GOES-14 SRSOR: from morning fog/stratus to afternoon convection

May 13th, 2014
Suomi NPP VIIRS and POES AVHRR IR brightness temperature difference

Suomi NPP VIIRS and POES AVHRR IR brightness temperature difference “fog/stratus product” images

An AWIPS comparison of nighttime Suomi NPP VIIRS and POES AVHRR IR brightness temperature difference “fog/stratus product” images (above) exhibited signals of fog and/or stratus forming in river valleys straddling the West Virginia and Virginia border on 13 May 2014.

The GOES-14 satellite continued to be operated in Super Rapid Scan Operations for GOES-R (SRSOR) mode, providing images at 1-minute intervals. Early morning 0.63 µm visible channel images (below; click image to play an MP4 animation; also available as a QuickTime movie) showed the narrow fingers of river valley fog/stratus, which began to burn off as heating and mixing increased during the morning hours. There was then a rapid transition to the formation of cumulus clouds across the region, some of which became organized areas of deep convection that produced hail and damaging winds (SPC storm reports).

GOES-14 0.63 µm visible channel images (click to play MP4 animation)

GOES-14 0.63 µm visible channel images (click to play MP4 animation)

A 3-panel comparison showing the difference between standard or routine 15-minute interval, 5-7 minute interval Rapid Scan Operations (RSO), and 1-minute interval SRSO GOES-14 0.63 µm visible channel images (below; click image to play an MP4 animation; also available as a very large Animated GIF) demonstrated the clear advantage of higher temporal resolution for monitoring the rate of dissipation of river valley fog/stratus features, as well as subsequent convective initiation and development.

GOES-14 0.63 µm visible channel images: Standard, RSO, and SRSOR scan strategies (click to play MP4 animation)

GOES-14 0.63 µm visible channel images: Standard, RSO, and SRSOR scan strategies (click to play MP4 animation)

Consecutive overpasses of the Suomi NPP satellite provided a look at the rapid rate of convective cloud development on VIIRS 0.64 µm visible channel images (below).

Suomi NPP VIIRS 0.64 µm visible channel images, with surface observations and frontal boundaries

Suomi NPP VIIRS 0.64 µm visible channel images, with surface observations and frontal boundaries

On a 18:59 UTC MODIS 11.0 µm IR channel image (below), the coldest cloud-top IR brightness temperature was -78º C near the West Virginia/Virginia border.

MODIS 11.0 µm IR channel image

MODIS 11.0 µm IR channel image

Fog and stratus along the California coast

March 14th, 2014

In their Area Forecast Discussion issued at 11:57 UTC or 4:57 AM local time on 14 March 2014, the NWS San Francisco/Monterey Bay Area forecast office mentioned the Suomi NPP VIIRS Day/Night Band imagery which showed the coverage of coastal fog in their area of responsibility:

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
457 AM PDT FRI MAR 14 2014

.DISCUSSION...AS OF 4:10 AM PDT FRIDAY...THE DRY TAIL END OF A
WEATHER SYSTEM MOVING IN TO THE PACIFIC NORTHWEST IS APPROACHING
OUR DISTRICT...AND RESULTING IN ENHANCEMENT OF THE MARINE LAYER
AND A RETURN OF THE MARINE STRATUS. LATEST GOES FOG PRODUCT
IMAGERY...AND IN RATHER SPECTACULAR DETAIL JUST REC`D SUOMI VIIRS
NIGHTTIME HIGH RES VISUAL IMAGE...SHOW COVERAGE ALONG MUCH OF THE
COAST FROM PT REYES SOUTH TO THE VICINITY OF THE MONTEREY
PENINSULA...AND A BROAD SWATH EXTENDING INLAND ACROSS SAN
FRANCISCO AND THROUGH THE GOLDEN GATE TO THE EAST BAY. LATEST
BODEGA BAY AND FT ORD PROFILER DATA INDICATE A MARINE LAYER DEPTH
OF ABOUT 1300 FT. SOME THIN HIGH CLOUDS ARE ALSO PASSING THROUGH ABOVE.

A comparison of AWIPS images of the Suomi NPP VIIRS 0.7 µm Day/Night Band (DNB) and the corresponding 11.45-3.74 µm IR brightness temperature difference (BTD) “fog/stratus product” (below) showed this band of fog and stratus at 09:39 UTC or 2:39 AM local time. With ample illumination by moonlight (the Moon was in the Waxing Gibbous phase, at 97% of full), the DNB image served as a “visible image at night” to help highlight the fog/stratus features along the coast. Farther inland over the eastern portion of the satellite scene, the bright signature of deep snow cover in the higher elevations of the Sierra Nevada was also very evident on the DNB image.

Suomi NPP VIIRS 0.7 µm Day/Night Band and IR BTD "Fog/stratus product" images

Suomi NPP VIIRS 0.7 µm Day/Night Band and IR BTD “Fog/stratus product” images

A sequence of three 1-km resolution IR BTD images (below) — Terra MODIS at 06:33 UTC, Suomi NPP VIIRS at 09:39 UTC, and Aqua MODIS at 10:44 UTC — offered detailed views of the inland progression of the fog/stratus features, especially in the San Francisco Bay area and also down the Salinas Valley. The appearance of degraded resolution of the features seen on the 10:44 UTC MODIS image is due to the so-called “bow-tie effect” near the edge of a MODIS scan swath — even with a bow-tie correction algorithm applied, the MODIS images tend to look less crisp and clear along the scan edges.

Terra MODIS, Suomi NPP VIIRS, and Aqua MODIS IR BTD "fog/stratus product" images

Terra MODIS, Suomi NPP VIIRS, and Aqua MODIS IR BTD “fog/stratus product” images

A GOES-R “Cloud Thickness – Highest Liquid Cloud Layer” product created using GOES-15 data (below; click image to play animation) showed the southward advancement of the band of fog/stratus during the overnight hours. The maximum thickness displayed was in excess of 1200 ft (lighter cyan color enhancement), which agreed well with the profiler depths mentioned in the NWS forecast discussion above.

GOES-15 Cloud Thickness product (click to play animation)

GOES-15 Cloud Thickness product (click to play animation)

Additional GOES-R products such as Marginal Visual Flight Rules (MVFR), Instrument Flight Rules (IFR), and Low Instrument Flight Rules (LIFR) Probability are shown below. These products help to better quantify the potential aviation impacts that features seen on the conventional BTD “fog/stratus product” might have.

GOES-15 MVFR Probability product (click to play animation)

GOES-15 MVFR Probability product (click to play animation)

GOES-15 IFR Probability product (click to play animation)

GOES-15 IFR Probability product (click to play animation)

GOES-15 LIFR Probability product (click to play animation)

GOES-15 LIFR Probability product (click to play animation)

For additional information on this event, see the GOES-R Fog Product Examples blog.

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

Persistent fog in British Columbia and the Pacific Northwest region of the US

October 22nd, 2013
Suomi NPP VIIRS IR brightness temperature difference "Fog/stratus product"

Suomi NPP VIIRS IR brightness temperature difference “Fog/stratus product”

A strong upper-level ridge of high pressure coupled with a moist, stagnant boundary layer led to the formation of widespread areas of fog for several days across much of the interior lowlands of western British Columbia and Washington State, along with valley fog in the Rocky Mountains farther to the east (as was documented during 21 October 2013 on the GOES-R Fog Product Examples blog). On 22 October 2013, two consecutive Suomi NPP VIIRS IR brightness temperature difference (BTD) “fog/stratus product” images (above) at 09:20 UTC (2:20 AM local time) and 10:58 UTC (3:58 AM local time) showed little change to the areal coverage of the fog/stratus located over the Puget Sound region and adjacent interior lowlands, but a significant growth of narrow fingers of valley fog from eastern British Columbia southward into far northern Washington, Idaho, and Montana.

A comparison of the 10:58 UTC VIIRS 0.7 µm Day/Night Band (DNB) image with the corresponding IR BTD fog/stratus product image (below) showcased the “visible image at night” capability of the Day/Night Band, given sufficient illumination by the Moon (which was in the Waning Gibbous phase, at 84% of Full). Not only are the fog (and other cloud) features evident in the DNB image, but the snow-covered higher elevations of the Rocky Mountains could also be seen. A number of ship tracks also appear over the Pacific Ocean in the far western portion of the satellite scene.

Suomi NPP VIIRS 0.7 um Day/Night Band and IR BTD "Fog/stratus product" images

Suomi NPP VIIRS 0.7 um Day/Night Band and IR BTD “Fog/stratus product” images

A post-sunrise sequence of GOES-15 (GOES-West) 0.63 µm visible channel images (below; click image to play animation) revealed that many of the fog features were very persistent and slow to dissipate — a strong boundary layer temperature inversion and light winds inhibited the rate of fog burn-off in those areas.

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

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

A comparison of two different AWIPS II false-color Red/Green/Blue (RGB) images (below) using VIIRS data at 20:44 UTC (1:44 PM local time) showed the value of using the 1.61 µm “snow/ice” channel to discriminate between snow cover (which appears as varying shades of red) and any fog, stratus, or other cloud features composed of water droplets (which appear as varying shades of white) in the area.

One other feature of interest can be seen on the VIIRS RGB images: in the far upper right corner, a pair of narrow aircraft dissipation trails (or “distrails”) can be seen within the broader band of mid-level supercooled water droplet clouds. As aircraft ascended (or descended) through the supercooled water droplet cloud layer, particles in the jet engine exhaust acted as ice condensation nuclei, causing thin streaks of the cloud to glaciate (hence their red appearance on the RGB image using the 1.61 µm VIIRS data) along the aircraft path. From the ground, these aircraft dissipation trails often appear as dramatic-looking “cirrus fall streaks”, as the larger, heavier ice crystals begin to descend from the supercooled cloud layer.

Suomi NPP VIIRS false-color RGB images (using Bands I1/I2/I5, and Bands I1/I3/I3)

Suomi NPP VIIRS false-color RGB images (using Bands I1/I2/I5, and Bands I1/I3/I3)