GOES sounder « CIMSS Satellite Blog

Moore, Oklahoma tornado

May 20th, 2013

GOES-15 (left) and GOES-13 (right) 0.63 µm visible channel images (click image to play animation)

A devastating tornado struck Moore, Oklahoma just after 20:00 UTC or 3:00 PM local time on 20 May 2013, causing extensive (EF4 to EF5) damage and at least 24 fatalities. McIDAS images of GOES-15 (GOES-West) and GOES-13 (GOES-East) 0.63 µm visible channel data (above; click image to play animation; also available as a QuickTime movie) showed the line of rapidly-developing thunderstorms over southern and central Oklahoma during the early afternoon hours — Moore is located about halfway between Oklahoma City (OKC) and Norman (OUN). Earlier in the day the GOES-13 satellite had been placed into Rapid Scan Operations (RSO) mode (providing images as frequently as every 5-10 minutes), while the GOES-15 satellite was placed into Super Rapid Scan Operations (SRSO) mode (providing bursts of imagery at 1-minute intervals) after 20:15 UTC. According to the preliminary NWS damage survey, the tornado began around 19:45 UTC just west of Newcastle, and ended around 20:35 UTC just east of Moore.

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

An AWIPS comparison of 1-km resolution Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images about an hour before the tornado arrived in Moore (above) revealed the presence of shadowing from overshooting tops and cloud-top IR brightness temperatures as cold as -68º C. About 30 minutes prior to the Moore tornado, a comparison of 1-km resolution Aqua MODIS 0.65 µm visible channel and 11.0 µm IR channel images (below) again indicated signatures of vigorous overshooting tops, with cloud-top IR temperatures as cold as -76º C.

Aqua MODIS 0.65 µm visible channel and 11.0 µm IR channel images

Comparisons of the 1-km resolution VIIRS 11.45 µm IR and MODIS 11.0 µm IR images with their corresponding 4-km resolution GOES-13 10.7 µm IR images (below) demonstrated the value of higher spatial resolution to aid in the earlier and more accurate detection of the cold cloud-top IR brightness temperatures values associated with these rapidly-developing convective cells. There were significant differences in the magnitude of the coldest cloud-top IR brightness temperatures with the more northerly cell that spawned the Moore tornado: -68 C on VIIRS vs -51 C on GOES, and -76 C on MODIS vs -62 C on GOES. The northwestward shift in the location of features on the GOES-13 images was due to parallax.

Comparison of 1-km resolution VIIRS 11.45 µm IR image and corresponding 4-km resolution GOES-13 10.7 µm IR image

Comparison of 1-km resolution MODIS 11.0 µm IR image and corresponding 4-km resolution GOES-13 10.7 µm IR image

A 250-meter resolution Aqua MODIS true-color Red/Green/Blue (RGB) image from the SSEC MODIS Today site (below; viewed using Google Earth) shows a closer view of the northernmost cell that produced the Moore tornado, along with hail as large as 3.25 inches in diameter (SPC storm reports).

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

GOES-13 sounder Convective Available Potential Energy (CAPE) derived product images (below; click image to play animation) showed how the atmosphere rapidly destabilized during the day, with CAPE values in excess of 5000 J/kg (lighter purple color enhancement) at 18:00 UTC east of the stationary frontal boundary just prior to convective development.

GOES-13 sounder CAPE derived product images (click image to play animation)

Posted in GOES sounder, GOES-13, GOES-15, Google Earth, MODIS, Red/Green/Blue (RGB) images, Severe convection, Suomi NPP, VIIRS | No Comments »

Tornado outbreak in the Dallas/Ft. Worth area in north Texas

May 15th, 2013

GOES-15 (left) and GOES-13 (right) 0.63 µm visible channel images (click image to play animation)

An outbreak of tornadoes across the Dallas/Ft. Worth area in north Texas on 15 May 2013 produced up to 16 tornadoes (NWS summary) which were responsible for 6 fatalities. Hail as large as 4.0 inches in diameter and a wind gust as high as 80 mph also accompanied these severe thunderstorms (SPC storm reports). A McIDAS image comparison of GOES-15 (GOES-West) and GOES-13 (GOES-East) 0.63 µm visible channel data (above; click image to play animation) showed the rapid development of convection across the north Texas region, with the storms exhibiting a number of overshooting tops. The locations of Granbury (G) and Cleburne (C) were noted on the images, where EF-4 and EF-3 tornado damage occurred.

A similar comparison of GOES-15 (GOES-West) and GOES-13 (GOES-East) 10.7 µm IR channel images (below; click image to play animation) showed the cold cloud top IR brightness temperatures associated with these storms, which were as cold as -63 C (darker red color enhancement) in the vicinity of Granbury and Cleburne around the time of the tornadoes.

GOES-15 (left) and GOES-13 (right) 10.7 µm IR channel images (click image to play animation)

GOES-13 sounder Lifted Index derived product images (click image to play animation)

These storms developed along an axis of instability and moisture that was located to the east of a dryline that was bulging eastward across north Texas — the GOES-13 sounder Lifted Index (LI) derived product images (above; click image to play animation) revealed LI values as low as -12.4 C (dark purple color enhancement) at 23:00 UTC, and the GOES-13 sounder Total Precipitable Water (TPW) derived product images (below; click image to play animation) showed that TPW values were as high as 46.7 mm or 1.84 inches (darker red color enhancement) at 22:00 UTC. METAR surface reports are plotted on the sounder images (Granbury is station identifier KGDJ, and Cleburne is station identifier KCPT).

GOES-13 sounder Total Precipitable Water derived product images (click image to play animation)

Posted in GOES sounder, GOES-13, GOES-15, Severe convection | No Comments »

Convective Downbursts and Heatbursts in Wisconsin

May 15th, 2013

GOES-13 Sounder Derived Lifted Index (click image to play animation)

Strong convection in the late afternoon/early evening produced wind damage and heat bursts over southern Wisconsin late in the day on May 14, 2013 in a region where severe convection was not considered likely. GOES Sounder data did an excellent job of depicting the instability that developed in the late afternoon. The animation above shows strong destabilization starting shortly after 1800 UTC, and persisting as the convection moved through southern Wisconsin.

GOES-13 Sounder Derived Lifted Index

The instability associated with this convective event was very localized, and easily slipped in between the radiosonde stations. This is therefore another example of the benefit of the GOES Sounder DPI products: Not only do they provide hour-by-hour coverage, so that an evolving situation can be monitored, but they can show mesoscale features that are poorly sampled by conventional radiosonde data. The above image shows the 2346 UTC 14 May GOES Sounder DPI LI over the upper midwest; superimposed upon the image are the Lifted Indices computed from radiosondes and the LI computed from the GFS model. The strongest instability is not well sampled by the radiosonde network.

GOES-13 Sounder Derived CAPE

Convective Available Potential Energy (CAPE) can also be used to diagnose the potential for convection. In regions where CAPE values are large, convection can grow explosively. The AWIPS screen capture of CAPE computed from the sounder, above, shows values exceeding 4000 J/kg even after the convection has passed!

GOES-13 Visible (0.63 µm) Imagery (click image to play animation)

Visible imagery from GOES-13, above, shows the development of the convection as it moves into the area of diagnosed instability. The Microburst Windspeed Potential Index (MWPI) predicts maximum wind gusts that might occur given the thermal profiles associated with developing convection. Attributes that promote downbursts are steep mid-level lapse rates (to enhance convective instability) and abundant dry air (to enhance evaporative cooling). The two animations below (created using McIDAS-V and this bundle) show a maximum in MWPI (with values near 50 — the relationship between MWPI and convective gusts is here) developing over southwest WI as the convection develops. (Data are from the Rapid Refresh model run at 2200 UTC on Tuesday 14 May). The animation of model soundings over Madison (bottom) indicates strong destabilization and mid-level drying, two components that enhance the potential for microbursts. (McIDAS-V animations courtesy of Ken Pryor, NOAA/NESDIS)

Microbust Windspeed Potential Index (MWPI) from 2200 UTC 14 May-0100 UTC 15 May over Wisconsin. Data from Rapid Refresh Model

Rapid Refresh Model Soundings over Madison, WI from 2200 UTC 14 May-0100 UTC 15 May over Wisconsin

GOES Sounder DPI products are available here. YouTube videos of the convection, obtained from the cameras on the roof of SSEC, are available here (looking east) and here (looking north).

Posted in General interpretation, GOES sounder, GOES-13, McIDAS-V, Severe convection | No Comments »