GOES-13 10.7 µm IR channel images (click to play animation)

AWIPS images of 4-km resolution GOES-13 10.7 µm IR channel data (above; click image to play animation) showed the development of a large shield of orographic cirrus clouds immediately downwind (to the east of) the high terrain of the Rocky Mountains in eastern Colorado and southeastern Wyoming on 18 December 2013. The development and persistence of such cloud features is important to monitor, due to their potential impact on daytime temperatures: if incoming solar radiation is significantly reduced by a canopy of dense cirrus, surface temperatures may not be as warm as forecast. Early in the cirrus shield development during the overnight hours, GOES-13 IR brightness temperatures were as cold as -66º C (darker red color enhancement) along the western edge of the cirrus shield, suggestive of a high and potentially dense ice cloud feature — but during the early morning hours the cirrus was seen to begin to rapidly dissipate after about 15 UTC.

While not directly related to the orographic cirrus cloud shield per se, the strong westerly winds interacting with the complex terrain of the Rocky Mountains produced some areas of turbulence across Colorado. At 14:05 UTC a pilot reported Moderate turbulence throughout a very deep layer (5,500 feet to 20,000 feet), and at 15:22 UTC a pilot reported occasional Severe turbulence between the altitudes of 13,000 and 16,000 feet.

Night-time comparisons of 1-km resolution Suomi NPP VIIRS 0.7 µm Day/Night Band (DNB) and 11.45 µm IR channel images at 08:12 UTC or 1:12 AM local time (above) and 09:51 UTC or 2:51 AM local time (below) revealed that the cirrus along the western (upwind) edge was quite cold on the IR images (with IR brightness temperatures as cold as -71º C at 08:12 UTC, and -76º C at 09:51 UTC), and also appeared much more optically thick along the western portion on the DNB images. However, on the DNB images the cirrus shield — although still exhibiting fairly cold IR temperatures — appeared to be much more optically thin along the eastern portion. Due to ample illumination by a nearly-full moon, the DNB provided vivid “visible images at night” to compliment the IR images; in the upper right corner of the DNB images, snow on the ground could also be seen across northern Nebraska into far southern South Dakota.

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel images

A 1-km resolution POES AVHRR Cloud Top Height product at 11:39 UTC or 4:39 AM local time (below) indicated that the tops of the cirrus shield were at 12 km (darker green color enhancement).

POES AVHRR Cloud Top Height product

The 12 UTC Denver rawinsonde data (below) showed that the tropopause was around 13 km, with an air temperature of -70º C. Winds at that altitude were from the west at 100 knots (with strong westerly winds at all altitudes throughout the tropopause).

Denver, Colorado rawinsonde data

Additional details and imagery of this orographic cirrus event can be found on the CIRA RAMMB GOES-R Proving Ground Blog.

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GOES-15 3.9 µm shortwave IR images (click to play animation)

The Pfeiffer Fire (InciWeb | Wildfire Today) began to burn in the Big Sur area of central California just after 08:00 UTC or Midnight local time on 16 December 2013. McIDAS images of 4-km resolution GOES-15 3.9 µm shortwave IR data (above; click image to play animation) showed the initial appearance of a fire “hot spot” (darker black to red color enhancement) at 08:11 UTC or 12:11 AM local time, with IR brightness temperatures increasing to 339.3 K or 66.2º C (red color enhancement) at 10:15 UTC or 2:15 AM local time. Although the fire hot spot was generally identifiable during most of the following 48 hours (even through cirrus cloud features passing overhead), it never was seen to reach that early intensity again.

Spatial resolution is very important for the accurate location and characterization of fires — this is demonstrated by an AWIPS image comparison of 1-km resolution Suomi NPP VIIRS 3.74 µm and 4-km resolution GOES-15 3.9 µm shortwave IR data just after 10 UTC on 17 December (below). The warmest IR brightness temperature on the GOES-15 image was 15º C (darker black pixels) compared to 54.5º C (red pixels) on the VIIRS image.

Suomi NPP VIIRS 3.74 µm and GOES-15 3.9 µm shortwave IR images

Suomi NPP VIIRS 3.74 µm shortwave IR images

The growth of the fire from 16 December to 17 December could be seen by comparing night-time images of Suomi NPP VIIRS 3.74 µm shortwave IR data (above) and the corresponding VIIRS 0.7 µm Day/Night Band data (below). Signatures of the fire — both the size of the fire hot spot on the shortwave IR images, and the bright glow from the fire complex on the Day/Night Band images — were seen to increase in size on 17 December. The fire was estimated to have burned about 500 acres by the afternoon of 17 December, and was only 5% contained at that time. A number of homes and other structures were lsot to the fire, and some evacuations had to be carried out.

On the 17 December VIIRS images, note the observation of smoke on the surface report for Monterey (station identifier KMRY) north of the Pfeiffer Fire. At that time, the surface visibility there was only being reduced to 10 statute miles — however, later in the day on 17 December the surface visibility was as low as 4 statute miles at 23 UTC (3 PM local time) and 00 UTC (4 PM local time), causing some air quality problems.

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

McIDAS images of GOES-13 0.63 µm visible channel data (above; click image to play animation) revealed a well-defined mesovortex moving southeastward across the southern part of Lake Superior during the day on 15 December 2013. As the feature approached the Upper Peninsula of Michigan, a secondary mesovortex could be seen to the east-southeast of the larger primary mesovortex. These mesovortices produced bands of heavy snowfall and strong winds (with gusts as high as 60 mph offshore at Stannard Rock, and 46 mph inland at Marquette), which reduced surface visibility to less than 0.1 miles at times. Farther to the south, another item of interest seen in the imagery was the slow eastward drift of ice floes in the northern portion of Green Bay.

During the preceding night-time hours, an AWIPS image of Suomi NPP VIIRS 0.7 µm Day/Night Band data at 07:24 UTC or 2:24 AM local time (below) showed cloud bands starting to wrap around the mesovortex as it was beginning to form in the northern part of Lake Superior (northeast of Isle Royale). This example highlights the “visible image at night” capability of the VIIRS Day/Night Band (given sufficient illumination by moonlight — in this case, the Moon was in the Waxing Gibbous phase, at 98% of full). An overlay of the 07 UTC RTMA surface wind field confirmed the presence cyclonic flow around the developing mesovortex.

Suomi NPP VIIRS 0.7 µm Day/Night Band image, with RTMA surface winds

During the morning hours, the circulation of the primary mesovortex could be seen on Metop ASCAT scatterometer surface winds at 15:28 UTC or 10:28 AM local time (below).

GOES-13 0.63 µm visible channel image, with Metop ASCAT scatterometer surface winds

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MODIS 0.65 µm visible channel images, with METAR surface and buoy reports

Cloud features associated with the pair of mesovortices could be seen in detail on 16:58 UTC (11:58 AM local time) and 18:40 UTC (1:40 PM local time) 1-km resolution MODIS 0.65 µm visible channel images (above) and 11.0 µm IR channel images (below). Cloud-top IR brightness temperatures on the MODIS IR images were in the -30ºC to -40ºC range (dark blue to green color enhancement), indicating significant vertical development of some of the banding structure.

MODIS 11.0 µm IR channel images, with METAR surface and buoy reports

Even greater detail can be seen using 250-meter resolution Terra and Aqua MODIS true-color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (below). Regarding the ice in Green Bay, there was a news story discussing the impact of this early ice formation on shipping.

Terra and Aqua MODIS true-color RGB images

Another indication of the vertical extent of some of the mesovortex banding features was the strong illumination of the southern sides of the bands by the low mid-December sun angle, as seen in a comparison of the 18:48 UTC (1:48 PM local time) Suomi NPP VIIRS 0.64 µm visible channel image with the corresponding VIIRS false-color “snow-vs-cloud discrimination” RGB image (below). In this RGB image, surface snow and ice (as well as glaciated cloud tops) appear as varying shades of red — in contrast, supercooled water droplet clouds appear as shades of white.

Suomi NPP VIIRS 0.63 µm visible and false-color RGB images

Signatures of the twin mesovortices were evident on NWS Marquette, Michigan radar base reflectivity (below). Additional radar imagery can be seen the WeatherMatrix Blog.

Marquette, Michigan radar base reflectivity

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

On the morning of 14 December 2013, GOES-13 0.63 µm visible channel images (above; click image to play animation) showed what appeared to be a plume of re-suspended volcanic ash moving northward from the region of the Cordón Caulle volcano in Chile. As the airborne ash plume begain to disperse later in the day, it then began to move in a more northeasterly direction. Since no volcanic ash advisories were issued by the Beunos Aires Volcanic Ash Advisory Center (VAAC), it was assumed that this was a case of re-suspended ash that covered the ground following previous eruptions.

Although there is not always a thermal anomaly or “hot spot” seen on shortwave IR satellite images accompanying a volcanic eruption, no such hot spot was seen on the corresponding GOES-13 3.9 µm shorwave IR imagery (below; click image to play animation). The higher terrain of the Cordón Caulle volcano complex — located in the center of the images — initially appeared cooler (lighter gray) prior to sunrise, but then their higher-elevation surfaces begain to warm (darker gray pixels) after sunrise. The plume of re-suspended volcanic ash also exhibited a darker appearance after sunrise, due to the reflection of solar radiation off the small particles.

GOES-13 3.9 µm shortwave IR images (click to play animation)

Quantitative products derived from Terra MODIS imagery (below) indicated that the plume had a maximum height of around 5-6 km, with ash/dust loading in the 4-5 g/m2 range, and a mean particle effective radius as large as 4-6 µm.

Terra MODIS Ash Height product

Terra MODIS Ash/Dust Loading product

Terra MODIS Ash Particle Effective Radius product

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