Outbreak of severe thunderstorms across the Deep South

April 12th, 2020 |

GOES-16 "Red" Visible (0.64 µm) images [click to play animation | MP4]

GOES-16 “Red” Visible (0.64 µm) images [click to play animation | MP4]

A major outbreak of severe thunderstorms (SPC Storm Reports) occurred across the Deep South on 12 April 2020. 1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) showed the development and propagation of deep convection during the 1200-2359 UTC period. The corresponding GOES-16 “Clean” Infrared Window (10.35 µm) images are shown below.

GOES-16

GOES-16 “Clean” Infrared Window (10.35 µm) images [click to play animation | MP4]

Some of the strongest long-track tornadoes occurred in southern Mississippi — a closer view of GOES-16 Visible, Infrared and Visible/Infrared Sandwich Red-Green-Blue (RGB) images (below) revealed the pulsing nature of overshooting tops — which exhibited cloud-top infrared brightness temperatures as cold as -77ºC at 2038-2039 UTC, about 35 minutes prior to the destructive tornado that moved through Bassfield — and well defined “enhanced-v” signatures were apparent in the Infrared and RGB imagery, with that signature’s warm wake immediate downwind (east) of the overshooting tops indicating the likely presence of Above-Anvil Cirrus Plumes.

GOES-16 "Red" Visible (0.64 µm ), "Clean" Infrared Window (10.35 µm), and Visible/Infrared Sandwich RGB images [click to play animation | MP4]

GOES-16 “Red” Visible (0.64 µm ), “Clean” Infrared Window (10.35 µm) and Visible/Infrared Sandwich RGB images [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]

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

1-minute GOES-16 Visible images (above) and Infrared images (below) include plots of time-matched SPC Storm Reports.

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]

NOAA/CIMSS ProbSevere is a tool that could have been used during this outbreak to identify which radar cells were most likely to produce severe weather.  The image below, from here, shows the reports of severe weather, the warning polygons, and ProbSevere locations (a closer view of the Mississippi tornadoes can be seen here).

Severe weather reports from 12 April 2020 (Green: Hail; Blue: Wind; Red: Tornado), NWS Warning Polygons and ProbSevere locations (plotted as boxes when ProbSevere exceeded 50% (Click to enlarge)

===== 14 April Update =====

GOES-16

GOES-16 “Red” Visible (0.64 µm) and Normalized Difference Vegetation Index images [click to enlarge]

Southwest-to-northeast oriented tornado damage paths in southern Mississippi were evident in a toggle between GOES-16 Visible and Normalized Difference Vegetation Index (NDVI) images (above). NDVI values within the damage path were generally 0.6, compared to 0.7-0.8 in adjacent areas. According the the NWS Jackson storm survey, the maximum path width of the longest-track (~67 mile) EF-4 tornado that began near Bassfield was about 2 miles — the widest ever measured in Mississippi, and one of the widest tornado damage paths ever measured in the US.

In a toggle between Aqua MODIS NDVI and Land Surface Temperature (LST) images (below), LST values were 5-10ºF warmer — low 80s F, darker shades of red —  within the tornado damage path, compared to areas adjacent to the path.

Aqua MODIS Normalized Difference Vegetation Index and Land Surface Temperature images [click to enlarge]

Aqua MODIS Normalized Difference Vegetation Index and Land Surface Temperature images [click to enlarge]

The tornado damage paths were also apparent in a comparison of before (26 March) and after (14 April) Aqua MODIS True Color RGB images (below) from the MODIS Today site. Note that 2 smoke plumes were seen on the 26 March image.

Aqua MODIS True Color RGB images from 26 March and 14 April [click to enlarge]

Aqua MODIS True Color RGB images from 26 March and 14 April [click to enlarge]

True and False-color imagery from NOAA-20 (from this (temporary) website) also show the damage path.

True- and False-Color imagery from the afternoon NOAA-20 overpass on 14 April 2020 (Click to enlarge)

NOAA-20 True Color RGB imagery of the Mississippi EF-4 tornado damage path that had a maximum with of 2 miles is shown below, using RealEarth.

NOAA-20 VIIRS True Color RGB image, including county outlines and map labels [click to enlarge]

NOAA-20 VIIRS True Color RGB image, including county outlines and map labels [click to enlarge]

Strong Tornado through Nashville Tennessee

March 3rd, 2020 |

GOES-16 Clean Window (10.3 µm) Infrared Imagery at 1-minute intervals, 0313 – 0722 UTC on 3 March 2020 (Click to play mp4 animation)

A long-track tornado moved through Nashville (north Nashville to Lockeland Springs then towards Lebanon) early in the morning on 3 March 2020. (ProbSevere for this event is also discussed in this blog post; A GLM View of the storm is here) The Band13 mp4 animation, above (Click here for an animated gif), from 0313 through 0722 UTC shows the long-lived storm forming over western Tennessee and rolling eastward into Nashville after midnight. As the storm approached Nashville, the storm top frequently showed isolated cold pixels (yellow in the enhancement) that are testament to the strong convection, and an above-anvil cirrus plume (AACP) might be there too. All of these structures are consistent with a tornadic storm. The 00 UTC Nashville Sounding shows a favorable environment as well.

1-minute GOES-16 Infrared images with plots of time-matched SPC Storm reports is shown below, covering the period 0300-0802 UTC. The color enhancement applied to those images is slightly different — and the pulsing overshooting tops are easier to see as highlighted with darker shades of orange.

GOES-16

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

Shortly after the tornado passed through Nashville, NOAA-20 overflew Tennessee. The toggle below shows the GOES-16 ABI Band 13 (10.3 µm) infrared imagery, the NUCAPS Sounding Location, and the computed Total Totals Index from the NUCAPS thermodynamic information. Values exceeding 50 are south and west of the thunderstorm complex. NUCAPS soundings are showing a thermodynamically unstable environment.

GOES-16 ABI Band 13 (10.3 µm) Infrared Imagery along with NUCAPS Sounding Points and Gridded Values of Total Totals Index computed from NUCAPS Soundings (Click to enlarge)

The high-resolution VIIRS instruments on NOAA-20 gives a high-resolution view of the storm, as shown below.  The figure includes the 11.45 µm VIIRS I05 infrared imagery (from Real Earth) and also shows a 5-minute GLM Group Density accumulation with a profound maximum (values exceeding 250!) over Lebanon TN.  The morning NOAA-20 orbit on 3 March was to the east of Tennessee (source), so a parallax shift between the GLM data from GOES-16 and the VIIRS I05 data will occur.

Real Earth captures of 11.45 µm VIIRS I05 infrared imagery and GOES-16 GLM 5-minute Group Density, 0700-0705 UTC

A zoomed-out toggle between VIIRS I05 and the Day Night Band (below, courtesy William Straka, CIMSS), (Click here to view the I05 with a different enhancement) shows the storm to the east of Nashville.  The quarter New Moon (that was below the horizon) offered no clear view of the cloud tops, but lightning illumination is apparent.

NOAA-20 11.45 µm VIIRS I05 infrared imagery and Day Night Band 0.70 µm visible imagery at 0717 UTC on 3 March 2020 (Click to enlarge)

This long storm in a favorable environment was captured well by the NOAA/CIMSS ProbSevere product.  The animation below tracks the storm across much of northwest and north-central Tennessee.  Time-series plots of the radar object (#181389) associated with the Nashville tornado are here:  ProbTor (including components), ProbSevere (including components), and ProbSevere, ProbHail and ProbTor values.  The cyclic nature of the storm is apparent.  ProbSevere/ProbTor/ProbHail values were very high when the Nashville tornado was on the ground (around 0640 UTC).

NOAA/CIMSS ProbSevere display over northwest to north-central Tennessee, 0330 to 0730 UTC. (Click to enlarge)


A project spearheaded by Bill Smith Sr and Qi Zhang at Hampton University (they are also affiliated with CIMSS) takes Polar Hyperspectral (PHS) data and blends it with GOES-16 ABI data.  Those fields that exploit the high spectral resolution from sounders in polar orbit (such as IASI or CrIS) and the high spatial and temporal resolution from GOES are then input into numerical models.  Output is here.  The better representation of moisture fields in these fields can help a model better define where strong convection will or will not occur.  The animation below shows initial fields of the Significant Tornado Parameter from 0300 – 0800 UTC on 3 March 2020. Compare the animation to initial fields of STP in a model that does not include the assimilated hyperspectral data here.

Significant Tornado Parameter at initial model run times from 0300 through 0800 UTC on 3 March 2020 (Click to enlarge). The number of assimilated retrievals is indicated in red; no retrievals were assimilated at 0700 UTC, and the STP field was affected!

What did the forecast for 0600 UTC look like from this model that includes polar hyperspectral data?  That is shown below, with a series of model runs.  There is run-to-run variability, but overall the forecast simulations show a peak in the STP parameter near Nashville. (This PDF compares model runs with and without Polar Hyperspectral Data; adding the satellite data helps the model focus convection where it occurs, mostly because the moisture fields are more accurately defined).

Forecasts valid at 0600 UTC on 3 March 2020, initialized at 0000, 0100, 0200, 0300, 0400 and 0500 UTC (Click to enlarge)

Severe thunderstorms in Arizona

September 23rd, 2019 |

GOES-17 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images, with surface reports plotted in cyan [click to play animation | MP4]

GOES-17 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images, with surface reports plotted in cyan [click to play animation | MP4]

1-minute Mesoscale Domain Sector GOES-17 (GOES-West) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images (above) showed the development of severe thunderstorms over southern/central Arizona from 1600-1900 UTC on 23 September 2019. The far western storm exhibited a well-defined Above-Anvil Cirrus Plume (AACP) that extended northeastward from the cold overshooting top (whose coldest infrared brightness temperature was -74ºC); note that the AACP feature appeared colder (shades of yellow to orange) on the Infrared images (for example, at 1817 UTC).

As the western storm began to weaken somewhat, a new storm just to the east (located about 20-30 miles north-northeast of the Phoenix metro area) began to intensify, prompting the issuance of a Tornado Warning at 1914 UTC (the last tornado warning issued by NWS Phoenix was 21 January 2010) — a brief EF0 tornado was documented (NWS Phoenix summary).

GOES-17 “Clean” Infrared Window (10.35 µm) images, with surface reports plotted in cyan [click to play animation | MP4]

GOES-17 “Clean” Infrared Window (10.35 µm) images, with surface reports plotted in cyan [click to play animation | MP4]

Much of the moisture helping to fuel the development of this severe convection was from the remnants of Tropical Storm Lorena in the East Pacific Ocean — the northward transport of this moisture could be seen using the hourly MIMIC Total Precipitable Water product (below).

MIMIC Total Precipitable Water product [click to play animation | MP4]

MIMIC Total Precipitable Water product [click to play animation | MP4]


 

GOES-17 ABI Band 13 (10.35 µm) Clean Window Imagery and Derived Convective Available Potential Energy, 1501 – 1856 UTC on 23 September 2019 (Click to animate)

 

Stability parameters from GOES-16 showed that the reigon of thunderstorm development was just east of a strong gradient in Convective Available Potential Energy.  The animation above shows the GOES-17 Clean Window;  in regions of clear sky, the baseline Derived Stability Index CAPE is shown.  CAPE values are zero over much of California (except for the southeasternmost corner) but they increase rapidly over Arizona to values approaching 1000 J/kg.

On 23 September, skies were clear enough that an instability signal was obvious in the clear-sky baseline CAPE. An ‘All-Sky’ product has been developed that can be used on days with more widespread cloudiness; it is available at this link. Values of All-Sky CAPE at 1156 and 1556 UTC on 23 September are shown below, and they also show a sharp gradient in the instability, and the link down to moisture from Lorena’s remants.

‘All-Sky’ values of Convective Available Potential Energy (CAPE) at 1156 and 1556 UTC on 23 September 2019 (Click to enlarge)

NOAA/CIMSS ProbSevere is a product designed to indicate the likelihood that a given object will produce severe weather within the next 60 minutes. An animation of the product at 5-minute intervals, below, shows that the right-moving radar cell (also associated, as noted above, with an AACP) that developed over far southwestern Arizona (becoming a warned storm at 1647 UTC) was very likely to produce severe weather.

NOAA/CIMSS ProbSevere from 16:30 UTC to 18:00 UTC. Contours surrounding radar objects are color-coded such that pink/magenta contours are the highest probability.  Warning polygons (yellow for severe thunderstorm) are also shown (Click to enlarge)

Parameters that are used to determine the probability can be revealed at the ProbSevere site by mousing over the colored object contours.  The values for the warned storm over SW Arizona are shown below at 1650 UTC, 3 minutes after the warning was issued.  This image shows the 1710 UTC readout with the highest ProbWind value (76%); this image shows the 1725 UTC readout with the highest ‘ProbHail’ value (99%); ProbTor values on this day were not exceptionally large — for the later tornado-warned storm farther east, they were 28% at 1915 UTC and 30% at 1920 UTC.

NOAA/CIMSS ProbSevere display from 1650 UTC on 23 September 2019; parameters used in the probability computation, and Severe Thunderstorm Warning polygon parameters are also shown (Click to enlarge)

CIMSS is developing a machine-learning tool that combines ABI and GLM imagery (that is, only satellite data) to identify regions where supercellular thunderstorms capable of producing severe weather might be occurring. An mp4 animation for this event (courtesy John Cintineo, CIMSS) is shown below.  (This experimental product was also shown in this blog post)

When Atmospheric Bores cause Severe Weather

June 1st, 2019 |

RadarScope imagery from shortly after 0900 UTC on 01 June 2019 (Click to play .mov animation)

Strong near-surface inversions over the upper-midwest early on 1 June 2019 (as shown by 1200 UTC Skew-Ts at Green Bay, WI, Detroit/WhiteLake, MI and Gaylord, MI) helped support the presence of southward-propagating bore features, as shown in the still image (an animation) of radar imagery above (Courtesy Fred Best, SSEC), and (more subtly) in the water vapor imagery (Courtesy Scott Bachmeier) below.

The pressure sensor at the top of the Atmospheric Oceanic and Space Science Building showed many small time-scale pressure perturbations on this day. (Image courtesy Pete Pokrandt)

Water Vapor Imagery from to on 1 June 2019; Low-level (GOES-16 ABI Band 10, 7.34 µm) on the left ; mid-level (GOES-16 ABI Band 9, 6.95 µm) in the center; upper-level (GOES-16 ABI Band 8, 6.19 µm) on the right


Later in the day, strong convection developed over southwestern Lower Michigan, starting shortly after 2215 UTC.  The visible imagery below shows 1-minute imagery (GOES-16 ABI Band 2, 0.64 µm) from a Mesoscale sector positioned over the convection.  At the start, the parallel lines of low clouds suggest a bore feature is propagating southward towards strong convection over northern Indiana and northern Ohio.  Two things happen when that feature meets the convective outflow: some energy is apparently reflected to the north, but very strong convection rapidly develops near Battle Creek MI, where 2″ hail was observed at 2235 UTC (SPC Storm Reports).

GOES-16 ABI 1-minute Visible (0.64 µm) imagery, 2115-2149 UTC on 1 June 2019 (Click to play animated gif)

The clean window (GOES 16 ABI Band 13, 10.3 µm) animation during the day, below, show many features suggesting bore/gravity wave propagation over the area. It is challenging to pick out the impulse from this animation that lead to the severe convection that hit Battle Creek.

GOES-16 ABI Infrared (10.3 µm, Band 13 “Clean Window”) imagery, 1001-2331 UTC on 1 June 2019 (Click to play animated gif)

The Low-Level water vapor animation, shown below, also shows many features that resemble gravity waves or bores, but it also shows a line of parallel features moving towards the site of convective initiation (Consider this short loop from 2126 to 2156 UTC, for example).

GOES-16 ABI Water Vapor (7.3 µm, Band 10 “Low-Level Water Vapor”) infrared imagery, 1001-2331 UTC on 1 June 2019 (Click to play animated gif)

For convection to initiate, instability should be present. The graphic below from the Storm Prediction Center mesoanalysis website shows a nose of unstable air (represented by high values of CAPE) encroaching into southwestern Lower Michigan.

SPC CAPE analysis, 2100 UTC on 1 June 2019 (Click to enlarge)

GOES-16 Baseline Products can also diagnose instability. On 1 June 2019, however, abundant cloudiness limited the utility of the Baseline clear-sky only products, but AllSky versions have been developed and are available online at this website. The animation below shows the evolution of the AllSky Lifted Index from 1826 through 2356 UTC on 1 June 2019. In agreement with the SPC analysis, the AllSky product shows a nose of instability pushing into southwestern lower Michigan. An southward-propagating impulse (apparent in both visible and low-level water vapor imagery) meeting this gradient in instability did initiate convection on this day.

GOES-16 AllSky Lifted Index, half-hourly from 1826 UTC to 2356 UTC on 1 June 2019 (Click to play animated gif)

NOAA/CIMSS ProbSevere (v.2), a tool designed to give confidence that severe weather might occur in the next 60 minutes, shown below, tracked the rapid evolution of the storm. ProbHail increased from 7% at 2220 UTC to 81% at 2230 UTC!

NOAA/CIMSS ProbSevere, with readout values, from 2200 to 2236 UTC on 1 June 2019 (Click to play animated gif)

The chart below, from John Cintineo, SSEC/CIMSS, graphically shows the very rapid development of Prob Hail values. Much of the increase in ProbHail was driven by MESH and Total Lightning observations. When an impulse enters a region of instability in a good environment, explosive growth can result.

NOAA/CIMSS ProbSevere readout for Radar Object 411723 (the storm that produced Hail in Battle Creek MI on 1 June 2019) (Click to enlarge)

Many thanks to TJ Turnage, NWS Grand Rapids, for alerting us to this very interesting case.