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.

Dust storm over the central and southern High Plains region

March 11th, 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)

AWIPS images of GOES-13 0.63 µm visible channel data (above; click image to play animation) show the hazy signature of an intense dust storm (sometimes locally referred to as a “haboob”) created by strong winds in the wake of a southward-moving cold front on 11 March 2014. This blowing dust reduced surface visibility to zero in parts of southwestern Kansas (where there were wind gusts of 59 mph), causing several traffic accidents. At Amarillo, Texas (KAMA) the wind gusted to 60 mph, and visibility was reduced to 0.25 mile at times. A pilot report indicated that the top of the blowing dust was as high as 11,000 feet over the Oklahoma panhandle region.

A sequence of Terra/Aqua MODIS and Suomi NPP VIIRS true-color Red/Green/Blue (RGB) images visualized using the SSEC RealEarth web map server (below) showed the southward advancement of the lighter tan colored areas of blowing dust.

Terra/Aqua MODIS and Suomi NPP VIIRS true-color RGB images

Terra/Aqua MODIS and Suomi NPP VIIRS true-color RGB images

A signal of the airborne dust (cyan color enhancement) was also seen on Terra/Aqua MODIS images of the 11-12 µm “reverse absorption” IR difference product (below).

MODIS 11-12 µm "reverse absorption" IR difference product

MODIS 11-12 µm “reverse absorption” IR difference product

GOES-13 6.5 µm water vapor channel images (below; click image to play animation) showed the development of a “cirrus bloom” over far northeastern New Mexico as the surface cold front and blowing dust moved through that region. It is interesting to note that there was a pilot report of severe turbulence at an altitude of 45,000 feet around that time (reportedly due to a mountain wave) — this raises the question as to whether a vertically-propagating wave generated by the strong cold front might have caused that high-altitude turbulence.

GOES-13 6.5 µm water vapor channel images, with pilot reports of turbulence (click to play animation)

GOES-13 6.5 µm water vapor channel images, with pilot reports of turbulence (click to play animation)

Additional satellite images of this event can be found on the Wide World of SPoRT blog.

===== 12 March Update =====

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

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

During the subsequent night-time hours, a Suomi NPP VIIRS 0.7 µm Day/Night Band image at 08:35 UTC or 2:35 AM local time (above) displayed a signature of the airborne dust over far southwestern Texas — the glow of the city lights below the dust layer was more diffuse than in dust-free areas farther to the east in central Texas. Also note that an undular bore had formed along the cold frontal boundary near the coast of southeast Texas.

A comparison of the VIIRS Day/Night Band image with a MODIS 11-12 µm image (below) confirmed the presence of airborne dust over southwestern Texas. As in the MODIS example above, the brighter cyan color enhancement was a signal of dust.

Suomi NPP VIIRS 0.7 µm Day/Night Band and MODIS 11-12 µm IR difference product images

Suomi NPP VIIRS 0.7 µm Day/Night Band and MODIS 11-12 µm IR difference product images

Strong storm off the coast of California

February 28th, 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)

McIDAS images of 4-km resolution GOES-15 6.5 µm water vapor channel data (above; click image to play animation; also available as an MP4 animation) showed the development of a strong and rapidly-occluding storm off the coast of California during the 27 February28 February 2014 period.

An AWIPS image of 17:30 UTC GOES-15 water vapor channel data with overlays of 17:28 UTC Metop ASCAT surface scatterometer winds and the 18:00 UTC tropical surface analysis (below) showed satellite-sensed surface winds as strong as 51 knots in the southwestern quadrant of the storm.

GOES-15 6.5 µm water vapor channel image with ASCAT surface scatterometer winds and surface analysis

GOES-15 6.5 µm water vapor channel image with ASCAT surface scatterometer winds and surface analysis

Greater detail in the storm structure could be seen in 1-km resolution MODIS 6.7 µm water vapor channel images at 10:32 UTC and 21:40 UTC (below).

MODIS 6.7 µm water vapor channel images

MODIS 6.7 µm water vapor channel images

One indication of the strength of the storm was the high amounts of GOES-15 sounder Total Column Ozone associated with the circulation (below; click image to play animation), which reached levels as high as 440-450 Dobson Units (lighter red color enhancement). Such high levels of total column ozone are also often associated with potential vorticity anomalies and a dramatically lowered tropopause — in this case, the GFS40 model indicated the the dynamic tropopause (taken to be the pressure of the PV1.5 surface) was as below the 480 hPa pressure level at 18:00 UTC. It is interesting to note that there was a pilot report of moderate turbulence at 36,000 feet, along the sharp western gradient of the total column ozone (and the sharp gradient of the PV1.5 pressure) — the pilot noted that the turbulene lasted for 10 minutes.

GOES-15 sounder Total Column Ozone product (click to play animation)

GOES-15 sounder Total Column Ozone product (click to play animation)

A comparison of 375-meter resolution Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images at 22:08 UTC (below) revealed a few convective elements offshore which exhibited cloud-top IR brightness temperatures as cold as -50º C (yellow color enhancement), with a few cloud-to-ground lightning strikes being detected.

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images (with cloud-to-ground lightning strikes)

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images (with cloud-to-ground lightning strikes)

===== 01 March Update =====

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel images

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel images

A comparison of Suomi NPP VIIRS 0.7 µm Day/Night Band (DNB) and 11.45 µm IR channel images at 10:22 UTC or 2:22 AM local time on 01 March (above) revealed the presence of numerous arc-shaped mesospheric airglow waves in the western semicircle of the storm circulation on the DNB image — note that there was no corresponding wave signature on the IR image.

These vertically-propagating mesospheric airglow waves were likely generated by the 140-knot jet streak that was moving southward around the rear side of the storm  (below).

Suomi NPP VIIRS 0.7 µm Day/Night Band image with NAM 250 hPa winds and isotachs

Suomi NPP VIIRS 0.7 µm Day/Night Band image with NAM 250 hPa winds and isotachs

Severe turbulence over Wyoming

February 17th, 2014
MODIS 6.7 µm water vapor channel image, with pilot reports of turbulence

MODIS 6.7 µm water vapor channel image, with pilot reports of turbulence

United Airlines flight 1676 enroute from Denver, Colorado KDEN to Billings, Montana KBIL (flight track) encountered severe turbulence at an altitude of 34,000 feet over Wyoming on 17 February 2014. Three crew members and two passengers were injured, and taken to hospitals upon landing in Billings. An AWIPS image of 1-km resolution Aqua MODIS 6.7 µm water vapor channel data (above) showed a number of pilot reports of moderate turbuence over Wyoming between the altitudes of 33,000 and 45,000 feet around that time; the United 1676 pilot report of severe turbulence is highlighted in red.

On the MODIS water vapor image, note the appearance of distinct signatures of non-parallel mountain waves just to the east of that turbulence plot (in the vicinity of KIDV) — these closely-spaced bands of descending dry air (darker blue to yellow color enhancement) and ascending moist air (lighter blue to pale white color enhancement) were just east (downwind) of the Bighorn Mountains. The corresponding MODIS 0.65 µm visible channel and 11.0 µm IR channel images (below) showed that there were no cloud features associated with the entire extent of these mountain waves — they were were essentially occurring in “clear air”. This example demonstrates the value of high spatial resolution water vapor imagery for helping to identify signatures of potential clear air turbulence.

MODIS 0.65 µm visible channel, 11.0 µm IR channel, and 6.7 µm water vapor channel images

MODIS 0.65 µm visible channel, 11.0 µm IR channel, and 6.7 µm water vapor channel images

An animation of 4-km resolution GOES-13 6.5 µm water vapor channel images (below; click image to play animation) showed that there were numerous other reports of moderate and even severe turbulence over Wyoming between about 20:00 UTC and 23:40 UTC. On the final 23:40 UTC image, there was a pilot report of severe turbulence as high as 47,000 feet in that same general area. The mountain wave signature to the lee of the Bighorn Mountains was not stationary, but was seen to exhibit some meandering during that time period.

GOES-13 6.5 µm water vapor channel images, with pilot reports of turbulence (click to play animation)

GOES-13 6.5 µm water vapor channel images, with pilot reports of turbulence (click to play animation)