When Atmospheric Bores cause Severe Weather

June 1st, 2019 |

RadarScope imagery from shortly after 0900 UTC on 01 June 2019 (Click to play .mov animation)

Strong near-surface inversions over the upper-midwest early on 1 June 2019 (as shown by 1200 UTC Skew-Ts at Green Bay, WI, Detroit/WhiteLake, MI and Gaylord, MI) helped support the presence of southward-propagating bore features, as shown in the still image (an animation) of radar imagery above (Courtesy Fred Best, SSEC), and (more subtly) in the water vapor imagery (Courtesy Scott Bachmeier) below.

The pressure sensor at the top of the Atmospheric Oceanic and Space Science Building showed many small time-scale pressure perturbations on this day. (Image courtesy Pete Pokrandt)

Water Vapor Imagery from to on 1 June 2019; Low-level (GOES-16 ABI Band 10, 7.34 µm) on the left ; mid-level (GOES-16 ABI Band 9, 6.95 µm) in the center; upper-level (GOES-16 ABI Band 8, 6.19 µm) on the right


Later in the day, strong convection developed over southwestern Lower Michigan, starting shortly after 2215 UTC.  The visible imagery below shows 1-minute imagery (GOES-16 ABI Band 2, 0.64 µm) from a Mesoscale sector positioned over the convection.  At the start, the parallel lines of low clouds suggest a bore feature is propagating southward towards strong convection over northern Indiana and northern Ohio.  Two things happen when that feature meets the convective outflow: some energy is apparently reflected to the north, but very strong convection rapidly develops near Battle Creek MI, where 2″ hail was observed at 2235 UTC (SPC Storm Reports).

GOES-16 ABI 1-minute Visible (0.64 µm) imagery, 2115-2149 UTC on 1 June 2019 (Click to play animated gif)

The clean window (GOES 16 ABI Band 13, 10.3 µm) animation during the day, below, show many features suggesting bore/gravity wave propagation over the area. It is challenging to pick out the impulse from this animation that lead to the severe convection that hit Battle Creek.

GOES-16 ABI Infrared (10.3 µm, Band 13 “Clean Window”) imagery, 1001-2331 UTC on 1 June 2019 (Click to play animated gif)

The Low-Level water vapor animation, shown below, also shows many features that resemble gravity waves or bores, but it also shows a line of parallel features moving towards the site of convective initiation (Consider this short loop from 2126 to 2156 UTC, for example).

GOES-16 ABI Water Vapor (7.3 µm, Band 10 “Low-Level Water Vapor”) infrared imagery, 1001-2331 UTC on 1 June 2019 (Click to play animated gif)

For convection to initiate, instability should be present. The graphic below from the Storm Prediction Center mesoanalysis website shows a nose of unstable air (represented by high values of CAPE) encroaching into southwestern Lower Michigan.

SPC CAPE analysis, 2100 UTC on 1 June 2019 (Click to enlarge)

GOES-16 Baseline Products can also diagnose instability. On 1 June 2019, however, abundant cloudiness limited the utility of the Baseline clear-sky only products, but AllSky versions have been developed and are available online at this website. The animation below shows the evolution of the AllSky Lifted Index from 1826 through 2356 UTC on 1 June 2019. In agreement with the SPC analysis, the AllSky product shows a nose of instability pushing into southwestern lower Michigan. An southward-propagating impulse (apparent in both visible and low-level water vapor imagery) meeting this gradient in instability did initiate convection on this day.

GOES-16 AllSky Lifted Index, half-hourly from 1826 UTC to 2356 UTC on 1 June 2019 (Click to play animated gif)

NOAA/CIMSS ProbSevere (v.2), a tool designed to give confidence that severe weather might occur in the next 60 minutes, shown below, tracked the rapid evolution of the storm. ProbHail increased from 7% at 2220 UTC to 81% at 2230 UTC!

NOAA/CIMSS ProbSevere, with readout values, from 2200 to 2236 UTC on 1 June 2019 (Click to play animated gif)

The chart below, from John Cintineo, SSEC/CIMSS, graphically shows the very rapid development of Prob Hail values. Much of the increase in ProbHail was driven by MESH and Total Lightning observations. When an impulse enters a region of instability in a good environment, explosive growth can result.

NOAA/CIMSS ProbSevere readout for Radar Object 411723 (the storm that produced Hail in Battle Creek MI on 1 June 2019) (Click to enlarge)

Many thanks to TJ Turnage, NWS Grand Rapids, for alerting us to this very interesting case.

Severe thunderstorms in Kansas and Missouri

May 28th, 2019 |

GOES-16 “Red” Visible (0.64 µm) images, with SPC Storm Reports plotted in red [click to play MP4 animation]

GOES-16 “Red” Visible (0.64 µm) images, with SPC Storm Reports plotted in red [click to play MP4 animation]

1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) depicted supercell thunderstorms forming along and south of a quasistationary frontal boundary (surface analyses) which produced a variety of severe weather (SPC Storm Reports) across eastern Kansas and far western Missouri late in the day on 28 May 2019 — including the long-track EF-4 tornado that affected Lawrence and Linwood in Kansas (NWS Kansas City), and prompted a Tornado Emergency to be issued for the Kansas City metro area.

The corresponding GOES-16 “Clean” Infrared Window (10.35 µm) images (below) showed that many of the overshooting tops had infrared brightness temperatures in the -70 to -75ºC range.

GOES-16 “Clean” Infrared Window (10.35 µm) images, with SPC Storm Reports plotted in cyan [click to play MP4 animation]

GOES-16 “Clean” Infrared Window (10.35 µm) images, with SPC Storm Reports plotted in cyan [click to play MP4 animation]

Severe thunderstorms in Indiana and Ohio

May 27th, 2019 |

GOES-16 “Red” Visible (0.64 µm) images, with SPC Storm Reports plotted in red [click to play animation | MP4]

GOES-16 “Red” Visible (0.64 µm) images, with SPC Storm Reports plotted in red [click to play animation | MP4]

1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) revealed supercell thunderstorms that developed within the warm sector of a midlatitude cyclone approaching from the Upper Midwest (surface analyses) — these thunderstorms produced a variety of severe weather (SPC Storm Reports | NWS Northern Indiana) across Indiana late in the day on 27 May 2019.

Many of these storms exhibited well-defined overshooting tops; the largest hail was 4.0 inches in diameter at 0000 UTC. A comparison of SPC Storm Reports at the time of this large hail (and a nearby wind gust to 72 mph) — plotting the reports at the actual ground location vs a “parallax-corrected” location which shifted them northwestward — showed that the severe report locations closely corresponded to the overshooting top (below).

GOES-16 “Red” Visible (0.64 µm) images, with SPC Storm Reports plotted in red [click to enlarge]

GOES-16 “Red” Visible (0.64 µm) image at 0000 UTC, with SPC Storm Reports plotted in red [click to enlarge]

The corresponding GOES-16 “Clean” Infrared Window (10.35 µm) images (below) showed that many of the overshooting tops had infrared brightness temperatures in the -70 to -75ºC range.

GOES-16 “Clean” Infrared Window (10.35 µm) images, with SPC Storm Reports plotted in cyan [click to play animation | MP4]

GOES-16 “Clean” Infrared Window (10.35 µm) images, with SPC Storm Reports plotted in cyan [click to play animation | MP4]

As the thunderstorms moved eastward across Ohio, they continued to produce all modes of severe weather (including EF-3 and EF-4 tornadoes in the Dayton area beginning around 0258 UTC). Additional information on these storms is available from the Hazardous Weather Testbed.

GOES-16 “Clean” Infrared Window (10.35 µm) images, with SPC Storm Reports plotted in cyan [click to play animation | MP4]

GOES-16 “Clean” Infrared Window (10.35 µm) images, with SPC Storm Reports plotted in cyan [click to play animation | MP4]

A Terra MODIS Infrared Window (11.0 µm) image at 0243 UTC with plots of SPC Storm Reports within +/- 45 minutes of the image time (below) showed cloud-top infrared brightness temperatures as cold as -73ºC.

Terra MODIS Infrared Window (11.0 µm) image with plots of SPC Storm Reports within +/- 45 minutes of the image time [click to enlarge]

Terra MODIS Infrared Window (11.0 µm) image with plots of SPC Storm Reports within +/- 45 minutes of the image time [click to enlarge]

Severe thunderstorms in Oklahoma

May 25th, 2019 |

GOES-16

GOES-16 “Clean” Infrared Window (10.35 µm) images, with SPC Storm Reports plotted in cyan [click to play animation | MP4]

1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Clean” Infrared Window (10.35 µm) images (above) showed squall line thunderstorms which produced tornadoes, large hail and damaging winds (SPC Storm Reports) across Oklahoma on the evening of 25 May 2019. Of significance was the EF-3 tornado that affected El Reno, Oklahoma which was responsible for 2 fatalities (NWS Norman).

The GOES-16 Infrared imagery revealed evidence of pulsing updrafts (clusters of colder, brighter white pixels) to the northwest of El Reno (KRQO) — between Watonga (KJWG) and Weatherford (KOJA) — that began at 0248 UTC. 1-minute Infrared brightness temperatures associated with the bowing segment then fluctuated between -73.3ºC and -76.3ºC during the subsequent 40 minutes leading up to the El Reno tornado at 0328 UTC (below). Correcting for parallax, this would have moved those pulsing updrafts southeastward, closer to KRQO.

1-minute Infrared brightness temperatures associated with the bowing segment that produced the El Reno tornado [click to enlarge]

1-minute Infrared brightness temperatures associated with the bowing segment that produced the El Reno tornado [click to enlarge]

One way of illustrating the magnitude of the GOES-16 parallax shift is to compare SPC Storm Reports at the time of the El Reno tornado — plotting the reports at the actual ground location vs a “parallax-corrected” location which shifts them northwestward to more closely correspond to the 13-km mean height of the storm-top Infrared features (below). Note that the parallax-corrected El Reno tornado report location is nearly coincident with that of a colder (lighter shade of white) overshooting top.

GOES-16 "Clean" Infrared Window (10.35 µm) images, with SPC Storm Reports plotted in cyan [click to enlarge]

GOES-16 “Clean” Infrared Window (10.35 µm) images, with surface and parallax-corrected SPC Storm Reports plotted in cyan [click to enlarge]

About an hour after the El Reno tornado, a Terra MODIS Infrared Window (11.0 µm) image (below) displayed cloud-top infrared brightness temperatures as cold as -73ºC as the thunderstorms moved eastward and spread severe weather into the Tulsa area.

Terra MODIS Infrared Window (11.0 µm) image, with plots of SPC Storm Reports with +/- 45 minutes of the image time [click to enlarge]

Terra MODIS Infrared Window (11.0 µm) image, with plots of SPC Storm Reports with +/- 45 minutes of the image time [click to enlarge]