GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) showed that most of Antarctica experienced 24 hours of full solar illumination during the Southern Hemisphere’s Summer Solstice on 21 December 2019. Through breaks in the cloud cover, a few bright areas of sun glint were also evident, moving from west to east, due to the reflection of sunlight off ice-free water.

In spite of receiving 24 hours of sunlight, interior areas of the continent remained quite cold — due to high elevation and deep snow cover. For example, surface air temperatures at station 8927 near the center of Antarctica remained within the -25 to -35ºF range on 21 December (source).

In the Northern Hemisphere, GOES-17 (GOES-West) Visible images (below) revealed a few hours of illumination of the southern summits of Denali and nearby portions of the Alaska Range. Note the presence of much colder surface air temperatures (-20s and -30s F) north of the Alaska Range.

Farther to the north across Interior Alaska, some locations reported minimum air temperatures in the -40s to -50s F. A Suomi NPP VIIRS Infrared image (below) showed surface brightness temperatures as cold as -50ºC or -58ºF (brighter yellow enhancement) in the Yukon Flats area around Fort Yukon (PFYU).

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A comparison of GOES-17 (GOES-West) Nighttime Microphysics RGB and “Clean” Infrared Window (10.35 µm) images (above) showed the formation and motion of patchy stratus clouds (RGB shades of yellow) over Interior Alaska on 17 December 2019.  Note how the clouds are difficult to detect and track on the 10.35 µm images, since the temperatures of cold land surfaces and stratus cloud tops were similar. Since these high latitudes receive little to no sufficient solar illumination to allow useful visible imagery during the winter season, the RGB product can be a helpful tool for monitoring the evolution of such low clouds.

Plots of surface data from Bettles (PABT) and Fort Yukon (PFYU) (below) showed that the stratus cloud deck — with bases in the 6,000-10,000 feet range — had an impact on surface air temperature trends, with warming occurring as radiational cooling was slowed and/or reversed as the clouds moved overhead. Temperatures continued to rise at Bettles as the cloud coverage remained broken to overcast, while the temperature briefly dropped again at Fort Yukon as the cloud coverage thinned to scattered.

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1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) showed thunderstorms that produced a variety of severe weather (SPC Storm Reports) across the Deep South on 16 December 2019. Numerous overshooting tops could be seen with these storms.

GOES-16 “Clean” Infrared Window (10.35 µm) images (below) indicated that many of the overshooting tops exhibited brightness temperatures as cold as -70ºC (darker black pixels) — which closely corresponded to the Most Unstable air parcel Maximum Parcel Level (MU MPL) calculated from 21 UTC rawinsonde data from Jackson, Mississippi.

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As a strong 170-knot jet streak (Satellite Liaison Blog) flowed southeastward over the High Plains on 13 December 2019, GOES-16 (GOES-East) Mid-level (6.9 µm) Water Vapor images (above) showed numerous pilot reports of moderate to severe turbulence at altitudes of 26,000-50,000 feet. The Turbulence SIGMETs were issued due to strong speed shear along the poleward (northeast) edge of the jet streak — this speed shear was evident by the closely-spaced isotachs of maximum wind speed from the RAP40 model.

Over southeastern Colorado, one aircraft encountered Severe Turbulence at an altitude of 36,000 feet at 1637 UTC, while another reported Moderate to Severe Turbulence at 37,000 feet at 1645 UTC (due to a mountain wave, which caused fluctuation in airspeed of +/- 20 knots) (below).

 

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