November « 2012 « CIMSS Satellite Blog

Cold air drainage into the valleys of the Yukon

November 29th, 2012

Suomi NPP VIIRS 11.45 µm IR image + METAR surface reports

As an area of arctic high pressure settled over the Yukon region of northwestern Canada on 29 November 2012, strong radiational cooling led to very cold surface air temperatures (-49º F at Mayo, station identifier CYMA) and drainage of this cold, dense air into the valleys and lower elevations. An AWIPS image of Suomi NPP VIIRS 11.45 µm IR channel data with an overlay of METAR surface reports (above) showed the dendritic pattern of cold air drainage into the valleys (darker blue color enhancement); the coldest IR brightness temperature on the image was -51º C (violet color enhancement).

Even though fog and freezing fog was being reported at a few of the surface stations, a comparison of the Suomi NPP VIIRS 11.45 µm IR, 0.7 µm Day/Night Band, and the 11.45-3.74 µm “fog/stratus product” images (below) indicated that not all of the valley fog features could be easily seen — in particular, most of the areas of shallow ice fog did not exhibit a signal on the Day/Night Band or the fog/stratus product IR brightness temperature difference images.

Suomi NPP VIIRS 11.45 µm IR, 0.7 µm Day/Night Band, and 11.45-3.74 µm “fog/stratus product”

Posted in Arctic, Fog detection, Suomi NPP, VIIRS | No Comments »

Strong Tornado in southern Italy

November 28th, 2012

Meteosat-9 10.8 µm infrared channel images (click image to play animation)

A rare November tornado moved through Taranto, (YouTube video, AccuWeather blog entry) in southern Italy, on Wednesday November 28th. A loop of 10.8 µm Meteosat-9 imagery (above) shows the development of an overshooting top in a thunderstorm that is moving over Taranto between 0900 and 0915 UTC (Note that the time indicated on the satellite image is the nominal time — the time that the satellite starts scanning. The actual scan time over southern Italy is approximately 10 minutes later than the nominal time). Such cloud-top features are frequently associated with severe weather. A faint suggestion of an enhanced-V/thermal couplet is apparent in the later imagery as the strong thunderstorm moves northward across the Salento peninsula and then into the Adriatic Sea. METOP-A infrared imagery (below) shows the thunderstorm complex about an hour before a tornadic storm moved inland from the Ionian Sea. The corresponding Meteosat-9 image is here. The higher spatial resolution of the polar orbiter METOP-A allows the discernment of much finer detail in the cloud-top features.

METOP-A 10.8 µm IR imagery

Meteosat-9 0.6 µm visible channel images (click image to play animation)

Visible imagery from Meteosat-9, above, also shows the development of the overshooting top associated with the tornadic cell. A higher-resolution visible imager from METOP-B, below, showed the line of thunderstorms in which the tornadic cell, indicated by the yellow arrow, was embedded.

METOP-B 0.63 µm Visible imagery

The tornadic weather was associated with an exceptionally deep extratropical cyclone. On Monday, that system was over the northwestern Mediterranean (see below), with ample evidence of exceptionally cold upper-level air over the Bay of Biscay. This storm also had a history of producing supercellular thunderstorms, as evidenced by the storm development just south of France in the animation below.

Meteosat-9 Visible imagery (0.6 µm) (click image to play animation)

A multi-day loop of the Meteosat-9 infrared window channel imagery is below. It shows the strong extratropical cyclone moving across southern Europe.

Meteosat-9 10.8 µm infrared channel images (click image to play animation)

Posted in General interpretation, Meteosat, Other Satellites, POES, Severe convection | No Comments »

Unusual pattern of cloud edge clearing

November 28th, 2012

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

Hat tip to Chad Gravelle (CIMSS), who asked about the curious pattern of trailing edge cloud clearing across South Carolina on the morning of 28 November 2012. Given that the etiology of these elongated cloud clearing line features is unknown at this point, this case is a perfect candidate for the “What the heck is this?” blog category. An animation of GOES-13 0.63 µm visible channel images (above; click image to play animation) shows the unusual cloud edge clearing pattern moving southwestward across South Carolina.

These cloud features were also seen on an AWIPS image of POES AVHRR 0.63 µm visible channel data at 13:53 UTC (below). Surface observations showed that air with drier dew point values was being advected southwestward into the trailing cloud edge, but the wind speeds were generally light at most reporting sites — so the cause of the elongated “clear slot” features is unclear.

POES AVHRR 0.63 µm visible channel image

The three POES AVHRR products shown below indicated that these trailing edge cloud features were liquid water clouds, which exhibited cloud top temperature values of +1 to +3º C, with a cloud top height value of 2 km.

POES AVHRR Cloud Type product

POES AVHRR Cloud Top Temperature product

POES AVHRR Cloud Top Height product

On the GOES-13 and POES AVHRR images, you can see some evidence of similar cloud edge clearing lines over the Alabama/Georgia border region. During the previous overnight hours, this cloud signature was very well-defined over Georgia, as seen on a Suomi NPP VIIRS 0.7 µm Day/Night Band “night-time visible image” at 06:43 UTC or 1:43 AM local time (below).