The corresponding 4-km resolution GOES-15 Infrared (10.7 µm) images (below) revealed that cloud-top IR brightness temperatures quickly cooled from -23º C at 2130 UTC to -42º C at 2200 UTC.There was a 30-minute gap in GOES-15 coverage from 2100 to 2130 UTC (due to a full disk scan), but a comparison of 1-km resolution NOAA-19 AVHRR Visible (0.63 µm) and Infrared (10.8 µm) caught the very early growth of the tornado-producing storm at 2115 UTC (below). The cloud-top IR brightness temperatures were as cold as -23º C at that time, indicating a high probability that cloud glaciation had begun. A timely overpass of the Suomi NPP satellite allowed a comparison of 375-meter resolution VIIRS Visible (0.64 µm) and Infrared (11.45 µm) images during the time that the tornado was srill on the ground (below). Once again, the strong slant of the storms due to increasing wind speeds aloft allowed the western/southwestern sides of the thunderstorm clouds to be brightly illuminated on the visible image. The coldest cloud-top IR brightness temperature was -51º C (yellow color enhancement), which was just shy of the -53º C tropopause temperature reported on the Oakland rawinsonde report at 12 UTC. A VIIRS true-color image of the storm visualized using RealEarth is shown below. The actual satellite overpass time was around 2151 UTC. GOES-15 sounder Lifted Index (LI) derived product images (below) showed the pockets of post-frontal instability over central California — LI values less than -4 C were seen (yellow color enhancement).
The Storm Prediction Center has revised its criteria for initiating GOES Rapid Scan Operations (RSO) calls. Previously, RSO was automatically activated when a Moderate Risk (MDT) appeared in the SPC Day 1 Convective Outlook. On October 1st that was changed per a September email from SPC:
Starting October 1, the SPC Lead Forecaster will contact the NCO/SDM to request GOES RSO whenever a Day 1 Convective Outlook includes an ENH Risk area. Data from the first six months of 2015 suggests SPC would request RSO on approximately 10-20 more days compared to the current MDT Risk criterion. Activating RSO on a more frequent basis using the ENH Risk criterion would improve NWS forecaster situational awareness on convectively active days and help prepare users for much higher temporal frequency GOES-R data.
An Enhanced Risk was issued on 11 November 2015 as a strong extratropical cyclone was developing over the midsection of the country. The image above shows the GOES-13 Water vapor imagery from 1145 UTC on 11 November. A strong jet extends from the southwestern United States northeastward. On the previous day (10 November, at 12 UTC) Albuquerque reported 135-knot winds at 300 hPa (and no winds at all at 200 hPa as the balloon was lost to the tracker); at 00 UTC on 11 November, winds were 162 knots just above the 250 hPa level. Strong veering, indicating warm advection, is apparent over the mid-Mississippi River Valley. Low-level warm advection is forecast to increase as the extratropical cyclone intensifies.
Update: GOES-East began RSO at 1545 UTC on 11 November 2015 — a few image animations are shown below.Of particular interest on 6.5 µm water vapor imagery, above, was the tightly-wrapped signature of the middle-tropospheric vorticity center moving northeastward along the Kansas/Nebraska border. The 10.7 µm Infrared images, above, showed the development of thunderstorms across Iowa which exhibited cloud-top IR brightness temperatures in the -50 to -60º C range (yellow to red color enhancement). Hail, damaging winds, and tornadoes were produced by these areas of deep convection (SPC storm reports). 3.9 µm Shortwave Infrared images, above, displayed numerous “hot spots” (black to yellow to red color enhancement) due to fire activity in parts of northeastern Oklahoma and southeastern Kansas. Finally, 0.63 µm Visible channel images, above, showed the hazy signature of smoke plumes from these Kansas/Oklahoma fires (along with a separate plume of blowing dust). In addition, as clouds cleared along the western edge of the storm, swaths of fresh snow cover could be seen over portions of Wyoming, Colorado, South Dakota, Nebraska, and Kansas. As much as 12.5 inches of snow was reported in northeastern Colorado, with wind gusts of 75 mph creating blizzard conditions.
A slowly-moving storm was migrating northeastward along the East Coast of the United States on 25 September 2015. The GOES-13 water vapor animation, above, shows the evolution of this system between 22 and 25 September 2015. The center of circulation in the water vapor imagery has wobbled around the state of Georgia for the past three days as a strong jet along the United States-Canada border has has maintained a series of surface High Pressure systems northeast of the storm, effectively blocking the Low Pressure’s exit from the southeast US.
Moisture available to this storm is depicted in the animation of MIMIC Total Precipitable Water, below. Moisture that moves southwestward towards the southeast US along the Gulf Stream is being joined by moisture moving northward from the tropical Atlantic Ocean.
This system has generated flooding rains over South Carolina. The GOES-13 Visible animation from 24 September 2015, below, shows persistent inflow off the Atlantic Ocean. Click here for a media report; Columbia SC reported 2.84″ of rain on 24 September, a record for the date.The thunderstorms associated with this system also caused a brief EF-2 tornado near Johns Island in Charleston County, SC (SPC Storm Reports). An animation of auto-detected Overshooting Tops, below, captures an overshooting top sequence persisting near Charleston at about the time of the tornado (0445 UTC). The toggle between Terra MODIS (0315 UTC) and Suomi NPP VIIRS (0618 UTC) 11 µm infrared data shows the general northwestward motion of the thunderstorm that produced the tornado (GOES-13 Infrared animation). The coldest cloud-top IR brightness temperature from MODIS was -75º C, with -76º C detected by VIIRS. The pressure gradient between the storm over the southeast US and the High Pressure over the Canadian Maritimes had caused long-fetch onshore winds over much of the mid-Atlantic coast. This (and a Full “Super” Moon on Sunday) presages a weekend of coastal flooding. The animation of ASCAT (from METOP-B) winds below, shows 20-25 knot winds over a large region of the Atlantic Ocean between the Gulf Stream and North America. That long fetch will help generate large waves. The surface circulation off the coast of Georgia is also apparent in the 0220 UTC image.