaust which may act as ice condensation nuclei cause the small water droplets to turn into larger ice crystals (which then often fall from the cloud layer, creating “fall streak holes“). Similar features have been discussed in previous blog posts.

A comparison of GOES-14 Visible (0.63 µm, 1-km resolution) and Shortwave Infrared (3.9 µm, 4-km resolution) images (below; also available as a large 71 Mbyte animated GIF) offered evidence that the cloud material within each “hole punch” was composed of ice crystals, which exhibited colder (lighter gray) IR brightness temperatures than the surrounding supercooled water droplet clouds. It is likely that many of the hole punch features were caused by aircraft ascending from or descending to the Charlotte Douglas International Airport in North Carolina (KCLT).

GOES-14 Visible 0.63 µm (left) and Shortwave Infrared 3.9 µm (right) images [click to play MP4 animation]

GOES-14 Visible 0.63 µm (left) and Shortwave Infrared 3.9 µm (right) images [click to play MP4 animation]

In a comparison 1-km resolution POES AVHRR Visible (0.86 µm) and Infrared (12.0 µm) images (below), the cloud-top IR brightness temperatures in the vicinity of the hole punch features were only as cold as -20 to -24º C (cyan to blue color enhancement), which again is supportive of the cloud layer being composed of supercooled water droplets.

POES AVHRR Visible 0.86 µm) and Infrared (12.0 µm) images [click to enlarge]

POES AVHRR Visible 0.86 µm) and Infrared (12.0 µm) images [click to enlarge]

GOES-14 SRSO-R: rapidly-intensifying storm off the US East Coast

February 7th, 2016 |

GOES-14 Visible (0.63 µm) and Water Vapor (6.5 µm) images, with surface weather symbols plotted [click to play animation]

GOES-14 Visible (0.63 µm) and Water Vapor (6.5 µm) images, with surface weather symbols plotted [click to play animation]

One-minute interval Super Rapid Scan Operations for GOES-R (SRSO-R) Visible (0.63 µm) and Water Vapor (6.5 µm) images (above) showed the development and rapid intensification (surface analyses) of a mid-latitude cyclone just off the East Coast of the US on 07 February 2016. The storm produced moderate to heavy rainfall across eastern North Carolina, along with some light to moderate snow and sleet at a few locations.

A closer view of the GOES-14 Visible (0.63 µm) images (below; also available as a large 85 Mbyte animated GIF) revealed the rapid motion of low-altitude clouds when gaps in the high-altitude clouds were present. Very strong winds were caused by the strong pressure gradient, with gusts as high as 72 mph, and a large Royal Caribbean cruise ship experienced some damage due to the winds (media report 1 | media report 2). The corresponding GOES-14 Water Vapor (6.5 µm) images, which also extend further in time after dark, are available here.

GOES-14 Visible (0.63 µm) images, with surface weather symbols plotted [click to play MP4 animation]

GOES-14 Visible (0.63 µm) images, with surface weather symbols plotted [click to play MP4 animation]

A comparison of 1-km resolution POES AVHRR Visible (0.86 µm) and Infrared (12.0 µm) images at 2202 UTC (below) displayed greater detail of the classic “cusp” signature of high clouds, indicative of an intensifying surface cyclone (VISIT lesson). At the time, wind gusts to 60 knots were seen at one the buoys off the coast of North Carolina.

POES AVHRR Visible (0.86 µm) and Infrared (12.0 µm) images [click to enlarge]

POES AVHRR Visible (0.86 µm) and Infrared (12.0 µm) images [click to enlarge]

At 0137 UTC, a closed-off low level circulation center could be seen on a POES AVHRR Infrared (12.0 µm) image (below).

POES AVHRR Infrared (12.0 µm) image [cluck to enlarge]

POES AVHRR Infrared (12.0 µm) image [cluck to enlarge]

Additional information on this storm can be found on the Satellite Liaison Blog.