Latest Forecast for Mauna Kea Observatories
5 PM HST Tuesday 22 July (0300 UTC Wednesday 23 July) 2008

Warnings
Fog and light rain
Moderate winds

Cloud Cover and Precipitation Forecast
Extensive fog, summit-level clouds, periodic light rain and broken to overcast high clouds will continue to be an issue through most of the night.

Summary of Key Meteorological Variables
Summit temperatures will be near -1 C, while easterly winds will taper from 20-35 mph for this evening to 15-30 mph for tomorrow morning. Seeing and precipitable water are expected to exceed 1 arcsecond and 4 mm, respectively, throughout the night.

Discussion
The atmosphere below 20 thousand feet will remain very moist through late tomorrow morning, then will dry out as the inversion rebuilds near 8-9 thousand feet for the remainder of the week. While this should ensure the summit remains dry/stable for tomorrow night onward, extensive fog and periods of light rain will likely be an issue throughout most of tonight. There is also an outside chance for isolated convection primarily to the south during the night. Some afternoon clouds are possible for tomorrow, but should taper for the remainder of the week.

Broken high clouds are expected to spread in from the south, and combined with summit-level clouds will likely result in extensive cloud cover for tonight. These clouds are slated to pass westward late tomorrow morning, opening up skies for Wednesday and Thursday night. However, another patch of isolated to scattered cirrus is expected to drift in from the south and slip through the area for Friday and perhaps Saturday night. Still, cloud cover should not exceed 50% for either night.

Precipitable water will likely exceed 4 mm for much of tonight, but should subside to 1.5 mm for tomorrow night and probably 1-1.25 mm for the remainder of the forecast period.

Boundary layer turbulence and wet conditions at the summit will result in poor/bad seeing for tonight. Seeing should start to improve with summit-level conditions, but boundary layer turbulence may remain an issue for at least tomorrow night. Weak flow at and above the summit and dry/stable conditions aloft will likely lead to better than average seeing for the remainder of the forecast period.

The remnants of Tropical Storm/Hurricane Elida will continue to scrape by to the south of the Big Island bringing fairly wet/unstable conditions to the area over the next 12 hours. This will likely result in mostly inoperable/cloudy conditions/skies, moderate winds, high PW and poor/bad seeing for much of tonight. Fortunately, Elida is slated to slip westward rather quickly, allowing the atmosphere to stabilize and dry out as the mid-level ridge regains control of the air mass near the Islands by early tomorrow afternoon. This should lead to more normal-like summit-level conditions for the remainder of the week, though summit-level winds will be a little slow to taper for tomorrow night. Winds are expected to ease up early Thursday morning, which should help to improve seeing for that night and into the weekend. In fact, there is a slight possibility for good/excellent seeing as a weak upper-level ridge tries to build in from the east and/or develop to the far north late in the week. If nothing else, this extra subsidence should significantly warm-up the air mass during that time.