Severe weather outbreak across the Deep South

March 17th, 2021 |

GOES-16 Air Mass RGB images, with and without contours of PV1.5 pressure [click to play animation | MP4]

GOES-16 Air Mass RGB images, with and without contours of RAP40 model PV1.5 pressure [click to play animation | MP4]

GOES-16 (GOES-East) Air Mass RGB images (above) showed the darker shades of red associated with dry and ozone-rich air within a lowered tropopause near the core of an upper-level low moving eastward across Oklahoma on 17 March 2021. One sequence of the Air Mass RGB images includes RAP40 model pressure contours of the PV1.5 surface (a representation of the “dynamic tropopause”), which descended to the 700 hPa pressure level — and as this Potential Vorticity (PV) anomaly propagated east toward the Lower Mississippi Valley, it helped to enhance large-scale forcing for ascent and upper-level diffluence across that region. As noted in this blog post, that morning the SPC had issued a High Risk for severe thunderstorms across parts of the Deep South.

GOES-16 “Red” Visible (0.64 µm) images, with time-matched SPC Storm Reports plotted in red [click to play animation | MP4]

GOES-16 “Red” Visible (0.64 µm) images, with time-matched SPC Storm Reports plotted in red [click to play animation | MP4]

1-minute Mesoscale Domain Sector GOES-16 “Red” Visible (0.64 µm) images (above) and “Clean” Infrared Window (10.35 µm) images (below) include time-matched plots of SPC Storm Reports that were produced by a number of supercell thunderstorms that developed and moved across across Mississippi and Alabama (where the concentration of tornadoes was highest).

GOES-16 “Clean” Infrared Window (10.35 µm) images, with time-matched SPC Storm Reports plotted in cyan [click to play animation | MP4]

GOES-16 “Clean” Infrared Window (10.35 µm) images, with time-matched SPC Storm Reports plotted in cyan [click to play animation | MP4]

In a time-matched comparison of Infrared images from Suomi NPP (overpass times) and GOES-16 (below)the coldest overshooting top infrared brightness temperatures sensed by the VIIRS instrument on Suomi NPP were about 5-7ºC colder than those from GOES. Note the small northwestward parallax displacement that is inherent with GOES-16 imagery over that region. The same color enhancement is applied to both images.

GOES-16 “Clean” Infrared Window (10.35 µm) and Suomi NPP VIIRS Infrared Window (11.45 µm) images at 1921 UTC [click to enlarge]

GOES-16 “Clean” Infrared Window (10.35 µm) and Suomi NPP VIIRS Infrared Window (11.45 µm) images at 1921 UTC [click to enlarge]

With a partial overlap of the 2 GOES-16 Mesoscale Domain Sectors, imagery was available at 30-second intervals in the vicinity of the Mississippi/Alabama border; Visible images with time-matched plots of SPC Storm Reports are shown below.

GOES-16 “Red” Visible (0.64 µm) images, with time-matched SPC Storm Reports plotted in red [click to play animation | MP4]

GOES-16 “Red” Visible (0.64 µm) images, with time-matched SPC Storm Reports plotted in red [click to play animation | MP4]

On a side note, strong winds along the rear flank of the surface low in Oklahoma lofted plumes of blowing dust across western Texas — a time-matched comparison of GOES-16 Dust RGB and Suomi NPP VIIRS True Color RGB images at 1921 UTC (below) highlighted the blowing dust features. Animations of GOES-16 Dust RGB images can be seen here: GIF | MP4.

GOES-16 Dust RGB and Suomi NPP VIIRS True Color RGB images at 1921 UTC [click to enlarge]

GOES-16 Dust RGB and Suomi NPP VIIRS True Color RGB images at 1921 UTC [click to enlarge]

Monitoring severe weather as it happens

March 17th, 2021 |

NUCAPS/MADIS Lifted Index, GLM Group Density, GOES-16 Band 13 Infrared Imagery, and ProbSevere polygons, all at ~0939 UTC on 17 March 2021 (Click to enlarge) All imagery from RealEarth

When NOAA’s Storm Prediction Center issues a High Risk of severe weather (below), people sit up and take notice. Are there easily accessible tools to monitor the state of the atmosphere in/around a region of expected severe weather?

The toggle above shows products (early in the morning on 17 March — at 439 AM CDT) in RealEarth that can help. NOAA-Unique Combines Atmospheric Processing System (NUCAPS)/MADIS (Meteorological Assimilation Data Ingest System) Lifted Indices combine tropospheric information from NUCAPS profiles with lower-tropospheric/surface information from MADIS to create Lifted Index fields, twice daily. These fields are generated using HEAP (Hyper-spectral Enterprise Algorithm Package) software (incorporated into CSPP — the Community Software Processing Package) at the UW-CIMSS Direct Broadcast site. A Suomi-NPP (or NOAA-20) overpass will quickly yield stability information. Today’s afternoon Suomi-NPP overpasses occurs around 1730 UTC (east of the High Risk area) and 1915 UTC (Link, from this site.) The toggle above also includes GOES-16 Band 13 infrared (Clean Window, 10.3 µm) information, GLM Group Density, and NOAA/CIMSS ProbSevere (ProbSevere has a stand-alone RealEarth-based site here).  All of these products are useful in monitoring this evolving, dangerous event.   As is often the case, the strongest convection was occurring at 0939 UTC along the edges of the most unstable air, that is, in the instability gradient.

People within the region of elevated risk of Severe Weather on 17 March 2021, especially the region High Risk, should pay especial attention to the weather.

NOAA Storm Prediction Center Risk assessment for 17 March 2021, issued 1300 UTC on 17 March (Click to enlarge)


Added: the Geosphere site (link) gives rapid access to GOES-16 imagery (including mesoscale sectors) and can be used to monitor this evolving situation.


The afternoon image of stability is shown below.

NUCAPS/MADIS Lifted Index, GLM Group Density, and GOES-16 Band 13 Infrared Imagery, all at ~1830 UTC on 17 March 2021 (Click to enlarge) All imagery from RealEarth