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.

Eruption of the Pavlof Volcano in Alaska

November 15th, 2014
Suomi NPP VIIRS 0.7 µm Day/Night Band and 3.74 µm shortwave IR images

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

According to the Alaska Volcano Observatory, an eruption of the Pavlof Volcano began around 01:50 UTC on 13 November 2014. A comparison of nighttime images of Suomi NPP VIIRS 0.7 µm Day/Night Band (DNB) and 3.74 µm shortwave IR data at 13:07 UTC or 4:07 am local time on 14 November (above) showed the bright glow of the eruption on the DNB image, with the hottest pixel being 52º C (red color enhancement) on the shortwave IR image.

With the subsequent arrival of daylight, a break in the clouds allowed the faint volcanic plume to be observed on GOES-15 0.63 µm visible channel images (below; click image to play animation), drifting northwestward over the Bering Sea.

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

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

At 22:02 UTC on 14 November, the radiometrically-retrieved maximum volcanic ash mass loading value was 1.8 tons per km2, the maximum ash height was 16.8 km, and the maximum ash mass effective radius was 7.81 µm (below).

MODIS volcanic ash mass loading, ash height, and ash mass effective radius products

MODIS volcanic ash mass loading, ash height, and ash mass effective radius products

About an hour later, the volcanic ash plume could be seen on a 23:03 UTC Suomi NPP VIIRS Day/Night Band image, with a maximum 3.74 µm shortwave IR brightness temperature of 46º C at the summit of the volcano (below).

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

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

The brown hue of the volcanic ash plume was very evident on Suomi NPP VIIRS true-color Red/Green/Blue (RGB) images from the SSEC RealEarth web map server (below).

Suomi NPP VIIRS true-color RGB images

Suomi NPP VIIRS true-color RGB images

The intensity of the Pavlof eruption increased on 15 November, and a well-defined volcanic ash plume could be seen on GOES-15 0.63 µm visible channel images (below; click image to play animation). Pilot reports estimated that the top of the plume was as high as 38,000 feet.

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

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

On a comparison of Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images at 22:45 UTC (below), the coldest cloud-top IR brightness temperature value was -55º C.

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

At 22:29 UTC, the CLAVR-x POES AVHRR Cloud Top Temperature product indicated a minimum value of -54º C, with a maximum Cloud Top Height value of 9 km; the -54º C cloud top temperature corresponded to an altitude of around 29,000 feet or 8.7 km on the 16 November/00 UTC Cold Bay AK rawinsonde profile.

POES AVHRR Cloud Top Temperature and Cloud Top Height products

POES AVHRR Cloud Top Temperature and Cloud Top Height products

A Suomi NPP VIIRS true-color RGB image at 23:04 UTC (below) suggested that the volcanic plume consisted of a dense layer of tan-colored ash, with a layer of mostly ice cloud at the top of the plume.

Suomi NPP VIIRS true-color RGB image

Suomi NPP VIIRS true-color RGB image

“River-effect” snow in South Dakota

November 13th, 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)

GOES-13 0.63 µm visible channel images (above; click image to play animation) revealed the presence of numerous cloud streamers originating over the Lake Oahe and Lake Sharpe reservoirs along the Missouri River in South Dakota on 13 November 2014. At times these cloud bands were producing snow that was reducing surface visibility to 4 miles at Pierre (KPIR) and 5 miles at Chamberlain (K9V9).

Aqua MODIS 0.65 µm visible channel image, False-color RGB image, and Sea Surface Temperature product at 19:48 UTC

Aqua MODIS 0.65 µm visible channel image, False-color RGB image, and Sea Surface Temperature product at 19:48 UTC

Comparisons of visible channel and false-color Red/Green/Blue (RGB) images from Aqua MODIS (above) and Suomi NPP VIIRS (below) demonstrated the value of RGB products to more easily identify such supercooled water droplet cloud features (which appear as varying shades of white) in areas that have underlying snow cover (which appears as varying shades of red). In addition, the MODIS Sea Surface Temperature (SST) product (above) showed that SST values were in the 40-50º F range (cyan color enhancement) in those Missouri River reservoirs, making them significantly warmer than the cold arctic air mass that had overspread the region.

Suomi NPP VIIRS 0.64 µm visible channel image and False-color RGB image at 19:51 UTC

Suomi NPP VIIRS 0.64 µm visible channel image and False-color RGB image at 19:51 UTC

Dusty Cold Front moves south through the Southern Plains

November 11th, 2014
GOES-13 0.63 µm Visible imagery (click to play animation)

GOES-13 0.63 µm Visible imagery (click to play animation)

A strong cold front moved southward over the High Plains of the US on Monday 10 November, and the strong winds produced a dust cloud that was apparent in GOES-13 visible imagery, above. The leading edge of the dust cloud in the satellite imagery indicated precisely the leading edge of the cold front. The animation below shows hourly observations plotted on top of the GOES-13 visible imagery. The correspondence between the leading edge of the dust and the wind shift is obvious. Note that multiple stations report Haze (H) after the wind shift occurs.

GOES-13 0.63 µm Visible imagery and surface observations (click to play animation)

GOES-13 0.63 µm Visible imagery and surface observations (click to play animation)

GOES-15 viewed this event as well (Visible animation; Visible animation with observations). The dust in the atmosphere was far more apparent in the GOES-13 imagery, however. This case is an excellent demonstration of how dust effectively forward scatters visible light from the setting sun towards GOES-13 at 75º W, but does not so effectively back scatter towards GOES-15 at 135º W. The toggle below shows visible imagery from GOES-13 and GOES-15, both at 2200 UTC.

GOES-13 0.63 µm Visible imagery and GOES-15 0.62 µm Visible Imagery, both at 2200 UTC 10 November (click to enlarge)

GOES-13 0.63 µm Visible imagery and GOES-15 0.62 µm Visible Imagery, both at 2200 UTC 10 November (click to enlarge)

Both Aqua (MODIS) and Suomi NPP (VIIRS) viewed this haboob in mid-afternoon on 10 November. What can the multispectral views of this feature tell us? Both the Visible and Snow/Ice channels give similar views of the leading edge of the cold front (the biggest difference between the visible and snow/ice channel in this image is that water features are so much darker in the snow/ice channel because water strongly absorbs 2.1 µm radiation; differences in the clouds between the visible and the snow/ice (2.1 µm) channel arise from viewing water-based vs. ice-based clouds). The cirrus channel — 1.37 µm — does not see the surface but it does clearly reveal high clouds. The 3.9-µm image — shortwave infrared — shows very warm temperatures right at the leading edge of the cold front in eastern Colorado. This is a region where the dust is effectively reflecting solar radiation. The longwave infrared imagery (10.7 µm) shows a more uniform cold edge to the cloud. Finally, even the water vapor imagery shows a signal from this cold front (known as a lee-side frontal gravity wave). It is unusual for surface features to have a signal in water vapor imagery; when it does occur, the atmosphere is usually very dry, and that’s the case in this event. Note in the toggle here between GOES water vapor channel weighting functions (computed here) at Amarillo between 0000 UTC — before the cold front — and 1200 UTC — after the cold front — shows how the layer from which 6.5 µm radiation will be detected has dropped in altitude.

Aqua MODIS Visible, Snow/Ice, Cirrus, Shortwave IR, Water Vapor and Longwave IR Imagery at 1917 UTC, 10 November (click to enlarge)

Aqua MODIS Visible, Snow/Ice, Cirrus, Shortwave IR, Water Vapor and Longwave IR Imagery at 1917 UTC, 10 November (click to enlarge)

Suomi NPP viewed the cold front 10 minutes before Aqua, below, and also about 90 minutes later (Favorable orbital geometry allowed sequential orbits to view eastern Colorado). The shortwave IR (3.74 µm) show warmer signatures in some of the dust plumes compared to the longwave IR (11.35 µm), similar to Aqua, a difference that is likely due to solar radiation being reflected by the dust.

Suomi NPP VIIRS data showing Visible, Day Night Band, Snow/Ice, Shortwave IR, and Longwave IR Imagery at 1907 UTC, 10 November (click to enlarge)

Suomi NPP VIIRS data showing Visible, Day Night Band, Snow/Ice, Shortwave IR, and Longwave IR Imagery at 1907 UTC, 10 November (click to enlarge)

Suomi NPP VIIRS data showing Visible, Day Night Band, Snow/Ice, Shortwave IR, and Longwave IR Imagery at 2049 UTC, 10 November (click to enlarge)

Suomi NPP VIIRS data showing Visible, Day Night Band, Snow/Ice, Shortwave IR, and Longwave IR Imagery at 2049 UTC, 10 November (click to enlarge)

Animations of 10.7 µm Brightness Temperature Data from GOES-13 showed the southward plunge of cold air overnight. The progress of this cold front could be monitored from space. Even the water vapor imagery continued to include a signature of the cold front.

GOES-13 Water Vapor (6.7 µm) Infrared Imagery (click to play animation)

GOES-13 Water Vapor (6.7 µm) Infrared Imagery (click to play animation)

The visible imagery at the top of this post ably captured the signature associated with blowing dust. Did the blowing dust continue through the night? Single-channel detection of dust at night is difficult. Historically, dust could be detected with brightness temperature differences between 10.7 µm and 12 µm channels on the GOES Imager, but that capability ended when the 13.3 µm channel replaced the 12 µm channel on the GOES Imager (the GOES-R ABI will contain a 12 µm channel). The VIIRS Day Night Band, below, from Suomi NPP at 0905 UTC on 11 November, does not show a distinct dust signature over south Texas. The leading edge of the front is obvious, however, as it is preceded by a Bore structure with parallel lines of clouds.

Suomi NPP VIIRS Day Night Band (.7 µm) Visible Imagery at 0905 UTC 11 November 2014 (click to enlarge)

Suomi NPP VIIRS Day Night Band (.7 µm) Visible Imagery at 0905 UTC 11 November 2014 (click to enlarge)