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)

Severe thunderstorms in Wyoming, Nebraska and South Dakota

September 10th, 2019 |

GOES-16

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 (above) showed  the development of thunderstorms that produced large hail, tornadoes and damaging winds (SPC Storm Reports) across eastern Wyoming, northern Nebraska and southern South Dakota on 10 September 2019. Note that many of the storms exhibited Above-Anvil Cirrus Plumes. Pulsing overshooting tops reached -80ºC and colder (violet pixels) just east of Valentine, Nebraska (KVTN) from 0001-0004 UTC (0002 UTC image) — and a few minutes following their collapse, a wind gust of 60 mph was reported in that general vicinity.

The corresponding GOES-16 “Clean” Infrared Window (10.35 µm) images are shown below.

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]

The animation shown below is from an experimental product at CIMSS/SSEC, whereby the contours were produced using a ‘deep learning’ artificial intelligence model that was trained on ABI imagery and GLM gridded products to generate the ‘probability of supercell-like features inferred from satellites’, or more concisely, the ‘probability of supercell’. Note that the model does a decent job of identifying active portions of the storms (e.g., persistent Overshooting Tops), which correspond well with severe weather reports.

GOES-16 Visible/Infrared Sandwich RGB and

GOES-16 Visible/Infrared Sandwich RGB and “Clean” Infrared Window (10.35 µm) images, with “probability of supercell” contours and SPC Storm Reports (courtesy of John Cintineo, CIMSS) [click to play MP4 animation]

During the subsequent nighttime hours, GOES-16 Infrared images (below) showed a convective cluster which produced 3 EF-2 tornadoes and damaging winds in and around Sioux Falls, South Dakota (NWS summary). Note that pulsing overshooting tops west of Sioux Falls (KFSD) exhibited infrared brightness temperatures of -80ºC and colder (violet pixels) from 0402-0406 UTC (0404 UTC image), which was about 20 minutes prior to the first tornado reports.

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]

 

Mesospheric airglow waves over the Northern Plains

September 2nd, 2019 |

VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images from NOAA-20 (0740 UTC) and Suomi NPP (0831 UTC) [click to enlarge]

VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images from NOAA-20 (0740 UTC), Suomi NPP (0831 UTC) and NOAA-20 (0921 UTC) [click to enlarge]

Kudos to Carl Jones (NWS Grand Forks) for spotting this vivid example of mesospheric airglow waves (reference) produced by severe thunderstorms that were responsible for a swath of hail across South Dakota from 0515-1010 UTC on 02 September 2019. In the toggles between VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images from NOAA-20 (at 0740 UTC), Suomi NPP (at 0831 UTC) and NOAA-20 (at 0921 UTC), note that the epicenter of the circular gravity wave patterns appeared to be located west of the convection on the earliest NOAA-20 image and east of the convection in the later NOAA-20 image — this is due to parallax (since the vertically-propagating waves were likely at an altitude near 90 km). This parallax shift was more pronounced in the NOAA-20 images since the high-altitude waves were near the limb of those two satellite swaths. The Moon was in the Waxing Crescent phase (at only 6% of Full), so features seen on the Day/Night Band images were primarily illuminated by airglow.

Closer views centered on the convection are shown below. Cloud-top infrared brightness temperatures in both South Dakota and Nebraska were -70ºC and colder in the NOAA-20 images (which are mislabeled as Suomi NPP), and -80ºC and colder in the Suomi NPP image. Bright white “lightning streak” signatures associated with the thunderstorms were more apparent in these closer views.

 VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images from NOAA-20 (0740 UTC), Suomi NPP (0831 UTC) and NOAA-20 (0921 UTC) [click to enlarge]

VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images from NOAA-20 (0740 UTC), Suomi NPP (0831 UTC) and NOAA-20 (0921 UTC) [click to enlarge]

GOES-16 (GOES-East) “Clean” Infrared Window (10.35 µm) images (below) revealed the rapid development of an isolated hail-producing thunderstorm that generated the mesospheric airglow waves.

GOES-16

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

Swan Lake Fire in Alaska

August 17th, 2019 |

GOES-17

GOES-17 “Red” Visible (0.64 µm) and Shortwave Infrared (3.9 µm) images [click to play animation | MP4]

1-minute Mesoscale Domain Sector GOES-17 (GOES-West) “Red” Visible (0.64 µm) and Shortwave Infrared (3.9 µm) images (above) revealed thick smoke and a pronounced thermal anomaly (hot pixels, darker black) associated with the Swan Lake Fire on the Kenai Peninsula in south-central Alaska on 17 August 2019. Later in the day, a few pyrocumulus jumps could be seen in Visible imagery over the fire source region, as fire behavior increased (another day when pyrocumulus jumps were apparent with this fire was 30 June, during a period when southerly winds were transporting dense smoke to the Anchorage area).

Strong northerly-northwesterly winds were transporting smoke from the Swan Lake Fire southward across the Kenai Peninsula and the Seward area — a time series of surface report data from Seward (below) showed that this smoke had reduced the visibility to less than 1 mile by 03 UTC (7 PM local time). South-central Alaska was experiencing drought conditions, which had worsened from the preceding week; the strong winds on this day acted to dry fuels even further, leading to a re-invigoration of the long-lived fire.

Time series of surface reports from Seward, Alaska [click to enlarge]

Time series of surface report data from Seward, Alaska [click to enlarge]

Seward Airport webcam image at 2358 UTC [click to enlarge]

Seward Airport webcam image at 2358 UTC [click to enlarge]

The PM2.5 Air Quality Index reached 427 at Cooper Landing, and 358 farther downwind at Seward (below).

Air Quality Index at Copper Landing and Seward [click to enlarge]

Air Quality Index at Copper Landing and Seward [click to enlarge]

The southward transport of smoke across the Seward area and out over the adjacent offshore waters of the Gulf of Alaska was evident in VIIRS True Color Red-Green-Blue (RGB) images from NOAA-20 and Suomi NPP, as viewed using RealEarth (below).

VIIRS True Color RGB images from NOAA-20 and Suomi NPP [click to enlarge]

VIIRS True Color RGB images from NOAA-20 and Suomi NPP [click to enlarge]