Contrails over eastern North Dakota

March 7th, 2011 |
POES AVHRR 10.8 µm "IR window" image

POES AVHRR 10.8 µm "IR window" image

A pair of interesting “Figure 8” aircraft condensation trails (or “contrails”) could be seen on a 1-km resolution POES AVHRR 10.8 µm “IR window” image over eastern North Dakota on 07 March 2011 (above). The contrails appeared slightly colder (brighter white) than the surrounding snow-covered ground surfaces. These contrail patterns were presumably made by military jets conducting training exercises from nearby Grand Forks Air Force Base.

The contrail patterns were even more apparent on the corresponding POES AVHRR 3.7 µm “shortwave IR” image (below). The contrail features appeared darker on the shortwave IR image due to reflection of solar radiation off the small supercooled water droplets that comprised the cloud features — and their shadows appeared as slightly cooler (brighter white) signatures on the surface.

POES AVHRR 3.7 µm "IR window" image

POES AVHRR 3.7 µm "IR window" image

On the 0.63 µm POES AVHRR visible image (below), the contrail shadows showed up very well as darker features against the bright snow-covered ground. Using an Interactive Image Fader Tool, the distance offset between the contrails themselves (darker features on the shortwave IR image) and their shadows (darker features on the visible image) was quite obvious — this distance offset was due to the fairly low sun angle at this time of the day over North Dakota in early March.

POES AVHRR 0.63 µm visible image

POES AVHRR 0.63 µm visible image

Tip of the hat to Gregg Gallina (NOAA/NESDIS/SAB) for bring this interesting feature to our attention!

Lake-effect snow in northeastern Minnesota

March 7th, 2011 |

 

GOES-13 0.63 µm visible channel images (click image to play animation)

GOES-13 0.63 µm visible channel images (click image to play animation)

 

AWIPS images of 1-km resolution GOES-13 0.63 µm visible channel data (above; click image to play animation) revealed the formation of convergence bands withing a weak cyclonic circulation over western Lake Superior on 07 March 2011. These convergence bands were responsible for producing some lake-effect snowfall along the north shore of the lake, over parts extreme northeastern Minnesota — Lutsen reported 8.5 inches of snow, with 5.8 inches falling north of Grand Marais.

 

 

POES AVHRR 0.86 µm visible images

POES AVHRR 0.86 µm visible images

A sequence of 1-km resolution POES AVHRR 0.86 µm visible channel images (above) and the corresponding 1-km resolution POES AVHRR 12.0 µm IR images (below) showed a slightly more detailed view of the convergence bands.

POES AVHRR 12.0 µm IR images

POES AVHRR 12.0 µm IR images

A comparison of 1-km resolution POES AVHRR Cloud Optical Depth products at 18:41 and 19:18 UTC (below) showed that the primary convergence band along the eastern side of the cyclonic circulation feature  exhibited significantly higher cloud optical depth values (blue to cyan color enhancement).

POES AVHRR Cloud Optical Depth product images

POES AVHRR Cloud Optical Depth product images

===== 08 MARCH UPDATE =====

Another well-defined vortex was observed over northern Lake Superior on the following day. A comparison of 250-meter resolution MODIS true color and false color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (below) showed the vortex cloud feature with a very long and narrow “tail” extending southward and westward from the center of the circulation, along with a complex ice structure across the far southern portion of Lake Superior. Ice and snow cover appear as cyan-colored features on the MODIS false color image, in contrast to supercooled water droplet clouds (which appear as brighter white features).

 

MODIS true color and false color images

MODIS true color and false color images