NOAA/CIMSS ProbSevere with a Nebraska Hailstorm

September 22nd, 2015 |
GOES-13 Visible (0.63 µm) images [click to play rocking animation]

GOES-13 Visible (0.63 µm) images [click to play rocking animation]

A severe hail-producing thunderstorm moved over northeast Nebraska before noon on 22 September (SPC Storm Reports). The region hit was just south of a Marginal Risk of Severe Weather (The update at 1630 UTC included the region of severe weather). The GOES-13 visible animation, above, shows the initial development occurring along a subtle cloud line aligned mostly east-west.

The NOAA/CIMSS ProbSevere model produces a probability that a developing thunderstorm will initially produce severe weather within the next sixty minutes. It consistently supplies information with a good lead time, and the storm on 22 September was no exception. The animation below shows the product for about an hour before the first storm report at 1408 UTC. The storm out of which the hail dropped was, at 1300 UTC, flagged as having a ProbSevere under 10%; values exceeded 10% at 1314 UTC and then jumped to 60+% at 1336 UTC (the first time that the value exceeded 50%) Values fluctuated between 60 and 80% between 1336 and 1400 UTC. After 1400 UTC, values increased into the mid-80s. The first report of hail was at 1408 UTC, 32 minutes after ProbSevere jumped above 50%. A severe thunderstorm warning for hail was issued at 1412 UTC.

NOAA/CIMSS ProbSevere values, 1300-1412 UTC on 22 September 2015 [click to play animation]

NOAA/CIMSS ProbSevere values, 1300-1412 UTC on 22 September 2015 [click to play animation]

The GOES Sounder Lifted index product, below, (also available here) showed the instability that was present over the central Plains.

GOES-13 Sounder DPI Values of Lifted Index [click to play animation]

GOES-13 Sounder DPI Values of Lifted Index [click to play animation]

Mountain wave clouds in western Montana

September 20th, 2015 |


As pointed out in a Tweet from NWS Great Falls (above), a “chinook arch” mountain wave cloud feature had formed in response to strong westerly winds interacting with the high terrain of the Rocky Mountains of western Montana on 20 September 2015. GOES-13 visible (0.63 µm) images (below; also available as an MP4 movie file) showed the development and evolution of the lower-altitude parallel bands of mountain wave clouds, as well as the larger patch of higher-altitude cloud immediately downwind of the eastern edge of the highest terrain (comparison of Suomi NPP VIIRS visible image and terrain) .

GOES-13 visible (0.63 µm) images [click to play animation]

GOES-13 visible (0.63 µm) images [click to play animation]

The corresponding GOES-13 infrared (10.7 µm) images (below; also available as an MP4 movie file) revealed that the large patch of high-altitude cloud (sometimes referred to as a “banner cloud”) began to grow in areal coverage after about 12 UTC, eventually exhibiting cloud-top IR brightness temperatures in the -50 to -55º C range (yellow to orange color enhancement).

GOES-13 infrared (10.7 um) images [click to play animation]

GOES-13 infrared (10.7 um) images [click to play animation]

The GOES-13 water vapor (6.5 µm) images (below; also available as an MP4 movie file) did not show the common signature of a jet streak axis (a well-defined moist-to-dry gradient) until later in the day.

GOES-13 water vapor (6.5 um) images [click to play animation]

GOES-13 water vapor (6.5 um) images [click to play animation]

A comparison of Aqua MODIS visible (0.65 µm) and “cirrus detection” (1.375 µm) images at 1949 UTC (below) demonstrated how the cirrus channel imagery can be used to better discriminate between the high-altitude ice clouds (brighter white features) and the low-altitude water and/or supercooled water droplet clouds.

Aqua MODIS visible (0.65 um) and

Aqua MODIS visible (0.65 um) and “cirrus detection” (1.375 um) images [click to enlarge]

A comparison of Suomi NPP VIIRS visible (0.64 µm), infrared window (11.45 µm) and shortwave infrared (3.74 µm) images at 2057 UTC (below) showed the high-altitude banner cloud feature as it was beginning to enter its dissipation phase. The 11.45 µm cloud-top IR brightness temperatures were as cold as -57º C; however, note that the 3.74 µm shortwave IR brightness temperatures were significantly warmer (in the +5 to +10º C range). These warm shortwave IR temperatures indicated that the banner cloud feature was composed of very small ice crystals, which were effective at reflecting incoming solar radiation back toward the satellite sensors.

Suomi NPP VIIRS visible (0.64 um), infrared window (11.45 um), and shortwave infrared (3.74 um) images [click to enlarge]

Suomi NPP VIIRS visible (0.64 um), infrared window (11.45 um), and shortwave infrared (3.74 um) images [click to enlarge]

Grass fire in Colorado

September 19th, 2015 |

GOES-15 (left panels) and GOES-13 (right panels) Visible (0.63 µm) and Shortwave infrared (3.9 µm) images [click to play animation]

GOES-15 (left panels) and GOES-13 (right panels) Visible (0.63 µm) and Shortwave infrared (3.9 µm) images [click to play animation]

GOES-15 (GOES-West) and GOES-13 (GOES-East) Visible (0.63 µm) and Shortwave infrared (3.9 µm) images (above; click to play animation; also available as an MP4 movie file) showed the smoke plume and “hot spot” (dark black to red pixels) associated with a large and fast-burning grass fire in north-central Colorado on the afternoon of 18 September 2015. The smoke plume was more apparent in the GOES-13 visible images, due a more favorable “forward scattering” sun-satellite geometry. The fire burned an estimated 12,669 acres, and dense smoke forced the closure of Interstate 76 for about an hour in the afternoon.

On the following day, the fire burn scar could be seen in a comparison of Suomi NPP VIIRS  true-color and false-color images from the SSEC RealEarth site (below).

Suomi NPP VIIRS true-color and false-color images [click to enlarge]

Suomi NPP VIIRS true-color and false-color images [click to enlarge]

Due to the darker color and the lack of vegetation, the grass fire burn scar also exhibited a much warmer signature on the Terra MODIS Land Surface Temperature (LST) product (below) — LST values were as high as 112º F (darker orange color enhancement) within the burn scar, compared to LST values in the 80s and 90s F in surounding areas.

Terra MODIS Land Surface Temperature product [click to enlarge]

Terra MODIS Land Surface Temperature product [click to enlarge]

Tropical Depression Nine in the Atlantic Ocean

September 17th, 2015 |

GOES-13 Visible (0.63 µm) images [click to play animation]

GOES-13 Visible (0.63 µm) images [click to play animation]

Tropical Depression Nine in the Atlantic Ocean, above, shows characteristics of a heavily sheared storm (longer sunrise-to-sunset animations: gif | mp4). The low-level circulation is displaced south and west of the strongest convection (which is vigorous enough to produce occasional overshooting tops, below, as shown on this page).

Autodetected Overshooting Tops as a function of time, from GOES-13 data [click to enlarge]

Autodetected Overshooting Tops as a function of time, from GOES-13 data [click to enlarge]

Metop-B overflew Tropical Depression Nine’s circulation just after 1300 UTC on 17 September (Orbital tracks for Metop-B are here). The image below shows a circulation with 20-30 knot winds displaced to the south and west of cold 10.7 µm brightness temperatures indicating high cloud tops detected by the GOES-13 Imager.

Metop-B ASCAT winds and GOES-13 10.7 µm Brightness Temperatures, ~1315 UTC [click to enlarge]

Metop-B ASCAT winds and GOES-13 10.7 µm Brightness Temperatures, ~1315 UTC [click to enlarge]

MIMIC Total Precipitable Water for the 72 hours ending 1400 UTC 17 September 2015 [click to enlarge]

MIMIC Total Precipitable Water for the 72 hours ending 1400 UTC 17 September 2015 [click to enlarge]

Total Precipitable Water images from MIMIC (above) suggest the circulation of Tropical Depression Nine is on the northern edge of deep moisture in the Intertropical Convergence Zone. Its projected path to the north and west is towards dryer air. The projected path (below) does take the storm towards warmer waters; however, it also moves it towards a region of even higher deep-layer wind shear (plots below were taken from the CIMSS Tropical Cyclones site). Only the warmer waters argue that this storm will persist; everything else suggests a struggle to survive. Several tropical cyclones this season have succumbed to wind shear while over the tropical Atlantic. Tropical Depression Nine may add to that total.

Projected Path of Tropical Depression Nine superimposed on SST and Wind Shear [click to enlarge]

Projected Path of Tropical Depression Nine superimposed on SST and Wind Shear [click to enlarge]