Bay-Effect Snow Showers over Virginia and North Carolina

January 24th, 2013 |
Suomi/NPP VIIRS Visible Image

Suomi/NPP VIIRS Visible Image

The Arctic airmass that has overspread the eastern two-thirds of the United States is cold enough that sustained northerly winds down the length of Chesapeake Bay yielded snow showers over extreme southeastern Virginia and northeastern North Carolina. The Suomi/NPP Visible image, above, shows a distinct cloud band over the eastern side of Chesapeake Bay that stretches southwards towards the Outer Banks of North Carolina. Snow was being reported at a number of stations across the Hampton Roads area in southeastern Virginia, with visibility being restricted to 2 miles at Oceana Naval Air Station (KNTU) — and snow was reported as far south as Currituck, North Carolina (KONX).

Bay-effect (or Lake-effect) snows typically occur when the temperature difference between the water surface and lower tropopshere (for example, 850 mb) exceeds about 13 to 15 C. The sounding from Roanoke, VA, from 1200 UTC on 24 January shows temperatures near -12 C at 850 mb. Sea-surface temperatures over the lower Bay are around 5 C. This animation of two MODIS visible images, from 1506 UTC and from 1640 UTC, shows the snow band shifting from the western shore to the eastern shore of the Bay. This event was also caught on radar.

POES AVHRR 0.86 µm visible channel and 12.0 µm IR channel images

POES AVHRR 0.86 µm visible channel and 12.0 µm IR channel images

A comparison of 1-km resolution POES AVHRR 0.86 µm visible channel and 12.0 µm IR channel images at 14:11 UTC or 9:11 AM local time on the morning of 24 January 2013 (above) showed a prominent bay-effect cloud band as it was becoming well-organized over the northern portion of Chesapeake Bay. Cloud top IR brightness temperatures were as cold as -25.5 C (darker blue color enhancement), indicating that the cloud band was almost certainly glaciated. Note the observation of blowing snow (reducing visibility to 2 miles) at Patuxent River Naval Air Station (station identifier KHNK) near the southern end of the cloud band.

The development and movement of the bay-effect snow bands could be seen on 1-km resolution GOES-13 0.63 µm visible channel images (below; click image to play animation).

GOES-13 0.63 µm visible channel images (click image to play animation)

GOES-13 0.63 µm visible channel images (click image to play animation)

On the previous day, the 1-km resolution MODIS Sea Surface Temperature (SST) product (below) revealed SST values greater than 40 F or 4.4 C (lighter blue color enhancement) over the central and southern portions of Chesapeake Bay.

MODIS Sea Surface Temperature image

MODIS Sea Surface Temperature image

 

Suomi NPP VIIRS imagery in AWIPS II

January 23rd, 2013 |
Suomi NPP VIIRS 0.64 µm visible channel images

Suomi NPP VIIRS 0.64 µm visible channel images

AWIPS II images of Suomi NPP VIIRS 0.64 µm visible channel images (above) showed a very detailed view of “transverse banding” cloud features across parts of northwestern Canada (primarily in northeastern British Columbia) on 23 January 2012. This transverse banding — with the cloud features oriented perpendicular to the flow — is a satellite signature that indicates an increased potential for turbulence. Suomi NPP VIIRS imagery is now being broadcast at full 375-meter resolution over the new “POLARSAT” NOAAPORT channel (currently only available for the Alaska Region), for display in the next generation of AWIPS (AWIPS II).

The corresponding Suomi NPP VIIRS 11.45 µm IR channel images are shown below. Cloud top IR brightness temperatures were colder than -60º C (dark red color enhancement) in many of the bands.

Suomi NPP VIIRS 11.45 µm IR channel images

Suomi NPP VIIRS 11.45 µm IR channel images

A comparison of the the VIIRS visible and IR images at 19:05 UTC (11:05 AM local time) are shown below.

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

Variations in Suomi/NPP Day/Night Band Lunar Illumination

January 22nd, 2013 |
Suomi/NPP VIIRS Day/Night Band Imagery (click image to toggle between times)

Suomi/NPP VIIRS Day/Night Band Imagery (click image to toggle between times)

The Day/Night band on Suomi/NPP produces Night-Time visible imagery using illumination from natural (the moon, forest fires) and man-made sources (city lights, gas flares). Interpretation of the imagery should be done, therefore, with a knowledge of the Lunar phase. In the example above, note the dimming of the clouds over the central plains of the United States between 0752 UTC and 0933 UTC. The 0933 UTC image also shows a gradation in the cloud brightness from east to west — clouds off the west coast of the United States are brighter than clouds over the Plains. The waxing gibbous moon is more than 80% full on 22 January, providing ample light when above the horizon. Moonset occurred over the central USA around 0900 UTC on 22 January; on the West Coast, moonset was closer to 1100 UTC. In the later image, only the regions west of the Rockies are illuminated by the Moon; elsewhere the moon has set, and this is reponsible for the differences in how the clouds are presented.

The 0752 UTC image also contains an excellent example of Moon Glint over the southern Gulf of California. The setting moon is low in the sky, and reflection off the ocean surface is detected.

These images can also be observed using the SSEC Web Map Server. The image below that includes Day/Night Band imagery and Suomi/NPP Tracks was produced with this url.

Suomi/NPP VIIRS Day/Night Band Imagery produced by SSEC WMS

Suomi/NPP VIIRS Day/Night Band Imagery produced by SSEC WMS

Multiple-vehicle accidents caused by snow squalls in the Cincinnati, Ohio area

January 21st, 2013 |
GOES-13 0.63 µm visible channel images (click image to play animation)

GOES-13 0.63 µm visible channel images (click image to play animation)

A number of multiple-vehicle accidents occurred in the Cincinnati, Ohio area when bands of heavy snow squalls moved through and caused white-out conditions that reduced visibility to near zero at times on 21 January 2012. McIDAS images of 1-km resolution GOES-13 0.63 µm visible channel data (above; click image to play animation) showed the development of widespread convective snow bands as they moved through the Ohio Valley region. KCVG denotes the location of the Cincinnati/Northern Kentucky International Airport, and Interstate highways are plotted in violet. As the clouds cleared to the west, the narrow streaks of snow on the ground seen in northern Illinois and Indiana revealed the mesoscale nature of the heavy snowfall produced by the more intense convective snow bands.

Three comparisons of AWIPS images of 1-km resolution visible and IR data from polar-orbiting satellites (below) — POES AVHRR at 14:47 UTC or 9:47 AM local time; MODIS at 16:10 UTC or 11:40 AM local time; and Suomi NPP VIIRS at 17:56 UTC or 12:56 AM local time — showed that the cloud top IR brightness temperatures of many of the more well-developed convective cloud bands were -20º C and colder (cyan to blue color enhancement), suggesting that those cloud bands had glaciated and were likely producing snowfall.

POES AVHRR 0.63 µm visible channel and 10.8 µm IR channel images

POES AVHRR 0.63 µm visible channel and 10.8 µm IR channel images

MODIS 0.65 µm visibe channel and 11.0 µm IR channel images

MODIS 0.65 µm visibe channel and 11.0 µm IR channel images

Suomi NPP VIIRS 0.63 µm visible channel and 11.45 µm IR channel images

Suomi NPP VIIRS 0.63 µm visible channel and 11.45 µm IR channel images

Finally, a comparison of 1-km resolution Suomi NPP VIIRS 11.45 µm IR and 4-km resolution GOES-13 IR channel images (below) demonstrated the advantage of higher spatial resolution imagery for locating the important cloud band features that were cold enough to be glaciated and were therefore capable of producing snowfall.

Suomi NPP VIIRS 11.45 µm IR and GOES-13 10.7 µm IR images

Suomi NPP VIIRS 11.45 µm IR and GOES-13 10.7 µm IR images