Current Conditions
Temp5.4 C
RH17 %
WindESE 24 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
9 AM HST (1900 UTC) Friday 29 April 2016
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 5.5 C this afternoon, 1 C this evening and 0.5 C tomorrow morning. Winds will be from the ENE at 10-20 mph for today and 5-15 mph for the night. Seeing will be near 0.5 arcseconds, while precipitable water is expected to be in the 1.25-1.75 mm range for the night.
Discussion
The tradewind inversion will continue to cap low-level moisture at or below 9 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 linger near 1.5 mm for tonight, slip back toward 1 mm or less for the following 2 nights, then increase to 2-3 mm for Monday and Tuesday night.

Slightly better than average seeing should prevail as relatively calm skies prevail for tonight. However, an increase in boundary layer turbulence and perhaps minor turbulence in the free atmosphere will contribute to poor seeing over the next 2 nights. Seeing should improve toward more average-like values as the boundary layer turbulence subsides for the early part of next week.

The mid/low-level ridge will continue to sit to the north of the state, promoting strong/steady large-scale subsidence well into next week, and easily negating the affects of a building upper-level trough over the next 24-36 hours. Nevertheless, the subsidence will help maintain a well-defined inversion primarily near 8-9 thousand feet and ensure a dry/stable summit-level air mass throughout the forecast period. The aforementioned trough is not expected to affect seeing much, but could inject minor mid-level moisture into the area and increase PW toward 1.5 mm for tonight. PW is slated to slip back toward 1 mm or less as dry air fills in over the summit in the wake of the trough. However, a new ridge also trailing the trough could briefly increase summit-level winds toward 25 mph, enough to stir up minor boundary layer turbulence and contribute to poor seeing for Saturday and Sunday night. Winds are set to subside once this new ridge slips further eastward, which should allow seeing to return toward more average-like values for the early part of next week. Unfortunately, there is a chance that mid/low-level moisture embedded with the ridge's associated easterly trades will make a push through the area, increasing PW toward 2-3 mm during that time.
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 Apr 29 - 2 PM0-20Clear0 / 05.5ENE/10-20NaN1-2
8 PM0-5Clear0 / 01E/5-150.45-0.551.25-1.75
Sat Apr 30 - 2 AM0-5Clear0 / 00.5ENE/5-150.45-0.551.25-1.75
2 PM0-20Clear0 / 06ENE/10-20NaN1-2
8 PM0-5Clear0 / 01NE/15-00.5-0.81-1.5
Sun May 01 - 2 AM0-5Clear0 / 01.5NE/15-300.5-0.90.8-1
2 PM0-20Clear0 / 07.5ENE/20-35NaN0.8-1.2
8 PM0-5Clear0 / 03ENE/15-300.5-0.80.7-0.9
Mon May 02 - 2 AM0-5Clear0 / 02.5NE/10-200.5-0.70.8-1
2 PM0-20Clear0 / 08.5NNE/5-15NaN1-2
Tue May 03 - 2 AM0-5Clear0 / 03.5NNE/5-150.45-0.652-3
2 PM0-20Clear0 / 09NE/5-15NaN3-4
Wed May 04 - 2 AM0-5Clear0 / 03.5NNE/5-150.45-0.652-3
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
Fri Apr 29 - Sat Apr 30 18:54 20:02 4:35 5:44 1:02 N/A 46 21 05.2 -13 59
Sat Apr 30 - Sun May 01 18:54 20:03 4:35 5:43 1:49 N/A 36 21 58.9 -10 44
Sun May 01 - Mon May 02 18:55 20:04 4:34 5:43 2:35 N/A 25 22 52.8 -6 49
Mon May 02 - Tue May 03 18:55 20:04 4:33 5:42 3:21 N/A 16 23 47.3 -2 27
Tue May 03 - Wed May 04 18:56 20:05 4:32 5:42 4:08 N/A 8 0 42.8 2 09
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Friday 29 April (0300 UTC Saturday 30 April) 2016.
Additional Information
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This message is also available at the MKWC road conditions page.
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