Severe thunderstorm strikes Virginia campground

July 24th, 2014 |
GOES-13 10.7 µm IR channel images (click to play animation)

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

A supercell thunderstorm intensified as it moved eastward across the Chesapeake Bay (just ahead of an approaching surface cold front) on the morning of 24 July 2014 — as it reached the Virginia shore of the Delmarva Peninsula, it produced an EF-1 tornado and damaging straight line winds that were responsible for 2 fatalities and 36 injuries at the Cherrystone Family Camping Resort (located at the * symbol on the images). The storm also produced golf ball to baseball size hail (NWS damage survey | SPC storm reports). McIDAS images of GOES-13 10.7 µm IR channel data (above; click image to play animation; also available as an MP4 movie file) showed that the cloud-top IR brightness temperatures associated with the storm cooled quickly, from -45º C at 11:15 UTC to -64º C at 12:30 UTC. The temperature value was close to that of the tropopause (at a height of 15.4 km) on the 12 UTC rawinsonde data from Wallops Island, Virginia.

The corresponding GOES-13 0.63 µm visible channel images (below; click image to play animation; also available as an MP4 movie file) revealed the presence of an overshooting top at 12:30 UTC  (the time that the IR cloud-top brightness temperature values reached their minimum), which was also flagged by the automated Overshooting Tops detection algorithm.

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

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

AWIPS-II images of the NOAA/CIMSS ProbSevere product (below) followed the radar feature associated with the supercell thunderstorm. Around 11:30 UTC, the ProbSevere value was low, around 5-10%, a result of weak satellite-detected growth (and moderate glaciation) early in the storm’s life, along with low values of MRMS Maximum Expected Size of Hail (MESH). Environmental parameters from the Rapid Refresh model that were supportive of convection: MUCAPE exceeded 2200 J Kg and Shear values were greater than 30 m/s. As the cell tracked to the east and began to move over Chesapeake Bay, both MUCAPE and Shear gradually increased, to values near 2400 J/kg and 35 m/s, respectively. MRMS MESH was oscillating as the cell approached Chesapeake Bay, from 0.44 inches at 11:42 UTC (ProbSevere value of 10%) to 0.37 inches at 11:46 UTC (ProbSevere of 7%) to 0.65 inches at 11:48 UTC (ProbSevere of 29%) to 0.56 inches at 12:00 UTC (ProbSevere of 18%). As the storm moved over the Bay, MESH sizes jumped, to 0.86″ at 12:04 UTC (ProbSevere of 58%, the first crossing of the 50% threshold), to 1.02″ at 12:06 UTC (ProbSevere of 71%), to 1.86″ at 12:12 UTC (ProbSevere of 92% , the first crossing of the 90% threshold), and to 3.09″ (!) at 12:16 UTC (ProbSevere of 91%). At 12:20 UTC, when the Tornado Warning was issued, MRMS MESH was 3.51″ and ProbSevere remained at 91%. Thus, the warning was issued 16 minutes after ProbSevere exceeded 50%, and 8 minutes after ProbSevere was greater than 90%. The NWS storm survey indicated that the campsite fatalities occurred around 12:33 UTC, or 13 minutes after the issuance of the tornado warning.

NOAA/CIMSS ProbSevere product

NOAA/CIMSS ProbSevere product

The rapid intensification of the system as it moved over the Chesapeake begs the question: was instability diagnosed? In the animation below, GOES-13 sounder Derived Product Images (DPI) of Lifted Index (top panel) and CAPE (bottom panel) showed a rich source of instability just south of the cloud-obscuring convection (and ahead of the southward-moving cold front). Lifted Index values derived at 1147 UTC were around -6 at the mouth of the Chesapeake Bay (bright yellow enhancement); CAPE values were around 2500 J/kg (yellow and red enhancements).

GOES-13 Sounder DPI estimates of Lifted Index (top) and CAPE (bottom) [click to play animation]

GOES-13 Sounder DPI estimates of Lifted Index (top) and CAPE (bottom) [click to play animation]

GOES-14 SRSOR: Thunderstorm development over Kentucky

May 22nd, 2014 |
GOES-13 DPI Convective Available Potential Energy (CAPE) on May 22, times as indicated (click to play animation)

GOES-13 DPI Convective Available Potential Energy (CAPE) on May 22, times as indicated (click to play animation)

GOES-14 operations in SRSOR mode deliver the ability to monitor convective development at very short time-scales. A good example of this occurred over the lower Ohio Valley/western Kentucky on May 22nd. The animation of GOES-13 Sounder Derived Product Imagery of CAPE (above) and of Lifted Index (1300 and 1700 UTC) showed considerable instability waiting to be released.

GOES-14 SRSOR animations can be used to monitor the evolving cumulus field in the search for the tower that will break the cap (Nashville, TN/Lincoln IL Soundings from 1200 UTC). The animation below shows visible imagery from 1800 UTC through 2011 UTC, at which time the convection has developed. Initial convection dissipates, but eventually develops along the Ohio River in western Kentucky (cumulus clouds continue to grow/dissipate over the Mississippi River valley throughout the animation).

GOES-14 Visible Imagery (0.62 µm) on May 22, times as indicated (click to play animation)

GOES-14 Visible Imagery (0.62 µm) on May 22, times as indicated (click to play animation)

By 1900 UTC, convective development over the lower Ohio Valley is vigorous enough that Cloud-Top Cooling algorithm from CIMSS (below) has flagged growing clouds, with values exceeding 20º C/15 minutes.

Instanteous Cloud-Top Cooling computed from GOES-13 at 1900 UTC 22 May 2014 (click to enlarge)

Instanteous Cloud-Top Cooling computed from GOES-13 at 1900 UTC 22 May 2014 (click to enlarge)

How does the NOAA/CIMSS ProbSevere model  then change with time as the convection intensifies? The 1904 and 1906 UTC ProbSevere products, toggled below, shows values increasing from 49% to 54% as Satellite Growth rates at 1900 UTC are incorporated at 1906 UTC. ProbSevere values then dropped (1912 UTC, 1922 UTC) as MRMS MESH decreased.

NOAA/CIMSS ProbSevere from 1904 and 1906 UTC on 22 May 2014 (click to enlarge)

NOAA/CIMSS ProbSevere from 1904 and 1906 UTC on 22 May 2014 (click to enlarge)

By 1936 UTC, ProbSevere has again increased above 50%, in two regions where MRMS has MESH sizes over 0.50″. MESH values are equivalent in the two regions, as are environmental values, but higher satellite predictors associated with the smaller eastern radar object drive higher ProbSevere values there.

NOAA/CIMSS ProbSevere from 1936 UTC on 22 May 2014 (click to enlarge)

NOAA/CIMSS ProbSevere from 1936 UTC on 22 May 2014 (click to enlarge)

The animation below shows the evolution of NOAA/CIMSS ProbSevere from 1948 UTC through 2000 UTC, with focus on a second cell that was warned. NOAA/CIMSS ProbSevere is designed to give an estimate of when severe weather might initially occur. Severe weather was not reported in Kentucky with these storms (link); however, observations of severe weather did occur as the storms moved near Nashville.

NOAA/CIMSS ProbSevere from 1948-2000 UTC on 22 May 2014 (click to animate)

NOAA/CIMSS ProbSevere from 1948-2000 UTC on 22 May 2014 (click to animate)

Related Hazardous Weather Testbed blog posts on this event can be found here, here, and here.

ProbSevere results over tidewater Virginia

May 6th, 2014 |
20140506_VA

NOAA/CIMSS ProbSevere superimposed on MRMS radar display over southeastern Virginia. Times as indicated. (Click to enlarge)

 

The Hazardous Weather Testbed (HWT) exercise (Click here for the HWT blog) is ongoing at the Storm Prediction Center.  One of the new products being tested by forecasters is the NOAA/CIMSS ProbSevere product. ProbSevere in the animation above highlighted a cell that produced hail. The AWIPS-2 readout suggests strong vertical growth, and strong glaciation, at 0215 UTC. (The HWT Blog entry on this storm is here) What did the satellite view?

VIS_VA_5MAY_2014loop

GOES-13 Visible Imagery (0.63 µm), times as indicated. (Click to enlarge)

Visible imagery, above, from just before sunset, shows nascent convective development east of Lynchburg over southeastern Virginia, and also older convection over the Chesapeake Bay and Delmarva Peninsula. The infrared imagery (10.7 µm), below, shows rapid development of convection over southeastern Virginia after 0000 UTC. The first convective cell, which cell is east of the Outer Banks of North Carolina at 0315 UTC, had cloud-tops that cooled about 12 C in 17 minutes (between 0115 and 0132 UTC); the storm that produced hail, and was warned, had cloud-tops that cooled 20 C in 13 minutes, between 0202 UTC and 0215 UTC. This strong vertical growth contributes to a big increase in the ProbSevere value.

GOES-13_VA_HAILER_6MAY2014loop

GOES-13 Infrared Imagery (10.7 µm), times as indicated. (Click to enlarge)

When interpreting the radar and satellite imagery, be aware of the effects of parallax on the satellite imagery. GOES-13 imagery displayed here is not corrected for parallax. GOES-13 data are parallax-corrected when used in ProbSevere computations, of course.

NOAA/CIMSS ProbSevere Performance during Tornadic Outbreak

April 27th, 2014 |

Severe weather occurred over the southern Plains/lower Mississippi Valley on Sunday 27 April 2014 (SPC storm reports | GOES-13 IR image animation). How did the NOAA/CIMSS ProbSevere product perform with these storms? Three examples are presented below.

NOAA/CIMSS ProbSevere estimates the likelihood that a growing convective storm will first produce severe weather within the next sixty minutes. The Product uses Rapid Refresh model environmental parameters (Most Unstable CAPE, and Environmental Shear), satellite (GOES-13 only, at present) observations of cloud growth and glaciation, and MRMS radar estimates of Maximum Expected Size of Hail (MESH). A convective tower that grows rapidly (as observed by satellite), for example, will be more likely to spawn severe weather in the next 60 minutes than one that grows more slowly. Similarly, as radar intensities increase, so too do the probabilities. The goal of this product is to increase the lead time for a warning by up to several radar scans.

MRMS Radar and ProbSevere readouts, 21:10, 21:22 and 22:08 UTC on 27 April 2014 [Click to enlarge]

MRMS Radar and ProbSevere readouts, 21:10, 21:22 and 22:08 UTC on 27 April 2014 [Click to enlarge]

The image above shows the radar at 21:10, 21:22 and 22:08 UTC, and also values used in the computation of the ProbSevere product, for a hail-producing storm just south of Dallas. The readout shows the most unstable CAPE and Environment Shear (averaged within the radar object that is outlined), the maximum satellite growth and the maximum glaciation rate that the radar object experienced, and also the MESH. In this case, MUCAPE is 4300-4400 J/kg and Environmental Shear is around 50 kts. The maximum satellite growth for the object being tracked is 1%/minute (% meaning percent of the depth of the troposphere) measured at 20:15 UTC (a time when the radar may or may not have been detecting the developing storm). This moderate growth rate stays attached to this growing convective feature at later times. The ProbSevere exceeded 50% at 21:10 UTC, the first warning was issued at 21:22 UTC and the first report of 1″ hail was at 21:45 UTC. (This storm later produced baseball-sized hail). The storm had moderate growth rates, but very large values of MUCAPE and Shear enhanced the probabilities. Glaciation Rate is reported as N/A, which typically means development under a pre-existing cirrus shield.  That was the case over Dallas, as shown in this animation of visible imagery from GOES-13.

As above, but at 21:20, 21:30 and 22:14 UTC 27 April 2014 [Click to enlarge]

As above, but at 21:20, 21:30 and 22:14 UTC 27 April 2014 [Click to enlarge]

The storm above, over northwestern Mississippi, showed strong satellite growth rates (2.4% per minute) and strong glaciation rates. Probabilities exceeded 50% at 21:14 UTC (just before the 21:20 UTC image shown above) and the first warning was issued at 21:30 UTC, with the first report at 22:31 UTC. This storm produced hail, wind and a tornado.

As above, but at 23:00, 23:08, 23:20 and 23:26 UTC 27 April 2014 [Click to enlarge]

As above, but at 23:00, 23:08, 23:20 and 23:26 UTC 27 April 2014 [Click to enlarge]

A third storm that affected the Kansas City metropolitan area is shown above. ProbSevere exceeded 50% at 23:00 UTC, the first warning was issued at 23:26 UTC and the first hail report occurred 23:31 UTC. Satellite growth for this storm is initially strong (1.5% per minute at 21:25 UTC), but the tracked object linked to that strong growth eventually were lost (Satellite Growth values were lost at 23:20 UTC) and probabilities decrease slightly; they remain relatively high because of the favorable environment and radar observations.

For all three examples above, the probabilities were highest with the convective system that produced the severe weather. The combination of the three components (Rapid Refresh, Radar, and Satellite) is key to the probability. Each individual component has strengths but the combination of predictors is what yields a skillful model with meaningful lead-time.



Severe weather continued on April 28th, including fatal storms in Mississippi.  The image below, however, is for a thunderstorm that formed in Missouri outside the region of SPC’s Slight Risk issued at 1300 UTC, and near the edge of the Slight Risk issued at 1630 UTC.

As above, but at 17:20, 17:22, 17:26 and 17:38 UTC 28 April 2014 [Click to enlarge]

As above, but at 17:20, 17:22, 17:26 and 17:38 UTC 28 April 2014 [Click to enlarge]

The ProbSevere for the developing cell is 24% at 17:20 UTC, with Strong Normalized Vertical Growth Rate (2.3%/min) and weak glaciation (0.01/min) observed at 1655 UTC. At 17:22 UTC, new satellite observations have been incorporated (from the 17:15 UTC scan): the Normalized Vertical Growth Rate is now 3.4%/min; in addition, Glaciation (0.17/Min) is also now strong. As a result, ProbSevere increases to 73%. The Severe Thunderstorm Warning was issued 15 minutes later, at 17:37 UTC, 2 minutes after the first report of severe hail with this storm (in Holts Summit MO, in Callaway County).

 

The ProbSevere product will be evaluated at the Hazardous Weather Testbed to be held in Norman OK in May.