Current Conditions
Temp4.3 C
RH22 %
WindNNE 6 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
10 AM HST (2000 UTC) Tuesday 22 January 2019
Warning(s)
Increasing 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 3 C this afternoon and -2 C for the night. Winds will be from the north at 15-30 mph, with seeing near 1 arcsecond. Precipitable water is expected to be in the 3-4 mm range for the first half of the night and 3.5-4.5 mm range for the second half.
Discussion
Although humidity is set to increase toward 40-50% as minor mid-level moisture builds in overhead, a fairly well-defined tradewind inversion will continue to cap low-level moisture near 8 thousand feet and ensure the summit steers free of fog and precipitation through at least Thursday night. There is a possibility that a band of moisture scraping through the area could weaken the inversion for Friday night, while another more organized batch of moisture and instability fills in for Saturday night. Nonetheless, this will raise the stakes on fog, ice, high humidity and light flurries at the summit during those night. Some minor daytime clouds are possible through the week and could turn extensive over the weekend.

Skies overhead will remain predominately clear through at least Thursday night. There is a chance that a narrow band of mid-level clouds will pass along the northern skies for Friday night, while more patches fill in from the NW and drift overhead late Saturday night.

Precipitable water is expected to increase toward 4+ mm for the next 3 nights, perhaps slip toward 2-3 mm for Friday night, then jump back to 4+ mm for the following night.

Despite relatively uniform northerly flow at and above the summit, a slow/steady increase in winds will contribute to boundary layer turbulence and likely poor/bad seeing throughout the forecast period.

The eastern tip of the mid-level ridge will continue to sit over the state and promote relatively steady large-scale subsidence in the area until a weak low passing to the north sends a cold front through late Friday night. Nonetheless, this subsidence will help maintain a well-defined tradewind inversion near 8-9 thousand feet and ensure a dry/stable summit-level air mass through at least Thursday night. Mid-level moisture filling in via the northerly winds along the eastern flank of the ridge will push summit-level humidity and PW toward 40-50% and 4 mm, respectively during this time. In addition, northerly winds along this flank are set to increase toward 30-40 mph, which will stir up boundary layer turbulence and contribute to poor/bad seeing probably well into the weekend. The aformentioned front may also bring a patch of mid-level moisture/instability the area, which could weaken the inversion and increase the risk for fog, ice and high humidity at the summit for Friday night. While this front will dissipate and lift off toward the NE relatively quickly, models suggest that a low/trough will rapidly fill in from the NW and intensify to the north of the state over the weekend. This could bring more widespread/organized moisture/instability to the area and further increase this risk for inoperable/poor conditions as the weekend progresses.
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 Jan 22 - 2 PM0-20Clear0 / 03N/15-30NaN2-4
8 PM0-5Clear0 / 0-2N/15-300.7-1.33-4
Wed Jan 23 - 2 AM0-5Clear0 / 0-2NNE/15-300.7-1.33.5-4.5
2 PM20-404-4.50 / 04.5NNE/20-35NaN4-6
8 PM0-5Clear0 / 0-1NNE/20-350.8-1.64-6
Thu Jan 24 - 2 AM0-5Clear0 / 0-1N/25-400.8-1.44-6
2 PM20-404-4.50 / 04N/25-40NaN4-6
8 PM0-5Clear0 / 0-1N/30-450.8-1.63.5-4.5
Fri Jan 25 - 2 AM0-5Clear0 / 0-1.5N/25-400.8-1.63-4
2 PM20-404-4.520 / 53.5NW/25-40NaN2-4
Sat Jan 26 - 2 AM10-304.5-660 / 15-2NNW/30-450.9-1.92-3
2 PM40-604-550 / 103.5NW/35-50NaN3-6
Sun Jan 27 - 2 AM20-404.5-765 / 20-3WNW/30-450.9-1.94-6
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 Jan 22 - Wed Jan 23 18:17 19:25 5:43 6:50 20:03 N/A 92 10 31.6 12 48
Wed Jan 23 - Thu Jan 24 18:18 19:25 5:43 6:50 21:07 N/A 85 11 29.4 7 56
Thu Jan 24 - Fri Jan 25 18:19 19:26 5:42 6:49 22:08 N/A 75 12 24.3 2 44
Fri Jan 25 - Sat Jan 26 18:19 19:26 5:42 6:49 23:06 N/A 65 13 16.9 -2 27
Sat Jan 26 - Sun Jan 27 18:20 19:27 5:42 6:49 0:03 N/A 54 14 08.0 -7 20
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Tuesday 22 January (0300 UTC Wednesday 23 January) 2019.
Additional Information
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This message is also available at the MKWC road conditions page.
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