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.

Severe Weather over the Southern Plains

March 25th, 2015

The Storm Prediction Center in Norman issued a Moderate Risk of severe weather over the Southern Plains on March 25, 2015. Convective products were available in AWIPS to help monitor the evolution of this event.

Cloud-Top Cooling (10.7 µm imagery) for GOES-13, 1907-2000 UTC on 25 March 2015 (Click to enlarge)

Cloud-Top Cooling (10.7 µm imagery) for GOES-13, 1907-2000 UTC on 25 March 2015 (click to enlarge)

For example, the Cloud-Top Cooling product, above, monitored rapid development of convection over eastern Arkansas just between 1915 and 2000 UTC (the 10.7µm imagery for about the same time is here). Cloud-Top Cooling depicts where the strongest vertical cloud growth is occurring and is most useful for the initiation of the convection (or subsequent re-energized growth). The NOAA/CIMSS ProbSevere product, below, can also monitor the evolution of the storm from initial growth through maturity and beyond.

NOAA/CIMSS ProbSevere Product, 1900-2028 UTC on 25 March 2015 (Click to animate)

NOAA/CIMSS ProbSevere Product, 1900-2028 UTC on 25 March 2015 (click to animate)

The NOAA/CIMSS ProbSevere product gauges the likelihood of a storm first producing severe weather (of any kind) in the next 60 minutes. It combines information about the environment (Most Unstable CAPE, Environmental Shear) from the Rapid Refresh Model, about the growing cloud (Vertical Growth Rate as a percentage of the troposphere per minute and Glaciation Rate, also as a percentage per minute), and Maximum Expected Hail Size (MESH) from the MRMS. The storm over east-central OK, crossing over the border of Arkansas, showed a ProbSevere value of 45% at 2004 UTC and of 87% at 2006 UTC; 1-inch hail was reported with this storm (in Roland, OK) at 2005 UTC, and a Severe Thunderstorm warning was issued at 2026 UTC. AWIPS-2 imagery that includes readouts for this storm are below.

NOAA/CIMSS ProbSevere product, 2000-2026 UTC on 25 March 2015 (Click to animate)

NOAA/CIMSS ProbSevere product, 2000-2026 UTC on 25 March 2015 (click to animate)

Suomi NPP overflew the region shortly before convection developed, and the NUCAPS soundings in the clear pre-convective air described the thermodynamics of the environment. The location of the NUCAPS soundings are shown below, overlain on top of the Suomi NPP VIIRS visible imagery. The Red and Yellow stars show two sounding locations to be discussed. It’s helpful when using NUCAPS soundings to know surface values of temperature and dewpoint, because it can be helpful to adjust the NUCAPS soundings so that surface values are more in line with observations as reported by METARS. Accordingly, the VIIRS visible image with surface METARS plotted is here. Dewpoints in eastern OK and western AR are close to 60 F/15 C.

NUCAPS Sounding Locations at 1833 UTC on 25 March 2015;  Red and Yellow Stars indicate sounding locations described below (Click to enlarge)

NUCAPS Sounding Locations at 1833 UTC on 25 March 2015; Red and Yellow Stars indicate sounding locations described below (Click to enlarge)

The soundings from the two starred sites are below. In both cases, the original sounding and a sounding that has been modified by increasing the lowest dewpoint by 2 C are shown. Most Unstable CAPE for the plotted soundings (original and modified) are indicated. NUCAPS Soundings suggest greater instability over west-central/northwest Arkansas than over southwestern Arkansas.

NUCAPS Sounding at the red star location, both original and modified (Click to enlarge)

NUCAPS Sounding at the red star location, both original and modified (Click to enlarge)

NUCAPS Sounding at the yellow star location, both original and modified (Click to enlarge)

NUCAPS Sounding at the yellow star location, both original and modified (Click to enlarge)

A short GOES-13 visible image animation as the convection started is shown below.

GOES-13 Visible 0.65 µm Imagery (Click to animate)

GOES-13 Visible 0.65 µm Imagery (Click to animate)

[Added: This severe weather outbreak caused the first tornado fatality of 2015, in Tulsa County, OK. Satellite imagery of those storms can be found here. ProbSevere product animations from 2024 to 2230 UTC on 25 March and also from 2206 UTC on 25 March to 0012 UTC on 26 March are shown below]

NOAA/CIMSS ProbSevere product, 2024-2230 UTC on 25 March 2015 (Click to animate)

NOAA/CIMSS ProbSevere product, 2024-2230 UTC on 25 March 2015 (click to animate)

NOAA/CIMSS ProbSevere product, 2206 UTC on 25 March 2015 to 0012 UTC on 26 March 2012 (Click to animate)

NOAA/CIMSS ProbSevere product, 2206 UTC on 25 March 2015 to 0012 UTC on 26 March 2015 (click to animate)

Sea fog along the northeast Florida coast

March 21st, 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)

GOES-13 (GOES-East) 0.63 µm visible channel images (above; click to play animation) showed a patch of sea fog just off the coast of northeastern Florida on 21 March 2015. As daytime inland heating increased, a sea breeze circulation began to draw some of the offshore sea fog toward the coast.

A closer view is provided by a Suomi NPP VIIRS true-color Red/Green/Blue (RGB) image at 18:08 UTC (below), visualized using the SSEC RealEarth web map server site. The surface visibility at New Smyrna Beach was reduced to 1 mile at the time.

Suomi NPP VIIRS true-color image

Suomi NPP VIIRS true-color image

A web camera image at 18:17 UTC or 2:17 PM local time (below) showed the dramatic reduction in visibility as the dense sea fog moved inland at Dunlawton Beach (near Daytona Beach).

Dunlawton Beach webcam image

Dunlawton Beach webcam image

A comparison of Suomi NPP VIIRS 0.64 µm visible channel, 3.74 µm shortwave IR channel, and 11.45 µm longwave IR images (below) showed that the patch of sea fog exhibited a strong signal on the shortwave IR image (due to the efficient reflection of incoming solar radiation by the spherical water droplets), but no signal at all on the longwave IR image (since the temperature of the sea fog feature was nearly identical to that of the surrounding ocean waters).

Suomi NPP VIIRS 0.64 µm visible channel, 3.74 µm shortwave IR channel, and 11.45 µm longwaveIR channel images

Suomi NPP VIIRS 0.64 µm visible channel, 3.74 µm shortwave IR channel, and 11.45 µm longwaveIR channel images

The easterly to northeasterly onshore flow along the coast (enhanced by the sea breeze circulation) was well-depicted by the 18 UTC Real-Time Mesoscale Analysis (RTMA) surface winds (below).

Suomi NPP VIIRS 0.64 µm visible channel image, with RTMA surface winds

Suomi NPP VIIRS 0.64 µm visible channel image, with RTMA surface winds

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