Report written by Vanda Grubisic, Thursday, March 11
Synoptic overview:
The high pressure ridge, which dominated the weather over the valley over the past several days, had shifted southward. This had brought weak westerly winds over southern California and Nevada. The Eta and COAMPS forecast for March 10 showed a development of a short wave with an episode of strong easterly flow over the Owens Valley. The 12 UTC March 9 runs of the two models differed in the timing of this event, with the Eta model predicting an earlier onset and a maximum around 10 p.m. on March 10, and the COAMPS predicting a later onset and a maximum at 4 a.m. on March 11. This easterly wind event was the focus of IOP 2.
The plan of operations for IOP 2 on March 10-11:
1. MAPR: on all the time
2. MISS: to be located on the east side of the valley along the road connecting Kearsage and the DRI ground network stations 12 and 16, as far south as possible
3. MGLASS: no activity
4. Lemoore: no activity
Two radiosonde launches were planned in the valley, one each from the MAPR and MISS sites. The exact times of the launches were to be specified before the beginning of the IOP based on the new forecast.
Summary of operations and observations:
In the subsequent initializations and runs of the two models, the onset of the easterly flow episode was shown earlier, especially in the new COAMPS forecast. Consequently, the beginning of the IOP was declared "as soon as it was possible to turn the MISS on". During the IOP, it was decided to call the end at 18 PST (0200 UTC March 11). This was a strong wind event with NNW (324 degrees) winds in the valley. The ground network data show that the winds started increasing between 8 and 9 PST, reached the peak between 10 and 12 PST (depending on the station), and the minimum at 18 PST. The strongest winds were recorded by stations 12 and 16 on the east side of the valley, with gusts up to 40 mph (17-18 m/s). There was an associated strong dust event, with a white dust cloud in the south part of the valley from the dry Owens Lake bed.
MISS was located at the "East Valley site" at Lat 36.778 N, Lon 118.102 W, and altitude 3775 ft, and was turned on at 11:20 a.m. Two radiosondes were launched from the MISS site, at 11:30 a.m. and 1:30 p.m. Both radiosondes transmitted temperature and humidity data on both the ascent and descent. (Note: The descent will not appear in the quality-controlled dataset, and the wind data was recorded only during the ascent.) The sounding profiles show NNW wind near the ground turning into NE winds just below the mountain height and increasing up to 500 mb, with a base of the stable layer at 600 mb. This stable layer was more pronounced in the second sounding, the winds were stronger in the first.
Both MISS and MAPR operated well throughout the IOP period. MAPR winds reached up to 3 km AGL, showing NNW winds turning into NNE winds above 2 km AGL. At the beginning of this event, between 15:30 and 17:30 PST, MAPR recorded positive vertical velocities (0.5-1 m/s), followed by a 1.5 hour period of negative vertical velocities (1-1.5 m/s) between 600 m and 2.5 km AGL (signature of waves?). Winds obtained by MISS were similar, except for reaching only up to 2.2 km AGL. At both sites, the wind direction became more uniform with height and more northerly toward the end of the event.