Suomi NPP VIIRS 11.45 µm IR image + 0.64 µm visible channel image

A cluster of thunderstorms developed over the interior of Alaska during the afternoon hours on 04 June 2012, and moved westward across the region — one of the stronger storms produced half-inch size hail in the Fairbanks area. AWIPS images of 375-meter resolution (projected onto a 1-km resolution AWIPS grid) Suomi NPP VIIRS 11.45 µm IR and 0.64 µm visible channel images (above) showed these storms before they moved over Fairbanks (station identifier PAFA); the coldest cloud-top IR brightness temperatures were -64º C, and the larger storm actually exhibited an “enhanced-V” signature (with a cold/warm thermal couplet differrence of 11º C).

A Fairbanks National Weather Service Special Weather Statement mentioned that the tops of the thunderstorms were around 40,000 feet. That height, along with the minimum VIIRS IR brightness temperature of -64º C suggests that the highest thunderstorm tops were overshooting the tropopause that was seen on a plot of the 00 UTC Fairbanks rawinsonde data (below).

Fairbanks, Alaska rawinsonde data (00 UTC 05 June)

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GOES-13 10.7 µm IR images + 0.63 µm visible images (click image to play animation)

A large Mesoscale Convective System (MCS) developed over far northeastern Oklahoma during the pre-dawn hours on 04 June 2012, which eventually produced a Mesoscale Convective Vortex (MCV) that moved into northwestern Arkansas the following morning. AWIPS images of 4-km resolution GOES-13 10.7 µm IR images (at night) followed by 1-km resolution  GOES-13 0.63 µm visible channel images during the day (above) showed the large nocturnal canopy of cold clouds (with cloud-top IR brightness temperatures as cold as -76º C at 05:01 UTC) — then the dissipating convection revealed the cyclonic circulation of the MCV during the late morning hours. As the atmosphere destabilized with daytime heating, new thunderstorms were seen to develop in the vicinity of the MCV as it moved toward Little Rock, Arkansas (station identifier KLIT).

A comparison of a 1-km resolution MODIS 11.0 µm IR image with the corresponding 4-km resolution GOES-13 10.7 µm IR image at 08:15 UTC or 3:15 AM local time (below) demonstrated that finer-scale cloud top details (such as subtle anvil-top gravity waves) were apparent on the higher resolution MODIS image.  Note that the satellite features are displaced slightly to the northwest on the GOES-13 IR images — this is due to parallax error resulting from the large viewing angle from the GOES-East satellite.

MODIS 11.0 µm IR image + GOES-13 10.7 µm IR image

These anvil-top gravity waves were even more evident on a comparison of 1-km resolution Suomi NPP VIIRS 11.45 µm IR channel and 0.7 µm Day/Night Band (DNB) images at 08:42 UTC or 3:42 AM local time (below). A full moon provided excellent illumination of the thunderstorm cloud top, allowing an very good night-time view of the subtle overshooting top and gravity wave structures (just as they might be seen on a daytime visible image). In addition, note that the city lights of the Wichita, Kansas area could be seen through the thin veil of cloud top cirrus along the northwestern edge of the storm.

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

As the MCV was approaching the Little Rock area, the CIMSS Cloud Top Cooling Rate product detected CTC rates in excess of 20º C per 15 minutes, just as the thunderstorms began to produce their first cloud-to-ground lightning strike at 17:45 UTC (below). This cluster of thunderstorms was responsible for a few reports of hail and damaging winds as it continued to move southeastward across Arkansas during the afternoon hours (SPC storm reports).

GOES-13 0.63 µm visible images + Cloud Top Cooling Rate + Cloud-to-ground lightning strikes

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GOES-13/GOES-15 Sounder DPI Total Precipitable Water (click image to play animation)

MCVs typically are sustained in regions of low shear and abundant moisture. A plot of 850-500 mb shear from the NAM for 1800 UTC on 4 June show very low values of vertical wind shear in place over Arkansas. GOES Sounder DPI Total Precipitable water (the loop above) shows that the MCV developed in an axis of enhanced moisture. The blended TPW product (a product that blends together GOES Sounder and GPS measurements of precipitable water) shows an axis of values at or above 100% of normal through the mid-south where the MCV formed.

A visible image loop (every half-hour) from June 4 2012 that shows the evolution of the system is below.

GOES-13 0.63 µm Visible Imagery (click image to play animation)

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GOES-15 (left) and GOES-13 (right) 0.63 µm visible images (click image to play animation)

The White Rock Fire — likely caused by a lightning strike — began in far eastern Nevada (near the Nevada/Utah border) late in the day on 01 June 2012. The fire quickly grew in size on 02 June — and a comparison of GOES-15 (GOES-West) and GOES-13 (GOES-East) 0.63 µm visible channel images (above; click image to play animation) offered another good example of how the viewing ange of different satellites can help to highlight different features associated with a large wildfire.

An abundance of dry fuels helped this to become a very hot fire, which produced bursts of pyrocumulus clouds which rose high above the top of the thick smoke plume. With the afternoon sun in the west, the view from the GOES-West satellite yeilded bright illumination of the overshooting pyrocumulus towers, while the view from GOES-East gave a better view of the long shadows cast by the pyrocumulus towers. In addition, with a favorable forward scattering angle later in the day, GOES-East also provided a better depiction of the areal coverage of the airborne smoke (03 June / 01:00 UTC image comparison).

Sadly, an air tanker carrying fire retardant to help contain this wildfire crashed on the afternoon of 03 June, killing both crewmembers.

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GOES Sounder DPI Lifted Index 1600 UTC on May 30 2012

Satellite descriptors of the atmosphere over the central High Plains on May 30th suggested an atmosphere ripe for convection. For example, the GOES Sounder DPI Lifted Index showed an axis of instability from central Oklahoma to northwest Kansas, with widespread values (yellows, reds, purples) at or below -4. (The unstable area overlaps nicely with the slight risk for the day diagnosed for the day by the Storm Prediction Center). The NearCasting product (below, and available on-line here) suggests that convective instability will persist over southern Nebraska and extend southward into Oklahoma for most of the day.

GOES-13 NearCast product (click image to play animation)

GOES-13 Visible Imagery and UW Cloud-Top Cooling Rate (click image to play animation)

Given this type of environment, what can cloud-top cooling rate tell you? The Cloud-Top Cooling Rate is a satellite-based product that diagnoses how quickly the growing convective towers are cooling with time, and strong cooling means rapid vertical convective growth. The strongest cooling is where the strongest convective growth is occurring, and that cooling is well-correlated with the subsequent development of NEXRAD signatures (MESH, maximum VIL, reflectivity at -10 C, etc.) The loop above shows GOES-13 visible imagery with the cloud-top cooling rate superimposed. (Real-time imagery of the cloud-top cooling rate product is available here) The The cloud-top cooling rate product highlights a persistently and quickly growing convective feature near McCook, Nebraska before and shortly after 1700 UTC. By 1800 UTC, that feature is a severe thunderstorm warned for high winds and hail.

The UW Cloud-Top Cooling Rate product is being evaluated at the Hazardous Weather Testbed taking place this month. At the HWT Blog, there are many examples of using the product in concert with knowledge of the synoptic and mesoscale conditions to anticipate strong thunderstorm development.

SPC storm reports show that the system with the strong Cloud-Top Cooling Rate subsequently produced 1-inch hail near Holdrege.

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