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 there was also a peak wind gust of 71 mph at Whitaker Peak. 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

Ice motion in the Chukchi Sea

December 9th, 2014
Suomi NPP VIIRS 0.7 µm Day/Night Band images (click to play animation)

Suomi NPP VIIRS 0.7 µm Day/Night Band images (click to play animation)

AWIPS II images of Suomi NPP VIIRS 0.7 µm Day/Night Band data covering the 05 December – 09 December 2014 period (above; click image to play animation; also available as an MP4 movie file) revealed a fairly abrupt increase in the southwesterly motion of drift ice in the Chukchi Sea (off the northwest coast of Alaska), with giant ice floes beginning to break away north of Barrow (station identifier PABR) on 08 December. Although the northern half of the satellite scene saw little to no sunlight during this time, abundant illumination from the Moon (in the Waning Gibbous phase, at 82% of full) helped to demonstrate the “visible image at night” capability of the VIIRS Day/Night Band.

This change in ice motion was caused by an increase in northeasterly wind over that region, in response to a tightening pressure gradient between a 1040 hPa high pressure centered north of Siberia and a 958 hPa low pressure centered south of Kodiak Island in the Gulf of Alaska (below). The strong winds were also creating the potential for heavy freezing spray over the open waters north and south of the Bering Strait.

Suomi NPP VIIRS 0.7 µm Day/Night Band image, with surface analysis

Suomi NPP VIIRS 0.7 µm Day/Night Band image, with surface analysis

Along the northwest coast of Alaska, northeasterly winds at Point Hope (station identifier PAPO) gusted as high as 62 knots or 71 mph on 09 December (below). Not far to the north at Cape Lisburne (PALU), the peak wind gust was 39 knots or 45 mph.

Point Hope, Alaska meteorogram

Point Hope, Alaska meteorogram

Significant rainfall event in California

December 2nd, 2014
MIMIC Total Precipitable Water product, with surface analysis overlays

MIMIC Total Precipitable Water product, with surface analysis overlays

As of 25 November 2014, much of the state of California was experiencing extreme to exceptional drought conditions.  However, the development of a large occluded mid-latitude cyclone over the far eastern Pacific Ocean during the 01 December – 02 December time period began to draw high values (up to 60 mm or 2.4 inches, darker red color enhancement) of total precipitable water (TPW) northward from the Inter-Tropical Convergence Zone (ITCZ), as seen on AWIPS images of the MIMIC TPW product (above). While the rainfall was beneficial in terms of drought mitigation, amounts of up to 12 inches did cause flooding and mudslide problems in some locations.

An animation of hourly MIMIC TPW images from 30 November – 02 December (below; click image to play animation) showed the northward surge of moisture toward the California coast, and also hinted at a complex inner structure associated with the occluded low.

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

MIMIC Total Precipitable Water product (click image to play animation

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

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

On 02 December, comparisons of AWIPS II images of 1-km resolution MODIS 6.7 µm and 4-km resolution GOES-15 6.5 µm water vapor channel data around 11 UTC (above) and around 22 UTC (below) demonstrated the importance of improved spatial resolution for more clearly identifying some of the smaller-scale structure features within the core of the occluded low.

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

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

A comparison of Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images at 22:18 UTC (below) shows a few areas of embedded convection, some of which had produced cloud-to-ground lightning strikes in the hour preceding the images.

Suomi NPP VIIS 0.64 µm visible channel and 11.45 µm IR channel images, with cloud-to-ground lightning strikes

Suomi NPP VIIS 0.64 µm visible channel and 11.45 µm IR channel images, with cloud-to-ground lightning strikes

Major lake effect snow event downwind of Lake Erie and Lake Ontario

November 18th, 2014
GOES-13 0.63 µm visible channel images (click to play animation)

GOES-13 0.63 µm visible channel images (click to play animation)

Cold arctic air (surface air temperatures in the upper teens to lower 20s F) flowing across the still-warm waters of Lake Erie and Lake Ontario (sea surface temperature values as warm as the middle to upper 40s F) were 2 ingredients that helped create a major lake effect snowfall event on 18 November 2014 (VIIRS visible image with surface analysis). Storm total snowfall amounts were as high as 65 inches in Erie County, New York (NWS Buffalo Public Information Statement). GOES-13 0.63 µm visible channel images (above; click image to play animation) showed the large and well defined single-band lake effect cloud features that developed over each of the lakes. The band over Lake Erie was nearly stationary for several hours, producing snowfall rates as high as 4 inches per hour at some locations in the Southtowns of Buffalo. The stationary behavior (and very sharp northern edge, due to a “locked thermal convergence zone“) of the Lake Erie snow band was quite evident on composite radar reflectivity (below; click image to play animation; images courtesy of the College of DuPage). The formation and growth of this band benefited from a long fetch of southwesterly winds oriented along the axis of Lake Erie.  Isolated negative cloud-to-ground lightning strikes were observed at 16:45 and 22:15 UTC, implying the presence of embedded pockets of thundersnow.

Composite radar reflectivity (click to play animation)

Composite radar reflectivity (click to play animation)

A comparison of Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images at 18:17 UTC or 1:17 pm local time is shown below. The coldest cloud-top IR brightness temperature was -37º C (green color enhancement), which corresponded to a pressure of 437 hPa (or an altitude around 6 km) on the 12 UTC Buffalo NY rawinsonde report.

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

Comparisons of Terra and Aqua MODIS true-color Red/Green/Blue (RGB) images covering the Lake Erie/Lake Ontario region along with a high-resolution view centered on Buffalo NY are shown below.

Terra and Aqua MODIS true-color RGB images

Terra and Aqua MODIS true-color RGB images

Terra and Aqua MODIS true-color RGB images

Terra and Aqua MODIS true-color RGB images

A 15-meter resolution Landsat-8 0.59 µm panochromatic visible channel image from the SSEC RealEarth web map server (below) showed great detail to the Lake Ontario snow band as it was moving inland over the Watertown NY area at 15:45 UTC.

Landsat-8 0.59 µm panochromatic visible image

Landsat-8 0.59 µm panochromatic visible image

Looking back to the preceding nighttime hours, a toggle between Suomi NPP VIIRS 0.7 µm Day/Night Band, 3.74 µm shortwave IR, 11.45 µm IR, and 11.45-3.74 µm IR brightness temperature difference “Fog/stratus product” images at 06:54 UTC or 1:54 am local time (below) showed that the lake effect bands were already well-developed, with minimum 11.45 µm IR brightness temperatures of -30º C and colder (yellow color enhancement). Even with minimal lunar illumination — the Moon was in the Waning Crescent phase, at only 7% of full — the lake effect cloud bands features could still be seen on the Day/Night Band image.

Suomi NPP VIIRS 0.7 µm Day/Night Band, 3.74 µm shortwave IR, 11.45 µm IR, and

Suomi NPP VIIRS 0.7 µm Day/Night Band, 3.74 µm shortwave IR, 11.45 µm IR, and “Fog/stratus product” images

For a more in-depth discussion of this lake effect snow event, watch the VISIT Satellite Chat session.