IOP 2, 29-30 Nov 2001

IOP 2: 29-30 November 2001

Time Period of IOP

1200 UTC 29 Nov-0000 UTC 30 Nov

Overview of IOP

The major storm of 28-29 November was followed the next day by a much less intense short wave trough, which passed over the radar area between 0900 UTC 29 November and 2100 UTC 30 November 2001. At 500 mb, this weak short wave moved rapidly from the west northwest from a longitude of 150^oW at 1200 UTC 29 November (Fig. 1a) to 135^oW by 0000 UTC 30 November (Fig. 1b). It was over the Oregon-Washington area at 1200 UTC 30 November (Fig. 1c). The trough was evident at 850 mb at 135^oW at 0000 UTC 30 November (Fig. 2a), and by 1200 UTC it was affecting Oregon with southwesterly winds and weak warm advection (Fig. 2b). The region of clouds associated with the trough was just off the Oregon coast at 2100 UTC 29 November (Fig. 3a). The S-Pol radar at 2200 UTC showed scattered small convective cells (Fig. 4a). The region of clouds was over western Oregon at 0300 UTC 30 November (Fig. 3b). The coldest cloud tops formed a patchy pattern. At 0900 UTC 30 November, the last of these patches of cold cloud top was approaching the radar area from the west (Fig. 3c). It was quite convective in character and just preceded the leading edge of the warm-frontal clouds of the next short wave. From 0600-0900 UTC the S-band profiler showed the echo lowering to the surface as the trough approached (Fig. 5a), and then from 0900-1200 it showed rather shallow and discontinuous convective cells (Fig. 5b). By 1500 GMT the echo on the S-band profiler had become deeper and more continuous (Fig. 5c). This echo area was located over the S-Pol area at 1500 UTC (Fig. 4b), and it continued to be located over the S-band until about 1630 UTC (Fig. 5d).