GOES-12 10.7 µm IR images + hail and wind reports

Severe convection developing over eastern South Dakota during the pre-dawn hours on 09 July 2009 exhibited an unusually large and well-defined “enhanced-v” storm top signature on AWIPS images of the GOES-12 10.7 µm IR channel (above) as it produced large hail (up to 2.50 inches in diameter) and damaging winds (gusting as high as 90 mph) across parts of South Dakota and extreme northeastern Nebraska.

An overlay of negative and positive cloud-to-ground lighting strikes (below) showed that this storm was producing a large amount of lightning in the vicinity of the overshooting top (near the vertex of the enhanced-v signature), but there was also a number of strikes located a fair distance to the northeast, far away from the coldest cloud tops.

GOES-12 10.7 µm IR images + cloud-to-ground lightning strikes

A comparison of the 4-km resolution GOES-12 10.7 µm IR data with 1-km resolution NOAA-15 AVHRR 10.8 µm IR data (below) demonstrated the advantage of improved spatial resolution in detecting the cloud top temperature structure of the enhanced-v signature. The coldest/warmest cloud top temperatures on the NOAA-15 IR image were -80º C / -59º C (deltaT = 21º C), compared to -68º C / -56º C (deltaT = 12º C) on the GOES-12 IR image.

4-km GOES-12 10.7 µm IR + 1-km NOAA-15 10.8 µm IR images

A NOAA-15 AVHRR Red/Green/Blue (RGB) false-color composite image (below) displayed a stunning view of the storm just after sunrise (at 11:33 UTC), about 20 minutes after it produced a wind gust to 90 mph, hail up to 1.00 inch in diameter, and brief heavy rain near Scotland in southeastern South Dakota.

Note that the overshooting top was casting a shadow onto the anvil of the storm below — and this very tall thunderstorm complex was casting an impressive shadow to the west and southwest across South Dakota and Nebraska. Also note the presence of a boundary layer gravity wave train oriented southwest-to-northeast across Nebraska, which was positioned in advance of a cold frontal boundary.

NOAA-15 AVHRR Red/Green/Blue (RGB) false color composite image

Additional radar and satellite images of this storm can be found on the AccuWeather WeatherMatrix Blog.

GOES-12 10.7 µm IR images

A cluster of thunderstorms developed over extreme northeastern Iowa and extreme southeastern Minnesota, and merged into a large Mesoscale Convective System (MCS) across southern Wisconsin during the early hours of 19 June 2009. AWIPS images of the 4-km resolution GOES-12 10.7 µm IR channel (above) displayed the rapid growth of this MCS, which was responsible for a number of reports of hail and damaging winds (SPC storm reports) along with heavy rainfall (5.60 inches was reported in Dodgeville, Wisconsin). GOES-12 IR brightness temperatures associated with this MCS were as cold as -75º C.

Even though the region was well to the north of a stationary frontal boundary, GOES-12 Sounder images (below) of the Lifted Index (LI), Convective Available Potential Energy (CAPE), and Total Precipitable Water (TPW) indicated that the pre-convective environment across much of southern Wisconsin was characterized by instability (LI values to -10º C and CAPE values to 3958 J/kg) and moisture (TPW values to 51 mm, or 2.00 inches).

GOES-12 sounder LI, CAPE, and TPW

A 1-km resolution MODIS 11.0 µm IR image at 04:11 UTC (11:11 pm local time) with an overlay of cloud-to-ground lightning strikes (below) showed the tendency for lightning strikes to cluster around the many “enhanced-v” and “cold/warm couplet” signatures on the IR image. During the 15-minute interval ending at 04:15 UTC this storm produced 881 negative lightning strikes and 158 positive lightning strikes.

MODIS 11.0 µm IR image + cloud-to-ground lightning strikes

The was a report of baseball-size hail (2.75 inch diameter) just to the northwest of Madison, Wisconsin (station identifier KMSN), which was near the coldest -80º C MODIS IR cloud top pixel (below).

MODIS 11.0 µm IR image + SPC storm reports