“Anvil plumes” associated with severe convection in NE and SD

September 22nd, 2010
GOES-13 10.7 µm IR images

GOES-13 10.7 µm IR images

Clusters of severe thunderstorms developed across parts of northeastern Nebraska and southeastern South Dakota ahead of a warm frontal boundary that was advancing northward across the region on 22 September 2010. These severe thunderstorms produced a number of reports of large hail and damaging winds. AWIPS images of GOES-13 10.7 µm IR data (above) showed that cloud top IR brightness temperatures were as cold as around -70º C (dark black enhancement) at times.

The corresponding GOES-13 3.9 µm shortwave IR images (below) revealed that a few interesting “darker plumes” developed on the cloud tops of some of the southernmost storms — this darker appearance was a signature of smaller ice crystal particles that were being ejected above the anvil top by some of the stronger thunderstorm updrafts. These smaller ice crystals were better reflectors of incident solar radiation, making them show up as warmer (darker) features on the shortwave IR images.

GOES-13 3.9 µm shortwave IR images

GOES-13 3.9 µm shortwave IR images

These darker anvil top plumes were also very evident at 16:33 UTC on 1-km resolution MODIS 3.7 µm shortwave IR imagery (below).

MODIS 3.7 µm shortwave IR image

MODIS 3.7 µm shortwave IR image

A closer view using 1-km resolution POES AVHRR 10.8 µm IR imagery at 18:56 UTC (below) displayed a well-defined “enhanced-v” signature in southeastern South Dakota (with the coldest cloud top IR brightness temperature value of -82º C, violet color enhancement) — and a large number of hail reports associated with this storm as it tracked through the area, including a report of 3.5 inch diameter hail near Vermillion, South Dakota.

POES AVHRR 10.8 µm IR image (with hail reports)

POES AVHRR 10.8 µm IR image (with hail reports)

Unusually clear September day across the interior of Alaska

September 19th, 2010
GOES-11 0.65 µm visible channel images

GOES-11 0.65 µm visible channel images

A persistent ridge of high pressure aloft was keeping the interior of Alaska unusually cloud-free, as was evident on McIDAS images of GOES-11 0.65 µm visible channel data on 19 September 2010 (above). Temperatures at many stations across the region had been averaging about 10 degrees F above normal during the previous week, with many daily high temperatures in the 60s and 70s F. On this particular day, the high temperatures ranged from 70º F (21º C) at Holy Cross (in the clear skies of the interior of southwestern Alaska) to only 37º F (+3º C) at Barter Island (beneath the stratus clouds along the northeast Arctic Coast).

The visible images showed that low stratus clouds and fog were attempting to work their way inland (southward) across the Arctic Slope region of northern Alaska. Widespread stratus clouds also covered much of the Gulf of Alaska, and was affecting some of the coastal regions in the far southern portions of the state. In addition, a smoke plume from a wildfire could also be seen drifting southwestward across the interior of Alaska later in the day.

AVHRR visible image + Cloud Type, Cloud Top Temperature, and Cloud Top Height products

AVHRR visible image + Cloud Type, Cloud Top Temperature, and Cloud Top Height products

AWIPS images of the 1-km resolution POES AVHRR visible channel data along with the corresponding Cloud Type, Cloud Top Temperature, and Cloud Top Height products (above) demonstrated how the various cloud features could be further characterized according to their type (for example, fog vs. supercooled clouds vs. cirrus clouds) along with the temperature and height of their tops.

AVHRR visible image + Cloud Type, Cloud Top Temperature, and Cloud Top Height products

AVHRR visible image + Cloud Type, Cloud Top Temperature, and Cloud Top Height products

Hail-producing thunderstorms in south-central Wisconsin

September 18th, 2010
GOES-13 10.7 µm IR images

GOES-13 10.7 µm IR images

Severe thunderstorms that developed along an advancing cold frontal boundary during the pre-dawn hours of 18 September 2010, producing hail up to 1.75 inch in diameter in south-central Wisconsin (NWS Milwaukee/Sullivan news story). AWIPS images of 4-km resolution GOES-13 10.7 µm IR channel data (above) showed the development of increasingly colder IR cloud top brightness temperatures as the storms moved over the Madison, Wisconsin area (station identifier KMSN).

A series of 1-km resolution MODIS 11.0 µm IR and POES AVHRR 10.8 µm IR images between 03:32 UTC and 10:23 UTC  (below) displayed greater detail in the cloud top brightness temperature structure as the thunderstorms moved southeastward across the region.

MODIS 11.0 µm IR + POES AVHRR 10.8 µm IR images

MODIS 11.0 µm IR + POES AVHRR 10.8 µm IR images

Large swath of wet ground in the central Plains region

September 15th, 2010
GOES-13 10.7 µm IR images

GOES-13 10.7 µm IR images

AWIPS images of 4-km resolution GOES-13 10.7 µm IR channel data (above) showed a large convective complex that developed over extreme eastern Colorado and then tracked eastward across Kansas and Nebraska during the pre-daylight hours on 15 September 2010. According to the SPC Storm Reports, this severe convection produced a few tornadoes, hail up to 1.75 inch in diameter, and surface winds gusts as high as 78 mph across Kansas.

A comparison of the 1-km resolution POES AVHRR 10.8 µm IR image with the corresponding 4-km resolution GOES-13 10.7 µm IR image (below) demonstrates the improved ability to detect such mesoscale storm top features as overshooting tops and packets of concentric gravity waves. At that particular time, the coldest AVHRR IR brightness temperature was -80º C, compared to -71º C on the GOES-13 IR image. The parallax error associated with geostationary satellite imagery was also apparent, with the slight northwestward shift of the location of the features on the GOES-13 image.

POES AVHRR 10.8 µm and GOES-13 10.7 µm IR images

POES AVHRR 10.8 µm and GOES-13 10.7 µm IR images

The AHPS 24-hour total precipitation analysis (below) indicated a large swath of substantial rainfall was produced by this convective system, which included amounts in excess of 4 inches in northern Kansas.

24-hour precipitation (ending at 12 UTC on 15 September 2010)

24-hour precipitation (ending at 12 UTC on 15 September 2010)

At 19:48 UTC, AWIPS images of 1-km resolution MODIS 0.65 µm visible channel and 3.7 µm shortwave IR data (below) revealed the very large swath of wet ground (as indicated by the lighter shades of gray on the shortwave IR image); however, little evidence of this wet ground could be seen on the visible image.

MODIS 0.65 µm visible channel and 3.7 µm shortwave IR images

MODIS 0.65 µm visible channel and 3.7 µm shortwave IR images

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MODIS 3. µm shortwave IR image + METAR surface reports

MODIS 3. µm shortwave IR image + METAR surface reports

Looking at plots of the surface METAR data (above) and the daily maximum temperatures (below), the large area of wet ground appeared to be holding surface air temperatures down a few degrees compared to adjacent sites across the region.

MODIS 3.7 µm shortwave IR image + daily maximum temperatures for 15 September

MODIS 3.7 µm shortwave IR image + daily maximum temperatures for 15 September

On a side note, it is interesting to point out that smoke from wildfires burning in the western US was concentrated along and just ahead of the cold frontal boundary that was moving across Nebraska – this was seen very clearly on a MODIS Red/Green/Blue (RGB) true color image from the SSEC MODIS Today site (below).

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

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