Current Conditions
Temp1.4 C
RH98 %
WindSW 32 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
10 AM HST (2000 UTC) Friday 19 October 2018
High humidity, fog and ice
Chance for convection and flurries
Cloud Cover and Fog/Precipitation Forecast
There is a high risk for periods of fog, high humidity and ice at the summit through the night; there is also a possibility for light flurries, while thick clouds continue to pass over the summit through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 3 C this afternoon and -0.5 C for the night. Winds will be from the WSW at 15-30 mph for today, diminishing to 10-20 mph for the night. Seeing and precipitable water are expected to exceed 1 arcsecond and 4 mm, respectively, through the night.
The atmosphere near the Big Island will remain mostly saturated and unstable, likely allowing extensive fog, high humidity and ice to plague the summit for at least the next 2 nights. There is also a possibility for periods of light flurries at the summit, as well as isolated convection in the area at virtually anytime, but particularly the afternoon hours and perhaps near sunrise. There is a good chance that the upper air mass will begin to dry out on Sunday, but an elevated inversion may still allow for short periods of fog/high humidity and ice for that night and maybe even the for the early part of next week. Extensive daytime clouds are expected through at least the weekend and probably the early part of next week. There is also a good chance for afternoon convection along the Big Island slopes throughout the forecast period.

Broken to overcast thick clouds will continue to blanket summit skies for tonight, then will begin to push off toward the east, gradually opening up skies through tomorrow night. There is a possibility for patches of residual mid and/or summit-level clouds for Sunday night and occasionally for Monday and Tuesday night.

Precipitable water will continue to exceed 4 mm through at least Sunday night, then may begin to slip toward 3 mm for Monday night and 2 mm for Tuesday night (there is an outside chance it will dip toward 1 mm for the latter night).Instability, moisture and turbulence at various layers in atmosphere will contribute to poor/bad seeing over the next 2 nights. There is a good chance that seeing will improves toward more average-like values as the air mass dries out and stabilizes through Sunday night. However, a patch of low-level turbulence could degrade briefly seeing a bit for Monday night. There is a possibility that seeing will slip back toward 0.5-0.6 arcseconds as this source of turbulence subsides for Tuesday night.

A slow moving mid/upper-level trough filling in from the northwest of the state will continue to destabilize the air mass and drag deep moisture/clouds in from the SW and over/near the summit area before shifting east of the Big Island just after sunrise tomorrow. Nonetheless, this will likely keep the air mass near the Big Island quite saturated and unstable, allowing extensive fog, high humidity, ice and overcast skies to plague the summit for most of the next 2 nights. There is a possibility for periods of flurries/light rain at the summit as well as convection in the area at virtually anytime (though the development of convection should favor the afternoon hours and near sunset). While there is a very good chance that the upper air mass will dry out as the trough shifts eastward on Sunday, a weak mid-level low/trough may persist in the area, prohibiting the ridge from fully building in from the west and rebuilding the inversion well into next week. This could allow for more periods of fog and high humidity at the summit and isolated afternoon convection along the Big Island slopes during that time. Fortunately, the absence of upper-level moisture/clouds will limit the risk for precipitation and supress any afternoon convection. It should also be noted that the latest model run (which is not consistent with the previous runs) suggested that the air mass could abruptly, but briefly dry out 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 Oct 19 - 2 PM80-1004-1095 / 753WSW/10-20NaN10-15
8 PM80-1004.5-1090 / 60-0.5WSW/10-200.8-1.48-12
Sat Oct 20 - 2 AM80-1005-1090 / 40-0.5WSW/10-200.7-1.38-12
2 PM80-1004-1095 / 803WSW/5-15NaN10-15
8 PM60-804.5-790 / 75-1.5ENE/5-150.9-1.58-12
Sun Oct 21 - 2 AM40-604.5-785 / 60-1.5NNE/5-150.7-1.38-12
2 PM70-904-690 / 503.5SE/5-15NaN4-8
8 PM20-404.5-675 / 250SE/5-150.55-0.954-8
Mon Oct 22 - 2 AM0-204.5-665 / 20-0.5SSE/5-150.5-0.84-8
2 PM60-804-675 / 255ENE/5-15NaN4-8
Tue Oct 23 - 2 AM0-204-4.550 / 101E/5-150.55-0.853-5
2 PM40-604-560 / 157NE/5-15NaN3-6
Wed Oct 24 - 2 AM0-204-4.540 / 102SSW/5-150.4-0.72-4
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 Oct 19 - Sat Oct 20 18:04 19:09 5:05 6:09 N/A 3:03 82 22 36.3 -12 05
Sat Oct 20 - Sun Oct 21 18:04 19:08 5:05 6:10 N/A 3:54 89 23 23.8 -8 07
Sun Oct 21 - Mon Oct 22 18:03 19:08 5:05 6:10 N/A 4:45 94 0 11.4 -3 42
Mon Oct 22 - Tue Oct 23 18:02 19:07 5:06 6:10 16:54 5:37 98 0 59.7 0 58
Tue Oct 23 - Wed Oct 24 18:02 19:07 5:06 6:11 17:33 6:31 100 1 49.3 5 41
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Friday 19 October (0300 UTC Saturday 20 October) 2018.
Additional Information
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