Latest Forecast for Mauna Kea Observatories
5 PM HST Thursday 03 December (0300 UTC Friday 4 December) 2020
Warnings
None
Cloud Cover and Precipitation Forecast
There is a small risk for periods of fog and high humidity mainly for early this evening; precipitation is not expected. There is a chance for patches of high clouds and mid-level clouds along the northern and southern skies, respectively, through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 1 C this evening and 0.5 C tomorrow morning. Winds will be from the SE at 15-25 mph, with seeing near 0.7-0.75 arcseconds. Precipitable water is expected to exceed 4 mm for the night.
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Graphical Summary
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Discussion
The tradewind inversion will remain a bit weak/elevated, which could allow for periods of fog and high humidity mainly for early this evening. The inversion is set to quickly restrengthen as the night progresses, becoming well-established near 7 thousand feet and will ensure a dry/stable summit-level air mass for the following 4 nights. There is a possibility for a some limited afternoon clouds at the summit through the weekend, then will become minimal and short-lived for the early part of next week.
There is a chance for residual patches of high clouds along the northern skiesfor much of tonight. In addition, mid-level clouds begin to fill in from the SE as the night progresses, then will linger along the southern skies through the weekend. Cloud cover should not exceed 25% for any prolong period and clear skies are expected for Monday night.
Precipitable water is expected to linger near or exceed 4 mm through the weekend, then could trend toward 2 mm through Monday night.
A mixture of light boundary layer turbulence as well as mid-level turbulence will contribute to poor seeing through the next 5 nights.
No change since the morning forecast...Mid/low-level winds are set to switch to a more SE direction as a relatively flat ridge to the north continues to split and shift off toward the east and west. While the ridge will still promote large-scale subsidence in the area well into next week the SE winds will advect mid/low-level moisture, which could negate this subsidence over the next 12-18 hours. This may result in a minor erosion of the inversion, which could lead to fog/high humidity at the summit mainly for early this evening. The bulk of the low-level moisture will slide westward as the night progresses, but patches of mid-level clouds associated with an inverted trough to the south will move from the SE during that time. The trough is set to weaken thereafter, but the mid-level clouds may persist in the area well into the weekend. In addition, a tight wind gradient between the ridge to the NE and dissipating trough will likely keep summit-level winds around 20 mph, enough to stir up boundary layer turbulence probably throughout the forecast period. There is also a possibility that mid-level turbulence/instability along the northern fringe of the trough will also contribute to some degradation in seeing, mainly over the weekend.
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