The Kilauea volcano on the Big Island of Hawai’i continued to be active into early June 2018 — and GOES-15 (GOES-West) Shortwave Infrared (3.9 µm) imagery (above) showed the thermal anomaly or “hot spot” (black to yellow to red enhancement) associated with lava flows from active fissures in the East Rift Zone on 06 June.

GOES-15 Visible (0.63 µm) images (below) showed clouds of steam from the East Rift Zone drifting to the south-southwest; a hazy plume of volcanic fog or “vog” was also evident, which was being transported farther to the southwest by the northeasterly trade wind flow.

A Suomi NPP VIIRS Visible (0.64 µm) image at 2307 UTC (below) showed clear skies over Kapoho on the eastern tip of the Big Island, with steam plumes from the active East Rift Zone fissures flowing southwestward.

The corresponding VIIRS Shortwave Infrared (3.74 µm) image (below) helped to discriminate between the hot brightness temperatures of recent (and old) lava flows and the cooler brightness temperatures exhibited by regions of vegetation.

A closer look at the Kilauea East Rift Zone (below) provided a detailed view of the recent lava flow and active fissures, including the lava field that entered and covered Kapoho Bay a few days earlier. Note the appearance of numerous multi-colored pixels in the center of the lava field — the 3.74 µm I04 band detectors on the VIIRS instrument saturate around 385 K, so the hottest lava features which exceeded that brightness temperature threshold ended up being displayed as cold pixels (the so-called “wrap-around” effect). There is a Moderate-resolution M13 band (4.05 µm) on VIIRS which saturates at a much hotter 700 K; while it is a lower spatial resolution (750 meters, vs 375 meters for the I04 band), the M13 band can be useful for sampling the actual temperature of very hot features such as lava flows or wildfires.

Thanks to Jordan Gerth (CIMSS) and Eric Lau (NWS Pacific Region Headquarters) for providing the VIIRS imagery for this case.

Update: This link shows Landsat-8 and Sentinel-2 imagery before and after the Kapoho Bay lava flow.

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The first Tropical Storm, Aletta, of the eastern Pacific Ocean basin has been named. One-minute imagery from a moveable Mesoscale Sector, above as an animated gif (or here as an mp4), shows a distinct low-or mid-level circulation center moving out from under higher clouds in the northeast quadrant of the storm at about 1621 UTC, being even more obvious at 1636 UTC.

The GOES-16 CONUS Sector scans at 5-minute intervals. The southern boundary of the CONUS sector (15º N Latitude), however, bisects this tropical storm, as shown at this link, and is therefore unhelpful for center diagnostics. Full Disk imagery captures the storm evolution at a 15-minute time step that is too coarse to provide a smooth animation. (Just two years ago, the time resolution for this storm formation would have been every 3 hours, as that was the time cadence for a Full Disk from GOES-13! GOES-16 really is life-changing for those who view satellite animations.)

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GOES-16 (GOES-East) “Clean” Infrared Window (10.3 µm) images (above) showed showed the development of thunderstorms over the northern Plains late in the evening on 05 June 2018 — these storm clusters exhibited upscale growth and merged into a large Mesoscale Convective System (MCS) over North Dakota and South Dakota during the overnight hours. SPC storm reports are plotted on the images, parallax-corrected to be at a location corresponding to cloud-top features at a mean elevation of 10 km; notable reports included wind gusts of 100 mph in South Dakota, 71 mph in North Dakota, and 67 mph in Minnesota.

A 1-km resolution Terra MODIS Infrared Window (11.0 µm) is shown below, with with plots of SPC storm reports that occurred within +/- 1 hour of the image. The coldest storm-top infrared brightness temperatures on the image were -77ºC in eastern North Dakota and central South Dakota.

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The Split Window Difference field (SWD, the 10.3 µm brightness temperature minus the 12.3 µm brightness temperature) can be used to identify regions of moisture and dust in the atmosphere.  (Click here for a previous blog post).  On 5 June 2018, the SWD showed a strong gradient over the upper Midwest, with large values over Iowa and relatively smaller values to the northeast over Wisconsin (and to the south over Missouri). Is this showing a moisture gradient between Iowa and Wisconsin? Do you trust its placement? Given that convection will frequently fire along the gradient of a field (HWT Link; Old HWT link), it’s important to trust the placement of the gradient.

The toggle below shows both the SWD and the (clear sky only) Baseline Derived Stability Lifted Index.  The Lifted Index shows negative values over the southern Plains, and also a lobe of instability stretching WNW-ESE from southwestern Minnesota to Chicago.  If you look carefully, you will note that the axis of instability in the Lifted Index is offset from the Split Window Difference field.  Why?

The toggles below show the Split Window Difference field and the Rapid Refresh Model estimates of moisture in the lowest 3 km of the atmosphere, followed by the Split Window Difference toggled with the Baseline Land Surface Temperature field. The maximum in moisture is along the northern edge of the Split Window Difference field, and aligns well with the Lifted Index (Toggle between those two is here).

The Split Window Difference better matches the Land Surface Temperature Baseline product, and that reinforces an important caveat in the use of the SWD to detect moisture: SWD is greatly influenced by the skin temperature. Gradients in surface temperature and gradients in moisture both will affect the Split Window Difference. Make sure you understand the underlying cause of the gradient in the Split Window Difference field.

By 2002 UTC on 5 June, the GOES-16 Lifted Index fields and the SWD more closely align, in part because the axis of moisture has shifted southward. See the toggle below.

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