Severe Weather over the southern United States

April 5th, 2017 |

GOES-16 “Red” Band (0.64 µm) from 1900 through 2100 UTC on 5 April 2017 (Click to animate)

GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing.

On 5 April 2017, The Storm Prediction Center in Norman OK issued a Day 1 Convective Outlook that included Moderate and High Risk areas over much of the southeastern United States. Mesoscale discussion 442 and 448 on 5 April discuss the area shown above. One of two GOES-16 Mesoscale Sectors on 5 April viewed this scene, and a 2-hour animation spanning the outbreak of convection is shown above. It is difficult to predict which particular towering cumulus is going to grow into a cumulonimbus based on the visible imagery alone.

GOES-16 Low-Level Water Vapor Band (7.34 µm) from 2002 through 2127 UTC on 5 April 2017 (Click to animate)

Water Vapor Imagery from GOES-16 might help in that prediction. The animation above, from 2000 UTC to 2130 UTC, shows multiple subtle gradients in the low-level water vapor field that could be associated with impulses influencing convective initiation. Convection appears to form along those subtle gradients. The 16 channels on ABI offer far more information than legacy GOES.


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CIMSS Scientists have been refining the NOAA/CIMSS ProbSevere product to account for individual threats (Hail, Wind, Tornado), and a screen capture of that product is shown below. Radar Objects are outlined in colors that relate to the Probability of a severe event. These outlines allow a forecaster to determine which cell is potentially most threatening based on the inputs into the determination of probability.

NOAA/CIMSS ProbSevere for All Hazards at 2130 UTC on 5 April (click to enlarge)

At 2130 UTC, shown above, a cell over Tennessee has the highest ProbTor probability; the readout (below) shows the variables that are used in computing all the hazard probabilities — ProbHail, ProbWind, and ProbTor (Not all variables are used for all products; for example, ProbTor does not use Satellite-derived growth rates; ‘PS‘ in the output is the value of the 2016 version of ProbSevere). ProbTor of 70% for the cell over Tennessee (compared to smaller values at nearby cells) suggests that particular cell deserves special attention from anyone monitoring the cell for development. The ProbTor for the warned cell in Alabama — a cell that produced Tennis Ball-sized hail near Heflin , showed a ProbTor value at this time of 43% — a larger value than for the storms on either side of it — again suggestive that it should be of most concern. Ten minutes later, at 2140 UTC, ProbTor for the Tennessee storm had dropped to 34%, and that of the Alabama storm had increased to 55%.

ProbTor will be one of the CIMSS products demonstrated at the Hazardous Weather Testbed in June and July this year.

NOAA/CIMSS ProbSevere for All Hazards at 2130 UTC on 5 April; The readout for the indicated cell is shown (Click to enlarge)

Note: ProbSevere products are computed using legacy GOES imagery only. GOES-16 data can be incorporated into this tool only after the statistical model has been trained on GOES-16 data, and that has not yet happened; A GOES-16 version is planned for the 2018 convective season.

NOAA/CIMSS ProbSevere with a tornadic cell in Kansas/Oklahoma

April 26th, 2016 |
GOES-14 Visible (0.63 µm) Imagery, 26 April 2016. An orphan anvil is indicated by the Green Arrow at the start of the animation (click to play animation)

GOES-14 Visible (0.63 µm) Imagery, 26 April 2016. An orphan anvil is indicated by the Green Arrow at the start of the animation (click to play animation)

April 26 2016 was a day of well-anticipated severe weather (even a week out!) over the central and southern Plains, with a Moderate Risk of Severe Weather predicted for parts of Nebraska, Kansas, Oklahoma and Texas. The GOES-14 visible animation, above, shows the development of strong thunderstorms in north-central Oklahoma that propagated into south central Kansas, producing hail around 2000 UTC. Note the presence of an orphan anvil just downstream of the developing convection (to the south of the Green Arrow) at the beginning of the GOES-14 SRSO-R animation (that unfortunately has a 15-minute data gap starting at 1900 UTC).

How did the NOAA/CIMSS ProbSevere product perform with this severe cell? ProbSevere provides a probabilistic estimate of whether a cell will produce severe weather within the next 60 minutes. The animation below shows the quick development of the radar feature that became the hail producer. The Satellite Growth of this particular storm was not observed to be strong. Moderate satellite growth and weak glaciation was diagnosed. However, ProbSevere values became very large because of the environment in which the cell developed, because of the presence of large MRMS MESH observations, and active lightning. ProbSevere exceeded a 50% threshold at 1912 UTC, 6 minutes before the Severe Thunderstorm Warning was issued.  The Table at the bottom shows the ProbSevere components as a function of time.

According to SPC storm reports, the cell produced a brief rope tornado at 2058 UTC in far southern Kansas. This storm was blogged about at the Hazardous Weather Testbed. Click here and here for blog posts on the environmental instability.

NOAA/CIMSS ProbSevere Output, 1824-1946 UTC on 26 April 2016 (click to play animation)

NOAA/CIMSS ProbSevere Output, 1824-1946 UTC on 26 April 2016 (click to play animation)

A zoomed-in animation of the Visible Imagery shows the orphan anvil developing around 1740 UTC. (A rocking animation is here).

GOES-14 Visible (0.63 µm) Imagery, 26 April 2016. The orphan anvil is indicated by the Cyan Arrows through the animation (click to play animation)

GOES-14 Visible (0.63 µm) Imagery, 26 April 2016. The orphan anvil is indicated by the Cyan Arrows through the animation (click to play animation)

 

Time (UTC) ProbSevere MUCAPE Env. Bulk Shear MRMS MESH (Inches) Satellite Growth Satellite Glaciation # Flashes
1854
1858 20% 4739 41.9 0.29 1.9% (Moderate) 0.02 (Weak) 0
1900 29% 4702 41.8 0.45 1.9% (Moderate) 0.02 (Weak) 0
1908 34% 4640 40.9 0.54 1.9% (Moderate) 0.02 (Weak) 5
1910 47% 4628 40.7 0.65 1.9% (Moderate) 0.02 (Weak) 13
1912 59% 4623 40.4 0.65 1.9% (Moderate) 0.02 (Weak) 24
1914 58% 4619 40.1 0.65 1.9% (Moderate) 0.02 (Weak) 24
1916 58% 4614 39.8 0.65 1.9% (Moderate) 0.02 (Weak) 24
1918 54% 4614 39.8 0.60 1.9% (Moderate) 0.02 (Weak) 24
1920 60% 4592 39.4 0.74 1.9% (Moderate) 0.02 (Weak) 20
1922 65% 4591 39.1 0.80 1.9% (Moderate) 0.02 (Weak) 20
1924 73% 4591 39.1 0.80 1.9% (Moderate) 0.02 (Weak) 25
1926 75% 4572 38.8 0.84 1.9% (Moderate) 0.02 (Weak) 26
1928 88% 4578 38.7 1.01 1.9% (Moderate) 0.02 (Weak) 31
1930 89% 4578 38.7 1.01 1.9% (Moderate) 0.02 (Weak) 36
1932 97% 4580 38.6 1.24 1.9% (Moderate) 0.02 (Weak) 49
1934 97% 4560 38.3 1.24 1.9% (Moderate) 0.02 (Weak) 58
1936 97% 4544 38.1 1.24 1.9% (Moderate) 0.02 (Weak) 58
1938 97% 4543 38.0 1.24 1.9% (Moderate) 0.02 (Weak) 58
1940 97% 4540 37.8 1.26 1.9% (Moderate) 0.02 (Weak) 58
1942 98% 4528 37.7 1.53 1.9% (Moderate) 0.02 (Weak) 56
1944 99% 4516 37.5 1.71 1.9% (Moderate) 0.02 (Weak) 56
1946 99% 4507 37.4 1.71 1.9% (Moderate) 0.02 (Weak) 56

 

Strong Winter Storm over the upper Ohio River Valley with severe weather in the Mid-Atlantic

February 24th, 2016 |
GOES-14 Water Vapor Infrared (6.5 µm) images [click to play mp4 animation]

GOES-14 Water Vapor Infrared (6.5 µm) images [click to play animation]

A strong winter storm produced a swath of winter weather from Arkansas through lower Michigan on 23-24 February. GOES-14 SRSO-R Imagery was centered on the occluded storm on 24 February, and the water vapor animation, above (available here as an animated gif image), shows strong flow north-northwest from the Mid-Atlantic states into the Upper Midwest, where Winter Storm and Blizzard Warnings were widespread. The end of the animation shows strong convection developing over the Mid-Altantic states where multiple reports of Severe Weather occurred. (A water vapor animation with weather symbols included is available here as an mp4 and here as an animated gif).

Rapid Refresh Model Simulation of 310 K Equivalent Potential Temperature Surface [click to play animation]

Rapid Refresh Model Simulation of 310 K Equivalent Potential Temperature Surface [click to play animation]

The thermal structure of the storm as revealed by Rapid Refresh analyses of the 310 Kelvin Equivalent Potential Temperature Surface, above, (and available here with contours of Mean Sea Level Pressure) suggests the presence of a Trough of Warm Air Aloft (TROWAL) that stretches from Tennessee to Michigan. Any dry air that moves northward over this region is likely to eroded from below as low-level moisture (not detected in the water vapor imagery) is forced upwards by frontogenetic circulations along the sloping isentropes. Note how cold cloud tops in the animation above appear with regularity over southern Michigan and northern Indiana. These cold clouds tops in the water vapor imagery could be manifestations of frontal forcings acting on the warm air in the TROWAL airstream. Simulated ABI Water Vapor Channels (available here or here), below, show the blossoming of cold cloud tops in the 7.3 µm channel. This toggle between the 6.2µm and 7.3µm channels at 2100 UTC shows how the different water vapor channels view different levels in the atmosphere because of different sensitivity to water vapor absorption at those two wavelengths: the 7.3µm channel typically sees deeper into the troposphere and therefore has warmer brightness temperatures.

Simulated ABI 7.3 µm Water Vapor Channel Imagery, hourly from 16-22 UTC on 24 February 2016 [click to play animation]

Simulated ABI 7.3 µm Water Vapor Channel Imagery, hourly from 16-22 UTC on 24 February 2016 [click to play animation]

GOES-13 Visible (0.65 µm) images [click to play animation]

GOES-13 Visible (0.65 µm) images [click to play animation]

When storms move north to the west of the spine of the Appalachians, downslope winds frequently cause clearing, and this occurred on 24 February, as shown in the half-hourly animation of GOES-13 Visible imagery above. Clear skies are widespread over southeastern Ohio and southwestern Pennsylvania. Cities in the region that cleared saw high temperatures in the mid-60s today. The visible imagery above shows evidence of strong shear in the warm sector (where SPC had issued a Moderate Risk). GOES-14 1-minute Visible Imagery for the 30 minutes ending at 2230 UTC, available here, shows a line of strong convection from the Piedmont of North Carolina northward to metropolitan Washington DC.

GOES-14 Visible (0.65 µm) images [click to play animation]

GOES-14 Visible (0.65 µm) images [click to play animation]

Visible SRSO-R Imagery from GOES-14, above, shows the strong storms moving rapidly to the northeast along a line stretching from Washington DC south to central North Carolina as the sun set on 24 February. (Animation available here as an mp4). Another animation of GOES-14 visible images centered on Virginia and North Carolina (covering the period from 1300-2159 UTC) with plots of station identifiers is available as an MP4 or an animated GIF.


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NOAA/CIMSS ProbSevere output superimposed on MRMS Merged QC Composite Reflectivity, times as Indicated [click to play animation]

NOAA/CIMSS ProbSevere output superimposed on MRMS Merged QC Composite Reflectivity, times as Indicated [click to play animation]

The NOAA/CIMSS ProbSevere model combines information about the storm environment (from the Rapid Refresh) with satellite indicators of cloud growth and with radar estimates of hail size. It is designed to predict when a developing convective cell will first produce severe weather. In the animation above, a growing cell has developed over South Carolina. At the start of the animation, 2134 UTC, the cell is displaying moderate growth rate, and weak glaciation. Two minutes later, at 2136 UTC, ProbSevere has jumped to 62% as the MRMS MESH (Maximum Expected Size of Hail) has jumped from 0.32 to 0.67 inches. By 2144 UTC, ProbSevere exceeds 90%, and it retains that value through the end of the animation at 2250 UTC. This cell produced wind damage three miles northwest of Brownsville SC at 2130 UTC. (SPC Storm Reports). The cell was associated with other wind events in Robeson County, NC at 2155 UTC.

NOAA/CIMSS ProbSevere with a Nebraska Hailstorm

September 22nd, 2015 |
GOES-13 Visible (0.63 µm) images [click to play rocking animation]

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

A severe hail-producing thunderstorm moved over northeast Nebraska before noon on 22 September (SPC Storm Reports). The region hit was just south of a Marginal Risk of Severe Weather (The update at 1630 UTC included the region of severe weather). The GOES-13 visible animation, above, shows the initial development occurring along a subtle cloud line aligned mostly east-west.

The NOAA/CIMSS ProbSevere model produces a probability that a developing thunderstorm will initially produce severe weather within the next sixty minutes. It consistently supplies information with a good lead time, and the storm on 22 September was no exception. The animation below shows the product for about an hour before the first storm report at 1408 UTC. The storm out of which the hail dropped was, at 1300 UTC, flagged as having a ProbSevere under 10%; values exceeded 10% at 1314 UTC and then jumped to 60+% at 1336 UTC (the first time that the value exceeded 50%) Values fluctuated between 60 and 80% between 1336 and 1400 UTC. After 1400 UTC, values increased into the mid-80s. The first report of hail was at 1408 UTC, 32 minutes after ProbSevere jumped above 50%. A severe thunderstorm warning for hail was issued at 1412 UTC.

NOAA/CIMSS ProbSevere values, 1300-1412 UTC on 22 September 2015 [click to play animation]

NOAA/CIMSS ProbSevere values, 1300-1412 UTC on 22 September 2015 [click to play animation]

The GOES Sounder Lifted index product, below, (also available here) showed the instability that was present over the central Plains.

GOES-13 Sounder DPI Values of Lifted Index [click to play animation]

GOES-13 Sounder DPI Values of Lifted Index [click to play animation]