Saturday, December 18, 2010

Stratocumulus ribs on 18 December 2010

The sky this morning featured a horizon to horizon series of parallel ribs of blue and orange.  This kind of sky doesn't come around often and so I decided to shoot interval shots facing to the south from the deck (east Norman, OK).  The shot below was taken around 0753 CST (1353 UTC).

Taken at 5 second intervals, this time lapse shows the bands hold together well enough that they don't appear to change much before the steering winds take the clouds toward the southeast horizon.  The vibrant contrast between blue and light orange decrease as the loop goes on because higher clouds began to filter in overhead.  See the GOES12 visible image below

1445 UTC GOES 12 image for 18 Dec 2010.  The white arrow corresponds to our location.

The surface observations, point to these clouds at 7.5 kft AGL. According to the sounding at Norman, that level is around -6 to -8 deg C.  Typically this cloud temperature would be prone to the formation of ice crystals that would eventually scavenge the remaining liquid water turning the cloud into fields of virga.  But perhaps here there isn't enough residence time in each band for that process to start before any air parcel within a cloud band dries upon leaving. 

KOUN 181451Z AUTO 00000KT 10SM SCT060 OVC075 04/02 A3018 RMK AO2
KOUN 181431Z AUTO 24003KT 10SM SCT060 OVC075 04/02 A3019 RMK AO2
KOUN 181411Z AUTO 00000KT 7SM OVC075 03/02 A3018 RMK AO2
KOUN 181310Z AUTO 00000KT 7SM SCT060 OVC075 03/02 A3017 RMK AO2

The 12 UTC Norman, OK sounding.  The banded altocumulus clouds probably reside near the base of the saturated inversion at 750 mb in the sounding. 

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