McIDAS-V « CIMSS Satellite Blog

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 »

Baroclinic leaf and conveyor belt satellite signatures

January 17th, 2013

MODIS 0.65 µm visible channel, 11.0 µm IR channel, and 6.7 µm water vapor channel images

A comparison of AWIPS images of 1-km resolution MODIS 0.65 µm visible, 11.0 µm IR, and 6.7 µm water vapor channel data (above) showed a textbook example of a “baroclinic leaf” satellite signature associated with the large storm affecting much of the eastern US on 17 January 2013. The baroclinic leaf represents a region of ascending air that originates at low levels on the warm side of the primary surface cold front (18 UTC surface analysis).

4-km resolution GOES-13 6.5 µm water vapor channel images (below; click image to play animation) showed the development several important satellite signatures: (1) the baroclinic leaf; (2) the primary warm conveyor belt;, (3) the cold conveyor belt (which was helping to produce snow across parts of northern Mississippi and Alabama); and (4) a secondary warm conveyor belt after about 19 UTC. For additional information on conveyor belts, see this blog post from January 2011.

GOES-13 6.5 µm water vapor channel images (click image to play animation)

A McIDAS-V representation of the GOES-13 (GOES-East) water vapor image brightness temperatures as a topographical surface (below; click image to play animation; also available as a QuickTime movie) helps to visualize the descending intrusion of dry air (which exhibited warm brightness temperatures, yellow to orange color enhancement) and the ascending streams of moist air (which exhibited blue to white to green colors) within the warm conveyor belt and baroclinic leaf structures.

GOES-13 6.5 µm water vapor images (click image to play animation)

Another McIDAS-V visualization (below; click image to play animation) shows the 3-dimensional structure of the various jet streams (cyan isosurface of 50 meters per second or higher winds) and the increasing values and ascending height of moisture (mixing ratio) within the primary warm conveyor belt as the cross section slice is moved from south to north. McIDAS-V images courtesy of Joleen Feltz and Mike Hiley (CIMSS).

GOES-13 water vapor image with Rapid Refresh model fields of wind speed and mixing ratio (click image to play animation)

Early in the day, a SIGMET was issued (below) to outline an area of risk for severe turbulence due to wind shear near the axis of the strong jet stream associated with this developing system.

GOES-13 6.5 µm water vapor image with outline of Turbulence SIGMET and Pilot reports of turbulence

===== 18 January Update =====

A comparison of AWIPS images of Suomi NPP VIIRS 0.64 µm visible channel and the corresponding VIIRS false-color Red/Green/Blue (RGB) image (below) aided in the discrimination of the resulting snow cover from the storm (shades of red) versus clouds (shades of white).

Suomi NPP VIIRS 0.64 µm visible channel and False-color Red/Green/Blue (RGB) images

Posted in Aviation, General interpretation, GOES-13, McIDAS-V, MODIS, Red/Green/Blue (RGB) images, Suomi NPP, VIIRS, Winter weather | No Comments »

Super Typhoon Bopha

December 3rd, 2012

Suomi NPP VIIRS 0.64 µm visible and 11.45 µm IR images

Super Typhoon Bopha reached peak intensity (ADT plot | Advisory text) just before making landfall in the island of Mindanao in the Philippines on 03 December 2012. Earlier in the day, a comparison of McIDAS-X images of 375-meter resolution Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel data (above) revealed detailed patterns of cloud top wave structure: (1) the formation of “transverse bands” oriented perpendicular to the flow (which is fairly common in strong tropical cyclones), and (2) an arc-shaped gravity wave train in the northwest quadrant, which was likely propagating outward, away from the storm center. There were also a number of convective overshooting tops which exhibited IR brightness temperatures of -90 to -95º C (yellow enhancement).

MTSAT-1R 10.8 µm IR images (click image to play animation)

McIDAS-X images of MTSAT-1R 10.8 µm IR channel images (above; click image to play animation) showed Super Typhoon Bopha as the eye made landfall around 20 UTC or 4 AM local time. Media reports indicated that there were as many as 270 fatalities as a result of flooding, mudslides, and falling trees.

A few hours prior to landfall, a comparison of McIDAS-V images of Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR data (below; images courtesy of William Straka, CIMSS) again showed a signature of gravity waves propagating outward from the storm center — at this time (17:09 UTC or 1:09 AM local time) these gravity waves could be seen in all four quadrants of the storm top. The eye was not entirely cloud-free, with the Day/Night Band image showing moonlight being reflected off of low-level stratus near the ocean surface.

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel images

During the 01-03 December period, the MIMIC or Morphed Integrated Microwave Imagery at CIMSS product (below; click image to play animation) showed that Bopha experienced multiple eyewall replacement cycles as it moved south of the island of Palau (where it produced a wind gust of 70 mph at Koror) and toward the Philippines.

Morphed Integrated Microwave Imagery at CIMSS (click image to play animation)

Bopha had an early storm track (below) that was unusually close to the Equator — in fact, the storm was classified as a typhoon at a latitude of 3.8º N on 30 November, making it the closest typhoon formation to the Equator on record for the West Pacific Basin.