Sunday, January 2, 2011

IOP 5: Clouds: Up High and Down Low?

Broken mid and high level clouds have moved over the Salt Lake Valley on Sunday night drastically altering the surface energy balance. In contrast to last night, the surface is only slowly cooling this evening as downwelling long wave radiation from the cloud bases alters the surface energy balance. Most sites are now reporting only a slightly negative net radiation, indicative of minor cooling. However, satellite imagery suggests that some clearing may occur for the second half of the night, which could lead to a deeper nocturnal inversion.

The nocturnal inversion isn't the only game in town though, with much of the stability found within the valley residing a sharp elevated inversion layer that formed due to subsidence and warm air advection (with some contribution from nocturnal cooling in its lowest portions).

Within this inversion layer there now appears to be a moistening layer which is seemingly close to forming clouds. This is very much in keeping with some of the model indicated evolution for this event and part of what we are hoping to observe overnight tonight and into the day tomorrow. The formation of clouds is both interesting in terms of deciphering the source of the moisture, but also because when (and if) clouds form, the nature of the cold air pool is drastically altered. Cooling is then driven by cloud top radiation while the layers below the clouds are dominated by overturning generated by negatively buoyant parcels.

Now it is just a waiting game to see what comes to pass.

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