Current Conditions
Temp4.8 C
RH12 %
WindE 15 mph
Mauna Kea Observatories Forecast
5 PM HST Friday 22 August (0300 UTC Saturday 23 August) 2014
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, with winds from the ENE at 15-25 mph and with seeing around 0.6-0.7 arcseconds. Precipitable water is expected to be in the 0.7-0.9 mm range for the first half of the night and 0.9-1.1 mm range for the second half.
The tradewind inversion will continue to cap low-level moisture near 7 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 through the next 5 nights.

Precipitable water is expected to start out near 0.8 mm for this evening then increase toward 1 mm as the night progresses and likely linger in the 1-1.5 mm range for the remainder of the forecast period (there is a possibility that PW will trend back toward 1 mm late Tuesday night).

Boundary layer turbulence will likely contribute to poorer than average seeing for tonight. This source of turbulence is slated to decrease through tomorrow, allowing seeing to improve toward better than average values for the following 3 nights. There is a possibility that a patch of mid/low-level turbulence will build in overhead and disrupt seeing again for Tuesday night.

No change since the morning forecast...A persistent mid/low-level ridge will continue to sit to the north of the state well into next week, while an upper-level ridge lingers overhead during the beginning and ending part of the forecast period. Regardless, this will allow strong/steady large-scale subsidence to prevail in the area, which will easily maintain the tradewind inversion near 7 thousand feet and ensure a clear, dry and stable summit-level air mass through the next 5 nights. PW will also benefit by the extra subsidence from the upper-level ridge and linger just below 1 mm mainly for tonight and perhaps again late Tuesday night (there is a very good chance that PW will increase subtly as the upper-level ridge weakens between those nights). Seeing, on the other hand, may trend in the opposite direction as the upper-level ridge may redistribute momentum/turbulence into the low-levels/boundary layer and disrupt seeing for tonight and again for Tuesday night. There is a good chance that better than average seeing will prevail as calm skies sets in at and above the summit for Saturday, Sunday and Monday 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 Aug 22 - 8 PM0-5Clear0 / 03NE/15-250.55-0.750.7-0.9
Sat Aug 23 - 2 AM0-5Clear0 / 03ENE/15-250.55-0.750.9-1.1
2 PM0-20Clear0 / 09E/10-20NaN1-1.5
8 PM0-5Clear0 / 03.5E/5-150.45-0.551-1.2
Sun Aug 24 - 2 AM0-5Clear0 / 03E/5-150.4-0.51-1.2
2 PM0-20Clear0 / 08SE/0-10NaN1-1.5
8 PM0-5Clear0 / 03E/0-100.4-0.51-1.5
Mon Aug 25 - 2 AM0-5Clear0 / 02.5E/0-100.4-0.51-1.5
2 PM0-20Clear0 / 08.5NNE/0-10NaN1-2
Tue Aug 26 - 2 AM0-5Clear0 / 03.5N/0-100.4-0.61-1.5
2 PM0-20Clear0 / 09NNE/5-15NaN1-2
Wed Aug 27 - 2 AM0-5Clear0 / 04NNE/5-150.5-0.90.8-1.2
2 PM0-20Clear0 / 08.5NE/5-15NaN0.8-1.2
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
Fri Aug 22 - Sat Aug 23 18:54 20:01 4:48 5:55 4:25 17:04 4 8 31.7 13 24
Sat Aug 23 - Sun Aug 24 18:53 20:00 4:49 5:56 5:14 17:44 1 9 18.0 10 34
Sun Aug 24 - Mon Aug 25 18:52 19:59 4:49 5:56 6:03 18:22 0 10 03.5 7 19
Mon Aug 25 - Tue Aug 26 18:52 19:58 4:50 5:56 6:52 19:00 1 10 48.4 3 44
Tue Aug 26 - Wed Aug 27 18:51 19:57 4:50 5:56 N/A 19:37 3 11 33.2 -0 01
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 25 August 2014.
Additional Information
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This message is also available at the MKWC road conditions page.
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