Latest Forecast for Mauna Kea Observatories
10 AM HST (2000 UTC) Wednesday 13 September 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 9 C this afternoon, 4 C this evening and 3.5 C tomorrow morning. Winds will be light and from the NNW, with seeing near 0.5-0.55 arcseconds. Precipitable water is expected to be in the 2.5-3.5 mm range for the night.
A fairly well-defined tradewind inversion will continue to cap low-level moisture at or below 10 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 will remain predominately clear for tonight, but strands of high clouds will begin to drift in from the south just after sunrise tomorrow and become more widespread through the day. These clouds will likely contribute to periods of extensive cloud cover for tomorrow night, then will rapidly shift off toward the NW through Friday, opening up skies for that night and leaving clear skies for the following 2 nights.
Precipitable water is expected to linger near 3-3.5 mm for the next 2 nights, slip toward 1.5 mm for Friday night, then settle in near 1-1.5 mm for the following 2 nights.
Despite relatively calm skies will prevail in the free atmosphere likely allowing for better than average seeing for the next 3 nights, there is a possibility for ground-level turbulence (induced by very weak summit-level winds), which could contribute to large variability particularly during the second half of the next 2 nights (there is a good chance seeing will briefly dip toward more excellent-like values for Friday night). Summit-level winds are set to increase, which will likely stir up boundary layer turbulence and contribute to average/poor seeing for Saturday night and most of Sunday night.
Although the ridge will remain somewhat displaced to the east in response to a fairly deep low to the north over the next 36-48 hours, organized moisture will be fairly hard to come by during this period. In addition, the ridge will remain close enough to promote large-scale subsidence in the area and maintain a fairly well-defined inversion near 9-10 thousand feet, ensuring a dry/stable summit-level air mass. However, there is a good chance that the low will draw tropical high clouds over the summit area, which could contribute to periods of extensive cloud cover for tomorrow night. These clouds will shift off toward the NW as an upper-level ridge builds in from the SE through Friday. This will not only help open up summit skies, but augment subsidence in the free atmosphere and perhaps allow seeing to slip near/below 0.4 arcseconds for Friday night. Unfortunately, the upper-level ridge will eventually help restrengthen the mid/low-level ridge, tightening the mid-level wind gradient over the weekend. This could result in an increase in summit-level winds, which will likely stir up boundary layer turbulence and contribute to poorer than average seeing for Saturday and Sunday night.