The trans-Atlantic flow of moisture and strong winds

January 14th, 2015
SSEC RealEarth™ Infrared satellite image featured on NBC Nightly News

SSEC RealEarth™ Infrared satellite image featured on NBC Nightly News

The SSEC RealEarth geostationary satellite infrared (IR) image composite shown above (which was first sent out via Twitter by Stu Ostro of The Weather Channel…thanks Stu!) was featured on the NBC Nightly News on 14 January 2015 (link) because it illustrated a vivid example of the trans-Atlantic flow of moisture from a disturbance off the US East Coast to a rapidly-deepening storm approaching the British Isles (surface analysis maps | water vapor images with surface analyses).

A sequence of hourly geostationary satellite water vapor channel image composites (below; click to play animation) showed that there was a clear trans-Atlantic connection in terms of middle to upper tropospheric moisture/clouds, and a comparison of the 20 UTC water vapor image with the corresponding MIMIC Total Precipitable Water product indicated that there was a lower to middle tropospheric moisture connection as well. This type of long and narrow fetch of TPW is often referred to as an “atmospheric river”.

Geostationary satellite water vapor image composites (click to play animation)

Geostationary satellite water vapor image composites (click to play animation)

Another interesting point brought up during the NBC Nightly News segment was the recent presence of unusually strong trans-Atlantic jet stream winds, which has allowed aircraft flying from New York City to London to set record times in terms of conventional passenger aircraft (such as the 08 January flight of British Airways 114). Note the strong dry-to-moist (darker blue to white to green color enhancement) along the northern edge of the trans-Atlantic water vapor image moisture feed: such a moisture gradient often coincides with the axis of a strong jet stream. AWIPS images of water vapor imagery with overlays of MADIS cloud-tracked and water-vapor-tracked winds (below; click image to play animation) showed many high-altitude wind vectors in the vicinity of the jet stream moisture gradient with speeds in the 150-160 knot range (with 175 knots seen on the previous day).

Water vapor images with MADIS atmospheric motion vectors (click to play animation)

Water vapor images with MADIS atmospheric motion vectors (click to play animation)

Tropical Cyclone Bansi in the Indian Ocean

January 13th, 2015
Advanced Dvorak Technique (ADT) intensity estimate

Advanced Dvorak Technique (ADT) intensity estimate

A plot of the Advanced Dvorak Technique intensity estimate for Tropical Cyclone Bansi (above) showed that the storm experienced a period of rapid intensification late in the day on 12 January 2015, reaching Category 4 intensity by 00 UTC on 13 January.

EUMESAT Metosat-7 11.5 µm IR channel images (below; click to play animation; also available as an MP4 movie file) revealed the formation of a well-defined eye, which also exhibited a notable amount of trochoidal motion or “wobble” as it moved across the southwest Indian Ocean (north of Reunion and Mascarene Island).

Meteosat-7 11.5 µm IR channel images (click to play animation)

Meteosat-7 11.5 µm IR channel images (click to play animation)

A more detailed view of Tropical Cyclone Bansi was provided by McIDAS-V images of Suomi NPP VIIRS 11.45 µm IR and 0.7 µm Day/Night Band data (below; credit: William Straka, SSEC) — deep convection with overshooting tops could be seen in the southern quadrant eyewall region, with gravity waves propagating radially outward across the northeastern and eastern portion of the cirrus canopy.

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

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

A DMSP SSMIS 85 GHz microwave image from the CIMSS Tropical Cyclones site (below) showed that a prominent “moat” of warm brightness temperatures (darker blue color enhancement) existed around the center of Bansi at 14:24 UTC on 13 January. The presence of such a moat usually signifies that the secondary (outer) eyewall formation process has completed, and an eyewall replacement cycle is underway (also signalling that the period of rapid intensification has ended). The moat feature is sustained by subsidence from the eyewall secondary circulations.

DMSP SSMIS 85 GHz microwave image

DMSP SSMIS 85 GHz microwave image

Note that there was no well-defined eye evident on the conventional Meteosat-7 IR image during this eyewall replacement cycle (below).

Meteosat-7 11.5 µm IR channel and DMSP SSMIS 85 GHz microwave images

Meteosat-7 11.5 µm IR channel and DMSP SSMIS 85 GHz microwave images

Storm “Nina” affects the northern British Isles and Norway

January 10th, 2015
Meteosat-10 6.25 µm water vapor channel images (click to play animation)

Meteosat-10 6.25 µm water vapor channel images (click to play animation)

The intense extratropical cyclone referred to in Norway as “Extreme Weather Nina” was described as the strongest storm to hit the western part of that country in 20 years, bringing high winds that caused widespread tree and property damage, disrupted power for an estimated 170,000 people, and halted some forms of transportation on 10 January 2015 (The Nordic Page). EUMETSAT Meteosat-10 6.25 µm water vapor channel images (above; click image to play animation; also available as an MP4 movie file) showed the well-defined circulation of the storm, which included a “scorpion tail” signature (10 UTC image) over the North Sea west of Norway suggesting that a sting jet feature may have been present. About 3 hours after the leading edge of this middle-tropospheric sting jet signature moved over Haugesund, winds there gusted to 71 knots/36.5 meters per second. Winds gusted as high as 89 knots/45.7 meters per second at the offshore oil platform Gullfax, and the Flesland airport at Bergen was briefly closed due to strong winds (which peaked at 65 knots/33.4 meters per second). In the northern British Isles, wind gusts as strong as 70 knots/36 meters per second were reported on Shetland Island, along with thunderstorms (water vapor image with 4-letter station identifier locations).

Meteosat-10 0.8 µm High Resolution Visible images (below; click image to play animation; also available as an MP4 movie file) revealed the development of numerous showers and thunderstorms across the southern sector of the storm.

Meteosat-10 0.8 µm High Resolution Visible images (click to play animation)

Meteosat-10 0.8 µm High Resolution Visible images (click to play animation)

A SSEC RealEarth Suomi NPP VIIRS true-color Red/Green/Blue (RGB) image around 12:00 UTC (below) showed the storm center just off the west coast of Norway.

Suomi NPP VIIRS true-color image

Suomi NPP VIIRS true-color image

Horizontal convective rolls: a satellite signature of blowing snow and ground blizzard conditions

January 8th, 2015
GOES-13 0.63 µm visible channel images with METAR surface reports (click to play animation)

GOES-13 0.63 µm visible channel images with METAR surface reports (click to play animation)

An Alberta Clipper disturbance quickly moved through the north-central US during the day on 08 January 2014, leaving only light amounts of snowfall (generally 1 inch or less). However, very strong winds in the wake of the system (with gusts as high as 59 mph at Bismarck, North Dakota and 69 mph at Bullhead, South Dakota) produced ground blizzard conditions as the newly-fallen light, fluffy snow was lofted and organized into long horizontal convective roll features. GOES-13 0.63 µm visible channel images with overlays of METAR surface reports (above; click image to play animation) and overlays of cloud ceilings and surface visibility (below; click image to play animation) distinctly showed the widespread horizontal convective rolls, along with their effect on the weather as they moved near or over various locations.

GOES-13 0.63 µm visible channel images with cloud ceilings and surfaces visibilities (click to play animation)

GOES-13 0.63 µm visible channel images with cloud ceilings and surfaces visibilities (click to play animation)

One question that arises is: are these horizontal convective roll features clouds, or simply highly-concentrated areas of blowing snow, or perhaps a little of both? A comparison of Suomi NPP VIIRS 0.64 µm visible channel, 3.74 µm shortwave IR, and 11.45 µm IR images at 19:00 UTC (below) might shed some light on the topic. As seen on the GOES-13 visible images, many of the roll features were tall enough to cast a shadow — this suggests vertical mixing to the top of the boundary layer, which appeared to be about 1 km deep on the morning Bismarck ND rawinsonde report. A few sites reported heavy snow (reducing visibility as low as 0.15 mile) as a horizontal convective roll moved overhead — however, the 11.45 µm IR brightness temperatures were barely colder than -20 to -25º C for even the most well-defined roll features (so their ability to produce heavy snow seems dubious). On the 3.74 µm shortwave IR image, if supercooled water droplet clouds had formed at the top of the roll features, they would appear darker (due to the reflection of solar radiation off the supercooled cloud droplets) — but this is not the case.

Suomi NPP VIIRS 0.64 µm visible channel, 3.74 µm shortwave IR channel, and 11.45 µm IR channel images

Suomi NPP VIIRS 0.64 µm visible channel, 3.74 µm shortwave IR channel, and 11.45 µm IR channel images

Suomi NPP VIIRS true-color Red/Green/Blue (RGB) images from the SSEC RealEarth web map server (below) demonstrated the value of overlaying Google Maps information, for example to see which highways might be impacted by the larger and more well-organized horizontal convective rolls at that particular time.

Suomi NPP VIIRS true-color RGB images

Suomi NPP VIIRS true-color RGB images