Latest Forecast for Mauna Kea Observatories
5 PM HST Friday 11 August (0300 UTC Saturday 12 August) 2017
Warnings
None
Cloud Cover and Precipitation Forecast
The summit will remain dry and stable, but there is a chance for scattered high clouds along the far northern skies through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 4.5 C this evening and 4 C tomorrow morning. Winds will be from the ENE at 10-20 mph, with seeing near 0.4-0.45 arcseconds. Precipitable water is expected to be in the 1.5-2 mm range for the first half of the night and 1.25-1.75 mm range for the second half.
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Graphical Summary
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Discussion
A strong well-defined tradewind inversion will continue to cap low-level moisture primarily near 8 thousand feet and ensure the summit remains dry and stable through the next 5 nights. Daytime clouds will be minimal and short-lived through the forecast period.
Skies overhead will remain predominately clear through the next 5 nights, but there is a possibility for isolated to scattered high clouds along the western and northern skies for tonight.
Precipitable water is expected to slip toward 1.5 mm for tonight, then settle in near 1 mm for the remainder of the forecast period.
Deep subsidence in the area, combined with light winds aloft should allow seeing to linger near 0.4-0.45 arcseconds through at Sunday evening. There is a possibility for a minor increase in shear and decrease in upper-level subsidence, which may result in a very slight degradation in seeing for the remainder of the forecast period (still better than average seeing should prevail).
No change since the morning forecast...The mid/low-level ridge will continue to sit to the north of the state and promote steady/strong large-scale subsidence in the area well into next week. This subsidence will easily maintain a well-defined tradewind inversion near 7-8 thousand feet and ensure the summit remains dry and stable throughout the forecast period. An upper-level ridge is also expected to linger just south of the Big Island, which will not only augment the subsidence in the area, but allow clear/calm skies to prevail through the weekend. This should help seeing to settle in near 0.4-0.45 arcseconds during this period and also drive PW back down toward 1 mm, especially after tonight. The upper-level ridge will eventually breakdown and shift off toward the SE as the tropical upper-tropospheric trough (TUTT) and an embedded upper-level low barges in from the NE toward the end of the weekend. While neither are expected to affect the stability of the atmosphere enough to impact summit-level conditions, it could help strengthen the sub-tropical jet a bit overhead for the early part of next week. This could contribute to minor shear/turbulence in the free atmosphere and degrade seeing toward 0.5-0.6 arceconds during that time. Fortunately, the STJ will likely maintain a relatively zonal orientation, thus limiting its access to high cloud flowing out of the tropics.
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