Latest Forecast for Mauna Kea Observatories
10 AM HST (2000 UTC) Wednesday 14 March 2018

Warnings
Fog, ice, frozen precipitation
Tapering winds

Cloud Cover and Precipitation Forecast
Fog, ice, clouds and possibly light snow are still likely through today and tonight.

Summary of Key Meteorological Variables
Summit temperatures will be near 2.5 C this afternoon, 0.5 C this evening and -0.5 C tonight. Winds will be from the S at 15-25 mph. Seeing and precipitable water are expected to exceed 1 arcsecond and 4 mm, respectively, through the night.

Discussion
The airmasses over and around the Big Island will remain saturated and slightly unstable through today, tonight and part of tomorrow. As a result fog will still be the main nuisance at the summit at least through late Thursday. Periods of light snow are still possible at times through tomorrow. Moisture will slowly trend down through tomorrow and Friday but the air masses will be slow in drying out. Moisture is likely to linger through the weekend as well and the air masses are likely to not dry out completely before another bout of moisture and adverse weather will invest the area late on Monday/Tuesday. Extensive afternoon clouds are expected through Friday, but may taper some over the weekend.

Broken high clouds will continue to pass over the summit today, while slowly breaking down through tomorrow, allowing some sky to partially show at times. Cloud cover is expected to slowly decrease in time through Friday and sky might open up some from Friday into the weekend. More clouds though are expected to approach the area from the WNW starting late on Sunday and summit skies are likely to be blanketed again from Monday and through the beginning of the coming week.

Precipitable water will continue to exceed 4 mm throughout the forecast period.

A mixture of abundant moisture (particularly in the low-levels), mid-level turblence, boundary layer turbulence and/or instability will contribute to poor/bad seeing probably through tomorrow night. There is a small/moderate chance for some improvement as the atmosphere begins to stabilize a tad and wind at the surface to taper for Friday, Saturday and possibly Sunday night.

The current weather scenario is still dominated by a high pressure system North of the State and an upper level trough ESE of the islands. This latter continues to advect deep moisture through the archipelago, pushing it northeastward. As a result high broken clouds, fog and frozen rain/snow are still a threat for the summit of Mauna Kea through today and possibly tomorrow. The upper level trough is supposed to lift norteastward through today and tomorrow, allowing for a slightly drier, more stable and warmer air mass to shift in, and for high clouds to opening up some then through the weekend. Winds will also taper. Neverthelss the airmasses will be slow in drying out and daily clouds and episodes of fog will still be possible throughout the forecast period. Unfortunately a front is expected to approach the State from the NW early next week, resulting in yet another spell of wet and wintery weather for the summit.