Standing wave clouds over Virginia and North Carolina

March 7th, 2019 |

GOES-16

GOES-16 “Red” Visible (0.64 µm), “Clean” Infrared Window (10.3 µm), Cloud Top Height, Cloud Particle Size Distribution, and Cloud Phase [click to play animation | MP4]

GOES-16 (GOES-East) “Red” Visible (0.64 µm), “Clean” Infrared Window (10.3 µm), Cloud Top Height, Cloud Particle Size Distribution, and Cloud Phase (above) helped to characterize standing wave clouds that developed to the lee of the Appalachian Mountains on 07 March 2019. The primary standing wave rotor clouds were composed of smaller supercooled water droplets,  with “banner clouds” composed of larger/colder ice crystals forming downwind of the rotor clouds. For example, at 1637 UTC cloud particle sizes associated with the rotor clouds were as small as 3-10 µm (darker shades of purple).

GOES-16 Day Cloud Phase Distinction Red-Green-Blue (RGB) images from the AOS site (below) also identified the rotor clouds as supercooled water droplet features (brighter shades of white), with the banner clouds being identified as high-level ice (shades of pink) or glaciating (shades of green) features. An unrelated phenomena was the brief brightening of the bare ground across much of the Southeast US midway through the animation — a result of transient solar reflectance that is seen around the Spring and Autumn equinox.

GOES-16 Day Cloud Phase Distinction RGB images [click to play animation | MP4]

GOES-16 Day Cloud Phase Distinction RGB images [click to play animation | MP4]

In a comparison of 1-km resolution Terra MODIS Visible (0.65 µm), Near-Infrared “Cirrus” (1.37 µm), Shortwave Infrared (3.7 µm) and Infrared Window (11.0 µm) images at 1631 UTC (below), note that the standing wave rotor clouds appeared much warmer (darker gray) in the Shortwave Infrared images — this is due to the fact that small supercooled water droplets are very efficient reflectors of incoming solar radiation.

Terra MODIS Visible (0.65 µm), Near-Infrared

Terra MODIS Visible (0.65 µm), Near-Infrared “Cirrus” (1.37 µm), Shortwave Infrared (3.7 µm) and Infrared Window (11.0 µm) images [click to enlarge]

There were a few pilot reports of light to moderate turbulence in the general vicinity of the standing waves, especially around 14 UTC (below).

Terra MODIS Visible (0.65 µm) image, with pilot reports of turbulence [click to enlarge]

Terra MODIS Visible (0.65 µm) image, with pilot reports of turbulence [click to enlarge]

Turbulence over the western United States

February 13th, 2019 |

GOES-17 Low-Level Water Vapor Imagery (7.3 µm) on 13 February 2019, 1932-2012 UTC (Click to animate)

A strong storm system affecting the western third of the United States on 13 February 2019 was responsible for turbulence that caused damage and injuries and forced an ERJ-170 aircraft flying from John Wayne Airport (in Orange County CA) to Seattle WA to make an unscheduled stop in Reno NV (News report). (Flight Aware information on the flight) Three passengers were hospitalized.

The water vapor imagery animation above, annotated so that the departure airport (SNA) and Reno (RNO) are shown in the first frame. During the second run-through of the animation, the approximate location of the turbulence is noted with a red square (Flight Aware data suggests it occurred very near 2030 UTC — Flight Aware times are EST), and the animation slows. Water Vapor imagery suggests that the aircraft encountered a convective element that likely was associated with the Sierra Nevada. A stepped animation between 2027 and 2032 UTC is shown below.

GOES-17 Low-Level Water Vapor Imagery (7.3 µm) on 13 February 2019, 2027 and 2032 UTC (Click to enlarge)

Cloud-top waves producing turbulence north of Hawai’i

February 6th, 2019 |
GOES-17 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images [click to play MP4 animation]

GOES-17 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images [click to play MP4 animation]

* GOES-17 images shown here are preliminary and non-operational *

Transient pockets of cloud-top waves were evident on GOES-17 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (above) north of Hawai’i on 06 February 2019. Some of the waves were located along the tops of convective cloud features, while others appeared to be randomly distributed.

Plots of rawinsonde data from Lihue, Hawai’i (below) showed that winds within the middle to upper troposphere had a general westerly component — so these mesoscale cloud-top wave features were oriented perpendicular to the flow.

Plots of rawinsonde data from Lihue, Hawai'i [click to enlarge]

Plots of rawinsonde data from Lihue, Hawai’i [click to enlarge]

There was only 1 pilot report of turbulence within the broad region exhibiting these waves, occurring at 2304 UTC at an altitude of 33,000 feet — and this appeared to coincide with a discrete wave packet that was propagating eastward (below).

GOES-17 Upper-level Water Vapor (6.2 µm) images within 30 minutes of the 2304 UTC pilot report of turbulence [click to enlarge]

GOES-17 Upper-level Water Vapor (6.2 µm) images within 30 minutes of the 2304 UTC pilot report of turbulence [click to enlarge]

While the more robust wave packets could also be seen in GOES-17 “Clean” Infrared Window (10.3 µm) images (below), their complete areal coverage was more obvious in the Water Vapor imagery — particularly where the wave features were more subtle.

GOES-17 Upper-level Water Vapor (6.2 µm) and “Clean” Infrared Window (10.3 µm) images at 2302 UTC [click to enlarge]

Aviation advisories for Significant Weather (SIGWX) had been issued for that region (below), which included a Moderate risk for Clear Air Turbulence (CAT) from 28,000-39,000 feet and the possibility of isolated/embedded Cumulonimbus (CB) clouds with tops to 38,000 feet, along with a west-northwest high-level jet stream from 290º at 90 knots. The pilot report of turbulence at 33,000 feet included winds from 261º at 81 knots.

GOES-17 Upper-level Water Vapor (6.2 µm) image, with plots of aviation Significant Weather advisories [click to enlarge]

GOES-17 Upper-level Water Vapor (6.2 µm) image, with plots of aviation Significant Weather advisories that were in effect at that time [click to enlarge]

The cloud-top waves were also seen in a sequence of VIIRS Infrared Window (11.45 µm) images from NOAA-20 and Suomi NPP, viewed using RealEarth (below).

VIIRS Infrared Window (11.45 µm) images from NOAA-20 (at 2230 and 0030 UTC) and Suomi NPP (at 2320 UTC) [click to enlarge]

VIIRS Infrared Window (11.45 µm) images from NOAA-20 (at 2230 and 0030 UTC) and Suomi NPP (at 2320 UTC) [click to enlarge]

Orographic standing wave cloud over the Mid-Atlantic states

December 17th, 2018 |

Topography + GOES-16 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images, with pilot reports of turbulence [click to play MP4 animation]

Topography + GOES-16 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images, with pilot reports of turbulence [click to play MP4 animation]

GOES-16 (GOES-East) Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (above) showed the development of an orographic standing wave cloud — downwind of the Appalachian Mountains (topography) — over the Mid-Atlantic states on 17 December 2018. North of the wave cloud, widespread short-wavelength mountain waves were seen at lower elevations over and to the lee of the high terrain (even extending out over the Atlantic Ocean off the coast of New Jersey and New York). There were scattered pilot reports of turbulence across the region, with Severe turbulence being reported around 18 UTC and 00 UTC.

A comparison of GOES-16 Mid-level Water Vapor, Cloud Top Phase and Cloud Top Height products at 2007 UTC (below) indicated that this wave cloud was composed of Cirrus with maximum cloud tops around 30,000 feet.

GOES-16 Mid-level Water Vapor (6.9 µm), Cloud Top Phase and Cloud Top Height products [click to enlarge]

GOES-16 Mid-level Water Vapor (6.9 µm), Cloud Top Phase and Cloud Top Height products [click to enlarge]

GOES-16 Mid-level Water Vapor (6.9 µm) image at 2102 UTC, showing the orientation of a nortwest-southeast cross section [click to enlarge]

GOES-16 Mid-level Water Vapor (6.9 µm) image at 2102 UTC, showing the orientation of a northwest-southeast cross section [click to enlarge]

A GOES-16 Water Vapor image at 2102 UTC (above) showed the orientation of a northwest-to-southeast cross section of RUC40 model Relative Humidity, Wind Speed and Adiabatic Omega fields (below). In the middle of the cross section, a couplet of downward/upward motion aloft was seen over the Glen Allen VA area, with higher relative humidity values (shades of blue) above the 500 hPa pressure level corresponding to the wave cloud.

Northwest-southeast cross section of RUC40 model Relative Humidity, Wind Speed and Adiabatic Omega [click to enlarge]

Northwest-southeast cross section of RUC40 model Relative Humidity, Wind Speed and Adiabatic Omega [click to enlarge]

The standing wave cloud developed in the exit region of a branch of the polar jet stream that was diving southeastward across the Great Lakes — strong deceleration created an axis of deformation oriented from southwest to northeast (below), helping the stretch the wave cloud  feature as it slowly pivoted toward the southeast and along the coast. The strong downward motion component of the Omega couplet seen in the cross section was responsible for the relatively sharp upwind (northwest) edge exhibited by the wave cloud.

GOES-16 Mid-level Water Vapor (6.9 µm) images, with RAP40 model 250 hPa isotachs and deformation vectors [click to play animation | MP4]

GOES-16 Mid-level Water Vapor (6.9 µm) images, with RAP40 model 250 hPa isotachs and deformation vectors [click to play animation | MP4]

A toggle between NOAA-20 VIIRS True Color Red-Green-Blue (RGB) and Infrared Window (11.45 µm) images viewed using RealEarth (below) provided a detailed view of the wave cloud at 1825 UTC. The coldest cloud-top infrared brightness temperatures were around -50ºC (bright yellow enhancement), which was just above the 300 hPa pressure level on 00 UTC soundings at Roanoke/Blacksburg and Wallops Island Virginia.

NOAA-20 VIIRS True Color RGB and Infrared Window (11.45 µm) images [click to enlarge]

NOAA-20 VIIRS True Color RGB and Infrared Window (11.45 µm) images [click to enlarge]

As pointed out by Jonathan Blaes (NWS Raleigh), these standing wave clouds can have an effect on surface temperatures beneath the feature:



A comparison of 1812 UTC Aqua MODIS Visible (0.65 µm), Infrared Window (11.0 µm), Near-Infrared “Cirrus” (1.37 µm) and Water Vapor (6.7 µm) images with plots of maximum temperatures on 17 December (below) revealed that high temperatures were confined to the upper 50s F beneath the wave cloud, in contrast to low 60s F on either side where incoming solar radiation was not diminished.

Aqua MODIS Visible (0.65 µm), Infrared Window (11.0 µm), Near-Infrared "Cirrus" (1.37 µm) and Water Vapor (6.7 µm) images, with plots of maximum temperatures on 17 December [click to enlarge]

Topography + Aqua MODIS Visible (0.65 µm), Infrared Window (11.0 µm), Near-Infrared “Cirrus” (1.37 µm) and Water Vapor (6.7 µm) images, with plots of maximum temperatures on 17 December [click to enlarge]