Current Conditions
Temp3.1 C
RH8 %
WindNNE 5 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Friday 07 December (0300 UTC Saturday 8 December) 2018
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, while there is a possibility for lingering patches of clouds along the eastern skies mainly during the early part of the night.
Summary of Key Meteorological Variables
Summit temperatures will be near -0.5 C this evening and -1 C for the morning hours. Winds will be from the WNW at 10-20 mph for this evening, switching to a more northerly direction for the night. Seeing will be near 0.6-0.7 arcseconds, while precipitable water is expected to start out near 3 mm for this evening, slipping toward 1.5 mm as the night progresses.
Discussion
A well-defined 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 throughout the forecast period.

There is a possibility for patches of mid/upoer-level clouds along the eastern skies mainly for the early part of the night. WHile these clouds will shift eastward through tomorrow, there is a possibility for light/thin isolated cirrus passing quickly overhead during the next 2 nights. A narrow band of high clouds is expected to set up along the southern skies for Monday night and part of Tuesday night, then will shift off toward the SE early Wednesday morning.

Precipitable water is expected to start out near 3 mm for this evening, then will trend toward 1.5 mm through the night, eventually settling in near 0.7-0.75 mm for the following 4 nights.

Summit-level winds are set to linger primarily near 15-20 mph, contributing to persistent light/moderate boundary layer turbulence and probably average/poor seeing throughout most of the forecast period. There is a possibility for a brief period of stronger boundary layer turbulence that could further degrade seeing mainly for Saturday night.

No change since the morning forecast...A relatively deep mid/low-level ridge currently sitting just north of the Big Island is expected to retreat further northward as a new ridge builds in from the west over the next 12-18 hours, then stretches across the eastern Pacific well into next week. Regardless, strong/steady large-scale subsidence associated with the ridge will easily maintain a well-defined inversion near 8 thousand feet and ensure the summit remains dry and stable through at least the next 5 nights. A weak trough passing to the north will drag mid/upper-level moisture/clouds in from the south, which will initially linger along the eastern skies, before pushing off toward the east as the night progresses. This moisture will likely push PW toward 3 mm for this evening, but it could slip toward 1-1.5 mm by late tomorrow morning. PW will eventually settle in near 0.7-0.75 mm as the ridge lifts northward and very dry air prevails along its southern flank. Seeing, on the other hand, will not benefit much from the ridge, which is expected to keep winds near 15-20 mph, contributing to light/moderate boundary layer turbulence and probably average/poor seeing throughout most of the forecast period. There is also possibility that winds will briefly top 30 mph as the new ridge intially builds in from the west mainly for tomorrow night. Upper-level flow will remain under the influence of a rather broad sub-tropical jet, which will have little impact on free atmospheric trubulence as relatively laminar westerly flow prevails above (and across) the summit throughout most of the forecast period. There is, however, a chance that high clouds embedded in the jet will pass over/near the summit for Saturday and Sunday night, while a narrow band eventually setting up along the southern skeis for Monday night.
WRF Astronomical Observing Quality Guidance
Cloud Cover and Precipitable Water Analyses
MK CN² Profiles
5 Day Forecast Summary (Graphical Trend)
HST Cloud Fog/Precip Temp Wind Seeing PW
Cover (%) Height (km) Probability (%) (Celcius) (Dir/MPH) (Arcseconds) (mm)
Fri Dec 07 - 8 PM10-307-90 / 0-0.5WNW/10-200.5-0.82-3
Sat Dec 08 - 2 AM0-208-90 / 0-1NNW/10-200.5-0.81.5-2
2 PM0-209.5-100 / 04NNE/15-30NaN1-1.5
8 PM0-209.5-100 / 0-1NNE/20-350.8-1.20.6-0.8
Sun Dec 09 - 2 AM0-209.5-100 / 0-1.5NNE/15-300.7-1.10.6-0.8
2 PM0-209.5-100 / 04ENE/10-20NaN0.8-1.2
8 PM0-209.5-100 / 00ENE/15-300.55-0.850.6-0.8
Mon Dec 10 - 2 AM0-10Clear0 / 00E/15-300.55-0.850.7-0.9
2 PM0-209.5-100 / 04E/15-30NaN0.8-1.2
Tue Dec 11 - 2 AM20-409-100 / 00E/15-300.6-0.90.6-0.8
2 PM10-309.5-100 / 04E/15-30NaN0.8-1.2
Wed Dec 12 - 2 AM0-20Clear0 / 0-1ESE/20-350.6-0.90.6-0.8
2 PM0-20Clear0 / 03ENE/25-40NaN0.8-1.2
Rise and Set times for the Sun and Moon
Night (HST) Sun Set Twilight End Twilight Beg Sun Rise Moon Rise Moon Set Illumination (%) RA DEC
Sun Dec 09 - Mon Dec 10 17:53 19:02 5:28 6:36 N/A 20:15 9 19 37.6 -21 08
Mon Dec 10 - Tue Dec 11 17:53 19:02 5:28 6:37 N/A 21:06 15 20 27.8 -19 48
Tue Dec 11 - Wed Dec 12 17:54 19:02 5:29 6:37 N/A 21:56 22 21 16.5 -17 37
Wed Dec 12 - Thu Dec 13 17:54 19:03 5:29 6:38 N/A 22:46 30 22 03.9 -14 43
Thu Dec 13 - Fri Dec 14 17:54 19:03 5:30 6:39 N/A 23:35 39 22 50.2 -11 13
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 10 December 2018.
Additional Information
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