Current Conditions
Temp1.7 C
RH23 %
WindNE 28 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Friday 14 December (0300 UTC Saturday 15 December) 2018
Warning(s)
Moderate winds
Cloud Cover and Fog/Precipitation Forecast
The summit will remain clear, dry and stable through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 0.5 C this evening and 0 C tomorrow morning. Winds will be from the ENE at 15-30 mph, with seeing near 0.9-1 arcseconds. Precipitable water is expected to start out near 0.6-0.7 mm for this evening, but will increase toward 1.5 mm by the end of the night.
Discussion
A strong well-defined inversion will continue to cap low-level moisture at or below 8 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.

Skies overhead will remain predominately clear through the weekend. There is a possibility that a patch of high clouds will fill in from the SSW late Monday morning and pass overhead for that night. These clouds will quickly shift off toward the east on Tuesday, leaving mostly clear skies again for that night.

Precipitable water is expected to start out near 0.6-0.7 mm for tonight, but will likely increase toward 1.5 mm by the end of the night and peak near 2 mm for Saturday night. It should settle back in near 1 mm for the following 3 nights.

A mixture of boundary layer and low-level turbulence will contribute to poor/bad seeing over the next 3 nights. There is a good chance for a brief break in this turbulence, allowing seeing to improve toward 0.5-0.6 arcseconds for Monday night. However, boundary layer turbulence is set to increase again, which will likely degrade seeing again for Tuesday night.

Little change since the morning forecast...The mid-level ridge will continue to sit to the north of the state, before briefly sagging southward as a trough passes well to the north around Monday/Tuesday, then will quickly rebound northward as a new ridge fills in from the west late Tuesday. Nonetheless, the ridge will remain close enough to promote steady/strong large-scale subsidence in the area, which will easily maintain a well-defined inversion primarily near 6-8 thousand feet over the next 5 nights. Stiff easterly flow will prevail along the southern flank of the ridge, which will stir up boundary layer turbulence and contribute to poor/bad seeing through the weekend. In addition, a patch of minor mid/upper-level moisture filling in alont the eastern flank of the ridge is expected to push PW toward 1.5 mm by the end the night and 2 mm for tomorrow night. PW will eventually settle back in near 1 mm for the following 3 nights, and there is a very good chance that winds will briefly taper as the ridge shifts over the state on Monday. This should help reduce boundary layer turbulence and dramatically improve seeing for that night. However, the new ridge building in from the west will likely strengthen winds again, which will probably degrade seeing for Tuesday 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 14 - 8 PM0-5Clear0 / 00.5NE/15-300.8-1.20.6-1
Sat Dec 15 - 2 AM0-5Clear0 / 00NE/15-300.7-1.11-1.5
2 PM0-20Clear0 / 05.5NE/20-35NaN1.5-2.5
8 PM0-5Clear0 / 01NE/25-400.9-1.51.75-2.25
Sun Dec 16 - 2 AM0-5Clear0 / 01ENE/25-400.9-1.51.75-2.25
2 PM0-20Clear0 / 06.5ENE/20-35NaN1-2
8 PM0-5Clear0 / 02E/20-350.8-1.20.9-1.1
Mon Dec 17 - 2 AM0-10Clear0 / 02E/20-350.8-1.21-1.2
2 PM10-308-90 / 08SE/15-30NaN1-1.5
Tue Dec 18 - 2 AM20-408-90 / 03SSW/10-200.4-0.70.8-1.2
2 PM10-308-90 / 06WSW/15-30NaN1-2
Wed Dec 19 - 2 AM0-20Clear0 / 0-0.5NNW/20-350.7-1.10.9-1.3
2 PM0-20Clear0 / 04N/25-40NaN1-2
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
Fri Dec 14 - Sat Dec 15 17:55 19:04 5:30 6:39 N/A 0:25 48 23 36.0 -7 13
Sat Dec 15 - Sun Dec 16 17:55 19:04 5:31 6:40 N/A 1:14 58 0 21.8 -2 52
Sun Dec 16 - Mon Dec 17 17:56 19:04 5:31 6:40 N/A 2:05 68 1 08.5 1 44
Mon Dec 17 - Tue Dec 18 17:56 19:05 5:32 6:41 N/A 2:58 77 1 57.0 6 24
Tue Dec 18 - Wed Dec 19 17:56 19:05 5:32 6:41 N/A 3:54 86 2 48.1 10 56
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 17 December 2018.
Additional Information
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