Persistent fog in British Columbia and the Pacific Northwest region of the US

October 22nd, 2013 |
Suomi NPP VIIRS IR brightness temperature difference "Fog/stratus product"

Suomi NPP VIIRS IR brightness temperature difference “Fog/stratus product”

A strong upper-level ridge of high pressure coupled with a moist, stagnant boundary layer led to the formation of widespread areas of fog for several days across much of the interior lowlands of western British Columbia and Washington State, along with valley fog in the Rocky Mountains farther to the east (as was documented during 21 October 2013 on the GOES-R Fog Product Examples blog). On 22 October 2013, two consecutive Suomi NPP VIIRS IR brightness temperature difference (BTD) “fog/stratus product” images (above) at 09:20 UTC (2:20 AM local time) and 10:58 UTC (3:58 AM local time) showed little change to the areal coverage of the fog/stratus located over the Puget Sound region and adjacent interior lowlands, but a significant growth of narrow fingers of valley fog from eastern British Columbia southward into far northern Washington, Idaho, and Montana.

A comparison of the 10:58 UTC VIIRS 0.7 µm Day/Night Band (DNB) image with the corresponding IR BTD fog/stratus product image (below) showcased the “visible image at night” capability of the Day/Night Band, given sufficient illumination by the Moon (which was in the Waning Gibbous phase, at 84% of Full). Not only are the fog (and other cloud) features evident in the DNB image, but the snow-covered higher elevations of the Rocky Mountains could also be seen. A number of ship tracks also appear over the Pacific Ocean in the far western portion of the satellite scene.

Suomi NPP VIIRS 0.7 um Day/Night Band and IR BTD "Fog/stratus product" images

Suomi NPP VIIRS 0.7 um Day/Night Band and IR BTD “Fog/stratus product” images

A post-sunrise sequence of GOES-15 (GOES-West) 0.63 µm visible channel images (below; click image to play animation) revealed that many of the fog features were very persistent and slow to dissipate — a strong boundary layer temperature inversion and light winds inhibited the rate of fog burn-off in those areas.

GOES-15 0.63 um visible channel images (click to play animation)

GOES-15 0.63 um visible channel images (click to play animation)

A comparison of two different AWIPS II false-color Red/Green/Blue (RGB) images (below) using VIIRS data at 20:44 UTC (1:44 PM local time) showed the value of using the 1.61 µm “snow/ice” channel to discriminate between snow cover (which appears as varying shades of red) and any fog, stratus, or other cloud features composed of water droplets (which appear as varying shades of white) in the area.

One other feature of interest can be seen on the VIIRS RGB images: in the far upper right corner, a pair of narrow aircraft dissipation trails (or “distrails”) can be seen within the broader band of mid-level supercooled water droplet clouds. As aircraft ascended (or descended) through the supercooled water droplet cloud layer, particles in the jet engine exhaust acted as ice condensation nuclei, causing thin streaks of the cloud to glaciate (hence their red appearance on the RGB image using the 1.61 µm VIIRS data) along the aircraft path. From the ground, these aircraft dissipation trails often appear as dramatic-looking “cirrus fall streaks”, as the larger, heavier ice crystals begin to descend from the supercooled cloud layer.

Suomi NPP VIIRS false-color RGB images (using Bands I1/I2/I5, and Bands I1/I3/I3)

Suomi NPP VIIRS false-color RGB images (using Bands I1/I2/I5, and Bands I1/I3/I3)

Super Typhoon Francisco

October 19th, 2013 |
MTSAT-2 10.8 µm IR channel images (click to play animation)

MTSAT-2 10.8 µm IR channel images (click to play animation)

Super Typhoon Francisco became the third Category 5 tropical cyclone of 2013 on 19 October 2013, as it intesified over the West Pacific Ocean northwest of Guam. 4-km resolution MTSAT-2 10.8 µm IR channel images (above; click image to play animation) showed the evolution and track of the eye of Francisco during the 17-19 October period (the island of Guam is in the lower right corner of the images). Note the trochoidal motion or “wobble” that is exhibited by the eye of the tropical cyclone as it tracked northwestward – this is caused by changes within the inner core structure of the storm, such as convective asymmetries.

1-km resolution MTSAT-2 0.73 µm visible channel images (below; click image to play animation) revealed better details of the eye and eyewall structure during the daylight portion of 18-19 October. The lowering October sun angle tended to more brightly illumimate the sloped surface of the northern quadrant of the eye.

MTSAT-2 0.73 µm visible channel images (click to play animation)

MTSAT-2 0.73 µm visible channel images (click to play animation)

A McIDAS-V comparison of 375-meter resolution Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm thermal IR channel images at 15:48 UTC on 18 October (below; images courtesy of William Straka, CIMSS) showed a good example of the so-called “stadium effect”: the eye diameter appeared larger on the VIIRS IR image than on the corresponding “visible image at night” from the VIIRS Day/Night Band, because the clouds along the edges of the eye were steeply sloping outward with height.

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

Mesoscale bands of snow cover in Kansas

October 19th, 2013 |
Suomi NPP VIIRS 0.7 µm Day/Night Band, IR BTD "Fog/Stratus Product", and 11.45 µm IR images

Suomi NPP VIIRS 0.7 µm Day/Night Band, IR BTD “Fog/Stratus Product”, and 11.45 µm IR images

Parts of Kansas received up to 5-6 inches of snowfall on 18 October 2013 (NWS Local Storm Reports). The following night, after the clouds associated with the storm system had moved eastward, the southwest-to-northeast oriented bands of snow cover could be clearly seen on an AWIPS image of Suomi NPP VIIRS 0.7 µm Day/Night Band data at 08:33 UTC or 3:33 AM local time (above). Due to ample illumination from a Full Moon, the bands of fresh snow appeared quite bright, as did the back edge of the stratus cloud deck that covered far eastern Kansas and western Missouri (which showed up well on the IR brightness temperature difference “fog/stratus product” image). A thin patch of mid-level clouds was also moving over north-central Kansas — the 11.45 µm IR brightness temperatures of that cloud feature were generally warmer than -20º C (cyan color enhancement).

After sunrise on the next day (19 October), GOES-13 0.63 µm visible channel images (below; click image to play animation) showed that the bands of snow cover melted rather quickly, due to the relatively high October sun angle.

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

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

Bush fires burning in the Sydney, Australia region

October 17th, 2013 |
MTSAT-2 visible channel (left) and shortwave IR channel (right) images (click to play animation)

MTSAT-2 visible channel (left) and shortwave IR channel (right) images (click to play animation)

Numerous bush fires began to burn in state of New South Wales near Sydney, Australia on 16-17 October 2013. On a comparison of MTSAT-2 visible channel and shortwave IR channel images (above; click image to play animation) some of the southeastward-drifting smoke plumes were evident on the visible images, while numerous fire “hot spots” (dark black pixels) could be seen on the shortwave IR images. Toward the end of the animation (06:32 UTC on 17 October), the hot fire pixels grew in areal coverage as winds increased in association with a cold frontal passage.

A 48-hour plot of surface data for Sydney Airport (below) showed that smoke reduced the surface visibility to 4-5 miles for several hours on 17 October. Prior to the passage of the cold front, surface air temperatures were unseasonably hot (in the middle 90s F), with wind gusts as high as 38 knots. In addition, note the sharp drop in dew point temperature to -2º F at 04 UTC on 17 October.

Plot of Sydney Airport surface meteorolofical data

Plot of Sydney Airport surface meteorolofical data

A 250-meter resolution Aqua MODIS true color image from the NASA EOSDIS Worldview site (below) offers a closer view of the smoke plumes in the Sydney area.

Aqua MODIS true color image

Aqua MODIS true color image