Latest Forecast for Mauna Kea Observatories
5 PM HST Thursday 08 September (0300 UTC Friday 9 September) 2011

Warnings
None

Cloud Cover and Precipitation Forecast
The summit will remain clear, dry and stable through the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 7 C, with winds from the SE at 5-15 mph, seeing around 0.45-0.5 arcseconds and precipitable water in the 1-1.5 mm range for the night.

Discussion
The tradewind inversion will continue to cap low-level moisture near 8 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.

Summit skies will remain clear through the next 5 nights.

Precipitable water will linger near 1.25 mm for tonight, then slip toward 0.8 mm for tomorrow night. It may increase subtly toward 0.9-1 mm for Saturday night, 1.2-1.3 mm for Sunday and Monday night.

Light relatively uniform easterly winds at and above the summit, combined with very stable conditions throughout the atmosphere will likely contribute to seeing near 0.4-0.5 arcseconds for tonight and most of Friday night. Seeing may actually begin to deteriorate as winds just above the summit picks up early Saturday morning. Boundary layer turbulence will pick up throughout that day, likely degrading seeing toward 0.7-0.8 arcseconds for Saturday night. Most of the boundary layer turbulence will subside throught Sunday, but there is possibility that low-level turbulence will linger, limiting much improvement in seeing for that night. Seeing should settle in back near 0.5-0.6 arcseconds as this turbulence subsides for the early part of next week.

No change since the morning forecast...The mid/low-level ridge will continue to sit to the north or over the Islands, while an upper-level ridge also either lingers over or to the east of the Big Island well into next week. This will ensure strong/steady large-scale subsidence prevails around the state and that the summit-level air mass remains clear, dry and stable throughout the forecast period. Initially, light relatively deep easterly flow will persist in the free atmosphere, which will keep shear/turbulence in the atmosphere to a minimum and resulting in good/excellent seeing through at least midnight Friday. However, mid-level flow (between 10-16 thousand feet) is slated to pick as the upper-level ridge fills in overhead for much of the weekend. This will likely increase boundary-layer and/or low-level turbulence (relative to the summit), which will probably degrade seeing for Saturday and Sunday night. This turbulence is slated to subside on Monday, allowing seeing to improve again for Monday night.