South Sandwich Islands lee waves

January 16th, 2021 |

GOES-16 "Red" Visible (0.64 µm) images [click to play animation | MP4]

GOES-16 “Red” Visible (0.64 µm) images [click to play animation | MP4]

GOES-16 (GOES-East) “Red” Visible (0.64 µm) images created using Geo2Grid (above) revealed long trails of lee waves extending northeastward from many of the South Sandwich Islands on 16 January 2021. These lee waves were generated by strong southwesterly winds within the marine boundary layer interacting with the topography of the islands — wind speeds had increased across that portion of the South Atlantic Ocean, in response to the tight pressure gradient between high pressure north of the islands and a deepening area of low pressure southeast of the islands (MSLP analyses).

A toggle between two NOAA-20 VIIRS True Color RGB images as viewed using RealEarth (below) provided a higher-resolution view of the lee waves extending from the island chain.

NOAA-20 VIIRS True Color RGB images [click to enlarge]

NOAA-20 VIIRS True Color RGB images [click to enlarge]

Many of these islands contain active volcanoes, which frequently produce plumes (which are primarily comprised of steam). A closer look at the lee waves emanating from one of the northernmost islands (below) appeared to suggest that a brighter white volcanic plume existed within the train of waves.

NOAA-20 VIIRS True Color RGB images [click to enlarge]

NOAA-20 VIIRS True Color RGB images [click to enlarge]

Blowing dust across the High Plains (Part 2)

January 15th, 2021 |

GOES-16 Dust RGB images, with and without hourly surface reports [click to play animation | MP4]

GOES-16 Dust RGB images, with and without hourly surface reports [click to play animation | MP4]

As discussed in this blog post, GOES-16 (GOES-East) Dust RGB images (above) displayed the distinct signature of a large blowing dust plume (brighter shades magenta/pink) that initially developed over drought-stricken areas of eastern Colorado and far western Kansas on 15 January 2021. Surface wind gusts in excess of 60 knots were seen in eastern Colorado near the source of the dust plume, with a peak gust of 63 knots or 72 mph — in fact, the anomalously-strong 925 hPa wind speeds were 5-6 sigma above the climatological mean (source). Pilot reports near the edges of the plume indicated visibility restrictions due to dust at altitudes of 5,000 feet over southwestern Kansas and 10,000 feet over northeastern New Mexico.

GOES-16 True Color RGB and Dust RGB images (created using Geo2Grid) are shown below.

GOES-16 Dust RGB and True Color RGB images [click to play animation | MP4]

GOES-16 True Color RGB and Dust RGB images [click to play animation | MP4]

Due to the presence of very dry throughout the lower/middle troposphere (Amarillo, Texas rawinsonde data), a signature of the dust plume was also evident in GOES-16 Near-Infrared “Cirrus” (1.37 µm) images (below).

GOES-16 Dust RGB and Near-Infrared

GOES-16 Dust RGB and Near-Infrared “Cirrus” (1.37 µm) images, with plots of Ceiling and Visibility [click to play animation | MP4]

After sunset, the plume signature persisted in GOES-16 Dust RGB images (below) as the blowing dust continued to move southeastward across Texas.

GOES-16 Dust RGB images, with and without hourly surface reports [click to play animation | MP4]

GOES-16 Dust RGB images, with and without hourly surface reports [click to play animation | MP4]

===== 16 January Update =====

GOES-16 Dust RGB and True Color RGB images [click to play animation | MP4]

GOES-16 Dust RGB and True Color RGB images [click to play animation | MP4]

On the following day, the dust plume began to flow off the Texas coast and over the Gulf of Mexico by 06 UTC — and although the plume signature began to diminish in the GOES-16 Dust RGB images after sunrise, it was very apparent in True Color RGB imagery (above). Note that the True Color images revealed some recirculation of dust which began to move inland toward the end of the day, as surface winds near the coast shifted to southeasterly (surface analyses).

GOES-16 Natural Color RGB images with plots of Ceiling and Visibility (below) showed that the dust reduced the visibility to 2.5 miles at a site located just off the Texas coast at 14 UTC, and to 5 miles at a site located about 100 miles offshore at 15 UTC.

GOES-16 Natural Color RGB images, with plots of Ceiling and Visibility [click to play animation| MP4]

GOES-16 Natural Color RGB images, with plots of Ceiling and Visibility [click to play animation| MP4]

In a toggle between VIIRS True Color and False Color RGB images from Suomi NPP (below), the dust plume was very evident over the Gulf of Mexico (where its lighter appearance stood out against the dark background of the water).

VIIRS True Color and False Color RGB images from Suomi NPP [click to enlarge]

VIIRS True Color and False Color RGB images from Suomi NPP [click to enlarge]

Freezing fog in the Carolinas and Virginia

January 13th, 2021 |

GOES-16 Nighttme Microphysics, Night Fog BTD (10.3-3.9 µm) and Cloud Thickness product [click to play animation | MP4]

GOES-16 Nighttime Microphysics RGB, Night Fog BTD (10.3-3.9 µm) and Cloud Thickness product [click to play animation | MP4]

GOES-16 (GOES-East) Nighttime Microphysics RGB, Night Fog BTD (10.3-3.9 µm) and Cloud Thickness product (above) showed an arc of relatively thin fog across northern South Carolina, eastern North Carolina and southeastern Virginia — which was becoming thicker/deeper in time during the hours leading up to sunrise on 13 January 2021. In areas where the Cloud Thickness increased to 400 meters or more (lighter shades of cyan), freezing fog was observed at nearby METAR sites.

GOES-16 Nighttime Microphysics RGB images with plots of surface observations (below) indicated that air temperatures were near or just below freezing at most sites across the region.

GOES-16 Nighttime Microphysics RGB images, with plots of surface observations [click to play animation | MP4]

GOES-16 Nighttime Microphysics RGB images, with plots of surface observations [click to play animation | MP4]

The band of fog over eastern North Carolina and southeastern Virginia was being pushed eastward by a lower-tropospheric trough, as shown by the NAM40 model 925 hPa wind field at 12 UTC (below).

GOES-16 Nighttime Microphysics RGB image, with a plot of NAM40 model 925 hPa winds at 12 UTC [click to enlarge]

GOES-16 Nighttime Microphysics RGB image, with a plot of NAM40 model 925 hPa winds at 12 UTC [click to enlarge]

After sunrise, GOES-16 “Red” Visible (0.64 µm) images (below) showed that most of the fog quickly dissipated across southeastern Virginia and eastern North Carolina, while thicker fog persisted over much of South Carolina.

GOES-16

GOES-16 “Red” Visible (0.64 µm) images [click to play animation | MP4]

Winter storm affecting the southern Plains and Lower Mississippi Valley

January 10th, 2021 |

GOES-16 Mid-level Water Vapor (6.9 µm) images, with hourly surface weather type plotted in yellow [click to play animation | MP4]

GOES-16 Mid-level Water Vapor (6.9 µm) images, with hourly surface weather type plotted in yellow [click to play animation | MP4]

GOES-16 (GOES-East) Mid-level Water Vapor (6.9 µm) images (above) showed widespread precipitation that was developing across the southern High Plains and Lower Mississippi Valley on 10 January 2021. A closed middle-tropospheric low was providing forcing for ascent as it moved eastward across the region — and its cyclonic circulation was evident in the Water Vapor imagery. Storm total snowfall accumulations were as high as 11 inches in Texas, 8 inches in New Mexico, 6.5 inches in Louisiana and 4.5 inches in Mississippi.

GOES-16 Day Cloud Phase Distinction RGB images (below) revealed pockets of banded convection, whose glaciated cloud tops appeared as shades of green to yellow.

GOES-16 Day Cloud Phase Distinction RGB images [click to play animation | MP4]

GOES-16 Day Cloud Phase Distinction RGB images [click to play animation | MP4]

===== 11 January Update =====

GOES-16 Day Cloud Phase Distinction RGB and Day Snow-Fog RGB images [click to play animation | MP4]

GOES-16 Day Cloud Phase Distinction RGB and Day Snow-Fog RGB images [click to play animation | MP4]

On the following day, gaps in low-level cloud cover allowed the areal extent of resulting snow cover to be seen in GOES-16 Day Cloud Phase Distinction (snow = brighter shades of green) and Day Snow-Fog (snow = darker shades of red) RGB images (above).

A toggle between VIIRS True Color and False Color RGB images from Suomi NPP at 1936 UTC (below) provided another example of a RGB variant that is useful for the discrimination of low cloud vs. snow — snow cover appeared as shades of cyan in the False Color image.

VIIRS True Color and False Color RGB images from Suomi NPP [click to enlarge]

VIIRS True Color and False Color RGB images from Suomi NPP [click to enlarge]