Living in the Earth's Atmosphere: Recreational Meteorology: Northerly Wave January 7, 2012

Northerly wind conditions prevailed for most of December 2011 and the first part of 2012. On at least two occasions conditions were favorable for exceptional mountain wave forming off of the Coast Ranges. The presence of a stable isothermal or inverted layer just above the mountain top with suitable wind speed profiles were present. Conditions were similar to "textbook conditions" described by Case 4 in UCAR MetEd module (see representative soundings below). The temperature profile was quite similar. Wind speeds actually ramped with altitude which is generally more favorable than uniform wind speed. Although low level wind speeds were not as high as the example the spring action of the stable layer being lifted over the ranges induced significant bounce. Downslope winds in the West side lee of the Santa Cruz Mtns. near the coast were significant. Several glider pilots were able to get to near 18,000' and wave was ubiquitous in the Bay Area.

The RASP BLIPMAPS for the region at the 3km and 750m resolution are also shown below. Notice the difference between the two resolutions. The http://www.meted.ucar.edu/mesoprim/mtnwave/print.htm module section 5 discusses the importance of the spatial scales in wave prediction. This often clearly evident how the different resolutions of the RASP VV charts will depict the location of wave. On some occasion no wave is evident at the 3km but very apparent in the 750km scale. This is often the case with higher frequency wave.

2PM Snapshot of Winds Aloft

The strong isentropic gradient in the x-sectional profile of the example below show the influence the stable layer has on initiating the oscillation (bounce). This was evident in soundings on 1/7/12.