Strong winds, gravity waves and turbulence across Northern California

January 19th, 2021 |

GOES-17 Mid-level Water Vapor (6.9 µm) images, with Pilot Reports of turbulence [click to play animation | MP4]

GOES-17 Mid-level Water Vapor (6.9 µm) images, with Pilot Reports of turbulence [click to play animation | MP4]

GOES-17 (GOES-West) Mid-level Water Vapor (6.9 µm) images which included Pilot Reports (PIREPS) of turbulence (above) revealed a diverse variety of gravity waves across much of Northern California on 19 January 2021. Three types of waves were prevalent: (1) quasi-stationary mountain waves caused by strong northeasterly flow interacting with topography of the Sierra Nevada and Coastal Ranges, (2) long, narrow corridors of fast-moving waves flowing offshore, and (3) west-to-east oriented arcs of waves drifting slowly northward (against the ambient flow). With such disparate wave structures and the intersections of their wave fronts, the prospects for atmospheric turbulence were elevated — in fact, there were a few pilot reports of moderate to severe turbulence, at both low and high altitudes.

GOES-17 Mid-level Water Vapor images with plots of NAM40 model 500 hPa wind streamlines/isotachs at 18 UTC and 00 UTC (below) showed the strong northeasterly flow in the middle troposphere, with speeds as high as 100-110 knots.

GOES-17 Mid-level Water Vapor (6.9 µm) images, with plots of NAM40 model 500 hPa wind streamlines/isotachs at 18 UTC and 00 UTC [click to enlarge]

GOES-17 Mid-level Water Vapor (6.9 µm) images, with plots of NAM40 model 500 hPa wind streamlines/isotachs at 18 UTC and 00 UTC [click to enlarge]

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]

A leeside cold frontal gravity wave in the Plains, and a strong polar jet stream over the Rockies

January 14th, 2021 |

GOES-16 Upper-level Water Vapor (6.2 µm) images, with plots of hourly surface wind barbs and gusts [click to play animation | MP4]

GOES-16 Upper-level Water Vapor (6.2 µm) images, with plots of hourly surface wind barbs and gusts [click to play animation | MP4]

GOES-16 (GOES-East) Upper-level Water Vapor (6.2 µm) images (above) displayed the signature of a leeside cold frontal gravity wave (reference) as it moved rapidly southward across the Plains (surface analyses) on 14 January 2021. Post-frontal wind gusts in the 50-70 knot range were seen, with a peak gust to 91 knots (105 mph) in eastern Wyoming.

In addition, an anomalously-strong (170-180 knot) meridional branch of the upper-tropospheric polar jet stream was progressing southward over the Rocky Mountains — and GOES-16 Water Vapor images with plots of Derived Motion Winds and contours of RAP40 model maximum wind speeds (below) revealed that the highest satellite-tracked Derived Motion Wind (DMW) speed was 182 knots over southern Montana at 1401 UTC. Some of the DMW speeds were nearly 10 knots faster than the RAP40 model maximum wind (for example, this 170-knot DMW over Wyoming at 1616 UTC).

GOES-16 Upper-level Water Vapor (6.2 µm) images, with plots of 6.2 µm Derived Motion Winds and contours of RAP40 model maximum wind speeds [click to play animation | MP4]

GOES-16 Upper-level Water Vapor (6.2 µm) images, with plots of 6.2 µm Derived Motion Winds and contours of RAP40 model maximum wind speeds [click to play animation | MP4]