Mauna Kea Stargazing

A fairly distinct inversion will continue to cap low-level moisture primarily near 7-8 thousand feet and ensure a dry/stable summit-level air mass through at least tonight. While there is a good chance that the inversion will intact near that height into Monday morning, mid-level moisture may scrape the southern tip of the Big Island and may allow for periods of fog/high humidity for Saturday and Sunday night (the risk is small). Deep widespread moisture is set to pour in from the south, quickly eroding the inversion around Monday afternoon, likely resulting in extensive fog, high humidity and light rain through Tuesday night. Daytime clouds will be minimal and short-lived through the weekend, but will turn extensive for early next week. The broken high clouds are expected break up and gradually southward over the next 12-18 hours, opening up skies through the night. However, another batch of deeper clouds will likely pass through the area, contributing to extensive cloud cover for at least the first half of Saturday night. Skies may open up again during the daytime Sunday, but more high are set to spread in from the SW for that night, while deep widespread clouds fill in overhead blanketing skies for the following 2 nights. Precipitable water is expected to linger near 3-4 mm for the next 2 nights, briefly drop into the 2-3 mm range for Sunday night, then jump to 10+ mm for early next week. Persistent moderate/strong shear in the free atmosphere, combined with increasing boundary layer turbulence will likely contribute to poor seeing over the next 3 nights. Boundary layer turbulence is set to strengthen further, and combined with an influx of deep moisture will likely result in bad seeing for Monday and Tuesday night. No change since the morning forecast...The surface ridge in the NE Pacific will continue to promote strong/steady large-scale subsidence in the area through the weekend. This subsidence will help maintain a fairly distinct inversion near 7-8 thousand feet, which will help minimize the risk for fog/precipitation during that time. While a rather deep low is expected to develop just NNE of the state and remain quasi-stationary/steady into next week, it will have little impact on the stability of the atmosphere in the area over the weekend. It will help draw rather deep moisture from the tropics further northward, perhaps occasionally scraping the southern tip of the Big Island between late tomorrow morning and sunrise Monday. This may allow for short-lived fog/high humidity during that period but the risk is quite low. The main issue over the next 3 nights will be tied to a deep/strong sub-tropical jet which will maintain a relatively zonal orientation, while flowing directly over the state. This will not only promote moderate/strong shear in the free atmosphere, it will likely deepen into the mid-levels, strengthening winds near the summit-level particularly after this evening. This will result in an increase in boundary layer turbulence and thus poor seeing over much of the weekend. In addition, mid/upper-level clouds will continue to build in from the west, contributing to periods of extensive cloud cover during that time. The low is set to gradually shift off toward the east as a short-wave trough digs in from the NW, producing a kink in the sub-tropical jet and veer low-level winds toward the south around Monday morning. This allow deep widesprad moisture to pour into the area, which is expected to rapidly erode the inversion by Monday afternoon. This will likely result in a saturated/cloudy air mass and inoperable conditions for Monday and Tuesday night.