Latest Forecast for Mauna Kea Observatories
10 AM HST (2000 UTC) Monday 18 June 2018

Warnings
Periods of high relative humidity
Moderate Winds.

Cloud Cover and Precipitation Forecast
Small patches of high clouds will be visible and approaching the area from the N through today. Daytime clouds are very likely. No precipitation is expected.

Summary of Key Meteorological Variables
Summit temperature will be near 9C this afternoon, 3.5C this evening and 2.5C tonight and tomorrow morning. Precipitable water will exceed the 4 mm threshold through the night. Winds will be moderate to sustained through today and tonight.

Discussion
The tradewind inversion will cap the bulk of the low-level moisture at or below summit level through most of this forecast period. However, episodes of high relative humidity are possible through today and tonight as patches of moisture linger in the area. Air masses are expected to slowly dry in time through today and tomorrow. The inversion is projected to lift and weaken some starting on Thursday but should still remain below summit level through the end of the working week.

Chances are that small patches of high clouds will be visible along the NW horizon today/tonight while some of them might occasionally drop down and pass near/over the summit area. Still cloud cover is not expected to exceed 20% through most of this forecast period, although daytime clouds today and possibly tomorrow might increase that during the afternoon hours.

Precipitable water will exceed the 4 mm threshold through Wednesday night. It is projected to start decreasing on Thurdays and linger close to 3 mm for that night and decrease further to range between 1.5 and 2 mm on Friday night.

Observing conditions will be less than average to poor tonight and tomorrow night as moisture continues to linger in the area and winds will stir up ground layer turbulence. Observing conditions are expected to improve toward a more average range by Wednesday and through Friday night.

The current weather scenario is dominated by a weak ridge north of the State and a mid/upper level trough to the NE, slowly shifting Eastward. This latter one is responsible for advecting some high clouds and pathes of moisture over the island chain through today and tonight, and for thightening the pressure gradients over the islands, resulting in moderated to sustained winds at the summit. As the trough moves eastward the winds will decrease and observing conditions will improve overall. Relative humidity will also decrese in time. The model project an upper level low to develop to the East of the island chain by late Thursday. This feature might slihgly affect stability and cloud conditions at the summit then and through Friday, but next updates will clarify on this more.