Waves over the Upper Midwest / Great Lakes

June 23rd, 2018 |

GOES-16

GOES-16 “Red” Visible (0.64 µm) images, with hourly plots of surface reports [click to play animation]

GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) revealed a curious pattern of waves moving east-northeastward across a patch of mid-level clouds over central Lake Michigan during the morning hours on 23 June 2018.

In an effort to determine the vertical extent of these waves, a look at GOES-16 Low-level Water Vapor (7.3 µm), Mid-level Water Vapor (6.9 µm) and Upper-level Water Vapor (6.2 µm) images from the UW-Madison AOS site (below) showed a signature of waves propagating northeastward across the region during the 0802-2102 UTC time period.

GOES-16 Low-level Water Vapor (7.3 µm) images [click to play MP4 animation]

GOES-16 Low-level Water Vapor (7.3 µm) images [click to play MP4 animation]

GOES-16 Mid-level Water Vapor (6.9 µm) images [click to play MP4 animation]

GOES-16 Mid-level Water Vapor (6.9 µm) images [click to play MP4 animation]

GOES-16 Upper-level Water Vapor (6.2 µm) images [click to play MP4 animation]

GOES-16 Upper-level Water Vapor (6.2 µm) images [click to play MP4 animation]

There also were scattered pilot reports of light to moderate turbulence across the region as these waves were moving through, including one report of continuous Clear Air Turbulence at 36,000 feet over eastern Wisconsin.  Due to the subtle nature of these waves, their signature was not as obvious in the 8-bit McIDAS-X Water Vapor images shown below as they were in 16-bit imagery displayed above (or what would be displayed using AWIPS II).

GOES-16 Low-level (7.3 µm) images, with hourly pilot reports of turbulence [click to play animation]

GOES-16 Low-level Water Vapor (7.3 µm) images, with hourly pilot reports of turbulence [click to play animation]

GOES-16 Mid-level (6.9 µm) images, with hourly pilot reports of turbulence [click to play animation]

GOES-16 Mid-level Water Vapor (6.9 µm) images, with hourly pilot reports of turbulence [click to play animation]

GOES-16 Upper-level (6.2 µm) images, with hourly pilot reports of turbulence [click to play animation]

GOES-16 Upper-level Water Vapor (6.2 µm) images, with hourly pilot reports of turbulence [click to play animation]

The waves were passing over eastern Wisconsin around the time of ascent of the 12 UTC sounding balloon launched from Green Bay (and continuous turbulence was reported at 38,000 feet) — a plot of weighting functions for the three GOES-16 Water Vapor bands (below) showed peak pressures in the 424-328 hPa (22,800-28,885 feet) range, although significant contributions of energy were still evident from the 300 hPa pressure level (31,000 feet) or higher.

GOES-16 Water Vapor weighting functions, calculated using 12 UTC rawinsonde data from Green Bay, Wisconsin [click to enlarge]

GOES-16 Water Vapor weighting functions, calculated using 12 UTC rawinsonde data from Green Bay, Wisconsin [click to enlarge]

About an hour prior to the start of the 2-km resolution (at nadir or sub-satellite point) GOES-16 Water Vapor animations, 1-km resolution Aqua MODIS Water Vapor (6.7 µm) imagery at 0801 UTC (below) showed a long narrow wave packet (oriented northwest to southeast) from far western Wisconsin to central Illinois — and these waves were also apparent along the tops of mid-level clouds along the Iowa/Illinois border. Was this the leading edge of the waves seen farther northeast over the Great Lakes during the subsequent morning and afternoon hours?

Aqua MODIS Water Vapor (6.7 µm) and Infrared Window (11.0 µm) images, with plots of pilot reports [click to enlarge]

Aqua MODIS Water Vapor (6.7 µm) and Infrared Window (11.0 µm) images, with plots of pilot reports [click to enlarge]

All things considered, the lack of a clear forcing mechanism for these waves qualifies this case to be placed into the “What the heck is this” blog category until a coherent explanation can be put forward…

High cloud shadow over eastern Iowa

June 18th, 2018 |

It’s always good to get a question that lends itself well to the “What the heck is this?” blog category. The answer, as is often the case, relies on an examination of imagery from a variety of GOES-16 ABI bands.  To begin, note the darker feature seen on 1-minute Mesoscale Domain Sector GOES-16 “Blue” Visible (0.47 µm), “Red” Visible (0.64 µm) and Near-Infrared “Vegetation” (0.86 µm) images (below), which was moving northeastward across eastern Iowa and passing just to the west of Waterloo (KALO) on the morning of 18 June 2018.

GOES-16 "Blue" Visible (0.47 µm), "Red" Visible (0.64 µm) and Near-Infrared "Snow/Ice" (1.61 µm) images

GOES-16 “Blue” Visible (0.47 µm, left), “Red” Visible (0.64 µm, center) and Near-Infrared “Vegetation” (0.86 µm, right) images [click to play animation | MP4]

To explore the initial hypothesis that this might be a shadow from a higher-altitude cloud feature, GOES-16 Near-Infrared “Cirrus” (1.37 µm), Mid-level Water Vapor (6.9 µm) and Upper-level Water Vapor (6.2 µm) images were examined (below), which did indeed reveal a small cloud element aloft that was drifting in the same direction as the darker feature seen above.

GOES-16 Near-Infrared

GOES-16 Near-Infrared “Cirrus” (1.37 µm, left), Mid-level Water Vapor (6.9 µm, center) and Upper-level Water Vapor (6.2 µm, right) images [click to play animation | MP4]

Finally, a comparison of GOES-16 Near-Infrared “Cirrus” (1.37 µm), Shortwave Infrared (3.9 µm) and “Clean” Infrared Window (10.3 µm) images (below) showed that this small (and likely thin) high-altitude cloud exhibited no signature in the Shortwave Infrared, but did exhibit a 10.3 µm brightness temperature as cold as -20ºC (cyan enhancement) at times.

GOES-16 Near-Infrared

GOES-16 Near-Infrared “Cirrus” (1.37 µm, left), Shortwave Infrared (3.9 µm, center) and “Clean” Infrared Window (10.3 µm, right) images [click to play animation | MP4]

12 UTC rawinsonde data from Davenport, Iowa (below) showed southwesterly winds and an air temperature just below -20ºC at an altitude of around 9.6 km.

12 UTC rawinsonde data from Davenport, Iowa [click to enlarge]

12 UTC rawinsonde data from Davenport, Iowa [click to enlarge]

Thanks to Andrew Ansorge (NWS DMX) and Rich Mamrosh (NWS GRB) for alerting us to this interesting feature!

Upwind-propagating bore over southern Lake Michigan

June 1st, 2018 |

GOES-16 Visible (0.64 µm) Visible Imagery at 1-minute intervals from 1337 to 1658 UTC on 1 June 2018 (Click to play mp4 animation)

GOES-16 Visible Imagery on 1 June revealed an interesting feature behind a lake-enhanced cold front that swept south into Indiana and Illinois (another aspect of this feature is discussed here). Atmospheric waves developed in the cloud layer over the south shore of Lake Michigan and propagated upwind towards Chicago. The mp4 animation above (Click here for a full-res very large animated gif) shows 1-minute imagery from the western default GOES-16 Mesoscale sector. (At 1659 UTC, that sector was repositioned to the west to monitor convection in the northern Plain States).

CONUS-scale imagery was able to sample the evolution of this system at 5-minute intervals, as shown below (Click here for an animation without the surface observations).

There is a considerable thermal gradient between the lake surface and the land over Indiana and Illinois. This Land Surface Baseline Product shows surface temperatures in the low 40s over the Lake and surface temperatures in the mid-80s over northwest Indiana. This strong thermal gradient likely influenced the development of these unusual waves. An aircraft sounding from 1535 UTC (here, courtesy TJ Turnage) shows the very strong inversion that was also important in the evolution of the waves.

GOES-16 Visible (0.64 µm) Visible Imagery at 5-minute intervals from 1102 to 1917 UTC on 1 June 2018, along with hourly surface plots (Click to play animated gif)

(Thanks to TJ Turnage, NWS GRR for alerting us to this event!)

Added, 5 June:  Clark Evans, UW-Milwaukee, hypothesizes that the waves may have been forced by the (relatively) tall dunes in Indiana along the south shore of Lake Michigan.   Those dunes may have been tall enough to block the flow under a very sharp inversion.

Gravity waves near Guadalupe Island

March 15th, 2018 |

GOES-16 Low-level (7.3 µm, left), Mid-level (6.9 µm, center) and Upper-level (6.2 µm, right) Water Vapor images [click to play animation]

GOES-16 Low-level (7.3 µm, left), Mid-level (6.9 µm, center) and Upper-level (6.2 µm, right) Water Vapor images [click to play 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) revealed an interesting packet of gravity waves in the vicinity of Guadalupe Island (west of Baja California) on 15 March 2018. The mechanism forcing these waves was not entirely clear, making it a suitable candidate for the “What the heck is this?” blog category.

A similar animation of GOES-16 “Red” Visible (0.64 µm), Mid-level Water Vapor (6.9 µm) and Upper-level Water Vapor (6.2 µm) images (below) did show some smaller-scale waves on Visible imagery within the marine boundary layer stratocumulus cloud field, but they did not appear to exhibit a direct correlation with the higher-altitude waves seen in the Water Vapor imagery. Surface winds were from the northwest at 10-15 knots, as a dissipating cold front was stalled over the region.

GOES-16

GOES-16 “Red” Visible (0.64 µm, left), Mid-level Water Vapor (6.9 µm, center) and Upper-level Water Vapor (6.2 µm, right) images [click to play animation]

A larger-scale view of Mid-level Water Vapor (6.9 µm) images (below) showed that these waves were located to the north of a jet streak axis — denoted by the sharp dry-to-moist gradient (yellow to blue enhancement) stretching from southwest to northeast as it moved over Baja California.

GOES-16 Mid-level (6.9 µm) Water Vapor images [click to play animation]

GOES-16 Mid-level (6.9 µm) Water Vapor images [click to play animation]

GOES-15 (GOES-West) Water Vapor (6.5 µm) images with overlays of upper-tropospheric atmospheric motion vectors and contours of upper-tropospheric divergence (below) indicated that Guadalupe Island was located within the “dry delta” signature often associated with a jet stream break — the inflection point between 2 strong jet streaks within a sharply-curved jet stream. Upper-tropospheric winds were from the west/northwest, with upper-tropospheric convergence seen over the region of the gravity waves.

GOES-15 Water Vapor (6.5 µm) images, with water vapor wind vectors [click to enlarge]

GOES-15 Water Vapor (6.5 µm) images, with atmospheric motion vectors [click to enlarge]

GOES-15 Water Vapor (6.5 µm) images, with contours of upper-tropospheric convergence [click to enlarge]

GOES-15 Water Vapor (6.5 µm) images, with contours of upper-tropospheric convergence [click to enlarge]

An early morning Aqua MODIS Water Vapor (6.7 µm) image with NAM80 contours of 250 hPa wind speed (below) showed the two 90-knot jet streaks on either side of the jet stream break — it could be that speed convergence due to rapidly decelerating air within the exit region of the western jet streak was a possible forcing mechanism of the gravity waves seen on the GOES-16 Water Vapor imagery.

Aqua MODIS Water Vapor (6.7 µm) image, with NAM80 contours of 250 hPa wind speed [click to enlarge]

Aqua MODIS Water Vapor (6.7 µm) image, with NAM80 contours of 250 hPa wind speed [click to enlarge]