The UW-CIMSS Cloud Top Cooling (CTC) product was once again utilized at the SPC mesoscale desk on 9/18/14 during a marginal severe weather event over parts of Nevada and Idaho. 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.
Figure 1: September 18, 2014 1715-2030 UTC GOES-West visible satellite imagery, Cloud Top Cooling product, NWS severe warnings.
With relatively weak instability in place, there was some uncertainty as to whether significant convection would develop in the region despite favorable shear and forcing associated with an approaching shortwave. The CTC product first indicated rapid initial convective growth in excess of -16 K/15 min at 1745 UTC in northeast Nevada (Fig. 1). By 1845, notable cooling rates were being measured along an area of confluence north into southeast Idaho. The first warning was issued in Nevada at 1911 UTC, with storms being warned on in Idaho shortly thereafter. The CTC product provided increased confidence that the environment would indeed support strong updrafts, and potentially severe weather. The forecaster referenced the CTC product in a related SPC Mesoscale Discussion: “THE GOES-R CLOUD TOP COOLING PRODUCT VERIFIES THIS TREND PER SEVERAL STORMS FROM NERN NV TO ERN ID HAVING STRONGER/SUSTAINED UPDRAFTS (Fig. 2).”
The storms that ravaged the southern United States this past week not only produced deadly severe weather, but also incredible flooding. Figure 1 shows parts of the Florida Panhandle and southern Alabama received in excess of 10 inches of rain on Tuesday, April 29 alone!
Figure 1: April 29 12Z to April 30 12Z precipitation analysis. More negative values indicate stronger OT’s
A previous blog post introduced the Overshooting Top Detection product and explained its utility in severe weather situations. Overshooting tops are also indicators of where heavy rainfall may be occurring. Furthermore, the constant presence of overshooting tops over a particular location over an extended period of time may indicate a prolonged period of heavy rainfall, which could lead to flooding.
The animation in Figure 2 shows GOES-East IR imagery with overshooting top detection’s overlaid from the afternoon of the April 29 into the early morning hours of the April 30. During much of this period, GOES-East was in Rapid Scan Mode, meaning images were often available every 5-10 minutes (instead of 15). Notice the persistence of overshooting tops centered over the Mobile area throughout the period, where copious amounts of rainfall were recorded. By about 09Z, a downward trend in overshooting top detection’s had begun as the storm system shifted eastward and weakened. The Overshooting Top Detection product provides a day/night capability for forecasters to easily identify where within a convective system the strongest updrafts are occurring, and where severe weather and/or heavy rainfall may be occurring given other meteorological factors.
Figure 2: April 29 22Z – April 30 10Z GOES-East IR with Overshooting Top Magnitude overlaid.
Figure 3 shows this same system during the early morning hours of April 30 at much higher resolution. This is a 375 m IR image taken with the Suomi NPP VIIRS instrument. Notice the visibility of features that aren’t easily seen in current GOES IR imagery such as gravity waves and overshooting tops.