A line of training thunderstorms produced heavy rainfall in parts of southeastern South Dakota on the evening of 27 August 2015, with the highest rainfall amount being 7.52 inches just southwest of Sioux Falls (Public Information Statement). 4-km resolution GOES-13 (GOES-East) 10.7 µm Infrared images (above; click to play animation) showed the development and motion of the storms that moved through the Sioux Falls (KFSD) area. The coldest cloud-top IR brightness temperature was -68º C (darker black color enhancement) just to the northwest of Sioux Falls on the 0115 UTC (8:15 PM local time) image. However, because of parallax resulting from the large satellite viewing angle, the actual location of that tall, cold cloud top would have been just to the southeast of Sioux Falls (the yellow + symbol on this image).

A comparison of 1-km resolution POES AVHRR Visible (0.86 µm) and Infrared (12.0 µm) images at 2330 UTC or 6:30 PM local time (below) showed the developing convective storms in greater detail. The coldest cloud-top IR brightness temperature was -73º C with the westernmost cluster of thunderstorms.

A closer view of the GOES-13 Infrared images with METAR surface reports is shown below. Note that Sioux Falls had a peak wind gust of 32 knots (37 mph).

The Blended Total Precipitable Water (TPW) Percent of Normal product (below; click to play animation) showed TPW values as high as 199% of normal just to the north-northeast of Sioux Falls at 0442 UTC (11:42 PM local time).

Check out the rainfall on the west side of Sioux Falls. Almost an inch of rain fell in 10 minutes! pic.twitter.com/OYavFY67pp

— NWS Sioux Falls (@NWSSiouxFalls) August 28, 2015

How unprecedented was the rain? At a SDSU automated rain gauge at Sertoma Park, it measured 2.73″ of rain within 25 minutes! Wow! — NWS Sioux Falls (@NWSSiouxFalls) August 28, 2015

 

 

 

 

 

 

At the same gauge at Sertoma Park, it recorded 0.71″ of rain within 5 minutes! That’s a lot of water!

— NWS Sioux Falls (@NWSSiouxFalls) August 28, 2015

Updated precip total map – thanks to NWS FSD for additional data. #sdwx #siouxfalls pic.twitter.com/fc9qHqZZ2y — Dennis Todey (@sdclimatologist) August 28, 2015

 

 

 

 

Wondering how much rain you received last night? Here is a map of rainfall reports we received. pic.twitter.com/rqUF6AVYdf

— NWS Sioux Falls (@NWSSiouxFalls) August 29, 2015

 

 

 

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August 28 2015 is the 10-year anniversary of Hurricane Katrina achieving Category 5 status (on the Saffir-Simpson Scale) in the central Gulf of Mexico. The mp4 animation above (available here as a 490 megabyte animated gif, and on YouTube) shows the evolution of Katrina from a thunderstorm cluster in the Bahamas to a weak hurricane off the west coast of Florida to a Category 5 Hurricane in the central Gulf before weakening somewhat at landfall along the central Gulf coast. (The archive of National Hurricane Center advisories is here. The post-storm write-up is here.)

GOES-12 was in service as GOES-East during Katrina’s life, and as a GOES I-M satellite it lacked batteries to allow imaging through eclipse, which occurs as the satellite passes through the Earth’s shadow (solar panels in shadow do not provide power) in the weeks surrounding the Equinoxes. The toggle above from 28 August 2005 shows the last pre-eclipse image (0402 UTC) and the first post-eclipse image (0615 UTC); considerable organization of the storm has occurred in those two hours! GOES satellites from GOES-13 on have sufficient battery capacity to provide imagery through eclipse periods (for example, see this GOES-13 vs GOES-12 comparison during the landfall of Hurricane Ike along the Texas coast in 2008).

Katrina was featured in the CIMSS GOES Gallery back in 2005 (Link).

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A large Mesoscale Convective System (MCS) developed over western South Dakota late in the day on 26 August 2015, moving eastward across the state and producing wind gusts as high as 79 mph (SPC storm reports). A nighttime comparison of Suomi NPP VIIRS Infrared (11.45 µm) and Day/Night Band (0.7 µm) images at 0842 UTC (above) showed the large cloud shield with cloud-top IR brightness temperatures as cold as -74º C at the central cluster of overshooting tops; bright white pixels on the Day/Night Band image were portions of the cloud illuminated by intense lightning activity. Various types of waves were also seen in the VIIRS imagery: (1) concentric gravity waves propagating outward from the central cluster of overshooting tops, (2) transverse banding emanating radially outward in portions of the northern semicircle of the MCS, and (3) a large arc of waves moving westward away from the back edge of the storm.

Regarding the large arc of waves along the back edge of the MCS, GOES-13 (GOES-East) water vapor (6.5 µm) images (below; click image to play animation) revealed a signal of strong subsidence (warming/drying, darker blue color enhancement) as the westward-expanding cloud mass was acting as an obstacle to the prevailing westerly winds coming from Wyoming and Montana.

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GOES-13 Infrared Imagery (above) for the 24 hours ending 1415 UTC on 26 August 2015 show Tropical Storm Erika approaching the Leeward Islands of the eastern Caribbean. A general increase in convection in the 24 hours shown is obvious. Visible imagery (below) from the morning of 26 August shows some overshooting tops within the central dense overcast (CDO) covering the low-level circulation. A plot of the number of overshooting tops in Erika is here (taken from this webpage). Outward-propagating gravity waves can also be seen at the top of the CDO.

Surface winds as observed by the Metop ASCAT Scatterometer early on 26 August (0056 UTC), below, show a modest circulation with winds that are mostly below tropical storm force (Added: The 1411 UTC image, bottom, shows some tropical-storm force wind flags). Dry Saharan Air Layer air should not limit intensification of Erika, but wind shear just north and west of the storm is strong (SAL and Wind Shear imagery taken from the CIMSS Tropical Cyclones site).

For the most recent forecasts on Erika’s future, see the National Hurricane Center website.

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