Latest Forecast for Mauna Kea Observatories
10 AM HST (2000 UTC) Thursday 07 August 2008

Warnings
Moderate winds

Cloud Cover and Precipitation Forecast
The summit will remain dry and stable throughout the night. There is a chance that cirrus will be visible along the northern skies throughout the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 8 C this afternoon and 4 C for the night. Winds will be from the ESE at 15-25 mph through this evening, increasing to 20-30 mph for the morning hours. Seeing will likely be around 0.8 arcseconds, while precipitable water is expected to be in the 1-1.5 mm range for the night.

Discussion
The tradewind inversion will continue to cap low-level moisture near 8-9 thousand feet and keep the mid/summit-level air mass dry and stable through the next 5 nights. Daytime clouds will be minimal and short-lived throughout the forecast period.

Scattered cirrus passing to the north will likely be visible in that direction for tonight and perhaps tomorrow night. Skies will remain predominately clear for the remainder of the forecast period.

Precipitable water will likely linger near 1.1-1.2 mm throughout most of the forecast period.

Although weak shear/turbulence will persist in the free atmosphere through at least Saturday night, boundary layer turbulence will probably result in poorer than average seeing through Friday night. Subsiding summit-level winds should help improve seeing toward 0.6 arcseconds for Saturday night and perhaps the following 2 nights. However, there is a chance for mesoscale turbulence in the area during the latter period.

Skies finally opened this morning (a bit behind schedule) and should remain predominately clear as an upper-level ridge sits overhead for the next few nights. This ridge will enhance the subsidence in the area, which help warm up summit temperatures, keep PW near 1.1 mm, and likely result in winds near 20-25 mph throughout most of the forecast period. Actually summit-level winds are expected to subside as the ridge shifts a bit southward over the weekend, which should reduce boundary layer turbulence during that time. Still, the upper-level ridge will continue to keep the tropical upper tropospheric trough and its associated jet well into next week. This should result in weak/calm flow aloft and probably better than average seeing, once summit-level winds taper over the weekend. Finally, the mid-level ridge will maintain steady large-scale subsidence in the area and keep the inversion well-defined near 8 thousand feet through at least the middle of next week.