The animation above (from the CSPP Geosphere site — click here for a direct link to the animation) shows True Color imagery (daytime) and Night Microphysics RGB (nighttime) from 2310 on 6 October through 0540 UTC on 7 October 2022 in 10-minute time-steps.

Convection developed over southwest Arizona after noon on 6 October, and the outflow boundary that developed generated a haboob that propagated from the Imperial and Coachella Valleys into San Diego County, California, and resulted in at least one Dust Storm Warning from the NWS in San Diego (The NWS San Diego Twitter Feed has plenty of surface-based images of the dust).   How well does the dust show up in the true-color imagery above?  Imagery before 0000 UTC on the 7^th suggest dust, and likely  even a linear feature at the leading edge of the dust, over the central part of extreme southern California, even though the background is about the same color as the dust cloud that is moving over it.  Zoomed in, however, below, the dust feature is indeed distinct!

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Did the GOES-West Dust RGB capture this wind event? Somewhat. The animation below shows the Dust RGB plotted with surface observations that testify to the vigor of the outflow boundary. Dust should show up as bright pink/magenta in the RGB, and there are some small regions where that color is apparent. Information on the Dust RGB is available here and here. For this case, True-color imagery better identifies the dust than does the Dust RGB.

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After sunset, the ability to track the dust (in the visible) is gone, and the dust RGB also loses its signal.  The focus of attention can then shift in the animation at the top of the blog post to the very interesting scouring of the low clouds along the northwest Mexican coast. Dry continental air moves over the ocean (in the form of an outflow boundary from decaying convection over the land). Mixing of this dry air with the marine boundary layer occurs, causing evaporation of clouds.  The bright cyan enhancement in the Night Microphysics depicts low clouds.  As the clouds evaporate, the purple enhancement that replaces cyan shows the underlying sea surface.  Notice also the ripples in the cyan enhancement showing gravity waves propagating along the top of the boundary layer stratus ahead of the outflow boundary! 

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The animation above shows ProbSevere LightningCast probabilities over the Island of Guam for 80 minutes near noon local time on 6 October 2022 (imagery taken from this RealEarth website). The animation above shows LightningCast probabilities increasing from 0110 UTC (when a 10% contour appears) through 0140 UTC and 0150 UTC (when a 75% contour — in magenta — is present. The sequence of events initially caused some astonishment when the 0110 UTC image appeared. The toggle below compares 0100 and 0110 UTC imagery; there appears to be little difference in the imagery between those two times, yet probabilities increase. It seemed odd at the time that maximum values were separated from the observed clouds!

Lightning was observed at 0141 UTC, just off the east coast of central Guam, and at 0152 UTC, close to the NWS Office in Barrigada (and in fact, that thunder was audible in the office). Both lightning events fell within (or very close to) the 75% contour, and were also close to the radar, so radar interrogation of the storm was difficult.

As noted in the blog title, atmospheric winds during this event were light. Click here to see a toggle of satellite-derived winds at upper levels (above 400 mb) and lower levels (below 400 mb) from the SSEC Tropical Website (direct link to western Pacific winds).

The image below shows the detected lightning (in the Guam Forecast Office AWIPS display system) at 0152 UTC. Click here to view a similar image showing one lightning strike at 0141 UTC.

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Overlapping 1-minute Mesoscale Domain Sectors provided GOES-16 (GOES-East) images at 30-second intervals from all 16 ABI spectral bands (above), which displayed the northeast-moving warm thermal signature of a SpaceX Falcon-9 rocket booster as the Crew-5 Mission was launched from Cape Canaveral Space Force Station in Florida at 16:00:57 UTC on 05 October 2022. The low-altitude rocket launch condensation cloud was also evident, drifting slowly eastward away from the launch site. One or both of these rocket launch signatures were detected in all 16 of the ABI spectral bands.

30-second GOES-16 Plume RGB images (below) provided a multi-band integrated view that highlighted both the northeast-moving hot thermal signature of the rocket booster (lighter shades of green to yellow), and the low-altitude rocket condensation cloud (darker shades of green) that drifted eastward.

In a time-matched comparison of Rocket Plume RGB images from GOES-16 and GOES-17 (GOES-West), valid at 16:02:55 UTC (below), the significant eastward displacement of the brighter yellow rocket thermal signature in the GOES-17 image was due to parallax — resulting from the very large viewing angle from that satellite, especially for such a high-altitude feature (approximately 39 km at that point in time).

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JMA Himawari-8 Visible (0.64 µm) and Infrared Window (10.4 µm) images (above) showed the development of “island-effect” thunderstorms over Guam on 05 October 2022 — as mentioned in the NWS Guam Area Forecast Discussion, these storms produced 2-3 inches of rainfall over parts of western/central Guam (prompting the issuance of a Flood Advisory: Text | Tweet).

This type of island-effect convection occurred because the typical easterly trade wind flow within the  boundary layer was disrupted when a trough of low pressure became situated across the region, which led to a regime of light surface winds across the Mariana Islands (below) — and daytime heating of the islands contributed to “land breeze” convergence which aided convective development.

Hourly images of the MIMIC Total Precipitable Water product, viewed using RealEarth (below), indicated that abundant moisture was in place over Guam and the Mariana Islands during this period — for example, 57.75 mm (2.27 inches) in the vicinity of Guam at 0000 UTC (the Guam rawinsonde TPW value at that time was 54.48 mm or 2.15 inches).

A toggle between Suomi-NPP VIIRS True Color RGB and Infrared Window (11.45 µm) images valid at 0332 UTC (below) showed a thunderstorm that was developing over the western edge of the island.

Another example of island-effect convection over Guam on the following day is discussed here.

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