Latest Forecast for Mauna Kea Observatories
5 PM HST Monday 21 May (0300 UTC Tuesday 22 May) 2018

Warnings
None

Cloud Cover and Precipitation Forecast
The summit will remain dry and stable, while scattered high clouds spread in from the SW and pass overhead for much of tonight.

Summary of Key Meteorological Variables
Summit temperatures will be near 3 C, with winds from the SW at 5-15 mph for the night. Seeing will be near 0.7-0.75 arcseconds, while precipitable water is expected to linger near 4 mm for the night.

Discussion
A well-defined tradewind inversion will continue to cap low-level moisture at or below 8 thousand feet and ensure the summit remains dry and stable through the next 5 nights. Daytime clouds will be minimal and short-lived throughout the forecast period.

Scatterd high clouds are set to spread in from the SW for tonight then will shift to the northern skies for tomorrow night. More cirrus may follow suit on Wednesday night, but should linger along the western skies, with occasional stray high clouds passing overhead through Thursday evening. There is a chance that these clouds will shift eastward early Friday morning perhaps contributing to periods of extensive cloud cover before breaking down and slipping to the east of the Big Island later that night.

Precipitable water is expected to linger near 3.5-4 mm probably throughout the forecast period.

Lingering low-level turbulence may contribute to slightly poorer than average seeing for most of tonight (some improvement is possible toward the end of the night). Calmer skies may allow seeing to return toward more average-like values for tomorrow night, but building moderate/strong turbulence in the free atmosphere could start to deteriorate seeing early Thursday morning, and perhaps contribute to poor seeing for the following 2 nights.

Little change since the morning forecast...A mid/low-level ridge building eastward (from the NW) will continue to promote strong/steady large scale subsidence, despite a persistent rather strong upper-level low to the west of the state. Nevertheless, this subsidence will easily maintain a well-defined tradewind inversion primarily near 6-8 thousand feet and ensure the summit remains dry/stable and quite warm probably through the week. While the low will not affect the stability of the atmosphere, a sub-tropical jet along the SE flank is set to build over the state and bring scattered high clouds over/near the summit through most of the next 5 nights (periods of clear skies are possible mainly for tomorrow night). Turbulence associated with the jet will intially remain quite light, but lingering low-level turbulence may contribute to poor seeing for tonight. Although seeing is set to improve as this source of turbulence subsides for tomorrow night, free atmospheric turbulence may significantly increase as a tight horizontal and vertical wind gradient drifts overhead, which could degrade seeing around Thursday/Friday.