Re-suspended ash from the Katmai volcano in Alaska

February 28th, 2021 |

GOES-17 “Red” Visible (0.64 µm) images [click to play animation | MP4]

GOES-17 “Red” Visible (0.64 µm) images [click to play animation | MP4]

1-minute Mesoscale Domain Sector GOES-17 (GOES-West) “Red” Visible (0.64 µm) images (above) showed the hazy signature of a plume of re-suspended ash from the 1912 Katmai volcanic eruption. Strong surface winds gusting to 50-55 knots — caused by a strong pressure gradient along the western periphery of a Storm Force low in the Gulf of Alaska (surface analyses) — lofted some of the thick layer of ash that has remained on the ground in the vicinity of the volcano. The most dense portion of the aerosol plume was  moving across the Barren Islands (between Kodiak Island to the south and the Kenai Peninsula to the north); near the northern edge of the aerosol plume, surface visibility was reduced to 5 miles at Homer and 7 miles at Seldovia.

A sequence of Suomi NPP VIIRS Day/Night Band (0.7 µm) images (below) showed that the plume had formed before sunrise — ample illumination from a Full Moon provided vivid “visible mages at night” (at 1131 UTC and 1311 UTC).

Suomi NPP VIIRS Day/Night Band (0.7 µm) images [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) images [click to enlarge]

ASCAT winds from Metop-C at 0743 UTC and 2124 UTC (source) are shown below — they indicated a dramatic increase in surface wind speeds  of 50 knots or greater emerging from the Barren Islands into the Gulf of Alaska later in the day.

ASCAT winds from Metop-C, at 0743 UTC and 2124 UTC [click to enlarge]

ASCAT winds from Metop-C, at 0743 UTC and 2124 UTC [click to enlarge]

GOES-17 True Color RGB images created using Geo2Grid (below) provided a clearer view of the re-suspended ash plume. North of the plume, note the tidal ebb and flow of ice within Cook Inlet and Turnagain Arm leading into the Anchorage area.

GOES-17 True Color RGB images [click to play animation | MP4]

GOES-17 True Color RGB images [click to play animation | MP4]

Geostationary satellite views of the most rain over 72-hours in 2007

February 27th, 2021 |

The record for the most rain over a 72-hour period was in late February 2007, with 3.930m (154.72″)! This was on Reunion Island, associated with Tropical Cyclone Gamede in South Indian Ocean. The island is east of Madagascar. This island also holds the record for the most rain (4,869 mm (191.7 in)) over a 96-hour period, associated with the same event. More on this case can be found in this 2009 BAMS article.

Meteosat-8

While the view of the cyclone from EUMETSAT‘s MET-8 was on the edge of the viewing area, the infrared window loop was still impressive.

A 3-day color-enhanced infrared window loop from EUMETSAT’s Meteosat-8 geostationary imager.

A longer loops of 3 and 4 days were also generated. Which shows Tropical Cyclone Favio as well. For these images, the coldest brightness temperatures have the green/yellow/red/pink colors. A one-day loop (February 25, 2007) in both mp4 and animated gif formats.

Meteosat-7

EUMETSAT’s Meteosat-7, due to its location over the Indian Ocean, had a more direct view of these cyclones.

A 3-day color-enhanced infrared window loop from EUMETSAT’s Meteosat-7 geostationary imager.

Note that the view angle is improved over Meteosat-8, but the image frequency is reduced. A longer Meteosat-7 loop was also generated. Again, Tropical Cyclone Favio can be seen.

A loop of Meteosat-7 visible band from February 25, 2007.

Visible loops (mp4 format) from February 23 and 24 and 26, 2007. The same loops as animated gifs: February 23, 24, 25 and 26, 2007.

H/T

Thanks to @Weather_History for the post on this event.

The above satellite data are from EUMETSAT, accessed via the University of Wisconsin-Madison Space Science and Engineering Center (SSEC) Data Services. The images were generated with McIDAS-X. More on EUMETSAT’s Meteosat Third Generation will appear in the Bulletin of the AMS.

Snow squalls in Montana

February 27th, 2021 |

GOES-16 “Red” Visible (0.64 µm) and Day Cloud Phase Distinction RGB images [click to play animation | MP4]

GOES-16 “Red” Visible (0.64 µm) and Day Cloud Phase Distinction RGB images [click to play animation | MP4]

GOES-16 (GOES-East) “Red” Visible (0.64 µm) and Day Cloud Phase Distinction RGB images (above) showed a cluster of convective features propagating south-southeastward over and to the east of Billings, Montana on 27 February 2021. The shades of green in the RGB images indicated that some of these cloud tops were glaciating, suggesting enough vertical development to produce significant precipitation — and the resulting snow squalls could have contributed to a multi-vehicle accident which closed down Interstate 90 (between Billings and the I-90/I-94 junction) shortly after 1900 UTC. A brief accumulation of 1.3 inches was reported just north of Billings around the time of the accident, and the 1900 UTC surface visibility dropped to 3/4 mile at Billings airport (but was likely lower where the more intense snow squalls were occurring farther east).

The corresponding GOES-17 (GOES-West) Visible/RGB animations are available here: GIF | MP4. A toggle between the 1901 UTC Day Cloud Phase Distinction RGB images from GOES-16 and GOES-17 is shown below. The satellite viewing angles are nearly equivalent from both satellites (around 60 degrees) — but the apparent location of the snow squall features is shifted, due to parallax.

1901 UTC Day Cloud Phase Distinction RGB images from GOES-16 and GOES-17 [click to enlarge]

1901 UTC Day Cloud Phase Distinction RGB images from GOES-16 and GOES-17 [click to enlarge]

Using NUCAPS lapse rates to evaluate atmospheric stability

February 26th, 2021 |

GOES-17 Visible Imagery (2300 UTC), NOAA-20 NUCAPS-derived lapse rate (925 – 700 mb, 23:03 UTC) and NUCAPS sounding points (2249 UTC) on 25 February 2021 (Click to enlarge)

NUCAPS profiles derived from CrIS and ATMS data on NOAA-20 provide model-independent estimates of atmospheric thermodynamics globally, including, for this case over the central Pacific Ocean, in regions otherwise bereft of data.  NUCAPS lapse rates show a minimum in stability in low-levels in between two cloud features; the region includes mostly ‘green’ NUCAPS retrieval points:  where infrared and microwave retrievals have both converged.  It is difficult in the case above to relate differences in cloud features to differences in the diagnosed stability.

Four minutes later (shown below), NOAA-20 was closer to the Pole on this ascending pass and the diagnosed stability does relate well to differences in cloud structures.  In particular, the change from lapse rates around 5 C/km northeast of Hawai’i to lapse rate closer to 2 or 3 C/km even farther northeast aligns with a boundary between cloud types.

GOES-17 Visible Imagery (2310 UTC), NOAA-20 NUCAPS-derived lapse rate (925 – 700 mb, 23:07 UTC) and NUCAPS sounding points (2249 UTC) on 25 February 2021 (Click to enlarge)

The subsequent NOAA-20 pass was west of the main Hawai’ian Island chain.  Again, differences in lapse rates are related to cloud features in the visible imagery.  Stable air — with lapse rates between 3 and 4 C/km — overlies a region of very little cumuliform development.  A region of larger lapse rates over the eastern 1/3rd of the pass, just to the west of the Hawai’ian Islands is accompanied by cumulus development.  NUCAPS thermodynamic fields, even though they have limited resolution in the vertical (at most 10 layers in the enter tropopause), can give useful information on stability over the ocean that can help in the real-time diagnosis of the atmosphere.