Strong convective winds over Arkansas

July 23rd, 2014 |
GOES-13 0.63 µm visible channel images (click to play animation)

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

Arkansas and surrounding states experiences strong convectively-forced winds on July 23 2014 (SPC Storm Reports for the day are shown below). The visible imagery, above, shows the merging of two convective systems: one is moving south-southeastward through eastern Kansas and one is building southwestward from the lower Ohio River Valley into northern Arkansas. (Mesoscale Discussions for this event were issued from SPC at 1656 UTC, 1827 UTC and 2001 UTC on the 23rd).

Storm Reports from 23 July 2014

Storm Reports from 23 July 2014

GOES-13 Sounder DPI Lifted Index (click to play animation)

GOES-13 Sounder DPI Lifted Index (click to play animation)

Analyses from the GOES-13 Sounder (above) showed the atmosphere into which the convective features were building to be very unstable. A large area with Lifted Indices around -10 (light red) is present; values exceed -12 (purple) at 1800 UTC. GOES Sounder DPI Analyses of CAPE (Convective Available Potential Energy, below) (from this site) likewise show strong instability at the start of the day. Convection is initially at both ends of the area of most unstable air; by 1900 UTC, the end of the animation, it has overspread the entire region of instability.

GOES Sounder CAPE (click to play animation)

GOES Sounder CAPE (click to play animation)

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

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

The GOES-13 Infrared Imagery, above, likewise shows the convective systems from Kansas and from the lower Ohio Valley merging over Arkansas.

Suomi-NPP VIIRS data were available over Arkansas on two successive passes on 23 July, at 1829 UTC and 2010 UTC, and these high-resolution infrared images show the quick development and vigor of the convection. The high resolution allowed for the detection of very cold cloud tops at 2010 UTC; minimum values were near -88ºC! Coldest GOES-13 10.7 Brightness Temperatures at 2015 UTC (not shown) were -78ºC.

Suomi NPP VIIRS 11.35 µm infrared channel images (click to enlarge)

Suomi NPP VIIRS 11.35 µm infrared channel images (click to enlarge)

The storms produced considerable lightning as well, as shown in the animation below that overlays hourly lightning strikes on top of the Suomi NPP 11.35 µm imagery: there were 5800 strikes (400 positive) in the hour ending at 1800 UTC, and 12000 strikes (800 positive) in the hour ending at 2000 UTC!

Suomi NPP 11.35 µm infrared channel imagery and Detected Lightning (click to play animation)

Suomi NPP 11.35 µm infrared channel imagery and Detected Lightning (click to play animation)

NOAA/CIMSS ProbSevere showed values from 80-95% at the leading edge of the convection as it moved southward through Arkansas. In this event, satellite data were not available as one of the ProbSevere predictors because of the widespread cirrus shield. MRMS Mesh was generally in the 3/4″ to 1-1/2″ range; that combines with model CAPE values exceeding 4000 and generous shear lead to the high ProbSevere values.

NOAA/CIMSS ProbSevere display including MRMS Base Reflectivity, 1922-2128 UTC 23 July 2013 (click to play animation)

NOAA/CIMSS ProbSevere display including MRMS Base Reflectivity, 1922-2128 UTC 23 July 2013 (click to play animation)

Overshooting Tops, such as those apparent in the 11.35 µm imagery from Suomi NPP, above, can be detected automatically in GOES-13 10.7 µm imagery. The animation of auto-detected overshooting tops, below, from this site, shows a peak in convective intensity (as measured by the number of overshoots) between 2000 and 2100 UTC on the 23rd. This image shows the daily sum of detected overshoots. There is good spatial correlation between that image and the storm reports.

Overshooting Tops Detected from GOES-13, 1545-2300 UTC 23 July 2013 (click to play animation)

Overshooting Tops Detected from GOES-13, 1545-2300 UTC 23 July 2013 (click to play animation)

Finally, CRiS/ATMS data can be used to generate soundings (NUCAPS Soundings) that are available in AWIPS II. The image below shows the spatial coverage of soundings at 2000 UTC on 23 July. The NUCAPS sounding from the easternmost column, third point south of the Oklahoma/Texas border, bottom, is shown at the bottom of the post. The boundary layer of this sounding is too cool and dry — the surface temperature is around 80º F and the surface dewpoint is in the mid-60s. Consequently, the MUCAPE is far too small (about 120 J per kilogram). If the sounding is edited so that surface values are closer to observations (it was 90º F with a 75º F dewpoint in Texarkana at this time) then MUCAPE values jump to near 5000. The sounding is also too dry; the precipitable water is 1.45″ vs. an actual value closer to 2″ at this time.

Suomi NPP VIIRS 11.35 µm Imagery at 2010 UTC, with NUCAPS Sounding Locations in Green (Click to enlarge)

Suomi NPP VIIRS 11.35 µm Imagery at 2010 UTC, with NUCAPS Sounding Locations in Green (Click to enlarge)

Suomi NPP NUCAPS Sounding at 32.7º N, 94.9º W (Click to enlarge)

Suomi NPP NUCAPS Sounding at 32.7º N, 94.9º W (Click to enlarge)

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