Latest Forecast for Mauna Kea Observatories
5 PM HST Tuesday 12 September (0300 UTC Wednesday 13 September) 2017
Chance for fog/high humidity
Cloud Cover and Precipitation Forecast
There is a small risk for short-lived fog and high humidity through the night; precipitation is not expected. A narrow strand of high clouds is set to pass over/through the summit area mainly during the first half of the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 3.5 C this evening and 3 C tomorrow morning. Winds will be from the NW at 5-15 mph, with seeing around 0.5 arcseconds. Precipitable water is expected to be in the 3.5-4.5 mm range for the night.
The tradewind inversion will remain somewhat weak/elevated near 11-12 thousand feet, which may allow for short-periods of fog and high humidity over the next 2 nights; precipitation is not expected. The inversion is set to recover near 8 thousand feet on Thursday and will ensure the summit steers free of moisture for the remainder of the forecast period. Extensive daytime clouds are possible through Wednesday, then will become minimal and short-lived for the remainder of the week.
A narrow strand of high clouds is set to pass over/near the summit area mainly during the first half of tonight. This strand is expected to breakdown and shift to the eastern skies during the second half of the night, but another stream is projected to fill in from the south and pass along the eastern half of the Big Island as tomorrow night progresses. This stream is set to become more widespread and shift westward, contributing to periods of extensive cloud cover for Thursday night. The bulk of these clouds will rapidly slip off toward the northwest by early Friday evening, leaving relatively clear skies for the remainder of that night and especially Saturday night.
Precipitable water is expected to linger near 4 mm probably through Thursday night, then will settle in near 1.5 mm for the following 2 nights (there is a small/moderate chance it will dip to 1 mm during this time).
Relatively calm skies will prevail in the free atmosphere, which should allow for better than average seeing over the next 4 nights. However, there is a possibility for some variability from ground layer turbulence mainly during the second half of Wednesday and Thursday night. Deep subsidence in the free atmosphere could allow seeing to dip toward more excellent-like values for Friday night. Unfortunately, an expected increase in boundary layer turbulence will likely contribute to poor seeing for Saturday night.
Minimal change since the morning forecast...A rather deep early season low to the north of the state will keep the ridge displaced off toward the NE and negate part of the subsidence in the area over the next couple of days. Fortunately, the bulk of the low and instability associated with the low will remain off toward the north of the Big Island, which should help keep the inversion from eroding entirely during its tenure. Still, the inversion will remain rather elevated near 11-12 thousand feet, which could allow for short-periods of fog and high humidity over the next 2 nights. In addition, the low will draw high clouds up from the tropics and advect it over/near the summit during the next 3 nights, Thursday night in particular. On the other hand, an upper-level ridge hanging off toward the SE should keep turbulence in the free atmosphere to a minimum and allow for better than average seeing during this time. This ridge is expected to drift westward and spread over the summit area, which should help push the high clouds out of the area, augment the subsidence in the area, and likely improve seeing for Friday night. However, mid-level flow may eventually respond to the upper-level momentum associated with the ridge and increase, which could strengthen boundary layer turbulence and degrade seeing for the followig night.