GOES water vapor images with pilot reports of turbulence (click image to play animation)

Strong southwesterly winds aloft interacting with the rugged terrain of the Sierra Nevada mountain range resulted in a number of pilot reports of mountain waves which were producing moderate turbulence over parts of the western US on 14 February 2011. AWIPS images of a composite of 8-km resolution GOES-11 (GOES-West) and 4-km resolution GOES-13 (GOES-East) water vapor imagery (above) revealed a classic mountain wave signature just downwind of the Sierra Nevada. The “seam” between GOES-11 and GOES-13 is fairly evident on the AWIPS water vapor image composite, mainly due to the difference in spatial resolution.

A comparison of the mountain waves on the 8-km resolution GOES-11 6.5 µm water vapor image versus the corresponding 1-km resolution Terra MODIS 6.5 µm water vapor image (below) demonstrates the clear advantage of improved spatial resolution for detecting the areal coverage of such features.

GOES water vapor image + MODIS water vapor image (with pilot reports of turbulence)

About 1.5 hours later, a similar comparison of the mountain waves on the 8-km resolution GOES-11 6.5 µm water vapor image versus the corresponding 1-km resolution Aqua MODIS 6.5 µm water vapor image can be seen below. Note that there is less “striping” (due to detector degradation) on the Aqua MODIS water vapor image — Aqua is a newer satellite , launched in 2002 (Terra was launched in 1999) .

GOES water vapor image + MODIS water vapor image (with pilot reports of turbulence)

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

McIDAS images of GOES-13 0.63 µm visible channel data (above; click image to play animation) showed the development of a batch of cumulus clouds over the central Gulf of Mexico during the day on 13 February 2011. Other features of interest on the visible imagery include the rapidly-melting snow cover over the portions of the southern Plains, and a few small smoke plumes drifting northeastward due to fires burning in some of the Gulf Coast states.

A comparison of AWIPS images of the 1-km resolution MODIS 0.65 µm visible channel and the corresponding MODIS Sea Surface Temperature (SST) product (below) indicated that this area of cumulus development was occurring over the warmer waters of the Gulf of Mexico “Loop Current”, where SST values were as warm as 78º F (darker orange color enhancement). As a seasonally cool northeasterly flow of air moved across the warmer Loop Current, enough instability was generated to lead to the formation of shallow cumulus clouds.

MODIS 0.65 µm visible image + MODIS Sea Surface Temperature product

About 3 hours later, a similar comparison of a 1-km resolution POES AVHRR 0.63 µm visible image with the corresponding POES AVHRR Sea Surface Temperature product (below) showed a few more cumulus lines forming over the northern portion of the Loop Current, with the cumulus cloud field becoming more dense in the southern portion.

POES AVHRR 0.63 µm visible image + POES AVHRR Sea Surface Temperature product

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

Following a record-setting 27 inches of snowfall in a 24-hour period on the previous day, new all-time record low temperature was set for the state of Oklahoma when Nowata dropped to -31º F (Tulsa OK Public Information Statement) on the morning of 10 February 2011. AWIPS images of 4-km resolution GOES-13 10.7 µm IR data (above; click image to play animation) showed a large region with very cold surface IR brightness temperatures (darker blue color enhancement) over the snow-covered portions of Kansas and Oklahoma. The GOES-13 IR imagery also showed a few thin bands of cirrus cloud moving eastward across the region — one could speculate as to whether these cirrus clouds may have had a small effect on briefly slowing the surface radiational cooling as they passed overhead, possibly preventing the surface air temperatures from dropping any further?

A 1-km resolution MODIS 11.0 µm IR image at 08:16 UTC (below) gave a more detailed view of the cold surface IR brightness temperatures, which were as cold as -38º C over northern Oklahoma at that time.

MODIS 11.0 µm IR image

Looking farther to the south, the 12:00 UTC surface analysis (cyan) overlaid on a GOES IR image (below) suggested that the leading edge of the cold frontal boundary associated with this outbreak of arctic air was approaching the Pacific coast of southern Mexico. About 3 hours later,  14:58 UTC  ASCAT scatterometer surface winds  (green wind vectors) indicated that the cold air had already crossed the high terrain of Mexico and and emerged as a well-defined “Tehuano wind event“ over the Gulf of Tehuantepec along the Pacific coast (hence the name “Tehuantepecer“ given to this type of strong wind event). This region was outlined as one of a “Developing Gale” on the surface analysis.

GOES IR image + ASCAT scatterometer surface winds + surface analysis

A closer view (below) showed a number of ASCAT wind vectors of 30-33 knots out over the near-shore waters of the Gulf of Tehuantepec — confirming that the cold frontal boundary had indeed emerged into the Pacific Ocean. Northerly surface winds at Ixtepec (station identifier MMIT) gusted to 45 knots later in the day.

GOES IR image + ASCAT scatterometer surface winds + surface METAR reports

McIDAS images of GOES-13 0.63 µm visible channel data (below; click image to play animation) showed the formation of distinct cloud lines that marked the edges of the emerging gap flow winds. In addition, the slightly hazy signal of blowing dust being carried offshore could be seen.

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

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GOES-13 6.5 µm water vapor imagery (click on image to play animation)

AWIPS images of GOES-13 6.5 µm water vapor channel data (above; click image to play an animated GIF; also available as a QuickTime movie) showed the evolution of the “Groundhog Day Blizzard” of 01 February – 02 February 2011. This was a particularly large storm, impacting a swath of the US over 2500 miles long and 700 miles wide with snow, sleet, and ice from New Mexico to Maine — snowfall amounts were as high as 27.0 inches at Antioch, Illinois (HPC storm summary). As the storm developed, the water vapor imagery displayed a very pronounced dry slot, along with an extensive cloud shield.

MODIS 6.7 µm water vapor image

With  higher spatial resolution (1 km) MODIS water vapor imagery, several interesting details could be seen, such as bands of convection in Texas (above) and “lee waves” within the dry slot, downwind of the areas of higher terrain on northern Arkansas and southern Missouri (below).

MODIS 6.7 µm water vapor image

One area that was hit particularly hard with heavy snow and blizzard conditions was northern Illinois (NWS Chicago summary) and southeastern Wisconsin (NWS Milwaukee summary) — in the Chicago area, the 20.1 inches of snow at O’Hare airport and 20.9 inches at Midway airport were the third largest snowfall amounts on record. Thundersnow was reported at a number of locations, where accompanying snowfall rates were several inches per hour; much of the lightning was likely in-cloud and/or cloud-to-cloud, but there were  several cloud-to-ground lightning strikes seen overlaid on GOES-13 10.7 µm IR images  (below; click image to play animation).

GOES-13 10.7 µm IR images + lightning (click image to play animation)

=========== 03 February Update ==========

In the aftermath of the winter storm, a comparison of MODIS true color and false color images from the SSEC MODIS Today site (above) showed extensive snow cover across the Upper Midwest region, along with ice forming in parts of Lake Michigan, Lake Huron, and most of Lake Erie (snow and ice appear as shades of cyan on the MODIS false color image, in contrast to supercooled water droplet clouds which are brighter white features). In fact, some movement of the ice features in the Great Lakes could be seen — especially in Lake Erie –  in a comparison of MODIS false color images from the Terra satellite overpass at 16:03 UTC and the Aqua overpass at 19:23 UTC (below), due to brisk southwesterly surface winds across the region.

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