MODIS true color image

Unusually cold temperatures were experienced across much of the Upper Midwest and Great Lakes region during  the month of December 2008 — as of 21 December, monthly temperatures were 6.4º F below normal at Milwaukee WI (their low that morning was -5º F), 7.2º F below normal at Chicago IL (their low that morning was -6º F), and 8.6º F below normal at Madison WI (their low that morning was -10º F). On the following day (22 December 2008), 250-meter resolution MODIS Red/Green/Blue (RGB) true color imagery from the SSEC MODIS Today site (above) revealed that significant amounts of ice had begun forming in the western and southern near-shore waters of Lake Michigan. During the previous winter season, similar ice formation was not seen until 19-20 January.

The satellite image confirms that there was abundant snow cover over the area (snow depths on the morning of 22 December were as great as 18 inches in southeastern WI, 12 inches in northeastern IL, and 30 inches in southwestern Lower Michigan). Also note that some of the smaller inland lakes in southeastern WI remained unfrozen — those particular lakes are quite deep, and take longer to freeze.

Another item of interest was the fact that there was a “convergence” of the Lake Michigan cloud bands seen over southwestern Lower Michigan: winds (and the resulting cloud bands) were oriented southwest-to-northeast over the southern portion of Lake Michigan, and oriented northwest-to-southeast farther to the north. Lake-effect snowfall amounts in that part of southwestern Lower Michigan included 13.4 inches at Muskegon and 12.6 inches at Grandville.

Farther to the north, ice was also seen forming in the far southwestern portions of Lake Superior — and the long tornado damage path from the 07 June 2007 EF3 tornado in northeastern WI was still quite visible in the MODIS true color imagery.

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GOES-13 6.5 µm water vapor images

Strong winds gusting to around 140 mph (63 m s-1) caused damage to the Reno/Virginia Peak radar in western Nevada at around 10:30 UTC on 19 December 2008. GOES-13 images of the 4-km resolution 6.5 µm “water vapor channel” (above) revealed a large area of “lee waves” immediately downwind of the Sierra Nevada Range — intense vertical motions associated with these lee waves were producing strong bands of subsidence (indicated by the darker blue to yellow color enhancement on the water vapor imagery), which were likely  contributing to the strong wind gusts at the surface.

The National Weather Service forecast office at Reno captured an AWIPS image of the 1-km resolution MODIS 6.7 µm water vapor channel (below) about 4 hours prior to the time of the radar damage. Reno is one of the NWS forecast offices that receives the MODIS product suite that CIMSS distributes in AWIPS format.

MODIS 6.7 µm water vapor image (courtesy of NWS Reno, Nevada)

The photos below (from the National Weather Service forecast office at Reno) show the damage suffered by the radome that encloses the radar antenna.

Photos of wind-damaged radome (courtesy of NWS Reno, Nevada)

— 25 DECEMBER UPDATE —

Another round of strong winds brought gusts to 95 mph on 25 December 2008, which caused even more damage to the radome and the actual radar antenna structure. GOES-13 water vapor images (below) again showed the presence of lee waves in the region for several hours prior to the period of the peak winds (which occurred around 10:15 UTC) — however, the arrival of dense cirrus clouds eventually masked the lee wave signature around the time of the additional radar damage.

GOES-13 6.5 µm water vapor images

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GOES-13 6.5 µm water vapor images (with surface weather)

A significant snowfall event occurred over the Desert Southwest region of the US on 17 December 2008 — as much as 30.0 inches of snow was reported at Wrightwood in the mountains of southern California (just northeast of Los Angeles), and Las Vegas, Nevada received 3.6 inches (setting a new record for the most snowfall during any December). Malibu Hills, California even received 0.5 inch of snow (at the 2000-foot level). GOES-13 6.5 µm water vapor imagery (above) showed the large and intense storm as is moved inland — note the appearance of convective elements that developed over parts of California, Arizona, and Nevada (along the leading edge of the dry slot). In addition, wave patterns downwind of Guadalupe Island and northern Baja California indicated the presence of very strong winds. These wave patterns were clearer on the 4-km resolution GOES-13 water vapor channel, compared to the 8-km resolution water vapor channel on GOES-11. Note that GOES-13 had recently replaced GOES-12 as the operational GOES East satellite.

An AWIPS image of the MODIS 6.7 µm water vapor channel with an overlay of MADIS water vapor winds (below) revealed that wind speeds aloft were as strong as 78 knots at the 387 hPa level, just ahead of the advancing dry slot. The GOES-11 Sounder Total Column Ozone product also showed a well-defined lobe of elevated ozone levels (in the 350-400 Dobson Unit range) associated with the developing storm.

MODIS 6.7 µm water vapor image + MADIS water vapor winds

Another interesting feature seen on the water vapor imagery was an elongated band of cloudiness that developed along a very pronounced deformation zone that formed over Nevada and Utah — there were a few pilot reports of moderate turbulence in the vicinity of this deformation zone (below), with one report of moderate to severe turbulence over central Nevada at 00:44 UTC (at the 33,000-foot flight level).

GOES water vapor images + pilot reports of turbulence

AWIPS images of the 1-km resolution MODIS water vapor, IR, and visible channels (below) showed a clearer view of the convective elements that were developing along the leading edge of the dry slot. These convective elements likely enhanced local precipitation rates as they moved across the region.

MODIS 6.7 µm water vapor, 11.0 µm IR, and visible channel

GOES-13 visible images on the following day (18 December, below) showed that extensive snow cover remained across much of the Desert Southwest, while some parts of the snow cover were seen to melt during the daytime hours. In extreme southern Nevada, note that there appeared to be very little snow on the ground in the northern portion of the Las Vegas Valley — Nellis Air Force Base in North Las Vegas (station identifier KLSV) and McCarran International Airport (station identifier KLAS) looked to be relatively snow-free, while Henderson (KHND) located just to the southeast still had enough snow on the ground to appear brighter white on the visible imagery. Up to 8 inches of snow accumulation was reported in the Henderson area — the Henderson Airport reported moderate snow for a time, with surface visibility reduce to 1/4 mile.

GOES-13 visible images

A comparison of AWIPS images of the MODIS visible and the near-IR “snow/ice” channel (below) confirms the presence of and the areal coverage of snow cover — snow and ice (along with water in oceans and lakes) are strong absorbers at the 2.1 µm wavelength, so they appear as darker features on the “snow/ice” image (in contrast to supercooled water droplet  clouds, which appear as brighter white features). Note the even darker appearance on the MODIS snow/ice image in the Henderson area (just southeast of KLAS), where higher amounts of snow fell. A darker signal is also apparent on the snow/ice image in the Barstow-Dagget (KDAG) and Edwards Air Force Base (KEDW) areas — the center of the storm circulation moved directly over that particular region, which may have helped to enhance local precipitation rates.

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

19 December Update: 250-meter resolution MODIS true color and false color imagery from the SSEC MODIS Today site (below) showed a stunning view of the area from Las Vegas, Nevada…to Lake Mead/Lake Mojave along the Nevada/Arizona border…to the Grand Canyon in Arizona, where significant snow cover still remained in many areas.

MODIS true color and false color images

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MODIS fog/stratus product and 11.0 µm IR images

Even though very cold arctic air had invaded much of the north-central US  (minimum temperatures on the morning of 15 December were -33º F at Havre, Montana and -28º F at Bottineau, North Dakota), the deeper man-made lakes (created by dams) along the Missouri River remained unfrozen on 16 December 2008. AWIPS images of the MODIS fog/stratus product and the 11.0 µm IR window (above) revealed long plumes of supercooled water droplet clouds (MODIS Cloud Phase product) streaming eastward from the relatively warm lakes — the cloud plumes were enhanced with yellow to orange colors on the fog/stratus product image, and the warm lakes were enhanced with yellow to orange colors on the IR window image.

GOES-12 10.7 µm IR images (below) showed the evolution of these “lake-effect cloud plumes” during the night-time and early morning hours on 16 December. While winds at the surface were fairly light, the winds higher aloft (at the 925 hPa or 3000 ft level) were advecting the cloud material eastward.

GOES-12 10.7 µm IR images

250-meter resolution MODIS true color and false color Red/Green/Blue (RGB) imagery from the SSEC MODIS Today site (below) showed a closer view of Fort Peck Lake in northeastern Montana and Lake Sakakawea in western North Dakota on the previous day (15 December). Small plumes of  lake-effect clouds could be seen beginning to stream southeastward off the unfrozen lakes at that time — these supercooled water droplet clouds exhibited a brighter white appearance on the false color images, in contrast to the cyan snow-covered ground.

MODIS true color and false color images (Fort Peck Lake, Montana)

MODIS true color and false color images (Lake Sakakawea, North Dakota)

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