GOES-15 continues to operate from 128W, providing imagery to the east Pacific and western US. GOES-15 imagery continues to be available to NWS forecasters in AWIPS. As a reminder of how far we’ve come from the previous generation of geostationary satellites, below are comparisons of GOES-16 (75W) 1-min imagery and GOES-15 routine imagery for thunderstorm development over west Texas on 27 April 2019. These thunderstorms developed at 100W, roughly in the middle (and north) of the two satellite subpoints. The animations are 1.5 hours long, running from 2030 UTC to 2200 UTC. Details such as cumulus cloud evolution, convective initiation, and storm top features (OTs, AACPs, texture) are all significantly easier to diagnose (and quicker) in the GOES-16 imagery. Be grateful for the GOES-R series!
These thunderstorms went on to produce severe hail and wind.
A late night tornado passed through the town of San Augustine, TX during the evening of 24 April 2019. GOES-16 GLM Flash Extent Density data showed a significant increase in lightning activity (lightning jump), during the 10-20 minute period prior to the tornado LSR at 0420 UTC on the 25th. Below are examples of the 1-min FED product (Fig 1), as well as the 5-min accumulation FED product (updating every 1-min as well; Fig 2), which provides a smoother view of the lightning trends. The rapid increase in lightning is distinguishable in both products with this case. ABI IR (gray-scale), tornado (red) and severe thunderstorm (yellow) warnings, along with the Tornado LSR (yellow symbol), are also included in both animations. The graphs below show the rapid increase in FED and peak prior to 0420 UTC (Fig 3).
Severe thunderstorms developed along a cold front across southwest and central Texas during the afternoon/evening of 23 April 2019. GOES-16 1-min imagery was available over the region aid forecasters in monitoring storm development and evolution.
Analysis of GOES-16 water vapor imagery reveals a mid-level low progressing east across northern Mexico, spreading increased southwesterly flow across Texas, increasing vertical wind shear (Fig 1).
A 4-hour long, 1-min animation of the day cloud phase distinction RGB leading up to convective initiation shows its utility in such situations. Recall, the blue to cyan (or similar) colors represent water clouds, while the transition to truer green indicates ice increasing in the cloud top (glaciation, loss of blue component), and the following transition to yellow is caused by the cooling cloud top (increasing red component). The southeast-moving boundary which eventually serves as the focus for convective development is obvious in the imagery as a line of increasingly agitated cu. Since the 1/2 km, 0.64 um visible channel is one component to this RGB, we are still viewing imagery at the highest resolution possible from GOES. Eventually, orphan anvils develop and blow off, and are obvious (more so than in VIS alone) in their rapid transition from ~cyan to green/yellow. These are often indicators that the atmosphere has destabilized, but the CAP is still present but on the verge of breaking. The failed initiation attempts (orphan anvils) become more abundant through the loop leading up to successful initiation by the end of the period.
One of the severe thunderstorms produced hail of at least 2.5″ in diameter southeast of Sweetwater, TX. The intensity of the storm updraft was captured in the 1-min visible imagery, with abundant storm top texture, overshooting tops, and above-anvil cirrus plumes, all apparent (Fig ). In this particular period of time, two plumes extend from the main (southwest) storm cluster, indicating multiple intense updraft cores.
IR imagery confirms a broad overshooting top, with a large cluster of pixels having a brightness temperature of <-67C and as cold as -70C, surrounded by anvil temperatures between -57C and -60C. Nearby soundings indicate the tropopause was indeed around -60C. A downstream warm region with temperatures around -54C completes a thermal couplet. The above anvil cirrus plume is evidenced by relatively warm and nearly uniform temperatures extending well downstream of the overshooting top. An enhanced-V/U (aka cold ring) extends from the overshooting top and around the plume. The overshooting top, thermal couplet, above anvil cirrus plume, and enhanced-V/U storm top signatures have all been noted in the literature as being indicators of particularly strong updrafts/thunderstorms, with the plume often associated with severe storms (Bedka, 2018).
The Sandwich RGB, now available in AWIPS, combines the VIS and IR into one image (Fig 3) for cold brightness temperatures (cold cloud tops), while maintaining VIS for warmer temperatures (surface and low clouds).
The March 2019 RPM included the addition of a VIS/IR Sandwich RGB to AWIPS-II. To create the VIS/IR sandwich in the past, forecasters were required to overlay a semi-transparent IR over-top VIS. The RGB automates the creation of this image combination in AWIPS. The benefit of the VIS/IR Sandwich RGB is that it combines the high spatial detail apparent in VIS, with the temperature information of the IR.
In a convective scenario, for example, a forecaster can utilize the RGB to monitor a cu field and boundaries as they normally would, since only the visible imagery will be present up to the point of convective initiation. Once the clouds have cooled enough during convective initiation, the IR component will be combined with the visible, allowing a forecaster to continue to visualize the detail in the cloud top via the VIS component, but also now the temperature information/trends from the IR in the developing storm. Post initiation, this combination improves identification of cloud top features such as overshooting tops, above anvil cirrus plumes, and gravity waves. In the RGB, forecasters are unable to sample the IR temperature, so trends must be gleaned from the colors. However, forecasters can underlay the IR channel so that brightness temperatures can be sampled.
Figure 1 includes an example of rapid convective initiation to mature convection over the Texas Panhandle on 17 April 2019. In a little over one hour, the storm initiates and develops an overshooting top and above anvil cirrus plume. The rapid cooling is apparent in the imagery while the high detail of the VIS is maintained. Figure 2 shows the same storm a little later. One-minute imagery was available over the region to help forecasters monitor the evolution of convection. These storms produced large hail and tornadoes.
An example from 18 April 2019 of a large QLCS advancing east across Louisiana and the adjacent Gulf shows the ability of the product to highlight storm top features such as overshooting tops, above anvil cirrus plumes, and storm top gravity waves (Fig 3).