Current Conditions
Temp0.1 C
RH5 %
WindNE 13 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Friday 14 February (0300 UTC Saturday 15 February) 2020
Warning(s)
Increasing winds
Chance for fog, ice and high humidity
Cloud Cover and Fog/Precipitation Forecast
There is a risk for periods of fog, lingering clouds ice and high humidity, mainly during the first half of the night; precipitation is unlikely.
Summary of Key Meteorological Variables
Summit temperatures will be near 1 C, with winds from the ESE at 10-20 mph for this evening, increasing to 15-30 mph toward the end of the night. Seeing will be near 0.8-1 arcsecond, while precipitable water is expected to start out near 8 mm, but will slip toward 2 mm by the end of the night.
Discussion
Although the tradewind inversion will continue to strengthen near 6-7 thousand feet, residual mid-level moisture may still allow for periods of fog, ice and high humidity, mainly during the first half of the night; precipitation is unlikely. The air mass above 8 thousand feet is expected to quickly dry out by sunrise tomorrow, and with a well-defined inversion will ensure the summit steers free of fog and precipitation for the remainder of the forecast period. Some daytime clouds are likely for today, then will become minimal and short-lived over the weekend and early part of next week.

There is a possibility for residual patches of dissipating mid-level clouds in area, mainly during the first half of the night. Clear skies are expected for the following 4 nights.

Precipitable water is expected to start out near 8 mm for this evening, but will slip toward 2 mm by the end of the night, then settle in near 0.7-0.8 mm for the following 4 nights.

Residual moisture combined with minor boundary layer turbulence will contribute to poor seeing for tonight. While the air mass is expected to dry out by the end of the night, the boundary layer turbulence may pick up a tad, and turbulence in the free atmosphere is also set to increase, limiting seeing from improving through the weekend. Calmer skies at and above the summit should eventually allow seeing to settle in near 0.5-0.6 arcseconds for the early part of next week.

A deep ridge to the NE of the state will continue to stabilize the air mass through strong large-scale subsidence, which will help re-establish a well-defined inversion near 6-7 thousand feet over the next 24 hours. Unfortunately, residual mid-level moisture from the departing/dissipating low may still allow for periods of fog, ice and high humidity at the summit mainly during the first half of tonight. The moisture will eventually detrain into the free atmospehre and shove off toward the SW by sunrise tomorrow, allowing the mid/low-level ridge to regain full control of the air mass for the remainder of the weekend and well into next week. This will ensure the summit remains free of fog and precipitation, and should also help PW to settle in near 0.7-0.8 mm during that time. The westerly jet will also maintain a rather zonal orientation, keeping high clouds from passing overhead throughout the forecast period. However, there is a good chance that a tighter mid-level wind gradient will build back over the Big Island, which will push winds toward 20-25 mph, enough to stir up boundary layer turbulence and contribute to poor seeing through the weekend. Winds are set to taper as the ridge expands westward, which should help to improve seeing for Monday and 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 Feb 14 - 8 PM0-204.5-660 / 101ESE/10-200.7-1.14-8
Sat Feb 15 - 2 AM0-205-620 / 51ESE/15-300.7-1.12-4
2 PM0-20Clear0 / 08ESE/25-40NaN1-2
8 PM0-5Clear0 / 02ESE/20-350.6-10.6-0.8
Sun Feb 16 - 2 AM0-5Clear0 / 02ESE/15-300.6-10.6-0.8
2 PM0-20Clear0 / 08.5ESE/15-40NaN0.8-1.2
8 PM0-5Clear0 / 03E/15-300.6-10.6-0.8
Mon Feb 17 - 2 AM0-5Clear0 / 02.5E/15-300.6-10.6-0.8
2 PM0-20Clear0 / 08.5E/15-30NaN0.8-1.2
Tue Feb 18 - 2 AM0-5Clear0 / 02E/10-200.45-0.750.6-1
2 PM0-20Clear0 / 07ENE/10-20NaN0.8-1.2
Wed Feb 19 - 2 AM0-5Clear0 / 01ENE/10-200.45-0.650.6-1
2 PM0-20Clear0 / 06.5ENE/10-20NaN0.8-1.2
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
Mon Feb 17 - Tue Feb 18 18:31 19:36 5:35 6:40 3:02 N/A 24 18 01.6 -22 50
Tue Feb 18 - Wed Feb 19 18:32 19:37 5:35 6:40 3:56 N/A 16 18 56.7 -23 20
Wed Feb 19 - Thu Feb 20 18:32 19:37 5:34 6:39 4:46 N/A 9 19 50.6 -22 39
Thu Feb 20 - Fri Feb 21 18:32 19:37 5:34 6:38 5:33 N/A 5 20 42.8 -20 54
Fri Feb 21 - Sat Feb 22 18:33 19:38 5:33 6:38 6:16 17:15 1 21 32.8 -18 14
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 17 February 2020.
Additional Information
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