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 (1900-2015 UTC) GOES-13 visible image animation as the convection started is shown below. Click here for a longer animation (1300 – 2345 UTC); Click here for a faster version of the 1300-2345 UTC animation.

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)

GOES-14 SRSOR: Thunderstorm development over Kentucky

May 22nd, 2014
GOES-13 DPI Convective Available Potential Energy (CAPE) on May 22, times as indicated (click to play animation)

GOES-13 DPI Convective Available Potential Energy (CAPE) on May 22, times as indicated (click to play animation)

GOES-14 operations in SRSOR mode deliver the ability to monitor convective development at very short time-scales. A good example of this occurred over the lower Ohio Valley/western Kentucky on May 22nd. The animation of GOES-13 Sounder Derived Product Imagery of CAPE (above) and of Lifted Index (1300 and 1700 UTC) showed considerable instability waiting to be released.

GOES-14 SRSOR animations can be used to monitor the evolving cumulus field in the search for the tower that will break the cap (Nashville, TN/Lincoln IL Soundings from 1200 UTC). The animation below shows visible imagery from 1800 UTC through 2011 UTC, at which time the convection has developed. Initial convection dissipates, but eventually develops along the Ohio River in western Kentucky (cumulus clouds continue to grow/dissipate over the Mississippi River valley throughout the animation).

GOES-14 Visible Imagery (0.62 µm) on May 22, times as indicated (click to play animation)

GOES-14 Visible Imagery (0.62 µm) on May 22, times as indicated (click to play animation)

By 1900 UTC, convective development over the lower Ohio Valley is vigorous enough that Cloud-Top Cooling algorithm from CIMSS (below) has flagged growing clouds, with values exceeding 20º C/15 minutes.

Instanteous Cloud-Top Cooling computed from GOES-13 at 1900 UTC 22 May 2014 (click to enlarge)

Instanteous Cloud-Top Cooling computed from GOES-13 at 1900 UTC 22 May 2014 (click to enlarge)

How does the NOAA/CIMSS ProbSevere model  then change with time as the convection intensifies? The 1904 and 1906 UTC ProbSevere products, toggled below, shows values increasing from 49% to 54% as Satellite Growth rates at 1900 UTC are incorporated at 1906 UTC. ProbSevere values then dropped (1912 UTC, 1922 UTC) as MRMS MESH decreased.

NOAA/CIMSS ProbSevere from 1904 and 1906 UTC on 22 May 2014 (click to enlarge)

NOAA/CIMSS ProbSevere from 1904 and 1906 UTC on 22 May 2014 (click to enlarge)

By 1936 UTC, ProbSevere has again increased above 50%, in two regions where MRMS has MESH sizes over 0.50″. MESH values are equivalent in the two regions, as are environmental values, but higher satellite predictors associated with the smaller eastern radar object drive higher ProbSevere values there.

NOAA/CIMSS ProbSevere from 1936 UTC on 22 May 2014 (click to enlarge)

NOAA/CIMSS ProbSevere from 1936 UTC on 22 May 2014 (click to enlarge)

The animation below shows the evolution of NOAA/CIMSS ProbSevere from 1948 UTC through 2000 UTC, with focus on a second cell that was warned. NOAA/CIMSS ProbSevere is designed to give an estimate of when severe weather might initially occur. Severe weather was not reported in Kentucky with these storms (link); however, observations of severe weather did occur as the storms moved near Nashville.

NOAA/CIMSS ProbSevere from 1948-2000 UTC on 22 May 2014 (click to animate)

NOAA/CIMSS ProbSevere from 1948-2000 UTC on 22 May 2014 (click to animate)

Related Hazardous Weather Testbed blog posts on this event can be found here, here, and here.

Severe thunderstorms in northwestern Kansas

August 5th, 2013
GOES-13 0.63 µm visible channel images with overshooting top detection icons (click image to play animation)

GOES-13 0.63 µm visible channel images with overshooting top detection icons (click image to play animation)

 

AWIPS images of 1-km resolution GOES-13 0.63 µm visible channel images with automated overshooting top detection icons (above; click image to play animation) showed the development of a large mesoscale convective system across northwestern Kansas during the afternoon hours on 05 August 2013. Note that the surface air temperature at Goodland, Kansas (KGLD) dropped from 91º F at 19 UTC to 69º F at 20 UTC (with southeasterly winds gusting to 34 knots).

4-km resolution GOES-13 10.7 µm IR channel images with automated overshooting top detection icons (below; click image to play animation) revealed the formation of a very broad and well-defined “enhanced-V” storm top signature, with cloud-top IR brightness temperatures becoming as cold as -80º C at 23:15 UTC. Overshooting top detection began after 19:45 UTC, once GOES-13 cloud-top IR brightness temperatures became -71º C or colder.

GOES-13 10.7 µm IR channel images with overshooting top detection icons (click image to play animation)

GOES-13 10.7 µm IR channel images with overshooting top detection icons (click image to play animation)

During the early stages of convective development, GOES-13 10.7 µm IR images combined with 15-minute cloud top cooling rates (below) showed the development of significant cloud top cooling rates along the Colorado/Kansas border area at 18:15 UTC (prior to the formation of weak, brief landspout tornadoes just northeast of Goodland, Kansas during the 18:28-18:40 UTC period) — a maximum cloud top cooling rate of 35.3º C in 15 minutes was detected at 18:45 UTC.

GOES-13 10.7 µm IR channel images with Cloud Top Cooling Rates

GOES-13 10.7 µm IR channel images with Cloud Top Cooling Rates

A comparison of 1-km resolution Soumi NPP VIIRS 11.45 µm IR channel and 4.-km resolution GOES-13 10.7 µm images (below) demonstrated the ability of higher spatial resolution VIIRS data to detect much colder IR brightness temperatures associated with the more vigorous overshooting tops (-82º C on VIIRS, vs -71º C on GOES). In addition, a northwestward GOES image parallax shift was seen, due to to the large viewing angle of the GOES-13 satellite positioned at 75º W longitude. Shortly after the time of these images, this storm produced hail of 1.0 inch in diameter at 20:11, 20:21, and 20:54 UTC (SPC storm reports)

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

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

Comparisons of 1-km resolution POES AVHRR Cloud Top Temperature and Cloud Top Height products at 20:21 UTC (above) and 21:16 UTC (below) showed that the coldest cloud top temperatures (-85º C and -87º C, respectively) were seen in regions where the maximum cloud top height values were generally around 15 km. It is likely that the most vigorous overshooting tops associated with the coldest cloud top temperature values were as much as 2-3 km higher than this mean 15 km thunderstorm anvil cloud top height. Conversely, cloud top height values were around 13 km in the “warm wake” region immediately downwind of the coldest overshooting tops.

Convective outflow boundary initiates new convection over Kansas

July 31st, 2013
GOES-13 0.63 µm visible channel images (click image to play animation)

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

AWIPS images of 1-km resolution GOES-13 0.63 µm visible channel data (above; click image to play animation) showed an undular bore marking a surface-based convective outflow boundary which formed over southwestern Nebraska early in the day on 31 July 2013 — this outflow boundary then propagated southwestward during the day and acted as a focus for the formation of severe thunderstorms over southwestern Kansas later that afternoon (SPC storm reports).

The southwestward-propagating outflow boundary / undular bore feature was also seen on 4-km resolution GOES-13 6.5 µm water vapor channel imagery (below; click image to play animation).

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

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

The GOES-13 imager 6.5 µm water vapor channel weighting function calculated using the 12 UTC rawinsonde data from Dodge City, Kansas (below) indicated that the weighting function peaked much lower in the atmosphere (around 500 hpa) than normal — this allowed a thermal signal (albeit a faint one) of the boundary layer convective outflow boundary cloud features to be seen on the water vapor imagery.

GOES-13 water vapor channel weighting function plot (using Dodge City, Kansas rawinsonde data)

GOES-13 water vapor channel weighting function plot (using Dodge City, Kansas rawinsonde data)

A good view of the undular bore (which was trailing the leading edge of the convective outflow boundary) could be seen on a comparison of 1-km resolution MODIS 0.64 µm visible channel and 11.0 µm IR channel images at 17:05 UTC (below).

MODIS 0.64 µm visible channel and 11.0 µm IR channel images

MODIS 0.64 µm visible channel and 11.0 µm IR channel images

New thunderstorms formed along the old convective outflow boundary (as it encountered increasing instability across southwestern Kansas during the afternoon hours), as seen on 1-km resolution Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images (below). This storm was producing 1-inch diameter hail and wind gusts of 50-60 mph.

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel mages, with SPC reports of hail

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel mages, with SPC reports of hail

A comparison of the 1-km resolution Suomi NPP VIIRS 11.45 µm IR channel image with the corresponding 4-km resolution GOES-13 10.7 µm IR channel image (below) displayed an unusually large 30-degree difference between the coldest cloud-top IR brightness temperatures of the northernmost of the newly-formed thunderstorms in Kansas (-92º C on VIIRS, vs -62º C on GOES).

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

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