Severe convection « CIMSS Satellite Blog

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 »

Mesoscale Convective System in the Gulf of Mexico

May 1st, 2013

Suomi NPP VIIRS 11.45 µm IR channel and 0.7 µm Day/Night Band images (with overlays of cloud-to-ground lightning strikes)

A large nocturnal mesoscale convective system (MCS) was moving eastward across the Gulf of Mexico during the pre-dawn hours on 01 May 2013. AWIPS images of Suomi NPP VIIRS 11.45 µm IR channel and 0.7 µm Day/Night Band (DNB) data with an overlay of cloud-to-ground lightning strikes (above) revealed numerous cloud-top gravity waves. In addition to providing a “visible image at night” that helped to highlight these gravity waves as well as shadows from overshooting tops, the DNB image also showed several bright “streaks” denoting cloud tops illuminated by areas of intense lightning activity. The coldest cloud top IR brightness temperatures (associated with some of the overshooting tops) were -76º C.

A Suomi NPP VIIRS 11.45 µm IR image with surface buoy reports (below) showed that there was a peak wind gust of 45 knots (52 mph) at Buoy 42003 (which occured at 06:50 UTC).

Suomi NPP VIIRS 11.45 µm IR channel image with surface buoy reports

A comparison of 1-km resolution Suomi NPP VIIRS 11.45 µm IR and 4-km resolution GOES-13 IR images (below) demonstrated the advantage of higher spatial resolution for showing the detailed cloud top structures exhibited by the MCS.

Suomi NPP VIIRS 11.45 µm IR channel and GOES-13 10.7 µm IR channel images

A great deal of lightning was associated with this MCS as it propagated eastward across the Gulf of Mexico, with the storm often producing over 1000 cloud-to-ground strikes within a 15-minute period (below; click image to play animation).