Severe Thunderstorms over Northern Illinois

June 10th, 2015

GOES-14 Visible (0.6263 µm, top) and GOES-13 Visible (0.63 µm, bottom) imagery centered over Illinois, 10 June 2015 [Click to animate]

GOES-14 Visible (0.6263 µm, top) and GOES-13 Visible (0.63 µm, bottom) imagery centered over Illinois, 10 June 2015 [Click to animate]

GOES-14, in SRSO-R mode, captured the quick development of severe thunderstorms over northern Illinois late in the afternoon on 10 June 2015. Many of these storms produced large hail — especially in Will County and in Grundy County, where the second largest hailstone on record for the state of Illinois was measured (NWS Chicago summary). This event is also discussed on the GOES-R Hazardous Weather Testbed (HWT) Blog: before initiation, during convective initiation, lightning jumps and ProbSevere (first post, second post), and Overshooting top detection. The animation above compares GOES-14 SRSO-R imagery (top) with GOES-13 in Routine Scanning mode (until 2045 UTC) and in Rapid Scan Operations (RSO) mode after 2115 UTC on 10 June 2015 (a smaller version of this large animated gif is also available as an mp4).

The GOES-14 SRSO-R imagery depicts the convection evolving in a fluid atmosphere. Even the relatively fast GOES-13 RSO time-step cannot capture the full evolution and decay of overshooting tops.  On the 1-minute GOES-14 images, note the development of prominent cloud-top plumes which spread out southeastward away from the more robust overshooting top regions, and also cloud-top gravity waves which form along the southeastern flank of some of the larger thunderstorm anvils. Another advantage of SRSO-R compared to the routine scanning strategy using visible imagery is discussed here.

A wider-scale view of the evolution of the atmosphere on 10 June over the Upper Midwest is available here as a YouTube video, here as an mp4, and here as an animated gif image (warning: 300+ Megabyte file). A closer-scale view of the developing convection with GOES-14 visible images is available as an mp4 movie file, or on YouTube; an animation of GOES-14 10.7 µm IR images is available as an mp4 file.

POES AVHRR 12.0 µm IR channel image, with SPC storm reports of large hail and damaging winds

POES AVHRR 12.0 µm IR channel image, with SPC storm reports of large hail and damaging winds

The line of severe thunderstorms developed just ahead of a cold frontal boundary (animation) that was sagging southward and stalling across northern Illinois during the day on 10 June. About an hour before the 4.75-inch diameter hail was reported in Minooka IL (located about 12 miles southwest of Joliet, KJOT), a 1-km resolution POES AVHRR 12.0 µm IR image at 2316 UTC (above) showed that particular cluster of thunderstorms just southwest of the Chicago area around the time of initial hail report (1.25 inch diameter at 2318 UTC); less than a half hour later there was a report of 2.00 inch hail at 2345 UTC. Farther to the southwest, the larger thunderstorm complex was also producing hail and damaging winds, near and to the southwest of the region of coldest cloud-top IR brightness temperatures (-77º C) exhibited by the overshooting tops.

GOES-13 sounder Lifted Index derived product images [click to play animation]

GOES-13 sounder Lifted Index derived product images [click to play animation]

Hourly derived product images (DPI) of GOES-13 sounder Lifted Index (above) and Total Precipitable Water (below) revealed that a broad axis of instability and moisture existed across northern Illinois ahead of the approaching cold frontal boundary. Lifted Index values reached the -8º to -10º C range (red colors); Total Precipitable Water values were generally in the 40 to 50 mm or 1.6 to 2.0 inch range (red colors), with some locations as high as 53 mm or 2.1 inches (violet colors). The presence of this instability and moisture helped to create an environment favorable for the rapid growth of strong to severe convection.

GOES-13 sounder Total Precipitable Water derived product images [click to play animation]

GOES-13 sounder Total Precipitable Water derived product images [click to play animation]

Tornadic Thunderstorm over eastern Colorado

June 5th, 2015
GOES-14 Visible 0.6263 µm Visible imagery over Colorado, 2345 UTC 5 June 2015.  See text for details (Click to enlarge)

GOES-14 Visible 0.6263 µm Visible imagery over Colorado, 2345 UTC 5 June 2015. See text for details (Click to enlarge)

The Storm Prediction Center in Norman OK had the Plains of northeast Colorado and adjacent States in a Slight Risk (or higher) threat of severe weather on 4 June 2015. The visible image, above, shows a tornado-producing severe thunderstorm over Elbert County that produced a long-lived tornado, according to the SPC Storm Reports. The reported start and end points of the tornado (and observed times) are indicated as well. Elbert (farther northeast) and El Paso (farther southwest) counties are outlined.

The evolution of the tornadic cell was captured while GOES-14 was operating in SRSO-R mode. An animated gif of the evolution from 1915 UTC 4 June through 0130 UTC on 5 June is (warning: 190M animation!) here. A YouTube video of the mp4 is below. Note that the tornado formed along the obvious moisture boundary made visible by the arc of cumulus clouds south and east of the severe storm. (This post from the Hazardous Weather Testbed blog shows the moisture gradient as a gradient in CAPE) One-minute imagery allows an extraordinarily detailed look at features in the very dynamic cloud-top; overshooting tops develop and decay very quickly as the storm develops and matures. An animation of 10.7µm imagery from 2100 UTC through 0600 UTC on 5 June is available on YouTube here. Click here (180M gif) for a storm-centered animated gif of the tornadic storm (Also available as an mp4 and on YouTube).



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.

Why 1-minute data matters: Orphan Anvils

June 4th, 2015
GOES-14 Visible (0.6263 µm) Imagery, 11 May 2014.  An orphan anvil is indicated (click to play animation)

GOES-14 Visible (0.6263 µm) Imagery, 11 May 2014. An orphan anvil is indicated (click to play animation)

‘Orphan anvils’ typically will develop before and just as a cap that prevents convective development breaks down. They can therefore be a precursor to strong thunderstorm development. The animation above shows an orphan anvil just before strong convection (Storm Reports) develops over south-central Nebraska. The anvil development is obvious in the 1-minute animation, above. (Click here for an un-annotated, smooth animation). This anvil was mentioned in the SPC Day-1 Convective Outlook updated at 2000 UTC (the 1-minute imagery is called 1km in that outlook).

The animation below compares 1-minute (top), 5-minute (middle) and present 15-minute GOES (bottom) time-steps over northwest Kansas on June 4 2015. It is a straightforward matter to notice the orphan anvils in the 1-minute imagery; it is far more challenging when using the 5-minute time-step and it’s nearly impossible with present-day 15-minute GOES time-steps. In this case, the cap was not broken. (Hat tips to Bill Line, SPC and Chad Gravelle, OPG, for these cases; Click here for additional comments and here for additional information on SRSO-R Operations).

GOES-14 Visible (0.6263 µm) Imagery, 4 June 2015, with 1-minute time-steps (top), 5-minute time-steps (middle) and routine 15-minute GOES time-steps (bottom) (click to play animation)

GOES-14 Visible (0.6263 µm) Imagery, 4 June 2015, with 1-minute time-steps (top), 5-minute time-steps (middle) and routine 15-minute GOES time-steps (bottom) (click to play animation)