Latest Forecast for Mauna Kea Observatories
830 AM HST (1830 UTC) Friday 19 May 2017
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 7.5 C this afternoon, 3.5 C this evening and 3 C tomorrow morning. Winds will be from the NW at 5-15 mph, with seeing near 0.4-0.45 arcseconds. Precipitable water is expected to be in the 2-3 mm range for the night.
The tradewind inversion will continue to cap low-level moisture at or below 8 thousand feet and ensure the summit remains dry and stable through the next 5 nights. Daytime clouds will be minimal and short-lived throughout the forecast period.
Skies overhead will remain predominately clear through at least Saturday evening. High clouds are set to build in from the south just after midnight on Saturday and will likely drift over or just scrape the southern tip of the Big Island through Monday evening. There is a possibility that these clouds will spread further northward contributing to extensive cloud cover during the second half of Monday night. These clouds will begin to shift eastward through Tuesday, opening up skies during that night.
Precipitable water is expected to linger in the 2-3 mm range for the next 2 nights, increase to 3-4 mm for Sunday and Monday night, then slip back into the 2-3 mm range for the following night.
Deep subsidence and calm skies are slated to fill in overhead, allowing seeing to improve toward 0.35-0.4 arcseconds through tonight and especially for tomorrow night. Upper-level westerly flow is set to strengthen a bit as the subsidence tapers a bit over the following 3 nights. Still, calm skies will prevail allowing seeing to settle in near 0.45-0.55 arcseconds during that time.
The persistent low-level ridge to the NE of the state will continue to promote strong/steady large-scale subsidence in the area, help maintain a well-defined inversion near 7-8 thousand feet and ensure a dry/stable summit-level air mass well into next week. In addition, a deep mid/upper-level ridge is expected to fill in from the west over the next 24 hours, then gradually dissipate in the area through the weekend. This ridge will not only enhance the subsidence in the area, but promote clear/calm skies, which should allow seeing to settle in near 0.35-0.4 mm for much of the next 2 nights. A trough passing far to the north will begin to breakdown the upper-portion of the ridge and gradually strengthen and drag the sub-tropical jet in from the south late in the weekend and for the early part of next week. While the trough is not expected to affect the stability of the atmosphere, the STJ will likely bring scattered/broken high clouds to the area mainly for Sunday and Monday night. There is a chance that light/moderate turbulence/shear associated with the jet will degrade seeing toward 0.5-0.55 arcseconds for the second half of the forecast period.