Latest Forecast for Mauna Kea Observatories
5 PM HST Thursday 06 December (0300 UTC Friday 7 December) 2018
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 0.5 C, with light westerly winds for the night. Seeing will be near 0.55-0.6 arcseconds, while precipitable water is expected to be in the 1.5-2 mm range throughout the night.
A well-defined tradewind inversion will continue to cap low-level moisture near 7-8 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.
Skies will remain predominately clear for tonight, but scattered mostly thin high clouds are expected to fill in from west and pass over/near the summit area between tomorrow afternoon and early Saturday evening. While these clouds will shift southward during the latter night, there is still a possibility that banding high clodus will set up to the south and be visible from the summit for Sunday and especially Monday night.
Precipitable water is expected to increase to 1.5-2 mm for tonight and 2-3 mm for tomorrow night, then settle back in near 0.6-0.8 mm range for the next 3 nights.
Calmer low-level skies with moderate turbulence in the free atmosphere will likely allow seeing to settle in near 0.55-0.6 arcseconds for the next 2 nights. There is a good chance for an increase in boundary layer turbulence and perhaps free atmospheric turbulence, while will contribute to poorer than average seeing for Saturday, Sunday and Monday night.
Little change since the morning forecast...The mid-level ridge is expected to briefly sag southward as a trough passes to the far north, then will rebound northward as a new ridge fills in from the west over the weekend. Nonetheless, large-scale subsidence will prevail in the area, which will help maintain a well-defined inversion near 7-8 thousand feet and ensure the summit remains dry and stable through the next 5 nights. Winds will respond to the southward progression of the ridge, which will significantly reduce boundary layer turbulence and likely allow seeing to improve toward 0.5-0.6 arcseconds over the next 2 nights. Mid-level moisture embedded in the ridge is expected to increase PW toward 1.5-2.5 mm during this time. Seeing and PW are set to trend in opposite directions (degrading and decreasing, respectively) as the ridge shifts northward over the weekend. Very dry air along the southern portion of the ridge, should help PW settle back in near 0.6-0.8 arcseconds for Saturday, Sunday and Monday night. However, deep somewhat stronger easterly flow along this edge of the ridge will likely increase boundary layer turbulence again, and contribute to poorer than average seeing during that time.