250-meter resolution MODIS true color and false color RGB images

A comparison of a 250-meter resolution MODIS true color Red/Green/Blue (RGB) image (created using Bands 1/4/3) with the corresponding MODIS false color image (created using Bands 7/2/1) obtained from the SSEC MODIS Today site confirmed that the brighter white area seen in far north-central Wisconsin on 05 November 2010 was a patch of snow that remained on the ground following a period of lake-effect snow 1-2 days earlier. Snow cover and/or ice appears as cyan-colored features in the MODIS 7/2/1 RGB false color image.

AWIPS images showing another set of MODIS false color RGB images (below, created using Bands 1/7/7) showed that the patch of snow cover — which appeared as a red-colored feature in these particular RGB images — remained stationary between the times of the Terra satellite overpass (around 16:58 UTC, or 11:58 am local time) and the Aqua satellite overpass (around 18:40 UTC, or 1:40 pm local time), which again confirmed that this was snow cover rather than a cloud feature. Upson in Iron county had received 3 inches of snow during the preceding 48 hours, with Butternut in Ashland county receiving 1.0 inch of snowfall.

MODIS false color RGB images

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AO&SS building rooftop camera (facing northwest)

Nocturnal radiation fog formed over Lake Mendota (the largest of the 4 lakes in the immediate vicinity of Madison, Wisconsin) on 02 November 2010 — the evolution and motion of this fog was captured by a northwest-facing camera (above; smaller 640×480 version) mounted on the top of the Atmospheric, Oceanic, and Space Sciences building on the University of Wisconsin – Madison campus (Google map). The camera video begins at 09:54 UTC (4:54 am local time) and ends at 15:39 UTC (10:39 am local time). During the daylight hours, there even appeared to be evidence of a local-scale cyclonic circulation within the fog feature along the southern shore of Lake Mendota. Thanks to Pete Pokrandt, AOS, for supplying the QuickTime animation.

AWIPS images of the 4-km resolution GOES-13 fog/stratus product at night (followed by 1-km resolution GOES-13 0.63 µm visible channel images after sunrise) are shown below. In spite of the high amount of noise and “false fog/stratus pixels” (yellow enhancement), the GOES-13 fog/stratus product did show a relatively persistent fog signal over Lake Mendota through much of the night-time hours — and then the fog features could then be seen dissipating on the GOES-13 visible images after sunrise. On both the rooftop camera video and the GOES-13 visible images, the fog features appeared to be drifting to the southwest — in fact, the surface visibility at the Middleton Municipal Airport (KC29, located just to the west of Lake Mendota) dropped to 0.15 mile, while the surface visibility at Madison’s Dane County Regional Airport airport (KMSN, located just to the east of Lake Mendota) only fell to 3.0 miles.

GOES-13 fog/stratus product + GOES-13 0.63 µm visible channel images

An AWIPS image of the POES AVHRR 1-km resolution Sea Surface Temperature product (below) indicated that SST values over the central portion of Lake Mendota were as warm as 54.5º F at 23:55 UTC (6:55 PM local time) before sunset. With light winds and strong radiational cooling during the night, the surface air temperate at nearby Madison Dane County Regional Airport (KMSN) cooled to 27º F — and with such a large difference in water vs air temperature, thick fog eventually began to form over Lake Mendota.

POES AVHRR Sea Surface Temperature product

Looking ahead to the future GOES-R era, Geostationary Cloud Algorithm Test-bed (GEOCAT) images of a GOES-R Fog Probability product (below) did indeed suggest that fog probabilities were increasing across south-central Wisconsin during the night-time hours as radiational cooling continued.

GEOCAT experimental GOES-R Fog Probability product

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GOES-13 0.63 µm "visible channel" image

Steve Nazar wrote in an email:

“For the first time, I’ve seen Luna in a GOES photo! Maybe this is commonplace, but I’ve only seen it this once in roughly 20 years of looking at your site. Luna was in GOES East at 2345H Oct 31, and in no others in the sequence. It showed just above the horizon over Vancouver Island, in all wavelengths.”

The GOES-13 (GOES East) 0.63 µm “visible channel” image (above) did indeed show a crescent of the Moon being illuminated just off the Earth’s horizon late in the day on 31 October 2010. A wide band of cloudiness moving over much of British Columbia and the Pacific Northwest was associated with a frontal boundary and an upper level trough of low pressure over that region . As it turns out, the Moon can actually be seen on GOES images a handful of times every year, depending on the viewing angle of the satellite in relation to the position of the Moon (for example, see https://cimss.ssec.wisc.edu/satellite-blog/archives/2106).

GOES-13 3.9 µm "shortwave IR channel" image

The GOES-13 3.9 µm “shortwave IR image (above) showed that the illuminated portion of the Moon exhibited very hot IR brightness temperatures (dark black enhancement) — the maximum value indicated using McIDAS was 340 K. The very hot sunlit surface of the moon can actually reach temperatures of 383 K / +110º C / +230º F, while surface temperatures on the very cold “dark” side of the moon can fall to 93 K / -180º C / -292º F.

GOES-13 6.5 µm "water vapor channel" image

The GOES-13 6.5 µm “water vapor channel” image (above) showed a rather interesting pattern of banded gradients — this was due to the fact that the water vapor channel detectors are designed to sample much colder features, so the extreme heat of the illuminated moon surface caused a supersaturation or “roll-over” from hot (black) to cold (white).

GOES-13 10.7 µm "IR window channel" image

The GOES-13 10.7 µm “IR window channel” image (above) also displayed very hot IR brightness temperatures across the sunlit portion of the Moon (as high as 330.5 K).

An animation of these 4 images is shown below:

GOES-13 visible, shortwave IR, water vapor, and IR window channels

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MODIS 0.65 µm visible channel + 2.1 µm "snow/ice channel" images

Snow cover was beginning to accumulate into the 12-24 inch range at some locations across the higher terrain of the Rocky Mountains in Colorado on 27 October 2010. While the snow-covered mountains appeared as brighter white features in contrast to the surrounding bare ground areas on AWIPS images of the MODIS 0.65 µm visible channel data, a comparison with the corresponding MODIS 2.1 µm “snow/ice channel” image (above) showed how it was possible to easily discriminate between areas with deep snow cover (which appeared as much darker features on the snow/ice image) and supercooled water droplet clouds (which appeared as brighter white features on the snow/ice image). The large area of cirrus clouds covering the northeastern corner of the image also appeared as a slightly darker shade of gray on the snow/ice image, due to their ice crystal composition.

Another method to easily discriminate between deep snow cover and supercooled water droplet clouds is to use a false color Red/Green/Blue (RGB) image (below), generated using the MODIS visible channel as the Red component and the MODIS snow/ice channel as the Green and Blue components of the image. Deep snow cover then appears as darker red features, in contrast to supercooled water droplet clouds which appear as brighter white features on the image. Again, the large area of cirrus clouds covering the northeastern corner of the image also appeared as a lighter shade of red on the RGB image, due to their ice crystal composition.

MODIS false color Red/Green/Blue (RGB) image

It can also be informative to compare the MODIS 3.7 µm shortwave IR image to the corresponding MODIS 11.0 µm IR window image (below). Some of the cloud features over northwestern Colorado were exhibiting 11.0 µm IR window brightness temperatures of -20º C and colder (cyan to blue color enhancement), suggesting that they could possibly be getting cold enough for glaciation to occur — however, these cloud features still appeared as darker features on the 3.7 µm shortwave IR image, indicating a strong component of reflection of incident solar radiation off of supercooled water droplets.

MODIS 3.7 µm shortwave IR image + MODIS 11.0 µm IR window image

One of the more interesting comparisons is between the 0.65 µm MODIS visible channel image and the corresponding MODIS 6.7 µm water vapor image (below). Note the presence of widespread mountain waves to the lee of the higher terrain of the Rocky Mountains on the water vapor image — the vast majority of these waves were in cloud-free air according to the visible channel image. Such mountain wave signatures on water vapor imagery can indicate regions where clear air turbulence might be likely.

MODIS 0.65 µm visible channel image + MODIS 0.67 µm water vapor image

CIMSS has been making MODIS imagery and products available in AWIPS format to National Weather Service forecast offices as a part of the GOES-R Proving Ground project.

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