Severe thunderstorm strikes Virginia campground

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

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

A supercell thunderstorm intensified as it moved eastward across Chesapeake Bay on the morning of 24 July 2014 — as it reached the Virginia shore of the Delmarva Peninsula, it produced an EF-1 tornado that was responsible for 2 fatalities and 36 injuries at the Cherrystone Family Camping Resort (located at the * symbol on the images). The storm also produced damaging straight line winds and golf ball to baseball size hail (Public Information Statement | SPC storm reports). McIDAS images of GOES-13 10.7 µm IR channel images (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 -45 C at 11:15 UTC to -64 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 um 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 um visible channel images (click to play animation)

GOES-13 0.63 um 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%. Various news reports suggested that the campsite fatalities occurred around 12:33 UTC, 13 minutes after the issuance of the tornado warning.

NOAA/CIMSS ProbSevere product

NOAA/CIMSS ProbSevere product

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)

Fog over Lake Superior

July 21st, 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)

The southerly flow of warm, moist air over the still-cold waters of Lake Superior on 21 July 2014 led to the formation of some interesting lake fog patterns, as seen in McIDAS images of GOES-13 0.63 µm visible channel data (above; click image to play animation; also available as an MP4 movie file). The images above are shown in their native GOES-13 satellite projection.

A similar animation of AWIPS images of re-mapped GOES-13 visible channel data with overlays of METAR surface reports and buoy reports (below; click image to play animation) showed that three of the northern Lake Superior buoys were reporting a water temperature of 38 to 39º F. As far north as Thunder Bay, Ontario (CYQT), air temperatures exceeded 90º F and the dew point exceeded 70º F.

GOES-13 0.63 µm visible images, with METAR and Buoy reports (click to play animation)

GOES-13 0.63 µm visible images, with METAR and Buoy reports (click to play animation)

A Terra MODIS Sea Surface Temperature (SST) product at 17:37 UTC (below) revealed that parts of the western half of Lake Superior exhibited SST values in the 40s F (cyan to blue color enhancement).

Terra MODIS Sea Surface Temperature product

Terra MODIS Sea Surface Temperature product

During the overnight hours preceding the images shown above, a Suomi NPP VIIRS IR brightness temperature difference “fog/stratus product” image at 07:43 UTC (below) showed a signal of widespread fog/stratus (yellow to red color enhancement) across much of the eastern half of Lake Superior.

Suomi NPP VIIRS IR brightness temperature difference

Suomi NPP VIIRS IR brightness temperature difference “fog/stratus product”

Large “hole punch cloud” over Wisconsin

July 18th, 2014

GOES-13 0.63 µm visible (upper left), 3.9 µm shortwave IR (upper right), 10.7 µm IR (lower left), and 6.5 µm water vapor (lower right) images [click to play animation]

GOES-13 0.63 µm visible (upper left), 3.9 µm shortwave IR (upper right), 10.7 µm IR (lower left), and 6.5 µm water vapor (lower right) images [click to play animation]

A large (approximately 50-mile diameter) “hole punch cloud” or “fall steak cloud” was seen over northwestern Wisconsin during the morning hours of 18 July 2014. An AWIPS 4-panel comparison of GOES-13 0.63 µm visible channel, 3.9 µm shortwave IR channel, 10.7 µm IR window channel, and 6.5 µm water vapor channel images (above; click image to play animation) showed that 10.7 µm IR cloud top brightness temperatures were not particularly cold with this feature (generally in the 0º C to -4º C range), and while 3.9 µm shortwave IR brightness temperatures warmed within the broad cloud deck surrounding the hole punch cloud after sunrise (due to reflection of solar radiation off of water cloud droplets), the center of the feature continued to exhibit colder (lighter gray enhancment) IR brightness temperatures which suggests cloud glaciation.

POES AVHRR Cloud Type, Cloud Top Height, and Cloud Top Temperature products at 09:32 UTC

POES AVHRR Cloud Type, Cloud Top Height, and Cloud Top Temperature products at 09:32 UTC

A comparison of CLAVR-x POES AVHRR Cloud Type, Cloud Top Height (CTH), and Cloud Top Temperature (CTT) products at 09:32 UTC or 4:32 am Central time (above) showed patches of water droplet clouds with CTH values in the 3-4 km range and CTT values in the 0º C to -4º C range.

A similar comparison at 12:05 UTC or 7:05 am Central time (below) revealed two areas of “cirrus” cloud type (orange color enhancement) exhibiting CTT values in the -35º to -40º C range (darker blue color enhancement) along the northern and southern periphery of the forming hole punch cloud.

POES AVHRR Cloud Type, Cloud Top Height, and Cloud Top Temperature prodcts at 12:05 UTC

POES AVHRR Cloud Type, Cloud Top Height, and Cloud Top Temperature prodcts at 12:05 UTC

These ranges of AVHRR Cloud Top Temperature and Cloud Top Height values agreed well with the regional rawinsonde data from Davenport IA (KDVN), Minneapolis MN (KMPX) and Green Bay WI (KGRB) shown below.

Davenport IA, Minneapolis MN, and Green Bay WI rawinsonde data at 12 UTC

Davenport IA, Minneapolis MN, and Green Bay WI rawinsonde data at 12 UTC

Terra MODIS visible and Cloud Phase products at 17:07 UTC or 12:07 pm Central time (below) indicated that a large area of glaciated ice cloud (salmon color enhancement) existed in the center portion of the hole punch cloud feature.

Terra MODIS 0.65 µm visible image and Cloud Phase products

Terra MODIS 0.65 µm visible image and Cloud Phase products

The cause of this large hole punch or fall streak cloud feature — and the other similar but smaller features seen across the region — was likely aircraft that had either ascended or descended through the cloud layer; particles in the aircraft exhaust acted as ice condensation nuclei, causing the process of cloud glaciation to begin.

GOES-15 0.62 µm visible images [click to play animation]

GOES-15 0.62 µm visible images [click to play animation]

GOES-15 imagery (above) shows the Hole Punch cloud from an oblique angle, and highlights how the region was overrun by smoke from wildfires in Canada. Smoke is most easily seen in visible satellite imagery when the sun is low in the sky, allowing for forward scatter. The smoke becomes less apparent in the imagery as the Sun rises. A similar animation for GOES-13 is below. Smoke is not quite so evident in this image because there is less forward scatter to GOES-13 over 75º W. Animations from both satellites show a hole punch cloud in Iowa as well.

GOES-15 0.62 µm visible images [click to play animation]

GOES-15 0.62 µm visible images [click to play animation]