Legacy Atmospheric Profiles and Large Hail in Iowa

June 29th, 2017 |

GOES-16 Visible Imagery (0.64 µm) from 1902 through 2307 UTC on 29 June 2017. Woodbury County in Northwest Iowa is outlined in Magenta (Click to play animated gif)

GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing

Softball-sized hail fell in northwestern Iowa on Thursday afternoon, 29 June (Storm Prediction Center Storm Reports). The visible animation above, from 1902 to 2307 UTC, shows the rapid development of convection over far northeast Nebraska. Woodbury County in Iowa is outlined in the animation, the largest reported hail occurred in that county along the shores of the Missouri River; the location of the 4.25″ diameter hail is shown as the green box on this imageThis visible image closely corresponds to the time of the hail fall.

Since a GOES-16 Mesoscale Sector was positioned over the region, imagery was available at 1-minute intervals — a comparison of “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.3 µm) images is shown below. Plots of SPC storm reports are parallax-corrected to match the location of the storm-top features. The rapid growth of the storm that produced the 4.25″ hail was apparent in the Infrared data, which showed cloud tops cooling from around -45ºC at 2000 UTC to -65.5ºC at 2130 UTC (the time of the hail report). Cloud-top cooling rates were consistently 3ºC/5 minutes during this time. Also, in far northeastern Nebraska, a supercell thunderstorm produced an EF-1 tornado that tracked 14.4 miles along with hail up to 2.75 inches in diameter (NWS Omaha summary).

GOES-16 Visible (0.64 µm, top) and Infrared Window (10.3 µm, bottom) images, with SPC storm reports plotted in red (on Visible) and black (on Infrared) [Click to play MP4 animation]GOES-16 Visible (0.64 µm, top) and Infrared Window (10.3 µm, bottom) images, with SPC storm reports plotted in red (on Visible) and black (on Infrared) [Click to play MP4 animation]

GOES-16 Visible (0.64 µm, top) and Infrared Window (10.3 µm, bottom) images, with SPC storm reports plotted in red (on Visible) and black (on Infrared) [Click to play MP4 animation]

One of the GOES-16 Baseline Products available to forecasters includes a series of stability parameters derived from the ABI channels (and using GFS data as a first guess): Legacy Atmospheric Profiles or LAP (Online Source). These products are similar to those produced from the GOES Sounder on GOES-15. The LAP Lifted Index at 2100 UTC, below, from the GOES-16 Mesoscale Sector sited over the convection, shows a remarkable pool of instability (Lifted Indices less than -8ºC) in the region near the developing convection (which was in the wam sector of an approaching surface low). CAPE values were in excess of 2000 J/kg. More information on the Legacy Atmospheric Profiles products is available here (as part of the Satellite Foundation Course for GOES-R).

LAP Profiles can be an excellent tool for situational awareness when convection develops in clear or partly-cloudy regions.

GOES-16 Legacy Atmospheric Profile (LAP) estimate of Lifted Index, 2100 UTC on 29 June 2017 (Click to enlarge)

Why a Cirrus Channel is useful

June 28th, 2017 |

GOES-16 Visible Image (0.64 µm) at 1557 UTC on 28 June 2017 (Click to enlarge)

GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing

Consider the visible image above. Can you tell where the eastern and southern edge of the cirrus shield is over the eastern United States? When the Sun is not on the horizon, thin cirrus can be very hard to detect in visible imagery because cirrus clouds are not efficient back-scatterers of solar radiation (all clouds forward-scatter very effectively, but cirrus are optically thin). In a still image, then, with a high sun angle, cirrus can be hard to discern.  There are brightness temperature difference fields that can also be used to infer the presence of cirrus.  For example, the Split Window Difference field (10.3 µm – 12.3 µm) and the Cloud Phase Difference (8.5 µm – 11.2 µm), toggled below, will highlight regions of cloudiness.  But do they also capture very thin cirrus?

Split Window Difference field (10.3 µm – 12.3 µm) and the Cloud Phase Difference (8.5 µm – 11.2 µm) fields at 1557 UTC on 28 June 2017 (Click to enlarge)

 

The Cirrus Channel on GOES-16 (1.38 µm), below, better captures the areal extent of the cirrus.  This is because it is very sensitive to reflective features such as cirrus clouds, and because it is in a region of the electromagnetic spectrum where water vapor absorption occurs — so surface features that might complicate the interpretation are masked (Note, for example, that cumuliform clouds over Northwestern Pennsylvania are not apparent in the Cirrus Band imagery). Click here to toggle between all 4 images.

GOES-16 “Cirrus Channel” (Band 4, 1.38 µm) fields at 1557 UTC on 28 June 2017 (Click to enlarge)

One of the GOES-16 Baseline Products is a Cloud Mask — this is important because many other Baseline Products use the output from the Cloud Mask in decision trees. The toggle below shows the Cirrus Band (1.38 µm), the Red Visible (0.64 µm) and the Cloud Mask for 1557 UTC on 28 June 2017.

 

GOES-16 “Cirrus Band” (Band 4, 1.38 µm), “Red Visible” (0.64 µm) and Cloud Mask Baseline Product (White=Cloud, Black= Clear) (Click to enlarge)

Severe thunderstorms producing strong winds and large hail in Wyoming, South Dakota, Nebraska and Kansas

June 28th, 2017 |

GOES-16 Infrared Window (10.3 µm) images, with SPC storm reports of wind and hail [click to play MP4 animation]

GOES-16 Infrared Window (10.3 µm) images, with SPC storm reports of wind and hail [click to play MP4 animation]

** GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing **

Clusters of severe thunderstorms developed over eastern Wyoming and the Nebraska panhandle during the afternoon on 27 June 2017, and increased in areal coverage and intensity as they moved eastward into the overnight hours. 1-minute interval Mesoscale Sector GOES-16 Infrared Window (10.3 µm) images with plots of SPC storm reports (above) showed a number of locations with wind gusts in excess of 60 mph — including 79 mph in Rapid City SD at 2341 UTC and 100 mph in Custer NE at 0200 UTC. Many of these high wind reports were in the general vicinity of thunderstorm overshooting tops, which exhibited cloud-top infrared brightness temperatures in  the -70 to -80º C range (black to white enhancement).

Hurricane Dora

June 26th, 2017 |

GOES-16 Visible (0.64 µm) and Infrared Window (10.3 µm) images [click to play MP4 animation]

GOES-16 Visible (0.64 µm) and Infrared Window (10.3 µm) images [click to play MP4 animation]

** GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing **

Dora became the first hurricane of the Eastern Pacific 2017 season on 26 June, and was also the first hurricane to be sampled by GOES-16. On Visible (0.64 µm) and Infrared Window (10.3 µm) images (above), Dora displayed an improving appearance as the day progressed — mesovortices were seen within the eye on Visible imagery, while the overall eye/eyewall structure improved as the eye diameter increased on Infrared Window imagery.

Early in the morning, a comparison between DMSP-17 SSMIS Microwave (85 GHz) and GOES-15 Infrared Window (10.7 µm) images from the CIMSS Tropical Cyclones site (below) showed  that a well-defined eye was more apparent on microwave imagery. Dora was moving over fairly warm Sea Surface Temperatures, and was also in an environment characterized by low values of deep-layer wind shear.

DMSP-17 SSMIS Microwave (85 GHz) and GOES-15 Infrared Window (10.7 µm) images [click to enlarge]

DMSP-17 SSMIS Microwave (85 GHz) and GOES-15 Infrared Window (10.7 µm) images [click to enlarge]