Convective outflow boundary initiates new convection over Kansas

July 31st, 2013 |
GOES-13 0.63 µm visible channel images (click image to play animation)

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

AWIPS images of 1-km resolution GOES-13 0.63 µm visible channel data (above; click image to play animation) showed an undular bore marking a surface-based convective outflow boundary which formed over southwestern Nebraska early in the day on 31 July 2013 — this outflow boundary then propagated southwestward during the day and acted as a focus for the formation of severe thunderstorms over southwestern Kansas later that afternoon (SPC storm reports).

The southwestward-propagating outflow boundary / undular bore feature was also seen on 4-km resolution GOES-13 6.5 µm water vapor channel imagery (below; click image to play animation).

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

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

The GOES-13 imager 6.5 µm water vapor channel weighting function calculated using the 12 UTC rawinsonde data from Dodge City, Kansas (below) indicated that the weighting function peaked much lower in the atmosphere (around 500 hpa) than normal — this allowed a thermal signal (albeit a faint one) of the boundary layer convective outflow boundary cloud features to be seen on the water vapor imagery.

GOES-13 water vapor channel weighting function plot (using Dodge City, Kansas rawinsonde data)

GOES-13 water vapor channel weighting function plot (using Dodge City, Kansas rawinsonde data)

A good view of the undular bore (which was trailing the leading edge of the convective outflow boundary) could be seen on a comparison of 1-km resolution MODIS 0.64 µm visible channel and 11.0 µm IR channel images at 17:05 UTC (below).

MODIS 0.64 µm visible channel and 11.0 µm IR channel images

MODIS 0.64 µm visible channel and 11.0 µm IR channel images

New thunderstorms formed along the old convective outflow boundary (as it encountered increasing instability across southwestern Kansas during the afternoon hours), as seen on 1-km resolution Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images (below). This storm was producing 1-inch diameter hail and wind gusts of 50-60 mph.

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel mages, with SPC reports of hail

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel mages, with SPC reports of hail

A comparison of the 1-km resolution Suomi NPP VIIRS 11.45 µm IR channel image with the corresponding 4-km resolution GOES-13 10.7 µm IR channel image (below) displayed an unusually large 30-degree difference between the coldest cloud-top IR brightness temperatures of the northernmost of the newly-formed thunderstorms in Kansas (-92º C on VIIRS, vs -62º C on GOES).

VIIRS 11.45 µm IR channel and GOES-13 10.7 µm IR channel images

VIIRS 11.45 µm IR channel and GOES-13 10.7 µm IR channel images

 

Cloud-Top Cooling Rate

May 30th, 2012 |
GOES Sounder DPI Lifted Index 1600 UTC on May 30 2012

GOES Sounder DPI Lifted Index 1600 UTC on May 30 2012

Satellite descriptors of the atmosphere over the central High Plains on May 30th suggested an atmosphere ripe for convection. For example, the GOES Sounder DPI Lifted Index showed an axis of instability from central Oklahoma to northwest Kansas, with widespread values (yellows, reds, purples) at or below -4. (The unstable area overlaps nicely with the slight risk for the day diagnosed for the day by the Storm Prediction Center). The NearCasting product (below, and available on-line here) suggests that convective instability will persist over southern Nebraska and extend southward into Oklahoma for most of the day.

GOES-13 NearCast product (click image to play animation)

GOES-13 NearCast product (click image to play animation)

GOES-13 Visible Imagery and UW Cloud-Top Cooling Rate

GOES-13 Visible Imagery and UW Cloud-Top Cooling Rate (click image to play animation)

Given this type of environment, what can cloud-top cooling rate tell you? The Cloud-Top Cooling Rate is a satellite-based product that diagnoses how quickly the growing convective towers are cooling with time, and strong cooling means rapid vertical convective growth. The strongest cooling is where the strongest convective growth is occurring, and that cooling is well-correlated with the subsequent development of NEXRAD signatures (MESH, maximum VIL, reflectivity at -10 C, etc.) The loop above shows GOES-13 visible imagery with the cloud-top cooling rate superimposed. (Real-time imagery of the cloud-top cooling rate product is available here) The The cloud-top cooling rate product highlights a persistently and quickly growing convective feature near McCook, Nebraska before and shortly after 1700 UTC. By 1800 UTC, that feature is a severe thunderstorm warned for high winds and hail.

The UW Cloud-Top Cooling Rate product is being evaluated at the Hazardous Weather Testbed taking place this month. At the HWT Blog, there are many examples of using the product in concert with knowledge of the synoptic and mesoscale conditions to anticipate strong thunderstorm development.

SPC storm reports show that the system with the strong Cloud-Top Cooling Rate subsequently produced 1-inch hail near Holdrege.

Aircraft turbulence east of Florida on August 9 2011

August 9th, 2011 |
GOES-13 Visible with Airplane Positions

GOES-13 Visible with Airplane Positions

Turbulence associated with a developing line of convection over the Atlantic Ocean east of Florida was severe enough on August 9th to cause five injuries on a Miami-to-Washington DC flight and force an unscheduled landing of the 737-800 aircraft in Charleston, SC. The GOES-13 image, above, shows the path that the aircraft took through a line of developing convection east of Florida (Click here for a flash-based animation). The time that the satellite was scanning the region east of Florida was between 1935 and 1936 UTC (the nominal time of the image, 1932 UTC, refers to the first line scanned in by GOES-13; it takes almost 5 minutes to completely scan North America. See this NESDIS website for the normal scanning schedule).

Animations of visible imagery, 10.7-micrometer infrared imagery, and 6.5-micrometer infrared imagery (the so-called ‘water vapor channel’) all show a similar evolution, namely strong thunderstorms at the coast of Florida at the start of the loop followed by the development of a line of thunderstorms northeastward. It is through this developing line that the airline penetrated. (The flight path is here).

GOES Satellite data are routinely monitored to detect both the initiation of convection, and the presence of Overshooting Tops and Thermal couplets, the latter two features being well-correlated with severe weather and turbulence. Detection suffers, however, because of the relatively poor spatial and temporal resolution afforded by routine GOES scanning. What was detected on this day?

Overshooting tops were detected over the Florida peninsula at 1715 UTC and at 1732 UTC. The top at 1732 UTC is quite apparent in both the visible and infrared loops. Overshooting tops were not detected in the area again before the turbulence event, but their detection prior to the event suggests an airmass with the potential for strong convective development.

Convective Initiation (CI) was flagged along the southwest-to-northeast line of developing convection at 1832 UTC and 1845 UTC, roughly an hour before the turbulence event. (See this link for all Blog Posts on Convective Initiation). Note that the CI detection in this case — occurring — means that glaciation of the clouds has started. CI is drawing the eye to the convective towers that are growing most rapidly; therefore, their tops cool most quickly. It is to these growing cells that a forecaster must pay attention, particularly when they appear in an environment that will sustain overshooting tops.

(Here is an article on this flight from The Aviation Herald).

Southeast US tornado outbreak of 27 April 2011

April 27th, 2011 |
GOES-13 0.63 µm visible images (click image to play animation)

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

The tornado outbreak that affected much of the Southeast US on 27 April 2011 was one of historic proportions, in terms of the number of strong to violent tornadoes produced and the number of resulting fatalities. McIDAS images of 1-km resolution GOES-13 0.63 µm visible channel data (above; click image to play animation; also available as a QuickTime movie) showed the multiple clusters of severe thunderstorms that developed across the region during the day. The GOES-13 satellite had been placed into Rapid Scan Operations (RSO), supplying imagery as frequently as every 5-10 minutes. Zoomed-in versions of GOES-13 RSO 0.63 µm visible images covering the period of the long-track (80 mile) EF-4 Tuscaloosa (KTCL) / Birmingham (KBHM) tornado are available here, which show that the storms exhibited a number of distinct overshooting tops during the time period between 20:40 UTC and 23:25 UTC.

AWIPS images of 4-km resolution GOES-13 10.7 µm IR channel data with overlays of severe weather reports (below; click image to play animation) showed the first round of large storms with cold cloud top IR brightness temperatures (red to black to white color enhancement) that moved through the area during the pre-dawn hours (which produced mainly damaging wind reports), followed by the development later in the afternoon and early evening hours of the stronger storms that produced numerous reports of large hail and strong tornadoes ahead of an advancing cold front (SPC storm reports). Zoomed-in versions of GOES-13 RSO 10.7 µm IR images covering the period of the long-track (80 mile) EF-4 Tuscaloosa (KTCL) / Birmingham (KBHM) tornado are available here — cloud top IR brightness temperature values during the 20:40 UTC to 23:25 UTC time period were as cold as -75º C at 22:25 UTC.

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

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

With the higher 1-km spatial resolution of the POES AVHRR IR imagery (below), more detail could be seen in the cloud top IR brightness temperature structure, and much colder cloud top temperatures could be detected in the vicinity of the strongest overshooting tops (as cold as -83º C, violet color enhancement). Other similar 1-km resolution POES AVHRR IR and MODIS IR image examples (with overlays of storm reports) are available at 16:28 UTC, 18:10 UTC, 18:12 UTC, 18:35 UTC, 19:48 UTC, 19:52 UTC, 20:13 UTC, 00:01 UTC, and 03:34 UTC.

POES AVHRR 12.0 µm IR image + SPC storm reports

POES AVHRR 12.0 µm IR image + SPC storm reports

Although there was widespread cloudiness across much of the Southeast US, hourly GOES-13 Sounder Convective Available Potential Energy (CAPE) derived product images (below) were still able to provide some indication as to the instability of the air mass that was feeding northward into the region that morning.

GOES-13 Sounder CAPE derived product imagery

GOES-13 Sounder CAPE derived product imagery

Another important ingredient was the approach of a strong trough aloft, along with an associated strong mid-level jet streak as seen in a comparison of 1-km resolution MODIS 6.7 µm water vapor imagery and CRAS model 500 millibar (hPa) wind speeds (below).

MODIS 6.7 µm water vapor channel image + CRAS model 500 MB wind speeds

MODIS 6.7 µm water vapor channel image + CRAS model 500 MB wind speeds

CIMSS participation in GOES-R Proving Ground activities includes making a variety of POES AVHRR, MODIS, and additional GOES Sounder images and products available for National Weather Service offices to add to their local AWIPS workstations. The VISIT training lessons “POES and AVHRR Satellite Products in AWIPS”, “MODIS Products in AWIPS“, and “Water Vapor Imagery and Potential Vorticity Analysis” are available to help users understand these products and their applications to weather analysis and forecasting.

To prepare for the upcoming GOES-R era, new products are being developed and tested at CIMSS using the current generation of satellite data — in fact, some of these new products are now being distributed to and evaluated by a few NWS Offices. Specially-tailored products such as Convective Initiation, Overshooting Tops, and Enhanced-V will allow for the automatic detection of the various developmental stages of convection.

 

Slide the “Set Fade Level” button located under examples of these images (above) to fade between the CIMSS Convective Initiation (CI) and CIMSS Overshooting Tops (OT) products (derived from satellite observations), along with Cloud-to-Ground (CG) lightning strikes observed from ground-based sensors. Note that there is good agreement between the locations of the satellite-derived CI and OT products and the SPC storm reports for the day (below).