GOES-11 10.7 µm InfraRed (IR) images

A strong thunderstorm which produced heavy rain and frequent lightning was apparently a factor in triggering a power blackout that affected the Hawaiian island of Oahu for at least 12 hours, beginning on the evening of 26 December 2008 — in fact, this was the first time all of Oahu had lost power since October 2006, when a 6.7 magnitude earthquake shook the Hawaiian Islands and knocked out power on Oahu and parts of other islands for up to two days. GOES-11 10.7 µm IR images (above) showed the rapid development — and the subsequent rapid dissipation — of this thunderstorm over Oahu (the island located at the center of the images), which formed around 04:00 UTC on 27 December (6 PM local time on 26 December). The IR cloud top brightness temperatures quickly cooled to a minimum value of -45º C (violet color enhancement) at 04:30 UTC, but then cloud top temperatures increased to values warmer than -40º C as the storm moved northwestward away from the island of Oahu by 06:00 UTC.

An upper-level low had been located to the east of the Hawaiian Islands for several days, and GOES-11 6.7 µm water vapor images (below) showed that this low moved slowly westward during the 25-27 December period. Also note the roll-up of smaller cyclonic “vorticies” along the northern edge of the moisture field of the upper low — CIMSS water vapor winds products indicated that these vorticies were forming in an environment of low wind shear that existed over the northern periphery of the low (and the wind shear tendency product showed that shear had been decreasing over that region during the previous 24 hours).

GOES-11 6.7 µm water vapor images

An AWIPS image of the CIMSS MIMIC Total Precipitable Water product (below) indicated that TPW values were certainly not as high over the Hawaiian Islands as those seen farther to the south in the region of the Inter-Tropical Convergence Zone (ITCZ), but PW values in excess of 40 mm (green to yellow color enhancement) were in place as the upper low moved westward across the region. Over the Big Island of Hawaii, several locations had received more than 10 inches of rainfall in 24 hours, with Waiakea Uka reporting 13.15 inches (and about a foot of snow fell at the higher elevations of Mauna Kea and Mauna Loa).

MIMIC Total Precipitable Water (TPW)

In advance of the arrival of the higher TPW values associated with the upper-level low, a pocket of dry air had been moving southwestward across the Hawaiian Islands on 25 December. It is interesting to note that GOES-11 water vapor images (below, with the map overlay removed) revealed the presence of “standing waves” due to the strong northeasterly winds interacting with the high terrain of the island chain.

GOES-11 6.7 µm water vapor images (with map overlay removed)

The GOES-11 water vapor channel weighting functions (below) showed that the mid-tropospheric dry air present over Hilo, Hawaii at 12:00 UTC on 25 December had the effect of shifting the peak of the water vapor weighting function downward, allowing features at a lower altitude to be resolved on the water vapor imagery (compared to what would be viewed at that location if a slightly cooler but more moist “US Standard Atmosphere” were in place).

GOES-11 water vapor channel weighting functions

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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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