Current Conditions
Temp-1.0 C
RH15 %
WindNE 51 mph
Mauna Kea Observatories Forecast
5 PM HST Friday 13 January (0300 UTC Saturday 14 January) 2017
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 0.5 C, with light easterly winds and seeing near 0.6 arcseconds. Precipitable water is expected to be in the 0.8-1 mm range for the night.
The tradewind inversion will continue to cap low-level moisture primarily near 5-6 thousand feet and ensure the summit remains dry and stable through the next 5 nights. Daytime clouds will be minimal and short-lived throughout the forecast period.

Skies will remain predominately clear for tonight. However, high clouds will begin to approach from the north on Saturday and could briefly pass overhead during that night. Clear skies will prevail for the following 3 nights.

Precipitable water is expected to slip just below 1 mm for tonight, increase to 1.5-2 mm for tomorrow night and 2-3 mm range for Sunday night, then drop back to 1 mm or less for the early part of next week.

An increase in upper-level turbulence may push seeing back toward 0.6 arcseconds, but calmer skies will allow for an improvement in seeing for Saturday night. Another round of stronger upper-level turbulence will degrade seeing toward poor values for Sunday night and there is a very good chance that boundary layer turbulence will further deteriorate seeing for the early part of next week.

Little change since the morning forecast...The mid/low-level ridge will continue to stretch across most of the Pacific and sit over the state before rebounding northward as an upper-level ridge passes to the north late in the weekend and for the early part of next week. Nonetheless, strong/steady large-scale subsidence associated with the ridge will easily maintain a well-defined inversion near 5-6 thousand feet and ensure a dry and stable summit-level air mass well into next week. Light winds embedded in the ridge should allow for a relatively calm summit-level air mass over the next 3 nights, but bouts of upper-level turbulence could contribute to some degradation in seeing for tonight and especially Sunday night (calmer skies and better than average seeing should prevail for Saturday night). Summit-level winds are set to increase beginning around sunrise Monday, which could stir up boundary layer turbulence and further deteriorate seeing for the that night and especially Tuesday night. PW, on the other hand, should benefit from the strong subsidence associated with the deep ridge and slip toward 1 mm or less during that time.

Please Note:There will be no forecasts on Monday, January 16, in observance of Martin Luther King Day. The normal forecast schedule will resume on Tuesday, January 17.
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 13 - 8 PM0-5Clear0 / 00.5ENE/0-100.5-0.70.8-1
Sat Jan 14 - 2 AM0-5Clear0 / 00ESE/0-100.5-0.70.8-1
2 PM0-20Clear0 / 04WNW/0-10NaN1-2
8 PM20-408-90 / 00ESE/0-100.35-0.551.5-2
Sun Jan 15 - 2 AM20-408-90 / 00WSW/0-100.4-0.61.75-2.25
2 PM0-20Clear0 / 04NE/5-15NaN2-4
8 PM0-5Clear0 / 00ENE/5-150.5-0.92-3
Mon Jan 16 - 2 AM0-5Clear0 / 0-0.5E/10-200.5-11.5-2.5
2 PM0-20Clear0 / 04ENE/15-30NaN1-2
Tue Jan 17 - 2 AM0-5Clear0 / 00ENE/20-350.6-1.20.9-1.4
2 PM0-20Clear0 / 05ENE/25-30NaN1-1.5
Wed Jan 18 - 2 AM0-5Clear0 / 01E/25-400.8-1.60.7-1.1
2 PM0-20Clear0 / 08E/25-40NaN0.8-1.2
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 Jan 16 - Tue Jan 17 18:14 19:22 5:42 6:50 22:20 N/A 73 12 04.4 2 01
Tue Jan 17 - Wed Jan 18 18:15 19:22 5:42 6:50 23:10 N/A 64 12 51.7 -2 01
Wed Jan 18 - Thu Jan 19 18:15 19:23 5:43 6:50 24:00 N/A 54 13 37.9 -5 52
Thu Jan 19 - Fri Jan 20 18:16 19:23 5:43 6:50 0:49 N/A 45 14 23.9 -9 25
Fri Jan 20 - Sat Jan 21 18:16 19:24 5:43 6:50 1:38 N/A 35 15 10.2 -12 33
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Tuesday 17 January 2017.
Additional Information
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