Lee-side cold frontal gravity wave

February 5th, 2018 |

GOES-16 Low-level (7.3 µm, left), Mid-level (6.9 µm, middle) and Upper-level (6.2 µm, right) Water Vapor images, with hourly surface wind barbs plotted in cyan [click to play animation]

GOES-16 Low-level (7.3 µm, left), Mid-level (6.9 µm, middle) and Upper-level (6.2 µm, right) Water Vapor images, with hourly surface wind barbs plotted in cyan [click to play animation]

As a cold front moved rapidly southward across the Great Plains (surface analyses) on 05 February 2018, the signature of a deep-tropospheric lee-side cold frontal gravity wave (reference) could be seen on GOES-16 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (above; also available as an MP4 animation). In addition, the initial gravity wave was soon followed by a secondary lee-side gravity wave, which could be seen moving southward over the northern Texas Panhandle by the end of the animation.

Plots of the weighting function (or “contribution function”) for each of the three GOES-16 Water Vapor bands (below) are calculated using 05 February/12 UTC rawinsonde data from Dodge City, Kansas — which was south of the cold front at that time. The peak pressure level for all three weighting function plots was in the 442-497 hPa range, giving some indication of the depth of these vertically-propagating gravity waves.

Weighting function plots for each of the three GOES-16 Water Vapor bands, calculated using 05 February/12 UTC rawinsonde data from Dodge City, Kansas [click to enlarge]

Weighting function plots for each of the three GOES-16 Water Vapor bands, calculated using 05 February/12 UTC rawinsonde data from Dodge City, Kansas [click to enlarge]

GOES-16 Water Vapor weighting functions using 06 February/00 UTC rawinsonde data from Amarillo, Texas — where the surface cold front had passed about 3 hours earlier — are shown below. Note that in the drier post-frontal air mass, the peak pressures for the 3 water vapor bands had increased, descending to the 477 to 684 hPa pressure levels. This comparison helps to underscore the dependence of water vapor weighting function height on the temperature and/or moisture profile of the atmosphere.

Weighting function plots for each of the three GOES-16 Water Vapor bands, calculated using 06 February/00 UTC rawinsonde data from Amarillo, Texas [click to enlarge]

Weighting function plots for each of the three GOES-16 Water Vapor bands, calculated using 06 February/00 UTC rawinsonde data from Amarillo, Texas [click to enlarge]

Lee-side cold frontal gravity wave

November 28th, 2017 |

GOES-16 Lower-level (7.3 µm, left), Mid-level (6.9 µm, center) and Upper-level (6.2 µm, right) Water Vapor images, with hourly surface wind barbs plotted in yellow [click to play MP4 animation]

GOES-16 Lower-level (7.3 µm, left), Mid-level (6.9 µm, center) and Upper-level (6.2 µm, right) Water Vapor images, with hourly surface wind barbs plotted in yellow [click to play MP4 animation]

* GOES-16 data posted on this page are preliminary, non-operational and are undergoing testing *

As a strong cold front (surface analyses) moved southward from Colorado and Nebraska across New Mexico, Texas and Oklahoma on 28 November 2017, the subtle curved arc signature of a lee-side cold frontal gravity wave could be seen on GOES-16 Lower-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (above).

Closer views of imagery from each of the 3 water vapor bands are shown below.

GOES-16 Upper-level (6.2 µm) images, with hourly surface wind barbs plotted in yellow [click to play MP4 animation]

GOES-16 Upper-level (6.2 µm) images, with hourly surface wind barbs plotted in yellow [click to play MP4 animation]

GOES-16 Mid-level (6.9 µm) images, with hourly surface wind barbs plotted in yellow [click to play MP4 animation]

GOES-16 Mid-level (6.9 µm) images, with hourly surface wind barbs plotted in yellow [click to play MP4 animation]

GOES-16 Lower-level (7.3 µm) images, with hourly surface wind barbs plotted in yellow [click to play MP4 animation]

GOES-16 Lower-level (7.3 µm) images, with hourly surface wind barbs plotted in yellow [click to play MP4 animation]

Lee-side cold frontal gravity wave

October 22nd, 2008 |
GOES-12 6.5 µm water vapor images

GOES-12 6.5 µm water vapor images

AWIPS images of the 4-km resolution GOES-12 6.5 µm water vapor channel (above) showed a southward-propagating  lee-side cold frontal gravity wave over New Mexico and Texas on 22 October 2008. This gravity wave was caused by a surface-based cold frontal boundary that was moving southward across the region.

MODIS 6.7 µm water vapor image + fog/stratus product image

MODIS 6.7 µm water vapor image + fog/stratus product image

A comparison of the 1-km resolution MODIS 6.7 µm water vapor channel and the MODIS fog/stratus product (above) indicated that there were narrow cloud bands along the leading edge of the frontal boundary / gravity wave, as well as more extensive patches of fog and/or stratus behind the front in the Texas panhandle.The MODIS Land Surface Temperature (LST) product (below) depicted LST values dropping into the 40s F (green colors) behind the front, with much warmer LST values in the 50s and 60s F (yellow to orange colors) ahead of the front.

MODIS 6.7 µm water vapor channel + Land Surface Temperature product

MODIS 6.7 µm water vapor channel + Land Surface Temperature product

NOAA wind profiler data from Jayton, Texas (below) showed the deepening of the cold northerly flow after the cold front moved through the area — the top of the cold air appeared to be close to the 700 hPa level (around 10,000 feet above ground level).

Jayton, Texas NOAA wind profiler data

Jayton, Texas NOAA wind profiler data

GOES-12 water vapor channel weighting functions calculated for the rawinsonde profiles at Amarillo, Texas (below) demonstrated a significant lowering of the layer being detected by the water vapor channel in the 12 hours between 00 and 12 UTC on 22 October. With the drier air mass in place at 12 UTC, the GOES-12 water vapor channel was able to detect a substantial amount of energy originating from within the 500-700 hPa layer, allowing the signature of the frontal gravity wave to appear on the GOES-12 water vapor imagery. The wave structure was better-defined on the MODIS water vapor image, due to the improved spatial resolution and the more direct satellite viewing angle.

GOES-12 water vapor channel weighting functions for Amarillo TX

GOES-12 water vapor channel weighting functions for Amarillo TX

Mountain waves over Colorado

June 22nd, 2009 |
MODIS 6.7 µm and GOES-12 6.5 µm water vapor images

MODIS 6.7 µm and GOES-12 6.5 µm water vapor images

Moderate southwesterly flow aloft over the Rocky Mountains was aiding in the formation of mountain waves across much of Colorado and parts of the adjacent states on 22 June 2009. AWIPS comparisons of the 1-km resolution MODIS 6.7 µm water vapor image with the corresponding 4-km resolution GOES-12 6.5 µm water vapor image (above) and the 8-km resolution GOES-11 6.7 µm water vapor image (below) demonstrated the value of better spatial resolution for detecting such mesoscale features.

MODIS 6.7 µm and GOES-11 8-km 6.7 µm water vapor images

MODIS 6.7 µm and GOES-11 6.7 µm water vapor images

The appearance of these banded “mountain wave signatures” on water vapor imagery indicates the potential for clear air turbulence in those areas; however, there were no pilot reports of turbulence until 13:02 UTC near Fort Collins (at an altitude of 15,000 feet). An animation of the GOES-12 6.5 µm water vapor imagery (below) also showed the presence of a lee-side cold frontal gravity wave, which could be seen propagating southward across eastern Colorado and western Kansas. In fact, a small packet of waves could be seen along and behind the leading edge of this lee-side cold frontal gravity wave on the MODIS water vapor images above — surface winds behind this front had gusted to 36 knots at McCook, Nebraska (station identifier KMCK) and 20 knots at Goodland, Kansas (station identifier KGLD).

GOES-12 6.5 µm water vapor images

GOES-12 6.5 µm water vapor images