Blowing dust in northeastern Arkansas

April 12th, 2016

GOES-13 Visible (0.63 um) images [click to play animation]

GOES-13 Visible (0.63 um) images [click to play animation]

Strong southwesterly winds (gusting as high as 39 knots or 45 mph) created areas of blowing dust that reduced visibility to near zero and caused 2 incidents of multiple-vehicle accidents (NWS Local Storm Reports) near Portia in northeastern Arkansas on 10 April 2016. GOES-13 (GOES-East) Visible (0.63 um) images (above) showed the faint hazy signature of a few narrow plumes of blowing dust moving northeastward, one of which moved across Lawrence County and between Portia (denoted by the red * symbol) and Walnut Ridge (station identifier KARG). The blowing dust plumes are perhaps a bit easier to see on these images without county outlines and highways, though they are still somewhat difficult to identify with the patches of thin cirrus and contrails drifting from west to east overhead. Video of the conditions on the ground can be seen here.

Time series plots of surface data for Walnut Ridge (KARG) located just to the northeast and Newport (KM19) located farther to the south-southwest are shown below. Surface reports indicated that the visibility was reduced to less than 1 mile at 1756 UTC at Newport, and less than 3 miles at 1735 UTC at Walnut Ridge.

Time series plot of surface data for Walnut Ridge, Arkansas [click to enlarge]

Time series plot of surface data for Walnut Ridge, Arkansas [click to enlarge]

Time series plot of surface data for Newport, Arkansas [click to enlarge]

Time series plot of surface data for Newport, Arkansas [click to enlarge]

On the previous day, a comparison of the 1849 UTC Aqua MODIS Visible (0.65 µm) image and the corresponding Normalized Difference Vegetation Index (NDVI) product (below) showed that there were many areas upwind (to the southwest of) Portia and Walnut Ridge — in both southern Lawrence and northern Jackson counties — that exhibited low NDVI values (tan color enhancement), indicative of recently-plowed and/or unplanted agricultural fields within that part of the Mississippi Alluvial Plain. It is possible that field plowing activities on that windy day may have been the catalyst for the some of the  blowing dust plumes.

Aqua MODIS Visible (0.65 um) and Normalized Difference Vegetation Index (NDVI) product [click to enlarge]

Aqua MODIS Visible (0.65 um) and Normalized Difference Vegetation Index (NDVI) product [click to enlarge]

Similarly, a comparison of the 1849 UTC Aqua MODIS NDVI and Land Surface Temperature (LST) products (below) showed that the land surface in areas with less vegetation were warming up more quickly, with some LST values in excess of 90º F (darker red enhancement).

Aqua MODIS Normalized Difference Vegetation Index (NDVI) and Land Surface Temperature products [click to enlarge]

Aqua MODIS Normalized Difference Vegetation Index (NDVI) and Land Surface Temperature products [click to enlarge]

Middle and upper-atmospheric wave structures in the vicinity of a subtropical jet stream

April 4th, 2016

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images, with ECMWF model maximum wind isotachs [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images, with ECMWF model maximum wind isotachs [click to enlarge]

A strong (120-knot) subtropical jet stream was moving eastward across the Gulf of Mexico during the 03 April – 04 April 2016 period. During the overnight hours between these 2 days, a Suomi NPP VIIRS Day/Night Band (0.7 µm) image at 0753 UTC (above) revealed a large packet of arc-shaped mesospheric airglow waves south of the axis of the jet stream (as indicated by isotachs of the maximum tropospheric wind speed from the ECMWF model). Note how there were no cloud features which corresponded to these waves in the 0753 UTC VIIRS Infrared Window (11.45 µm) image; since the Moon was in the waning Gibbous phase (at 13% of Full), there was very little lunar illumination of cloud features, so airglow — essentially the “night glow” emitted from a variety of high-altitude (80-105 km) gases (primarily the sodium layer) near the mesopause — was allowing these high-altitude waves to be detected using the sensitive Day/Night Band (reference: “Suomi satellite brings to light a unique frontier of nighttime environmental sensing capabilities”).

During the subsequent daytime hours on 04 April, more interesting (tropospheric) waves were seen in the vicinity of this subtropical jet stream — small packets of waves that were propagating westward, against the ambient flow –one over Florida/Georgia/South Carolina, and another over South Texas. Unfortunately, these features fall into the “What the heck is this?” blog category, so no coherent explanation of them can be offered at this time.

GOES-13 Water Vapor (6.5 µm) images, with ECMWF model maximum wind isotachs [click to play animation]

GOES-13 Water Vapor (6.5 µm) images, with ECMWF model maximum wind isotachs [click to play animation]

An interesting question from Shea Gibson:

Convective snow squalls in the Upper Midwest

April 2nd, 2016

GOES-13 Visible (0.63 µm) images, with hourly surface weather symbols [click to play animation]

GOES-13 Visible (0.63 µm) images, with hourly surface weather symbols [click to play animation]

A vigorous clipper-type shortwave moved rapidly southeastward across the Upper Midwest on 02 April 2016; there were widespread convective elements associated with this system as seen in GOES-13 Visible (0.63 µm) images (above), which produced moderate to heavy snowfall at times (and even thundersnow) creating brief white-out conditions (time-lapse video from the AOSS rooftop camera in Madison, Wisconsin). A sequence of visible images from the polar-orbiting MODIS, VIIRS, and AVHRR instruments (below) provided another detailed view of these convective elements. This disturbance produced strong winds and accumulating snowfall; more information can also be found here from the NWS Chicago.

MODIS, VIIRS, and AVHRR visible images [click to enlarge]

MODIS, VIIRS, and AVHRR visible images [click to enlarge]

A pronounced warm/dry signature of middle-tropospheric subsidence (yellow color enhancement) was evident on GOES-13 Water Vapor (6.5 µm) images (below), which appeared to be along or just ahead of the areas of stronger wind gusts at the surface.

GOES-13 Water Vapor (6.5 µm) images with hourly wind gusts in knots [click to play animation]

GOES-13 Water Vapor (6.5 µm) images with hourly wind gusts in knots [click to play animation]

This area of middle-tropospheric subsidence was located along the leading edge of a strong (110-120 knot) 500 hPa jet, as indicated by the NAM40 model isotachs (below).

GOES-13 Water Vapor (6.5 µm) images with METAR surface reports, surface fronts, and NAM40 500 hPa wind isotachs [click to play animation]

GOES-13 Water Vapor (6.5 µm) images with METAR surface reports, surface fronts, and NAM40 500 hPa wind isotachs [click to play animation]

The convective elements were relatively shallow, with cloud-top infrared brightness temperatures only in the -20 to -30º C range (cyan to darker blue color enhancement) as seen in 4-km resolution GOES-13 Infrared Window (10.7 µm) images (below) and also in 1-km resolution MODIS, VIIRS, and AVHRR infrared images.

GOES-13 Infrared Window (10.7 µm) images, with hourly surface weather symbols [click to play animation]

GOES-13 Infrared Window (10.7 µm) images, with hourly surface weather symbols [click to play animation]

The 24-hour snowfall amounts ending at 12 UTC on 02 and 03 April are shown below, from the NOHRSC site. There was a narrow swath of snowfall in excess of 3 inches just north of the track of the surface low (surface analyses), from northeast Minnesota across Wisconsin to southwest Lower Michigan.

24-hour snowfall amounts (in inches) ending at 12 UTC on 02 and 03 April [click to enlarge]

24-hour snowfall amounts (in inches) ending at 12 UTC on 02 and 03 April [click to enlarge]

Eruption of the Mount Pavlof volcano in Alaska

March 28th, 2016

Himawari-8 AHI Shortwave Infrared (3.9 µm) images [click to play animation]

Himawari-8 AHI Shortwave Infrared (3.9 µm) images [click to play animation]

A major eruption of the Mount Pavlof volcano on the Alaska Peninsula began shortly before 0000 UTC on 28 March, or 4:00 pm on 27 March Alaska time (AVO report), as detected by a thermal anomaly (or “hot spot”, yellow to red color enhancement) on Himawari-8 AHI Shortwave Infrared (3.9 µm) images (above). The hot spot decreased in size and intensity toward the later hours of the day, signaling a lull in the volcanic eruption.

It is interesting to note on a comparison of the 0000 UTC Himawari-8 and GOES-15 Shortwave Infrared (3.9 um) images the large difference in the magnitude of the thermal anomaly — even though the viewing angle was larger for Himawari-8, the superior spatial resolution (2 km at nadir, compared to 4 km with GOES-15) detected a hot spot with an Infrared Brightness Temperature (IR BT) that was 36.6 K warmer (below). The Infrared channels on the GOES-R ABI instrument will also have a 2 km spatial resolution.

Himawari-8 AHI (left) and GOES-15 Imager (right) 3.9 µm Shortwave Infrared images [click to enlarge]

Himawari-8 AHI (left) and GOES-15 Imager (right) 3.9 µm Shortwave Infrared images [click to enlarge]

With the aid of reflected light from the Moon (in the Waxing Gibbous phase, at 75% of Full), a nighttime view using the Suomi NPP VIIRS Day/Night Band (0.7 µm) from the SSEC RealEarth site (below) revealed the bright glow of the eruption, along with the darker (compared to adjacent meteorological clouds) volcanic ash cloud streaming northeastward. The corresponding VIIRS Shortwave Infrared (3.74 µm) image showed the dark black hot spot of the volcano summit.

Suomi NPP VIIRS Shortwave Infrared (3.74 µm) and Day/Night Band (0.7 µm) image [click to enlarge]

Suomi NPP VIIRS Shortwave Infrared (3.74 µm) and Day/Night Band (0.7 µm) image [click to enlarge]

The volcanic ash cloud continued moving in a northeastward direction, as seen in a sequence of GOES-15 Infrared Window (10.7 µm) and either Terra/Aqua MODIS or Suomi NPP VIIRS retrieved Volcanic Ash Height products from the NOAA/CIMSS Volcanic Could Monitoring site (below).

GOES-15 Infrared (10.7 µm) images, with Terra/Aqua MODIS and Suomi NPP VIIRS Ash Height products [click to play animation]

GOES-15 Infrared (10.7 µm) images, with Terra/Aqua MODIS and Suomi NPP VIIRS Ash Height products [click to play animation]

Due to the oblique satellite view angle, the shadow cast by the tall volcanic ash cloud was easily seen on the following early morning (Alaska time) Himawari-8 AHI Visible (0.64 µm) images (below). A closer view (courtesy of Dan Lindsey, RAMMB/CIRA) revealed overshooting tops and gravity waves propagating downwind of the eruption site.

Himawari-8 AHI Visible (0.64 um) images (click to play animation]

Himawari-8 AHI Visible (0.64 um) images (click to play animation]

A few select Pilot reports (PIREPs) are shown below, plotted on GOES-15 Infrared Window (10.7 µm) and Aqua MODIS Ash Height derived products. Numerous flights were canceled as the ash cloud eventually began to drift over Western and Interior Alaska (media report).

GOES-15 Infrared Window (10.7 um) image, with METAR surface reports and Pilot reports [click to enlarge]

GOES-15 Infrared Window (10.7 µm) image, with METAR surface reports and Pilot reports [click to enlarge]

GOES-15 Infrared Window (10.7 um) image, with METAR surface reports and Pilot reports [click to enlarge]

GOES-15 Infrared Window (10.7 µm) image, with METAR surface reports and Pilot reports [click to enlarge]

GOES-15 Infrared Window (10.7 um) image, with METAR surface reports and Pilot reports [click to enlarge]

GOES-15 Infrared Window (10.7 µm) image, with METAR surface reports and Pilot reports [click to enlarge]

Aqua MODIS Ash Height product, with METAR surface reports and Pilot reports [click to enlarge]

Aqua MODIS Ash Height product, with METAR surface reports and Pilot reports [click to enlarge]

GOES-15 Infrared Window (10.7 um), with METAR surface reports and Pilot reports [click to enlarge]

GOES-15 Infrared Window (10.7 µm), with METAR surface reports and Pilot reports [click to enlarge]

A comparison of Suomi NPP VIIRS Shortwave Infrared (3.74 µm), Day/Night Band (0.7 µm), and true-color Red/Green/Blue (RGB) images (below) showed the volcanic hot spot and the brown to tan colored ash cloud at 2141 UTC on 28 March. Significant ash fall (as much as 2/3 of an inch) was experienced at the village of Nelson Lagoon, located 55 miles northeast of Pavlof (media report).

Suomi NPP VIIRS Shortwave Infrared (3.74 µm), Day/Night Band (0.7 µm), and true-color RGB images [click to enlarge]

Suomi NPP VIIRS Shortwave Infrared (3.74 µm), Day/Night Band (0.7 µm), and true-color RGB images [click to enlarge]

A comparison of the 3 Himawari-8 AHI Water Vapor bands (7.3 µm, 6.9 µm and 6.2 µm) covering the first 14 hours of the eruption from 0000 to 1400 UTC is shown below. Note that volcanic plume was best seen on the 7.3 µm images, which indicated that it began to move over the coast of Western Alaska after around 0600 UTC; this is due to the fact that the 7.3 µm band is not only a “water vapor absorption” band, but is also sensitive to high levels of SO2 loading in the atmosphere (as was pointed out in this blog post).

Himawari-8 AHI Water Vapor 7.3 µm (left), 6.9 µm (center) and 6.2 µm (right) images [click to play animation]

Himawari-8 AHI Water Vapor 7.3 µm (left), 6.9 µm (center) and 6.2 µm (right) images [click to play animation]