Persistent fog/stratus over the central and southern Rocky Mountains region

November 30th, 2013 |
Suomi NPP VIIRS fog/stratus BTD product (with overlays of METAR surface reports and ceilings/visibilities)

Suomi NPP VIIRS IR brightness temperature difference “fog/stratus product” (with overlays of METAR surface reports and ceilings/visibilities)

A night-time AWIPS image of the Suomi NPP VIIRS IR brightness temperature difference (BTD) “fog/stratus product” at 08:47 UTC or 1:47 AM local time (above) displayed an expansive area of fog and stratus cloud across much of the central and southern Rocky Mountains region on 30 November 2013. Overlays of the hourly METAR surface reports and plots of cloud ceilings and visibilities showed that the BTD “fog/stratus product” had no skill in determining whether there was fog or stratus cloud at any given location — and there was a lack of surface reports beneath large portions of the fog/stratus feature (especially across southwestern Utah).

Of the 3 rawinsonde sites in that area, Grand Junction, Colorado (KGJT) was the only one that remained covered by the fog/stratus deck; their sounding profile at 12 UTC showed a very strong temperature inversion whose base was around 7943 feet (2422 meters) above the surface. With a quasi-stationary ridge of high pressure over the region, this strong capping temperature inversion helped to hold the fog in place for several days.

A comparison of the 375-meter resolution (projected onto a 1-km AWIPS grid) VIIRS BTD fog/stratus product with the corresponding 4-km resolution GOES-15 image (below) demonstrated the advantage of higher spatial resolution in helping to diagnose the locations of edges and small-scale variations in coverage of the large fog/stratus feature.

Suomi NPP VIIRS vs GOES-15 IR brightness temperature difference "fog/stratus product" images

Suomi NPP VIIRS vs GOES-15 IR brightness temperature difference “fog/stratus product”

Products designed to provide qualitative information on fog and low stratus clouds have been developed for use on the future GOES-R ABI data; applying these GOES-R algorithms to current GOES-15 imagery offered some insight as to the low cloud thickness, as well as the probabilities of Marginal Visual Flight Rules (MVFR), Instrument Flight Rules (IFR), or Low Instrument Flight Rules (LIFR) conditions (below). Again, data-sparse regions such as southwestern Utah could benefit from the use of such products for aviation forecasting purposes. See the GOES-R Fog Product Examples blog for additional examples of these types of “data fusion” products.

During the subsequent daytime hours, McIDAS images of 1-km resolution GOES-15 0.63 µm visible channel data (below; click to play animation) showed that although the large area of fog/stratus persisted into the late afternoon hours, there was still a surprising amount of variability to the exact location of the edges of the features (which was likely driven by differential terrain heating and local wind circulations). Something to note in the visible imagery: fog in the eastern portion of the Grand Canyon in northern Arizona, which is apparently quite rare (photos)

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

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

A comparison of the 20:11 UTC (1:11 PM local time) Suomi NPP VIIRS 0.64 µm visible channel image with the corresponding false-color Cloud-vs-snow discrimination Red/Green/Blue (RGB) image (below) helped to differentiate between the areas of snow cover (which appeared as varying shades of red on the RGB image) and the supercooled water droplet fog and stratus cloud features (which appeared as varying shades of white). Again, note the westward protrusion of fog located just to the north of Grand Canyon National Park (station identifier KGCN).

Suomi NPP VIIRS 0.64 µm visible channel and false-color Cloud-vs-snow discimination RGB image

Suomi NPP VIIRS 0.64 µm visible channel and false-color Cloud-vs-snow discimination RGB image

There were not many pilot reports availble to offer information on the height of the tops of the stratus clouds – however, one report placed the cloud tops at 8000 feet above ground level over far northwestern New Mexico at 19:08 UTC (below).

Suomi NPP VIIRS 0.64 µm visible channel image with pilot report of cloud top height

Suomi NPP VIIRS 0.64 µm visible channel image with pilot report of cloud top height

An image of the 1-km resolution POES AVHRR Cloud Top Height product at 21:00 UTC or 2:00 PM local time (below) indicated that the tops of the stratus clouds were generally in the 3-4 km range (green to yellow color enhancement).

POES AVHRR Cloud Top Height product

POES AVHRR Cloud Top Height product

===== 01 December Update =====

On the following day, an AWIPS-2 image comparison of the afternoon Suomi NPP VIIRS 0.64 um visible channel data with the corresponding Cloud-vs-snow discrimination RGB product (below) again showed how entrenched the fog/stratus still was across that region at 19:54 UTC or 12:54 PM local time.

Suomi NPP VIIRS 0.64 um visible image and Cloud-vs-snow discrimination RGB image

Suomi NPP VIIRS 0.64 um visible image and Cloud-vs-snow discrimination RGB image

Mesoscale vortex over western Lake Superior

November 28th, 2013 |
GOES-13 0.63 µm visible channel images (click to play animation)

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

McIDAS images of GOES-13 0.63 µm visible channel data (above; click image to play animation) revealed the well-defined circulation of a mesocale vortex over far western Lake Superior on 28 November 2013. During the day, this mesovortex was slowly migrating southward toward the Apostle Islands of Wisconsin. As much as 7.5 inches of snow was reported north of Bayfield in far northern Wisconsin, likely a result of enhanced snowfall rates associated with the passage of the mesovortex.

Suomi NPP VIIRS 0.64 µm visible channel images (17:27 and 19:07 UTC)

Suomi NPP VIIRS 0.64 µm visible channel images (17:27 and 19:07 UTC)

AWIPS images of VIIRS 0.64 µm visible channel data from consecutive overpasses of the Suomi NPP satellite at 17:27 and 19:07 UTC (above) showed better detail in the structure of the mesovortex; the corresponding VIIRS 11.45 µm IR images (below) indicated that cloud top IR brightness temperatures were generally in the -25 to -30º C range (darker blue color enhancement), suggesting that cloud glaciation was likely.

Suomi NPP VIIRS 11.45 µm IR channel images (17:17 and 19:07 UTC)

Suomi NPP VIIRS 11.45 µm IR channel images (17:17 and 19:07 UTC)

A comparison of the 17:27 UTC VIIRS visible image with the 17 UTC RTMA surface winds and the 18 UTC NAM12 surface, 925 hPa, and 850 hPa winds (below) showed that neither the RTMA nor the NAM12 wind fields did a good job of locating the actual center of primary mesovortex circulation — demonstrating the value of satellite imagery for a more accurate diagnosis of such small-scale features.

Suomi NPP VIIRS 0.64 µm visible image (with RTMA surface winds, NAM12 surface, 925, and 850 hPa winds)

Suomi NPP VIIRS 0.64 µm visible image (with RTMA surface winds, NAM12 surface, 925, and 850 hPa winds)

Tehuano wind event

November 27th, 2013 |
GOES-13 6.5 µm water vapor channel image, with surface pressure and surface front analysis

GOES-13 6.5 µm water vapor channel image, with surface pressure and surface front analysis

An AWIPS-1 image of GOES-13 6.5 µm water vapor channel data (above) showed a large storm that was affecting much of the eastern US during the 26 November 27 November 2013 period. Arctic air surging southward behind this storm system crossed the Gulf of Mexico, was funnelled through the mountain passes of southern Mexico, and eventually emerged into the Pacific Ocean in the Gulf of Tehuantepec. This type of “Tehauno wind event” tends to occur a few times each year during the cold season — a few other cases have been documented on this blog.

A series of AWIPS-2 images of GOES-13 10.7 µm IR channel data with overlays of surface and buoy reports and tropical surface analyses (below; click image to play animation) showed that the Gulf of Tehuantepec region was highlighted on 26 November as a region susceptible to developing Storm Force (48-55 knot) winds as the cold front approached from the north. Once the strong gap winds emerged from the southern coast of Mexico, parts of that area likely began to experience storm force winds.

GOES-13 10.7 µm IR images, with surface and buoy reports and tropical surface analysis (click to play animation)

GOES-13 10.7 µm IR images, with surface and buoy reports and tropical surface analysis (click to play animation)

The plume of dry air associated with the Tehuano wind event could be seen on AWIPS-1 images of the MIMIC Total Precipitable Water product (below; click image to play animation).

MIMIC Total Precipitable Water product, with tropical surface analysis (click to play animation)

MIMIC Total Precipitable Water product, with tropical surface analysis (click to play animation)

During the day on 27 November, the hazy signature of blowing dust and sand could be seen streaming southward across the Gulf of Tehuantepec on McIDAS images of GOES-13 0.63 µm visible channel data (below; click image to play animation).

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

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

Eruption of the Mount Etna volcano

November 23rd, 2013 |
Meteosat-10 0.75 µm visible channel images (click to play animation)

Meteosat-10 0.75 µm visible channel images (click to play animation)

The Mount Etna volcano — the tallest on the European continent, and one of the most active in the world — experienced an eruption on 23 November 2013. EUMETSAT Meteosat-10 0.75 µm visible channel images (above; click image to play animation) showed the explosive development of the volcanic plume beginning around 09:30 UTC; the plume then moved rapidly northeastward across far southern Italy, eventually moving over Albania around 13:00 UTC. A number of lightning strikes within the billowing ash plume can be seen in an HD-quality YouTube video.

Satellite signatures of an earlier eruption were discussed here and here.