Severe Weather over the Upper Midwest

June 2nd, 2020 |

GOES-16 ABI Band 13 (10.3 µm) imagery and clear-sky estimates of Convective Available Potential Energy (CAPE), 1921-2146 UTC (Click to enlarge)

Severe weather occurred over Minnesota and Wisconsin on 2 June 2020, and the storms developed in clear skies. This allowed GOES-16 Derived Stability Indices (a clear-sky product) to provide information on the near-storm environment. The animation above combines GOES-16 Clean Window infrared (10.3 µm) imagery (where clouds exist) with Convective Available Potential Energy (CAPE) estimated from GOES-16 Advanced Baseline Imager channel information (that adjusts an initial field created using GFS data); this Baseline product (and others including all-sky products) can be found online here).  Strong convection over Minnesota at this time was supported in part by instability diagnosed to its south.

Note how, south of the main convection, a second line of convection initiated over southern Minnesota at around 2030 UTC, along the northern edge of the diagnosed CAPE maximum.  When do you think lightning initiated with this second line of convection? What imagery/products will help in that assessment?

The 4-panel animation, below, shows the initiation of convection in the southern line, from 2031 to 2101 UTC.  The developing convection is fairly bright in the Snow/Ice channel initially, consistent with the presence of clouds made up of water droplets.  The Cloud Phase product shows water (or supercooled water) at these times, and the Day Cloud Phase Distinction color of the clouds is mostly greenish.

As glaciation occurs, the clouds in the Snow/Ice channel become darker:  ice absorbs (rather than reflects) energy at 1.61 µm so less is detected by the satellite.  The change in the 1.61 µm channel reduces the amount of blue in the Day Cloud Phase Distinction RGB (so pixels acquire a yellow or red hue), and the Cloud Phase product also detects mixed phase and ice clouds.  Once the glaciation has occurred, lightning production is more likely, and at 2101 UTC, the GLM detects lightning activity.  (Here is the 2101 UTC Day Cloud Phase Distinction image without GLM overlain; here are toggles between 2056 and 2101 UTC without and with GLM overlain;  a toggle between the 2056 and 2101 UTC Cloud Phase product is here; ice is present at 2056 UTC (and actually at 2051 UTC!) but more widespread at 2101 UTC). Of course, a 1-minute mesoscale sector could give even better temporal resolution of cloud phase changes than CONUS scans’ 5-minute time steps.

GOES-16 ABI Band 2 Visible (0.64 µm, upper left), the Band 5 “Snow/Ice” channel (1.61 µm, upper right), the derived level 2 Cloud Phase  Product (lower left), and the Day Cloud Phase Distinction Red/Green/Blue Composite (with GLM observations of Flash Extent Density, lower right) from 2031 to 2101 UTC

NOAA-20 overflew this region shortly after noon on 2 June, and the thermodynamic information from the infrared and microwave sounder instruments on board can be used to diagnose instability. The toggle below compares the total totals index computed from gridded NUCAPS data with the GOES-16 clear-sky estimates of CAPE.

Both measures of instability agree that the region of instability is narrow, and that its axis extends from central Wisconsin west-southwestward to southwest Minnesota and southeast South Dakota.

GOES-16 Derived Convective Available Potential Energy and Gridded NUCAPS field of total totals index, ca. 1830 UTC on 2 June 2020 (Click to enlarge)

Gridded NUCAPS fields are created from soundings that may or may not have converged (that is, from points displayed in AWIPS as green — infrared and microwave retrievals converged), yellow (infrared retrieval failed, microwave retrieval converged) or red (infrared and microwave retrievals failed)).  The image below shows surface observations with the G16 Clean Window (10.3 µm) overlain with NUCAPS Sounding Points (This figure shows the total totals index overlain with the NUCAPS sounding points).  As expected because of the clear skies, most of the NUCAPS Soundings south of the convection show both infrared and microwave retrieval convergence: dots are green.

GOES-16 Clean Window (Band 13, 10.3 µm) infrared imagery, surface observations, and NUCAPS Sounding observation points, 1831 UTC on 2 June 2020 (Click to enlarge)

NUCAPS data that is gridded can include effects that are related to how well (or how poorly) a NUCAPS sounding observes and estimates the boundary layer. The sounding below is from a ‘green’ point in extreme south-central Minnesota (to the northeast of the observation plotted at Spencer Iowa). Surface dewpoints are observed in the mid-60s; however, the original NUCAPS sounding, shown below, shows a dewpoint near 60. When the lower-tropospheric dewpoints values are increased towards more representative values, estimated MLCAPE and MUCAPE as reported in the NSharp readout in AWIPS increase as well, from 2466 to 3404, and from 2635 to 3630, respectively. When using gridded NUCAPS estimates of thermodynamic variables that include surface or near-surface variables, consider just how well the NUCAPS soundings can observe that part of the troposphere.

NUCAPS Sounding, original and modified, at 43.78 N, 94.73 W at ~1800 UTC on 2 June 2020 (Click to enlarge)

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

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

1-minute Mesoscale Domain Sector GOES-16 “Red” Visible (0.64 µm) images with time-matched plots of SPC Storm Reports (above) showed the development of these storms during the 1700-0112 UTC period.

The corresponding GOES-16 “Clean” Infrared Window (10.35 µm) images (below) revealed pulsing overshooting tops which exhibited cloud-top infrared brightness temperatures in the -70 to -79ºC range (darker black to brighter shades of white). Evidence of Above-Anvil Cirrus Plumes (reference | VISIT training) was seen in the Visible and Infrared imagery.

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

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

When is an ABI hot (bright) spot not a fire?

May 30th, 2020 |

An ABI hot (bright) spot is not a fire when it’s a fleet of solar farms. For example, recall the CIMSS Satellite Blog entry regarding solar farms in California. 

ABI band 2 visible

ABI band 2 visible animation on May 30, 2020 (mostly) in southeastern Minnesota. Click to play mp4.

Note how some reflections are so bright that the ABI reports dark surrounding pixels. This is part of the remapping process from detector to pixel space. 

 

9-panel

A multiple-spectral ABI comparison on May 30, 2020. The rows are: band 2, band 5, band 6 band 7, band 7 – 14 brightness temp, band 14 fire mask, band 7-14 radiance difference, band 7-14 radiance difference minus the rolling average

From left to right, top to bottom the panels are:
1) ABI band 2 reflectance, dynamically scaled to enhance contrast (will appear to flicker)
2) ABI band 5 reflectance, dynamically scaled to enhance contrast (will appear to flicker)
3) ABI band 6 reflectance, dynamically scaled to enhance contrast (will appear to flicker)
4) ABI band 7 brightness temperature, dynamically scaled to enhance contrast (will appear to flicker)
5) ABI band 7 minus band 14 brightness temperature. Red indicates positive values (extra thermal energy due to the sun and fires, if present), dynamically scaled to enhance contrast (will appear to flicker)
6) ABI band 14 brightness temperature, dynamically scaled to enhance contrast (will appear to flicker)
7) ABI Fire Detection and Characterization Algorithm (FDCA, aka WFABBA) fire detection metadata mask.  Fires are red, orange, magenta, and shades of blue indicating different confidence levels.  Green indicates fire-free land, shades of gray indicate clouds, dark  blue indicates water.
8) Radiance difference of band 7 minus band 14 radiance in band 7 space.  Red indicates positive values (extra thermal energy due to the sun and fires, if present), dynamically scaled to enhance contrast (will appear to flicker)
9) Radiance difference of band 7 minus band 14 radiance in band 7 space minus a rolling average of the 5 prior frames, to highlight changes. Red indicates positive values (extra thermal energy due to the sun and fires, if present), dynamically scaled to enhance contrast (will appear to flicker).

Aside from the solar farms, water clouds show up in the difference panels due to their reflection of shortwave radiation. 

H/T to Chris Schmidt for the 9-panel ABI imagery.  More about quantitative ABI products, including fire detection. 

The original tweet from the La Crosse WFO: “We saw some awfully bright looking “clouds” showing up via satellite in southeast Minnesota earlier this afternoon. Well after some investigation, we were able to determine they were actually solar panel arrays that the sun was hitting just right!”

NWS tweet

Solar farms and GOES-16 ABI visible imagery from the La Crosse NWS WFO.

A View of the Development of Geostationary Imagers through the lens of BAMS

May 14th, 2020 |

A collection of 60 BAMS covers spanning the years, to highlight the rapid advance of imaging from the geostationary orbit, is shown above (a version that loops more slowly can be seen here). The first cover is the first of BAMS, in January of 1920, while the second, from January of 1957 is the first time artificial ‘satellite’ was in a title of a BAMS article. The third image, from November of 1957, is a remarkable article on potential uses of satellites. This included both qualitative uses: (1) Clouds, (2) Cloud Movements, (3) Drift of Atmospheric Pollutants, (4) State of the Surface of the Sea (or of Large Lakes), (5) Visibility or Atmospheric Transparency to Light — and quantitative uses: (1) Albedo, (2) Temperature  of  a  Level  at  or  Near  the Tropopause, (3) Total Moisture Content., (4) Total  Ozone  Content, (5) Surface  (Ground-Air Interface) Temperature, and (6) Snow Cover. Early covers showcase rockets, balloons and high-altitude aircraft to prepare the way to human space travel (Gemini, Apollo, etc.), polar-orbiters (TIROS, NIMBUS, VHRR, NOAA, etc.) and finally geostationary orbit (ATS-1, ATS-3, SMS, GOES, Meteosat, INSAT, Himawari, etc.).

Reasons to look back at the BAMS covers:

Interactive web page, with links to the original “front matter”.

Montage of select BAMS covers

Montage of select BAMS covers

Note: All cover images are from the Bulletin of the American Meteorological Society.

Supercells in the Southeast

May 6th, 2020 |

A cold front with ample moisture and instability ahead of it spawned numerous strong storms in the Southeast U.S. yesterday; particularly one long-lived supercell in South Carolina. A convolutional neural network model (CNN) was deployed in realtime on the 1-min GOES-16 mesoscale sector imagery. The model produces an “Intense Convection Probability” (ICP). The inputs for the model are the GOES-16 ABI 0.64 µm reflectance, 10.3 µm brightness temperature, and GLM flash extent density. It was trained to identify “intense” convection as humans do, associating features with intense convection such as strong overshooting tops, thermal couplets (“cold-U/V”), above anvil cirrus plumes (AACP), and strong cores of total lightning.

The animation below shows the ICP contours overlaid ABI 0.64 µm + 10.3 µm sandwich imagery, annotated with preliminary severe storm reports.


The long-lived supercell in South Carolina exhibited AACP and cold-U features, and produced numerous severe wind and hail reports (up to the size of tennis balls). While the NOAA/CIMSS ProbSevere models handled this storm well, the ICP ramped up on a couple of severe storms in northern Georgia before ProbSevere did. ICP for these cells exceeded 90% 15-18 min before ProbWind reached 50%. The ICP may be able to provide additional lead time and confidence to ProbSevere guidance for certain storms, utilizing spectral and electrical information from geostationary satellites. Incorporating ICP into ProbSevere is an active area of current research.

ProbSevere storm contours and MRMS MergedReflectivity for storms in GA and SC. The main or “inner” ProbSevere contour is shaded by the probability of any severe weather, while the outer contour is shaded by the probability of tornado, which appeared when that value was at least 3%, in this example.


An accumulation of ProbSevere storm centroids (white to pink squares, 50% --> 100%), NWS severe weather warnings, and SPC severe local storm reports from 12Z on May 5th to 12Z on May 6th [click to enlarge]

An accumulation of ProbSevere storm centroids (white to pink squares, 50% –> 100%), NWS severe weather warnings, and SPC severe local storm reports from 12Z on May 5th to 12Z on May 6th [click to enlarge]