Cold air diving southward across the Plains

October 30th, 2006

AWIPS 4-panel satellite image animation
A strong cyclone centered over the northcentral US was producing heavy snow across much of North Dakota on 30 October; an associated cold frontal boundary was moving rapidly southward across Nebraska, Colorado, and Kansas during the morning and afternoon hours. The southward push of the cold air behind the front can be seen on an animation of GOES imagery from AWIPS (above), evident as an area of lighter gray enhancement on the 10.7 µm IR window and 3.9µm shortwave IR images (above, upper left and lower left panels) — the leading edge of this cold air was well south of the low cloud deck that was covering parts of South Dakota and northern Nebraska.

In addition, if you look closely, you can also see a subtle reflection of this surface-based boundary moving southward across northeastern Colorado on the 6.5µm “water vapor channel” imagery (above, lower right panel), even though this is a channel which normally senses radiation from altitudes higher in the middle troposphere. A plot of the GOES-12 imager water vapor channel’s weighting function at North Platte, Nebraska (below) indicates that the altitude of the peak contribution for that particular air mass had indeed shifted downward to near 500 hPa (~ 18,000 feet in altitude).
North Platte NE water vapor weighting function

Heavy snow in the Colorado plains

October 27th, 2006

MODIS true color and false color composite images
An early season winter storm dumped up to 25 inches of snow across parts of Colorado on 26 October (NWS snowfall reports); as fate would have it, on that particular day Alaska also reported its first below zero temperature of the season (-7ËšF at Bettles), making for two ominous signs that winter is fast approaching. Aqua MODIS imagery from one day after the storm (above) shows the extent of the resulting snow cover, both in the mountains and also in the eastern Plains of the state; the false-color composite using MODIS channels 2 and 7 (above, right) displays the snow cover as dark red features on the image. Note how the snow cover is distributed both north and south of the Palmer Divide (a west-to-east oriented ridge of higher terrain across eastern Colorado) — upslope flow played an important role in focusing heavy snowfall during different stages of the storm.
A closer view of the Denver area using a MODIS 500-meter resolution true color image (below) shows that many of the small lakes are still unfrozen, and stand out against the surrounding snow covered land surfaces.
MODIS true color image (Denver area)

Fatal fire in California

October 26th, 2006

GOES-11 3.9µm IR animation
The large (40,000 acre or 63 square mile)  “Esperanza wildfire” started during the early morning hours on 26 October 2006 in a portion of the San Bernardino National Forest near Banning, California (west of Palm Springs); this fire quickly burned out of control, and was responsible for the deaths of 5 firefighters. Santa Ana winds across the region were creating favorable conditions for rapid fire growth (the dew point at nearby Palm Springs dropped from 55ËšF at 19 UTC on 25 October to -1ËšF at 07 UTC on 26 October). GOES-11 3.9µm IR imagery (QuickTime animation, above) showed very hot brightness temperatures (yellow to red enhancement) in the vicinity of this large fire — hot fire pixels were first evident at 08:15 UTC (01:15 AM local time), and image pixel values reached the saturation temperature of the GOES-11 3.9µm detectors (337.2ËšK / 64ËšC / 147ËšF) as early as 12:45 UTC (5:45 AM local time). The Wildfire ABBA product (GOES-11 | GOES-12) also indicated saturated fire pixels (yellow) in that area (20:45 UTC WF_ABBA image).

GOES-11 visible channel imagery (QuickTime animation, below) showed a very large smoke plume from this fire, which was dispersed in different directions due to directional wind shear between the surface and the 500 hPa level (~18,000 feet in altitude). MODIS imagery of the fire from 26 October is posted on the UMBC Air Quality Smog Blog, while the IDEA Aerosol Optical Depth product from the following day shows continued smoke transport out across the adjacent Pacific Ocean.
GOES-11 visible image animation

Power plant plumes

October 19th, 2006

AWIPS MODIS fog/stratus product
The AWIPS image of MODIS 11.0µm-3.7µm “fog/stratus product” (above) reveals several long plumes embedded within the extensive stratus cloud deck (yellow to red enhancement) that covered much of northern and central Minnesota during the pre-dawn hours on 19 October. These plumes likely originated at large coal-fired power plants (or paper mills?) located across that region — emissions from these industrial sources may have acted as cloud condensation nuclei, causing a higher concentration of smaller supercooled cloud droplets downwind of the plants.

The MODIS Cloud Phase product (below, lower left panel) showed that this stratus deck was primarily a water-phase cloud (blue enhancement); MODIS 11.0µm IR window channel brightness temperatures were generally around -14 C across that region, indicating that the stratus cloud was composed of supercooled water droplets. Note that these power plant plumes were not evident on the 4 km resolution GOES fog/stratus product (below, upper right panel). The GOES sounder Cloud Top Height values were around 11-12 kft over the area.
AWIPS MODIS + GOES comparison