Fatal severe weather outbreak in Oklahoma

March 25th, 2015
GOES-13 0.63 µm visible channel images (click to play animation)

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

Severe thunderstorms developed in the vicinity of a quasi-stationary frontal boundary which stretched from northeastern Oklahoma into northern Arkansas and southern Missouri late in the day on 25 March 2015. A plot of the SPC storm reports shows that these storms produced widespread large hail, damaging winds, and tornadoes —  including the first tornado-related fatality of 2015 at a trailer home park near Sand Springs, Oklahoma (just west/southwest of Tulsa). Storm reports also included hail as large as 4.25 inches in diameter, and wind gusts as high as 80 mph. 1-km resolution GOES-13 (GOES-East) 0.63 µm visible channel images (above; click image to play animation) showed the development of numerous thunderstorms across the region, some of which grew to be very large discrete supercells late in the afternoon and toward sunset. The tell-tale signature of cloud-top shadows from small-scale “overshooting tops” could be seen with many of these storms, indicating the presence of vigorous updrafts which penetrated the thunderstorm top (and likely the tropopause). Also note the presence of parallel bands of stable wave clouds over parts of northeastern Kansas and northwestern Arkansas: these clouds highlighted areas where boundary layer warm air advection was over-running shallow pockets of cool, stable air north frontal boundary.

The corresponding 4-km resolution GOES-13 10.7 µm IR channel images (below; click image to play animation) revealed very cold cloud-top IR brightness temperatures (as cold as -71º C, dark black color enhancement), along with the formation of a well-defined Enhanced-V/Thermal Couplet (EV/TC) signature with the storm that produced large hail, damaging winds, and the fatal tornado southwest of Tulsa (station identifier KTUL). The EV/TC signature was first evident on the 22:00 UTC IR image, with cold/warm thermal couplet values of -65º/-53º C; the maximum thermal couplet spread was at 22:25 UTC, with -71º/-52º C, after which time the minimum IR brightness temperatures of the overshooting tops then began a warming trend: -67º C at 22:30 UTC, and -64º C at 22:37 UTC (suggesting a collapse of the vigorous updraft and overshooting top). Note that the storm-top EV/TC signature was displaced to the northwest of the surface hail/wind/tornado storm reports just west of Tulsa, due to parallax resulting from the large satellite viewing angle of GOES-East (which is positioned over the Equator at 75º W longitude). In addition, see the bottom of this blog post for examples of the NOAA/CIMSS ProbSevere product applied to these storms.

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

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

Automated overshooting top (OT) detection icons (small yellow thunderstorm symbols) are also plotted on the GOES-13 IR images. The initial OT detections began at 20:15 UTC, over the general area where there was later a report of 1.0-inch diameter hail at 20:40 UTC. A comparison of the 4-km resolution GOES-13 10.7 µm IR image at 20:15 UTC with a 375-meter (projected onto a 1-km AWIPS grid) Suomi NPP VIIRS 11.45 µm IR image at 20:16 UTC (below) demonstrates (1) the advantage of improved spatial resolution for detecting the minimum cloud-top IR brightness temperature of thunderstorm overshooting tops (-60º C with GOES, vs -75º C with VIIRS), and (2) minimal parallax effect with polar-orbiting satellite imagery such as that from Suomi NPP, for more accurate geolocation of such potentially important storm features.

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

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

A comparison of 1-km resolution POES AVHRR 0.86 µm visible channel and 12.0 µm IR channel images (below) provided a detailed view of the storms at 22:54 UTC, which were electrically very active at that time (producing over 1900 cloud-to-ground lightning strikes in a 15-minute period). The coldest cloud-top IR brightness temperature was -77º C, located just southwest of Tulsa — this was likely the overshooting top associated with the supercell thunderstorm that produced the fatal tornado.

POES AVHRR 12.0 µm IR channel and 0.86 µm visible channel images, with METAR surface reports, lightning, and SPC storm reports

POES AVHRR 12.0 µm IR channel and 0.86 µm visible channel images, with METAR surface reports, lightning, and SPC storm reports

10-km resolution GOES-13 sounder Convective Available Potential Energy (CAPE) derived product images (below; click image to play animation) showed the rapid trend in destabilization of the air mass along and south of the frontal boundary, with CAPE values eventually exceeding 4300 J/kg (purple color enhancement).

GOES-13 sounder Convective Available Potential Energy (CAPE) derived product images (click to play animaton)

GOES-13 sounder Convective Available Potential Energy (CAPE) derived product images (click to play animaton)

10-km resolution GOES-13 sounder Total Precipitable Water (TPW) derived product images (below; click image to play animation) indicated that TPW values of 30 mm or 1.18 inch and greater (yellow enhancement) were present along and south the frontal boundary in northeastern Oklahoma.

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

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

At 19:19 UTC, the 4-km resolution MODIS Total Precipitable Water derived product image (below) showed a plume of moisture with TPW values as high as 41.7 mm or 1.64 inches (red enhancement) moving toward the Tulsa area.

MODIS 0.65 um visible channel and Total Precipitable Water derived product images

MODIS 0.65 um visible channel and Total Precipitable Water derived product images

Additional information about this event can be found at the NWS Tulsa and United States Tornadoes sites.

Solar Eclipse as seen from GOES-13 and NOAA-18

March 20th, 2015
GOES-13 0.65 µm visible channel images (click to enlarge)

GOES-13 0.65 µm visible channel images (click to enlarge)

A total solar eclipse occurred on 20 March before sunrise over the USA. Its appearance on visible imagery from Meteosat-10 was documented here and here. Did GOES-13 also view this event? The imagery above, half-hourly from 0845 through 0945 UTC, shows evidence of darkening (the lunar shadow) initially near 40 N, then a very dark slice in the atmosphere at 0915 UTC and a hint of darkness at 0945 UTC at the extreme limb of the satellite, beyond Iceland. Note also how the terminator in the image, the boundary between day and night, is parallel to longitudinal lines. Happy Equinox!

The shadow of totality was also captured on a NOAA-18 AVHRR 0.86 µm visible channel image at 0907 UTC (below). The shadow extends out over the Atlantic Ocean well to the northeast of Newfoundland.

NOAA-18 AVHRR 0.86 µm visible channel image

NOAA-18 AVHRR 0.86 µm visible channel image

Test of GOES-15 (GOES-West) Rapid Scan Operations (RSO) sectors for the Alaska Region

March 17th, 2015
GOES-15

GOES-15 “Sitka” RSO Sector

During a 4-hour period on 17 March 2015, NOAA/NESDIS conducted a test of two special GOES-15 (GOES-West) Rapid Scan Operations (RSO) sectors for the Alaska Region. From 16:00 to 18:00 UTC, the test was conducted for the “Sitka” sector (above) — and GOES-15 0.63 µm visible channel images over a portion of that sector (below; click image to play animation) showed the circulation of a mid-latitude cyclone that was producing gale force winds in the eastern portion of the Gulf of Alaska (IR image with surface analysis), as well as clusters of deep convection which were forming along an occluded front approaching from the south.

GOES-15 0.63 µm visible images -

GOES-15 0.63 µm visible images – “Sitka” sector (click to play animation)

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GOES-15

GOES-15 “TPARC” RSO sector

Then from 18:00 to 20:00 UTC, the RSO test was conducted for the “TPARC” sector (above) — and GOES-15 0.63 µm visible channel images (below; click image to play animation) showed the circulation of two cyclones south of the Aleutian Islands, in addition to a large “banner cloud” and a few mountain waves which had formed downwind (to the north) of the rugged terrain of the Alaska Peninsula and the Aleutian Islands. GOES-15 IR brightness temperatures associated with the banner cloud were as cold as -65 C, which according to the nearby Bethel, Alaska rawinsonde data at 12 UTC corresponded to an altitude of around 27,700 feet (IR image with Bethel Skew-T and surface analysis).

GOES-15 0.63 µm visible channel images -

GOES-15 0.63 µm visible channel images – “TPARC” sector (click to play animation)

Regarding the Alaska Peninsula banner cloud seen on the GOES-15 visible images, a sequence of Terra/Aqua MODIS 11.0 µm and Suomi NPP VIIRS 11.45 µm IR images (below; click image to play animation) showed the evolution of this feature several hours before and after the RSO test. There were a few pilot reports of moderate turbulence, at altitudes as high as 36,000 feet – and some of these pilot reports specifically mentioned “MNT WAVE” in their remarks.

Suomi NPP VIIRS 11.45 µm IR image (click to play animation of VIIRS and MODIS IR images)

Suomi NPP VIIRS 11.45 µm IR image (click to play animation of VIIRS and MODIS IR images)

The CLAVR-x POES AVHRR Cloud Top Height product (below; click image to play animation) indicated that the banner cloud reached heights of 9 km (darker green color enhancement).

POES AVHRR Cloud Top Height product (click to play animation)

POES AVHRR Cloud Top Height product (click to play animation)

Mountain wave clouds over southern California

December 21st, 2014
GOES-15 6.5 µm water vapor channel images click to play animation)

GOES-15 6.5 µm water vapor channel images click to play animation)

AWIPS images of 4-km resolution resolution GOES-15 (GOES-West) 6.5 µm water vapor channel data (above; click image to play animation) showed the development of a patch of mountain wave or “lee wave” clouds immediately downwind of the higher elevations of the western Transverse Ranges in southern California on 21 December 2014.  These clouds developed in response to strong northerly winds interacting with the west-to-east oriented topography (12 UTC NAM 700 hPa wind and height). As seen on the plotted surface reports, at Sandberg (station identifier KSDB) the highest wind gust was 52 knots or 59 mph  at 17:42 UTC — and later in the day there also a peak wind gust of 87 mph at Whitaker Peak and 86 mph at Montcito Hills. In addition, there were isolated pilot reports of moderate turbulence in the vicinity of the mountain wave cloud at 20:21 UTC and 23:06 UTC;  farther to the east there was a pilot report of moderate to severe turbulence at 01:27 UTC.

A comparison of 1-km resolution MODIS 6.7 µm and 4-km resolution GOES-15 6.5 µm water vapor channel images around 21:00 UTC (below) demonstrated the advantage of higher spatial resolution (and the minimal parallax offset) of the polar-orbiter MODIS imagery for more accurate location of the mountain wave cloud.

MODIS 6.7 µm and GOES-15 6.5 µm water vapor channel images

MODIS 6.7 µm and GOES-15 6.5 µm water vapor channel images

At 20:42 UTC (below), the coldest 1-km resolution POES AVHRR Cloud Top Temperature value associated with the mountain wave cloud feature was -69º C (darker red color enhancement), with the highest Cloud Top Height value being 14 km or 45,900 ft (cyan color enhancement)., which is actually colder and higher than the tropopause on  the 12 UTC rawinsonde report at Vandenberg AFB. The highest elevation in the western portion of the Transverse Ranges where the mountain wave cloud formed is Mount Pinos at 8847 feet or 2697 meters, so it appears that a vertically-propagating wave developed which helped the cloud reach such a high altitude.

POES AVHRR Cloud Top Temperature and Cloud Top Height products

POES AVHRR Cloud Top Temperature and Cloud Top Height products

At 21;20 UTC, a comparison of 375-meter resolution (projected onto a 1-km resolution AWIPS grid) Suomi NPP VIIRS 0.64 µm visible channel, 3.74 µm shortwave IR channel, and 11.45 µm IR channel images (below) showed that while the coldest cloud-top 11.45 µm IR brightness temperatures were around -60º C, the 3.74 µm shortwave IR temperatures were in the +5 to +10º C range — this indicates that the mountain wave cloud was composed of very small ice particles, which were efficient reflectors of solar radiation contributing to much the warmer shortwave IR brightness temperatures.

Suomi NPP VIIRS 0.64 µm visible, 3.74 µm shortwave IR, and 11 45 µm IR channel images

Suomi NPP VIIRS 0.64 µm visible, 3.74 µm shortwave IR, and 11 45 µm IR channel images

A 375-meter resolution Suomi NPP VIIRS true-color Red/Green/Blue (RGB) image from the SSEC RealEarth web map server is shown below.

Suomi NPP VIIRS true-color image

Suomi NPP VIIRS true-color image