Lake-effect cloud plumes in the Dakotas

December 10th, 2009 |
MODIS visible channel and 2.1 µm near-IR snow/ice channel images

MODIS visible channel and 2.1 µm near-IR "snow/ice channel" images

An influx of arctic air (surface plot) moved southeastward across North Dakota and South Dakota in the wake of a large and powerful Midwest blizzard on 09 December 2009. Since many sections of the Missouri river were still unfrozen — the MODIS Sea Surface Temperature product showed that water temperatures were still in the 30s F — the large difference in temperature created enough instability to allow a number of “lake-effect cloud plumes” to form. AWIPS images of the 1-km resolution MODIS visible channel and 2.1 µm near-IR “snow/ice” channel (above) showed how the snow/ice imagery can be useful for detecting supercooled water droplet clouds against a background of snow cover. Snow and ice are strong absorbers at the 2.1 µm wavelength, so they appear darker (in contrast to supercooled water droplet clouds, which appear as brighter white features). Note that these cloud features were not readily apparent on standard IR imagery, due to the lack of a good temperature contrast between the shallow cloud features and the background snow cover.

A false-color MODIS Red/Green/Blue (RGB) image (below) is another example of using the 2.1 µm data to aid in the detection of supercooled water droplet clouds — the background snow cover appears as varying shades of red, while the supercooled cloud features stand out as brighter white features. The capability create such RGB images will be available in the upcoming AWIPS II software.

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

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

MODIS 250-meter resolution true color and false color images

MODIS 250-meter resolution true color and false color images

A closer view using 250-meter resolution MODIS true color and false color images from the SSEC MODIS Today site shows finer details of the lake-effect cloud plumes over North Dakota (above) and South Dakota (below). On these false-color images, the background snow cover appears as varying shades of cyan.

MODIS 250-meter resolution true color and false color images

MODIS 250-meter resolution true color and false color images

Similar lake-effect cloud plumes were seen on the previous day (08 December 2009) streaming southward from Fort Peck Lake in northeastern Montana.

Terrain-induced cloud features off the coast of western North America

December 7th, 2009 |
GOES-11 and GOES-14 visible channel images

GOES-11 and GOES-14 visible channel images

A comparison of GOES-11 and GOES-14 (which was undergoing its NOAA Science Test) visible channel images (above; also available as a QuickTime animation) showed a series of standing waves to the lee of Isla Guadalupe and also to the lee of Baja California on 07 December 2009. These terrain features were acting as an obstacle to strong westerly flow within the marine boundary layer, which initiated the formation of the lee waves.

A signature of these lee waves was also evident on GOES-14 (and to a lesser extent, GOES-11) water vapor channel images (below; also available as a QuickTime animation). The spatial resolution of the 6.5 µm GOES-14 water vapor channel is 4 km, compared to the 8 km resolution of the 6.7 µm water vapor channel on GOES-11 — this allowed the wave structure to be observed with greater clarity using GOES-14.

GOES-11 and GOES-14 water vapor images

GOES-11 and GOES-14 water vapor images

A MODIS 11.0 µm IR image with an overlay of 1-hour MADIS atmospheric motion vectors (below) showed that lower tropospheric wind speeds were as high as 50 knots over the region.

MODIS IR image + MADIS 1-hour wind vectors

MODIS IR image + MADIS 1-hour wind vectors

AVHRR Cloud Top Height (CTH) and Cloud Top Temperature (CTT) products (below) indicated the the crests of the waves immediately downwind of Isla Guadalupe exhibited CTH values as high as to 5 km and CTT values as cold as -30º C — the surrounding marine stratoculumus clouds had CTH values near 2 km and CTT values around +2º C.

AVHRR Cloud Top Height and Cloud Top Temperature products

AVHRR Cloud Top Height and Cloud Top Temperature products

Farther to the north, GOES-11 and GOES-14 visible channel images (below; also available as a QuickTime animation) revealed a long cloud plume that had formed downwind of Mount Olympus in far northwestern Washington. Strong northeasterly flow had developed over the region in response to the formation of a broad trough of low pressure over the western US. Note the improvement in GOES-14 Image Navigation and Registration (INR), with much less image-to-image wobble compared to GOES-11.

GOES-11 and GOES-14 visible channel images

GOES-11 and GOES-14 visible channel images

A MODIS fog/stratus product image (below) showed that this cloud plume was also apparent during the pre-dawn hours, before any visible channel imagery would have been available.

MODIS fog/stratus product

MODIS fog/stratus product

A MODIS 3-channel Red/Green/Blue (RGB) image (below) suggested that this cloud plume was comprised primarily of supercooled water droplets, which exhibit a brighter appearance on the RGB image — ice crystal clouds would have more of a pink-colored look on such an RGB image (like that seen with the deep snow cover over the interior mountains)

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

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

A MODIS visible channel image with an overlay of RUC80 850 hPa winds (below) confirmed the presence of northeasterly flow over the region. As the flow moved around the obstacle of Mount Olympus, lee-side convergence helped to aid in the formation of the cloud plume.

MODIS visible image + RUC80 850 hPa winds

MODIS visible image + RUC80 850 hPa winds

Historic snowfall event in the Gulf Coast region

December 4th, 2009 |
GOES-14 10.7 µm IR images

GOES-14 10.7 µm IR images

An historic snowfall event (SPC watches and warnings) impacted parts of the Gulf Coast region of the US on 04 December 2009 — this event produced the earliest snowfall on record at both Houston, Texas and Lake Charles, Louisiana, and total snowfall amounts were as high as 5.0 inches in Mississippi, 4.0 inches in Texas, and 3.0 inches in Louisiana. McIDAS images of the GOES-14 10.7 µm IR channel data (above) showed the development of the bands of elevated convection that produced the snowfall (the symbols of precipitation type are also plotted on the IR images).

AWIPS images of the GOES-12 10.7 µm IR channel data with overlays of surface METAR reports and cloud-to-ground lightning strikes (below) did indicate that there were a few lightning strikes early in the development of the bands of elevated convection over far southeast Texas (with a small number of strikes immediately offshore later in the morning), but as the snowfall event was unfolding farther north toward the Houston area there were no cloud-to-ground strikes seen. GOES-14 and GOES-12 IR cloud top brightness temperatures were in the -40 to -50º C range, which was near the tropopause on the Corpus Christi, Texas and Lake Charles, Louisiana rawinsonde data.

GOES-12 10.7 µm IR images + METARs + Cloud-to-Ground Lightning

GOES-12 10.7 µm IR images + METARs + Cloud-to-Ground Lightning

1-km resolution MODIS visible channel, 2.1 µm near-IR “snow/ice channel”, and 11.0 µm IR channel images (below) offered a view of the event at 16:58 UTC or 10:58 AM local time. Shadows from the tall convective elements could be seen on the visible image — and since the tops of the elevated convection were glaciated, they showed up as darker features on the snow/ice image. As was seen on the GOES-12 and GOES-14 IR images above, the IR cloud top brightness temperatures were in the -40 to -50º C range.

MODIS visible, 2,1 µm near-IR snow/ice, and 11.0 µm IR channel images

MODIS visible, 2,1 µm near-IR "snow/ice", and 11.0 µm IR channel images

1-km resolution AVHRR cloud products at 20:11 UTC or 2:11 PM local time (below) showed that the glaciated cirrus cloud type elements (red enhancement) had cloud top heights in the 9-10 km range (cyan color enhancement), with cloud top temperatures in the -40 to -50º C range (darker blue enhancement).

AVHRR Cloud Type, Cloud Top Height, and Cloud Top Temperature products

AVHRR Cloud Type, Cloud Top Height, and Cloud Top Temperature products

UPDATE: On the following morning, GOES-14 visible images (below) revealed the areal extent of the resulting snow cover that had not yet melted. Note the brighter white band of deeper snow cover near the Texas coast, where Lane City and Boling had received 4.0 inches. Some of the bright features seen in southwestern Louisiana were low stratiform clouds that were burning off as daytime heating increased.

GOES-14 visible images

GOES-14 visible images

MODIS true color image (displayed using Google Earth)

MODIS true color image (displayed using Google Earth)

MODIS true color images (displayed using Google Earth) showed another view of the remaining snow cover on the late morning hours on 05 December over Texas (above) and over Louisiana and Mississippi (below). The highest snowfall totals reported in each region are noted on the images.

MODIS true color image (displayed using Google Earth)

MODIS true color image (displayed using Google Earth)

GOES-14: Full Disk images at 30-minute intervals

December 1st, 2009 |
GOES-14 Full Disk 6.5 µm water vapor images

GOES-14 Full Disk 6.5 µm water vapor images

On Day 2 (01 December 2009) of the GOES-14 NOAA Science Test, the satellite was placed into a continuous “Full Disk” scan mode, providing images of the entire hemisphere at 30 minute intervals — full disk images of the GOES-14 6.5 µm “water vapor channel” are shown above. While the current GOES operational scan schedule provides 1 full disk image every 3 hours, the ABI instrument on the upcoming GOES-R satellite will have the ability to provide full disk images every 5 minutes!