Latest Forecast for Mauna Kea Observatories
10 AM HST (2000 UTC) Wednesday 14 May 2014

Warnings
None

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 8.5 C this afternoon, 3.5 C this evening and 3 C tomorrow morning. Winds will be from the SW at 5-15 mph, with seeing around 0.55-0.6 arcseconds. Precipitable water is expected to be in the 1.75-2.25 mm range for the first half of the night and 1.5-2 mm range for the second half.

Discussion
The tradewind inversion will continue to cap low-level moisture at or below 8 thousand feet and keep the mid/summit-level air mass 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 a narrow band of thin high clouds is slated to fill in from the west early tomorrow afternoon and will start to cross over the summit area during that night. These clouds are expected to shift eastward by late Friday morning, but there is a possibility that banding scattered high clouds will set up along the southern skies, occasionally scraping the Big Island for Friday and especially Saturday night.

Precipitable water will start out near 2 mm for this evening, but will trend toward 1.5 mm as the night progresses, then settle in near 1 mm for Thursday and Friday night. It will likely increase back to 2-3 mm for Saturday night and 3-4 mm for Sunday night.

Average-like seeing will prevail for most of tonight, but building turbulence will likely degrade seeing toward 0.65-0.7 arcseconds for tomorrow night. This turbulence is slated to subside on Friday, allowing seeing to improve back to 0.5-0.55 arcseconds for the remainder of the forecast period.

The mid/low-level ridge will continue to sit over or just north of the Big Island and promote steady/strong large-scale subsidence in the area well into next week. This will easily maintain a well-defined tradewind inversion at or below 8 thousand feet and ensure a dry/stable summit-level air mass throughout the forecast period. Clear and mostly calm skies will prevail for most of tonight, but the sub-tropical jet is expected to fill in from the west bringing thin scattered high clouds and turbulence to the summit area mainly for tomorrow night. The jet is slated to sag southward again on Friday, which should help open up skies and improve seeing once again for much of the weekend. However, there is a possibility that a band of scattered high clouds will set up along the southern skies on Saturday night. This band is expected to fall apart again leaving predominately clear skies for Sunday night and the early part of next week.