by James Doyle
Report written by Jim Doyle and Qingfang Jiang, Saturday, April 17
Synoptic overview:
A developing trough moved from the Pacific to the California coast bringing southwesterly flow over the Sierras beginning Tuesday at 12 UTC. The entire week featured periods of strong cross mountain (i.e., southwesterly or westerly) flow with a chance of mountain wave activity every day from Tuesday (April 13) through Friday (April 16).
The plan of operations for IOP 12 from 12 UTC April 13 to 12 UTC April 17:
1. MAPR: on all the time
2. MISS: on all the time, at the Independence airport
3. Radiosonde launches from MAPR and MISS:
| April 13 (Tuesday) | 12 UTC, 18 UTC (MISS) |
| April 14 (Wednesday) | 00 UTC (MISS), 12 UTC (MAPR) |
| April 15 (Thursday) | 00 UTC, 06 UTC, 12 UTC, 15 UTC, 18 UTC, 21 UTC (MAPR) |
| April 16 (Friday) | 00 UTC, 03 UTC, 06 UTC, 12 UTC, 18 UTC (MAPR) |
| April 17 (Saturday) | 00z, 06z, 12z (MAPR) |
4. Radiosonde launches from MGLASS:
| April 13 (Tuesday) | 12 UTC (Tulare), 18 UTC (Tulare) |
| April 14 (Wednesday) | Downtime |
| April 15 (Thursday) | Downtime |
| April 16 (Friday) | 00 UTC (test), 12 UTC, 15 UTC, 18 UTC (Tulare), 21 UTC (Tulare) |
| April 17 (Saturday) | 00 UTC, 03 UTC, 06 UTC, 12 UTC |
5. Radiosonde launches from Lemoore:
| April 14 (Wednesday) | 00 UTC, 06 UTC, 18 UTC |
| April 15 (Thursday) | 00 UTC, 06 UTC, 14 UTC, 16 UTC, 18 UTC, 21 UTC |
| April 16 (Friday) | 00 UTC, 06 UTC, 14 UTC (failed), 18 UTC |
| April 17 (Saturday) | 00 UTC |
Summary of operations and observations:
The extended IOP 12 featured fairly strong westerly or southwesterly flow near and above the mountain top level. Surface network documented quasi-diurnal variation of the wind in the valley; the wind in the valley was easterly or southerly in the morning and early afternoon and shifted to westerly in the afternoon or late afternoon. Wave clouds were often observed around late afternoon.
April 13 (Tuesday)
On April 13, radiosondes from both the upstream side (i.e. MGLASS) and the valley (i.e. MISS site at the airport of Independence) showed southwesterly wind at the 700 mb level and aloft. The wind speed at 700 mb was 20-25 knots. The surface network documented southeasterly flow in the morning and early afternoon. Station 1 documented strong westerly flow approximately between 1400 and 1900 PST with a peak gust of 50 mph. Station 4 indicated westerly flow as well, until evening hours, when the flow became weak and from the northeast.
Both MISS and MAPR documented the general westerly flow evolution as well. Additionally, between 2100 and 2200 UTC, MAPR showed an easterly component near the surface and westerlies aloft.
In the valley, rather thick cirrus overcast with some lenticular clouds were observed in the morning of April 13. In the late afternoon, after the wind shifted to westerly, lenticular clouds were observed. Dust devils were seen along the eastern end of the valley, particularly near the time of the wind shift.
April 14 (Wednesday)
While soundings showed strong westerly wind at the mountain top level and aloft, the surface network documented a wind shift from moderate northerly flow in the morning to strong westerly flow in the afternoon. According to station 1, the strong westerly flow started around 1200 PST and became weak toward the evening with a peak gust of 54 mph. Station 6 indicated a period of northeasterly winds were present between 1500-1600 PST, during which station 1 was experiencing strong westerly wind.
No wave clouds were observed in the valley until later afternoon. Some lenticular clouds were seen toward the late afternoon.
by James Doyle
April 15 (Thursday)
Soundings showed southwesterly flow above the mountain top level with an inversion located between 500-600 mb. Soundings launched from the valley (i.e. MAPR site) in the afternoon indicated that the flow was southeasterly below 700 mb. The 00 UTC (April 16) sonde experienced a sharp descent around the 500 mb level. Surface station 1 indicated the presence of wave clouds underneath thin cirrus to the north of Bishop. Associated with the development of the westerly flow in the valley, nice lenticular clouds were observed to the lee of Mount Whitney and between Independence and Bishop. Dust devils were seen near Big Pine around 0500 PST.
by James Doyle
April 16-17 (Friday-Saturday)
Radiosondes from both the valley and the upstream side showed a strong southwesterly flow aloft and southeasterly flow below the mountain top level. Both MISS and MAPR documented southwesterly winds above 2 km and southeasterly winds under 2 km in the afternoon.
Station 1 showed that the northwesterly flow penetrated into the valley around 1400 PST with a peak gust of 34 mph which was weaker than the earlier days of the week. No easterly flow was observed in the valley.
In the morning, the clouds included altocumulus and cirrus overcast with snowfall over the mountain tops. Toward late afternoon (1500 PST), lee-wave clouds were observed over the valley with a well-defined "Foehn wall". The lee-side clearance ("Foehn gap") is clearly seen from MODIS images as well.
Northern Owens Valley; Independence Airport
by Shane Mayor