Current Conditions
Temp0.0 C
RH5 %
WindWSW 21 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Tuesday 18 December (0300 UTC Wednesday 19 December) 2018
Warning(s)
Increasing winds
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, while there is a possibility for lingering patches of mid/upper-level clouds in the area mainly for the early evening hours.
Summary of Key Meteorological Variables
Summit temperatures will be near -2 C this evening and -1 C tomorrow morning. Winds will be from the WNW at 10-20 mph for this evening, switching to a more northerly direction and increasing to 15-30 mph through the night. Seeing will be near 0.7 arcseconds for this evening, but will likely increase toward 0.8-0.9 arcseconds for tomorrow morning. Precipitable water is expected to start out near 3 mm, but slip toward 1 mm (or less) 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.

There is a chance for lingering patches of mid/upper-level clouds in the area mainly for the early evening hours of tonight; clear skies are expected for the remainder of the forecast period.

Precipitable water is expected to start out near 3 mm, but slip to 1 mm by the end of the night and eventually settle in near 0.8-1 mm for Wednesday and Thursday night, only to increase back toward 1.5-1.75 mm for the following 2 nights.

Building mid/low-level turbulence will likely contribute to poor seeing for tonight, while strengthening boundary layer turbulence further degrades seeing for tomorrow night. While winds are set to taper through Thursday, it may remain strong enough to contribute to light/moderate boundary layer turbulence and poorer than average seeing for the following 3 nights.

Mostly negative changes have been made to the seeing forecast...The mid-level ridge will briefly sag over the state as a trough passes to the north over the next 24 hours, then will rebound northward as a new reinfocing ridge fills in from the west and gradually shifts eastward over the remainder of the week. Nonetheless, the ridge will continue to promote steady/strong large-scale subsidence in the area, which will easily maintain a well-defined inversion at or below 8 thousand feet and ensure a dry/stable summit-level air mass through the next 5 nights. While the southward displacement of the ridge will also help reduce summit-level winds for this evening, building mid/low-level turbulence associated with the passing trough will likely contribute to poor seeing for tonight. In addition, the new building ridge will push a very tight wind gradient over the area, which will likely further degrade seeing mainly for Wednesday night. Although winds are set to taper as this area passes off toward the south and the ridge settles in to the north of the state on Thursday, light/moderate boundary layer may still persist, limiting seeing from improving much for the remainder of the forecast period.
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)
Tue Dec 18 - 8 PM0-207-80 / 0-2WNW/10-200.6-0.82-3
Wed Dec 19 - 2 AM0-10Clear0 / 0-1N/15-300.7-11-2
2 PM0-20Clear0 / 05NNE/20-35NaN1-1.5
8 PM0-5Clear0 / 0-1NNE/35-501-20.8-1
Thu Dec 20 - 2 AM0-5Clear0 / 0-1NE/35-501-20.8-1
2 PM0-20Clear0 / 06ENE/20-35NaN1-1.5
8 PM0-5Clear0 / 01NE/15-300.7-1.10.8-1
Fri Dec 21 - 2 AM0-5Clear0 / 01NE/10-200.6-0.90.8-1
2 PM0-20Clear0 / 06NE/10-20NaN1-2
Sat Dec 22 - 2 AM0-5Clear0 / 01ENE/15-300.6-11.5-2
2 PM0-20Clear0 / 06.5ENE/20-35NaN1.5-2.5
Sun Dec 23 - 2 AM0-5Clear0 / 01ENE/20-350.7-1.11.5-2
2 PM0-20Clear0 / 05.5E/20-35NaN1-2
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
Tue Dec 18 - Wed Dec 19 17:56 19:05 5:32 6:41 N/A 3:54 86 2 48.1 10 56
Wed Dec 19 - Thu Dec 20 17:57 19:06 5:33 6:42 N/A 4:53 92 3 42.7 15 03
Thu Dec 20 - Fri Dec 21 17:57 19:06 5:33 6:42 16:12 5:55 97 4 41.1 18 26
Fri Dec 21 - Sat Dec 22 17:58 19:07 5:34 6:43 17:05 6:59 100 5 43.1 20 42
Sat Dec 22 - Sun Dec 23 17:58 19:07 5:34 6:43 18:05 N/A 99 6 47.6 21 34
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Wednesday 19 December 2018.
Additional Information
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