Latest Forecast for Mauna Kea Observatories
9 AM HST (1900 UTC) Monday 20 March 2017

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 this afternoon, 2.5 C this evening and 2 C tomorrow morning. Winds will be from the north at 5-15 mph, with seeing near 0.65-0.7 arcseconds. Precipitable water is expected to be in the 1.75-2.25 mm range for the night.

Discussion
The tradewind inversion will continue to cap the fairly limited supply of low-level moisture at or below 8 thousand feet and ensure the summit steers free of fog and precipitation through the next 5 nights. Daytime clouds will be minimal and short-lived throughout the forecast period.

Skies will remain predominately clear for the next 2 nights. Broken high clouds are set to build in from the NW late Wednesday afternoon and drift over the summit through Friday morning. These clouds will shift off toward the SE thereafter, leaving clear skies again for Friday night.

Precipitable water is expected to linger near 1.75-2 mm for the next 3 nights, then increase toward 2.5 mm for Thursday and Friday night.

Low-level turbulence will likely contribute to average or perhaps slightly poorer than average seeing for tonight. Calmer skies should allow seeing to improve toward 0.5-0.6 arcseconds for the following 3 nights, but an increase free atmospheric turbulence could degrade seeing back toward more average-like values for Friday night.

The mid/low-level ridge will continue to sit directly over the state and promote steady/strong large-scale subsidence in the area through the week. This subsidence will easily maintain a well-defined tradewind inversion near 7-8 thousand feet and ensure a dry/stable summit-level air mass throughout the forecast period. Skies will start out predominately clear for the next 2 nights, but low-level turbulence will likely could contribute to slightly poorer than average seeing for tonight. An improvement in seeing is expected as this source of turbulence subsides and calm skies prevail in the free atmosphere for the following 3 nights. However, a weak short-wave trough is expected to push broken high clouds over the summit, which could contribute to periods of extensive cloud cover for Wednesday and Thursday night. While skies should open up as this trough shifts eastward on Friday, turbulence along the western side of the trough could disrupt seeing a bit for that night.