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]

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]

Shear vorticies over the western US

November 9th, 2020 |

GOES-16 Upper-level Water Vapor (6.2 µm) and Air Mass RGB images [click to play animation | MP4]

GOES-16 Upper-level Water Vapor (6.2 µm) and Air Mass RGB images [click to play animation | MP4]

GOES-16 (GOES-East) Upper-level Water Vapor (6.2 µm) and Air Mass Red-Green-Blue (RGB) images (above) displayed a series of shear vortices migrating southwestward over the western US on 09 November 2020. The “dynamic tropopause” — taken to be the pressure of the PV1.5 surface — descended to the 500-600 hPa level within the largest and most well-defined vortex that was moving over Montana and Idaho. These features displayed hues of red to orange in the Air Mass RGB images (for example, at 2101 UTC), indicative of the dry and ozone-rich stratospheric air within the vortices. Aircraft reports of turbulence are sometimes seen in the general vicinity of these shear vortices, as the local tropopause is deformed (such as on 07 June 2017); in this case, there were only two instances of turbulence reported (at 1545 UTC and 0200 UTC).

GOES-16 Upper-level Water Vapor (6.2 µm) image at 2101 UTC, with contours of PV1.5 pressure (red) and the orientation of cross section I-I' (cyan) [click to enlarge]

GOES-16 Upper-level Water Vapor (6.2 µm) image at 2101 UTC, with contours of PV1.5 pressure (red) and the orientation of cross section line I-I’ (cyan) [click to enlarge]

The GOES-16 Water Vapor image at 2101 UTC (above) showed the northwest-to-southeast oriented cross section line I-I’ — and RAP40 model fields along that line (below) revealed the descent of stratospheric air (characterized by low values specific humidity along with high values of potential vorticity) within the shear vortex when it was located near the Idaho/Montana border.

Cross section of RAP40 model Potential Vorticity (color image + red contours), Specific Humidity (green contours) and wind barbs (cyan) [click to enlarge]

Cross section of RAP40 model Potential Vorticity (color image + red contours), Specific Humidity (green contours) and Wind (cyan) [click to enlarge]

Long-range transport of California wildfire smoke across the Upper Midwest

August 24th, 2020 |

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

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

GOES-16 (GOES-East) True Color Red-Green-Blue (RGB) images created using Geo2Grid (above) revealed the hazy signature of dense smoke aloft moving eastward across much of the Upper Midwest on 24 August 2020 — smoke that had been transported from large wildfires burning in California.

Images of 532 nm and 1064 nm lidar attenuated backscatter collected and processed by the University of Wisconsin Lidar Group at Madison from 00 UTC on 24 August to 00 UTC on 25 August (below) indicated that this smoke existed within altitudes between 2 km and 6 km.

532 nm and 1064 nm lidar attenuated backscatter during 24 August at Madison, Wisconsin [click to enlarge]

532 nm and 1064 nm lidar attenuated backscatter over Madison, Wisconsin [click to enlarge]

CIMSS Natural Color RGB images with plots of Pilot Reports are shown below. While this “simple” RGB does not depict the haziness of the smoke as well as the True Color RGB images above — which are corrected for the effect of Raleigh scattering — s subtle smoke signature was still apparent. Not many of the available Pilot Reports (PIREPs) explicitly mentioned any effects of the smoke, but one 1955 UTC PIREP indicated a reduction to Marginal Visual Flight Rules (MVFR, visibility of 3-5 miles) at at altitude of 11,500 feet (3.5 km).

CIMSS Natural Color RGB images, with plots of Pilot Reports [click to play animation | MP4]

CIMSS Natural Color RGB images, with plots of Pilot Reports [click to play animation | MP4]