Elevated stratus cloud deck over Texas

January 13th, 2011 |
GOES-13 10.7 µm IR images (click image to play animation)

GOES-13 10.7 µm IR images (click image to play animation)

AWIPS images of 4-km resolution GOES-13 10.7 µm 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 µm 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.

Blended Total Precipitable Water (TPW) product

Blended Total Precipitable Water (TPW) product

A comparison of the 1-km resolution POES AVHRR 10.8 µm 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 -5º C and -12º C — was composed of primarily supercooled water droplets (green color enhancement on the Cloud Type product).

POES AVHRR 10.8 µm IR + POES AVHRR Cloud Type Product

POES AVHRR 10.8 µm IR + POES AVHRR 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 µm IR image, it’s appearance on the corresponding 1-km resolution MODIS 3.7 µm 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.

MODIS 11.0 µm IR + MODIS 3.7 µm shortwave IR images

MODIS 11.0 µm IR + MODIS 3.7 µm shortwave IR images

This was confirmed by a comparison of the 1-km resolution POES AVHRR 3.7 µm 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 µm 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 µm radius, darker blue color enhancement).

POES AVHRR 3.7 µm shortwave IR image + Cloud Particle Effective Radius product

POES AVHRR 3.7 µm shortwave IR image + Cloud Particle Effective Radius product

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 µm visible image as the Red component and the MODIS 2.1 µm near-IR “snow/ice channel” as the Green and Blue components of the image.

MODIS false-color Red/Green/Blue (RGB) image (created using channels 01/07/07)

MODIS false-color Red/Green/Blue (RGB) image (created using channels 01/07/07)

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.

MODIS Land Surface Temperature product

MODIS Land Surface Temperature product

Northeast US winter storm

January 13th, 2011 |
GOES-13 6.5 µm water vapor images (click image to play animation)

GOES-13 6.5 µm water vapor images (click image to play animation)

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 µm “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 µm water vapor image at 18:15 UTC and the corresponding MODIS 6.7 µm 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 75º West longitude).

MODIS 6.7 µm and GOES-13 6.5 µm water vapor channel images

MODIS 6.7 µm and GOES-13 6.5 µm water vapor channel images

GOES-13 water vapor + RUC80 PV1.5 pressure + Cross Section line

GOES-13 water vapor + RUC80 PV1.5 pressure + Cross Section line

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 UTC  (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).

RUC80 model cross section

RUC80 model cross section

A sequence of 1-km resolution MODIS 11.0 µm IR and POES AVHRR 10.8 µm IR image (below) showed the development of banding features with IR brightness temperatures as cold as -50 to -60º C (orange to red color enhancement).

MODIS 11.0 µm and POES AVHRR 10.8 µm IR images

MODIS 11.0 µm and POES AVHRR 10.8 µm IR images

After the storm departed, a comparison of a 13 January MODIS 0.65 µm 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 gray and lighter shades of red on the RGB image, respectively).

MODIS 0.65 µm visible image + MODIS false-color Red/Green/Blue (RGB) image

MODIS 0.65 µm visible image + MODIS false-color Red/Green/Blue (RGB) image