Bore-like Gravity Wave Signatures over Texas

December 15th, 2015 |

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

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

GOES-13 (above) and GOES-15 (below) both captured the propagation of gravity waves that displayed Bore-like attributes along an inversion with a cold front over central Texas. (Click here for an animation of GOES-13 and GOES-15 side-by-side that includes observed surface winds).

GOES-15 Visible (0.63 µm) images [click to play animation]

GOES-15 Visible (0.63 µm) images [click to play animation]

There was a temperature drop across the front, and modest wind gusts occurred just after the lowest pressure associated with the feature passed, but those gusts occurred only in a narrow corridor in central Texas: KSNK (Snyder) reported gusts of 14 knots (0925 UTC); KSWW (Sweetwater) reported gusts of 15 knots (1035 UTC); KABI (Abilene) reported gusts to 17 knots (1152 UTC); KBWD (Brownwood) reported gusts to 24 knots at 1335 UTC; KMKN (Comanche) reported gusts of 22 knots at 1355 UTC (See also the image below). The narrowness of this corridor is likely related to the strength of the inversion along which the bore is propagating (The 1200 UTC Soundings from Fort Worth and from Del Rio both show a very strong inversion; perhaps there was a weakness in the inversion over central Texas that allowed for more vertical mixing).

GOES-13 Visible (0.63 µm) imagery at 1400 UTC; Station Locations are indicated, including the 5 stations with identifiable Wind Gusts associated with the Bore Feature [click to enlarge]

GOES-13 Visible (0.63 µm) imagery at 1400 UTC; Station Locations are indicated, including the 5 stations with identifiable Wind Gusts associated with the Bore Feature (Gust Strength in knots and time of Gust indicated) [click to enlarge]

During the preceding nighttime hours, the early stage of the undular bore feature was detected on an Aqua MODIS Water Vapor (6.7 µm) image, below, along the leading edge of the colder air and colder surface brightness temperatures (light to medium blue colors) seen on the corresponding MODIS Infrared (11.0 µm) image at 0807 UTC or 2:07 am local time.

Aqua MODIS Water Vapor (6.7 µm) and Infrared (11.0 µm) images [click to enlarge]

Aqua MODIS Water Vapor (6.7 µm) and Infrared (11.0 µm) images [click to enlarge]

(Hat tip to Mike Johnson, NWS in San Angelo for tweeting about this feature!)

How long can Tornado Scars last?

July 15th, 2015 |
MODIS True-Color Image, June 9, 2007 (left) and July 15, 2015 (right) (click to enlarge)

MODIS True-Color Image, June 9, 2007 (left) and July 15, 2015 (right) (click to enlarge)

On 07 June 2007, severe thunderstorms moved through the Upper Midwest (blog post on that event), spawning strong tornadoes; from the SPC Storm Reports comments:

HUNDREDS OF TREES DOWN NORTH OF ZOAR. (GRB)

NUMEROUS TREES DOWN OF 1 FOOT DIAMETER AND GREATER. TRACK WAS APPROXIMATELY 1/4 MILE IN LENGTH AND 125 YARDS WIDE (MQT)

Terra MODIS data on 09 June 2007 (in the image above, at left) showed a tornado scar (much longer than 1/4 mile in length) running southwest-to-northeast through heavily forested Menominee County into Langlade County and then Oconto County in northeast Wisconsin. Terra MODIS True-Color imagery from 15 July 2015 (also in the image above, at right) (cropped from imagery at the MODIS Today website), shows that a scar persists more than 8 years later! (This persistent scar has been mentioned before on this blog here in 2009 and here in 2011).

Landsat-8 overflew northeast Wisconsin on 15 July 2015, at nearly the same time as the Terra MODIS imagery above, and those views, captured via SSEC‘s RealEarth are shown below. The scar is more evident in the shortwave infrared (Band 6, 1.61 µm) than the visible (Band 3, 0.56 µm) because the shortwave infrared channel is more sensitive to changes in vegetation. Lakes are also far more apparent in the 1.61 µm imagery because water absorbs 1.61 µm radiation; little is scattered back to the satellite for detection and water therefore appears black.

Landsat-8 band 3 (0.56 µm) and Band 6 (1.61 µm) imagery, ~1640 UTC July 15, 2015 (click to enlarge)

Landsat-8 band 3 and Band 6 imagery, ~1640 UTC July 15, 2015 (click to enlarge)


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In April 2011, an historic tornadic event occurred over the Deep South that spawned numerous strong long-track tornadoes (blog post). The tornado paths from this event were also visible from both MODIS and GOES imagery (Link). The animation below shows MODIS true color imagery from before the tornadoes, from several days after, and from early May this year. Three distinct tornado scars remain in Alabama: One runs from Tuscaloosa to Birmingham, a second is south of Tuscaloosa, and a third is north of Tuscaloosa.

MODIS True-Color Imagery over Alabama, 13 April and 29 April in 2011 and 01 May in 2015 (click to enlarge)

MODIS True-Color Imagery over Alabama, 13 April and 29 April in 2011 and 01 May in 2015 (click to enlarge)

Why 1-minute data matters: Beavertails

June 4th, 2015 |
GOES-14 Visible (0.6263 µm) Imagery, 04 June 2015.  1-minute imagery on the left, 5-minute imagery on the right (click to play animation)

GOES-14 Visible (0.6263 µm) Imagery, 04 June 2015. 1-minute imagery on the left, 5-minute imagery on the right (click to play animation)

Beavertails are ephemeral cloud features that form in the inflow of supercell thunderstorms. They are horizontally long and roughly parallel to the inflow warm front. Its appearance (and presence) is affected by and influences inflow into the storm, and by inference, it affects radar returns. That is — a change in the Beavertail cloud can precede a change in radar. Accurate detection of this cloud type, then, aids the understanding of evolving storm morphology. The animation above shows a severe convective system over southeastern Wyoming, viewed at 1-minute intervals (Left) and at 5-minute intervals. Beavertails that form persist for about 30 minutes, so 5-minute imagery will resolve them; however, the resolution of the 1-minute data is far better to monitor the small changes in size and shape that are related to storm inflow.

Do beavertail changes affect the radar? The animation below shows the ProbSevere product readout from 2000-2220 UTC (Courtesy John Cintineo, CIMSS) (Click here for a slow animation). (Click here for an animation (from 1918-2058 UTC) that includes warning polygons). The increases and decreases in the MRMS MESH appear unrelated to the formation/decay of the various beavertails.

NOAA/CIMSS ProbSevere Product, 2000-2020 UTC on 4 June 2015 (click to animate)

NOAA/CIMSS ProbSevere Product, 2000-2020 UTC on 4 June 2015 (click to play animation)

This storm was captured by different chasers. This YouTube video from Scott Longmore shows the evolution of the convective system from the ground. Hat/tip to Jennifer Laflin, NWS EAX and Chad Gravelle, OPG, for alerting us to this case.

Bore over Kansas

June 3rd, 2015 |
GOES-13 Imager 0.63 µm visible channel images (click to play animation)

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

Visible imagery after sunrise on 3 June 2015 over Kansas, above, shows the parallel lines of low clouds that characterize a bore feature. As the bore penetrated southward, winds initially shifted before becoming more variable. Bore propagation requires the presence of an inversion, and 1200 UTC Soundings from both Dodge City and from Topeka contain inversions. Because inversions are present, it is unusual for convection to form in the presence of a bore.

The initial southward push the became the bore may have emerged from strong convection over central Nebraska early in the morning of 3 June. Suomi NPP VIIRS imagery captured that convection; the Day Night Band (under near-Full Moon conditions) and 11.45 µm infrared imagery, below, show the strong convection at 0848 UTC on 3 June 2015).

Suomi NPP VIIRS 0.70 µm visible Day Night Band and 11.45 µm infrared imagery at 0848 UTC on 3 June 2015 (click to enlarge)

Suomi NPP VIIRS 0.70 µm visible Day Night Band and 11.45 µm infrared imagery at 0848 UTC on 3 June 2015 (click to play animation)

GOES-14 was performing SRSO-R observations over Kansas on 3 June. One-minute imagery of the bore evolution is available here in animated gif format (74 M in size) and here in mp4 format (2.8M in size). The YouTube video is embedded below.