Latest Forecast for Mauna Kea Observatories
5 PM HST Thursday 11 January (0300 UTC Friday 12 January) 2018

Warnings
Chance for fog/ice and high humidity

Cloud Cover and Precipitation Forecast
There is a for fog, ice, high humidity and light flurries throuhout the night. Banding high clouds will also continue to stream over or just east of the summit through the night.

Summary of Key Meteorological Variables
Summit temperatures will be near -3 C this evening and -2 C tomorrow morning. Winds will be from the SE at 5-15 mph, with seeing near 0.8-0.9 arcseconds. Precipitable water is expected to exceed 4 mm through the night.

Discussion
The atmosphere near the Big Island will remain somewhat saturated and unstable, which could allow for periods of fog, ice, high humidity and perhaps light flurries at the summit through tonight. The inversion is set to recover through tomorrow, reducing this risk (for moisture) throughout that night, and will eventually a dry/stable conditions for the following 3 nights. Extensive daytime clouds are likely for today, then will taper for tomorrow and become minimal and short-lived over the weekend and early part of next week.

The banding high clouds are expected to shift just east of the Big Island and gather into a large batch of clouds, but will likely contribute to periods of extensive cloud cover over the next 2 nights. These clouds will begin to breakdown and shift southward on Saturday, opening up skies for that night and eventually leaving clear skies for the following 2 nights.

Precipitable water is expected to exceed 4 mm for tonight, briefly slip to 1 mm for tomorrow night, then settle in the 2-3 mm range for the following 3 nights.

Instability, moisture and low-level turbulence will contribute to poor seeing for tonight. While conditions are set to improve through tomorrow night, an increase in light/moderate boundary layer turbulence will limit, if not prohibit, much improvement in seeing probably for most of the following 4 nights. There is a small chance that winds will briefly taper a bit, which could reduce boundary layer turbulence mainly for Sunday evening.

Minor changes have been made, mainly to tomorrow night's PW forecast...A rather sharp trough filling in from the west will continue to destabilize the air mass and help keep the inversion rather indistinct as mid/low-level moisture accumulates in the area mainly over the next 24 hours. This could allow for periods of fog, ice, high humidity and light flurries at the summit during this time. Banding high clouds will also contribute to periods of extensive cloud cover, but should shift to the eastern skies as the trough closes in on the area later tonight. The trough is expected to rapidly flatten out and weaken as a deep ridge builds in from the SW through tomorrow. This should help rebuild the inversion and quickly reduce the risk for moisture at the summit through tomorrow and especially for the following 3 nights. However, there is a possibility that banding high clouds will gather into a large batch of clouds and persist to the east into Saturday afternoon. In addition, a somewhat tight wind gradient along the eastern flank of the advancing ridge will result in an increase in summit-level winds and thus boundary layer turbulence for at least Friday and Saturday night. While there is a slight possibility that winds will briefly taper as the ridge spreads eastward and sags southward on Sunday, the ridge will rebound northward and strengthen again for the early part of next week. Consequently, there is a good chance that boundary layer turbulence, moisture/instability and/or low-level turbulence will contribute to poor seeing throughout most of the next 5 nights (the exception could be mainly for Sunday evening).