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.

Intense mid-latitude cyclone in the North Atlantic Ocean

October 13th, 2014
GOES-13 6.5 µm water vapor channel images (click to play animation)

GOES-13 6.5 µm water vapor channel images (click to play animation)

A large mid-latitude cyclone exhibited explosive development over the North Atlantic Ocean (south of Greenland) on 13 October 2014. This storm produced hurricane-force winds, according to surface analyses from the Ocean Prediction Center. GOES-13 6.5 µm water vapor channel images (above; click image to play animation; also available as an MP4 movie file) showed the intrusion of very dry air (yellow to orange color enhancement) associated with the approach of a potential vorticity anomaly early in the day, followed by the the cyclone wrapping up after it reached the occluded phase during the afternoon hours.

GOES-13 0.63 µm visible channel images (below; click image to play animation) revealed the very pronounced signature of cold air advection from the western to the southern quadrants of the storm, in the form of open-cell and closed-cell convective clouds.

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

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

Gonzalo in the Leeward Islands

October 13th, 2014
GOES-13 0.63 µm Visible Imagery, 13 October (click to play animation)

GOES-13 0.63 µm Visible Imagery, 13 October (click to play animation)

Tropical Storm Gonzalo is moving through the Leeward Islands today, October 13. The animation above shows the visible imagery from GOES-13. Slow strengthening of the storm is indicated. Eye formation may be occurring in the later part of the animation. (Note that imagery over the Leeward Islands is available only every half-hour because of an RSO called for GOES-13 associated with severe weather; in normal operations, the Caribbean is scanned every 15 minutes as discussed here).

Suomi NPP Day Night Band visible (0.70 µm) and 11.35 µm infrared imagery at 0456 UTC, 13 October (click to enlarge)

Suomi NPP Day Night Band visible (0.70 µm) and 11.35 µm infrared imagery at 0456 UTC, 13 October (click to enlarge)

Suomi NPP overflew the developing system at 0456 UTC on 13 October, and a toggle between the Day Night Visible Band and the 11.35 infrared imagery (courtesy of W. Straka, CIMSS) is above. Cold cloud tops associated with numerous overshooting tops are obvious. (Click here for a graph of the number of overshoots as detected from GOES-13 as a function of time)

Saharan Air Analysis from Meteosat, 1200 UTC 12 October through 1200 UTC 13 October (click to play animation)

Saharan Air Analysis from Meteosat, 1200 UTC 12 October through 1200 UTC 13 October (click to play animation)

The Atlantic Tropical Storm season has been comparatively quiet this year in part because of strong Saharan Air Layer events (discussed in Blog Posts here and here). When this dry air that originates over the Sahara moves over the tropical Atlantic, the convection necessary for tropical storm formation is suppressed. Lately, however, Saharan Air Layer events have decreased, and tropical systems are developing in the tropical Atlantic. The 24-hour animation above (from CIMSS Tropic Web site) shows very little Saharan Air over the Atlantic, and two named storms — Fay (at 50 º W on the northern border of the domain) and Gonzalo (approaching the Leeward Islands) — are present. In addition, a strong tropical wave is moving across the tropical Atlantic at 15 º N, 40 º W. MIMIC Total Precipitable Water animations (below) also show a moist environment over much of the tropical Atlantic.

MIMIC Total Precipitable Water for the 72 hours ending 1200 UTC 13 October 2014 (click to enlarge)

MIMIC Total Precipitable Water for the 72 hours ending 1200 UTC 13 October 2014 (click to enlarge)

GOES-13 10.8 µm Infrared Imagery every six hours from 2045 UTC 12 October through 1445 UTC 13 October (click to play animation)

GOES-13 10.8 µm Infrared Imagery every six hours from 2045 UTC 12 October through 1445 UTC 13 October (click to play animation)

A storm-centered animation of the 10.8 µm imagery from GOES-13, above, shows the gradual organization of Gonzalo as it moved towards the Leeward Islands. In particular, between 0845 and 1445 UTC on 13 October (the last two images in the 4-frame loop), a central dense overcast (CDO) has formed, and outflow to the east has become established. Gonzalo’s projected path (see below, from here) is over very warm water, and through an atmosphere with little shear; slow strenghtening is expected. See the National Hurricane Center website for more details, including warnings for the Leeward Islands.

Analyses of Sea Surface Temperatures and Shear, 1200 UTC 13 October 2014 (click to enlarge)

Analyses of Sea Surface Temperatures and Shear, 1200 UTC 13 October 2014 (click to enlarge)

High-resolution Imagery of Stratus along the West Coast

October 10th, 2014
Suomi NPP 0.7 µm Day Night Band imagery at 0907 and 1048 UTC over central California with surface observations of ceilings and visibilities (click to enlarge)

Suomi NPP 0.7 µm Day Night Band imagery at 0907 and 1048 UTC over central California with surface observations of ceilings and visibilities (click to enlarge)

The Suomi NPP VIIRS Day Night Band during a Full (or near-Full) Moon yields striking visible imagery at night because of abundant reflected lunar illumination. Sequential orbits along the west coast of the Pacific on the morning of 10 October showed the penetration of coastal stratus and fog inland at two times (click here for the images above without the surface observations). A similar case study from 9 October is shown here. The slow inland penetration of stratus/fog is captured by the scenes: tendrils of fog extend up small valleys along the edge of the Salinas Valley, for example, and the fog extends farther down the valley at 1048 UTC. Similar expansion of fog occurs over Sonoma Valley north of San Francisco Bay.

Careful inspection of the imagery shows parallel lines along the western edge at 0907 UTC and along the eastern edge at 1048 UTC. In addition, city lights and topographic features are displaced somewhat along the eastern edge of the 1048 UTC image. These are all artifacts of the VIIRS instrument viewing geometry (that is, parallax) and post-processing that is necessary near the edges to maintain high-resolution imagery there.

A toggle between the corresponding VIIRS 11.45 µm – 3.74 µm infrared brightness temperature difference images (commonly referred to as the “fog/stratus product”), below, similarly shows gradual expansion of water-based clouds between 0907 and 1048 UTC. There are also image features, color enhanced as black, that suggest very thin cirrus is moving over the coast. These clouds are thin enough that they cannot be discerned in the Day Night Band imagery, but their presence nevertheless inhibits the detection of low clouds in places, such as over the southernmost part of the Salinas Valley at 1048 UTC.

Suomi NPP Brightness Temperature Difference (11.45 µm - 3.74 µm) Imagery at 0907 and 1048 UTC over central California (click to enlarge)

Suomi NPP Brightness Temperature Difference (11.45 µm – 3.74 µm) Imagery at 0907 and 1048 UTC over central California (click to enlarge)

Suomi NPP 0.7 µm visible Day Night Band imagery at 0907 and 1048 UTC over Washington State with surface observations of ceilings and visibilities (click to enlarge)

Suomi NPP 0.7 µm visible Day Night Band imagery at 0907 and 1048 UTC over Washington State with surface observations of ceilings and visibilities (click to enlarge)

The image toggle above shows similar features over Washington State. Fog/stratus tendrils move up river valleys in the ~90 minutes between the two polar-orbiting satellite passes, and areas of fog increase in size. (click here for the same images without observations). Because the first image is very near the edge of the VIIRS instrument scan swath, there is also a shift in city lights and some geographic features, again an artifact of scanning geometry (parallax) and the post-processing to maintain high-resolution imagery at the scan edges.

Suomi NPP Brightness Temperature Difference (11.45 µm - 3.74 µm) Imagery at 0907 and 1048 UTC over Washington State (click to enlarge)

Suomi NPP Brightness Temperature Difference (11.45 µm – 3.74 µm) Imagery at 0907 and 1048 UTC over Washington State (click to enlarge)

The IR brightness temperature difference product over Washington, above, also shows evidence of a slow increase in the areal coverage of fog/stratus near the coast. The effects of limb brightening are also present in the first image. When a satellite scans near the edge of its domain, the path from the point on the Earth to the satellite traverses more of the upper atmosphere, and a colder sensed temperature results. This effect is wavelength-dependent. For example, at one point (47º N, 125º W) in the stratus (with fairly uniform temperature) off the west coast of the Washington, in the stratus (which should have a fairly constant temperature), brightness temperatures were about 1º C cooler in 11.35 µm imagery, but closer to 2.5º C cooler in the 3.74 µm imagery. Hence, the brightness temperature difference signal is larger at 0906 UTC.

Both brightness temperature difference fields show signals over dry land that are related to emissivity differences in the soils. These occur over central Washington, above and over Nevada in the images centered over California.