Severe Weather Outbreak Across the Deep South

October 14th, 2014
Suomi NPP 11.35 µm Infrared  Imagery, 1933 UTC 13 October 2014, with Lightning strike data overlain  (click to enlarge)

Suomi NPP 11.35 µm Infrared Imagery, 1933 UTC 13 October 2014, with Lightning strike data overlain (click to enlarge)

An intense extratropical cyclone over the central United States spawned a Quasi-Linear Convective System that moved through the Deep South on 12-13 October 2014; the QLCS was responsible for a spate of severe weather including wind damage, hail and tornadoes (Storm reports from 12 October, 13 October). The image above, from 1933 UTC on 13 October, shows Suomi NPP 11.35 µm imagery over Mississippi. Widespread cold cloud tops are apparent, with embedded overshooting tops. Indeed, the top in southern Hinds County may have been associated with severe Hail. Visible imagery from Suomi NPP (link) also show overshooting tops. The amount of solar reflectance at mid-day, however, makes it difficult to identify all features. The 1.61 µm imagery, below, is darker because ice crystals at cloud top will absorb some energy at that wavelength, yet most features are still recognizable.

Suomi NPP 1.61 µm Near-Infrared  Imagery, 1933 UTC 13 October 2014 (click to enlarge)

Suomi NPP 1.61 µm Near-Infrared Imagery, 1933 UTC 13 October 2014 (click to enlarge)

The GOES-13 Water Vapor Animation, below, is a textbook example of cyclogenesis. Strong sinking in and around the comma head is indicated by the warm water vapor brightness temperatures observed there. This system is also characterized by a very sharp upstream trough and developing warm conveyor belt that turns anticyclonic as it moves over the upper Great Lakes.

GOES-13 Water Vapor 6.7 µm Infrared  Imagery, 1200-2100 UTC 13 October (click to animate)

GOES-13 Water Vapor 6.7 µm Infrared Imagery, 1200-2100 UTC 13 October (click to animate)

GOES-13 10.7 infrared imagery animation, below (also available here as an mp4 file or here as a YouTube video), shows evidence of many overshooting tops in the strong thunderstorms that developed across the deep south. (Indeed, automatic detection of overshooting tops(and cumulative totals from this website) — show some on the 12th, but many more on the 13th) as the extratropical cyclone became organized.

GOES-13 10.7 µm Infrared Imagery, 1600 UTC 13 October - 0700 UTC 14 October 2014 (click to animate)

GOES-13 10.7 µm Infrared Imagery, 1600 UTC 13 October – 0700 UTC 14 October 2014 (click to animate)

The strong system enjoyed a vigorous moisture feed from the Gulf of Mexico, as shown in the MIMIC Total Precipitable Water animation below. Moisture surged northward especially after 1200 UTC on 13 October, and the 24-hour precipitation totals ending at 1200 UTC on 14 October (from this site) showed heavy rain over much of Tennessee and Alabama (and adjacent states).

MIMIC Total Precipitable Water for 72 hours 1200 UTC 14 October 2014 (click to enlarge)

MIMIC Total Precipitable Water for 72 hours 1200 UTC 14 October 2014 (click to enlarge)

GOES Sounder data also shows a quick moistening on 13 October as high Precipitable Water air over the Gulf of Mexico surges northward. Moisture from Pacific Hurricane Simon is unlikely to be a contributing factor to this storm.

GOES Sounder DPI estimates of Total Precipitable Water from through 6 October through October 14 2014 (click to enlarge)

MIMIC Total Precipitable Water for 72 hours 1200 UTC 14 October 2014 (click to enlarge)

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MTSAT-2 and GOES-15 Water Vapor (6.5 µm)Infrared imagery, times as indicated (click to enlarge)

MTSAT-2 and GOES-15 Water Vapor (6.5 µm)Infrared imagery, times as indicated (click to enlarge)

An interesting question arises: Where did some of the energy and moisture for this (somewhat early in the season) storm originate? Water Vapor imagery from MTSAT-2 and GOES-15 show clearly that the Super-Typhoon Phanfone, that was near Japan on 4-5 October, contributed some of the energy to the impulse that moved across the Pacific Ocean and then over the Ridge on the West Coast of North America before diving southeast and forcing cyclogenesis. In the animation above, Phanfone approaches Japan, and is picked up by a mid-latitude jet that crosses the Pacific (tracked by red arrow), induces strong cyclogenesis in the Gulf of Alaska on 8 October and then continues up and over the ridge on the west coast of North America.

Mesoscale Convective System over the Southern Plains

October 6th, 2014
<strong>Suomi NPP VIIRS Day/Night Band (0.70 µm), Infrared Imagery (11.45 µm) and Day/Night Band imagery with lightning strikes at 0842 UTC on 6 October 2014</strong> (click to animate)

Suomi NPP VIIRS Day/Night Band (0.70 µm), Infrared Imagery (11.45 µm) and Day/Night Band imagery with lightning strikes at 0842 UTC on 6 October 2014 (click to animate)

The Suomi NPP VIIRS image toggle, above, from the pre-dawn hours (3:42 am local time) on 6 October 2014 shows a 0.7 µm Day/Night Band image and an 11.45 µm Infrared image, along with observations of postive and negative lightning strikes. With ample illumination by moonlight, the “visible image at night” Day/Night Band image highlighted areas of convective overshooting tops, but also included bright horizontal stripes that are associated with intense lightning activity; after scanning a particularly bright area of lightning in Arkansas, this image also showed a darker “post-saturation recovery” stripe downscan (to the southeast), which stretched from central Arkansas into Mississippi. This vigorous convective system dropped southeastward from Oklahoma towards the Gulf of Mexico, eventually becoming a Quasi-Linear Convective System (QLCS) which produced hail and wind damage (with one fatality) across parts of northeastern Texas and far northwestern Louisiana (SPC storm reports).

GOES Sounder DPI Lifted Index (click to animate)

GOES Sounder DPI Lifted Index (click to animate)

The southward-dropping Mesoscale Convective System followed a channel of unstable air as diagnosed by the GOES Sounder, above. Note that the Lifted Index values were smaller (less instability) along the path that the system had moved. Total Precipitable water was also enhanced in that corridor, suggesting a region where moisture return from the Gulf of Mexico was ongoing and concentrated.

GOES Infrared Imagery(10.7 µm) at 1600 UTC, and Pilot Reports of Turbulence (click to enlarge)

GOES Infrared Imagery (10.7 µm) at 1600 UTC, and Pilot Reports of Turbulence (click to enlarge)

Mesoscale Convective Systems can exhibit signatures that suggest the presence of turbulence in the atmosphere. In the GOES-13 IR image above, parallel filaments or “transverse bands” of cirrus  (extending approximately north-south) on the poleward side of the MCS suggest the presence of turbulence, and scattered pilot reports of Moderate Turbulence confirm that. Visible MODIS Imagery, below, also shows the transverse bands, as well as the outflow boundary arcing from Houston to the northwest and north.

Terra MODIS visible imagery (0.65 µm) at 1705 UTC  (click to enlarge)

Terra MODIS visible imagery (0.65 µm) at 1705 UTC (click to enlarge)

An animation of hourly GOES-13 Visible imagery, below, shows the motion of the western portion of the outflow boundary as the decaying QLCS moved into the Gulf of Mexico.

GOES-13 Visible (0.65µm) imagery (click to animate)

GOES-13 Visible (0.65µm) imagery (click to animate)

GOES-13 6.5 µm water vapor channel imagery, below, displayed a signature of subsidence immediately upstream of the dissipating MCS, in the form of an arc of warmer/drier (yellow to orange color enhancement) brightness temperatures that extended from the Texas coast into central Arkansas. One rapidly-developing convective cell which formed along the advancing outflow boundary was responsible for severe turbulence in eastern Texas; the subtle signal of the westward-propagating outflow boundary could also be followed on the water vapor imagery.

<strong>GOES-13 6.5 µm water vapor channel images, with pilot reports of turbulence</strong> (click to play animation)

GOES-13 6.5 µm water vapor channel images, with pilot reports of turbulence (click to play animation)

GOES Cloud Top Cooling Rate product used for SPC Mesoscale Discussion

September 17th, 2014
Storm Prediction Center Mesoscale Discussion #1724

Storm Prediction Center Mesoscale Discussion #1724

Using the GOES-R Cloud Top Cooling Rate product (applied to GOES-13 data), the Storm Prediction Center issued a Mesoscale Discussion (above) highlighting the risk of strong thunderstorms producing hail and/or strong wind gusts over parts of the Georgia/South Carolina border region on 17 September 2014. According to the SPC storm reports, there was hail up to 1.0 inch in diameter in addition to some tree and power line damage in southern South Carolina.

AWIPS II image combinations of the Cloud Top Cooling (CTC) rate product (colors) and the GOES-13 10.7 µm IR channel gray-scale images  (below; click image to play animation) showed that CTC rate values for the storm north of Augusta, Georgia (KAGS) at 19:00 UTC were as high as -16º C per 15 minutes; at 19:15 UTC, the CTC rate value for that storm was as high as -39º C per 15 minutes. The first Severe Thunderstorm Warning for this storm was later issued at 19:34 UTC.

Cloud Top Cooling Rate (colors) and GOES-13 10.7 µm IR (grayscale) images [click to play animation]

Cloud Top Cooling Rate (colors) and GOES-13 10.7 µm IR (grayscale) images [click to play animation]

GOES-13 10.7 µm IR channel images (below; click image to play animation) showed the rapidly cooling cloud-top IR brightness temperatures associated with these thunderstorms as they moved southeastward and intensified: the coldest value for the aforementioned thunderstorm was -40º C at 19:00 UTC, dropping to -62º C by 20:45 UTC.

GOES-13 10.7 µm IR channel images [click to play animation]

GOES-13 10.7 µm IR channel images [click to play animation]

About an hour later, another Severe Thunderstorm Warning was issued at 20:30 UTC for a storm near and south of Orangeburg, South Carolina (KOGB).

GOES-14 SRSOR: Thunderstorms over Florida

August 21st, 2014
GOES-14 0.63 µm visible channel images (click to play YouTube movie)

GOES-14 0.63 µm visible channel images (click to play YouTube movie)

The GOES-14 satellite was in Super Rapid Scan Operations for GOES-R (SRSOR) mode, providing images at 1-minute intervals over the southeastern US on 21 August 2014. An animation of 0.63 µm visible channel images (above; click to play YouTube movie) showed the development of numerous large thunderstorms, many of which were focused along surface boundaries such as the sea breeze and  convective outflow boundaries from adjacent storms. The YouTube video is best viewed in Full Screen mode, using the “Gear” icon to select 1080p HD resolution.