Wildfire smoke over ice in Hudson Bay

July 28th, 2014
GOES-13 0.63 µm visible channel images (click to play animation)

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

Large wildfires continued to burn during much of the month of July in the Northwest Territories of Canada, and McIDAS-X images of GOES-13 0.63 µm visible channel data on 28 July 2014 (above; click image to play animation) showed large amounts of smoke aloft streaming southwestward across the western and southwestern portion of Hudson Bay. This pattern of middle-tropospheric smoke transport was caused by the juxtaposition of a highly-amplified ridge of high pressure over central Canada and a deep area of low pressure over Quebec (500 hPa map). During the later part of the day, the clearing of patchy low clouds and the thinning of the smoke aloft revealed the presence of large ice floes over southwestern Hudson Bay. According to the Canadian Ice Service, this was thick first year ice from the previous winter season, with ice concentration values as high as 9-10/10s.

A Suomi NPP VIIRS true-color Red/Green/Blue (RGB) image combination prepared using McIDAS-V (below; courtesy of Joleen Feltz, CIMSS) showed the variety of smoke, ice, and cloud formations over Hudson Bay at 18:45 UTC.

Suomi NPP VIIRS true-color RGB image

Suomi NPP VIIRS true-color RGB image

Severe thunderstorm strikes Virginia campground

July 24th, 2014
GOES-13 10.7 µm IR channel images (click to play animation)

GOES-13 10.7 µm IR channel images (click to play animation)

A supercell thunderstorm intensified as it moved eastward across the Chesapeake Bay (just ahead of an approaching surface cold front) on the morning of 24 July 2014 — as it reached the Virginia shore of the Delmarva Peninsula, it produced an EF-1 tornado and damaging straight line winds that were responsible for 2 fatalities and 36 injuries at the Cherrystone Family Camping Resort (located at the * symbol on the images). The storm also produced golf ball to baseball size hail (NWS damage survey | SPC storm reports). McIDAS images of GOES-13 10.7 µm IR channel data (above; click image to play animation; also available as an MP4 movie file) showed that the cloud-top IR brightness temperatures associated with the storm cooled quickly, from -45º C at 11:15 UTC to -64º C at 12:30 UTC. The temperature value was close to that of the tropopause (at a height of 15.4 km) on the 12 UTC rawinsonde data from Wallops Island, Virginia.

The corresponding GOES-13 0.63 µm visible channel images (below; click image to play animation; also available as an MP4 movie file) revealed the presence of an overshooting top at 12:30 UTC  (the time that the IR cloud-top brightness temperature values reached their minimum), which was also flagged by the automated Overshooting Tops detection algorithm.

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

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

AWIPS-II images of the NOAA/CIMSS ProbSevere product (below) followed the radar feature associated with the supercell thunderstorm. Around 11:30 UTC, the ProbSevere value was low, around 5-10%, a result of weak satellite-detected growth (and moderate glaciation) early in the storm’s life, along with low values of MRMS Maximum Expected Size of Hail (MESH). Environmental parameters from the Rapid Refresh model that were supportive of convection: MUCAPE exceeded 2200 J Kg and Shear values were greater than 30 m/s. As the cell tracked to the east and began to move over Chesapeake Bay, both MUCAPE and Shear gradually increased, to values near 2400 J/kg and 35 m/s, respectively. MRMS MESH was oscillating as the cell approached Chesapeake Bay, from 0.44 inches at 11:42 UTC (ProbSevere value of 10%) to 0.37 inches at 11:46 UTC (ProbSevere of 7%) to 0.65 inches at 11:48 UTC (ProbSevere of 29%) to 0.56 inches at 12:00 UTC (ProbSevere of 18%). As the storm moved over the Bay, MESH sizes jumped, to 0.86″ at 12:04 UTC (ProbSevere of 58%, the first crossing of the 50% threshold), to 1.02″ at 12:06 UTC (ProbSevere of 71%), to 1.86″ at 12:12 UTC (ProbSevere of 92% , the first crossing of the 90% threshold), and to 3.09″ (!) at 12:16 UTC (ProbSevere of 91%). At 12:20 UTC, when the Tornado Warning was issued, MRMS MESH was 3.51″ and ProbSevere remained at 91%. Thus, the warning was issued 16 minutes after ProbSevere exceeded 50%, and 8 minutes after ProbSevere was greater than 90%. The NWS storm survey indicated that the campsite fatalities occurred around 12:33 UTC, or 13 minutes after the issuance of the tornado warning.

NOAA/CIMSS ProbSevere product

NOAA/CIMSS ProbSevere product

The rapid intensification of the system as it moved over the Chesapeake begs the question: was instability diagnosed? In the animation below, GOES-13 sounder Derived Product Images (DPI) of Lifted Index (top panel) and CAPE (bottom panel) showed a rich source of instability just south of the cloud-obscuring convection (and ahead of the southward-moving cold front). Lifted Index values derived at 1147 UTC were around -6 at the mouth of the Chesapeake Bay (bright yellow enhancement); CAPE values were around 2500 J/kg (yellow and red enhancements).

GOES-13 Sounder DPI estimates of Lifted Index (top) and CAPE (bottom) [click to play animation]

GOES-13 Sounder DPI estimates of Lifted Index (top) and CAPE (bottom) [click to play animation]

Air Algerie Plane Crash in Mali

July 24th, 2014
Meteosat-10 10.8 µm infrared channel images (click to enlarge)

Meteosat-10 10.8 µm infrared channel images (click to enlarge)

An Air Algerie Flight AH5017 crashed less than an hour after taking off from Ouagadougou, Burkina Faso (the southern asterisk in the animation above). Contact was lost at 0155 UTC (Press Report) and wreckage was found southeast of the Gossi, Mali (the northern asterisk in the animation above). Cloud-top IR Brightness Temperatures in the Mesoscale Convective System through which the plane flew were as cold as -78º C.

Suomi NPP was flying over Mali and Burkina Faso at 0152 UTC on 24 July and provided high-resolution infrared and Day/Night Band imagery along the flight path. The toggle below, of the VIIRS 11.45 µm infrared and 0.70 µm Day/Night Band (Imagery courtesy of William Straka, UW CIMSS) shows the convective storm. The bright lights of Ouagadougou are evident, as well as lightning streaks within the storm. (Click for zoomed-in versions of 11.45 µm and Day Night Band images)

Suomi NPP VIIRS 11.45 µm infrared and 0.7 µm Day/Night Band images (click to enlarge)

Suomi NPP VIIRS 11.45 µm infrared and 0.7 µm Day/Night Band images (click to enlarge)

============================= Added 28 July 2014 =========================

Suomi NPP VIIRS 0.7 µm Day/Night Band image (click to enlarge)

Suomi NPP VIIRS 0.7 µm Day/Night Band image (click to enlarge)

The image above includes the light flare from the actual plane crash, circled in red. Suomi NPP was passing over the crash site between 1:55:00 and 1:55:30 UTC on 24 July 2014 (Link, navigation computed from Two Line Element files). The animation below shows Day/Night Band imagery (also courtesy of William Straka, UW CIMSS) from before the crash (21 July), the time of the crash on the 24th, and after the crash (25 July).

Suomi NPP VIIRS 0.7 µm Day/Night Band imagery on three days in July (click to Animate)

Suomi NPP VIIRS 0.7 µm Day/Night Band imagery on three days in July (click to Animate)

Strong convective winds over Arkansas

July 23rd, 2014
GOES-13 0.63 µm visible channel images (click to play animation)

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

Arkansas and surrounding states experiences strong convectively-forced winds on July 23 2014 (SPC Storm Reports for the day are shown below). The visible imagery, above, shows the merging of two convective systems: one is moving south-southeastward through eastern Kansas and one is building southwestward from the lower Ohio River Valley into northern Arkansas. (Mesoscale Discussions for this event were issued from SPC at 1656 UTC, 1827 UTC and 2001 UTC on the 23rd).

Storm Reports from 23 July 2014

Storm Reports from 23 July 2014

GOES-13 Sounder DPI Lifted Index (click to play animation)

GOES-13 Sounder DPI Lifted Index (click to play animation)

Analyses from the GOES-13 Sounder (above) showed the atmosphere into which the convective features were building to be very unstable. A large area with Lifted Indices around -10 (light red) is present; values exceed -12 (purple) at 1800 UTC. GOES Sounder DPI Analyses of CAPE (Convective Available Potential Energy, below) (from this site) likewise show strong instability at the start of the day. Convection is initially at both ends of the area of most unstable air; by 1900 UTC, the end of the animation, it has overspread the entire region of instability.

GOES Sounder CAPE (click to play animation)

GOES Sounder CAPE (click to play animation)

GOES-13 10.7 µm infrared channel images (click to play animation)

GOES-13 10.7 µm infrared channel images (click to play animation)

The GOES-13 Infrared Imagery, above, likewise shows the convective systems from Kansas and from the lower Ohio Valley merging over Arkansas.

Suomi-NPP VIIRS data were available over Arkansas on two successive passes on 23 July, at 1829 UTC and 2010 UTC, and these high-resolution infrared images show the quick development and vigor of the convection. The high resolution allowed for the detection of very cold cloud tops at 2010 UTC; minimum values were near -88ºC! Coldest GOES-13 10.7 Brightness Temperatures at 2015 UTC (not shown) were -78ºC.

Suomi NPP VIIRS 11.35 µm infrared channel images (click to enlarge)

Suomi NPP VIIRS 11.35 µm infrared channel images (click to enlarge)

The storms produced considerable lightning as well, as shown in the animation below that overlays hourly lightning strikes on top of the Suomi NPP 11.35 µm imagery: there were 5800 strikes (400 positive) in the hour ending at 1800 UTC, and 12000 strikes (800 positive) in the hour ending at 2000 UTC!

Suomi NPP 11.35 µm infrared channel imagery and Detected Lightning (click to play animation)

Suomi NPP 11.35 µm infrared channel imagery and Detected Lightning (click to play animation)

NOAA/CIMSS ProbSevere showed values from 80-95% at the leading edge of the convection as it moved southward through Arkansas. In this event, satellite data were not available as one of the ProbSevere predictors because of the widespread cirrus shield. MRMS Mesh was generally in the 3/4″ to 1-1/2″ range; that combines with model CAPE values exceeding 4000 and generous shear lead to the high ProbSevere values.

NOAA/CIMSS ProbSevere display including MRMS Base Reflectivity, 1922-2128 UTC 23 July 2013 (click to play animation)

NOAA/CIMSS ProbSevere display including MRMS Base Reflectivity, 1922-2128 UTC 23 July 2013 (click to play animation)

Overshooting Tops, such as those apparent in the 11.35 µm imagery from Suomi NPP, above, can be detected automatically in GOES-13 10.7 µm imagery. The animation of auto-detected overshooting tops, below, from this site, shows a peak in convective intensity (as measured by the number of overshoots) between 2000 and 2100 UTC on the 23rd. This image shows the daily sum of detected overshoots. There is good spatial correlation between that image and the storm reports.

Overshooting Tops Detected from GOES-13, 1545-2300 UTC 23 July 2013 (click to play animation)

Overshooting Tops Detected from GOES-13, 1545-2300 UTC 23 July 2013 (click to play animation)

Finally, CRiS/ATMS data can be used to generate soundings (NUCAPS Soundings) that are available in AWIPS II. The image below shows the spatial coverage of soundings at 2000 UTC on 23 July. The NUCAPS sounding from the easternmost column, third point south of the Oklahoma/Texas border, bottom, is shown at the bottom of the post. The boundary layer of this sounding is too cool and dry — the surface temperature is around 80º F and the surface dewpoint is in the mid-60s. Consequently, the MUCAPE is far too small (about 120 J per kilogram). If the sounding is edited so that surface values are closer to observations (it was 90º F with a 75º F dewpoint in Texarkana at this time) then MUCAPE values jump to near 5000. The sounding is also too dry; the precipitable water is 1.45″ vs. an actual value closer to 2″ at this time.

Suomi NPP VIIRS 11.35 µm Imagery at 2010 UTC, with NUCAPS Sounding Locations in Green (Click to enlarge)

Suomi NPP VIIRS 11.35 µm Imagery at 2010 UTC, with NUCAPS Sounding Locations in Green (Click to enlarge)

Suomi NPP NUCAPS Sounding at 32.7º N, 94.9º W (Click to enlarge)

Suomi NPP NUCAPS Sounding at 32.7º N, 94.9º W (Click to enlarge)