Latest Forecast for Mauna Kea Observatories
10 AM HST (2000 UTC) Friday 31 July 2020
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 12 C this afternoon, 6 C this evening and 5 C tomorrow morning. Winds will be from the ENE at 5-15 mph for today, increasing to 10-20 mph for the night. Seeing will be near 0.45-0.5 arcseconds, while precipitable water is expected to be in the 0.8-1 mm range for the night.
A distinct inversion will continue to cap low-level moisture near 8 thousand feet and ensure a dry/stable summit-level air mass through the next 4 nights. There is a chance that a patch of moisture will drift into the area, weakening the inversion and increasing the risk for fog/high humidity at the summit for Tuesday night. Daytime clouds will be minimal and short-lived through Tuesday, but could pick up on Wednesday.
Skies will remain predominately clear for tonight, but there is a chance for thin patches of light cirrus moving in from the east and/or south through the remainder of the forecast period.
Precipitable water is expected to linger just below 1 mm for tonight, briefly increase toward 2 mm for early tomorrow evening, then slip back to 1 mm as that night progresses and settle in near 0.8 mm for Sunday and Monday night. There is a chance that it will increase to 3+ mm for Tuesday night.
While winds aloft will maintain a relatively light/laminar easterly flow throughout most of the forecast period, there is a chance for periods of light low-level turbulence, induced by a slight increase in winds just above the summit. Nevertheless, better than average seeing (near 0.5 arcseconds) should prevail over the next 4 nights. There is a possibility that an influx of moisture and perhaps instability could degrade seeing for Tuesday night.
A deep ridge will continue to sit to the north of the state before the upper portion begins to fall apart as the tropical upper-tropospheric trough (TUTT) begins to take shape around the middle part of next week. Nevertheless, subsidence associated with the ridge will easily maintain a well-defined inversion near 7-8 thousand feet and ensure a dry/stable summit-level air mass through at least Monday night. There is a chance that redevelopment of the TUTT combined with an influx of tropical wave/moisture will weaken/lift the inversion toward 12-13 thousand feet and increase the risk for fog and high humidity at the summit for Tuesday night. Regardless, prior to this, a stable air mass combined with relatively laminar easterly flow at and above the summit will minimize free atmospheriec turbulence and should allow for better than average seeing. There is a chance for minor low-level turbulence as winds just above the summit creep toward 20 mph, which could result in slight degradation/variability in seeing over the next 4 nights. PW, for the most part, will also benefit from the deep subsidence and settle in below 1 mm over most of this time. The only exception could be as a patch of mid/upper-level moisture scrapes through, increasing PW toward 2 mm for tomorrow evening. However, the influx of moisture may further degrade seeing and raise PW (perhaps significantly) for Tuesday night.