Current Conditions
Temp1.8 C
RH8 %
WindENE 7 mph
RoadClosed
Mauna Kea Observatories Forecast
5 PM HST Friday 13 December (0300 UTC Saturday 14 December) 2019
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
There is a small risk for periods of fog and high humidity, mainly during the second half of the night; precipitation is not expected. Broken mid/upper-level clouds will continue to block most of the sky through the night.
Summary of Key Meteorological Variables
Summit temperatues will be near 1 C, with winds from the NNE at 5-15 mph for this evening, switching to a more ENE direction and increasing to 10-20 mph through the night. Seeing will be near 0.8-1 arcsecond, while precipitable water is expected to exceed 4 mm for the night.
Discussion
Persistent instability will continue to enhance in the incoming low-level cloud field and may allow for periods of fog, high humidity and perhaps ice at the summit over the next 2 nights; precipitation is not expected. A stronger more well-defined inversion is set to cap low-level moisture at or below 8 thousand feet and ensure the summit remains dry and stable for Sunday, Monday and Tuesday night. Some afternoon clouds are possible for tomorrow, then will taper again for Sunday and especially the early part of next week.

Broken mid/upper-level clouds will conitnue to pass overhead and block most of the sky for the next 2 nights. These clouds are set to break up and shift off toward the east through Sunday, opening up skies through that night and leaving clear skies for the following 2 nights.

Precipitable water is expected to exceed 4 mm for the next 2 nights, slip toward 2 mm through Sunday night and probably settle in near 0.7-0.8 mm for the early part of next week.

A mixture of an elevated inversion, free atmospheric turbulence and instability will likely contribute to poorer than average seeing over the next 2 nights. There is a possibility that seeing will improve for early Sunday evening, but an increase in boundary layer turbulence could degrade seeing as that night progresses and lead to poor seeing again for Monday and Tuesday night.

NO change since the morning forecast...A rather broad trough to the NW will continue to displace the mid-level ridge off toward the east, destabilize the air mass and enhance the incoming low-level cloud flow before lifting off toward the NE early Sunday morning. While fortunately, the trough may actually flatten out a bit as it deposits a low well to the west of the state, minimizing the risk for strong dynamic instability near the Big Island, this incoming cloud field may still allow for periods of fog and high humidity at the summit through Saturday night. In addition, the trough/low is expected to draw deep mid/upper-level moisture/clouds out of the tropics and send it over the summit, contributing to periods of extensive cloud cover during this time. A deep ridge is set to build in from the west as the trough shifts off toward the east on Sunday. Subsidence associated with the ridge will help rebuild a well-defined inversion near 7-8 thousand feet, clear out summit skies (of clouds), and ensure a dry/stable summit-level air mass for Sunday night and early part of next week. However, there is a good chance that summit-level winds will pick up as a rather tight wind gradient along the eastern and southern flank of the mid-level ridge moves over the area during those nights. On the other hand, there is a very good chance that the deep subsidence will drive PW below 1 mm for the early part of next week.
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 13 - 8 PM60-806-930 / 01NNE/10-200.7-1.14-6
Sat Dec 14 - 2 AM60-806-940 / 01ENE/10-200.7-1.14-6
2 PM80-1004-1050 / 56ENE/5-15NaN4-8
8 PM60-806-930 / 02ENE/5-150.7-1.14-6
Sun Dec 15 - 2 AM60-806-920 / 01.5ESE/5-150.6-14-6
2 PM40-606-80 / 06NNW/5-15NaN3-5
8 PM20-406-70 / 01.5NNW/5-150.45-0.652-3
Mon Dec 16 - 2 AM0-20Clear0 / 00.5N/10-200.5-0.81.5-2.5
2 PM0-20Clear0 / 06ENE/15-30NaN1-2
Tue Dec 17 - 2 AM0-5Clear0 / 02E/25-400.7-1.10.6-1
2 PM0-20Clear0 / 06.5E/20-35NaN0.8-1.2
Wed Dec 18 - 2 AM0-5Clear0 / 02.5ENE/15-300.7-1.10.6-1
2 PM0-20Clear0 / 06.5SE/5-15NaN0.8-1.2
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
Sat Dec 14 - Sun Dec 15 17:55 19:03 5:30 6:39 20:22 N/A 88 8 28.6 21 28
Sun Dec 15 - Mon Dec 16 17:55 19:04 5:31 6:40 21:24 N/A 79 9 27.6 18 34
Mon Dec 16 - Tue Dec 17 17:55 19:04 5:31 6:40 22:25 N/A 69 10 24.5 14 35
Tue Dec 17 - Wed Dec 18 17:56 19:05 5:32 6:41 23:26 N/A 58 11 19.1 9 46
Wed Dec 18 - Thu Dec 19 17:56 19:05 5:32 6:41 0:25 N/A 47 12 11.8 4 27
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 16 December 2019.
Additional Information
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