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]

GOES-14 SRSO-R imagery: “mystery feature” over eastern Tennessee

May 21st, 2015


 

GOES-14 remained in Super Rapid Scan Operations for GOES-R (SRSO-R) demonstration mode on 21 May 2015, providing 1-minute images for much of the eastern US (see this blog post) — and another interesting feature was seen over eastern Tennessee that was rather perplexing. Since this easily qualified for the “What the heck is this?” blog category, we thought it might be fun to have a contest of sorts and invite readers to submit their wild guesses and/or educated explanations. We will post more imagery later in the day on 22 May as to our explanation — but in the meantime, leave a comment on the blog (comments are moderated, so they will not appear until approved), or send your thoughts to our Twitter account.

—– 22 May Update —–

Thanks to all who submitted their suggestions here and on Twitter of an explanation of the “What the heck is this” feature; Here is our best guess:

GOES-13 (GOES-East) visible, 3.9 µm shortwave IR, 6.5 µm, and 10.7 µm IR images [click to play animation]

GOES-13 (GOES-East) visible, 3.9 µm shortwave IR, 6.5 µm, and 10.7 µm IR images [click to play animation]

The first step in trying to understand what might be causing this interesting feature was to examine 4-panel images showing imagery from other GOES channels (or spectral bands): in this case, the 3.9 µm “shortwave IR” channel, the 6.5 µm “water vapor” channel, and the 10.7 µm “IR window channel” (above; click image to play animation). The 3.9 µm IR brightness temperatures of cloud features were in the +20 to +25º range, while the 10.7 µm IR brightness temperatures were in the +3 to +5º C range — the significantly warmer shortwave IR temperatures indicates that the clouds were comprised of liquid or supercooled cloud droplets. Otherwise, no significant clues were seen on the IR (or the water vapor) images.

However, the METAR surface reports offer an important clue: a rain shower moved from southwest to northeast through the region during the preceding overnight hours with the passage of a weak low pressure system (surface analyses), with Knoxville (station identifier KTYS) receiving 0.23″ and Oak Ridge (KOQT) receiving 0.10″ of rainfall (radar-estimated 24-hour precipitation). Therefore, one plausible explanation of the feature seen on visible imagery is that it was a shallow pool of stable, rain-cooled air near the surface that was spreading out and flowing downslope (westward) into the Great Valley of East Tennessee during the morning and early afternoon hours.

While the outer edges of this rain-cooled stable air feature remained generally cloud-free, the inner core exhibited a good deal of cloud development (including what appeared to be a more dense northwest-to-southeast oriented cloud band through the middle). An overlay of hourly RTMA surface winds (below; click image to play animation) indicated that there was convergence within the feature (to the lee of higher terrain within the Cumberland Plateau), which along with daytime heating of the moist soil would have helped to promote such shallow cloud development.

GOES-13 0.63 µm visible channel images, with RTMA surface winds [click to play animation]

GOES-13 0.63 µm visible channel images, with RTMA surface winds [click to play animation]

For clouds within expanding the rain-cooled boundary at 1534 UTC, the CLAVR-x POES AVHRR Cloud Type was liquid, with Cloud Top Height values of 1-3 km and Cloud Top Temperature values of +2 to +10º C (below).

CLAVR-x POES AVHRR Cloud Type, Cloud Top Height, and Cloud Top Temperature products

CLAVR-x POES AVHRR Cloud Type, Cloud Top Height, and Cloud Top Temperature products

Severe thunderstorm over West Texas, as viewed from 3 GOES satellites

May 19th, 2015

GOES-15 (left), GOES-14 (center), and GOES-13 (right) 0.62 µm visible channel images [click to play animation]

GOES-15 (left), GOES-14 (center), and GOES-13 (right) 0.62 µm visible channel images [click to play animation]

Thunderstorms began to develop across West Texas during the afternoon hours on 19 May 2015, along and ahead of an eastward-moving dryline. One of the storms went on to produce a few brief tornadoes, and hail as large as 3.0 inches in diameter (SPC storm reports). Different views of this storm were provided by GOES-15 (GOES-West), GOES-14 (in SRSO-R mode), and GOES-13 (GOES-East) 0.62 µm visible channel images (above; click image to play 190 MB animated GIF; also available as an MP4 movie file, or on YouTube). This comparison highlights the advantages of 1-minute interval Super Rapid Scan images (which will be available from GOES-R) compared to the standard 15-minute interval Routine Scan images provided by the current generation of GOES.

One interesting feature seen on the visible channel images above was the apparent merger of the large dominant dryline storm and a smaller northward-moving storm that had formed in Mexico (radar animation). In GOES-13 10.7 µm IR imagery with an overlay of SPC storm reports (below; click image to play animation), one report of 2.0-inch diameter hail was seen around or shortly after the time of the storm merger.

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

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

With higher spatial resolution IR imagery from MODIS (1-km), VIIRS (375-meter), and AVHRR (1-km), much colder cloud-top IR brightness temperatures were seen (below) compared to the corresponding 4-km resolution GOES IR imagery at those times — especially during the early formative stages of the thunderstorms captured with MODIS and VIIRS. The coldest cloud-top IR brightness temperature on the 2128 UTC AVHHRR image was -80º C, compared to -67º C on the 2130 UTC GOES image.

Terra and Aqua MODIS 11.0 µm, Suomi NPP VIIRS 11.45 µm, and POES AVHRR 12.0 µm IR channel images

Terra and Aqua MODIS 11.0 µm, Suomi NPP VIIRS 11.45 µm, and POES AVHRR 12.0 µm IR channel images

A more detailed discussion of this event can be found on the RAMMB GOES-R Proving Ground Blog.

Atmospheric Bore between the Grand Banks and New England

May 8th, 2015
GOES-13 0.63 µm Visible images (click to play animation)

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

Atmospheric Bores form in stable air and create horizontal cloud bands that propagate perpendicular to the along-band direction. The feature seen above in GOES-13 visible imagery formed in stable air south of a High Pressure system that pushed a backdoor cold front into New England (surface analyses). The southern edge of this bore was likely eroding as it became influenced by warmer less-stable air over with the Gulf Stream — the warm waters of the Gulf Stream were apparent in the toggle, below, of POES AVHRR 0.86 µm visible and 12.0 µm infrared imagery at 1055 UTC. The bore was apparently moving over the top of a shallow layer of sea fog that had formed in the colder waters north of the Gulf Stream.

POES AVHRR 0.86 µm Visible image and 12.0 µm Infrared image at 1055 UTC on 8 May 2015 (click to enlarge)

POES AVHRR 0.86 µm Visible image and 12.0 µm Infrared image at 1055 UTC on 8 May 2015 (click to enlarge)

Suomi NPP overflew the area at ~1800 UTC, affording a very high resolution view of the bore structures with the VIIRS 0.65 µm visible channel, below.

SNPP_DNB_1807UTC_08May2015

Suomi NPP VIIRS Visible (0.65 µm) imagery, 1807 UTC on 8 May 2015 (Click to enlarge)

The daytime propagation of the bore feature could also be followed on POES AVHRR 0.86 µm visible channel images, shown below.

POES AVHRR 0.86 µm visible images (click to enlarge)

POES AVHRR 0.86 µm visible images (click to enlarge)