Airborne glacial silt over the Gulf of Alaska

February 1st, 2015
GOES-15 0.63 µm visible channel images (click to play animation)

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

Due to a tight pressure gradient between a high over the Yukon and a low over the Gulf of Alaska (surface analysis), strong offshore winds (with gusts as high as 78 mph) were lofting glacial silt from the northern portion of the Alaska Panhandle region and carrying it westward over the Gulf of Alaska on 01 February 2015. Hints of the narrow light grey plumes could be seen streaming southwestward then westward on GOES-15 (GOES-West) 0.63 µm visible channel images (above; click to play animation).

A closer look using a comparison of Suomi NPP VIIRS 0.7 µm Day/Night Band (DNB) and 0.64 µm visible channel images (below) showed that the areal extent of the airborne aerosols was much more evident on the DNB image (in part due to it’s more broad spectral response). However, other more intricate patterns were seen on the DNB image in the general vicinity of Middleton Island (station identifier PAMD) that did not appear to match the character of the airborne glacial silt features being blown westward from the Alaska Panhandle region.

Suomi NPP VIIRS 0.7 µm Day/Night Band and 0.64 µm visible channel images

Suomi NPP VIIRS 0.7 µm Day/Night Band and 0.64 µm visible channel images

A Suomi NPP VIIRS true-color Red/Green/Blue (RGB) image from the SSEC RealEarth web map server (below) offers a clue to help explain the meandering features that stretched from the coast east of Prince William Sound toward the Middleton Island area: strands of phytoplankton, fed by nutrients in the river waters draining from the interior into the Gulf of Alaska. Sun glint along the edge of the VIIRS scan may have helped to highlight these features in the DNB image above. In fact, these water features were less obvious — and the airborne glacial silt more obvious — in a subsequent VIIRS DNB vs Visible image at 23:20 UTC.

Suomi NPP VIIRS true-color image

Suomi NPP VIIRS true-color image

Tropical Storm Niko (07P) in the South Pacific Ocean

January 20th, 2015
MIMIC Total Precipitable Water product, with Tropical Surface Analyses (click to play animation)

MIMIC Total Precipitable Water product, with Tropical Surface Analyses (click to play animation)

AWIPS images of the MIMIC Total Precipitable Water product (above; click image to play animation) showed a broad moist plume in the equatorial South Pacific Ocean, within which Tropical Storm Niko began to develop during the 19 January – 20 January 2015 period. By the end of the animation, Gale Force winds were being analyzed within the eastern semicircle of the developing cyclone. Metop ASCAT surface scatterometer winds at 08:01 UTC (below) showed winds as strong as 42 knots (though the direction of the stronger yellow wind barbs was suspect, likely due to rain contamination).

MIMIC TPW product, with Metop ASCAT surface scatterometer winds

MIMIC TPW product, with Metop ASCAT surface scatterometer winds

After daybreak on 20 January, McIDAS images of GOES-15 (GOES-West) 0.63 µm visible channel data (below; click image to play animation) showed the development of spiral banding wrapping into the central low-level circulation center as the system reached tropical storm intensity by 18 UTC.  In addition, a few strong convective pulses with distinct overshooting tops could be seen near the core of Niko.

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

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

An animation of GOES-15 10.7 µm IR channel images from the CIMSS Tropical Cyclones site (below) included an overlay of contours of the deep layer (200 – 850 hPa) wind shear at 18 UTC — Tropical Storm Niko developed in a region characterized by low wind shear, which enabled the storm to rapidly intensify.

GOES-15 10.7 µm IR channel images, with contours of deep layer wind shear

GOES-15 10.7 µm IR channel images, with contours of deep layer wind shear

Rare low-elevation snowfall in the eastern Mojave Desert

January 1st, 2015
Aqua MODIS 0.65 µm visible channel image and False-color Red/Green/Blue (RGB) images

Aqua MODIS 0.65 µm visible channel image and False-color Red/Green/Blue (RGB) images

A cold storm system moving through the Southwest US on 31 December 2014 produced significant snowfall in many of the higher-elevation mountain ranges of California, Baja California, Nevada, and Arizona (up to 20 inches at Mountainaire AZ), but also left lighter amounts of snowfall at some low-elevation locations of the eastern Mojave Desert where snowfall is considered to be quite rare (NWS Las Vegas Public Information Statement) | Event  Summary). This event marked the first time that snowfall had been recorded during the month of December at Needles, California.

As clouds began to clear over the region on the following day (01 January 2015), areas which still had snow on the ground could be seen using satellite imagery. On a comparison of Aqua MODIS 0.65 µm visible channel and false-color Red/Green/Blue (RGB) images at 20:33 UTC or 1:33 PM local time (above), snow cover that appeared as shades of white on the visible image also appeared as darker shades of red on the RGB image.

As the day progressed, the sun had the effect of melting the lighter amounts of snow cover, as seen on GOES-15 (GOES-West) 0.63 µm visible channel images (below; click image to play animation). However, due to the presence of the unusually cold air mass, new records for coldest 01 January daily maximum temperature were set for Phoenix (46ºF) and Tucson (41ºF).

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

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

White Christmas in Hawai’i

December 25th, 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)

According to the National Operational Hydrologic Remote Sensing Center, only 35.5% of the Lower 48 states had snow cover on 25 December 2014. However, a deep cutoff low over the Hawaiian Islands had brought unusually cold air aloft (the 500 hPa temperature on the Lihue rawinsonde report was as cold as -18º C, which is extremely cold by Hawaiian standards) and strong winds, which prompted Blizzard Warnings to be issued for the high elevation summits of the Big Island of Hawai’i on 23-24 December. As the cutoff low departed and skies began to clear, GOES-15 (GOES-West) 0.63 µm visible channel images (above; click image to play animation) revealed the bright white snow-covered summits of Mauna Kea and Mauna Loa on Christmas Day.

A toggle between a Suomi NPP VIIRS 0.64 µm visible channel and a false-color Red/Green/Blue (RGB) “snow vs cloud discrimination” image at 23:22 UTC (below) confirmed that the bright white features seen in the GOES-15 visible images was indeed snow cover — snow (and fully-glaciated ice clouds) appear as darker shades of red on the RGB image. Cloud tops that are partially glaciated appear as lighter shades of pink.

Suomi NPP VIIRS 0.64 µm visible channel and false-color

Suomi NPP VIIRS 0.64 µm visible channel and false-color “snow vs cloud discrimination” RGB images

===== 26 December Update =====

Using the SSEC RealEarth web map server, the comparison below shows 375-meter resolution Suomi NPP VIIRS true-color RGB images of the Big Island of Hawai’i on 20 December (before the snowfall on the Mauna Kea and Mauna Loa summits) and also on 25-26 December (after the snowfall). On the 26 December image, you can see that the patches of snow had melted somewhat at the 2 summits; in addition, an increase in hazy volcanic fog (vog) can be seen drifting southeastward off the island; this vog was being generated by the ongoing eruption of the Kilauwea volcano in the Hawai’i Volcanoes National Park.

Suomi NPP VIIRS true-color RGB images

Suomi NPP VIIRS true-color RGB images