IOP 11: 1200 UTC April 10 - 0000 UTC April 11
(0500 PST April 10 - 1700 PST April 10)

Report written by Jim Doyle, Sunday, April 11

Synoptic overview:

A strong shortwave trough propagated along the downstream portion of a short-wavelength ridge that resulted in strong northerly flow over the Sierras.


The plan of operations for IOP 11 on April 10:

1. MAPR: on all the time, one radiosonde launch at 12 UTC 10 April (one practice sonde at 00 UTC 10 April at MAPR)
2. MISS: on all the time, located at the Independence Airport
3. MGLASS: no activity
4. Lemoore: no activity


Summary of operations and observations:

This event was characterized by dry, northerly flow in the valley. The valley was partly cloudy late in the day on April 9 with a few roll clouds oriented normal to the axis of the valley that were apparent just south of Big Pine and some cumulus over the Sierra and Inyos. On April 10, the conditions were clear skies and good visibility.

MISS was located at the Independence airport and documented a northerly low-level jet in the 1-2 km layer with a maximum near 25 m/s at 12 UTC and a deeper layer of northwesterly flow at 00 UTC 11 April.

The sounding launched from MAPR at 1200 UTC 10 April showed strong northerly flow present between 1 and 2 km (v component). A shallow stable layer was present near 650 mb and a nocturnal inversion was present at the surface.

MAPR documented northerly winds early on April 10. During the evening, the MAPR data was contaminated by migratory birds. A possible signature of wave activity was apparent in the MAPR vertical velocity data in the time period 17-21 UTC 10 April. Periods of rising and sinking motion that were coherent in time were present in the low-levels at MAPR during this time period.

The surface network indicated weak flow near 12 UTC and as the solar radiation increased after sunrise, the strong northerlies were mixed downward. Gusty northerly winds were present in Owens Valley with most surface stations indicating sustained winds greater than 20 mph for a period of time in the morning with peak gusts around 36 mph. A second period of strong northerly winds at the surface occurred at around 00 UTC 11 April.