5-minute CONUS Sector GOES-18 (GOES-West) Shortwave Infrared (3.9 µm) and Fire Mask derived product images (above) displayed a pronounced thermal signature associated with an eruption in the Halema’uma’u crater (located within the Kilauea summit caldera) on the Big Island of Hawai’i, which began around 1220 UTC (2:20 AM HST) on 23rd December 2024. Yellow pixels in the Fire Mask product denoted 3.9 µm brightness temperatures that had reached 137.88ºC — the saturation temperature of GOES-18 ABI Band 7 detectors — which first occurred at 1251 UTC, about 30 minutes after eruption onset.

Since the Kilauea eruption began during the nighttime hours, its thermal signature was also apparent in GOES-18 Near-Infrared 0.86 µm, 1.61 µm and 2.24 µm spectral bands (below).

GOES-18 True Color RGB images from the CSPP GeoSphere site (below) showed the southwest transport of volcanic fog (vog) — a mixture of SO₂, CO₂ and water vapor — from the Kilauea eruption site.

GOES-18 SO2 RGB images from RealEarth (below) confirmed the presence of SO2 (lighter shades of cyan) within the vog plume that was drifting southwest from Kilauea — the cluster of dark blue pixels denoted the thermal anomaly associated with the eruption site.

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CSPP Geosphere imagery, above, (link for the latest animation) shows extensive snowcover over Wisconsin in the wake of the season’s first large-scale snowfall on 19-20 December. WFO MKX shows reported accumulations below (from their weather story). Note that Lake Winnebago south of Green Bay is ice-covered, but various other lakes (Mendota/Monona, Green Lake, Lake Geneva) in Wisconsin have not yet frozen.

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10-minute JMA Himawari-9 AHI “Red” Visible (0.64 µm), Shortwave Infrared (3.9 µm) and “Clean” Infrared Window (10.4 µm) images (above) showed the formation of a pyrocumulonimbus (pyroCb) cloud that was spawned by a bushfire in Grampians National Park in far southeast Australia on 20th December 2024. The pyroCb cloud exhibited cloud-top 10.4 µm infrared brightness temperatures (IRBTs) of -40ºC and colder (denoted by the shades of blue) — attaining a minimum IRBT of -44º C at 0530 UTC (the air temperature at an altitude around 10 km, according to rawinsonde data from Melbourne: plot | text). The pyroCb cloud eventually drifted southeast over Melbourne Airport (YMML).

Himawari-9 True Color RGB images created using Geo2Grid (below) displayed the broad smoke plume that was being transported east-southeastward from the Grampians bushfire — along with the high-altitude pyroCb cloud that cast a shadow upon the smoke layer below.

A NOAA-20 (mislabeled as NPP) VIIRS Day/Night Band (0.7 µm) image valid at 0450 UTC (below) provided another view of the pyroCb cloud shortly after its formation.

As a surface trough of low pressure was moving east-northeastward across the state of Victoria (surface analyses), strong S-SW winds behind the trough axis (surface observations at Melbourne and Avalon) helped to intensify the Grampians fire complex — and the pyroCb cloud developed just after the trough passed through the area. Himawari-9 Fire Temperature RGB images (below) revealed (1) the rapid northward run of the Grampians bushfire following the ~0400 UTC trough passage, (2) the pyroCb formation shortly after the time of the trough passage, and (3) the northeastward surge of cooler air (darker shades of purple over cloud-free land surfaces) in the wake of the trough passage. Note that in the Himawari-9 True Color RGB images shown above, the trough passage also initiated a northward transport of boundary layer smoke from the bushfire source region.

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The possibility of heavy rain over the Samoan islands led the Pacific Region to request 1-minute imagery over American Samoa, imagery that ended at 2107 UTC on 18 December when the domain was moved to cover the southwestern US (where a significant fire risk was occurring on 18 December). GREMLIN observations from 13-19 UTC on 18 December, shown below with Total Precipitable Water (TPW), suggest the heaviest rains were over the Manu’a Islands to the east of Tutuila Island. Note the region of slightly drier air — TPW < 2″ — (orange/rust in the enhancement) south of the Samoan Islands, where TPWs are closer to 2.3″ (magenta in the enhancement).

Day Cloud Phase Distinction fields as sun rose over Samoa on 18 December show convection developing over the main Samoan Islands as active convection continues to the east. (Click here for the Day Cloud Phase Distinction overlain by GREMLIN).

One of the ABI fields used in the Machine Learning algorithm that estimates radar echoes is Band 9 (Mid-level water vapor at 6.95 µm). The animations below show Band 9 and also Band 9 overlain with GREMLIN.

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What kind of winds accompanied this convection? ASCAT observations can give a hint, as the observations below from Metop-C show. However, large regions are unsampled.

Derived Motion Winds calculated from GOES-18 imagery (Bands 2, 7, 8, 9, 10, 14) can give wind information, and values are shown below. Low-level winds (violet and dark blue in the imagery below) are from the northwest whereas upper-level winds (shades or red) are from the southwest, so there is considerable shear over the Islands (Here is a still image from 1940 UTC). There is a noticeable increase in the number of derived wind vectors as the sun rises and visible imagery becomes available! Low level winds are not moving the dry air to the southwest of Samoa over the islands.

Microwave estimates of TPW, below, taken from the MIMIC website, also show Samoa deep within the moisture of the South Pacific Convergence Zone. Heavy rain chances will likely continue there for the next few days.

GREMLIN fields for GOES-West are also available here on the CIRA SLIDER. Finally, maybe you’re wondering why, if the Mesoscale sector was over Samoa, didn’t I show 1-minute imagery!? I matched the time increment to that of the GREMLIN product, which is a full-disk field, produced every 10 minutes.

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