Re-suspended volcanic ash from the Novarupta volcano in Alaska

September 29th, 2014
GOES-15 0.63 µm visible channel images (click to play animation)

GOES-15 0.63 µm visible channel images (click to play animation)

McIDAS images of GOES-15 0.63 µm visible channel data (above; click image to play animation) showed the hazy signature of a plume of re-suspended volcanic ash originating from the region of the Novarupta volcano in Alaska, moving southeastward over the Shelikof Strait toward Kodiak Island on 29 September 2014. The 1912 eruption of Novarupta left a very deep deposit of volcanic ash, which often gets lofted by strong winds in the early Autumn months before snowfall covers the ash (another example occurred on 22 September 2013). Surface winds gusted as high as 30 knots at regional reporting stations, with numerical models estimating terrain-enhanced winds as high as 40-50 knots over the Novarupta ash field.

An AWIPS II image of POES AVHRR 0.86 µm visible channel data (below) showed the ash plume at 22:46 UTC; a pilot report at 22:45 UTC indicated that the top of the ash plume was between 4000 and 6000 feet above ground level.

POES AVHRR 0.86 µm visible channel image, with METAR surface reports and Pilot reports (PIREPs)

POES AVHRR 0.86 µm visible channel image, with METAR surface reports and Pilot reports (PIREPs)

A sequence of 3 Suomi NPP VIIRS true-color Red/Green/Blue (RGB) images from the SSEC RealEarth web map server (below) indicated that the re-suspended ash plume had been increasing in areal extent during that period.

Suomi NPP VIIRS true-color images from 27, 28, and 29 September

Suomi NPP VIIRS true-color images from 27, 28, and 29 September

A sequence of 4-panel products from the NOAA/CIMSS Volcanic Cloud Monitoring site (below) shows False-color images, Ash/dust cloud height, Ash/dust particle effective radius, and Ash/dust loading (derived from either Terra/Aqua MODIS or Suomi NPP VIIRS data).

4-panel MODIS/VIIRS products: False color image; Ash/dust cloud height; Ash/dust particle effective radius; Ash/dust loading

4-panel MODIS/VIIRS products: False color image; Ash/dust cloud height; Ash/dust particle effective radius; Ash/dust loading

Hat tip to Mark Ruminski (NOAA/NESDIS) for alerting us to this event.

Large “hole punch cloud” over Wisconsin

July 18th, 2014

GOES-13 0.63 µm visible (upper left), 3.9 µm shortwave IR (upper right), 10.7 µm IR (lower left), and 6.5 µm water vapor (lower right) images [click to play animation]

GOES-13 0.63 µm visible (upper left), 3.9 µm shortwave IR (upper right), 10.7 µm IR (lower left), and 6.5 µm water vapor (lower right) images [click to play animation]

A large (approximately 50-mile diameter) “hole punch cloud” or “fall steak cloud” was seen over northwestern Wisconsin during the morning hours of 18 July 2014. An AWIPS 4-panel comparison of GOES-13 0.63 µm visible channel, 3.9 µm shortwave IR channel, 10.7 µm IR window channel, and 6.5 µm water vapor channel images (above; click image to play animation) showed that 10.7 µm IR cloud top brightness temperatures were not particularly cold with this feature (generally in the 0º C to -4º C range), and while 3.9 µm shortwave IR brightness temperatures warmed within the broad cloud deck surrounding the hole punch cloud after sunrise (due to reflection of solar radiation off of water cloud droplets), the center of the feature continued to exhibit colder (lighter gray enhancment) IR brightness temperatures which suggests cloud glaciation.

POES AVHRR Cloud Type, Cloud Top Height, and Cloud Top Temperature products at 09:32 UTC

POES AVHRR Cloud Type, Cloud Top Height, and Cloud Top Temperature products at 09:32 UTC

A comparison of CLAVR-x POES AVHRR Cloud Type, Cloud Top Height (CTH), and Cloud Top Temperature (CTT) products at 09:32 UTC or 4:32 am Central time (above) showed patches of water droplet clouds with CTH values in the 3-4 km range and CTT values in the 0º C to -4º C range.

A similar comparison at 12:05 UTC or 7:05 am Central time (below) revealed two areas of “cirrus” cloud type (orange color enhancement) exhibiting CTT values in the -35º to -40º C range (darker blue color enhancement) along the northern and southern periphery of the forming hole punch cloud.

POES AVHRR Cloud Type, Cloud Top Height, and Cloud Top Temperature prodcts at 12:05 UTC

POES AVHRR Cloud Type, Cloud Top Height, and Cloud Top Temperature prodcts at 12:05 UTC

These ranges of AVHRR Cloud Top Temperature and Cloud Top Height values agreed well with the regional rawinsonde data from Davenport IA (KDVN), Minneapolis MN (KMPX) and Green Bay WI (KGRB) shown below.

Davenport IA, Minneapolis MN, and Green Bay WI rawinsonde data at 12 UTC

Davenport IA, Minneapolis MN, and Green Bay WI rawinsonde data at 12 UTC

Terra MODIS visible and Cloud Phase products at 17:07 UTC or 12:07 pm Central time (below) indicated that a large area of glaciated ice cloud (salmon color enhancement) existed in the center portion of the hole punch cloud feature.

Terra MODIS 0.65 µm visible image and Cloud Phase products

Terra MODIS 0.65 µm visible image and Cloud Phase products

The cause of this large hole punch or fall streak cloud feature — and the other similar but smaller features seen across the region — was likely aircraft that had either ascended or descended through the cloud layer; particles in the aircraft exhaust acted as ice condensation nuclei, causing the process of cloud glaciation to begin.

GOES-15 0.62 µm visible images [click to play animation]

GOES-15 0.62 µm visible images [click to play animation]

GOES-15 imagery (above) shows the Hole Punch cloud from an oblique angle, and highlights how the region was overrun by smoke from wildfires in Canada. Smoke is most easily seen in visible satellite imagery when the sun is low in the sky, allowing for forward scatter. The smoke becomes less apparent in the imagery as the Sun rises. A similar animation for GOES-13 is below. Smoke is not quite so evident in this image because there is less forward scatter to GOES-13 over 75º W. Animations from both satellites show a hole punch cloud in Iowa as well.

GOES-15 0.62 µm visible images [click to play animation]

GOES-15 0.62 µm visible images [click to play animation]

GOES-14 SRSOR: severe thunderstorms over the central Plains

May 11th, 2014
GOES-14 0.63 µm visible channel images (click to play animation)

GOES-14 0.63 µm visible channel images (click to play animation)

The GOES-14 satellite continued to be in Super Rapid Scan Operations for GOES-R (SRSOR) mode on 11 May 2014, capturing the development of thunderstorms along a dryline that stretched from the Texas Panhandle into far southwestern Kansas. As a southward-moving cold front intersected this dryline, McIDAS images of 1-minute interval GOES-14 0.63 µm visible channel data (above; click image to play animation; also available as an MP4 movie file) showed that the narrow line of storms later developed into large discrete supercell thunderstorms over Kansas, with widespread reports of tornadoes, large hail, and damaging winds (SPC storm reports).

Farther to the northeast, other large supercell thunderstorms could be seen growing over eastern Nebraska along a warm frontal boundary — these storms exhibited numerous signatures of vigorous overshooting tops. Near the end of the animation, winds gusted to 82 mph at Omaha, Nebraska at 00:51 UTC.

GOES-13 sounder Convective Available Potential Energy (CAPE) derived product imagery (click to play animation)

GOES-13 sounder Convective Available Potential Energy (CAPE) derived product imagery (click to play animation)

AWIPS images of GOES-13 sounder Convective Available Potential Energy or CAPE (above; click image to play animation) and Total Precipitable Water or TPW (below; click image to play animation) with surface frontal analyses revealed the sharp gradient of both instability and moisture across the dryline — just to the east of the dryline, CAPE values exceeded 4000 J per kg (darker purple color enhancement), while TPW values were generally in the 30-40 mm or 1.2-1.6 inch range (shades of yellow). In addition, GOES-13 sounder Lifted Index values were in the -8 to -10º C range across parts of Kansas into southeastern Nebraska prior to convective initiation.

GOES-13 sounder Total Precipitable Water (TPW) derived product imagery (click to play animation)

GOES-13 sounder Total Precipitable Water (TPW) derived product imagery (click to play animation)

A 19:36 UTC Suomi NPP VIIRS 11.45 µm IR channel image (below) showed the early stages of convective development along the dryline in far southwestern Kansas; the coldest cloud-top IR brightness temperature value at that time was -80º C, just west of Dodge City, Kansas KDDC (corresponding GOES-14 visible image).

Suomi NPP VIIRS 11.45 µm IR channel image, with METAR surface reports

Suomi NPP VIIRS 11.45 µm IR channel image, with METAR surface reports

A comparison of POES AVHRRR 12.0 µm IR channel images (below) showed the explosive convective growth over Kansas and Nebraska in the 3-hour period between 19:56 UTC and 22:53 UTC.

POES AVHRR 12.0 µm IR channel images

POES AVHRR 12.0 µm IR channel images

Additional details on this event can be found on the RAMMB GOES-R Proving Ground Blog.

Mesoscale Convective System along the Gulf Coast region

April 30th, 2014
Radar-estimated Storm Total Precipitation for the 24-hour period ending at 13:47 UTC on 30 April

Radar-estimated Storm Total Precipitation for the 24-hour period ending at 13:47 UTC on 30 April

A large Mesoscale Convective System (MCS) developed ahead of a slow-moving cold front and moved over the Gulf Coast region of the US on 29 April30 April 2014, producing record rainfall totals (WeatherUnderground) and creating widespread severe flooding across parts of southern Alabama and the western Florida Panhandle. The 24-hour WSR-88D Storm Total Precipitation as visualized using the SSEC RealEarth web map server (above) showed swaths of radar-estimated precipitation in excess of 10 inches (violet color enhancement) — but some locations reported actual storm total rainfall amounts exceeding 20 inches (NWS Mobile/Pensacola).

AWIPS images of the MIMIC Total Precipitable Water (TPW) product (below; click image to play animation; Atlantic sector animation) indicated that there were multiple northward surges of TPW values in the 45-50 mm or 1.78-2.0 inch range (darker orange color enhancement) during the 28-30 April time period.

MIMIC Total Precipitable Water product (click image to play animation)

MIMIC Total Precipitable Water product (click image to play animation)

4-km resolution GOES-13 10.7 µm IR channel images (below; click image to play animation) displayed large areas of unusually cold GOES cloud-top IR brightness temperatures (colder than -80º C, violet color enhancement) — in fact, the coldest GOES-13 10.7 µm IR cloud-top brightness temperature seen was -86º C at 12:15 UTC.

GOES-13 10.7 µm IR channel images (click to play animation)

GOES-13 10.7 µm IR channel images (click to play animation)

This MCS also produced very large amounts of cloud-to-ground lightning (below; click image to play animation), with the highest number of 15-minute interval lightning strikes being 5379 negative and 697 positive at 11:15 UTC.

GOES-13 10.7 µm IR channel images with cloud-to-ground lightning strikes (click to play animation)

GOES-13 10.7 µm IR channel images with cloud-to-ground lightning strikes (click to play animation)

A 1-km resolution MODIS IR image at 04:11 UTC on 30 April (below) displayed a minimum cloud-top IR brightness temperature of -87º C (darker violet color enhancement).

MODIS 11.0 µm IR channel image

MODIS 11.0 µm IR channel image

375-meter resolution (mapped onto a 1-km AWIPS grid) Suomi NPP VIIRS 11.45 µm IR channel images (below) displayed a minimum cloud-top IR brightness temperature of -90º C (dark violet color enhancement) at 06:57 UTC on 29 April.

Suomi NPP VIIRS 11.45 µm IR channel images

Suomi NPP VIIRS 11.45 µm IR channel images

1-km resolution POES AVHRR 12.0 µm IR channel images (below) exhibited a minimum cloud-top IR brightness temperature of -93º C at 10:12 UTC and 11:07 UTC on 30 April.

POES AVHRR 12.0 µm IR channel images

POES AVHRR 12.0 µm IR channel images

Brightness temperatures seen on a single-channel IR image do not always indicate the true cloud top temperature value — but in this case, the -93º C value (which was also seen on the corresponding POES AVHRR 10.8 µm IR image) agreed with minimum value on the POES AVHRR CLAVR-x Cloud Top Temperature product. The POES AVHRR Cloud Top Height product indicated values of 15-16 km in these areas of extremely cold IR temperatures (below).

POES AVHRR 10.8 µm IR channel, Cloud Top Temperature product, and Cloud Top Height product at 11:07 UTC

POES AVHRR 10.8 µm IR channel, Cloud Top Temperature product, and Cloud Top Height product at 11:07 UTC

As we have seen with previous cases of strong convection exhibiting intense overshooting tops, nighttime Suomi NPP VIIRS 0.7 um Day/Night Band imagery (below) showed that this MCS produced a large pattern of concentric mesospheric airglow waves that could be seen traveling away from the storm for a considerable distance.

Suomi NPP VIIRS 0.7 um Day/Night Band image

Suomi NPP VIIRS 0.7 um Day/Night Band image