Mesovortex over Lake Michigan

July 19th, 2012 |
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)

A mesoscale vortex developed in northern Lake Michigan early in the day on 19 July 2012; AWIPS images of 1-km resolution GOES-13 0.63 µm visible channel data (above; click image to play animation) showed that the mesovortex then propagated southward across the western portion of the lake during the afternoon hours. Early in the animation, ship WBD4889 (plotted in red) appeared to have captured the periphery of the circulation of the developing vortex, with south-southeast winds at 20 knots (at 15 UTC)  which transitioned to northeasterly winds at 25 knots (at 17 UTC). Along the coast of Wisconsin, winds gusted to 19 knots at Sheboygan (KSBM) at 20 UTC, 23 knots at Milwaukee (KMKE) at 22 UTC, and 19 knots at Racine (KRAC) at 23 UTC as the vortext was moving to the east of those locations.

POES AVHRR Cloud Top Height product

POES AVHRR Cloud Top Height product

The 1-km resolution POES AVHRR Cloud Top Height product (above) indicated that the tops of the clouds associated with the mesovortex were only around 1 km (light pink color enhancement), so the mesovortex was not a vertically-deep feature. This low cloud top height was supported by the relatively warm Suomi NPP VIIRS IR cloud top brightness temperatures (below), which were around +10 C.

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

A 250-meter resolution MODIS true-color Red/Green/Blue (RGB) image from the SSEC MODIS Today site (below; viewed using Google Earth) showed hints of some organized cloud banding structure within the center of the mesovortex as it was just east of Sheboygan, Wisconsin at 18:58 UTC (1:58 PM local time).

MODIS true-color Red/Green/Blue (RGB) image (viewed using Google Earth)

MODIS true-color Red/Green/Blue (RGB) image (viewed using Google Earth)

As noted by the NWS Milwaukee/Sullivan forecast office:

AREA FORECAST DISCUSSION   NATIONAL WEATHER SERVICE   MILWAUKEE/SULLIVAN WI   914 PM CDT THU JUL 19 2012

.UPDATE… AN INTERESTING MESO LOW THAT LIKELY FORMED OVER THE NORTHERN REACHES OF LAKE MICHIGAN WHERE COOL AIR INTERACTED WITH THE WARM LAKE TEMPS…ROLLED DOWN THE LAKE SHORE AND HAD REACHED THE SOUTHERN TIP OF THE LAKE BY MID EVENING. THE ADDED FORCING AND LOW LEVEL CONVERGENCE FROM THIS FEATURE LEAD TO SHOWERS ACROSS THE FAR SOUTHEAST CORNER OF THE CWA THIS EVENING. THAT SHOULD ALL END BY MIDNIGHT.

The following day was cloud-free across Lake Michigan, allowing a nice view of the lake using the 1-km resolution MODIS Sea Surface Temperature (SST) product (below) — this showed a transition from SST values in the upper 60s F (green color enhancement) in the middle of the lake to middle 70s F (orange color enhancement) in the southern part of the lake.

MODIS Sea Surface Temperature product

MODIS Sea Surface Temperature product

Smoke being drawn over the Gulf of Alaska, and ship tracks converging on the remnants of Hurricane Fabio

July 19th, 2012 |
GOES-15 0.63 µm visible channel images (click image to play animation)

GOES-15 0.63 µm visible channel images (click image to play animation)

McIDAS images of 1-km resolution GOES-15 0.63 µm visible channel data (above) showed a large area of low pressure in the eastern Gulf of Alaska which was helping to draw a large amount of wildfire smoke southward on 19 July 2012. The hazy smoke aloft originated from wildfires in Alaska and in northeastern Asia.

GOES-15 0.63 µm visible channel images (click image to play animation)

GOES-15 0.63 µm visible channel images (click image to play animation)

Meanwhile, farther to the south, 1-km resolution GOES-15 visible channel images (above; click image to play animation) revealed that the circulation of the remnants of Hurricane Fabio was drawing marine boundary layer “ship track” clouds into its circulation — while some ships actually appeared to be headed right for the center of the dissipating tropical cyclone.

The ship tracks were also evident on 4-km resolution GOES-15 3.9 µm shortwave IR images (below; click image to play animation). The ship tracks appeared darker (warmer) on the shortwave IR imagery, due to the fact that the smaller cloud droplets of the ship track clouds reflected a higher amount of incoming solar radiation back toward the satellite sensors.

GOES-15 3.9 µm shortwave IR channel images (click image to play animation)

GOES-15 3.9 µm shortwave IR channel images (click image to play animation)

250-meter resolution Terra and Aqua MODIS true-color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (below) showed greater details of the ship tracks as they were drawn into the circulation center of the dying storm (along with the other ship tracks approaching the storm from the south).

Terra MODIS true-color Red/Green/Blue (RGB) image

Terra MODIS true-color Red/Green/Blue (RGB) image

Aqua MODIS true-color Red/Green/Blue (RGB) image

Aqua MODIS true-color Red/Green/Blue (RGB) image

City lights shining through clouds

July 19th, 2012 |
VIIRS Day/Night Band from Suomi/NPP satellite

VIIRS Day/Night Band from Suomi/NPP satellite

The New Moon on 18 July means that no visible light reflected from the Moon can illuminate clouds, and the day/night band on the Suomi-NPP satellite can therefore view any clouds only with difficulty. However, it still views city lights, and illuminated roads, or gas field flares, among other things. The region above shows data contaminated by stray light. The Suomi/NPP satellite as it took this image was, although on the night side of the planet, nevertheless outside the shadow of the Earth, and radiation from the Sun was able to contaminate the image. Despite this, the lights of Minnesota and Iowa, both the main cities and the smaller towns, are plainly visible. City lights in eastern Wisconsin and Illinois have a more diffuse character because they are being viewed through cirrus clouds from a departing convective complex, as evident in this enhanced 10.7 micrometer imager from 0800 UTC.

VIIRS Day/Night Band from Suomi/NPP satellite

VIIRS Day/Night Band from Suomi/NPP satellite

The GOES-R IFR Proabability image from 0801 UTC, above, shows high probabilities of low clouds over north-central Iowa and south-central Minnesota. Surface observations plotted on the image confirm IFR conditions, with low visibilities and low ceilings. In addition, GOES-R Cloud Thickness values in the region are from 800 and 1000 feet thick. It is interesting that the Day/Night band can view the city lights through a low stratus deck that is hundreds of feet thick.

It is very difficult to distinguish between low stratus and clear regions in the stray light zone. That task is somewhat easier when there is no stray light, as shown in this image over the southern United States: In low light conditions, such as during a New Moon, low clouds have a smudgey appearance, but that signature is overwhelmed in the stray light zone. How thick does a cloud have to be before it is opaque to visible light?