Current Conditions
Temp4.5 C
RH10 %
WindNE 16 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
10 AM HST (2000 UTC) Thursday 18 April 2019
Warning(s)
None
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 5 C this afternoon and 0 C for the night. Winds will be from the ENE at 15-25 mph, with seeing near 0.75-0.8 arcseconds. Precipitable water is expected to be in the 0.7-0.9 mm range for the night.
Discussion
A strong well-defined tradewind inversion will continue to cap low-level moisture at or below 8 thousand feet and ensure a dry/stable summit-level air mass over the next 5 nights. Daytime clouds will be minimal and short-lived throughout the forecast period.

Skies will remain predominately clear for at least the next 2 nights. Scattered high clouds are set to pass along the northern skies for the following 3 nights, and may pass over the summit mainly for Saturday and Monday night.

Precipitable water is expected to linger near 0.8 mm fo rotnight, increase toward 0.9 mm for tomorrow night, 1-1.5 mm for Saturday night and probably 2-2.5 mm for the following 2 nights.

Despite relatively weak winds and mostly calm skies in the free atmosphere light/moderate boundary layer turbulence will contribute to poorer than average seeing probably for the next 2 nights. There is a good chance that seeing will settle in near average-like values as the boundary layer turbulence tapers a bit for Saturday, Sunday and Monday night.

A rather broad ridge will continue to sit to the north of the state and promote steady/strong large-scale subsidence in the area and negate the instability associated with a weak tropical upper-tropospheric trough passing through as well as a a persistent reflecting mid-level low to the south well into next week. This subsidence will easily maintain a well-defined inversion at or below 8 thousand feet and ensure a dry/stable summit-level air mass throughout the forecast period. The aforementioned low to the south may initially provide a tighter (than normal) wind gradient in the area, which will keep winds near 20 mph over the next 36 hours or so. This could stir up boundary layer turbulence and contribute to poorer than average seeing during that time.While winds are set to taper a bit as the low dissipates over the weekend, it may still remain strong enough (near 15 mph) to limit seeing from improving (beyond more average-like values), despite relatively calm skies in the free atmosphere for the remainder of the forecast period.

Please Note: There will be no forecasts tomorrow, Apr 19, in observance of Good Friday. The normal forecast schedule will resume on Monday, April 22.
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)
Thu Apr 18 - 2 PM0-20Clear0 / 05ENE/15-25NaN0.8-1.2
8 PM0-5Clear0 / 00ENE/15-250.6-10.7-0.9
Fri Apr 19 - 2 AM0-5Clear0 / 00ENE/15-250.6-0.90.7-0.9
2 PM0-20Clear0 / 06ENE/15-25NaN0.8-1.2
8 PM0-5Clear0 / 01E/15-250.6-0.90.7-0.9
Sat Apr 20 - 2 AM0-5Clear0 / 01E/10-200.6-0.80.8-1
2 PM0-209-100 / 07.5E/10-20NaN1-2
8 PM10-309-100 / 02.5E/10-200.55-0.751-1.5
Sun Apr 21 - 2 AM10-309-100 / 02ENE/10-200.5-0.71.25-1.75
2 PM0-209.5-100 / 07.5ENE/10-20NaN1.5-2.5
Mon Apr 22 - 2 AM0-109.5-100 / 02.5ENE/10-200.5-0.71.5-2.5
2 PM0-209.5-100 / 07NE/10-20NaN2-3
Tue Apr 23 - 2 AM0-209-100 / 02NE/10-200.5-0.72-3
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
Thu Apr 18 - Fri Apr 19 18:50 19:57 4:45 5:52 18:13 6:37 100 13 53.1 -6 42
Fri Apr 19 - Sat Apr 20 18:50 19:57 4:44 5:51 19:12 N/A 99 14 47.9 -11 42
Sat Apr 20 - Sun Apr 21 18:51 19:58 4:43 5:50 20:11 N/A 95 15 43.1 -15 56
Sun Apr 21 - Mon Apr 22 18:51 19:58 4:43 5:50 21:10 N/A 89 16 38.6 -19 13
Mon Apr 22 - Tue Apr 23 18:51 19:59 4:42 5:49 22:06 N/A 81 17 34.0 -21 23
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Thursday 18 April (0300 UTC Friday 19 April) 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.
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