Heavy rainfall and snowfall in Southern California

January 23rd, 2021 |

GOES-17 Air Mass RGB images, with contours of PV1.5 pressure [click to play animation | MP4]

GOES-17 Air Mass RGB images, with contours of PV1.5 pressure [click to play animation | MP4]

As an anomalously-deep 500 hPa low began to move inland over Southern California during the 23 January24 January 2021 period, GOES-17 (GOES-West)  Air Mass RGB images (above) showed a compact Potential Vorticity (PV) anomaly approaching the coast — and the RAP40 model indicated that the “dynamic tropopause” (defined here as the pressure of the PV1.5 surface) was descending to the 675 hPa pressure level at 18 UTC.

A west-to-east oriented cross section of RAP40 model fields along Line A-A’ (below) depicted the descending dynamic tropopause at 19 UTC.

Cross section of RAP40 model fields along line A-A' [click to enlarge]

Cross section of RAP40 model fields along line A-A’ [click to enlarge]

GOES-17 Mid-level Water Vapor (6.9 µm) images (below) showed the increasing reports of rain and snow that resulted as the PV Anomaly moved inland and provided additional forcing for ascent. Near the coast, thunderstorms were reported at Fulton and Long Beach around 03 UTC. Storm total precipitation amounts included rainfall of 1.40 inch and snowfall of 12-18 inches.

GOES-17 Mid-level Water Vapor (6.9 µm) images, with plots of hourly surface weather type [click to play animation | MP4]

GOES-17 Mid-level Water Vapor (6.9 µm) images, with plots of hourly surface weather type [click to play animation | MP4]

GOES-17 Water Vapor images at 2301 UTC and 0246 UTC (below) revealed sporadic lightning activity (indicated by small clusters of GLM Groups).

GOES-17 Mid-level Water Vapor (6.9 µm) image at 2301 UTC, with GLM Groups plotted in red [click to enlarge]

GOES-17 Mid-level Water Vapor (6.9 µm) image at 2301 UTC, with GLM Groups plotted in red [click to enlarge]

GOES-17 Mid-level Water Vapor (6.9 µm) image at 0246 UTC, with GLM Groups plotted in red [click to enlarge]

GOES-17 Mid-level Water Vapor (6.9 µm) image at 0246 UTC, with GLM Groups plotted in red [click to enlarge]

===== 24 January Update =====

GOES-17 Day Snow-Fog RGB images [click t play animation | MP4]

GOES-17 Day Snow-Fog RGB images [click to play animation | MP4]

On the following day, as clouds began to clear the areal extent of resulting fresh snow cover (darker shades of red) was seen in GOES-17 Day Snow-Fog RGB images (above). Even parts of the high desert — north and east of the mountain ranges — received some snowfall (for example, 2-3 inches were reported at Hesperia).

Suomi NPP VIIRS True Color RGB and False Color RGB images (below) showed the snow cover (shades of cyan) at 2036 UTC.

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

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

Tropical Storm Eta over the Gulf of Mexico

November 10th, 2020 |

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.

Hurricane Eta in the Caribbean Sea

November 2nd, 2020 |

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 animation | MP4]

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 animation | MP4]

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 (above) showed Hurricane Eta as it was rapidly intensifying from a Category 2 to a Category 4 storm on 02 November 2020. For a few hours there was notable lightning activity within the inner eyewall of Eta.

GOES-16 Longwave Infrared (11.2 µm) images, with contours of 02 UTC deep-layer wind shear from the CIMSS Tropical Cyclones site (below) showed that the hurricane was moving through an environment of low shear, which favored intensification.

GOES-16 Longwave Infrared (11.2 µm) images, with contours of 18 UTC deep-layer wind shear [click to enlarge]

GOES-16 Longwave Infrared (11.2 µm) images, with contours of 02 UTC deep-layer wind shear [click to enlarge]

GOES-16 Infrared – Water Vapor Brightness Temperature Difference images (below) indicated that cloud tops within much of the central dense overcast surrounding the eye were likely above the local tropopause.

GOES-16 Infrared - Water Vapor Difference images [click to enlarge]

GOES-16 Infrared – Water Vapor Difference images [click to enlarge]

===== 03 November Update =====

NOAA-20 VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images (credit: William Straka, CIMSS) [click to enlarge]

NOAA-20 VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images (credit: William Straka, CIMSS) [click to enlarge]

A toggle between NOAA-20 VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images (above) displayed Eta at 0729 UTC. Illumination from the Moon — in the Waning Gibbous phase, at 93% of Full — provided a distinct visible image at night.

Eta made landfall along the Caribbean coast of Nicaragua as a Category 4 hurricane around 2100 UTC;1-minute GOES-16 Infrared and Visible images during the period 1000-2100 UTC (below) showed that the overall appearance of Eta had deteriorated somewhat compared to the previous day, with warming cloud-top infrared brightness temperatures and a cloud-filled eye. There was no GOES-16 GLM-detected lightning activity during those 11 hours leading up to landfall.

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

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

Hurricane Zeta over the Gulf of Mexico

October 27th, 2020 |

GOES-16 “Clean” Infrared Window (10.35 µm) images, with an overlay of GLM Flash Extent Density [click to play animation | MP4]

GOES-16 “Clean” Infrared Window (10.35 µm) images, with an overlay of GLM Flash Extent Density [click to play animation | MP4]

After making landfall as a Category 1 Hurricane along Mexico’s Yucatan Peninsula a day earlier, a weakened Tropical Storm Zeta (NHC advisories) began to slowly re-intensify as it moved northward across the Gulf of Mexico after sunset on 27 October 2020 — 1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Clean” Infrared Window (10.35 µm) images with an overlay of GLM Flash Extent Density (above) displayed increasing organization, with the gradual emergence of a ragged eye. Zeta once again reached hurricane intensity at 0600 UTC on 28 October.

===== 28 October Update =====

NOAA-20 VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 0739 UTC (credit: William Straka, CIMSS) [click to enlarge]

NOAA-20 VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 0739 UTC (credit: William Straka, CIMSS) [click to enlarge]

In a toggle between NOAA-20 VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 0739 UTC (above), the coldest cloud-top infrared brightness temperature just east-northeast of the eye was -96ºC. Ample illumination from the Moon (in the Waxing Gibbous phase, at 91% of Full) helped to highlight the “visible image at night” utility of the Day/Night Band.

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 animation | MP4]

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 animation | MP4]

Zeta experienced a period of rapid intensification during the day on 28 October (ADT | SATCON) — 1-minute GOES-16 Infrared images (with and without an overlay of GLM Flash Extent Density) and Visible images (above) showed a trend of increasing organization and the emergence of a fairly well-defined eye. Periodic lightning activity within the inner eyewall region began after 1800 UTC (when Zeta was upgraded to a Category 2 hurricane), along with overshooting tops exhibiting cloud-top infrared brightness temperatures as cold as -90ºC. The hurricane made landfall along the coast of Louisiana around 2100 UTC.

GOES-16 Longwave Infrared (11.2 µm) images, with contours of 20 UTC deep-layer wind shear [click to enlarge]

GOES-16 Longwave Infrared (11.2 µm) images, with contours of 20 UTC deep-layer wind shear [click to enlarge]

Zeta was intensifying in spite of the fact that it was moving across progressively colder water, and approaching an atmospheric environment that was more hostile in terms of increasing deep-layer wind shear (above) — however, these factors were likely offset by a broad and well-defined upper level outflow channel north of the hurricane, shown by 6.2 µm Derived Motion Winds with velocities around 100 knots over Arkansas (below).

GOES-16 Upper-level Water Vapor (6.2 µm) images, with plots of Derived Motion Winds [click to play animation | MP4]

GOES-16 Upper-level Water Vapor (6.2 µm) images, with plots of Derived Motion Winds [click to play animation | MP4]

===== 29 October Update =====

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

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

On the day after Zeta’s landfall, GOES-16 True Color Red-Green-Blue (RGB) images created using Geo2Grid (above) showed an increase in turbidity within the shallow shelf waters off the Texas and Louisiana coasts. Also of note were the patches of fresh snow cover across portions of New Mexico, Texas and Oklahoma — areas having less snow depth experienced melting during the day.

A higher-resolution view of the nearshore turbidity was provided by 250-meter resolution Terra MODIS True Color RGB imagery from the MODIS Today site (below). Vigorous mixing of the water by the strong winds of Zeta stirred up a great deal of sediment.

Terra MODIS True Color RGB image [click to enlarge]

Terra MODIS True Color RGB image [click to enlarge]