Current Conditions
Temp4.9 C
RH27 %
WindESE 12 mph
RoadOpen
Mauna Kea Observatories Forecast
730 AM HST (1730 UTC) Thursday 12 December 2013
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, but high clouds will continue to fill in from the west and become more widespread as the night progresses.
Summary of Key Meteorological Variables
Summit temperatures will be near 6.5 C this afternoon, 1.5 C this evening and 1 C tomorrow morning. Winds will be from the ESE at 10-20 mph, with seeing around 0.5-0.55 arcseconds. Precipitable water is expected to be in the 1-1.5 mm range for tonight.
Discussion
The tradewind inversion will continue to cap low-level moisture near 6-8 thousand feet and the mid/summit-level air mass dry and stable through the next 5 nights. Daytime clouds will be minimal and short-lived through the weekend, but could pick up a tad as summit-level humidity increases toward 40-60% on Monday.

Thin high clouds are expected to fill in from the west through the day, then thicken and become more widespread through tomorrow. This could lead to periods of extensive cloud cover for much of tomorrow and perhaps Saturday night as well. However, the bulk of these clouds are slated to move toward the northern skies late Friday night and continue to pass in that direction through the weekend. The clouds will shift off toward the east on Monday, leaving predominately clear skies for that night.

Precipitable water is expected to briefly slip toward 1.25 mm for tonight, then increase back to 1.5-2 mm for Friday and Saturday night and perhaps 3-4 mm for Sunday and Monday night.

Seeing is slated to linger near 0.5 arcseconds as skies remain relatively calm through tomorrow evening. However, building mid/upper-level turbulence could degrade seeing through tomorrow night, likely contributing to poor seeing for the remainder of the forecast period. There is also a verry good chance for strong upper-level turbulence in the area for Monday night.

The mid/low-level ridge will continue to sit just north of the Big Island for another 24 hours, then will slide off toward the east as a trough brews to the northwest and creeps closer to the state over the weekend. Fortunately, this trough is slated to lift off toward the NE and weaken prior to reaching the Big Island area. This will allow the ridge to remain close enough to the area to maintain relatively strong large-scale subsidence over the Big Island, which will keep the inversion fairly well-established at or below 8 thousand feet and ensure the summit steers free of fog and precipitation throughout the forecast period. There is a chance that the trough will bring minor mid-level moisture which could increase PW and summit-level humidity toward 4 mm and 40-60%, respectively, for Sunday and Monday night. However, the bigger concern will be the clouds and turbulence that this trough is expected to push through the area. The clouds will likely preceed the turbulence, arriving later today, and persisting probably through the weekend. The turbulence will likely begin to affect seeing later tomorrow night and continue to be an issue well into next week. There is also a possibility for separate bout of upper-level turbulence in the wake of the departing trough for the early part of next week.
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 Dec 12 - 2 PM20-409.5-100 / 06.5ESE/10-20NaN1-2
8 PM40-609-100 / 01.5ESE/10-200.5-0.61-1.5
Fri Dec 13 - 2 AM60-808-100 / 01SE/10-200.45-0.551-1.5
2 PM70-908-100 / 05.5SSE/10-20NaN1.5-2
8 PM60-808-100 / 00.5S/5-150.45-0.551.5-2
Sat Dec 14 - 2 AM50-708-9.50 / 00SSW/0-100.5-0.71.5-2
2 PM40-608-9.50 / 05SSW/0-10NaN1.5-2
8 PM50-707.5-9.50 / 0-0.5WSW/0-100.6-11.5-2
Sun Dec 15 - 2 AM40-608-9.50 / 0-1WSW/0-100.7-1.12-3
2 PM40-608-90 / 04.5W/5-15NaN3-5
Mon Dec 16 - 2 AM40-608-90 / 0-1.5W/10-200.6-1.23-5
2 PM20-404-50 / 03WNW/10-20NaN3-6
Tue Dec 17 - 2 AM0-20Clear10 / 0-3NNW/10-200.7-1.33-5
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 Dec 12 - Fri Dec 13 17:54 19:03 5:29 6:38 N/A 3:49 85 2 16.1 13 42
Fri Dec 13 - Sat Dec 14 17:54 19:03 5:30 6:39 N/A 4:41 92 3 07.3 16 26
Sat Dec 14 - Sun Dec 15 17:55 19:04 5:30 6:39 N/A 5:33 96 3 59.0 18 21
Sun Dec 15 - Mon Dec 16 17:55 19:04 5:31 6:40 16:40 6:24 99 4 51.0 19 23
Mon Dec 16 - Tue Dec 17 17:56 19:05 5:32 6:40 17:28 7:12 100 5 42.8 19 30
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Thursday 12 December (0300 UTC Friday 13 December) 2013.
Additional Information
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