Latest Forecast for Mauna Kea Observatories
5 PM HST Wednesday 13 June (0300 UTC Thursday 14 June) 2018
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 1.5 C, with light southerly winds and seeing near 0.5-0.6 arcseconds. Precipitable water is expected to be in the 1-1.5 mm range for the first half of the night and 1.25-1.75 mm range for the second half.
The tradewind inversion will continue to cap low-level moisture at or below 9 thousand feet and ensure the summit remains dry and stable through the next 5 nights. Daytime clouds will be minimal and short-lived for the remainder of the week, but could pick up for Monday.
Clear skies are expected for tonight, but there is a chance that stray patches of thin cirrus will occasionally drop down from the north and pass over/near the summit area over the next 4 nights. Still, cloud cover should rarely exceed 20% for any prolong periods during those nights.
Precipitable water is expected to mostly hang near 1.2-1.3 mm over the next 2 nights, trend toward 2 mm through Friday night and likely exceed 4 mm for Saturday and Sunday night.
Relatively calm skies will prevail in the free atmosphere as fairly laminar flow persists aloft, allowing for better than average seeing through most of Friday night. However, there is a possibility for periods of variability and/or degradation in seeing should summit-level winds die completely, particularly toward the end of tonight and for tomorrow night. An increase in boundary layer turbulence could contribute to a more significant deterioration in seeing for Saturday and especially Sunday night.
Subtle favorable changes have been made to the PW forecast....An upper-level trough passing overhead will not affect the stability of the atmosphere and will eventually give way to a deep ridge building in from the west late tonight, which will persist to the north into the early part of next week. Nonetheless, large-scale subsidence will persist in the area, which will help maintain a fairly well-defined inversion at or below 9 thousand feet and ensure the summit remains dry and stable throughout the forecast period. In addition, the deep ridge will prevent the sub-tropical jet from loitering in the area, allowing relatively calm skies to prevail in the free atmosphere probably throughout the forecast period. This combined with fairly laminar/weak flow aloft, will help minimize turbulence and likely permit for better than average seeing for at least the next 3 nights. However, there is a possiblity periods of variability and/or degradation in seeing should summit-level winds die completely, particularly toward the end of tonight and for tomorrow night. While a slight increase in winds should help mix the air mass up a bit and stabilize seeing for Friday night, winds may continue to climb and eventually stir up boundary layer turbulence, which could further degrade seeing for Saturday and especially Sunday night. There is a possibility mid-moisture revolving around a relatively deep upper-level low to the east will increase PW and RH late Sunday night and into the early part of next week.