Largest US hailstone on record in central South Dakota

July 23rd, 2010 |
GOES-13 (top) and GOES-15 (bottom) 10.7 µm IR images

GOES-13 (top) and GOES-15 (bottom) 10.7 µm IR images

McIDAS images of GOES-13 and GOES-15 10.7 µm IR images (above) showed the development of severe thunderstorms that produced very large hail, tornadoes, and damaging surface winds (SPC storm reports) in central South Dakota on 23 July 2010. This storm produced the largest US hailstone on record: 8 inch diameter, 18.6 inch circumference, 1.9375 pound weight — photos of the record-setting largest hailstone were taken by staff from the Aberdeen, South Dakota NWS forecast office. The coldest cloud top IR brightness temperatures were -71º C (darker black color enhancement) at 23:25 and 23:32 UTC. Since the GOES-13 satellite had been placed into Rapid Scan Operations (RSO), images were available as often as every 5-10 minutes (as opposed to every 15 minutes via the routine image scan schedule on GOES-15).

The corresponding GOES-13 and GOES-15 0.63 µm visible channel images (below) displayed a well-defined storm top anvil with distinct overshooting tops (GOES-13 visible images only: Animated GIF). Prior to convective development, the appearance of the quasi-stationary low-level parallel cloud bands suggests that there was strong warm air advection into the region from the southwest (HPC surface forecast).

GOES-13 (top) and GOES-15 (bottom) 0.63 µm visible images

GOES-13 (top) and GOES-15 (bottom) 0.63 µm visible images

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GOES-13 Sounder Total Precipitable Water (TPW) product

GOES-13 Sounder Total Precipitable Water (TPW) product

AWIPS images of the GOES-13 Sounder Total Precipitable Water (above) and Lifted Index (below) depicted a broad axis of moisture and instability that extended northwestward into central South Dakota on that day.

GOES-13 Sounder Lifted Index (LI) product

GOES-13 Sounder Lifted Index (LI) product

A comparison of the 1-km resolution GOS-13 0.63 µm visible image and the 4-km resolution GOES-13 10.7 µm IR image at 22:45 UTC (around the time of a report of 85 mph surface winds) is seen below. The apparent offset between the location of the overshooting top and the location of the surface wind gust is due in part to parallax error (a result of the large viewing angle from the GOES-13 satellite, which is positioned over the Equator at 75º West longitude).

GOES-13 visible and IR images at 22:45 UTC (near the time of a 85 mph wind gust)

GOES-13 visible and IR images at 22:45 UTC (near the time of a 85 mph wind gust)

A comparison of the 1-km resolution 0.63 µm GOES-13 visible image and the 4-km resolution 10.7 µm IR image at 23:10 UTC (around the time of a report of “softball size” 4.25 inch diameter hail) is shown below.

GOES-13 visible and IR images at 23:10 UTC (near the time of 4.25 inch diameter hail)

GOES-13 visible and IR images at 23:10 UTC (near the time of 4.25 inch diameter hail)

As noted above, the coldest cloud top IR brightness temperatures observed for this storm were -71º C — according to the rawinsonde profile data from Rapid City, South Dakota (below) this temperature corresponded to an altitude of around 55,000 feet or 16,800 meters.

Rawinsonde profile from Rapid City SD at 00 UTC on 24 July

Rawinsonde profile from Rapid City SD at 00 UTC on 24 July

Tropical Storm Bonnie downgraded to a Tropical Depression

July 23rd, 2010 |
GOES-13  0.63 µm visible images

GOES-13 0.63 µm visible images

GOES-13 0.63 µm visible images (above) and GOES-13 10.7 µm IR images (below) from the CIMSS Tropical Cyclones site showed Tropical Storm Bonnie crossing southern Florida on 23 July 2010.

GIES-13 10.7 µm IR images

GIES-13 10.7 µm IR images

Bonnie was encountering increasing amounts of southeasterly deep layer (850-200 hPa) wind shear (below), which was acting to displace the strongest convection to the north and northwest of the low-level center of the tropical cyclone.

GOES-13 IR image + Deep layer wind shear

GOES-13 IR image + Deep layer wind shear

Hourly Atmospheric Motion Vectors (AMVs) produced using GOES-13 and Meteosat-9 data (below) showed that Bonnie was being steered northwestward by the flow between a strong ridge over the southeastern US and an upper level low over the western Gulf of Mexico.

Hourly GOES-13 + Meteosat-9 water vapor winds

Hourly GOES-13 + Meteosat-9 water vapor winds

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MODIS 0.65 µm visible + 11.0 µm IR images

MODIS 0.65 µm visible + 11.0 µm IR images

AWIPS images of 1-km resolution visible and IR channel data from MODIS (above) and POES AVHRR (below) show Bonnie as it moved across the Florida peninsula and weakened from a Tropical Storm to a Tropical Depression.

AVHRR 0.63 µm visible + 10.8 µm IR images

AVHRR 0.63 µm visible + 10.8 µm IR images

Severe turbulence causes injuries to passengers and diverts aircraft

July 20th, 2010 |
United Airlines Flight 967 flight track diversion (courtesy of FlightAware.com)

United Airlines Flight 967 flight track diversion (courtesy of FlightAware.com)

On 20 July 2010, United Airlines Flight 967 en route from Washington Dulles to Los Angeles encountered severe turbulence over the central US, and had to divert and land at Denver to medically treat nearly 30 passengers who suffered significant injuries. The flight track diversion is shown above (courtesy of FlightAware.com).

AWIPS images of 4-km resolution GOES-13 10.7 µm IR channel data (below) and GOES-13 6.5 µm water vapor channel data revealed large clusters of rapidly-developing thunderstorms over Kansas and Missouri during the afternoon and evening hours. The coldest GOES-13 cloud top IR brightness temperature was -81º C (violet color enhancement) at 22:45 UTC. However, it is unclear of the exact location of the turbulence encounter, since AWIPS plotted a SEVERE TURB report from UAL967 at Flight Level 34,000 feet over both Missouri and Kansas. Some media reports suggest that the event occurred over southwestern Missouri.

GOES-13 10.7 µm IR images + Pilot reports of turbulence

GOES-13 10.7 µm IR images + Pilot reports of turbulence

These strong thunderstorms were developing along a surface trough axis just south of a stationary frontal boundary, where the GOES-13 Sounder CAPE product indicated that the air mass was quite unstable. According to the SPC Storm Reports, there were a number of damaging wind reports associated with these thunderstorms, including surface wind gusts to 70 mph in Missouri and 80 mph in Kansas.

A comparison of 1-km resolution POES AVHRR 10.8 µm IR and 0.63 µm visible images at 22:25 UTC (below) showed cloud top IR brightness temperatures as cold as -88º C over Missouri and -90º C over Kansas (darker violet color enhancement). The visible image revealed tell-tale shadows of overshooting tops from intense updrafts.

POES AVHRR 10.8 µm IR image + 0.63 µm visible image

POES AVHRR 10.8 µm IR image + 0.63 µm visible image

1-km resolution GOES-13 0.63 µm visible channel images (below) also showed a number of overshooting tops associated with these thunderstorms. The rawinsonde report from Springfield, Missouri indicated a maximum vertical velocity of 73 meters per second!

GOES-13 0.63 µm visible channel images + Pilot reports of turbulence

GOES-13 0.63 µm visible channel images + Pilot reports of turbulence

A closer view using McIDAS images of 1-km resolution GOES-15 and GOES-13 0.63 µm visible channel data (below) also shows the times of the aircraft positios as it approached the southeastern edge of the thunderstorm anvil.

GOES-15 (left) and GOES-13 (right) visible channel images (with aircraft position times)

GOES-15 (left) and GOES-13 (right) visible channel images (with aircraft position times)

Examples of two of the SNAAP Convective Storm Monitoring and Nowcasting products (below) demonstrate the ability to use satellite data to help detect overshooting tops that might pose increased risks for turbulence.

SNAAP Overshooting Top + Turbulence Risk satellite products

SNAAP Overshooting Top + Turbulence Risk satellite products

An example of the NCAR Turbulence Detection Algorithm (below) showed the potential for turbulence at 36,000 feet across a large portion of Kansas and Missouri.

NCAR Turbulence Detection Algorithm

NCAR Turbulence Detection Algorithm

For additional satellite image analysis of this case, see the VISIT Meteorological Interpretation Blog.

Was there a waterspout/tornado in western Puerto Rico?

July 17th, 2010 |
GOES-13 0.63 µm visible images

GOES-13 0.63 µm visible images

There were numerous media reports of a waterspout/tornado that moved inland near Mayaguez (station identifier TJMZ) in far western Puerto Rico around 16:45 UTC (12:45 pm local time) on 17 July 2010, causing tree and structural damage along with multiple injuries. However, due to a lack of visual confirmation, the NWS is not classifying this as a waterspout or a tornado event. McIDAS images of 1-km resolution GOES-13 0.63 µm visible channel data (above) did show a fast-moving outflow boundary / gust front moving from east to west across the island, causing wind gusts in excess of 50 mph at a number of locations. A strong thunderstorm then developed along this fast-moving boundary as it reached the far western end of the Puerto Rico.

Surface analyses from the NWS Ocean Prediction Center (below) depicted a westward-moving tropical wave  along the InterTropical Convergence Zone (ITCZ) that may have played a role in providing forcing for the convection that produced the initial  outflow boundary / gust front that raced westward across Puerto Rico.

NWS Ocean Prediction Center surface analysis

NWS Ocean Prediction Center surface analysis

The corresponding 4-km resolution GOES-13 10.7 µm IR images (below) revealed that cloud top IR brightness temperatures were as cold as -68º C (black color enhancement) at 17:45 UTC as the thunderstorm continued to grow and intensify.

GOES-13 10.7 µm IR images

GOES-13 10.7 µm IR images

A closer look using 1-km resolution Aqua MODIS 11.0 µm IR imagery at 17:44 UTC (below) showed what appeared to be a subtle “enhanced-v” storm top signature associated with this thunderstorm. The color enhancement is slightly different than that shown with the GOES-13 IR imagery, but the coldest/warmest IR brightnes temperatures within the enhanced-v signature were -75º C / -67º C respectively, making for a delta-T of 8º C. Enhanced-v storm top signatures over the continental US can exhibit delta-T values as large as 20-30º C, but to see an enhanced-v signature (even a subtle one) over Puerto Rico is rather unusual.

MODIS 11.0 µm IR image

MODIS 11.0 µm IR image

Related information:

Radar animation

YouTube damage video