IOP 9: 1800 UTC March 30 - 0600 UTC March 31
(1000 PST March 30 - 2200 PST March 30)

Report written by Vanda Grubisic, Wednesday, March 31

Synoptic overview:

Ahead of an extended trough, located off the coast of northern California, Oregon, and Washington, strong generally southerly winds were predicted over the project area for the period of two days starting on 12 UTC March 30. Predicted winds over Owens Valley are strong at 35-40 knots at 500 mb and 30 knots at 700 mb. COAMPS predicted some wave activity over Owens Valley (at the bend in the Sierra near Lone Pine and downwind of the Inyo range) with vertical velocity at 4 km in the range of 3 m/s.


The plan of operations for IOP 9 on March 30:

1. MAPR: on all the time
2. MISS: to be located at OV5 location, between stations 1 and 2 of the ground network, one radiosonde launch at 00 UTC March 31
3. MGLASS: one radiosonde launch from Porterville (Rt. 190 off US 99, south of Tulare)
4. Lemoore: no activity


Summary of operations and observations:

This was a strong southerly wind event in the valley. Moderate wave activity was recorded by the wind profilers. Dust from the dry Owens Lake bed was picked up by the strong surface winds and transported north to Bishop and beyond. Nice lenticulars formed over the Inyo Range, and some fractocumulus was observed over the valley (see below).

Owens Lake; west of Lone Pine
1452 PST
by Alex Reinecke

MISS was located in the Sierra foothills at the OV5 location, between stations 1 and 2 of the ground network. The wind profiler data is available only from the second half of the IOP period 00 UTC to 06 UTC March 31 (Note: satellite communications were not working at OV5, data transferred afterward). It shows predominantly southerly winds from the ground up to 5 km. In the first half of this period, winds above 3 km had a small westerly component and reached up to 18 m/s. Vertical velocity obtained by MISS shows 1.5 h long periods of first negative, then positive vertical velocity close to 1-2 m/s between 00 and 03 UTC. A fractocumulus cloud (roll cloud?) was observed visually south of the MISS site at about that time.

Sierra Nevada; MISS site, west of Independence
1708 PST
by Alex Reinecke

MAPR also documented generally southerly winds that had a weak westerly component above 3 km, and vertical motions above 3 km suggestive of waves. The surface station at the MAPR site showed sustained southerly winds reaching a maximum of 15 m/s around 19 UTC March 30, and starting to die out around 02 UTC March 31 (18 PST, after sunset). MAPR site was in the middle of the dust cloud.

The MGLASS sounding shows a strong stable layer (actual inversion) close to 4 km (around 550 mb), moisture profile increasing with height up to that level, southerly winds below 2 km, and SSW winds aloft.

Strong southerly winds were documented by the ground network stations east of the highway between 10 PST March 30 and 02 PST March 31. The first occurrence of southerly winds at station 1 on the western slope was around 14 PST. Up to that point, a thermal, upslope circulation prevailed. At other stations on the western slope, the southerly episode started even later (approximately 18 PST). An intrusion of air with slightly higher moisture content (an increase in RH and dew point at constant temperature) was recorded at all stations on the western slope between 18 and 19 PST.