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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GOES-11 6.7 µm water vapor channel images (click image to play animation)

An animation of 8-km resolution GOES-11 6.7 µm “water vapor channel” images (above; click image to play animation) revealed a mid-latitude cyclone over the eastern North Pacific Ocean on 28 January – 29 January 2011 — and this cyclone was reaching the occluded stage of its life cycle, as seen by the classic water vapor image signature of dry air wrapping into the center of the circulation.

AWIPS images of the 10-km resolution GOES-11 sounder Total Column Ozone product (below) showed there were elevated levels of ozone (350 to 400 Dobson Units, green to red color enhancement) associated with this occluding cyclone.

GOES-11 sounder Total Column Ozone images

An AWIPS comparison of the 1-km resolution MODIS 6.7 µm water vapor image with the corresponding 8-km resolution GOES-11 6.7 µm water vapor image  (below) demonstrated the advantage of higher spatial resolution for visualizing some of the finer details of the cyclone structure.

MODIS 6.7 µm and GOES-11 6.7 µm water vapor images

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MODIS 6.7 µm water vapor image

The third major storm  of the 2010/2011 winter season  (storm #1 | storm #2) impacted much of the Mid-Atlantic and Northeast states on 26 January 2011 – 27 January 2011. An AWIPS image  of MODIS 6.7 µm water vapor channel data at 18:28 UTC  (above) revealed a large and complex dry slot, with convective elements developing ahead of the leading edge of the dry slot across Virginia. In addition, to the east of the dry slot over the western Atlantic Ocean a well-defined packet of high altitude “transverse bands” was seen (close-up view) which was forming in the right entrance region of an upper level jet streak.

On a POES AVHRR false-color Red/Green/Blue (RGB) image at that same time (below), high cloud features appeared brighter white, with low clouds taking on a slight yellow tint.

POES AVHRR Red/Green/Blue (RGB) false color image

An animation of GOES-13 10.7 µm IR images (below; click image to play animation) showed the development of the transverse banding cloud structures — the bands were oriented perpendicular to the southwesterly high-altitude wind flow over that region. This transverse banding pattern is a cloud signature that is often associated with areas of turbulence — and in this case there were two pilot reports of moderate turbulence at altitudes of 34,000 feet and 36,000 feet.

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

A comparison of a GOES-13 10.7 µm IR image with the corresponding MODIS 11.0 µm IR image (below) demonstrated the advantage of higher spatial resolution, with the fine transverse band structure more apparent on the 1-km resolution MODIS image. The coldest IR brightness temperatures within the bands on the MODIS image were -58º C (red color enhancement).

MODIS 11.0 µm IR + GOES-13 10.7 µm IR images

A number of cloud-to-ground lightning strikes were associated with the convective elements that had formed over Virginia (below), ahead of the leading edge of the dry slot that was seen on water vapor imagery. Thundersnow was reported across a wide portion of the Mid-Atlantic and Northeast states, with snowfall rates as high as 1-4 inches per hour at some locations.

MODIS 11.0 µm IR image + lightning strikes + METAR surface reports

=========== 27 JANUARY UPDATE ===========

MIMIC Total Precipitable Water product (click image to play animation)

This storm was not particularly intense in terms of a low central pressure or strong winds, but it was able to tap a significant plume of deep moisture (in excess of 30-40 mm or 1.2-1.6 inches) from the Gulf of Mexico and the Caribbean, as can be seen on AWIPS images of the MIMIC Total Precipitable Water (TPW) product (above; click image to play animation) and the Blended Total Precipitable Water product (below; click image to play animation). This contributed to the high snowfall totals at many locations (Weather Underground blog| WeatherMatrix blog).

Blended Total Precipitable Water product (click image to play animation)

Parts of this plume of moisture represented TPW values in excess of 200% of normal (below; click image to play animation).

Percent of Normal TPW product (click image to play animation)

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