Isolated cirrus cloud feature over Louisiana

November 10th, 2017 |

GOES-16 Visible (0.64 µm) images, with surface station identifiers plotted in yellow [click to play MP4 animation]

GOES-16 Visible (0.64 µm) images, with surface station identifiers plotted in yellow [click to play MP4 animation]

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

An isolated cloud feature moving east-southeastward across Louisiana on 10 November 2017 caught the attention of several people on Twitter — GOES-16 “Red” Visible (0.64 µm) images (above) showed the motion of this cloud during the 1317-2052 UTC period.

In a 3-panel comparison of GOES-16 “Red” Visible (0.64 µm), Near-Infrared “Cirrus” (1.37 µm) and “Clean” Infrared Window (10.3 µm) images (below), the strong signature (bright white) on the 1.37 µm imagery indicated that this feature was a cirrus cloud. The uncharacteristically-warm Infrared brightness temperatures exhibited by this feature were due to the fact that the thin cirrus allowed warmer thermal radiation from the surface to pass through the cloud and reach the satellite detectors.

GOES-16 Visible (0.64 µm, top), Near-Infrared

GOES-16 Visible (0.64 µm, top), Near-Infrared “Cirrus” (1.37 µm, middle) and “Clean” Infrared Window (10.3 µm, bottom) images [click to play MP4 animation]

Rawinsonde profiles from Lake Charles and Slidell, Louisiana at 12 UTC (below) showed the presence of a moist layer aloft (at an altitude around 9.5 km or 31,100 feet) — the cirrus cloud feature likely resided within this moist layer, which would explain why the cloud was slow to dissipate. Air temperatures within this moist layer were in the -40 to -50ºC range, and winds were from the west-northwest at speeds of 30-35 knots (which was consistent with the cloud motion seen on satellite imagery).

Rawinsonde data for Lake Charles and Slidell, Louisiana at 12 UTC on 10 November [click to enlarge]

Rawinsonde data for Lake Charles and Slidell, Louisiana at 12 UTC on 10 November [click to enlarge]

Even with the higher spatial resolution Infrared Window imagery (1 km, vs 2 km at the satellite sub-point for GOES-16) of Terra MODIS (below), the minimum Infrared brightness temperature of the cirrus cloud feature was still a relatively warm -31ºC.

Terra MODIS Visible (0.65 µm), Cirrus (1.375 µm) and Infrared Window (11.0 µm) images [click to enlarge]

Terra MODIS Visible (0.65 µm), Cirrus (1.375 µm) and Infrared Window (11.0 µm) images [click to enlarge]

Another interesting aspect of this small cirrus cloud is that it was casting a shadow to the north (due to the low November sun angle) — and the Terra MODIS Land Surface Temperature product (below) indicated that LST values were about 10 degrees F cooler within the shadow (low to middle 60s F) compared to adjacent sunlit ground (low to middle 70s F). That particular area was not normally cooler in terms of LST values (because of varying vegetation, soil type, a deep lake, etc.), since it did not show up as a cooler feature on the following day.

Terra MODIS Visible (0.65 µm) image and Land Surface Temperature product [click to enlarge]

Terra MODIS Visible (0.65 µm) image and Land Surface Temperature product [click to enlarge]

Additional images and ground-based photos of the cirrus cloud feature can be found on this AccuWeather blog.

Aircraft “hole punch” clouds over Wisconsin

November 10th, 2017 |

GOES-16 Visible (0.64 µm, top) and Near-Infrared

GOES-16 “Red” Visible (0.64 µm, top) and Near-Infrared “Snow/Ice” (1.61 µm, bottom), with surface station identifiers plotted in yellow [click to play MP4 animation]

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

GOES-16 “Red” Visible (0.64 µm) and Near-Infrared “Snow/Ice” (1.61 µm) images (above) revealed a number of aircraft “hole punch” clouds over western Wisconsin on the morning of 10 November 2017.  These cloud features were caused by aircraft that were either ascending or descending through a layer of cloud composed of supercooled water droplets — cooling from wake turbulence (reference) and/or particles from the jet engine exhaust acting as ice condensation nuclei cause the small supercooled water droplets to turn into larger ice crystals (which then often fall from the cloud layer, creating “fall streak holes“). The darker gray appearance of the hole punch clouds on 1.61 µm images confirms that the features were composed of ice crystals (since ice is a strong absorber of radiation at that wavelength).

One isolated  hole punch cloud was also seen in 250-meter resolution Terra MODIS false-color Red-Green-Blue (RGB) imagery (source) over central Wisconsin around 16:52 UTC (below). In this type of RGB image (created using MODIS Bands 7/2/1), ice crystal clouds appear as shades of cyan, in contrast to supercooled water droplet clouds which appear as shades of white. With the low November sun angle, this cloud deck was casting a long shadow to the north — and sunlight filtering through the hole punch feature was brightening up a spot in the cloud shadow on the ground.

Terra MODIS false-color images [click to enlarge]

Terra MODIS false-color image [click to enlarge]