Latest Forecast for Mauna Kea Observatories
10 AM HST (2000 UTC) Wednesday 22 February 2017

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 -2 C this evening and -6 C for the night. Winds will be from the NE at 5-15 mph for today, increasing to 15-30 mph through the night. Seeing will be near 0.7-0.8 arcseconds, while precipitable water is expected to settle in near 0.6-0.7 mm for the night.

Discussion
A strengthening inversion near 7 thousand feet coupled with a drier more stable air mass will ensure the summit steers free of fog and precipitation through the next 3 nights. There is a chance that the inversion will weaken, while mid-level moisture creeps into the area over the weekend. This could raise the stakes on fog, ice and perhaps light flurries for Saturday and particularly Sunday night. Daytime clouds will be minimal and short-lived through Friday, but could pick up over the weekend.

Skies will remain predominately clear for tonight, but broken high clouds are set to quickly move in from the northwest through tomorrow, with banding high clouds developing over and/or filling in from the south on Thursday. These clouds will contribute to extensive cloud cover for tomorrow night and likely overcast skies for the remainder of the forecast period. In fact, there is a chance that these clouds will thicken significantly during the second half of the weekend.

Precipitable water is expected to settle in near 0.6-0.7 mm for tonight, increase toward 0.8 mm for tomorrow night, 3-4 mm for Friday night and probably 4+ mm for the following 2 nights.

Moderate turbulence in the free atmosphere, coupled with an increase in boundary layer turublence will likely contribute to slightly poorer than average seeing for tonight. There is a chance for calmer skies and more average-like seeing for tomorrow night, but strong turbulence is expected to build overhear in the free atmosphere, while boundary layer turbulence also increases over the weekend. This will likely result in poor to possibily bad seeing for the following 3 nights.

Although the mid-level ridge will remain weak/indistinct well into next week, the low-level ridge will continue to promote large-scale subsidence in the area, which will easily maintain a fairly well-defined tradewind inversion near 7 thousand feet and ensure a dry/stable summit-level air mass through at least Friday night. In addition, very mid/upper-level dry air along the western flank of a low to the NE is set to move in over the summit area for the next 36 hours. While this should help plummet PW toward 0.6-0.7 mm and allow for clear skies for tonight, a large trough will begin to develop to the NW through tomorrow. This trough will initially send high clouds in from the NW through that night, and will eventually drag more banding high clouds in from the south for the following 3-4 nights. An embedded short-wave trough is also set to dig toward the state, bringing more mid-level clouds/moisture and instability to the area over the weekend. There is a chance that this instability will erode the inversion and/or saturate the air mass above the summit particularly as the weekend progresses. This could raise the stakes on fog, ice and flurries at the summit mainly for Sunday night. Regardless, the abundant supply of clouds/moisture advecting into and/or developing in the area will likely contribute to extensive cloud cover for most of tomorrow night and probably overcast skies for the following 3 nights.