Latest Forecast for Mauna Kea Observatories
10 AM HST (2000 UTC) Wednesday 13 January 2021
Chance for fog, ice and high humidity
Cloud Cover and Precipitation Forecast
There is a good chance that high humidity, fog, ice and perhaps light flurries will continue to be an issue throughout the night. Scattered high clouds are also expected to pass along the northern skies and occasionally over the summit through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 3 C this afternoon and -0.5 C for the night. Winds will be from the west at 10-20 mph for today, switching to a more northerly direction and easing through the night. Seeing will be near 0.8 arcseconds, while precipitable water is expected to linger near or exceed 4 mm for the night.
Mid-level moisture congregating in the area will keep the inversion rather weak/elevated, likely allowing for more fog, high humidity, ice and perhaps light flurries at the summit for tonight. The risk for fog and precipitation is expected to subside as the inversion begins to take shape near 7-8 thousand feet through tomorrow and eventually allowing dry/stable conditions to return to the summit for the remainder of the forecast period. Extensive daytime clouds and afternoon convection are possible for today, then will taper through tomorrow and become minimal and short-lived for Friday, the weekend and early part of next week.
Scattered high clouds are expected to pass along the northern skies and occasionally over the summit for tonight and early part of tomorrow night. There is also an outside chance for isolated patches of clouds lingering in the area from daytime clouds and/or afternoon convection over the next 2 evenings. Clear skies will prevail for the remainder of the forecast period.
Precipitable water is expected to linger near or exceed 4 mm for the next 2 nights, slip toward 2 mm through Friday night, increase subtly into the 2-3 mm range for Saturday night, then trend to 1 mm through Sunday night.
An elevated/indistinct inversion and the possibility for moisture at the summit will contribute to poor seeing for tonight. A drying air mass combined with a building inversion and relatively laminar northerly flow at and above the summit should allow seeing to improve beginning early Thursday evening and eventually settle in near 0.5-0.6 arcseconds as that night progress and the following 2 nights. However, an increase in boundary layer and perhaps upper-level turbulence will likely degrade seeing through Sunday night.
Mid/low-level moisture drawn toward a trough/low passing to the north will continue to linger in the area for another 12-18 hours, then will begin to disperse and shift off toward the east through tomorrow. Nevertheless, this moisture combined with weak instability associated with the trough will keep the inversion elevated/indistinct near 14 thousand feet and likely allow for more periods of fog, ice, high humidity and perhaps light flurries at the summit for tonight. Daytime heating could also help spark afternoon convection along the Big Island slopes for today and maybe even tomorrow. The inversion is set to gradually strengthen beginning tomorrow afternoon, which will help to diminish the risk for fog/precipitation at the summit through that night. Dry and stable conditions will return to the summit as the inversion becomes well-established near 7 thousand feet and the mid-level ridge fills in overhead over the weekend. Relatively calm/laminar flow will also eventually fill in over the summit, which should allow for better than average seeing for at least Friday and Saturday night (perhaps even the latter part of Thursday night). However, a rather tight mid/upper-level low is expected to dig into toward the state and could increase summit-level flow and thus boundary layer turbulence on Sunday night. Previous model runs suggested that this low could also bring instability and moisture to the summit for Monday night.