Thunderstorms producing very large hail near Paris, France

June 9th, 2014 |
Meteosat-10 0.7 µm visible channel images (click to play animation)

Meteosat-10 0.7 µm visible channel images (click to play animation)

Severe thunderstorms developed over parts of France on 09 June 2014, some of which produced very large hail (photos). EUMETSAT Meteosat-10 1-km resolution 0.7 µm visible channel images (above; click image to play animation; also available as an MP4 movie file) and 3-km resolution 10.8 µm IR channel images (below; click image to play animation; also available as an MP4 movie file) revealed some interesting details in the thunderstorm structure: a narrow flanking line was seen on the visible imagery, and the storms exhibited well-defined “enhanced-V” signatures and thermal couplets on the IR imagery. For reference, the asterisk marks the location of the Charles De Gaulle Airport in Paris.

Meteosat-10 10.8 µm IR channel images (click to play animation)

Meteosat-10 10.8 µm IR channel images (click to play animation)

The Suomi NPP satellite overpass of the region occurred around 12:15 UTC, allowing the VIIRS instrument to provide a 375-meter resolution true-color Red/Green/Blue (RGB) image of the developing thunderstorms (below, visualized using the SSEC RealEarth web map server).

Suomi NPP VIIRS true-color RGB image

Suomi NPP VIIRS true-color RGB image

Severe Mesoscale Convective System over the central US

June 5th, 2014 |
GOES-13 10.7 µm IR channel images (click to play animation)

GOES-13 10.7 µm IR channel images (click to play animation)

AWIPS images of 4-km resolution GOES-13 10.7 µm IR channel data with overlays of SPC storm reports (above; click image to play animation; also available as an MP4 movie file) showed the growth of a large mesoscale convective system (MCS) that formed over eastern Colorado late in the day on 04 June 2014 and became very intense as it moved east-southeastward across Kansas during the overnight hours on 05 June 2014.  Although severe weather reports were not as widespread after daybreak on 05 June, the MCS still produced large hail and damaging winds across Missouri into the Mississippi River Valley (SPC storm reports: 04 June | 05 June). Note the cluster of high wind reports across northeastern Kansas into northwestern Missouri after about 12:00 UTC — these were due to the formation of a “wake low” in the rear portion of the exiting MCS.

At 08:46 UTC (3:46 AM local time), a comparison of 375-meter resolution Suomi NPP VIIRS 11.45 µm IR channel and 750-meter resolution Day/Night Band images (below) revealed cloud-top IR brightness temperatures as cold as -90º C (darker violet color enhancement), along with subtle cloud-top gravity waves propagating radially outward away from the central core of intense overshooting tops. On the Day/Night Band (DNB) image, numerous bright white streaks indicated portions of the cloud top that were illuminated by intense lightning activity. Although the Moon was in the Waxing Gibbous phase at nearly 50% of full, it had set a few hours earlier, limiting its “visible image at night” capability. Another item of interest on the DNB image was the presence of larger bands of mesospheric airglow waves propagating southwestward away from the storm, seen over southwestern Kansas into far northeastern New Mexico.

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

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

Via Twitter, the NWS CWSU in Oakland provided the corresponding 08:45 UTC GOES-13 IR image with overlays of radar-based VIL, echo tops, and lightning (below). Note that the maximum radar-based echo top was 63,000 feet.

GOES-13 IR image with overlays of VIL, lightning, and echo tops (courtesy of NWS CWSU Oakland)

GOES-13 IR image with overlays of VIL, lightning, and echo tops (courtesy of NWS CWSU Oakland)

Not surprisingly, there were numerous overshooting tops (OT) and thermal couplets (TC) associated with this severe MCS, as seen in this animation (where OT detections are blue, and TC detection are red). Icons of Automated Overshooting Top Detections (green) are plotted on GOES-13 10.7 µm IR channel images (below; click image to play animation; also available as an MP4 movie file). Of particular interest was the image at 10:00 UTC or 5:00 AM local time, when a report of hail of 3.0 inches in diameter and estimated winds of 60-70 mph beneath a cluster of overshooting top detection icons (the easternmost storm in central Kansas). Jim LaDue of the NWS WDTB in Norman OK provided this image showing Maximum Expected Size of Hail (MESH) of 2.0 inches for that particular supercell thunderstorm.

GOES-13 10.7 µm IR images, with Automated Overshooting Top Detection icons (click to play animation)

GOES-13 10.7 µm IR images, with Automated Overshooting Top Detection icons (click to play animation)

1-km resolution GOES-13 0.63 µm visible channel images after sunrise (below; click image to play animation; also available as an MP4 movie file) revealed a vivid display of transverse banding along the northwestern periphery of the MCS (primarily over Nebraska). This transverse banding is a satellite signature indicating a high potential for turbulence.

GOES-13 0.63 µm visible channel images (click to play animation)

GOES-13 0.63 µm visible channel images (click to play animation)

A comparison of GOES-13 1-km resolution 0.63 µm visible channel and 4-km resolution 10.7 µm IR channel images at 12:30 UTC (below) showed that portions of the transverse banding signature were resolved differently by the 2 different images.

GOES-13 0.63 µm visible channel and 10.7 µm IR channel images at 12:30 UTC

GOES-13 0.63 µm visible channel and 10.7 µm IR channel images at 12:30 UTC

Offshore mesovortex affecting the inland penetration of marine stratus along the California coast

June 2nd, 2014 |
GOES-15 0.63 µm visible channel images (click to play animation)

GOES-15 0.63 µm visible channel images (click to play animation)

On 02 June 2014, McIDAS images of 1-km resolution GOES-15 0.63 µm visible channel data (above; click image to play animation) revealed the presence of a cyclonic mesoscale vortex in the vicinity of Point Reyes along the California coast, which appeared to be playing a role in enhancing the inland penetration of marine fog/stratus into areas such as the San Francisco Bay region just south of the mesovortex.

An AWIPS image of 375-meter resolution (projected onto a 1-km AWIPS grid) Suomi NPP VIIRS 0.64 µm visible channel data at 21:07 UTC (below) included overlays of surface station and buoy reports, along with MADIS 1-hour satellite-derived atmospheric motion vectors within the 1050-900 mb layer at 21 UTC. The satellite cloud-tracked winds appeared to be picking up on the cyclonic circulation of the mesovortex. At this particular time, winds at San Francisco (station identifier KSFO) were southwesterly gusting to 23 knots.

Suomi NPP VIIRS 0.64 µm visible channel image, with surface and buoy observations and 1-hour MADIS satellite winds

Suomi NPP VIIRS 0.64 µm visible channel image, with surface and buoy observations and 1-hour MADIS satellite winds

A time series of surface observation at San Francisco International Airport (below) showed the increase in layered stratus clouds (with ceilings of 1000 to 1500 feet) after the southwesterly winds began to increase around 19 UTC.

Time series of surface observations at San Francisco International Airport

Time series of surface observations at San Francisco International Airport

AWIPS images of the GOES-R Cloud Thickness product — with the GOES-R algorithm for Fog and Low Stratus products applied to GOES-15 data — indicated that the thickness of the stratus clouds moving inland across the San Francisco Bay area was only about 500 feet (below; click image to play animation). The thicker stratus clouds with depths of 1000-3000 feet remained off the coast of California.

GOES-15 Cloud Thickness product (click to play animation)

GOES-15 Cloud Thickness product (click to play animation)

The corresponding GOES-15 Marginal Visual Flight Rules (MVFR) product (below; click image to play animation) showed that MVFR probability values were generally below 50-60% in the San Francisco Bay area, with much higher probabilities existing within the offshore marine boundary layer stratus cloud field.

GOES-15 Marginal Visual Flight Rules (MVFR) Probability product (click to play animation)

GOES-15 Marginal Visual Flight Rules (MVFR) Probability product (click to play animation)