Heavy rain event in southeastern South Dakota

August 28th, 2015

GOES-13 Infrared (10.7 um) images [click to play animation]

GOES-13 Infrared (10.7 um) images [click to play animation]

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.

POES AVHRR Visible (0.86 m) and Infrared (12.0 um) images [click to enlarge]

POES AVHRR Visible (0.86 m) and Infrared (12.0 um) images [click to enlarge]

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).

GOES-13 Infrared (10.7 um) images with METAR surface reports [click to play animation]

GOES-13 Infrared (10.7 um) images with METAR surface reports [click to play animation]

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).

Blended Total Precipitable Water Percent of Normal [click to play animation]

Blended Total Precipitable Water Percent of Normal [click to play animation]


 

 

 

 

 

 


 

 

 

 

 

 

 

Mesoscale Convective System in South Dakota

August 27th, 2015

Suomi NPP VIIRS Infrared (11.45 µm) and Day/Night Band (0.7 µm) images [click to enlarge]

Suomi NPP VIIRS Infrared (11.45 µm) and Day/Night Band (0.7 µm) images [click to enlarge]

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.

GOES-13 water vapor (6.5 µm) images [click to play animation]

GOES-13 water vapor (6.5 µm) images [click to play animation]

Tropical Storm Erika approaches the eastern Caribbean

August 26th, 2015

GOES-13 10.7 µm IR images [click to play animated GIF]

GOES-13 10.7 µm IR images [click to play animated GIF]

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.

GOES-13 Visible Imagery (0.63 µm) [click to play animated GIF]

GOES-13 Visible Imagery (0.63 µm) [click to play animated GIF]

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).

ASCAT Winds and GOES-13 Water Vapor IR (6.5 µm) [click to enlarge]

ASCAT Winds and GOES-13 Water Vapor IR (6.5 µm), ~0100 UTC 26 August 2015 [click to enlarge]

ASCAT Winds and GOES-13 Water Vapor IR (6.5 µm) [click to enlarge]

ASCAT Winds and GOES-13 Water Vapor IR (6.5 µm), ~1400 UTC 26 August 2015 [click to enlarge]

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

Tropical Storm Danny in the eastern Atlantic Ocean

August 19th, 2015
GOES-13 10.7 µm IR images [click to play animated GIF]

GOES-13 10.7 µm IR images [click to play animated GIF]

The first tropical storm of the season in the eastern Atlantic (Ana, Bill and Claudette all formed over the western Atlantic) has formed from a cluster of thunderstorms that emerged from Africa. The multi-day animation, above, from GOES-13, shows the steady progress of the disorganized system across the eastern Atlantic basin. Visible Imagery from GOES-13 and Meteosat-10, below, from the morning of 19 August, show the system near 40 W. The cyclonic curvature to the clouds is apparent; identification of the center in infrared imagery, below, is more difficult. Convection to the east of Danny has colder cloud top temperatures.

Meteosat-10 0.6 µm Visible Imagery (Top, 1200 UTC) and GOES-13 0.63 µm Visible imagery (Bottom, 1145 UTC) on 19 August 2015 [click to enlarge]

Meteosat-10 0.6 µm Visible Imagery (Top, 1200 UTC) and GOES-13 0.63 µm Visible imagery (Bottom, 1145 UTC) on 19 August 2015 [click to enlarge]

Meteosat-10 10.8 µm Infrared Imagery (Top, 1200 UTC) and GOES-13 10.7 µm Infrared imagery (Bottom, 1145 UTC) on 19 August 2015 [click to enlarge]

Meteosat-10 10.8 µm Visible Imagery (Top, 1200 UTC) and GOES-13 10.7 µm Visible imagery (Bottom, 1145 UTC) on 19 August 2015 [click to enlarge]

ASCAT Winds with GOES-13 Water Vapor Imagery (6.5 µm), 0100 UTC 19 August 2015 [click to enlarge]

ASCAT Winds with GOES-13 Water Vapor Imagery (6.5 µm), 0100 UTC 19 August 2015 [click to enlarge]

ASCAT winds from 0100 UTC on 19 August 2015 (above) show a compact circulation center with winds of 40 knots just north of 10 N and east of 40 W.

Saharan Air Layer Tracking Product [click to play animated GIF]

Saharan Air Layer Tracking Product [click to play animated GIF]

A persistent impediment to Tropical Cyclone initiation in the eastern Atlantic this year has been widespread Saharan Air Layer dust. The one-day animation, above (taken from this website), shows the SAL persists over the Atlantic; Danny has formed just to the south. Wind shear over Danny at present is weak (see below [source]), and slow strenghtening is expected as Danny approaches the Caribbean.

Mid-level Wind Shear [click to enlarge]

Mid-level Wind Shear [click to enlarge]

The Discussion from the National Hurricane Center at 0900 UTC on 19 August included this phrase: “The center is difficult to locate on infrared images,…” The Day Night Band from VIIRS on Suomi NPP can sometimes be used to locate low-level circulation centers of tropical systems. This relies on the presence of moonlight, however, and when Suomi NPP overflew Danny just before 0500 UTC on 19 August, the moon was below the horizon. Thus, the Day Night Band, below (Courtesy of William Straka) gave very little information.

VIIRS 10.35 µm Infrared Imagery and 0.70 µm Visible Imagery, 0441 UTC 19 August 2015 [click to enlarge]

VIIRS 10.35 µm Infrared Imagery and 0.70 µm Visible Imagery, 0441 UTC 19 August 2015 [click to enlarge]

More information on Danny is available at the CIMSS Tropical Weather Website. Consult the National Hurricane Center for the latest updates and official forecasts.