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Snow cover and ice accrual across the Upper Midwest

By Scott Bachmeier •

GOES-16 (GOES-East) “Red” Visible (0.64 µm), Near-Infrared “Snow/Ice” (1.61 µm) and Day Snow-Fog Red-Green-Blue (RGB) images (above) showed a broad swath of fresh snow cover across parts of Nebraska, South Dakota, Iowa, Minnesota, Wisconsin and Upper Michigan on 11 November 2020. The band of heavy snow developed northwest of an intensifying midlatitude cyclone on the... Read More

GOES-16 “Red” Visible (0.64 µm), Near-Infrared

GOES-16 “Red” Visible (0.64 µm), Near-Infrared “Snow/Ice” (1.61 µm) and Day Snow-Fog RGB images [click to play animation | MP4]

GOES-16 (GOES-East) “Red” Visible (0.64 µm), Near-Infrared “Snow/Ice” (1.61 µm) and Day Snow-Fog Red-Green-Blue (RGB) images (above) showed a broad swath of fresh snow cover across parts of Nebraska, South Dakota, Iowa, Minnesota, Wisconsin and Upper Michigan on 11 November 2020. The band of heavy snow developed northwest of an intensifying midlatitude cyclone on the previous day (surface analyses) — storm total snowfall amounts included 11 inches in Nebraska, 11 inches in Minnesota, 8 inches in South Dakota, 7.5 inches in Iowa and 6.8 inches in Wisconsin.

GOES-16 “Red” Visible (0.64 µm), Near-Infrared "Snow/Ice" (1.61 µm) and Day Snow-Fog RGB images at 1501 UTC [click to enlarge]

GOES-16 “Red” Visible (0.64 µm), Near-Infrared “Snow/Ice” (1.61 µm) and Day Snow-Fog RGB images at 1501 UTC [click to enlarge]

In a comparison of images at 1501 UTC (above), note the darker shades of gray/black on the 1.61 µm image and the darker shades of red on the RGB image along the southeastern edge of the heavy snow band — this highlighted areas where a significant accrual of ice resulted from freezing rain/drizzle. As seen in a plot of ABI Spectral Response Functions (below), snow and ice are efficient absorbers of radiation (and therefore exhibit a low relectance) at the 1.61 µm wavelength, making them appear darker on the Snow/Ice and RGB images — and since ice absorbs more strongly than snow, it appears as the darkest shades of gray/black (1.61 µm) or red (RGB).

Plots of Spectral Response Function for ABI Bands 1-5 [click to enlarge]

Plots of Spectral Response Function for ABI Bands 1-5 (credit: Mat Gunshor, CIMSS) [click to enlarge]

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Tropical Storm Eta over the Gulf of Mexico

By Scott Bachmeier •

A toggle between Suomi NPP VIIRS Infrared Window (11.45 µm) and Day/Night Band (0.7 µm) images at 0734 UTC (above) showed Tropical Storm Eta over the Gulf of Mexico (northwest of Cuba) on 10 November 2020. A large convective burst was seen southeast of the storm center, with concentric cloud-top... Read More

Suomi NPP VIIRS Infrared Window (11.45 µm) and Day/Night Band (0.7 µm) images at 0734 UTC [click to enlarge]

Suomi NPP VIIRS Infrared Window (11.45 µm) and Day/Night Band (0.7 µm) images at 0734 UTC [click to enlarge]

A toggle between Suomi NPP VIIRS Infrared Window (11.45 µm) and Day/Night Band (0.7 µm) images at 0734 UTC (above) showed Tropical Storm Eta over the Gulf of Mexico (northwest of Cuba) on 10 November 2020. A large convective burst was seen southeast of the storm center, with concentric cloud-top gravity waves propagating radially outward from its lightning-illuminated core (intense lightning activity was causing the cluster of bright pixels on the Day/Night Band image).

1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Clean” Infrared Window (10.35 µm), GLM Flash Extent Density and “Red” Visible (0.64 µm) images (below) showed Tropical Storm Eta from sunrise to sunset, as it continued a slow northward movement — pulsing overshooting tops occasionally exhibited infrared brightness temperatures of -90ºC and colder (yellow pixels embedded within darker shades of purple), and lightning activity persisted for much of the day.

GOES-16 “Clean” Infrared Window (10.35 µm) images (with and without an overlay of GLM Flash Extent Density) and “Red” Visible (0.64 µm) images [click to play MP4 animation]

GOES-16 “Clean” Infrared Window (10.35 µm) images (with and without an overlay of GLM Flash Extent Density) and “Red” Visible (0.64 µm) images [click to play MP4 animation]

===== 11 November Update =====

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]

Eta once again reached Hurricane intensity at 1235 UTC on 11 November, as it approached the west coast of Florida. 1-minute GOES-16 Visible images (above) showed the partially exposed low-level circulation of Eta; however, it then weakened back to a Tropical Storm several hours later, at 1800 UTC.

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Shear vorticies over the western US

By Scott Bachmeier •

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... Read More

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]

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Tropical Storm Eta enters the Florida Straits

By Scott Bachmeier •

1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Clean” Infrared Window (10.35 µm) and “Red” Visible (0.64 µm) images (above) showed Tropical Storm Eta as it began to move across the Florida Straits after 15 UTC on 08 November 2020. Deep convection began to develop across far southern Florida around 02 UTC on 09 November, just north of Eta’s broad circulation center — and... Read More

GOES-16

GOES-16 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images [click to play animation | MP4]

1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Clean” Infrared Window (10.35 µm) and “Red” Visible (0.64 µm) images (above) showed Tropical Storm Eta as it began to move across the Florida Straits after 15 UTC on 08 November 2020. Deep convection began to develop across far southern Florida around 02 UTC on 09 November, just north of Eta’s broad circulation center — and the tropical storm made landfall in the Florida Keys at 0400 UTC. The strongest wind gusts were found to the north/northeast of the storm.

Sea Surface Temperature and Ocean Heat Content [click to enlarge]

Sea Surface Temperature and Ocean Heat Content [click to enlarge]

Maps of Sea Surface Temperature and Ocean Heat Content from the CIMSS Tropical Cyclones site (above) indicated that Eta was moving over warm water (SST around 28ºC, and a pocket of modest OHC) north of Cuba. GOES-16 Longwave Infrared (11.2 µm) images, with contours of 02 UTC deep-layer wind shear (below) showed that the hurricane was moving through an environment of moderate southwesterly shear, which limited intensification.

GOES-16 Longwave Infrared (11.2 µm) images, with contours of 19 UTC deep-layer wind shear [click to enlarge]

GOES-16 Longwave Infrared (11.2 µm) images, with contours of 19 UTC deep-layer wind shear [click to enlarge]

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