Tornadic Thunderstorm over eastern Colorado

May 28th, 2015 |

NOAA/CIMSS ProbSevere Product, 1902-1922 UTC on 27 May 2015 [click to play very very large animation]

GOES-14 Visible Imagery (0.626 µm) animation, 1708 UTC 27 May 2015 – 0059 UTC 28 May 2015 [click to play very very large animation]

A tornado was reported near Yuma, CO, (SPC Storm Reports) at 1910 UTC on 27 May 2015. GOES-14 was in SRSO-R scanning mode, and a storm-centered animation of the visible imagery (0.626 µm) is shown above (Warning: the animation above is 270M; click here for an mp4, or view it on YouTube). Note that GOES-14 produces no imagery from 1900-1915 UTC when the satellite is performing daily station-keeping maneuvers. The tornado occurred early in the life of the supercell on which the animation centers.

The NOAA/CIMSS ProbSevere output for this storm is shown below. ProbSevere increased above 50% at 1904 UTC. The satellite information for the storm object was derived from GOES-13 data between 1730 and 1745 UTC, when strong growth occurred, and from 1745-1815 UTC when weak glaciation occurred (how the reduced time resolution at that time, when GOES-13 is scanning a full-disk image, affected the Glaciation estimates is not certain — ‘weak’ is probably a lower bound).

NOAA/CIMSS ProbSevere Product, 1902-1922 UTC on 27 May 2015 [click to play animation]

NOAA/CIMSS ProbSevere Product, 1902-1922 UTC on 27 May 2015 [click to play animation]

GOES-14 SRSO Imagery over Texas

May 20th, 2015 |
GOES-14 0.62 µm visible imagery; Andrews County is highlighted [click to play animation]

GOES-14 0.62 µm visible imagery; Andrews County is highlighted [click to play animation]

GOES-14, in SRSO-R mode, animation, above (YouTube video), captured the development of an isolated cell over northeastern Andrews County in west Texas. Intersecting boundaries helped force the isolated convection, above, that was strong enough to produce a signal in the NOAA/CIMSS ProbSevere product, with ProbSevere peaking at around 15%.

NOAA/CIMSS ProbSevere output, 1400 UTC on 20 May 2015 [click to enlarge

NOAA/CIMSS ProbSevere output, 1400 UTC on 20 May 2015 [click to enlarge]

NOAA/CIMSS ProbSevere Product and storms over Texas

April 24th, 2015 |
NOAA/CIMSS ProbSevere Output from AWIPS on 24 April, 1902, 1908, 1912, 1930, 1938, 1944, 1948, 1950, 1954 and 1958 UTC (click to play animation)

NOAA/CIMSS ProbSevere Output from AWIPS on 24 April, 1902, 1908, 1912, 1930, 1938, 1944, 1948, 1950, 1954 and 1958 UTC (click to play animation)

Severe thunderstorms moved across central Texas on April 24th (Link). The NOAA/CIMSS ProbSevere product can be used with storms like this to alert a forecaster to when severe weather will develop. ProbSevere output tells you the probability that a given storm cell will first produce severe weather in the next 60 minutes. (The type of severe weather — hail, high winds or tornado) are not specified by the product. In the animation, a strong thunderstorm is just entering Coke county from Sterling county to the north of Tom Green county. The list below shows ProbSevere values with the three storms shown in the animation above.

  1. 1902 UTC  (Northern Cell)  ProbSevere 46%
  2. 1908 UTC (Northern Cell) ProbSevere 50%
  3. 1912 UTC (Northern Cell) ProbSevere 85%
  4. 1930 UTC (Northern Cell) ProbSevere 95%
  5. 1932 UTC (Northern Cell) ProbSevere 95% (Severe Thunderstorm Warning active)
  6. 1948 UTC (Southern Cell) ProbSevere 23%
  7. 1950 UTC (Southern Cell) ProbSevere 50%
  8. 1954 UTC (Middle Cell) ProbSevere 57%
  9. 1956 UTC (Middle Cell) ProbSevere 70%

So, the northern cell crossed the 50% ProbSevere threshold at 1908 UTC, the southern cell crossed the 50% ProbSevere threshold at 1950 UTC, and the small middle cell had a >50% ProbSevere from the start, at 1954 UTC.

Severe hail (1.25″ in diameter) was reported at 1928 UTC (20 minutes after ProbSevere crossed the 50% threshold) 8 miles west (31.89 N, 100.62 W)of Robert Lee, TX (the county seat of Coke County). At 1957 UTC, 1.75″ Hail was reported four miles north (31.94 N, 100.30 W) of Bronte, TX (also in Coke County).

The middle cell in the animation above eventually merged with the southern cell, and intensified. The animation from 1958 through 2014 UTC is below. ProbSevere with the middle storm (that merges with the southern cell) is 70%, rising to 98% at 2014 UTC.

NOAA/CIMSS ProbSevere Output from AWIPS on 24 April, 1958, 2000, 2008, 2010, 2012, 2014 UTC (click to play animation)

NOAA/CIMSS ProbSevere Output from AWIPS on 24 April, 1958, 2000, 2008, 2010, 2012, 2014 UTC (click to play animation)

At 2015 UTC, the National Weather Service issued a Severe Thunderstorm Warning. At this time, 2.75″ Hail was falling five miles northwest of Tennyson in Coke County. (31.79N, 100.35W). The 2016 UTC ProbSevere output is here.

The ProbSevere product is something that distills many bytes of information: model output that describes the environmental conditions, satellite data that describes the initial growth of convection, and MRMS radar data that captures the present state of a storm. The distilled data can be used to increase the confidence that a severe event will occur within the next 60 minutes.

An animation of the 10.7 µm imagery from 1800 through 2015 UTC is shown below. The locations of the severe hail reports noted above are included on the relevant images.

GOES-13 10.7 Brightness Temperature 1800-2015 UTC on 24 April 2015;  Coke County is highlighted (click to play animation)

GOES-13 10.7 Brightness Temperature 1800-2015 UTC on 24 April 2015; Coke County is highlighted (click to play animation)

Severe thunderstorms in the Midwest

April 9th, 2015 |
GOES-13 0.63 µm visible images, with Cloud-Top Cooling Rate, Overshooting Tops Detection, and SPC storm reports (click to play animation)

GOES-13 0.63 µm visible images, with Cloud-Top Cooling Rate, Overshooting Tops Detection, and SPC storm reports (click to play animation)

A deepening area of low pressure (21 UTC surface analysis) was moving northeastward across the Midwest region of the US on 09 April 2015; GOES-13 0.63 µm visible images combined with the Cloud-Top Cooling Rate and Overshooting Tops Detection products (above; click image to play animation) showed a line of severe thunderstorms which quickly developed along the associated cold frontal boundary as it moved eastward across Iowa and Missouri during the afternoon hours. Cloud-Top Cooling Rates with some of the storms in Missouri were in excess of 50º C per 15 minutes (violet color enhancement) during their early stage of development (18:25 UTC image).

A comparison of Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images at 18:51 UTC or 1:51 PM local time (below) showed that the line of thunderstorms was beginning to produce a number of cloud-to-ground lightning strikes.

Suomi NPP VIIRS 11.45 µm IR channel image and 0.64 µm visible channel image with cloud-to-ground lightning strikes

Suomi NPP VIIRS 11.45 µm IR channel image and 0.64 µm visible channel image with cloud-to-ground lightning strikes

Focusing our attention on eastern Iowa and northern Illinois — where there were widespread reports of large hail, damaging winds, and tornadoes (SPC storm reports) — the organization of large, discrete supercell thunderstorms can be seen on GOES-13 0.63 µm visible channel images (below; click image to play animation), which exhibited numerous overshooting tops.

GOES-13 0.63 µm visible channel images, with SPC storm reports (click to play animation)

GOES-13 0.63 µm visible channel images, with SPC storm reports (click to play animation)

The corresponding GOES-13 10.7 µm IR channel images (below; click image to play animation) showed that the coldest cloud-top IR brightness temperatures were -67º C (darker black enhancement).

GOES-13 10.7 µm IR images, with Overshooting Top Detection and SPC storm reports (click to play animation)

GOES-13 10.7 µm IR images, with Overshooting Top Detection and SPC storm reports (click to play animation)

The NOAA/CIMSS ProbSevere product (below; click image to play animation) gauges the likelihood of a storm first producing severe weather (of any kind) within the next 60 minutes. It combines information about the environment (Most Unstable CAPE, Environmental Shear) from the Rapid Refresh Model, information about the growing cloud (Vertical Growth Rate as a percentage of the troposphere per minute and Glaciation Rate, also as a percentage per minute), and Maximum Expected Hail Size (MESH) from the MRMS. In this event, the ProbSevere product performed well for the storm that spawned the EF-4 tornado, although due to the cloudiness of the satellite scene the ProbSevere model was unable to diagnose vertical growth rate and glaciation rate (which diminished the potential lead-time). Below is a chronological timeline of events for that storm:

2308 UTC: first ProbSevere > 50%
2310 UTC: first ProbSevere > 70%
2311 UTC: NWS Severe T-Storm Warning
2312 UTC: ProbSevere = 88%
2323 UTC: 1.00″ hail 2 SE Dixson (15 min lead-time for ProbSevere@50, 13 min for ProbSevere@70, 12 min for NWS Svr Warning)
2335 UTC: NWS Tornado Warning (ProbSevere = 94%)
2340 UTC: Tornado report 2 NE Franklin Grove

Radar reflectivity with NOAA/CIMSS ProbSevere model contours and NWS warning polygons (click to play animation)

Radar reflectivity with NOAA/CIMSS ProbSevere model contours and NWS warning polygons (click to play animation)

In spite of widespread cloudiness, the GOES-13 Sounder single-field-of-view Lifted Index (LI), Convective Available Potential Energy (CAPE), and Total Precipitable Water (TPW) derived product images (below) were able to portray that the air mass in the warm sector of the low ahead of the strong cold front was was both unstable — LI values of -4 to -8º C (yellow to red color enhancement) and CAPE values of 3000-4000 J/kg (yellow to red color enhancement) — and rich in moisture, with TPW values of 30-40 mm or 1.2 to 1.6 inches (yellow to red color enhancement).

GOES-13 Sounder Lifted Index derived product images (click to play animation)

GOES-13 Sounder Lifted Index derived product images (click to play animation)

GOES-13 Sounder Lifted CAPE derived product images (click to play animation)

GOES-13 Sounder CAPE derived product images (click to play animation)

GOES-13 Sounder Total Precipatable Water (TPW) derived product images (click to play animation)

GOES-13 Sounder Total Precipatable Water (TPW) derived product images (click to play animation)

On the following day (10 April), it was cloud-free as the Landsat-8 satellite passed over northern Illinois at 16:41 UTC or 11:41 AM local time — and the 30.2 mile long southwest-to-northeast oriented tornado damage path that produced EF-4 damage and was responsible for 2 fatalities and 22 injuries (NWS Chicago event summary) was evident on 15-meter resolution Band 8 0.59 µm panchromatic visible images viewed using the SSEC RealEarth web map server (below). An aerial survey of part of the tornado damage path can be seen here.

Landsat-8 0.59 µm panchromatic visible image of southwestern portion of tornado damage track (click to enlarge)

Landsat-8 0.59 µm panchromatic visible image of southwestern portion of tornado damage track (click to enlarge)

Landsat-8 0.59 µm panchromatic visible image of northeastern portion of tornado damage path (click to enlarge)

Landsat-8 0.59 µm panchromatic visible image of northeastern portion of tornado damage path (click to enlarge)

A Landsat-8 false-color image (using Bands 6/5/4 as Red/Green/Blue) is shown below. The 2 tornado-related fatalities occurred in Fairdale.

Landsat-8 false-color image (using Bands 6/5/4 as R/G/B)

Landsat-8 false-color image (using Bands 6/5/4 as R/G/B)

On a side note, in the cold (northwestern) sector of the low it was cold enough for the precipitation type to be snow — and up to 4 inches of snow fell in western Iowa. GOES-13 0.63 µm visible channel images (below; click image to play animation) showed the swath of snow cover as it rapidly melted during the daytime hours on 10 April.

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

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

In fact, the swath of snow cover across eastern Nebraska and western/northern Iowa was also evident on a Suomi NPP VIIRS Day/Night Band (DNB) image at 08:49 UTC or 3:39 AM local time (below), highlighting the “visible image at night” capability of the DNB (given ample illumination from the Moon).

Suomi NPP VIIRS 0.7 µm Day/Night Band image

Suomi NPP VIIRS 0.7 µm Day/Night Band image