The surface air temperature at Watson Lake in the southern Yukon Territory of Canada (station identifier CYQH) fell to -56Âº F (-49Âº C) at 16 UTC on 14 January 2011. About 2 hours later, a comparison of AWIPS images of 4-km resolution GOES-11 10.7 Âµm IR and 1-km resolution POES AVHRR IR data (above) showed the signature of cold air that had settled into the valleys across that region — this signature was naturally much clearer on the higher resolution POES AVHRR image. The coldest surface IR brightness temperature on the POES AVHRR IR image was -52Âº C (-62Âº F) just to the southeast of Watson Lake. Also note the northeastward “parallax shift” of the warmer cloud features on the GOES-11 image, due to the high viewing angle from that geostationary satellite (which was situated over the Equator at 135Âº West longitude).
AWIPS images of 4-km resolution GOES-13 10.7 Âµm IR data (above; click image to play animation) showed an expansive deck of elevated stratus clouds covering much of eastern Texas and far southern Oklahoma on 13 January 2011.
The Blended Total Precipitable Water (TPW) product (below) suggested that this elevated stratus cloud feature may have been associated with a plume of moisture that was beginning to move northward from the Gulf of Mexico. The bulk of this moisture plume was likely confined to the lower troposphere, since the MODIS 6.7 Âµm water vapor image showed that the middle to upper troposphere was fairly dry across the region. The Fort Worth, Texas rawinsonde data indicated that the stratus deck was probably located near the 750-800 hPa pressure level, well aloft of the dry arctic air near the surface.
A comparison of the 1-km resolution POES AVHRR 10.8 Âµm IR image with the corresponding 1-km resolution POES AVHRR Cloud Type product (below) indicated that the stratus deck — which exhibited relatively warm cloud top IR brightness temperatures between -5Âº C and -12Âº C — was composed of primarily supercooled water droplets (green color enhancement on the Cloud Type product).
Even though the elevated stratus cloud deck did not exhibit much of a temperature contrast on the 1-km resolution MODIS 11.0 Âµm IR image, it’s appearance on the corresponding 1-km resolution MODIS 3.7 Âµm shortwave IR image was much more complex (below). Since the shortwave IR channel is very sensitive to reflected solar radiation, portions of the cloud top that were composed of smaller cloud droplets (which tend to be more effective reflectors of solar radiation) appeared warmer (darker) on the shortwave IR image.
This was confirmed by a comparison of the 1-km resolution POES AVHRR 3.7 Âµm shortwave IR image with the corresponding 1-km resolution POES AVHRR Cloud Particle Effective Radius product (below). The warmer (darker) areas on the shortwave IR image matched well with the areas of smaller cloud particles (10-20 Âµm radius, lighter blue color enhancement) on the Cloud Particle Effective Radius product — while the cooler (lighter gray) areas on the shortwave IR image corresponded to the larger cloud particle regions (25-35 Âµm radius, darker blue color enhancement).
The stratus cloud deck was beginning to move northward over areas that had received significant snowfall a few days earlier — deep snow cover that remained on the ground showed up as the darker red areas on a MODIS false-color Red/Green/Blue (RGB) image (below), which was created using the MODIS 0.65 Âµm visible image as the Red component and the MODIS 2.1 Âµm near-IR “snow/ice channel” as the Green and Blue components of the image.
The MODIS Land Surface Temperature (LST) product (below) indicated that LST values within the swath of snow cover remained in the upper 20s to low 30s F (darker blue color enhancement), in contrast to the warmer LST values in the low to mid 40s F (yellow to green color enhancement) over the adjacent bare ground areas.
A strong “Nor’easter” winter storm impacted much of the northeastern US on 12 January – 13 January 2011. The storm exhibited a nice presentation on AWIPS images of the GOES-13 6.5 Âµm “water vapor channel” data (above; click image to play animation). Storm total snowfall amounts included 36.0 inches at Wilmington, Vermont, 34.5 inches at Savoy, Massachusetts, and 29.5 inches at North Haven, Connecticut (HPC Storm Summary).
A comparison of the GOES-13 6.5 Âµm water vapor image at 18:15 UTC and the corresponding MODIS 6.7 Âµm water vapor image at 18:16 UTC (below) demonstrates the value of better spatial resolution (1 km on the MODIS image) for depicting subtle storm structures. Also note the slight northwestward “parallax shift” of the features on the GOES-13 image, due to the large viewing angle from GOES-13 (which is positioned over the Equator at 75Âº West longitude).
There was a strong Potential Vorticity (PV) anomaly associated with this storm — in fact, a northwest-to-southeast oriented cross section of RUC80 model fields through the developing “comma structure” seen on GOES-13 water vapor imagery at 15 UTCÂ (above) showed that the tropopause (taken to be the pressure of the PV1.5 surface) had been drawn downward to near the 800 hPa pressure level (below).
A sequence of 1-km resolution MODIS 11.0 Âµm IR and POES AVHRR 10.8 Âµm IR image (below) showed the development of banding features with IR brightness temperatures as cold as -50 to -60Âº C (orange to red color enhancement).
After the storm departed, a comparison of a 13 January MODIS 0.65 Âµm visible channel image with the corresponding MODIS Red/Green/Blue (RGB) image — created using MODIS channels 01/07/07 — showed the extent of some of the snow cover (which appears as the darkest shades of red on the RGB image), as well as the presence of supercooled water droplet clouds and glaciated ice crystal clouds (which show up as light grayÂ and lighter shades of red on the RGB image, respectively).
A comparison of MODIS Red/Green/Blue (RGB) “true color” (created using Bands 1/4/3) and “false color” (created using Bands 7/2/1) images from the SSEC MODIS Today site (above) showed a well-defined single lake-effect snow (LES) band running down the length of Lake Michigan on 08 January 2011. On the false color image, snow cover, ice, and glaciated clouds appeared as cyan-colored features, in contrast to the brighter white supercooled water droplet cloud features.
A mesoscale vortex formed during the day along the southern end of the Lake Michigan LES band, which helped to enhance snowfall rates as the band moved inland across southwestern Lower Michigan and northern Indiana. With the heavy snow from this LES band and mesoscale vortex, South Bend, Indiana (station identifier KSBN) set a new record for both 1-day and 2-day snowfall — 26.0 inches and 36.6 inches, respectively. With the MODIS Sea Surface Temperature (SST) product showing mid-lake SST values over 40Âº F (+10Âº C) and the 12 UTC 850 hPa air temperatures at Green Bay WI and Gaylord MI around +4Âº F (-16Âº C), the delta-T values were certainly large enough to support the formation of intense LES bands.
A closer view of the southern end of the LES band and the mesoscale vortex using 250-meter resolution MODIS true color RGB images at 17:04 UTC and 18:46 UTC (below) also revealed the movement of small ice floes in the nearshore waters of Lake Michigan.
The evolution of the mesoscale vortex was evident on McIDAS images of 15-minute interval GOES-13 0.65 Âµm visible channel data (below; click image to play animation). Also note the numerous long, narrow streaks of snow on the ground across parts of northern Illinois into northern Indiana, left behind from previous events.
AWIPS images of MODIS 0.65 Âµm visible channel data with overlays of MADIS 1-hour interval satellite winds (below) indicated that the LES band features were generally propagating southward at speeds of 20-30 knots.
A comparison of a 1-km resolution MODIS 11.0 Âµm IR image with the corresponding 4-km resolution GOES-13 10.7 Âµm IR image (below) showed that IR brightness temperatures within parts of the LES band feature were as cold as -25 to -30Âº C (cyan to darker blue color enhancement).
The 1-km resolution POES AVHRR Cloud Top Height (CTH) product (below) indicated that the LES feature exhibited CTH values which were generally in the 2-3 km range (darker violet color enhancement).
The POES AVHRR Cloud Particle Effective Radius product (below) helped to highlight the glaciated portions of the LES band, where the radius of the larger ice crystals was in the 50-60 Âµm range (green color enhancement), compared to the supercooled water droplet clouds consisting of smaller particles in the 15-25 Âµm range (cyan color enhancement).