VIIRS views of the surface and atmosphere, late September 2020 version

September 24th, 2020 |

VIIRS True-Color imagery on 02 and 22 September 2020 (Click to enlarge). Data from the VIIRS Today website

VIIRS True-Color imagery taken from the VIIRS Today website, above, shows the reddening/yellowing of trees over the upper midwest between 2 September and 22 September 2020. The inexorable slip into autumn and winter is ongoing.

Early in the morning on 24 September, Direct Broadcast NOAA-20 data downloaded at CIMSS and processed with CSPP showed an extensive aurora over much of Canada. (These data are available from the Direct Broadcast ftp site: link; direct link to the NOAA-20 data used below: link — note that this direct link is ephemeral and will disappear after about a week). The Day Night Band imagery is toggled with 11.45 µm infrared imagery.

NOAA-20 remapped VIIRS Day Night Band visible (0.7 µm) imagery and infrared 11.45 µm imagery, 0804 UTC on 24 September 2020

Hurricane Sally in the northern Gulf of Mexico

September 14th, 2020 |

Sally was upgraded to a Hurricane at 1600 UTC on 14 September. (Link)

MIMIC total precipitable water, 12 UTC 13 September – 11 UTC 14 September 2020 (Click to enlarge)

Hurricane warning have been issued along the central Gulf Coast on 14 September as strengthening tropical storm Sally approached.  MIMIC estimates of total precipitable water, above, for the 24 hours ending at 11 UTC on 14 September show the moist airmass in the Gulf that is helping to sustain the storm.  (Also apparent in the imagery:  Hurricane Paulette, moving over the island of Bermuda, and Pacific Tropical Storm Karina.  (For more information on these storms (and other storms during this active Atlantic Hurricane Season), and for the latest on Sally, refer to the National Hurricane Center)

Both Suomi NPP and NOAA-20 overflew Sally between 0700 and 0800 UTC on 14 September, and Day Night Band imagery for the storm (source) is shown below. The 50-minute time step between the two images show little because of a lack of lunar illumination, but westward expansion of the cloud shield near the Mississippi River delta is apparent. This suggests adequate upper-level divergence for continued storm intensification.

Suomi NPP (0707 UTC ) and NOAA-20 (0757 UTC) Day Night Band imagery on 14 September 2020 (Click to enlarge)

GOES-16 animations of infrared imagery for the 12 hours endings near 1300 UTC on 14 September, below, also show an expansion in the size of the coldest cloud tops in the storm’s center. A frontal zone is also apparent in the infrared imagery, stretching from New York/Pennsylvania southwestward to north Texas. This front will limit how far north the effects of Sally — post landfall — can move. (The forecast as of 14 September moves the post-landing remnants of Sally through Georgia).

GOES-16 Clean Window Infrared (10.3 µm) Imagery over Sally, 0116 – 1316 UTC 14 September 2020 (Click to animate)

Low-level Water vapor infrared imagery (GOES-16 Band 10, at 7.3 µm; click here for the Upper-level Water vapor infrared imagery, at 6.2 µm), below, using an enhancement courtesy William Churchill, WFO Key West (Click here for the Band 10 animation with a more familiar, perhaps, ‘dry yellow’ enhancement), also shows the expansion of the clouds in the central core of the storm. An apparent outflow channel from the storm south over Cuba also shows up in the animation.

GOES-16 Low-Level water vapor Infrared (7.3 µm) Imagery over Sally, 0926 – 1331 UTC 14 September 2020 (Click to animate)

A GOES-16 mesoscale sector is viewing the development of Sally, allowing for 1-minute imagery.  Visible imagery below, for two hours shortly after sunrise, shows active convection ongoing in the center of the storm and an obvious expansion of the central dense overcast. Both things support strengthening is the inner core structure.

GOES-16 Visible (0.64 µm) imagery, every minute, from 1233 to 1432 UTC on 14 September 2020 (Click to animate)

===== 21 UTC Update =====

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

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

1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images — with and without an overlay of GLM Flash Extent Density (above) showed Hurricane Sally after it was upgraded to a Category 2 storm at 21 UTC. A series of convective bursts could be seen developing near the center of Sally; as is usually the case, very little GLM-detected lightning activity was associated with these types of convective bursts located within close proximity to the eye. Winds at Viocsa Knoll — an elevated oil platform, located just northwest of the storm center — gusted to 94 knots or 108 mph at 2100 UTC (shortly after gusting to 102 knots or 117 mph at 2020 UTC).

You can find more information on Sally at the SSEC Tropical Website (Link). For official forecasts, refer to the pages of the National Hurricane Center. Interests along the central Gulf Coast should be preparing for the arrival of this storm, in addition to monitoring its progress.

Using NUCAPS soundings in and around fire locations

September 7th, 2020 |

GOES-16 Visible (0.64 µm) hourly imagery, 1811-2311 UTC on 6 September 2020 (click to enlarge)

GOES-16 Visible imagery, above, during the late afternoon on 6 September, shows an invigoration of the Cameron Peak fire in Larimer County, Colorado, with visible evidence of a pyrocumulus development.  Are there tools a forecaster can use to anticipate such extraordinary afternoon fire growth?

NOAA-20 overflew Colorado shortly after (NOAA-20 orbits can be viewed at this website) 2000 UTC on 6 September (see NUCAPS Sounding availability points below;  note that the date of these plots — 1951 UTC — corresponds to the time of  the first NUCAPS swath is available in AWIPS from this NOAA-20 pass;  for this ascending pass, that swath is near 40 S latitude!)

NUCAPS Sounding Points from the 2000 UTC overpass on 6 September 2020 (Click too enlage)

What do the NUCAPS Sounding surrounding Larimer County Colorado look like?  The animation below steps through the profiles surrounding the fire.  Consider using the LCL and EL information (and other information) in these profiles when diagnosing the likelihood of convection developing in response to an intense fire.  On this day, NUCAPS showed steep mid-tropospheric lapse rates that help support pyrocumulonimbus.

Select NUCAPS Soundings and thermodynamic variables (from AWIPS, locations as indicated) on 6 September 2020 (Click to enlarge)

Lake water color changes at Pyramid Lake in Nevada

September 4th, 2020 |

NOAA-20 VIIRS True-Color imagery of Pyramid Lake in Nevada, daily from 01 July through 03 September 2020

The animation above shows NOAA-20 VIIRS true color imagery of Pyramid Lake (The Paiute tribe maintains a Pyramid Lake Twitter Account: Link)  in western Nevada. The Lake was closed on 21 July 2020 because cyanotoxins released during a toxic algae bloom (link). The algae bloom is apparent before the lake closure on 21 July, as shown, for example in this Sentinel-2 image.  The color change due to the algal bloom is obvious between 01 and 20 July, as shown below.

The algal bloom was followed by a ‘whiting’ event during which calcium carbonate precipitates into the water (link with description).  On 1 August (below), that suspended calcium carbonate is apparent in far southern Pyramid Lake (Here is an image from 2 August, and here are photographs of the Lake from 5 August).  The discoloration spreads slowly north, covering the entire lake by mid-August.   The animation above shows swirls in both algae and turquoise waters that are related to surface currents in the lake.  The shimmery turquoise color remains as of 3 September 2020.  Check out VIIRS today daily into the future to see how the color changes.

NOAA-20 VIIRS Imagery of Pyramid Lake, times as indicated, between 1 July and 3 September 2020 (Click to enlarge)

Hat tip to Mike Stavish, SOO at WFO MFR for alerting us to this event!