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Comments on the 4JAN07 Storm (IOP-3)

This storm, still in progress as of 16 UTC, has exhibited the following characteristics that are different from the earlier IOPS, and most of the ones we saw las winter:

1) It is shallow.
Satellite IR cloud top temperatures have been everywhere unusually warm over the ARB and the S-band precip profiler echo tops have remained below about 5 km. Consistent with this shallowness, the storm in the Coast Range has was a non-brightband, warm-rain kind of event at the Cazadero site. In addition to not exhibiting a melting layer bright band (even though echo tops may be above the 0C level), these periods generally contain very high concentrations of small raindrops and very low concentrtions of large drops. Most of the Z-R relations commoly applied by NEXRAD underestimate rain rates in these situations. Whether the non-brighband rain is also prevailing over the ARB in the Sierra is less clear. Some period of brightband have definitely been observed there by the profiling radars during part of the storm, but other time periods may well be non-brightband.

2) Orographic enhancement of precipitation is impressive.
Sacramento and most of the Central Valley are receving very little precip, while the foothills and mountain sites in the Sierra have accumulated over 2 inches of liquid and isn't finished yet.

3) Low level jet is developing.
As John Brown predicted, a low level jet has developed with this storm, at least in the northern part of the Central Valley. The LLJ can be seennicely in the maxima pattern of strong southerly winds about 1 km above the surface in the HMT wind porfiler data a Chico.

4) As a test of this forum blog, I will buy a beer for the first HMT preson to comment on these comments.

- Martner


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