The Australian icebreaker Aurora Australis was resupplying at Mawson Station along the Indian Ocean coast of Antarctica (map) when a strong storm (surface analysis) producing blizzard conditions — with winds as high as 86 knots gusting to 98 knots at 0936 UTC — caused it to break free from its mooring lines and run aground on 24 February 2016 (news release). Antarctic infrared composite images (using data from both geostationary and polar-orbiting satellites), above, showed the evolution and movement of the storm as it intensified close to Mawson Station early in the day on 24 February.

View only this post Read Less

JMA Himawari-8 Visible (0.64 µm) images (above) revealed the presence of mesovortices within the large and well-defined eye of Category 5 Severe Cyclone Winston as the storm approached the largest Fiji islands of Vanua Levu and Viti Levu during the 19-20 February 2016 period.

A longer animation of Himawari-8 Infrared Window (10.4 µm) images (below) showed a degradation of the eye as it moved over the slightly rugged terrain of Viti Levu, suggesting a slight decrease of intensity (ADT plot | SATCON wind | SATCON pressure). However, when Winston initially made landfall on that island with sustained winds of 185 mph it tied as the second strongest landfalling tropical cyclone on record — and Winston could also be the strongest tropical cyclone on record in the Southern Hemisphere (Capital Weather Gang blog). The images include plots of surface observations from Nadi (NNFN) and Nausori (NNFA) on the island of Viti Levu.

Nighttime comparisons of Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images showed Cyclone Winston as the storm was well east of Fiji on 18 February, and just west of Fiji on 20 February (below). With abundant illumination from the Moon in the Waxing Gibbous phase (from 82 to 95% of full), the “visible image at night” capability of the Day/Night Band was effectively demonstrated.

As Winston began to decrease in intensity from a Category 4 to a Category 2 storm after 12 UTC on 21 February, a large eye was still present in DMSP-16 SSMIS Microwave (85 GHz) imagery from the CIMSS Tropical Cyclones site (below).

View only this post Read Less

Extensive wildfires (well-forecast by the Storm Prediction Center) occurred over the southern Plains on Thursday 18 February 2016, while GOES-14 was operating in SRSO-R mode. A comparison of 1-minute GOES-14 Visible (0.63 µm) and Shortwave Infrared (3.9 µm) images (above; also available as a large 112 Mbyte animated GIF) showed the broad areal coverage of smoke plumes and fire hot spots (dark black to yellow to red pixels) during the day over eastern Oklahoma.

Of particular interest was a rapidly-intensifying and fast-moving grass fire over northwestern Oklahoma, in Harper County just west-northwest of the town of Buffalo, which burned 17,280 acres (media report). Note the warm air temperatures as seen in the surface plots — the high of 90º F at Gage OK (KGAG, south of the fire) tied for the warmest February temperature on record at that site. A closer view of the Buffalo fire is shown above — county outlines are shown as dashed white lines, while US and State highways are plotted in violet (also available as a large 63 Mbyte animated GIF). The shortwave infrared images revealed the initial appearance of a color-enhanced fire hot spot (exhibiting an IR brightness temperature of 327.5 K) at 2045 UTC; three minutes later (at 2048 UTC), the IR brightness temperature had already increased to 341.2 K (red enhancement) which is the saturation temperature of the GOES-14 shortwave IR detectors. The hot spots could also be seen racing northeastward toward the Oklahoma/Kansas border, with the fire eventually crossing US Highway 183 (which runs south-to-north through Buffalo and across the Kansas border). The early detection and subsequent accurate tracking of such rapid fire intensification and propagation could only have been possible using 1-minute imagery.

The two plots below show GOES-14 pixel values of 3.9 µm IR brightness temperature at the initial Buffalo fire site (top plot, at 36:51º N, 99:48º W) and at a site just to the northeast (bottom plot, at 36:54º N, 99:43º W) through which the moving fire propagated. The blue line shows every value, nominally at 1-minute intervals. The red dots show points sampled every five minutes. Very small temporal scale changes in the fire cannot be captured with a 5-minute sampling interval.

 

For the Buffalo fire, a three-satellite comparison of Shortwave Infrared (3.9 µm) images from GOES-15 (operational GOES-West), GOES-14, and GOES-13 (operational GOES-East) is shown for the initial 30-minute time period 2030-2100 UTC (above). The images are displayed in the native projection of each satellite. In terms of the first unambiguous fire hot spot detection (via a hot color-enhanced image pixel) during that initial period, it would appear from the image time stamps that both GOES-14 and GOES-13 detected the fire at 2045 UTC — however, because GOES-14 was scanning a much smaller sector, it did indeed scan the fire at 20:45 UTC (while GOES-13 scanned the fire at 2049 UTC, 4 minutes after its larger scan sector began in southern Canada). Also note that there were no GOES-15 images during that 30-minue period between 2030 and 2100 UTC, due to the satellite having to perform various “housekeeping” activities — so if a NWS forecast office AWIPS were localized to use GOES-15, initial fire detection would not have been posible until reception of the 2100 UTC image (which actually scanned the fire at 2104 UTC).

A faster animation covering a longer 2.5-hour period from 2030-2300 UTC is shown below. Again, a true sense of the fast northeastward speed of fire propagation could only be gained using 1-minute imagery.

The animation above shows another view of 1-minute GOES-14 Shortwave Infrared (3.9 µm) imagery, centered over northeastern Oklahoma — in these images, the hottest fire pixels are darkest black. Time series of infrared brightness temperature values at two individual fire pixels (shown here) are plotted below. The Blue lines show the 1-minute data; Red dots show how 5-minute monitoring would have adequately captured the events. Pixel Brightness Temperature changes that occur on the order of 1 or 2 minutes are common, and peak values can be missed with 5-minute granularity.

In the GOES-R era, Fire Products will be produced every 5 minutes. Individual NWS Forecast Offices will be able to request Rapid-Scan Imagery (1-minute intervals) over a 1000 km x 1000 km mesoscale sector.

===== 19 February Update =====

Seen below are RealEarth comparisons of Aqua MODIS and Suomi NPP VIIRS true-color Red/Green/Blue (RGB) images from the early afternoon of 18 February (before the Buffalo OK fire) and 19 February (after the Buffalo OK fire), which revealed the long southwest-to-northeast oriented burn scar. As seen on the GOES-14 animation above, the fire crossed US Highway 183 just to the north of Buffalo (that portion of the highway was closed for several hours).

In addition, a comparison of Suomi NPP VIIRS true-color and false-color images (below) helps to discriminate between the darker burn scar and the cloud shadows seen on the true-color image — the Buffalo fire burn scar appears as varying shades of brown in both the true-color and the false-color images.

===== 27 February Update =====

A comparison of 30-meter resolution Landsat-8 false-color (created using OLI bands 6/5/4) RGB images from 18 February (about 3.5 hours prior to the start of the Buffalo OK fire) and 27 February (several days after the fire) provided a very detailed view of the burn scar. Note that a few green fields remained within the burn scar, and also appeared to prevent the spread of the fire along portions of its perimeter — this is a result of the vast difference between the very low moisture content of the dry grassland (which burned quickly and easily) and the high moisture content of the well-irrigated fields of winter wheat, alfalfa, and canola crops.

View only this post Read Less

GOES-13 Visible (0.63 µm, 1-km resolution) images (above) showed the development of lake effect snow bands across the Great Lakes region following the passage of a strong arctic cold front on 12 February 2016. As a result of the atmospheric instability (due to the advection of very cold air aloft), several distinct convective elements could be seen developing within a few of the lake effect bands —  especially over Lower Michigan where moderate to heavy snow was reported at some locations during brief snow squalls.

Many of these lake effect snow bands could also be seen on the corresponding GOES-13 Water Vapor (6.5 µm, 4-km resolution) images (below).

A comparison of 1-km resolution Aqua MODIS Visible (0.65 µm) and Water Vapor (6.7 µm) images at 1854 UTC (below) revealed much better detail of the lake effect cloud band features in the water vapor image.

Conventional wisdom states that water vapor imagery generally portrays features located within the middle to upper troposphere, due to the altitude of the peak of the water vapor channel weighting function calculated using a relatively warm and moist “US Standard Atmosphere” (plot). However, in air masses that are very cold and/or very dry, the altitude of the water vapor channel weighting function peak is shifted to much lower altitudes, allowing a look at features that are located in (or at least rooted within) the lower to middle troposphere. Such was the case on this day, with the flow of very cold and dry arctic air behind the cold front. A comparison of the GOES-13 imager* water vapor channel weighting function plots at 12 UTC for Green Bay WI (behind the cold front) and Detroit MI (ahead of the cold front) showed the dramatic drop in the peak altitude over Green Bay (below).

Similarly, a comparison of GOES-13 imager water vapor channel weighting function plots for Detroit MI at 12 UTC (before the passage of the cold front) and 00 UTC on 13 February (after the passage of the cold front) showed a sharp drop in the altitude of the weighting function peak. This allowed radiation emitted from the tops of the more pronounced and vertically-developed lake effect cloud bands to reach the water vapor detectors on the satellite.

*Note: there are also 3 unique water vapor channels on the GOES sounder instrument (6.5 µm, 7.0 µm, and 7.4 µm) — however, due to an ongoing problem with the GOES-13 sounder, said water vapor imagery was not available (as it was for this example). However, the ABI instrument on GOES-R will provide imagery from 3 separate water vapor channels that are similar to those found on the current-generation sounder (but at much higher spatial and temporal resolution).

Hat tip to @turnageweather for the suggestion to blog about this case!

Hey @CIMSS_Satellite, ystdy aftn very shallow lake effect clouds over Lower MI clearly seen on WV channel. Willing to blog on this? #miwx

— T.J. Turnage (@turnageweather) February 13, 2016

View only this post Read Less