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

Mountain wave clouds over southern California

December 21st, 2014
GOES-15 6.5 µm water vapor channel images click to play animation)

GOES-15 6.5 µm water vapor channel images click to play animation)

AWIPS images of 4-km resolution resolution GOES-15 (GOES-West) 6.5 µm water vapor channel data (above; click image to play animation) showed the development of a patch of mountain wave or “lee wave” clouds immediately downwind of the higher elevations of the western Transverse Ranges in southern California on 21 December 2014.  These clouds developed in response to strong northerly winds interacting with the west-to-east oriented topography (12 UTC NAM 700 hPa wind and height). As seen on the plotted surface reports, at Sandberg (station identifier KSDB) the highest wind gust was 52 knots or 59 mph  at 17:42 UTC — and later in the day there also a peak wind gust of 87 mph at Whitaker Peak and 86 mph at Montcito Hills. In addition, there were isolated pilot reports of moderate turbulence in the vicinity of the mountain wave cloud at 20:21 UTC and 23:06 UTC;  farther to the east there was a pilot report of moderate to severe turbulence at 01:27 UTC.

A comparison of 1-km resolution MODIS 6.7 µm and 4-km resolution GOES-15 6.5 µm water vapor channel images around 21:00 UTC (below) demonstrated the advantage of higher spatial resolution (and the minimal parallax offset) of the polar-orbiter MODIS imagery for more accurate location of the mountain wave cloud.

MODIS 6.7 µm and GOES-15 6.5 µm water vapor channel images

MODIS 6.7 µm and GOES-15 6.5 µm water vapor channel images

At 20:42 UTC (below), the coldest 1-km resolution POES AVHRR Cloud Top Temperature value associated with the mountain wave cloud feature was -69º C (darker red color enhancement), with the highest Cloud Top Height value being 14 km or 45,900 ft (cyan color enhancement)., which is actually colder and higher than the tropopause on  the 12 UTC rawinsonde report at Vandenberg AFB. The highest elevation in the western portion of the Transverse Ranges where the mountain wave cloud formed is Mount Pinos at 8847 feet or 2697 meters, so it appears that a vertically-propagating wave developed which helped the cloud reach such a high altitude.

POES AVHRR Cloud Top Temperature and Cloud Top Height products

POES AVHRR Cloud Top Temperature and Cloud Top Height products

At 21;20 UTC, a comparison of 375-meter resolution (projected onto a 1-km resolution AWIPS grid) Suomi NPP VIIRS 0.64 µm visible channel, 3.74 µm shortwave IR channel, and 11.45 µm IR channel images (below) showed that while the coldest cloud-top 11.45 µm IR brightness temperatures were around -60º C, the 3.74 µm shortwave IR temperatures were in the +5 to +10º C range — this indicates that the mountain wave cloud was composed of very small ice particles, which were efficient reflectors of solar radiation contributing to much the warmer shortwave IR brightness temperatures.

Suomi NPP VIIRS 0.64 µm visible, 3.74 µm shortwave IR, and 11 45 µm IR channel images

Suomi NPP VIIRS 0.64 µm visible, 3.74 µm shortwave IR, and 11 45 µm IR channel images

A 375-meter resolution Suomi NPP VIIRS true-color Red/Green/Blue (RGB) image from the SSEC RealEarth web map server is shown below.

Suomi NPP VIIRS true-color image

Suomi NPP VIIRS true-color image