Portland, Oregon heavy snow event

January 11th, 2017

GOES-15 Infrared Window (10.7 µm) images, with hourly reports of surface weather type [click to play animation]

GOES-15 Infrared Window (10.7 µm) images, with hourly reports of surface weather type [click to play animation]

A surface low moving inland (3-hourly surface analyses) helped to produce widespread rain and snow across much of Oregon and southern Washington during the 10 January11 January 2017 period. 4-km resolution GOES-15 (GOES-West) Infrared images (above) and Water Vapor images (below) showed the development of a deformation band that helped to focus and prolong moderate to heavy snowfall over the Portland, Oregon area (accumulations | historical perspective). The GOES-15 images are centered at Portland International Airport (station identifier KPDX).

GOES-15 Water Vapor (6.5 µm) images, with hourly reports of surface weather type [click to play animation]

GOES-15 Water Vapor (6.5 µm) images, with hourly reports of surface weather type [click to play animation]

1-km resolution GOES-15 Visible (0.63 µm) images (below) during the last few hours of daylight on 10 January revealed the shadowing and textured signature of numerous embedded convective elements moving inland, which were helping to enhance precipitation rates (and even produce thundersnow at a few locations, a phenomenon which is very unusual for the Pacific Northwest).

GOES-15 Visible (0.63 µm) images, with hourly reports of surface weather type [click to play animation]

GOES-15 Visible (0.63 µm) images, with hourly reports of surface weather type [click to play animation]

===== 12 January Update =====

As clouds cleared in the wake of the storm, a comparison of 375-meter resolution Suomi NPP VIIRS true-color and false-color Red/Green/Blue (RGB) images viewed using RealEarth (below) revealed the extent of the snow cover; snow appears as shades of cyan in the false-color image, in contrast to clouds which appear as shades of white. [Note: with 5 inches of snow remaining on the ground, a new record low temperature was set in Portland on 13 January]

Suomi NPP VIIRS true-color and false-color RGB images [click to enlarge]

Suomi NPP VIIRS true-color and false-color RGB images [click to enlarge]

The fresh snowfall was also apparent in a 30-meter resolution Landsat-8 false-color RGB image (below) along the south face of Mount Hood (located about 98 miles or 158 km east of Portland). The ski slopes of Timberline Lodge and  Mount Hood Meadows received 13-14 inches of new snow during this event; the snow base depth at Timberline was greater than the average amount for this time of year.

Landsat-8 false-color RGB image [click to play zoom-in animation]

Landsat-8 false-color RGB image [click to play zoom-in animation]

Christmas Blizzard

December 26th, 2016

GOES-13 Water Vapor (6.5 µm) images, with hourly surface weather symbols [click to play animation]

GOES-13 Water Vapor (6.5 µm) images, with hourly surface weather symbols [click to play animation]

A mid-latitude cyclone intensified as it moved northeastward across Nebraska, the eastern Dakotas and northern Minnesota (3-hourly surface analyses) during 25 December26 December 2016. GOES-13 (GOES-East) Water Vapor (6.5 µm) images (above) showed distinct banding within the warm conveyor belt, a well-defined dry slot, and a large comma head that formed from the cold conveyor belt. The storm produced blizzard conditions across much of the Northern Plains and Upper Midwest, with heavy snowfall (as much as 22.0 inches in western North Dakota), freezing rain (ice accretion as thick as 0.5 inch in Minnesota and North Dakota) , sleet (up to 2.0 inches deep in Minnesota) and heavy rainfall; in Kansas there were also a few tornadoes (SPC storm reports).

A noteworthy characteristic of the storm was very strong winds — a closer view of GOES-13 Water Vapor imagery with hourly plots of surface wind gusts (in knots) is shown below.

GOES-13 Water Vapor (6.5 µm) images, with hourly surface wind barbs and wind gusts in knots [click to play animation]

GOES-13 Water Vapor (6.5 µm) images, with hourly surface wind barbs and wind gusts in knots [click to play animation]

Note the swath of wind gusts in the 50-60 knot range which progressed across central and northeastern Nebraska into northwestern Iowa and finally southwestern Minnesota during the 02 UTC to 12 UTC period on 26 December — this was pointed out in a tweet by Anthony Sagliani as a “sting jet” feature:


As observed in previous sting jet cases (03 Jan 2012 | 28 Oct 2013), the strongest winds occurred near the curved “scorpion tail” signature seen in the water vapor imagery (which marked the leading edge of the cold conveyor belt as it advanced into the rear edge of the dry slot of the cyclone circulation).

A comparison of Aqua MODIS Visible (0.65 µm), Infrared Window (11.0 µm) and Water Vapor (6.7 µm) images at 2001 UTC on 25 December is shown below.

Aqua MODIS Visible (0.65 µm), Infrared Window (11.0 µm) and Water Vapor (6.7 µm) images [click to enlarge]

Aqua MODIS Visible (0.65 µm), Infrared Window (11.0 µm) and Water Vapor (6.7 µm) images [click to enlarge]

A closer view with Suomi NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images at 1952 UTC on 25 December (below) showed a detailed view of the banded cloud structures from Kansas into South Dakota, as well as small overshooting tops associated with thunderstorms in southeastern South Dakota and southwestern Minnesota. This storm produced the first Christmas Day thunderstorms on record in both Sioux Falls and Rapid City, South Dakota; thundersnow was also observed in Bismarck, North Dakota.

Suom NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images [click to enlarge]

Suom NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images [click to enlarge]

Super Typhoon Nock-Ten strikes the Philippines

December 25th, 2016

Himawari-8 Infrared Window (10.4 µm) images [click to play MP4 animation]

Himawari-8 Infrared Window (10.4 µm) images [click to play MP4 animation]

Rapid-scan (2.5-minute interval) 2-km resolution Himawari-8 Infrared Window (11.45 µm) images (above; also available as a 173 Mbyte animated GIF) showed Category 4 Super Typhoon Nock-Ten making landfall in the Philippines on 25 December 2016. Nock-Ten became the strongest typhoon on record (SATCON | ADT | source) in the Philippines so late in the year:

A 375-meter resolution Suomi NPP VIIRS Infrared Window (11.45 µm) image at 1724 UTC on 24 December (below; courtesy of William Straka, SSEC) was acquired just before the beginning of the Himawari-8 animations above; note the presence of cloud-top gravity waves propagating southeastward away from the eye of Nock-Ten, in addition to prominent larger-scale transverse banding farther out within the eastern semicircle of the storm.

Suomi NPP VIIRS Infrared Window (11.45 µm) image [click to enlarge]

Suomi NPP VIIRS Infrared Window (11.45 µm) image [click to enlarge]

Gatlinburg, Tennessee wildfire

November 29th, 2016

GOES-13 Shortwave Infrared (3.9 µm) images, with METAR surface reports [click to play animation]

GOES-13 Shortwave Infrared (3.9 µm) images, with METAR surface reports [click to play animation]

Wildfires had been burning in the Great Smoky Mountains for a few weeks (see previous blog posts) as extreme to exceptional drought persisted over the region. However, on 28 November 2016 weather conditions became conducive to extreme fire behavior — and this allowed the Chimney Tops 2 Fire south of Gatlinburg, Tennessee to race rapidly northward (fire perimeter map), driven by strong southerly winds gusting to at least 30-40 knots (as were recorded in Knoxville KTYS, located about 25 miles northwest of Gatlinburg). Widespread evacuations were necessary, and at least 13 fatalities were reported.  4-km resolution GOES-13 Shortwave Infrared (3.9 µm) images (above) showed the development of a fire “hot spot” (the cluster of pixels at the center of the images exhibiting a black to yellow color enhancement) during the day, before clouds moved overhead to mask the fire hot spot signature. The warmest infrared brightness temperature seen during this time period was 326.8 K (brighter yellow pixels) on the 1700 UTC image.

Even though cloud cover was increasing, a detailed view of the fire hot spot was provided by an AWIPS II image of 375-meter resolution Suomi NPP VIIRS Shortwave Infrared (3.74 µm) data at 1815 UTC on 28 November (below). An AWIPS I version of this image is available here. Due to the cloudiness, no discernible hot spot appeared on the lower-resolution 1815 UTC GOES-13 Shortwave Infrared image.

Suomi NPP VIIRS Shortwave Infrared (3.74 µm) image [click to enlarge]

Suomi NPP VIIRS Shortwave Infrared (3.74 µm) image [click to enlarge]

Props to NWS meteorologist Carl Jones for spotting this somewhat unexpected result: the glow of the fire was evident on the following nighttime Suomi NPP VIIRS Day/Night Band (0.7 µm) image, even though there was a thick layer of clouds over the fire itself:


An AWIPS II image comparison of VIIRS Infrared Window (11.45 µm), Shortwave Infrared (3.74 µm) and Day/Night Band (0.7 µm) data at 0816 UTC on 29 November is shown below. Cloud-top Infrared Window brightness temperatures were in the -40 to -55º C range over the fire region (such air temperatures were foundd within the 9.5-10.5 km altitude range on the Nashville sounding when the cloud band was over central Tennessee at 00 UTC). While no fire hot spot signature was evident on the Shortwave Infrared image (due to masking by the clouds), the very distinct bright glow of the fire (which appeared rather large in size, due to scattering of light by the water and ice particles present in the various cloud layers) was seen on the Day/Night Band image. AWIPS I versions of these images are available here.

Suomi NPP VIIRS Infrared Window (11.45 µm), Shortwave Infrared (3.74 µm) and Day/Night Band (0.7 µm) images [click to enlarge]

Suomi NPP VIIRS Infrared Window (11.45 µm), Shortwave Infrared (3.74 µm) and Day/Night Band (0.7 µm) images [click to enlarge]

Additional information is available on the Wildfire Today site (post 1 | post 2 | post 3 | post 4 | post 5).