Drifting ice in Green Bay

December 27th, 2009
GOES-14 and GOES-12 visible images

GOES-14 and GOES-12 visible images

McIDAS images of GOES-14 and GOES-12 visible channel data (above) showed that a large portion of the land-fast ice in the southern half of Green Bay began to break away and drift slowly northeastward on 27 December 2009. Unlike a similar case seen on 11 March 2009 with strong surface winds, the southwesterly winds on this particular day were quite light (generally 10 knots or less at inland stations over northeastern Wisconsin) — however, winds were gusting to 13-18 knots farther to the northeast at coastal sites with an upwind exposure to the bay.

As part of its ongoing NOAA Science Test, the GOES-14 satellite had been placed into Rapid Scan Operations (RSO) mode, supplying imagery as frequently as every 5 minutes. The more frequent RSO imaging (along with the improved GOES-14 Image Navigation and Registration) allowed the motion of the drifting ice to be more accurately visualized compared to the 15-minute interval GOES-12 imagery with poorer image navigation.

250-meter resolution MODIS true color images from the SSEC MODIS Today site (below) showed a more detailed view of the motion of the ice between the overpass of the Terra satellite at 17:10 UTC and the Aqua satellite at 18:55 UTC.

MODIS true color images

MODIS true color images

Stratospheric intrusion vortices over the Pacific Northwest

December 27th, 2009
GOES-14 6.5 µm water vapor images

GOES-14 6.5 µm water vapor images

McIDAS images of the GOES-14 6.5 µm water vapor channel data (above; also available as a QuickTime animation) revealed that a pair of stratospheric intrusion vortices developed over the Pacific Northwest region of the US on 26 December27 December 2009. The spin-up of these vortices occurred within the pronounced dry band that had formed along the western periphery of the large central US Christmas Blizzard. As a part of its ongoing NOAA Science Test, the GOES-14 satellite had been placed into Rapid Scan Operations (RSO) mode, providing imagery as frequently as every 5 minutes.

There have been cases where turbulence aloft has been associated with these types of stratospheric intrusion vortices — and in this instance, AWIPS images of the GOES-West/GOES-East composite water vapor channels with overlays of pilot reports (below) did indeed show a few reports of moderate turbulence between 26,000 feet and 40,000 feet above ground level in the vicinity of the vortices.

GOES water vapor images + pilot reports of turbulence

GOES water vapor images + pilot reports of turbulence

As the trailing vortex began to pass over Vancouver Island around 12 UTC on 27 December (water vapor image), a north-to-south oriented vertical cross section of NAM80 model fields (below) showed how the dynamic tropopause (taken to be the PV1.5 potential vorticity surface) was being pulled downward to around the 450 hPa pressure level. The GOES Sounder Total Column Ozone product also showed a slight increase in ozone values — to around 350 Dobson Units — associated with the stronger (trailing) stratospheric intrusion vortex.

NAM80 vertical cross section

NAM80 vertical cross section

The Christmas Blizzard of 2009

December 26th, 2009
GOES-12 10.7 µm IR images (with overlay of surface weather type)

GOES-12 10.7 µm IR images (with overlay of surface weather type)

An intense blizzard affected much of the central US on 24 December25 December 2009, significantly disrupting travel and commerce from North Dakota to Texas. Oklahoma City OK received 14.1 inches of snow, which was both their greatest 24-hour snowfall and their greatest storm total snowfall on record. McIDAS images of the GOES-12 10.7 µm IR channel data (above; also available as a QuickTime animation) showed the evolution of a well-defined Trough of Warm Air Aloft (TROWAL) signature across Oklahoma and Texas — with moderate to heavy snow falling just to the north and west of the pivot point of the southern/eastern edge of the colder (-30º to -50º C, dark blue to violet color enhancement) cloud top temperatures. Surface winds gusted as high as 64 mph in Oklahoma, creating white-out conditions with blowing and drifting snow.

On the morning of 25 December, a comparison of AWIPS images of the MODIS visible channel and a false-color Red/Green/Blue (RGB) composite (below) showed the areal extent of significant snow remaining on the ground — snow cover on the RGB image was highlighted with a red color enhancement, in contrast to supercooled water droplet clouds which appeared as brighter white features. This also offers a glimpse at the type of RGB image capability that should be available with the upcoming AWIPS-2 software. For higher-resolution MODIS true color and false color images from 25 December, see the SSEC MODIS Today site.

MODIS visible image and false-color Red/Green/Blue (RGB) image

MODIS visible image and false-color Red/Green/Blue (RGB) image

GOES-12 6.5 µm water vapor images (below; also available as a QuickTime animation) displayed the impressively large size of the circulation associated with the storm as it intensified from 25 December to 26 December. In the north-central US, entire Interstate highway systems were shut down for an extended period across the Dakotas — snowfall amounts were as high as 40.0 inches at Lead, South Dakota (with amounts over 24 inches in North Dakota and Minnesota). Significant accruals of ice (up to 0.4 inch) from freezing rain occurred in parts of Iowa, Illinois, and Indiana. Winds gusted as high as 76 mph in western South Dakota (HPC storm summary).

GOES-12 6.5 µm water vapor images

GOES-12 6.5 µm water vapor images

Blowing dust in Arizona

December 22nd, 2009
MODIS true color image (displayed using Google Earth)

MODIS true color image (displayed using Google Earth)

Strong winds associated with a developing storm over the southwestern US caused areas of blowing dust across southern Arizona on 22 December 2009. A MODIS true color image from the SSEC MODIS Today site  (above) showed one of the larger plumes of blowing dust which was moving northeastward across the region. On a smaller scale, there were also localized areas of very thick blowing dust that reduced visibility and caused a number of multiple-vehicle accidents along Interstate 10 between Tucson and Phoenix — fatalities were reported with one of the larger vehicle pile-ups near Casa Grande.

AWIPS images of the AVHRR Cloud Top Temperature (CTT) and Cloud Particle Effective Radius products (below) indicated that CTT values associated with the large-scale blowing dust plume were around +10 to +15º C, which was between the 921 and 850 hPa pressure levels on the Tucson AZ rawinsonde report. The dust particle effective radius values were in the 15-25 µm range — much smaller than the 50-100 µm values seen for the cloud features located in other parts of the image scene.

AVHRR Cloud Top Temperture and Cloud Particle Effective Radius products

GOES-14 visible images

GOES-14 visible images

As part of its ongoing NOAA Science Test, GOES-14 was emulating GOES-West operations on that day. McIDAS images of the GOES-14 visible channel data (above) showed the evolution of the large-scale dust plume as it became more organized along the Arizona/Mexico border and moved northeastward toward the Casa Grande (station identifier KCGZ) area. Also worthy of mention is the fact that the convection that moved through the Phoenix area generated a few reports of 0.25 inch diameter hail.

A clue to the approach of strong mid-tropospheric winds could be seen in a comparison of 4-km resolution GOES-14 6.5 µm water vapor and 8-km resolution GOES-11 6.7 µm water vapor images (below) — lee waves were apparent immediately downwind of the higher terrain, particularly over Baja California. Note how the improvement in spatial resolution from 8-km to 4-km improves the ability to detect the complexity and the areal extent of the lee waves on water vapor imagery. When GOES-11 is due for replacement as the operational GOES-West satellite, GOES-14 will likely take over that duty.

GOES-14 6.5 µm and GOES-11 6.7 µm water vapor images

GOES-14 6.5 µm and GOES-11 6.7 µm water vapor images

A MODIS 11.0 µm – 12.0 µm IR difference image (below) was useful for helping to highlight the large-scale blowing dust plume at 20:09 UTC. Beginning with GOES-12, the Imager instrument 12.0 µm IR channel was replaced with a 13.3 µm channel, preventing the application of this type of IR difference blowing dust identification on the more recent GOES satellites — however, the 12.0 µm IR channel will return on the ABI instrument aboard GOES-R.

MODIS 11.0 µm - 12.0 µm IR difference image

MODIS 11.0 µm - 12.0 µm IR difference image