Satellite Liaison Blog

During the evening of May 20, 2017, a fog layer developed off of the Pacific Northwest coast and streamed into the Strait of Juan de Fuca. The NWS Seattle office sent out this great tweet showing the evolution of the fog deck in GOES-16 visible imagery.

After sunset, of course, visible imagery can no longer be used. Additionally, IR imagery alone is not ideal for detecting and tracking liquid water clouds (low clouds and fog). Instead, the 3.9 um – 10.3 um channel difference highlights liquid water clouds well. Figure 1 below depicts the continued evolution of fog after sunset on the 20th into the early morning hours of the 21st just prior to sunrise. The darkest gray (low negative) color represents low clouds and fog (liquid clouds), the lightest gray to white (positive) color represents high/ice clouds, and the medium grays (near 0) are clear sky.

Figure 1: 21 May 2017 GOES-16 3.9 um – 10.3 um Fog Difference. Full resolution: https://satelliteliaisonblog.files.wordpress.com/2017/05/20170521_fog_nw2_anno1.gif

For low clouds and fog (liquid water clouds), cloud top emissivity at 3.9 um is lower than for the same cloud at 11 um. Therefore at night, low clouds and fog will appear cooler at 3.9 um than at 11 um. So by taking the difference, low clouds will stand out as relatively low negative values.

During the day, the sign is flipped due to reflectance and scattering of solar radiation at 3.9 um. So 3.9 um will become warmer than 11 um. The difference will be positive for low clouds and fog during the day.

The 3.9 um – 10.3 um difference will be positive for high clouds day/night. It is ideal to use visible imagery during the day to monitor low cloud and fog evolution

– Bill Line, NWS

“The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing. Users bear all responsibility for inspecting the data prior to use and for the manner in which the data are utilized.”

On 18 May 2017,  SPC issued a high risk for severe thunderstorms across portions of Oklahoma and Kansas. A closed upper low centered over UT/CO sent a shortwave through the TX PH into S Kansas through the day. At the surface, a low deepened over the Texas PH with associated southerly flow drawing warm/moist air into OK and KS. A N-S dryline positioned itself near the TX/OK border while a W-E warm front pushed north into central Kansas.

The first storms of the day initiated along the dryline in northwest Texas and western Oklahoma around 1800 UTC. Initiation took place during the GOES-East full disk scan, which causes a 30-min gap in data. Below is a an image combo known as the “sandwich product” which overlays semi-transparent IR on VIS.

Figure 1: 18 May 2017 GOES-16 IR/VIS combo. Full resolution: https://satelliteliaisonblog.files.wordpress.com/2017/05/20170518_sandwich_anno2.gif

– Bill Line

“The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing. Users bear all responsibility for inspecting the data prior to use and for the manner in which the data are utilized.”

Severe storms impacted a broad region of the US on May 16, 2017 from the Texas/Mexico border north to the Great Lakes. The widespread severe weather developed in response to a a synoptic-scale trough pushing east towards the middle of the country.  GOES-16 imagery captured the severe convection from development early in the afternoon to their evolution through the evening hours.

The broad upper-level trough was analyzed in water vapor imagery pushing east across the Rocky Mountain region by early afternoon. The upper jet could be visualized in the imagery rounding the base of the trough as an area of warming/drying. Convection initiated from the Texas Panhandle north into Kansas as nose of the jet/leading edge of drying poked into the region (Figure 1).

Figure 1: 16 May 2017 GOES-16 6.19 Upper-Level Water Vapor Imagery. Full Resolution: https://satelliteliaisonblog.files.wordpress.com/2017/05/20170516_ulwv_anno.gif

Further north, a long-lived, tornado-producing supercell thunderstorm developed in northwest Wisconsin during the afternoon and traversed east across the northern part of the state through the evening. The 10.3 um IR imagery shows that this area of convection had a persistent overshooting top from shortly after initial development, with virtually no break for over 4 hours (Figure 2). Also apparent is an associated Enhanced-V signature. This storm was accompanied by a few other severe hail and wind producers.

Figure 2: 16 May 2017 GOES-16 10.3 um IR. Full resolution: https://satelliteliaisonblog.files.wordpress.com/2017/05/20170516_irwi_anno.gif

Convection developed during the evening further south in Texas along the collision of two boundaries. The dryline retreated west and collided with the cold front as it accelerated east. These boundaries are easily identified in the GOES-16 Split Window Difference (10.3 – 12.3 um). The split window difference is covered in a previous blog post. The animation below overlays coldest IR brightness temperatures on the split window difference imagery.

Figure 3: 16 May 2017 GOES-16 Split Window Difference and 10.3 um IR combination. Full Resolution: https://satelliteliaisonblog.files.wordpress.com/2017/05/20170516_irswd2_anno.gif

Finally, what was that small feature skirting across the Oklahoma sky yesterday afternoon? Not a witch, but a very resilient orphan anvil, casting it’s shadow on the clouds below.

Figure 4: 16 May 2017 GOES-16 0.64 um VIS. Full resolution: https://satelliteliaisonblog.files.wordpress.com/2017/05/20170517_witch_orphan2_anno.gif

– Bill Line

“The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing. Users bear all responsibility for inspecting the data prior to use and for the manner in which the data are utilized.”

On May 14, 2017, SPC had a Marginal Risk for Severe Weather out for a region from far SE CO/SW KS south through much of the TX Panhandle. With a broad ridge centered over  the central plains and deep trough over the west coast, southwest flow dominated over the Rocky Mountain region. A shortwave embedded in the flow was spreading upper-level cloud cover across the region. At the surface, a stalled northwest to southeast oriented boundary had draped itself across southern Colorado into the Texas Panhandle. This blog post focuses on the threat in SE Colorado, OK Panhandle, SW Kansas.

By early afternoon, dew points were only in the mid 40s to low 50s and EB shear was only around 30 knots per SPC mesoanalysis. However, intense daytime heating had risen surface temperatures to the mid-80s, creating steep low-level lapse rates, and inverted-V profiles with high based instability.  Mid-level lapse rates were also impressive given cool temperatures aloft. Given the thermodynamic environment, gusty winds and large hail were possible with and storm that managed to develop.

Morning GOES-16 imagery was useful in identifying the area where convective initiation would be most likely later in the day, well before the development of a single cumulus cloud. The Split-Window Difference (10.33 – 12.3) showed a narrow band of relatively high positive values, indicating locally elevated low-level moisture content (Fig 1a). The Split Window Difference is useful for identifying variations in low-level moisture The 10.33 um channel is the cleanest IR window band, so is seeing closest to the surface. The 12.3 um band is known as a dirty window IR band because it is slightly sensitive to moisture. Given the sensitivity, the 12.3 um channel will sense higher in the atmosphere and appear slightly cooler than the 10.33 um channel. Differencing the two channels reveals spatial variations in low-level moisture since the greatest concentration of atmospheric moisture is located in the lower part of the atmosphere. Locally greater difference values relative to the surrounding area reveals locally high concentrations of low-level moisture and moisture convergence.

Similarly, the low-level water vapor channel (7.34 um) showed relatively cool values along the same area, again indicating high low-level moisture content relative to the rest of the region (Fig 1b). Given the dry atmosphere, we can be confident that this channel was sensing moisture low in the atmosphere.

The narrow region of enhanced low-level moisture as detected by GOES-16 points to likely low-level convergence, and therefore a region of possible future storm development. Surface METAR observations showed convergence in the region, but the GOES-16 imagery provides better precision to the location of greatest moisture pooling/convergence.

Short loop:

Figure 1: 14 May 2017 GOES-16 a) split window difference (upper left), b) 7.34 um low-level water vapor channel (upper right), c) 0.64 um visible channel (lower left), d) 6.19 um upper-level water vapor channel (lower right).

Long loop:

As upper level clouds (indicators of large scale lift) moved over the region, cumulus clouds developed within this strip of elevated low-level moisture and convergence in the early afternoon. Storm initiation took place  around 2100 UTC in the OK Panhandle. This storm would move northeast into Kansas, split, and produce severe hail. The evolution of the storm and it’s split is depicted in GOES-16 visible imagery in figure 2.

Figure 2: 14 May 2017 GOES-16 0.64 um VIS. Full resolution: https://satelliteliaisonblog.files.wordpress.com/2017/05/20170514_vis_anno.gif

– Bill Line, NWS

“The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing. Users bear all responsibility for inspecting the data prior to use and for the manner in which the data are utilized.”

On May 10, 2017, widespread and slow-moving convection brought heavy rainfall and flooding to parts of southern Colorado. This convection was in association with a closed low passing to the south of the state. The upper-level system had been sitting nearly stationary to the southwest of Colorado over the previous couple of days, bringing convection and heavy precip to areas of southern Colorado. Of particular concern on the 10th was training convection in the Beulah area southwest of Pueblo. Burn scars from Fall 2016 wildfires caused these areas to be particularly prone to flooding.

GOES-16 imagery was utilized to monitor the development and evolution of convection during the period. Persistent, nearly stationary overshooting tops indicated strong updrafts with potentially heavy rainfall over the region leading to a dangerous flooding situation. In the animation below, the wide view reveals the low center spinning over Albuquerque, and zoomed in view shows persistent convection west of Pueblo.

– Bill Line, NWS

“The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing. Users bear all responsibility for inspecting the data prior to use and for the manner in which the data are utilized.”

On May 8, Colorado experienced its first widespread severe convective event of the 2017 season. Storms developed across the eastern half of the state by early afternoon in response to a closed upper low slowly shifting east toward the region. Given the setup, storms moved from south to north across the state, producing widespread large hail and heavy rainfall. Below is a GOES-16 0.64 um visible imagery animation of storm development and evolution across the state from 1802 UTC – 2357 UTC. Strong updraft signatures are obvious with many of the storms in the 0.5 km imagery, including overshooting tops and above anvil cirrus plumes.

1802 UTC – 2357 UTC 08 May 2017 GOES-16 0.64 um VIS. Full resolution: https://satelliteliaisonblog.files.wordpress.com/2017/05/20170508_vis_convection3_anno.gif

– Bill Line, NWS

“The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing. Users bear all responsibility for inspecting the data prior to use and for the manner in which the data are utilized.”