The UW-CIMSS Cloud Top Cooling (CTC) product was utilized at the SPC mesoscale desk on 9/17/14 during a marginal severe weather event over South Carolina. The CTC product not only highlights where initial rapid convective development is occurring, but it also quantifies the vigor of said growth. See past blog posts (eg. http://satelliteliaisonblog.com/2014/04/02/cloud-top-cooling-product-with-kansas-severe-weather/) for background information on the CTC product and its use in SPC operations.
The CTC product first signaled cooling of around -10 K/15 min in the IR at 1830 UTC in South Carolina near the Georgia border (Fig. 1), indicating convection was at least trying to develop. Over the next few scans, the product signaled multiple areas of significant growth with increasing intensity over much of the southern half of South Carolina. At 1915 UTC, cooling of over -40 K/15 min was measured with a storm that would be warned on 19 minutes later. Several of the storms would go on to produce severe wind and hail, with the first severe report coming in at 2035 UTC.
Figure 1: September 17, 2014 1815-2030 UTC GOES-East visible satellite imagery, Cloud Top Cooling product, NWS severe warnings, SPC storm reports.
The SPC forecaster on the mesoscale desk was monitoring the CTC product over the region, and referenced it in a related Mesoscale Discussion: “THE MODERATE INSTABILITY AND -10 C 500 MB TEMPERATURES ARE PROVING SUFFICIENT FOR RAPID CLOUD TOP COOLING WITH MOST OF THE STORM CELLS IN THIS REGION PER GOES-R CLOUD TOP COOLING PRODUCT” (Fig. 2). The forecaster mentioned that seeing many areas of significant cooling gave him confidence that the environment would be conducive to the development of severe weather. This is a good example of a forecaster using the CTC product output to enhance his understanding of the environment.
The Cloud Top Cooling (CTC) product was utilized by an SPC forecaster in monitoring for severe weather development across northern Utah into western Wyoming on Wednesday, May 28 2014. This region is characterized by especially poor radar coverage due to mountain beam-beam blocking and coarsely spaced radars (Fig. 1). For this reason, satellite-based products are especially useful to SPC forecasters in the western third of the the United States. In this particular case, the CTC product was helpful in highlighting when rapid convective development was beginning, as well as where the most rapid development was occurring (Fig. 2). Severe winds were eventually reported with these storms. The CTC product was mentioned in SPC Mesoscale Convective Discussion (MCD) 748 (Fig. 3): “THE GOES-R CLOUD TOP COOLING PRODUCT INDICATED COOLING TOPS OVER SWRN TO WEST-CENTRAL WY AND ONGOING CLOUD TOP COOLING IN NERN UT.”
Fig. 1: United States radar coverage map.
Fig. 2: 140528/1715 – 2245 UTC GOES-West visible imagery, Cloud Top Cooling (color fill), storm reports.
By late afternoon on April 2, a fairly broad risk area for severe storms existed across Oklahoma, eastern Kansas and the Mid/Lower Mississippi Valley, with the main concern of large hail existing in western and northern Oklahoma into southern Kansas (Fig 1). Strong surface heating and increasing low level moisture throughout the day resulted in increasing instability in the region, and with veering wind profiles, the environment supported supercell thunderstorm development. Forcing mechanisms were, however, fairly weak. While a dryline existed in western Oklahoma, a west-east oriented frontal boundary slowly shifted northward through northern Oklahoma.
Figure 1: April 02, 2014 SPC 1630 UTC Day 1 Probabilistic Large Hail outlook.
Between 1900 and 2200 UTC, it appeared more and more likely that convection would initiate along the frontal boundary as an associated cu field showed signs of strengthening per visible imagery. A main forecast concern at that point was when and where significant convection would initiate within that cu field.
One proxy GOES-R product currently being demonstrated to forecasters in the Storm Prediction Center (SPC) is the University of Wisconsin (UW) Cloud Top Cooling (CTC) product. This product measures changes in brightness temperature in GOES infrared imagery that have occurred since the previous GOES scan, displayed as cooling rates. The CTC product may be useful to SPC forecasters by indicating areas of initial/significant convective growth as it’s occurring and by quantifying the vigor of developing convection. It has been shown that CTC rates can be a useful prognostic tool in predicting future radar echo intensification and in increasing lead times for maximum values in several NEXRAD fields. SPC forecasters generally have had a positive attitude toward this product thus far, most notably liking: its non-intrusive display (an overlay on imagery), that it is easy to understand (measures brightness temperature trends in the infrared, displays cooling rates), and that it makes obvious (and quantifies) where in the imagery significant convective growth is occurring, which may otherwise be difficult to see, especially in the absence of visible imagery at night.
On April 2, the CTC product was quiet through 2200 UTC as SPC forecasters watched for signs of initiation. At 2215 UTC, the first CTC rate was indicated along the boundary in far south-central Kansas (Fig 2). Though this convection did not mature further, the rapid cooling was evidence that the cap was likely close to breaking and upscale convective growth might be imminent. By the next GOES scan (2230 UTC) this appeared to be the case, as significant cooling (<-20 C /15 min) was measured for a developing storm further east, which continued to grow rapidly through 2245 UTC when a very strong rate of <-40 C /15 min was measured. This storm had its first severe thunderstorm warning issued at 2249 UTC, and went on to produce severe hail, some of which was significant (>=2” diameter; Fig 3). Over the next hour along the boundary in southern Kansas, the CTC product continued to highlight areas where significant cooling was occurring in the infrared, indicating the initial growth of thunderstorms that would go one to produce severe weather throughout eastern Kansas.
Figure 2: April 02, 2014 2002-0015 UTC GOES-East visible imagery, Cloud Top Cooling rates. Color fill is cooling per 15 minutes.
Figure 3: April 02, 2014 2115-0200 UTC GOES-East infrared imagery, Cloud Top Cooling rates, NWS watches and warnings, 2100-0300 UTC severe weather reports (a=hail, w=wind, t=tornado). Color fill is cooling per 15 minutes.
A SPC forecaster viewing the CTC product during this event mentioned that it was helpful to see when and where significant cooling rates were NOT being measured, evidence that rapid convective growth was not occurring in such areas. It was noted that the product was helpful in highlighting when and where storms finally began to grow rapidly along the boundary, indicating that the cap had been broken, and increasing situational awareness as to which developing storms may become the strongest.
Forecasters understand that the CTC product is a proxy GOES-R product, and that it will benefit from the higher temporal and spatial resolution that will be available with the Advanced Baseline Imager aboard the next generation of GOES satellites.