Fog and stratus clouds over the Pacific Northwest region of the US

January 20th, 2013 |
Suomi NPP VIIRS 0.64 µm visible channel and false-color Red/Green/Blue (RGB) image

Suomi NPP VIIRS 0.64 µm visible channel and false-color Red/Green/Blue (RGB) image

A comparison of AWIPS images of Suomi NPP VIIRS 0.64 µm visible channel and false-color Red/Green/Blue (RGB) images (above) showed areas of fog and stratus clouds over portions of the Pacific Northwest region of the US, the adjacent offshore waters of the Pacific Ocean, and far southwestern Canada at 20:15 UTC or 12:15 PM local time on 19 January 2013. On the false-color RGB image, snow cover appeared as darker shades of red, bare ground was varying shades of cyan, and fog and cloud features were brighter shades of white. Persistent high pressure over this region for several days led to strong temperature inversions that acted to trap the fog and stratus in lower elevations, leading to poor air quality at some locations.

During the following night-time hours, a comparison of 1-km resolution Suomi NPP VIIRS and 4-km resolution GOES IR brightness temperature difference (BTD) “fog/stratus product” images just after 10 UTC or 2 AM local time (below) indicated that many of the fog and low cloud features seen during the previous day had persisted into the night. The higher spatial resolution of the VIIRS image revealed ship tracks in the stratus deck offshore, and helped to better define the areal coverage of inland fog/stratus features (especially those in narrow river valleys).

Suomi NPP VIIRS and GOES IR brightness temperature difference

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

Although the “fog/stratus product” has some utility in locating those particular features, it cannot discriminate between fog on the ground and elevated stratus decks. However, examples of three Fog and Low Stratus (FLS) products that blend satellite data with model fields to offer more quantitative information are shown below: (1) Instrument Flight Rules (IFR) probability, (2) Low Instrument Flight Rules (LIFR) Probability, and (3) Cloud Thickness products. For the FLS features over Washington state, there were some areas where IFR probabilities were greater than 90%, LIFR probabilities were greater than 70%, and Cloud Thickness values were 1000 feet or greater. For the FLS feature located over southeastern Washington, these products would be valuable for aviation guidance purposes (given the relatively sparse network of observations in that part of the state).

GOES-15 IFR Probability product

GOES-15 IFR Probability product

GOES-15 Low IFR Probability product

GOES-15 Low IFR Probability product

GOES-15 Cloud Thickness product

GOES-15 Cloud Thickness product

A sequence of GOES-15 IFR Probability product images (below; click image to play animation) indicated that the areal coverage of higher IFR probability values had been gradually increasing during the 6 hour period leading up to 10:15 UTC or 2:15 AM local time.

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

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

Ground blizzard conditions across the north-central US

January 19th, 2013 |
Suomi NPP VIIRS 0.64 µm visible channel and False-color Red/Green/Blue images

Suomi NPP VIIRS 0.64 µm visible channel and False-color Red/Green/Blue images

A comparison of AWIPS images of Suomi NPP VIIRS 0.64 µm visible channel and the corresponding False-color Red/Green/Blue (RGB) composite (above) showed a number of horizontal convective roll clouds over parts of eastern North Dakota and northwestern Minnesota that had formed in response to strong northwesterly winds in the wake of an arctic cold frontal passage on 19 January 2013. On the false-color image, snow cover appeared as shades of red, bare ground was cyan, and cloud features were varying shades of white.

McIDAS images of GOES-13 0.63 µm visible channel data (below; click image to play animation) showed the development and evolution of the long horizontal convective roll clouds. Although new snowfall amounts on this day were very light (generally 0.5 inch or less), the strong northwesterly winds — with wind gusts as high as 61 mph in northwestern Minnesota, 59 mph in North Dakota, and 53 mph in northeastern South Dakota — created significant blowing snow that was reducing visibility to 1/4 mile or less across parts of the region. The blowing snow (along with some brief, heavy snow showers) tended to be more focused and intense in the vicinity of the horizontal convective rolls and their associated cloud streamers.

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

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

Baroclinic leaf and conveyor belt satellite signatures

January 17th, 2013 |
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

A comparison of AWIPS images of 1-km resolution MODIS 0.65 µm visible, 11.0 µm IR, and 6.7 µm water vapor channel data (above) showed a textbook example of a “baroclinic leaf” satellite signature associated with the large storm affecting much of the eastern US on 17 January 2013. The baroclinic leaf represents a region of ascending air that originates at low levels on the warm side of the primary surface cold front (18 UTC surface analysis).

4-km resolution GOES-13 6.5 µm water vapor channel images (below; click image to play animation) showed the development several important satellite signatures: (1) the baroclinic leaf; (2) the primary warm conveyor belt;, (3) the cold conveyor belt (which was helping to produce snow across parts of northern Mississippi and Alabama); and (4) a secondary warm conveyor belt after about 19 UTC. For additional information on conveyor belts, see this blog post from January 2011.

GOES-13 6.5 µm water vapor channel images (click image to play animation)

GOES-13 6.5 µm water vapor channel images (click image to play animation)

A McIDAS-V representation of the GOES-13 (GOES-East) water vapor image brightness temperatures as a topographical surface (below; click image to play animation; also available as a QuickTime movie) helps to visualize the descending intrusion of dry air (which exhibited warm brightness temperatures, yellow to orange color enhancement) and the ascending streams of moist air (which exhibited blue to white to green colors)  within the warm conveyor belt and baroclinic leaf structures.

GOES-13 6.5 µm water vapor images (click image to play animation)

GOES-13 6.5 µm water vapor images (click image to play animation)

Another McIDAS-V visualization (below; click image to play animation) shows the 3-dimensional structure of the various jet streams (cyan isosurface of 50 meters per second or higher winds) and the increasing values and ascending height of moisture (mixing ratio) within the primary warm conveyor belt as the cross section slice is moved from south to north. McIDAS-V images courtesy of Joleen Feltz and Mike Hiley (CIMSS).

GOES-13 water vapor image with Rapid Refresh model fields of wind speed and mixing ratio (click image to play animation)

GOES-13 water vapor image with Rapid Refresh model fields of wind speed and mixing ratio (click image to play animation)

Early in the day, a SIGMET was issued (below) to outline an area of risk for severe turbulence due to wind shear near the axis of the strong jet stream associated with this developing system.

GOES-13 6.5 µm water vapor image with outline of Turbulence SIGMET and Pilot reports of turbulence

GOES-13 6.5 µm water vapor image with outline of Turbulence SIGMET and Pilot reports of turbulence

===== 18 January Update =====

A comparison of AWIPS images of Suomi NPP VIIRS 0.64 µm visible channel and the corresponding VIIRS false-color Red/Green/Blue (RGB) image (below) aided in the discrimination of the resulting snow cover from the storm (shades of red) versus clouds (shades of white).

Suomi NPP VIIRS 0.64 µm visible channel and False-color Red/Green/Blue (RGB) images

Suomi NPP VIIRS 0.64 µm visible channel and False-color Red/Green/Blue (RGB) images

 

Sea ice motion in the Arctic Ocean

January 15th, 2013 |
Suomi NPP VIIRS 11.45 µm IR images (click image to play animation)

Suomi NPP VIIRS 11.45 µm IR images (click image to play animation)

A sequence of AWIPS images of Suomi NPP VIIRS 11.45 µm IR data from 13 January to 15 January 2013 (above; click image to play animation) revealed a great deal of motion of the sea ice in the Arctic Ocean off the north coast of Alaska. Surface stations along the Alaskan coast were reporting strong easterly winds during this time period, with gusts in excess of 40-50 knots — these strong winds were helping to push the sea ice westward. Also evident in the images was the relatively warm signature (cyan to yellow color enhancement) exibited by numerous “cracks” in the sea ice — it is unclear whether these features are simply weaknesses in the thick ice pack, or actual leads of open water.