Thunderstorms over the Chukchi Sea and Beaufort Sea north of Alaska

July 12th, 2021 |

Suomi NPP VIIRS Infrared Window (11.45 µm) and Visible (0.64 µm) images [click to play animation | MP4]

Suomi NPP VIIRS Infrared Window (11.45 µm) and Visible (0.64 µm) images [click to play animation | MP4]

A sequence of Suomi NPP VIIRS Infrared Window (11.45 µm) and Visible (0.64 µm) images (above) showed snapshots of thunderstorms over parts of the Chukchi Sea and the Beaufort Sea off the northern coast of Alaska on 12 July 2021. The coldest convective cloud-top infrared brightness temperatures were in the -30 to -40ºC range. Unusual aspects of these thunderstorms included their high latitude location over ice-covered waters — as far north as 75ºN latitude — and the large amount of cloud-to-surface lightning strikes that they produced.



These thunderstorms were not surface-based — instead, they were forced by an approaching cold front (surface analyses) which helped to release elevated instability within the 500-300 hPa layer (below).

Suomi NPP VIIRS Infrared Window (11.45 µm) images, with contours of NAM40 lapse rate within the 500-300 hPa layer [click to enlarge]

Suomi NPP VIIRS Infrared Window (11.45 µm) images, with contours of NAM40 lapse rate within the 500-300 hPa layer [click to enlarge]

Rawnsonde data from Utqiagvik (PABR) were not available (due to ongoing equipment malfunction at that site) — but a NUCAPS profile near the southernmost cluster of convection around 15 UTC (below) showed the layer of instability aloft.

NUCAPS profile near thunderstorms off the northern coast of Alaska [click to enlarge]

NUCAPS profile near thunderstorms off the northern coast of Alaska [click to enlarge]

Using Polar-Orbiting Satellite Imagery from Direct Broadcast sites to understand Elsa

July 6th, 2021 |

Suomi NPP Adapative Day Night Band imagery, 0636 UTC on 6 July 2021 (Click to enlarge)

AOML (The Atlantic Oceanographic and Meteorological Laboratory) maintains a Direct Broadcast antenna site that holds satellite imagery (created using CSPP — the Community Satellite Processing Package) created when a tropical system — such as Elsa — is within the download footprint of the AOML antenna.  This imagery — particularly in the microwave — is useful to describe the system’s structure. The Day Night Band image above, from Suomi NPP at 0636 UTC, shows a non-symmetric storm with the bulk of clouds to the east and south of the surface center (at that time near 23.9 N, 82.3 W, i.e., in the Florida Straits to the south of Dry Tortuga).  Rainfall, as diagnosed using MIRS algorithms and microwave ATMS (Advanced Technology Microwave Sounder) data from NPP, below, shows the asymmetry of the storm as well:  almost all the diagnosed rain is east of the center. (It’s helpful that both infrared imagers and microwave sounders are on the same satellite!)

Suomi NPP ATMS-derived Rain Rate, 0637 UTC on 6 July 2021 (Click to enlarge)

The GCOM-W1 (supported by JAXA) satellite also scanned Elsa shortly before 0700 UTC on 6 July.  Microwave observations at ~36 GHz, below, and at 89 GHz, farther below, can help to characterize the structure of the storm. Indeed, observations at/around 85-89 GHz are used in the MIMIC TC product as described here.

GCOM AMSR-2 observations at 36.5 GHz, 0649 UTC on 6 July 2021 (Click to enlarge)

GCOM AMSR-2 observations at 89.0 GHz, 0649 UTC on 6 July 2021 (Click to enlarge)

In addition to the AOML site, the CIMSS Direct Broadcast site contains Polar Orbiting imagery in near-real time. The afternoon 88.2 GHz image from (NOAA-20) ATMS is shown below.  Cold cloud tops associated with strong scattering by ice of the 88.2 GHz signal are apparent.

NOAA-20 ATMS Channel 16 Brightness Temperature, 1845 UTC on 6 July 2021 (Click to enlarge)


There are a multitude of polar orbiters such that observations show up in clusters of time.  However, for a better time animation, it’s still best to rely on GOES-16!  The animation below, from CSPP Geosphere, shows a sheared storm south and west of Ft Myers FL.  Indeed, an 1800 UTC 6 July 2021 shear analysis from the CIMSS Tropical website (here, from this site), shows westerly shear of 25-30 knots.

GOES-16 True-Color imagery, 6 July 2021 from 1730 to 1920 UTC (Click to animate)

For the latest information on Elsa, consult the webpages of the National Hurricane Center, or the SSEC/CIMSS Tropical Weather Page.

Tropical Depression Four off the South Carolina coast

June 28th, 2021 |

GOES-16 Red Visible (Band 2, 0.64 µm) imagery, 1056 -1431 UTC on 28 June 2021 (click to animate)

Update: Tropical Depression 4 strengthened to become Tropical Storm Danny at 1905 UTC on 28 June (link).

GOES-16 visible imagery (0.64 µm), above, from the morning of 28 June 2021, shows a compact low-level circulation east of South Carolina, steadily moving towards the coast. Deep convection with this system is offset to the east, suggestive of shear, and the shear analysis from the SSEC Tropical website, below, does show easterly shear over the system.

Wind shear analysis, 1200 UTC on 28 June 2021 (Click to enlarge)

VIIRS Day Night Band imagery, below, from Suomi-NPP at 0723 UTC on 28 June, a time with ample lunar illumination, shows convection over the center of the storm at that time.

Suomi-NPP VIIRS Day Night Band Visible (0.70 µm) imagery, 0723 UTC on 28 June 2021 (Click to enlarge)


The wind shear analysis from 1900 UTC, below, is more in line with what might be expected in a system with an exposed low-level circulation center.

Wind shear analysis, 1900 UTC on 28 June 2021 (Click to enlarge)

 

The National Hurricane Center initiated statements on this tropical system at 1500 UTC on 28 June 2021. Refer to those webpages (link) for further information. Tropical Storm warnings are in effect for parts of the South Carolina coast, from Edisto Beach to the S. Santee River.

Lake Surface Temperatures in the Great Lakes in mid-June

June 16th, 2021 |

Lake-surface temperatures over the Great Lakes, 0747 UTC on 16 June 2021

Mostly clear skies over the Great Lakes early in the morning on 16 June allowed the VIIRS instrument on Suomi-NPP an unobstructed view of the surface waters.  Advanced Clear-Sky Processing for Oceans (ACSPO) Lake-surface temperatures, above, show the temperature distributions in the five lakes.  The warmest region is western Lake Erie where water temperatures are already in the 70s.  Saginaw Bay in Lake Huron (and Green Bay in Lake Michigan — although clouds at this time prevented a good view) are also in the 70s.  Much of Lake Superior remains around 40 F;  Lake Michigan is unusually warm — with a large region of 60+ — following an early-season heat wave (graph from GLERL’s Lake Statistics webpage).

Clear skies continued into the afternoon of the 16th;  the true-color image, below, derived from VIIRS data from NOAA-20 shows cloud over Lake Huron and some sun glint over Lakes Michigan and Superior. A zoomed-in view of Lake Erie (link) shows remarkable detail to the water color in the lake.

VIIRS True-Color image over the Great Lakes, 1819 UTC on 16 June 2021 (Click to enlarge)

Suomi-NPP and NOAA-20 VIIRS data were downloaded at the CIMSS Direct Broadcast site and processed using CSPP software. Great Lakes SST fields and VIIRS imagery over CONUS are available via LDM feed to National Weather Service Offices. True-Color imagery can be found at VIIRS Today and at the CIMSS direct broadcast ftp site.