Current Conditions
Temp-1.6 C
RH9 %
WindNNE 12 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Friday 18 January (0300 UTC Saturday 19 January) 2019
Warning(s)
Moderate (tapering) winds
Chance for fog/ice
Cloud Cover and Fog/Precipitation Forecast
There is a risk for periods of fog, ice, high humidity and light flurries mainly during the first half of the night. Broken clouds will continue to shift overhead and eastward, opening up skies as the night progresses.
Summary of Key Meteorological Variables
Summit temperatures will be near -5 C, with winds from the WNW at 15-30 mph for this evening, switching to a more northerly direction as the night progresses. Seeing will exceed 1 arcsecond, while precipitable water is expected to start out near 4 mm, but will plummet toward 0.7-0.8 mm through the night.
Discussion
The tradewind inversion is expected to briefly weaken/lift toward 15 thousand feet as a band of moisture/instability sweeps through the area this afternoon/evening. This may allow for periods of fog, ice, high humidity and light flurries at the summit mainly through the first half of the night. The inversion is set to recover near 6-7 thousand feet by sunrise tomorrow, which will ensure the summit will remain dry and stable for at least the following 3 nights. However, building instability/moisture may begin to erode the inversion again and increase the risk for more fog/ice and perhaps light flurries at the summit through Tuesday night. Extensive daytime clouds are possible for today, then will become minimal and short-lived over the weekend and the early part of next week, only to pick up again on Wednesday.

The broken mid/upper-level clouds will continue to shift overhead and eastward, opening up skies as the night progresses and leaving clear skies for the following 2 nights. There is a possibility that another patch of mid/upper-level clouds will pass along the northern skies on Monday and into early Tuesday, then will lift northward as more quick moving high clouds fill in from the west for that night.

Precipitable water is expected to start out near 4 mm for early this evening, then will plummet toward 0.7-0.8 mm by the second half of the night. There is a good chance that it will subtly increase toward 1 mm for Saturday and Sunday night, then jump to 3-4 mm for the early part of next week.

Lingering boundary layer turbulence and increase in mid/low-level turbulence will likely contribute to poor/bad seeing over the next 2 nights. Calmer skies will eventually settle in over the area on Sunday, allowing seeing to improve toward 0.5-0.6 arcseconds for that night and most of Monday night. However, another round of boundary layer turbulence and building instability could degrade seeing once again on Tuesday night.

No change since the morning forecast...A sharp trough and its associated low will send a dissipating cold front through the Big Island later this afternoon, which will briefly erode/weaken the inversion and increase the risk for periods of fog, ice and flurries at the summit mainly during the first half of the night. The front and trough are set to rapidly shift off toward the NE as a tight ridge builds in from the west and rapidly expands eastward while settling in over the state into the early part of next week. This will help re-instill large-scale subsidence in the area, which will easily maintain a well-defined inversion near 6-7 thousand feet during this period. Unfortunately, mid/low-level turbulence in the wake of the front (as well as lingering boundary layer turbulence) will contribute to poor/bad seeing over the next 2 nights. PW, on the other hand, will benefit from very dry air behind the front and plummet toward 0.7-0.8 mm by the end of tonight. There is good chance that PW will subtly increase back to 1 mm as minor mid-level moisture embedded in the ridge settles in overhead for Saturday and Sunday night. Seeing is expected to eventually improve (toward 0.5-0.6 arcseconds) as calmer skies settle in overhead for Sunday and Monday night. However, a very weak trough may begin to weaken/erode the ridge and perhaps destablize the air mass beginning late Tuesday. This could help weaken the inversion once again and increase the risk for moisture at the summit and cloudy/turbulent skies as that night progresses and into Wednesday.
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 Jan 18 - 8 PM40-606-860 / 20-5WNW/15-301-22-4
Sat Jan 19 - 2 AM0-20Clear20 / 5-5NNW/15-300.9-1.70.6-1
2 PM0-20Clear0 / 03.5NNE/5-15NaN0.8-1.2
8 PM0-5Clear0 / 0-1N/5-150.7-1.30.8-1
Sun Jan 20 - 2 AM0-5Clear0 / 0-1N/5-150.6-11-1.2
2 PM0-20Clear0 / 05NNE/5-15NaN1-1.5
8 PM0-5Clear0 / 00ENE/5-150.5-0.71-1.2
Mon Jan 21 - 2 AM0-5Clear0 / 0-0.5SSE/0-100.45-0.650.9-1.1
2 PM20-407-80 / 03.5WNW/5-15NaN2-4
Tue Jan 22 - 2 AM0-207-80 / 0-2.5WNW/5-150.4-0.72.5-3.5
2 PM0-208-90 / 01NW/10-20NaN3-5
Wed Jan 23 - 2 AM20-408-940 / 10-3.5NNW/15-300.5-0.93-5
2 PM0-204-960 / 302NNW/20-35NaN6-10
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 Jan 18 - Sat Jan 19 18:15 19:22 5:42 6:50 N/A 5:40 95 6 15.2 21 19
Sat Jan 19 - Sun Jan 20 18:16 19:23 5:43 6:50 16:45 6:42 99 7 20.4 21 25
Sun Jan 20 - Mon Jan 21 18:16 19:24 5:43 6:50 17:50 7:42 100 8 26.2 19 55
Mon Jan 21 - Tue Jan 22 18:17 19:24 5:43 6:50 18:57 N/A 98 9 30.3 16 57
Tue Jan 22 - Wed Jan 23 18:17 19:25 5:43 6:50 20:03 N/A 92 10 31.6 12 48
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 21 January 2019.
Additional Information
For public road conditions and snow report message please call (808) 935-6268.
This message is also available at the MKWC road conditions page.
NWS Hawaiian Islands Synoptic Discussion and Guidance
Honolulu National Weather Service Data and Products