GOES-16 (GOES-East) Nighttime Microphysics RGB and Day Snow-Fog RGB images (above) displayed the nocturnal formation — followed by the daytime dissipation — of shallow fog/stratus across snow-covered (shades of red in Day Snow-Fog RGB imagery) parts of southeastern Saskatchewan, southwestern Manitoba and northern North Dakota on 22 December 2023. With surface air temperatures dropping into the teens F, several METAR sites began to report freezing fog (that occasionally restricted surface visibility to near zero). Note that the shallow fog/stratus did not extend to the height of a few of the plateaus in the region (such as Turtle Mountain along the North Dakota/Manitoba border, Moose Mountain Provincial Park in Saskatchewan and Riding Mountain National Park in Manitoba).

A toggle between the GOES-16 Nighttime Microphysics RGB image at 1301 UTC and Topography (below) helped to highlight the 3 aforementioned plateau features (darker shades of tan to brown).

The GOES-16 Cloud Thickness derived product (below) — a component of the Fog and Low Stratus suite — indicated that much of the shallow fog/stratus was generally in the 600-1200 ft thickness range.

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Suomi NPP Day Night Band imagery from the NASA Worldview site, had a large increase in luminance over southwest Iceland on 19 December, to the southwest of the Capitol of Reykjavik. That is shown below in the toggle of 18 December and 19 December 2023 imagery. (Click here for a map of southwest Iceland) Light emitted by the ongoing volcanic eruption on the Reykjanes peninsula is detected by the Day Night band sensor on VIIRS on 19 December (when Aurora Borealis are also apparent!). An annotated view of the 19 December image is also shown below.

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JPSS data are available via an Amazon Webservices portal (here, for NOAA-20). The CSPP software package Polar2Grid can be used to turn the SDRs available at the portal into imagery. Appropriate VIIRS-DNB-SDR and matching VIIRS-DNB-GEO files, and the VIIRS-I04-SDR and VIIRS-IMG-GEO files (a sample of which are shown below), were saved to the local machine holding the Polar2Grid software. The times of the data to select were estimated from the NOAA-20 orbit paths on 18 December and on 19 December; on the 19th, NOAA-20 flew directly over the Reykjanes peninsula.

SVDNB_j01_d20231218_t0414482_e0416128_b31508_c20231218042644378000_oeac_ops.h5
GDNBO_j01_d20231218_t0414482_e0416128_b31508_c20231218042449010000_oeac_ops.h5
SVI04_j01_d20231218_t0414482_e0416128_b31508_c20231218042651572000_oeac_ops.h5
GIMGO_j01_d20231218_t0414482_e0416128_b31508_c20231218042458113000_oeac_ops.h5

Then, 4 different Polar2Grid calls were used to create I04 (3.74 µm) and Day Night Band visible (0.7 µm) imagery on 18 December 2023 (before the eruption) and 19 December 2023 (during the eruption), and to add maps. Those 4 images are shown below with 18 December on the left and 19 December on the right. Note the great increase in brightness and the increase in sensed temperature on 19 December!

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In spite of frequent dense cloud cover and an oblique satellite viewng angle, a distinct hot thermal signature of the Sundhnúksgígar fissure eruption (yellow to red pixels) was occasionally apparent in GOES-16 (GOES-East) Shortwave Infrared (3.9 µm) imagery (below). Station identifier BIRK is Reykjavik Airport, and BIKF is Keflavik International Airport.

Given that the fissure eruption and subsequent lava flows were occurring during the nighttime hours, the thermal signature also showed up well in GOES-16 Near-Infrared 1.61 µm and 2.24 µm imagery (below).

NOAA-21 Imagery (courtesy William Straka, CIMSS), below, show that the eruption continued during the morning hours of 20 December 2023.

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The National Weather Service forecast office in Wilmington OH (Twitter link) has noted via tweets during the day on 18 December 2023 (link, link, link) that road visibility conditions are variable in the extreme as snow showers move through Indiana and Ohio. The Day Cloud Phase distinction imagery below at 1701, 1801 and 1901 UTC on 18 December suggests that the color of the RGB might be related to snowfall. This can occur because the Day Cloud Phase Distinction RGB color signature changes as a cloud glaciates. Consider, for example, the reddish cloud that extends at 1701 UTC from Benton Harbor MI (KBEH) to the east of South Bend (KSBN) and through Goshen (KGSN) and Fort Wayne (KFWA); note that snow is associated with that cloud. What might you expect to be occurring in Paulding County (the east of Fort Wayne) or in Jay County (to the south of Fort Wayne) where a similar-colored signal exists?

Cloud Top Phase for the same 3 hours as above, shown below, indicate (in dark green) mixed-phase clouds (that is, liquid and ice co-existing) and ice clouds (in red) over the region where snow is occurring. This should not surprise: appreciable snow requires the presence of ice within the cloud for ice crystals to grow at the expense of small water droplets. Of greater interest is the back edge of the mixed phase/ice region; by 1901 UTC most of the cloud tops over eastern Indiana are shown (light green) to be entirely supercooled liquid water. Will snow continue to occur in such conditions? There have been cases where supercooled cloud-top droplets nevertheless supported snowfall (blog post; FDTD Satellite Applications webinar). At 1901 UTC, however, there were not many observations of snow underneath clouds that were supercooled.

The Slider Juxtaposes below compare Day Cloud Phase Distinction and Level Cloud Top Phase a 1701 UTC (below) and 1901 UTC (bottom).

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The GOES-16 GLM instrument has occasionally observed lightning over southern Ohio and West Virginia during the afternoon. How did LightningCast Probabiity do in predicting the flashes? Imagery from 1901 to 1951 UTC on the 18th, below, from this website, doesn’t show large values of LightningCast probability in regions where GLM observations occurred. However, small LightningCast probabilities are noted occasionally within the environment that is spawning occasional GLM observations.

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These snow showers and lightning events occurred on the back side of a very large extratropical cyclones that moved up the east coast of the United States, bringing heavy rains from Georgia to Maine. The 2-day animation of GOES-16 hourly airmass RGB images (created using geo2grid), below, shows the evolution of the system. On 18 December, a strong potential vorticity anomaly was present over the Ohio River Valley as suggested by the orange color in the RGB. (Click here to see a model cross section at 1800 UTC — the corresponding airmass RGB is here) in the midwest, created from the awesome TropicalTidbits website that confirms that suspicion).

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10-minute JMA Himawari-9 AHI Shortwave Infrared (3.9 µm) and Clean Infrared Window (10.4 µm) images (above) showed he development of a pyrocumulonimbus (pyroCb) cloud northwest of Tamworth (YSTW) in New South Wales, Australia on 18 December 2023. The coldest cloud-top Infrared Window brightness temperature was -53.4ºC at 1230 UTC.

The southern flank of the large wildfire complex flared up after a convective outflow boundary moved southwestward across the area between 1000-1100 UTC — the pyroCb cloud then developed by 1200 UTC.

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